late glacial and early holocene vegetation succession, altitudinal vegetation zonation, and climatic...

ELSEVIER Review of Palaeobotany and Palynology 97 (1997) 239 285

REVIEW OF

PALAEOBOTANY A N D

PALYNOLOGY

Late Glacial and early Holocene vegetation succession, altitudinal vegetation zonation, and climatic change

in the Serra da Estrela, Portugal

W . O . van der K n a a p 1 , , J . F . N . van L e e u w e n 2

Laboratory of Palaeobotany and Palynology, Budapestlaan 4, NL-3584 CD Utrecht, The Netherlands

Received 31 May 1996; received in revised form 14 January 1997; accepted 21 January 1997

Abstract

In the Serra da Estrela, a granitic mountain in central eastern Portugal, the Late Glacial and early Holocene vegetation history between ca. 14 800 and 9525 cal yr B.P. (ca. 12 600-8660 14C yr B.P.) was studied palynologically at eight sites less than 6 km apart at 1409-1845 m elevation. The chronology is based on radiocarbon dating and on correlation of the Quercus pollen curve with the GISP2 Greenland ice-core curve. The development and altitudinal zonation of past vegetation were reconstructed, inferences made on relative lake levels, and interpreted in terms of climatic change as follows: ca. 14 800 14 270 cal yr B.P. (first part of Bolling) scarce plant growth: climate cool and dry; ca. 14 270-14 100 cal yr B.P. (end of Belling) rapid succession of pioneer vegetation, closed herb vegetation, heathlands, and open woodland, and, at lower elevations, expansion of Quercus: climate moister and warmer; ca. 14 100-14 060 cal yr B.P. (Older Dryas) minor regression of trees: minor cooling of climate; ca. 14 060 12 850 cal yr B.P. (Allered) upper limit of open woodland between 1409 and 1600 m elevation, closed treeless vegetation extending to above 1845 m elevation, high lake levels: climate warmer and moister; ca. 12 850-12 435 cal yr B.P. (Younger Dryas, first part) strong reduction of open woodland, upper limit of closed treeless vegetation between 1700 and 1800m elevation, and, at lower elevation, reduction of Quercus, low lake levels: climate drier and cooler; ca. 12 435 11 875 cal yr B.P. (Younger Dryas, second part) further opening of tree, shrub, and herb vegetation, and expansion of vegetation types having no modern analogue in Portugal at 1409 m including Meum and Bupleurum and at 1600 1730m including Plantago lanceolata-type: climate still drier; 11 875-11 630 calyr B.P. (end of Younger Dryas) expansion of herb and shrub vegetation, high lake levels: climate moister and warmer; ca. 11 630-11 490 cal yr B.P. (start of Holocene) strong expansion open woodland, and, at lower elevations, of Quercus, high lake levels: climate much warmer and moister; ca. 11 490-11 050 cal yr B.P. (Preboreal oscillation) halt in tree expansion, low lake levels: climate not warmer; ca. 11 050-10 525 cal yr B.P. Quercus forest gradually replacing the open woodland up to 1645-1730 m elevation, above it treeless vegetation, low lake levels: climate warmer; ca. 10 525-10 175 cal yr B.P. Quercus optimum, very open woodland up to 1770 m, lake levels higher: beginning of a xerothermic period; ca. l0 175 9525 cal yr B.P. denser forest, lake levels higher: climate moister. © 1997 Elsevier Science B.V.

Keywords." palynology; Late-Glacial; early Holocene; Portugal; mountains; vegetation zonation; climatic change

* Corresponding author. Tel.: +41-31-6313868. Fax: +41-31-3322059. E-mail: [email protected] 1 Present address: Geobotanical Institute, Altenbergrain 21, CH-3013 Bern, Switzerland. 2 Present address: Geobotanical Institute, Altenbergrain 21, CH-3013 Bern, Switzerland.

0034-6667/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. PH 0034-6667(97)00008-0

240 W.O. van der Knaap. J. F.N. van Leeuwen / Review o[Palaeohotany and Palynology 97 (1997) 239 285

1. Introduction 2. Description of the study area

This study aims to reconstruct altitudinal zonation of Late Glacial and early Holocene vegetation in the Serra da Estrela (a granitic mountain in central eastern Portugal ), and to infer past climatic change with help of pollen diagrams from an altitudinal transect of study sites. The study is part of a long-term project at the Laboratory of Palaeobotany and Palynology (Utrecht, The Netherlands) initiated and supervised by C.R. Janssen and aiming at the study of the vegetation development in a transect of four contrasting West European mountain ranges, viz. the Vosges in northeastern France, the Monts du Forez in central eastern France, the Sierra da Cabrera Baja in northwestern Spain, and the Serra da Estrela in Portugal; for details see Janssen (1996). The methods are ( 1 ) to study the Holocene and Late Glacial vegetation histories by means of pollen and macro- remains from lakes and mires in altitudinal tran- sects that should ideally cross the tree limit, (2) to combine this with the study of recent pollen depos- ition in moss polsters in relation to surrounding vegetation, and (3) to relate the results to meso- climate (i.e., macro-climate as modified by geo- morphology) and to immigration histories of trees and macro-climatic features differing among the mountain ranges. We described this project more fully in Van der Knaap and Van Leeuwen (1994, 1995) and gave Holocene results for the Serra da Estrela in Portugal, the southernmost mountain range, based on six pollen diagrams. The aim of this paper is to describe the history and altitudinal zonation of the vegetation during the Late Glacial and early Holocene in the Serra da Estrela and to make inferences on climatic history. The Holocene key site for the Serra da Estrela, Charco da Candieira, was studied in great detail; it is also the key site for the Late Glacial, and its results are presented here along with those of seven additional sites studied in less detail. In this paper the pollen diagrams of the additional sites are frequently indicated collectively as ~the other pollen diagrams'.

The Serra da Estrela ( Fig. 1 ) is a granitic mountain that features glacier cirques, glacial valleys, and many depressions with natural lakes and ponds in its central part above 1400 m elevation (Daveau, 1971 ). The climate and vegetation are oceanic-mediterranean. The mountain was covered with open deciduous Quercus pyrenaica forests during much of the Holocene, but today the vegetation consists mostly of heavily grazed shrubland, heath, and grassland. The sites studied here lie within 6 km of each other. We refer to Van der Knaap and Van Leeuwen ( 1994, 1995) for a more detailed description of the study area, the zonation of vegetation, and the setting of four sites discussed in this paper (Charco da Candieira, Lagoa Comprida 2, Covfio do Boieiro, Chafariz do Rei). New topographic maps (Carta Militar de Portugal 1:25 000, 1993) enabled a more exact determina- tion of geographic characteristics than in earlier publications (Table 1 ).

Lagoa Clareza is a small lake ca. 100 m long and 50 m broad. Surficial inflows are absent, but a tiny outflow is present at the eastern end. It lies on an open north-facing slope. The shores are rocky and little vegetated. Sparganium angust(/ol- ium grows in the lake.

Lagoa das Salgadeiras is a filled-in lake ca. 100m across covered by Nardus stricta. A few small inlets and a small outlet dry up in summer. It is partly surrounded by steep slopes. The west side is the wettest and has pools partly connected by irregular channels, which may retain a few tens of centimetres of water in summer and are connected with the outflow. The core was taken on a little island ca. 5 m across surrounded by intercon- nected pools not far from the outflow but far removed fi'om the inflows. The entire mire showed frequent layers of coarse sand and pebbles, and only at one place was more than a fcw metres of sediment obtained. This is similar to the situation at Covfio do Boieiro, and it indicates in both areas that erosion has been an important process in the catchment.

Charca dos C6es has a hydrological catchment within that of Lagoa do Peixfio. It is a round shallow pool with permanent water in a peaty area

W.O. van der Knaap, J .~N. van Leeuwen / Review o f Palaeobotany and Palynology 97 (1997) 239 285 241

J,s

Fig. 1. Palynologically investigated sites in the Serra da Estrela, Portugal (adapted from Daveau, 1971 ). Sites discussed in this paper: 1 = Charco da Candieira ( 1409 m); 2 = Lagoa Comprida 1 ( 1600 m); 3 = Lagoa Comprida 2 ( 1645 m); 4 = Cov io do Boieiro ( 1730 m); 5 = C h a f a r i z do Rei (1770 m); 6 = C h a r c o dos C6es (1795 m); 7= Lagoa das Salgadeiras (1835 m); 8 = Lagoa Clareza (1845 m). Additional sites: 9 = Fraga do Vale Mourisco ( 1535 m); 10 = Lagoacho das Favas ( 1645 m); 11 = Canariza ( 1700 m); 12 = Charcos da Lagoa Comprida (1695 m); 1 3 = N a v e de Santo Ant6nio (1540 m); 14=Tor t e (1925 m); 15=Albergar ia (1080 m); 1 6 = Q u i n t a da Alagoa (550 m; outside map); 1 7 = L a g o a do Peixio (1670 m; no pollen diagram). Site 3 and a summary of site 2 have been published by Van den Brink and Janssen (1985); sites 3 5, 9, 10 and a summary of site 1 (Holocene part) have been published by Van der Knaap and Van Leeuwen (1994); site 1 (Holocene part) has been published by Van der Knaap and Van Leeuwen (1995).

242

Table 1 Site description

W. O. van der Knaap. J..~ N. van Leeuwen Review o/'Palaeobotan) and Palyno&gy 97 (19971 239 285

Site name Latitude Longitude Elev. Size of lake, / Water Lake/ Hydrological (m a.s.I.) mire (ha) depth (m) Pond~Mire catchment (ha)

Lagoa Clareza 40 20'08"N 7 '36'18"E 1845 0.4 2.6 L 3.5 Lagoa das Salgadeiras 40~20'10"N 7 36'35"E 1835 1 0.2 M 20 Charca dos C6es 4020'21 "N 7 36'40"E 1795 0.02 0.2 L 5.5 Chafariz do Rei 40'20'06"N 7 37'08"E 1770 (}.02 0.5 L 5.5 Cov~o do Boieiro 40 20'02"N T37'20"E 1730 2 --0.2 M 110 Lagoa do Peixfio 40 20'30"N 7 36'15"E 1670 2 4.7 L 30 Lagoa Comprida 2 40 21'46"N 7 38'10"W 1645 0.3 0.0 L + M 3.5 Lagoa Comprida 1 4021'48"N 7 38'30"W 1600 0.3 -0 .5 M 13 Charco da Candieira 40 20'15"N 7 34'47"W 1409 1.5 0.0 P + M 12

ca. 100 m across dominated by Nardus stricta. The site lies on an open plateau.

Lagoa do Peix~,o lies at the head of the Candieira valley, 2.3 km upstream from Charco da Candiera. It is ca. 150 m across in a steep east-facing former glacier cirque; the plateau 0.5 km to the west is 1800 m a.s.1. A few tiny streams flow into the lake, which has a small outflow.

Lagoa Comprida 1 is now a flat grassland 50 to 100 m across sheltered between rock outcrops. It is heavily grazed, but the relatively high nutrient status of the vegetation compared to other grazed areas nearby (indicated by a dominance of Festuca rubra) suggests that it was a rye field not long ago. Similar rye fields were observed between Lagoa Comprida 1 and 2 up to ca. 10 years ago, but they are now abandoned and have a vegetation resem- bling that of Lagoa Comprida 1. Prior to rye cultivation the site was probably a Nardus stricta- dominated mire similar to that of Lagoa Comprida 2. Lagoa Comprida 2 lies ca. 400 m east of Lagoa Comprida 1 and has a hydrological catchment within that of Lagoa Comprida 1.

3. Methods

3.1. Field and laboratory methods" and pollen counting

Table 2 gives data on coring in the field. The first coring at Lagoa do Peixfio was aimed

at recovering Late Glacial sediments. The second

coring was made after several explorations aimed at finding the deepest sediments.

Charco da Candieira was cored in two bore holes less than 0.5 m apart. The samples are distrib- uted over the cores as follows (even-numbered cores from bore hole 1, odd-numbered cores from bore hole 2): 735-795 cm in core 9; 800 885 cm in core 10; 890 970cm in core 11; 975 1065 cm in core 12:1070 1155, 1160 and 1162.5 cm in core 13; 1159and 1164 1263 cm in core 14.

Laboratory methods followed Van der Knaap and Van Leeuwen (19951. All sample depths are measured from the top of the sediment downwards, also in the case of Lagoa Clareza where the upper, very loose sediments were lost during coring. Pollen concentrations were determined for six sites (Figs. 5, 9, 11, 13, 15 and 17). Volume of pollen samples for Charco da Candieira is 1 x 0.28 cm 3 between 735 and 1164 cm, 2 x0.28 cm 3 between 1166.5 and 1189cm, 1 x0.28 cm 3 between 1191.5 and 1202cm, 2x0,28 c m 3 between 1204 and 1214 cm, 3 x 0.28 c m 3 between 1219 and 1244 cm, and 1 c m 3 between 1249 and 1263 cm. The pure white silty sediments between 1264 and 1450 cm contained very little pollen; even after use of heavy liquid and HE on samples of 5 ml, little more than the added exote was regained.

Sediment bulk density of dried samples was measured on parallel samples of 0.28 c m 3 for Charco da Candieira.

Stomata in pollen slides were counted in some of the sites: Lagoa Comprida 1, Charca dos C6es, Lagoa das Salgadeiras, and Lagoa Clareza. Erica

W.O. van der Knaap, J. F N. van Leeuwen / Review q/Palaeobotany and Palynology 97 (1997) 239-285 243

Table 2 Coring data

Site Coring equipment a Coring date Water Coring place Corers b Pollen depth (m) analysts b

Lagoa Clareza Dr<443 cm; Da 21 Sep 1989 2.6 centre 7 12 15 11 28 5 22 20 (5) Lagoa das Salgadeiras Li 22 Aug 1983 - 0 . 2 island 18 20 12 16 2 7 9 20 (1) Charca dos C6es Li 12 Sep 1987 0.2 centre 12 7 4 19 20 (5) Chafariz do Rei Li < 250 cm; Da 14 Sep 1987 0.5? centre 7 15 12 26 29 2 19 21 20 Covao do Boieiro Li 23 Aug 1983 - 0 , 2 7 16 18 20 2 9 2 Lagoa do Peixfio (1) Wr Jun 1981 4.73 centre 8 13 32 14 10 24 (13) Lagoa do Peix~o (2) Dr 24-30 May '91 3.30 7 16 27 25 2 15 Lagoa Comprida 1 g o < 195 cm; Da Sep 1975 0.5 15 31 20 (33) Lagoa Comprida 2 g o < 175 cm; Da 16 May 1981 -0.1 shore 15 16 3 3 6 19 Charco da Candieira Li 18-19 Aug '85 0.0 centre 15 7 16 17 30 12 2 23 18 20 20

a Coring equipment: Da=Dachnowski corer 20 cm long 2.5 cm diameter: D r = D r u t o n (=modified Livingstone piston corer 8 cm diameter): go =gouge 6 cm diameter; Li = Livingstone piston corer 8 cm diameter; Wr= Wright square-rod piston corer. b Corers, pollen analysts (in brackets: preliminary analysis): 1 = Ronald Bakker: 2= Hanneke Bos; 3 = Wies van den Brink; 4 = J o h a n and Jenny van den Burgh; 5 = Bart Derks; 6 = Frank van Dongen; 7 =Ton van Druten; 8 = Eric Grimm; 9 = Harry van Helvoort; 10=Gina Hannon; 11 =Wire Hoek; 12=Peter Hoen; 13=Brian Huntley; 14~Jacqueline Huntley; 15=Roel Janssen; 16=Hans Joosten; 17 = Ine Joosten; 18 = Pim van der Knaap; 19 = Ruth van de Laarschot; 20 = Jacqueline van Leeuwen; 21 = Ruud Lutgerink; 22 = Bart Makakse; 23 = Marlies Marbus; 24 = Madeline McKeever; 25 = Hans Middelkoop; 26 = Tjeerd Okkes; 27 = Ben Paffen; 28 = Eric Schorn; 29 = Charlotte Swertz; 30 = Torbj6rn T6rnqvist; 31 = Evert J. de Valk; 32 = Bill Watts; 3 3 - Rob Woldringh.

and Juniperus stomata were encountered; Pinus stomata were absent. In Charco da Candieira, pollen slides of 15 selected depths were scanned for stomata (in zones LG2a, LG3a e, LG4a, LG5d, Ala , and Alb) ; Pinus stomata were encountered in zones LG3a and LG3c (1160 and 1125 cm). In addition, a needle of Pinus cf. sylvestris was encountered in a sample prepared for AMS radiocarbon dating (1103-1107cm; zone LG3d).

A preliminary pollen diagram of Lagoa Comprida 1 was published in Janssen and Woldringh ( 1981 ) and a summary of it in Van den Brink and Janssen (1985). No pollen diagram was made for Lagoa do Peixfio.

3.2. Pollen diagrams

We use the terms 'pollen types' and 'pollen diagram' for simplicity, but they include spores and palynomorphs other than pollen grains. Pollen-percentage diagrams are presented for all sites Figs. 4, 6-8, 10, 12, 14 and 16, and pollen- concentration diagrams of selected types are given for Charco da Candieira and five other sites.

Nomenclature of pollen types follows the rules

set out in Van der Knaap and Van Leeuwen (1995). A few pollen types are renamed from earlier publications: Plantago radicata-type (from P. alpina-type); Fraxinus angustiJolia [erroneously called F. excelsior, not occurring in Portugal today, in the pollen diagrams of Van der Knaap and Van Leeuwen ( 1994)].

The pollen sum includes all pollen and spore types of vascular plants except moss spores and pollen of obligate aquatic taxa. The pollen sum differs from that in earlier published pollen diagrams (Van der Knaap and Van Leeuwen, 1994, 1995) in the inclusion of pollen and spores derived from taxa that were inferred to grow in peaty areas around lakes (mainly Betula alba, Salix, Gramineae, Cyperaceae, and Dryopteris-type). Such peaty areas were probably scarce or not yet developed in the Late Glacial. The pollen zones are considered chronozones and are numbered identically in all pollen diagrams, as discussed below. Late Glacial zone numbers are preceded by LG; Holocene zone numbers for Charco da Candieira follow the earlier publication (Van der Knaap and Van Leeuwen, 1995).

The pollen diagrams were drawn with the program TILIA (Grimm, 1990).

244 w, o. van der Knaap, J.F.N. van Leeuwen / Review oj Palaeobotany and Palynology 97 (1997) 239 285

Pollen types in the pollen diagrams are grouped as Trees, Shrubs, Herbs and Aquatics. For Charco da Candieira they are ordered within these groups on weighted average by depth and numbered here and in the discussions for ease of reference. In the other pollen diagrams they are ordered alphabeti- cally within the groups. The pollen diagrams differ somewhat in pollen-morphological resolution. In order to make the comparison among pollen diagrams easier in such cases, a number of summed pollen types are given (e.g. Umbelliferae total) followed by the constituent pollen types.

3.3. Methods of interpretation and indicative value of pollen types

The present-day flora and vegetation of the Serra da Estrela are rather well known (Pinto da Silva and Teles, 1980) and include a wide range of climax to pioneer communities, with emphasis on degradational stages ranging from shrub vegetation to heaths, herb vegetation, and open vegetation on mineral soils. This is the best we have as modern equivalents of Late Glacial and early Holocene flora and vegetation. The present and the Late Glacial/early Holocene vegetation share the entire range from pioneer vegetation on open ground to open forest. However, organic soils, degraded vegetation types and soils, and erosion are prominent today due to human pressure, whereas inorganic soils, buildup of organic soils, and progressive vegetation succession were prominent in the Late Glacial and early Holocene. Degradation of vegetation and soil erosion, if it occurred in the Late Glacial, was likely related to periods of climatic cooling (such as the beginning of the Younger Dryas). An additional uncertainty in the interpretation is that pollen types common to the Late Glacial and the present time might be from different species. We give below a list of approximate indicative values of selected pollen types as used in the interpretation; the indications concern mainly density of vegetation, humus content of the soil, and soil moisture. Occurrence or increase of a single pollen type is not considered significant; in our interpretations we suggest ecological changes only if several pollen types point in the same direction.

Pioneers on open mineral soils: Anthemis-type, Arenaria, Artemisia, Armeria, Chenopodiaceae- type, Compositae liguliflorae, Echium, Filago-type, Gentiana campestris-type, Jasione-type, Minuartia recurva, Paronychia polygonifolia-type, Radiola linoides, Reseda/Sesamoides, Sagina, Sedum-type.

Closed herb vegetation: Anthriscus sylvestris, Chaerophyllum temulentum, Daucus, Dryopteris- type, Galium-type, Gramineae, Rumex acetosella- type.

Closed herb vegetation on moist soils: Cyperaceae, Dryopteris-type, SaxiJraga stellaris- type, Lotus, Parnassia palustris, Potentilla.

Closed herb vegetation on wet soils: Narcissus bulbocodium, Peucedanum-type.

Peat-forming vegetation: Sphagnum. Organic soils: Botrychium. Shrub vegetation: Calluna vulgaris, Erica arb-

orea-type, Genista-type, Juniperus communis, Sarothamnus grandiflorus.

Open woodland: Betula alba, Frangula alnus, Salix, Sorbus aucuparia.

Denser forest: Fraxinus angustifolia, Quercus, Taxus baccata.

4. Results

4.1. Lithology

The deposits studied are described in Table 3. Bulk density of dried samples (measured in

Charco da Candieira) reflects directly the propor- tions of the organic component (very low sediment bulk density) and silt or sand (high sediment bulk density). It is thought that the silt and sand have been blown-in or washed-in during periods of erosion and little vegetation in the surroundings. Sediment bulk density is therefore used as a relative measure for erosion and the quantity of vegetation in the catchment area. Only in the upper 50 cm (zone A5b) the production of the lake may have increased with the expansion of Potamogeton.

4.2. Radiocarbon dating

Conventional radiocarbon dates relevant for the Late Glacial and early Holocene are listed in Table 4.

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Table 3 Lithology of studied deposits

Lagoa Clareza 385-440 cm: brown-black gyttja; lower boundary sharp 440 465 cm: silt

Lagoa das Salgadeiras 345 367 cm: brown-black gyttja with some sand; lower boundary gradational 367 371 cm: slightly sandy gyttja; lower boundary gradational 371-380 cm: organic silt with some sand

Charca do C6es 145 166 cm: brown-black gyttja; lower boundary sharp 166 177 cm: grey compact silt

ChaJariz do Rei 195-227.5 cm: brown-black soft detritus-gyttja with some sand; lower boundary well defined 227.5 239.5 cm: grey compact silt with some sand; lower boundary rather sharp 239.5 250 cm: brown-black compact gyttja with coarse sand; lower boundary rather sharp 250-262 cm: grey compact sandy silt; lower boundary rather sharp 262 276 cm: light grey compact silt with rather clear stratification

Covao do Boieiro 740 795 cm: brown-black gyttja 795-807 cm: light brown silty gyttja with some sand 807 809.5 cm: light brown-grey compact silt with some sand 809.5-822 cm: light grey compact sandy silt 822 841 cm: gradual transition 841-867 cm: light grey-brown compact silt with some sand

Lagoa do Peixgto, first coring 0-787 cm: brown-black gyttja with very little sand

Lagoa do Peix~o, second coring 0-ca. 700 cm: brown-black soft gyttja with very little sand; solid rock at bottom

Lagoa Comprida 2 360~140 cm: brown-black soft gyttja 440~160 cm: compact silty gyttja with some bands of moss 460-475 cm: compact organic silt 475 485 cm: very compact clayey silt

Lagoa Comprida 1 450-491 cm: dark grey-brown silty gyttja 491 500 cm: (core not recovered) 500-511 cm: light grey organic silt 511 515 cm: light grey organic silt with detritus layers 515 530 cm: light grey organic silt

Charco da Candieira 735-952 cm: brown-black wet soft gyttja; lower boundary sharp. This type of deposit in the Serra da Estrela is characteristic for Holocene deposits in lakes (with water all the year round) 952 1054 cm: brown-grey very silty gyttja; lower boundary gradational 1054-1158 cm: brown silty gyttja; lower boundary gradational 1158-1168 cm: yellowish brown silty gyttja with clear, irregularly spaced dark and light laminations; lower boundary gradational 1168-1180 cm: grey-brown silty gyttja with clear, irregularly spaced dark and light laminations; lower boundary gradational 1180-1190 cm: white inorganic silt; lower boundary very sharp 1190 1200 cm: yellowish brown silty gyttja with clear, irregularly spaced dark and light laminations (identical to 1158 1168 cm); lower boundary gradational 1200 1212 cm: grey-brown silty gyttja with clear, irregularly spaced dark and light laminations (identical to 1168-1180 cm); lower boundary gradational 1212 1264 cm: white rather soft inorganic silt; lower boundary gradational 1264 1450 cm: white very soft inorganic silt

246 IV. O. van der Knaap, J. F N. van Leeuwen / Review qf Palaeobotany and Palvnology 97 (1997) 239 285

Table 4 Radiocarbon dates

Depth Radiocarbon age Calibrated age Lab. No. Method Material (cm) (yr B.P.) (cal yr B.P.)

Charco da Candieira 725 734.5 8660+_50 9660+ 139 GrN-16 764 decay 790 795 9390±50 10380+_80 GrN-16770 decay 840 850 9450_+60 10 575 +_210 GrN-16 765 decay 940 950 10190±60 11 895+_235 GrN-16766 decay

1013 1017 10040__120 11 385±349 UTC-4049 AMS 1040 1050 ll 100±70 13015±85 GrN-16767 decay 1103 1107 11 370_+70 13280±100 UtC-4050 AMS 1138 1142 12060±100 14070_+170 UtC-4051 AMS 1154 1163 11 730±110 13675±160 GrN-16768 decay 1190 1201.5 11910±160 13890+-220 GrN-16769 decay

Lagoa do PeixSo, .first coring 759 764 9980+_100 11 275±275 WIS-1778 decay

Lagoa Comprida 1 476 480 9080+200 10 105±230 GrN-9917 decay 501 505 9200±270 10 340_+435 GrN-9918 decay

Charca dos COes 147 153 6430±45 7320_+55 GrN-18350 decay

Lagoa das Salgadeiras 345 355 8230±60 9135±125 GrN-16967 decay

Lagoa Clareza 385 390 9050±50 10005_+125 GrN-18347 decay

bulk bulk bulk bulk seeds + wood bulk Qvtisus purgans + cf. Betula alba twigs cf. Betula alba twigs bulk bulk

bulk

bulk bulk

bulk

bulk

bulk

Radiocarbon dates were calibrated to cal yr B.P. (calendar years before A.D. 1950) with the program CALIB3 (Stuiver and Reimer, 1993) version 3.0.3c. The expression 'cal yr B.P.' is here also used for interpolated and inferred ages in the same time scale. According to the GISP2 ice core (Stuiver et al., 1995), the beginning of the Holocene is dated at 11 6 4 0 + 2 0 0 cal yr B.P,

5. Interpretation

5.1. Chronology

5.1.1. Charco da Candieira In Charco da Candieira (Fig. 4), the trends in

pollen and lithology between 1222 and 1190 cm are similar to those between 1190 and 1158cm. We feel certain that the two sequences represent the same time span. Slumping of the sediment in

the rather steep-sided basin (ca. 100 m across, at that time ca. 12 m deep) probably accounts for the repetition. Both intervals lie within a single one- meter core; a coring artefact is therefore excluded as an explanation for this phenomenon. Pollen zones occurring twice have been given the same number.

Late Glacial climatic fluctuations are known from Greenland ice cores such as GISP2 (Stuiver et al., 1995). The interpretation of the pollen diagram from Charco da Candieira in climatic terms can be compared to the ice record. Quercus pollen is the most important climatic indicator and changes in its percentages reflect variations in temperature: concurrent changes in other pollen types support this interpretation. The inferred response includes not only tree expansion during increasing temperatures, but also increased pollen production. Parts of the Quercus pollen curve bear

14~ O. van der Knaap, J.F.N. van Leeuwen / Review of Palaeobotany and Palynology 97 (1997) 239 285 247

remarkable resemblance to 6180 curves during approximately the same period (synchronicity judged on radiocarbon dating) not only of GISP2 but also of lakes on the Swiss Plateau (Ammann and Lotter, 1989). Fig. 2 shows an attempted detailed correlation between the Quercus pollen curve and the 6180 curve of GISP2; the chronozones Bolling, Allerod, Younger Dryas, and Holocene (Mangerud et al., 1974) are delimited according to Stuiver et al. (1995), as is the Intra- Allerod Cold Period, whereas the Preboreal Oscillation follows Ammann and Lotter (1989). The resulting depth-age relationship is shown in Fig. 3 together with calibrated radiocarbon dates in Charco da Candieira. The radiocarbon date for 1013-1017 cm is out of sequence and rejected as too young.

Stuiver et al. (1995) observed that calibrated radiocarbon ages of major climatic shifts in Europe during the Late Glacial and early Holocene match closely the ice-layer ages of these climatic shifts in the GISP2 ice core, despite uncertainties in both time scales. The calibration of Late Glacial and early Holocene radiocarbon dates with the CALIB3 (Stuiver and Reimer, 1993) program are considered with some caution, because they are U-Th dates on corals (rather than on tree rings as for the remaining Holocene). The calibration curve used in CALIB3 is corrected for the effect of reservoir carbon in the ocean by subtracting the present-day reservoir age (400 years) from the measured conventional yr B.P. ages.

The depth-age relationship for Charco da Candieira is based on four linear segments (Fig. 3). Average sediment accumulation is 10.5 yr/cm, subdivided as follows:

1244-1055 cm (Boiling and Allerod): 10,7 yr/cm;

1055-950 cm (Younger Dryas): 12.4 yr/cm; 950-860 cm (early Holocene: Betula alba domi-

nance): 9.0 yr/cm; 860-735cm (Holocene: Quercus dominance):

10.0 yr/cm. The slight variations in the sediment-accumula-

tion rates (10.5 yr/cm or 0.95 mm/yr_+ 15%) means that the pollen-concentration diagram (Fig. 5) can be read as a pollen-influx diagram (grains/ mm2/yr).

5.1.2. The other pollen diagrams The chronology of the other pollen diagrams is

inferred from the chrono-zonation at Charco da Candieira and radiocarbon dates from Holocene sediments. We used the same correlation method as in Van der Knaap and Van Leeuwen (1994), in which the results for three sites studied here are given for the Holocene (Fig. 1, sites 3-5). A minor modification is made here by correlating the basal Holocene pollen spectrum of the three sites with zone Ala. As a result, the inferred early Holocene hiatus (Van der Knaap and Van Leeuwen, 1994) is placed one pollen spectrum higher up. The correlation of Late Glacial zones is mainly based on dominant regional pollen types (Quercus, Pinus, Artemisia, and Chenopodiaceae-type); a few additional pollen types were used for adjacent sites (Botrychium, Compositae tubuliflorae, C. liguliflorae, Plantago radicata-type, and P. lanceolata- type); pollen types of inferred local origin were not used (e.g., Betula alba).

The radiocarbon date of 9200_+270 yr B.P. at 501 505cm in Lagoa Comprida 1, apparently more than a millennium too young, might be caused by contamination of younger material recovered with a small Dachnowski corer. The radiocarbon date at 476-480 cm (9080 + 200 yr B.P.) in the same pollen diagram also seems too young, possibly for similar reasons. Radiocarbon dates listed for other sites are all accepted.

5.1.3. Lagoa do Peix6o during the Late Glacial In the first core of Lagoa do Peixgo, a radiocar-

bon date of 9980_+100yr B.P. at 759-764cm suggests an early Holocene age. The pollen assemblage at 776 cm (Table 5), showing high Pinus and low Quercus and Betula alba percentages, resem- bles that of the very end of the Younger Dryas in lower-lying sites and the very start of the Holocene in higher-lying sites. The lithology of brown-black gyttja down to 787 cm is characteristic of Holocene lake deposits in this region and not of Late Glacial deposits. The same stratigraphy was recovered in the second core. Lagoa do Peixao apparently did not become ice-free until the end of the Late Glacial; the lake lies just east of the wind-swept plateau in a steep east-facing cirque where snow might easily have accumulated.

248 W.O. van der Knaap, J .F N. van Leeuwen / Review o/'Palaeobotany and Palynolo~y 97 (1997) 239- 285

Depth 735: 745 • 755: 765 775 78~ 79 [ 80~ 815 825 835 845 855 865 875 885 895 9O5 915 925 935 945 955 965 975 985 995

1005 101 1025- 10:55: 1045: 1055: 1065: 1075: 1085: 1095: 1105: 111£ 112£ 113~ 114~ 115~ 116~ 117~ 1185 1195 1205 121£ 122~ 123~

Pollen zones

A5b

A5a

A4

A3

A2

Alc

Alb

Ale

LG5d

6180 (/60 yr)

Charco do Candieiro, Quercus pollen percentages ~ _ ~ . . . . . _

~ - -- - ~ ] Holocene

2'CL LGSc

LG5b ~ Younger Dryas LG5o ~ _

L.G4b LG4o LG3f

LG3e

LG3d

LG2c LG2b LG2e Older Dr~/as

LGIb )-

I 5 10 15 20 25 30 35 40 . . . .

Oldest Dryas

J

J

- 4 ~ ' - 4 o ' ' -38 ' -36 ' - 3 4

cal yr~ 90007

92004

94003

9600~

98004

00004

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04004

0600 ~

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11200-

11400-

11600-

11800-

12000-

122O0-

12400-

12600-

12800-

13000-

13200-

13400-

13600-

13800

14000

14200

14400

14600

14800

15000

15200

15400

15600

15800

16000

1620C

1640C

1660C

V~ O. van der Knaap, J.F N. van Leeuwen / Review of Palaeobotany and Palynology 97 (1997) 239-285 249

15000 I ~/*~/'÷÷"

14000 !÷

r 13000 - -

+c+*l]

F l~+ e* ++

.+ +*

1 2 0 0 0 - - ~. +.+*

~+ I i 0 0 0 - -

+*

0 iO000 /

,*÷

g o 0 0 I [ ~ I I --

700 800 QO0 i000 1100 1200 1300 D e p t h ( cm)

Fig. 3. Depth-age relationship of Charco da Candieira for the studied period based on correlation of the Quercus curve with the GISP2 6180 curve (Stuiver et al., 1995) as given in Fig. 2. Circles represent the correlated points (drawn lines between the two curves in Fig. 2); rectangles represent calibrated radiocarbon dates (horizontal=sample thickness; vertical=calibrated age 1~); pluses (-- + +) represent pollen samples. The depth age relationship adopted is based on linear interpolation between selected points.

5.2. Charco da Candieira." vegetation history (Figs. 4 and 5)

5.2.1. Zone LGO (before ca. 14 800 cal yr B.P.; absent f rom pollen diagram)

T h e sed imen t s be twe en 1450 a n d 1264 cm cons is t o f fine silt wi th o n l y few coa r se r par t ic les a n d c o n t a i n very li t t le po l l en or o t h e r o rg an i c ma t t e r . T h e absence even o f po l l en t r a n s p o r t e d long-d i s - t ance suggests r ap id f low o f wa te r t h r o u g h the lake, p r e v e n t i n g the s e d i m e n t a t i o n o f b o t h c lay

a n d pol len . I t m i g h t r ep resen t a pe r iod w h e n glaciers were p re sen t a n d vege t a t i on in the ca tch- m e n t was absent .

5.2.2. Zone LG1 (ca. 14 800-14 270 cal yr B.P.; Bolling p.p. )

The absence o f o rgan ic m a t e r i a l in the lake s ed imen t (white silt, h igh s ed imen t b u l k dens i ty) suggests tha t n o or few p l an t s grew in the ca tch- m en t . Al l tree po l l en a n d m u c h o f the s h r u b a n d he rb po l l en was l ikely to have been l ong -d i s t ance

Fig. 2. Correlation of the Quercus pollen curve in Charco da Candieira (the standard pollen diagram of this paper) with the 6180 curve of the Greenland ice core GISP2 (Stuiver et al., 1995). Depth scale, pollen zones, and the Quercus pollen-percentage curve follow Fig. 4 with the difference that overlapping pollen zones are removed; ~180 curve, time scale (cal yr B.P.; yearly ice-layer counts before A.D. 1950), and chronozones follow Stuiver et al. (1995) with exception of 'Preboreal Oscillation' derived from Ammann and Lotter (1989). The bidecadal 6180 values in the published graphs have been redrawn to a 60-year moving average (a time span similar to that of pollen-sample intervals in large part of the pollen diagram). Drawn lines connecting the two curves indicate correlated points used in the depth-age relationship (Fig. 3); dashed lines indicate additional correlations resulting from this relationship.

250 w.o. van der Knaap, J.F.N. van Leeuwen / Review (?['Palaeobotany and Palynology 97 (1997) 239 285

transported. The nearest Pinus 2 and Quercus 13 trees may have grown along the foothills of the mountains, and Betula alba s trees might have grown in sheltered valleys. It is likely that Gramineae grew not far from the site. Several herb pollen types have relatively high percentages, but their concentrations are not especially high, and their local presence is doubtful because of their reputation for good dispersal (Artemisisa 5°, Plantago radicata-type sg, Chenopodiaceae-type sS, Cruciferae96). Herb pollen types having limited dispersal capacities and possibly derived from plants growing near the site include plants typical of open, sandy soils (Gentiana campestris-type 44, Sagina 43, Filago-type 63, Minuartia recurva 67, Aren aria 52, Radiola linoides 81, Paronychia polygoniJolia- type 79, Jasione-type 9~, and Armeria m~) and a few others (Anthemis-type 4~, Lotus ~7, Saxf/?aga granulata-type 65, Compositae liguliflorae 7°, and CampanulaS°°). The nearest likely place for herb vegetation more closed is the valley of Rio Zezere, which runs at an elevation of 1000m l km east of the site in northern direction and thence through sheltered valleys below 700m elevation about 8 km to the northeast.

The transition from zones LGIa to L G l b is marked by a decline of Artemisia 5° and increases of Gramineae 98 and Rumex acetosella-type ll°. It might suggest a slightly more closed vegetation around the site in the time of zone LGlb .

The vegetation reconstructed for zone LG1 suggests a cool periglacial climate.

5.2.3. Zone LG2 (14 270 14 060 cal yr B.P.; end of Boiling and Older D1Tas)

Pollen types common to zones LG1 and LG2 and suggesting presence of plants near the site but declining at the base of zone LG3 are mainly those indicative of pioneer vegetation on inorganic soils (Filago-type 63, Minuartia recurva 67, Armeria 1°1, Compositae liguliflorae 7°, Radiola linoides 8~, Paronychia polygoniJi)lia-type 79, Jasione-type 9s, and CampanulaS°°). Other taxa with the same indicative value have a maximum in zone LG2 (Sagina 43, Reseda/Sesamoides 7~, and Sedum- type~3°). This assemblage indicates that pioneer vegetation on inorganic soils was abundant in zone LG2, even more so than in zone LGI. Other pollen

types that show a maximum in zone LG2 are derived from herbs (Lotus 57, Pentaglottis sempervirens 69, Aster-type 97, Gramineae 98, Rumex acetosella-type 11°, and Sax(fraga stellaris-typel°V); to this list can be added a few types for which presence of plants near the site is uncertain (Eryngium~3, Lysimachia 111, and Echium13V). Herb vegetation must have expanded considerably in this zone. A few other herb pollen types show a maximum in zones LG2b and LG2c (Hypericum perforatum-type 92, Cyperaceae 84, and DJ3,opteris- type 1°2 in zone LG2c; weak maxima of Tri/~diumT~ MelandriumSS, Cirsium_type ll5 and Hepaticael('6). Increases of Bottivchium 1°~' and Potentilla 94 in zone LG2c might be related to the development of organic soils. A strong increase of Betula alba s and a marked maximum of Calluna vul~;ari5 "23 during zones LG2b and LG2c indicate that woody species also became important in the vegetation near the site. Shrub vegetation shows maximum development near the site in zone LG2c (maxima of Juniperus communis 2° and Salix ~, and increase of Erica arborea-type25). Five pollen types only show decreasing percentages in zone LG2 (Pinus 2, Anthemis-type 47, Artemisia 5°, Plantago radicata-type 59, and Chenopodiaceae-type55). However, the declines are not matched by decreases in concentrations; percentages are apparently suppressed by increasing production of pollen types derived from the expanding vegetation around the site.

The decreased percentages and concentrations of both Betula alba s and Pinus 2 and a cessation in the increase of Quercus ~3 concentrations in both representations of zone LG2c are synchronous with the short-lived Older Dryas cooling (Fig. 2). However, the rapid changes in vegetation that start in the late Bolling (zone LG2a) were hardly interrupted by the Older Dryas cooling (zone, LG2c).

The vegetation near the site during zone LG2 shifted towards increasing density, diversity, and structural complexity. A decline in sediment bulk density confirms the expansion of vegetation on formerly open soils around the site. Quercus 13 started to increase in zone LG2b, suggesting an expansion of oaks, probably far away. The vegeta-

W. 0. van der Knaap, J.F. N. van Leeuwen / Review of Pc

Charco da Candieira (1409 m), Late-Glacial and early Holocene Pollen types ordered within groups by weighted averages on depth

Analysis: Jacqueline F.N. van Lewwen

Fig. 4. Pollen-percentage diagram of Charco da Candieira, Late Glacial and early Holocene part. Pollen zones are deli

indicates the inferred Late Glacial/Holocene transition.

tlaeobotany and Palynology 97 (1997,) 239-285 pp, 251-252

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mited with horizontal lines; dotted lines indicate subdivisions of pollen zones into smaller units, the thi~k line

pp. 253 254

Charco cla Condieira continued

W.O. van der Knaap, J.EN. van Leeuwen / Re'

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Fig. 4. Continued.

~iew of Palaeobotany and Palynology 97 (1997) 239-285

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LClo

VK O. van der Knaap, J.FN. van Leeuwen / Review of Palaeobotany and Palynology 97 (1997) 239-285 255

Charco P o l l e n c o n c e n t r a t i o n selected pollen types

9500

9750

10000

10250

10500

10750

1100{

1125C

1150C

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1400(

14251

1450C

14750

da Candieira (1409 m), LatemGlacial and early Holocene diagram (grains/O.O01 ml) .~

g

Pollen

Fig. 5. Pollen-concentration diagram of Charco da Candieira, Late Glacial and early Holocene part; selected pollen types. Pollen zones are delimited with horizontal lines; dotted lines indicate subdivisions of pollen zones into smaller units, the thick line indicates the inferred Late Glacial/Holocene transition. Note that the scale differs between the first three and the remaining pollen types.

256 W. O. van der Knaap, J.F N. van Leeuwen Review ¢?] Palaeobotany and Pa@nology 97 (1997) 2.39 285

Table 5 Pollen analysis of Lagoa do Peixfio. Pollen sample at 776 cm deep of first coring (1981) in Lagoa do Peixao, counted by Brian Huntley. Some pollen types have been lumped and the names of pollen types are adapted to this paper. The pollen sum is 550

37.8% Pinus 5.8% Quercus 2.2% Betula alha 0.2% Ulmus 0.4% Juniperus communis 0.4% Ericaceae 21.5% Gramineae 4.6% Rumex 2.9% A rtemisia 2.0% Bolrychium 1.6% Cyperaceae 1.6% Umbelliferae 0.9% Compositae liguliflorae 0.5% Caryophyllaceae 0.5% Chenopodiaceae-type 0.5% Linaria 0.4% Anthemis-type 0.2% Filipendula 0.2% Rh#mnthus/ Veronica (/.2% Spergula-type 0.2% Ranunculus subgenus Batrachium 16.5% lndet.

tion changes suggest rapidly increasing temperatures and precipitation.

Our climatic reconstruction of zones LG1 (first part of Bolling: cool periglacial ) and LG2 (end of Boiling and Older Dryas: rapidly increasing temperatures and precipitation) contrast with the 6tsO values of the Greenland ice (Fig. 2) suggesting temperatures comparable to the early Holocene for zone LG1 and markedly lower temperatures for zone LG2, Stuiver et al. (1995) refer to this wide-spread phenomenon as "the failure of the strong Bolling warming pulse to produce an 'Early Holocene" ' , implying that in spite of temperatures during part of BMling comparable to the early Holocene no vegetation development comparable to early Holocene is reconstructed. Walker et al. (1993) discussed for the British Isles a similar apparent contradiction between temperature reconstructions based on past vegetation (cool during early Boiling, increasing temperatures during Older Dryas, warmer during Allerod) and on beetles (warm during early Boiling comparable

to early Holocene, cooling during Older Dryas towards less warm conditions during Allerod). Van Geel et al. (1989), noting a similar situation for The Netherlands, tried to reconcile the avail- able evidence for The Netherlands and the British Isles by explaining the lag of the vegetation by insufficient soil formation and strongly fluctuating climatic conditions, which, however, would not hamper quickly responding organisms like beetles; after the Older Dryas the vegetation seems generally to be more in equilibrium with climate.

5.2.4. Zone LG3 (14 060 12 850 ca lyr B,P.: Allerod)

All pollen types indicative of pioneer vegetation mentioned for zone LG2 decline. An increase of Quereus 13 at the base of zone LG3 to nearly 10% suggests a marked expansion of oak. Quereus is a good pollen producer, and the pollen is easily dispersed; the expansion may have taken place on a modest scale or far away, probably at lower elevations. A strong, abrupt increase of Betula alba 5 to ca. 30%, an increase of Erica arborea- type 25, and a strong, abrupt decline of Gramineae 9s from ca. 40 to ca. 15% suggest a rapid invasion by birch trees and tree-heather into grass-rich vegetation near the site. Frangula alllbIS 12, a tree producing little pollen, was present near the site. Juniperus communis 2° and Calluna vu[garis 23 decline, possibly overshadowed by the taller-growing trees and tree-heather. Declines of pollen types indicative for moist soils (Lotus 5v, Parnassia palustris 61, Cyperaceae 84, Potentilla 94, Dt3,0pteris-type m2, and Sax(l?aga stellaris-type 1°7) suggest that also the marsh vegetation near the site was invaded by trees and tree-heather. Declines of many herbs (Thymelaeaceae ~6, Lyehnis/Silene elegans ~'6, Pentaglottis sempervirens 69, Hvpericum perforatum-type 92, Centaurea nigra-type v2, Aster- t.vpe 9v, Campanula ~°°, and Rumex acetosella- O'pe ~l°) suggest that trees and shrubs invaded species-rich herb vegetation near the site. Declines in both percentages and concentrations of Ephedra ji-agilis-type 22, Artemisia 5°, and Chenopodiaceae- type ss may be explained in two ways: a disappearance of inorganic soils through humus accumulation in lower-lying areas, or (more probably) a filtering of pollen by the taller and denser vegeta-

141..0. van der Knaap, J.F.N. van Leeuwen / Review

Lagoa Comprida Pollen-percentage diagram.

++ /

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1 (1600 m), Late-Glacial and early Holocene Analysis: Jacqueline van Leeuwen

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Fig. 6. pollen-percentage diagram of lagoa Comprida 1, Late Glacial and early Holocene part. Pollen zones are line indicates an inferred hiatus in the sediment.

9f Palaeobotany and Palynology 97 (1997) 239 285 pp. 257 258

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p p . 2 5 9 - 2 6 0 W..O. van der Knaap, J.F..N. van Leeuwen / Re

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262 II1/. O. van der Knaap, J. £ N. van Leeuwen / Review o/Palaeobotany and Palynologv 97 (1997) 239-285

Covdo do Boieiro (1750 m), Lete-Gl(~ciGt Pollen-concentrution diagram (gruins/O.O01 ml) s e l e c t e d p o l l e n l yPes

I / 75C . . . . y

76C - -

770 }

\,

i / i | i

/

// /

- - - 7

/ _ _ /

\,

\,

! I,

rind eorly Holocene

/ Chrono-

</ / ; '~ - L---I .....

! '!t ' A5

%\ !, x\

\\

i v.

A4,

8 4 0

850"

Be01 . . . .

87t - - - -

///// f '

/

/

i ̧ ,

- j 250 250 ' ' ' ' ~ ~ - - ~ " ~ 2~0

i LG5 ,~

i !

LG4 !

LG3

Fig. 9. Pollen-concentration diagram of Covfio do Boieiro, Late Glacial and early Holocene part; selected pollen types. Pollen zones are delimited with horizontal lines; the thick line indicates the inferred Late Glacial/Holocene transition, the hatched line indicates an inferred hiatus in the sediment.

tion directly around the site. Similarly, declines of herbs of poorly developed soils (Plantago mdicata- type 59, Arenaria ~2, Compositae liguliflorae ~°, Radiola linoides sl, Paronychia polygonifolia-type vg, and Reseda/Sesamoides 78) suggest either soil formation near the site or filtering of pollen by a belt of tall vegetation. An increase of Botrvchium 1°(' suggests soil development. A decrease in sediment bulk density confirms the idea of denser vegetation. it is clear that soil formation and development of taller, denser vegetation took place simulta-

ne ous ly . P i f t u s 2 percentages declined, but concentrations increased, suggesting some expansion of pine trees. A needle of Pinus cf. ~vlvestris in zone LG3d and Pinus stomata in zones LG3a and LG3c prove that pine trees grew near the site. The low pollen percentages of generally no more than 15% suggest, however, that pine trees must have been rare, The climatic implication of the inferred vegetation changes at the base of zone LG3 is a marked increase in temperatures and precipitation.

Zone LG3 shows little variation in percents of

V~ O. van der Knaap, .LF N. van Leeuwen / Review o f Palaeobotany and Palynology 97 (1997) 239-285 263

the dominant pollen values, suggesting little change in the vegetation dominants around the site (e.g., Betula alba, Salix, Frangula alnus, Rumex acetosella, Botrychium). In contrast, vegetation changes are suggested by many minor pollen types (values below 0.5%) at different levels: 10 pollen types disappear in zone LG3a; 5 disappear and 4 appear in zone LG3c; 2 disappear and 4 appear in zone LG3d; and 3 disappear and 3 appear in zone LG3e. In addition, other minor pollen types (<4%) increase or decline at subzone boundaries: 10 pollen types decline and 4 increase in zone LG3a; 4 decline and 3 increase in zone LG3b; 6 decline in zone LG3c; 1 declines and 2 increase in zone LG3d; 3 increase in zone LG3e; 1 declines and 4 increase in zone LG3f. These changes might reflect either autogenous vegetation succession resulting from soil formation and plant interactions or climatic change. We consider possible climatic impacts below.

Zone LG3b is a short transitional zone in which Betula alba 5 increases and Erica arborea-type 25 and Gramineae 98 decline, suggesting denser stands of birch that overshadow tree-heather and grass- rich vegetation near the site, suggesting increased precipitation. Zone LG3c shows the highest Betula alba 5 percentages recorded for this site (ca. 60%), suggesting abundant birch trees nearby. Closed Betula alba thickets are probably responsible for declines in sediment bulk density and in percents of Pinus 2, Juniperus communis 2°, Calluna vulgaris 23, Artemisia s°, and Botrychium 1°6. The appearance of Sphagnum ~65 indicates development of peat along the lake. The changes in zone LG3c might be the outcome of autogenous vegetation succession following the increased precipitation suggested for zone LG3b. In zone LG3d, a decline of Quercus 13 to 5% also suggests cooling. This is supported by a slight increase in sediment bulk density, possibly caused by increased erosional input. Sorbus aucuparia ~° may have arrived near the site at this time, and the presence of Cytisus purgans (Genista-type 3° pollen) is evidenced by a twig. In zone LG3e, a slight decrease of Betula alba 5 and increases of Narcissus bulbocodium 116 and Peucedanum-type tz° suggest paludification and opening of Betula alba stands around the lake. This transition might reflect autogenous vegetation

succession independent of climatic change. In zone LG3f, a Quercus 13 maximum in a few spectra and a minimum in sediment bulk density suggest increased temperatures. The Intra-Allerod Cold Period of Stuiver et al. (1995) may correlate with a minor Quercus 13 minimum (zone LG3e).

5.2.5. Zone LG4 (12 850 12 435 cal yr B.P.; first phase of Younger Dryas)

A marked decline of Quercus 13 to 3% and the disappearance of Fraxinus angustifolia 7 pollen (present since zone LG2) suggest decreased vitality of forests at lower elevation. Declines of Betula alba 5 and Salix s suggest an opening of the thickets near the site. Increases of Compositae liguliflorae 7°, Botrychium 1°6, Gramineae 98, Cruciferae 96, Saxifraga stellaris-type 1°7, and Umbelliferae undiff.~33 suggest expansion of open vegetation, probably replacing the birch-willow thickets. A marked increase in sediment bulk density suggest increased erosion in the catchment and/or decreased productivity in the lake. These trends are spread out over a ca. 150 cal yr period, suggesting a gradual cooling.

In zone LG4b, increases of Plantago radicata- type 59, Meum-type 123, and Bupleurum 124 might reflect colonization of organic soils during a period of open vegetation and cooling. Plantago radicata grows well today in wind-exposed localities of the highest subalpine vegetation zone on organic soils where other vegetation is destroyed through over- grazing. Bupleurum does not grow in the Serra da Estrela today and might represent a local species extinction. Meum-type is not produced by any modern Portuguese species as far as we are aware. It might be derived from Meum athamanticum, a common species in temperate European mountains on organic soils on acid bedrock.

In zone LG4c, disappearance of Frangula alnus ~z and Sorbus aucuparia 1° and minor declines of Salix 8, Calluna vulgaris 23, and Genista-type 3° suggest impoverishment and reduction of shrub and dwarf-shrub vegetation near the site. Increases of Artemisia 5°, Paronychia polygonifolia-type 79, Aster-type 97, and Gentiana lutea/pneumonanthe 125 suggest expansion of herbs near the site, possibly as a replacement of shrubs and dwarf-shrubs.

264 W. O. van der Knaap, J. 1~ N. van Leeuwen / Review of Palaeobotany and Palynology 97 (1997) 239 285

Causes for these changes could be a slightly cooler or drier climate.

5.2.6. Zone LG5 (12 435-11 630 calyr B.P.; second phase of Younger Dryas)

Several pollen trends move in the direction of values in zone LG1 (Boiling), when pioneer vegetation was predominant: Quercus ~3 declined to 1% in zone LG5a and Betula alba s to 20% in zone LG5b, suggesting a strong reduction in number or in flowering of trees, and Pinus 2 percents increase, as do Artemisia s°, Plantago radicata-type sg, and Chenopodiaceae-type 5s. A change in the direction of pioneer vegetation is also suggested by a second maximum (in some cases for zones LG4 and LG5 jointly), after the first maximum in zone LG2, for various herb pollen types (Hypericum perJbratum- type 92, Reseda/Sesamoides 78, Aster-type 9v, Campanula 1°°, and LysimachiaXl~). A decline in sediment bulk density may suggest decreasing erosional input. This shift may be explained by a drier but not necessarily cooler climate, which reduced inflow into the lake. Betula alba seeds were abundant in zones LG3b and LG3d, but absent in zone LG5a. Unique features of zone LG5 are the very high maximum of Meum-type 123 and maxima of Peucedanum-type ~2°, Compositae tubuliflorae undiff. 121, Gentiana lutea/pneumonanthe 12s, Bupleurum lz4, and Veratrum album 126, suggesting a vegetation type that has no modern analogue in Portugal. The ecological conditions must have combined a periglacial climate with well-developed soils.

Zone LG5 can be subdivided on the basis of dominant pollen types. Zone LG5a includes the entire Quercus ~3 decline, suggesting that the inferred decrease in precipitation took effect imme- diately at lower elevation (where Quercus is inferred to have grown). Betula alba s declines only marginally in zone LG5a and was apparently not (yet) fully affected; but increases of Meum- type 123 and Compositae tubuliflorae undiff.~21 indicate that the vegetation near the site changed. Zone LG5b shows a decline of Betula alba s and increases of Plantago radicata-type s9, Gramineae 98, and Meum-type ~23 suggesting that the vegetation near the site changed further as a result of climatic change. Zone LG5c shows increases of

Pinus 2 and Rumex acetosella-type11°; dominant species near the site might be Meum athamanticum, Rumex acetosella, and various grasses. Zone LG5d shows a decline of Meum-type 123, small maxima of some shrubs (Calluna vulgaris 23, Sarothamnus grandiflorus 28, and Genista-type3°), and maxima or increases of various herbs (maxima of Lychnis/Silene elegans 66, Paronychia polygonijolia -type 79, Gramineae 98, Rumex acetosella-type 11°, Bupleurum 124, Veratrum album 126, Umbelliferae undiff.133, and Anthriscus sylvestris ~36 and increases of Sedum-type 13°, Chaerophyllum temulentum 13s, and Daucus143), suggesting an increase in vegetation cover near the site. The latter might be explained by simultaneous rises in temperature and precipitation in zone LG5d, which would also explain that sediment bulk density remains constant (increased run-off compensated by denser vegetation). Also Quercus 13 increased in this zone, suggesting improved conditions in the lowlands.

5.2.7. Hoh)cene In the complete Holocene pollen diagram of

Charco da Candieira published in Van der Knaap and Van Leeuwen (1995) a different pollen sum was applied, excluding pollen from plants of moist habitats. Such a pollen sum is not optimal for the early Holocene; we argued, for example, that Betula alba might better be included in zones A1 and A2 and Gramineae in zones AI to B3 (Van der Knaap and Van Leeuwen, 1995), as is done in this paper. The inferred vegetation dynamics are more clearly reflected in the pollen diagram this way. We will summarize here the results with short references to climatic implications.

For zone A la (11 630-11 490 calyr B.P.), a rapid expansion of Betula alba s, Salix 8, and Frangula alnus 12 near the site is inferred. The dominant vegetation type on dry ground was probably an open, Betula alba-dominated woodland. Quercus 13 expanded probably at lower elevations in mountain valleys. In zone Alb ( 11 490-11 265 cal yr B.P.) the Quercus expansion is minor, probably still away from the site, and a pronounced maximum of Sorbus aucuparia 1° suggests an open tree canopy near the site. In zone Alc (11265 11090 ca lyr B.P.) Quercus ~3 expanded again, possibly still not near the site.

W.O. van der Knaap, J .FN. van Leeuwen / Review o f Pal

Chafariz Pollen-percentage dlagram.

195

200

205

210

215

220

225

230

235

240

245

250

255

260

265

270

275

do Rei (1770 m), Late-Glacial Analysls: dacqueline van Leeuwen

?

j] '

Ii - - i

4 / } ' / I / X l I / / / , ' / ,

I . i ill , / i "]'t

• i i

1 i,lii !

i I

¢'-'I'

i i ,

and early Holocene

,,~/ 2/+,

_~ F:,

i -" i l

J ' i .'I, t

L ii i

[.,

i i

i , i ;

.~l}i! !I ii!i~ i,i ri+i-i~

llli i /,,),G-.

Fig. 10. pollen-percentage diagram of chafariz do Rei, Late Glacial and early Holocene part. Pollen zones are delimit, lines indicate inferred hiatuse

aeobotany and Palynology 97 (1997) 239-285 pp. 265-266

/ Gl~ono-

~d with horizontal lines; the thick line indicates the inferred Late Glacial/Holocene transition, the hatched Js in the sediment.

pp. 267-268 W.O. van der Knaap, J.EN. van Leeuwen / Review of Palaeobotany and Palynology 97 (1997)

Chafariz do Rei (1770 m), Late-Glacial and early Hoto Pollen-concentration diagram (grains/O.O01 ml) selected pollen types

q

£

f f Ch Z

i ~////////~ Z

L

2 5 0 5 0 0 ~ ' ' ' ~ 5 0 2 5 0

Fig. l 1. Pollen-concentration diagram of Chafariz do Rei, Late Glacial and early Holocene part; selected are delimited with horizontal lines; the thick line indicates the inferred Late Glacial/Holocene transition, inferred hiatuses in the sediment.

239-285

c e n e

r o n o - ones

A5

A4 / / / / / / i

G5d v / / / / / x

.G3

.G2

.G1

pollen types. Pollen zones the hatched lines indicate

Charca dos C6es Pollen-percentage diagram.

IV.. O. van der Knaap, J.EN. van Leeuwen / Review of Palaet

(1795 m), Late-Glacial and early Holocene Analysis: dacquellne van Leeuwen

6 4 3 0 ,h 45

Fig. 12. pollen-percentage diagram of charco dos C~Ses, Late Glacial and early Holocene part. Pollen zones are delimited lines indicate inferred hiatuses il

~botany and Palynology 97 (1997) 239-285 pp. 269-270

t i F

/

7 ~

?Sg

B4

812

?82

TI!I ~]/~!I ..... ! ! i I :;[

with horizontal lines; the thick line indicates the inferred Late Glacial/Holocene transition, the hatched a the sediment.

pp. 271-272 IV.. O. van der Knaap, J. F N. van Leeuwen / Review o f Palaeobotany and Palynology 97 (19!

Charca dos C~es (1795 m), Late-Glocial and early Holoc Pollen-concentration diagram (grains/O.O01 mt) selected pollen types

Fig

- -1 151

_ _<. \ L -~ ") \

i

, f

Fig. 13. Pollen-concentration diagram of Charco dos C6es, Late Glacial and early Holocene part; select~ are delimited with horizontal lines; the thick line indicates the inferred Late Glacial/Holocene transitio inferred hiatuses in the sediment.

[ ~d pollen types. Pollen zones n, the hatched lines indicate

e~

-6 e~

o

e-~

~2

t -

z ~

W.O. van der Knaap, J.FN. van Leeuwen / Review of Palaeobotany and Palynology 97 (1997) 239-285 273

+

+

! ~ ~.~. L~

+ ~

+ ~

< < i ~ ~

< <

O

b

=

+ <

e~0

e~

~. The slowness of expansion of Quercus to higher ii elevations in zones A l b and A l c (ca.

11 490 11 050 cal yr B.P.) is most clearly reflected ~= in the pollen-concentration diagram and might o have had a climatic cause; we correlate the period o

with the Preboreal Oscillation of Ammann and ~. Lotter (1989). Zone A2 ( 11 050-10 900 cal yr B.P.) ©

shows declines of various herbs and of Sorbus b aucuparia 1°, but not of Betula alba 5, and a next

rl phase of Quercus 13 expansion, suggesting denser

~" woodlands and the first arrival of oaks near the '= site as a result of climatic warming. In the first

part of zone A3 (10900-10525 ca ly r B.P.) ~. ~ Quercus 13 increased while Betula alba 5 declined,

.= suggesting a replacement of birch woodland with ~ ~" oak forest near the site as a result of climatic

~ warming, and Taxus baccata TM appeared. From "~ ~ then onwards (855 cm; 10 750 cal yr B.P.) oaks

~ became dominant and birches were restricted to .= ~ moist habitats. In zone A4 (10 525-10 175 cal yr • ~_ ~ B.P.) inferred abundant flowering of oaks and

inferred scarcity of mesophytic taxa suggest the = start of a xerothermic period. In zone A5

.= -~ (10 175-9525 cal yr B.P.) slightly moister condi- gn. tions are implied by the expansion of mesophytic

-~ ~ herbs and closure of the forest canopy, suggested H by a reduction of low-tree and high-shrub taxa. I The Quercus expansion may have occurred in

pulses marked by zone boundaries, rather than as -= ~ = a gradual rise. This episodic pattern may reflect -~ ~ fluctuations in temperatures and precipitation evi-

: - dent in the ~180 curve from Greenland. ~ ~ The two-fold role of Betula alba as an invader

"~ on dry inorganic soils and as a climax tree on ~ N 2 E ~;~ ~ ~ moist organic and peaty soils is supported by the _~ ~ ~ habitat description in Flora iberica II (Castroviejo

~ .-= et al., 1990, p. 40), where the species is said to ~. ~= occur on peaty soils and along streams mainly in :~° ~ the montane zone, and also to behave as an invader

~ ~ ~ on stony ground and in burned or deforested areas.

5.3. Zonation in past vegetation

The vegetation history at Charco da Candieira in terms of structure and cover (irrespective of species composition) may be summarized as follows: zone LG1 (14800 ca ly r B.P.), no trees, mainly unvegetated soils and open pioneer vegeta-

274 W.O. van der Knaap, J.F.N. van Leeuwen / Review ~f Palaeobotany and Palynology 97 (1997) 239 285

tion; zone LG2 (14 270 cal yr B.P.), replacement of most of the open pioneer vegetation by more closed shrub and herb vegetation and open woodland; zones LG3 (14060 ca ly r B.P.), LG4, and LG5, mainly open woodland, reaching its maximum density in zone LG3c, becoming more open in zone LG4 (12 850 cal yr B.P.), and very open in zone LG5 (12435 ca ly r B.P.); zone LG5d, expansion of both open woodland and treeless shrub vegetation; zone A (beginning of Holocene; 11 630 cal yr B.P.), mainly forest, rather open in zones A1 ( 11 630 cal yr B.P.) and A2 ( 11 050 cal yr B.P.) but becoming denser in zone A3 ( 10 900 cal yr B.P.). Tentative palynological criteria for vegetation structure are: Anthemis-type, Chenopodiaceae- type, and high values of Artemisia characterize open pioneer vegetation; Calluna vulgaris and Juniperus communis characterize treeless shrub vegetation; Plantago radicata-type ranges from open pioneer vegetation to more closed treeless vegetation and to very open woodland; Botrychium ranges from more closed treeless vegetation to very open woodland and, in low values, to rather open forest; Betula alba indicates open woodland or forest; very low values or absence of all non- arboreal pollen types mentioned indicate forest. Pinus and Quercus pollen are considered unsuited as indicators for vegetation structure, because these pollen types are dispersed easily over large dis- tances. These criteria applied to the other pollen diagrams leads to the results shown in Table 6.

The scheme in Table 6 suggests an altitudinal zonation changing with time as follows. In zone LG1 (Boiling) no zonation can be observed. In zone LG3 (Allerod) open woodland occurred at 1409 m elevation and treeless vegetation at higher elevations. In zone LG4 (Younger Dryas, first phase) open woodland occurred at 1409 m elevation, treeless vegetation at 1600-1730 m elevation, and open pioneer vegetation at 1845 m elevation. In zone LG5 (Younger Dryas, second phase) very open woodland occurred at 1409 m elevation, treeless vegetation was present at 1600 1730 m elevation and localized open pioneer vegetation at 1600 m elevation, and open pioneer vegetation pre- vailed at 1835-1845 m elevation. In zones A l a to A3 (beginning of Holocene) forest occurred at 1409-1645 m elevation and treeless vegetation at

1730 1845 m elevation. In zone A4 localized very open woodland was present at 1770 m elevation. In zone A5 denser forest occurred at 1409 1645 m elevation, rather open forest at 1730 m elevation, both open woodland and treeless vegetation at 1770m elevation, and treeless vegetation at 1835 1845 m elevation. The vegetation at 1770 m elevation during zones A4 and A5 can be charac- terized as the struggle zone at the upper forest limit.

I f we assume that periods when vegetation shifted to higher elevation were times of warmer and possibly also wetter conditions, the following climatic changes can be inferred. Zone LG2 (end of Bolling and Older Dryas) shows climatic warming, zone LG3 (Allerod) shows a thermal optimum, zones LG4 and LG5 (Younger Dryas) show two steps of cooling, zone A l a (start of Holocene) shows the dramatic warming at the onset of the Holocene, and zones A4 and A5 show (weakly and more strongly, respectively) the next climatic improvement. This climatic reconstruction is in accordance with that based on Charco da Candieira alone, although it is less detailed and lacks information on precipitation.

5.4. Hiatuses in the record and lake-level changes

In Table 6, pollen zones for which there is no record (marked with dot) might be present in the sediment between adjacent pollen samples or below the lowest pollen sample. On the other hand, missing pollen zones (marked with hyphen) may represent sedimentary hiatuses. Because the trends in dominant pollen curves at each site are b road ly similar for both percentage and concentration diagrams, sediment-accumulation rates are assumed to have been generally constant at each site, implying that thicknesses of pollen zones relative to each other must be approximately similar in all sites. Based on this assumption, pollen zones that disappeared between two pollen samples, although present in the sediment, can be distinguished from those that are actually missing from the sediment.

Sites without missing pollen zones mostly have soft Late Glacial sediments, whereas sites with missing pollen zones have compact Late Glacial sediments (Tables 6 and 3). This suggests that the hiatuses were caused by drying of the lakes after

Lagoa das Salgadeiras (1835 m), Late-Glacial and early Holocene Pollen-percent~e dla~m~r~. Anolysls: Jocqueline yon Leeuwen

W. O. van der Knaap, J.F.N. van Leeuwen / Review o f Pala,

B2~O ~, 6 0 I

Fig. 14. pollen-percentage diagram of lagoa das Salgadeiras, Late Glacial and early Holocene part. Pollen zones are c hatched line indicates an inferred h

zobotany and Palynology 97 (1997) 239-285 pp. 275 276

. - , . / /~, , . . . . -y

/

,t,ilti,it, , i i

t221 t B2

I

701

801 A5 / / / / s

A l a

Jelimited with horizontal lines; the thick line indicates the inferred Late Glacial/Holocene transition, the iatus in the sediment.

Fi

pp. 277 278 W.O. van der Knaap, J.F.N. van Leeuwen / Review of Palaeobotany and Palynology 97 (199

Lagoa dos Salgadeiras (1835 m), Late-Glacial and early H

Pollen concentration diagram (grains/O.O01 ml) selected pollen types

~J 345-

350 !

355 - -

560

i

365

37(

57~

3

/ \

\

x, \

/ -<

\

"/~///~ ~ V////// // /////////////,

j /

\ \

250 250

///////,

'l

\

\ \

\ /

/

_# \

D <

~ "////////////////~////////,

250

Fig. 15. Pollen-concentration diagram of Lagoa das Salgadeiras, Late Glacial and early Holocene part; s zones are delimited with horizontal lines; the thick line indicates the inferred Late Glacial/Holocene I indicates an inferred hiatus in the sediment.

17; 239-285

blocene S /

,¢

Chrono- z o n e s

B2

BI

A5 Y/////////////

A1a

LG5

elected pollen types. Pollen ransition, the hatched line

Lacjoa E:lareza (1L]4b m), Late-Glacial Pollen-percenloqe diogrom, Anolysis docqueline van Leeuwen

9050 * 50 BP I

W.O. van der Knaap, J .FN. van Leeuwen / Review o f PaL

and early Hotocene

i

i _

ii

Fig. 16. pollen-percentage diagram of lagoa Clareza, Late Glacial and early Holocene part. Pollen zones are de

~eobotany and Palynology 97 (1997) 239-285 pp. 279 280

I FI I

i i i : ! i

• ' : : : .' : : :

~7~ ~

i i i i : : i

i ~ i i i

i i i i

6 4 @

777

608

limited with horizontal lines; the thick line indicates the inferred Late Glacial/Holocene transition.

LGO

LG~

LG3

pp. 281-282 I4~ O. van der Knaap, J.F.N. van Leeuwen / Review o f Palaeobotany and Palynology 97 (1997) 239

Lagoa Clareza (1845 m), Late-Glacial and early Halo Pollen-concentration diagram selected pollen types

,oQ. 385-

390-

3 9 5 - -

400-

405= - -

4 1 0

4151

4 2 0

4 2 5

4 3 0

"=~ / 440

445

4 5 0

4 5 5

4 6 0

4 6 5 2 5 0

/ /

/

/

S

(grains/O.O01 ml)

)

\ \

/

/ ¢

\

/

v/

)

5 0 0 ' 2 5 0 ' 2 5 0

1 3

Chr 7 zc

/

I

I /

__~ / i

, l

A t i

_ ~ A I

L

L

k , , L

Fig. 17. Pollen-concentration diagram of Lagoa Clareza, Late Glacial and early Holocene part; selected pollel are delimited with horizontal lines; the thick line indicates the inferred Late Glacial/Holocene transition.

-285

,:ene

6

~ono- 'iRes

\5

i ~4 l

i I

15

~2

b-c

1G

iG5

bG4

h types. Pollen zones

I~ O. van der Knaap, J .FN. van Leeuwen / Review o f Palaeobotany and Palynology 97 ( 19971 239 285 283

7

6

5

4

3

2

1

0

1 depth (m)

1795 m x

1770 m x

1835 m x

1600 m x

1730 m x

1645 m 1845 m 1409 m x x x

~ ~ ~ ~ Io

Fig. 18. Relation between number of missing pollen zones (hiatuses in the sediment; see Table 6) and depth of the Late Glacial/Holocene boundary below the present water or peat surface. Each cross represents a site. The sites are indicated by their elevation; this is underlined for sites with a Holocene sediment stratigraphy of brown-black gyttja lacking sand layers.

the Late Glacial. The similarity in dominant pollen curves at each site for both percentage and concentration diagrams suggests, however, that com- pacted sediments (mostly silt) shrunk only little. Fig. 18 shows the relation between the duration of hiatuses (expressed as number of missing pollen zones) and the depth of the Late Glacial/Holocene boundary below the present water or peat surface. This boundary is used as an approximation of water depth at the onset of the Holocene. This approximation is assumed correct for sites with a Holocene sediment stratigraphy consisting of brown-black gyttja throughout without sand layers (indicated with underlined elevations in Fig. 18), which is typical for lakes with little erosional input. It may be incorrect for sites with frequent sand layers in their sediments, of which lake levels might have changed due to changes in the morphometry of the basins. Fig. 18 shows a negative correlation between depth and number of missing pollen zones; the two sites that lie out of sequence ( 1730 m and 1645 m elevation) lack brown-black gyttja and may have been shallow lakes that dried intermit- tently. Periods of low lake level suggest low precipitation and/or high temperatures and/or dense vegetation (high evapo-transpiration). Relative lake levels for each zone might be estimated from the number of lakes showing a hiatus: high in

Allerod (zone LG3); low in most of Younger Dryas (zones LG4 and LG5a-c) ; high just before and after the start of the Holocene (zones LG5d and Ala); very low for the millennium following (zones Alb to A3); gradually increasing in the centuries thereafter (zones A4 and A5). Numerous missing records during Bolling time (zone LG1) make it difficult to estimate lake levels for this period.

Inferred lake-level changes help refine climatic reconstructions based on palaeo-vegetation alone. Low lake levels during zones LG4 and LG5 (Younger Dryas), a period with inferred low temperatures and therefore little evapo-transpiration, suggest very low precipitation. The lack of hiatuses in zone LG5d (end of Younger Dryas) suggests a strong increase of precipitation. The lowest lake levels probably occurred during zones Alb to A3 (most of Preboreal), as a result of increased temperatures and expanding vegetation at the Late Glacial/Holocene transition zone Ala, which increased evapo-transpiration. Changes in precipitation cannot be reconstructed for zone A la (beginning of Holocene) from lake-level changes because of the strong rise in temperatures counteracting the effect of increased precipitation. Increasing lake levels during zones A4 and A5 suggest phases of strongly increased precipitation. The evidence for increased precipitation during zones LG5d, A4 and A5 based on lake-level changes is much stronger than that based on Charco da Candieira alone.

5.5. Selected palaeo-ecological groups of plants

A number of pollen types can be summarized in groups according to their behaviour in the pollen diagrams, and the ecology of the groups may be described in terms of the three major ecological factors (climatic change, the altitudinal climatic gradient and soil development) as follows:

Group 1. Pollen types with the highest values in zone LG1 (Boiling) and in some cases a second maximum in zones LG4 and LG5 (Younger Dryas) represent plant species adapted to cold/dry periglacial conditions but losing ground under rising temperatures and/or precipitation (Pinus, Artemisia, Chenopodiaceae-type, Anthemis-type).

284 H/O. van der Knaap, J.F. N. van Leeuwen / Review of Palaeobotany and Palynology 97 (1997) 239~85

Group 2. Pollen types that increase when temperatures and/or precipitation increase and decline when vegetation becomes denser represent plant species of expanding vegetation on developing organic soils and include Botrychium (early in the succession), Calluna vulgaris (later in the succession), Juniperus communis (still later in the succession, with optimum at higher elevations), and Betula alba (still later in the succession, with low upper limit).

Group 3. Pollen types with a maximum in the Younger Dryas (zones LG4 and LG5) reflect pioneer vegetation on open organic soils ( 'secondary' pioneer vegetation) and include Meum-type, Bupleurum, and Plantago lanceolata-type. Meum- type and Bupleurum are mainly restricted to Charco da Candieira ( 1409 m) and suggest a vegetation type for this elevation that has no modern analogue in Portugal. We have no suggestion which species might have produced Plantago lanceolata- type; Plantago lanceolata itself today grows only in lower vegetation zones and is a highly improba- ble candidate, whereas other species producing the pollen type are absent in the area today. The pollen type is therefore likely to be derived from a species extinct from the Serra da Estrela today. The plants were probably absent near Charco da Candieira (1409 m) but grew at higher elevations (Lagoa Comprida 1 and 2, Cov~o do Boieiro: 1600-1730m) during the Younger Dryas (zones LG4 and LG5), suggesting a vegetation type having no modem analogue in Portugal.

Group 4. Pollen types associated with a defined vegetation density or structure (Table 6) include Rumex acetosella-type associated with the struggle zone of the forest and Plantago radicata-type associated with the upper limit of moderately open vegetation on both virgin and organic soils.

For Pinus, pollen percentages are of little help in determining local presence or absence of pine trees. Stomata and plant macro-fossils at a few sites were helpful. At Charco da Candieira ( 1409 m), a Pinus cf. sylvestris needle encountered in zone LG3d and Pinus stomata in zones LG3a and LG3c prove occurrence of pines near the site, in spite of minimum pollen percentages in this zone. Pines were therefore present around Charco da Candieira during Allerod (zone LG3), but

probably not in other periods. Stomata were counted but those of Pinus were absent at four higher-lying sites (1600, 1795, 1835, 1845 m), suggesting absence of pine trees at these elevations and an upper limit between 1409 and 1600m during Allerod. The Serra da Estrela lies just outside the present-day natural geographical distri- bution of Pinus sylvestris, which occurs in adjacent mountain areas to the north (Serra do Geras, Portugal) and to the east (Sierra de Gredos, Spain). It is not clear why the species died out in the Serra da Estrela after the Late Glacial.

Gramineae grew abundantly at all times around all sites save Lagoa Clareza (1845 m), where they were scarce or less abundant. The surroundings of this site are more stony and less vegetated today than those of other sites; this might have been so since the beginning of our records.

Zone Ala, representing the very beginning of the Holocene, has common features in pollen trends between Charco da Candieira (1409m), Lagoa Comprida 1 (1600 m) and 2 (1645 m), and Lagoa Clareza (1845 m). These are maxima of Gramineae and Rumex acetosella-type, suggesting abundance of plants near the sites, and of Betula alba, dependent on percentages suggesting abundance at 1409m and presence at 1600m, but absence around higher sites. Covfio do Boieiro (1730m) and Chafariz do Rei (1770m) (lying close together) differ from this pattern in a minimum of Gramineae and relatively high maximum of Calluna vulgaris, suggesting that the latter rather than the former was important in this phase of vegetation succession around these sites.

6. Discussion

The number of localities at a range of elevations (1409-1845 m) on a single mountain and the use of one site as a standard allowed us to reconstruct the altitudinal zonation of past vegetation. This approach would not have been possible if the study sites had been more scattered (e.g., in different mountain valleys with potentially different vegetation histories), or were at similar elevation (in the same altitudinal vegetation zone), or if no detailed standard pollen diagram had been

I4A O. van der Knaap, J.F N. van Leeuwen / Review of Palaeobotany and Palynology 97 (1997) 239-285 285

p roduced . The s t anda rd site was s tudied in enough detai l to cor re la te the record with the 61so curve o f the G r e e n l a n d ice core GISP2. M i n o r cl imatic f luctuat ions are reflected in the pol len curves and p rov ide a de ta i led chrono logy . This s t anda rd fo rmed a basis for es tabl ishing a ch rono logy for the less de ta i led pol len d iagrams , and the differ- ences a m o n g pol len d i ag rams were in te rpre ted in terms o f pas t changes in a l t i tud ina l zona t ion o f vegeta t ion. The inferred a l t i tud ina l vege ta t ion zona t ion and its changes in t ime are interes t ing in itself, but they p roved also useful for conf i rming and refining the c l imat ic recons t ruc t ion based on the s t a n d a r d pol len d iagram. A high po l l en -mor - pholog ica l reso lu t ion fo rmed the basis on which it cou ld be shown tha t dur ing the Younger D r y a s vege ta t ion types occur red that have no m o d e r n ana logue in Por tuga l , which forms an i m p o r t a n t ind ica t ion for a un ique c o m b i n a t i o n o f envi ron- menta l factors dur ing this per iod.

Only casual mac ro -ana lys i s was carr ied out, but it was enough to show its great usefulness. I t p roved the presence o f P i n u s cf. sy lves t r i s at 1409 m for the Al le rod as did the presence o f s t oma ta in pol len slides and their absence in o ther pe r iods and at o ther e levat ions studied.

Acknowledgements

We thank the I so tope Physics L a b o r a t o r y in Gron ingen and the Van de G r a a f f L a b o r a t o r y in Utrecht , The Ne ther lands , for p rov id ing the rad io- c a rbon dates, Dr. Br ian Hunt ley , D u r h a m , U K , and Dr. Eric G r i m m , I l l inois Sta te Museum, U S A , for shar ing unpub l i shed da t a and cor ing in forma- t ion on L a g o a do Peixao, H a n n e k e Bos, Wies van den Brink, and F r a n k van D o n g e n for their permis- sion to use their pol len analyses once again, the Pa rque N a t u r a l da Serra da Est re la for their suppor t dur ing field work , all persons who helped cor ing for their skill and their perseverance under somet imes difficult c i rcumstances , and H e r b Wright for l inguist ic improvements . We thank Bas van Geel , C a t h y Whi t lock , and H e r b Wr igh t for their comments . The N e t h e r l a n d s Organ iza t i on for Scientific Research suppo r t ed pa r t o f this study.

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