impact of forest disturbance on the pollen influx in lake sediments during the last century

Review of Palaeobotany and Palynology 111 (2000) 19–29www.elsevier.nl/locate/revpalbo

Impact of forest disturbance on the pollen influx in lakesediments during the last century

T. Koff *, J.-M. Punning, M. KangurInstitute of Ecology, Tallinn University of Educational Sciences, Kevade 2, Tallinn 10137, Estonia

Received 13 July 1999; accepted for publication 2 February 2000

Abstract

The pollen accumulation rates of four lakes in different regions of Estonia were estimated in order to study therelationship between pollen influx and the character and intensity of disturbances in the pollen catchment area. Thepollen influx data obtained are in accordance with model calculations on the size of the pollen source areas. Theinflux of arboreal pollen and that of the dominant taxa (mainly Pinus) in the lakes investigated shows that, in thecase of small lakes (area 3–6 ha) in a forested landscapes, the bulk of the pollen originates from an area within 100–200 m around the lake. The distribution patterns of influx from two lakes situated close to each other but at differentdistances from forest fires show that past disturbances can be reliably detected when the disturbance occurred in theimmediate vicinity of the lake and at least 25% of the local pollen source area was involved. In the case of a largelake (137 ha) only fires embracing thousands of hectares can be detected in the pollen diagrams. © 2000 ElsevierScience B.V. All rights reserved.

Keywords: Estonia; forest disturbances; pollen influx; recent lake sediments

1. Introduction Knaap and Van Leeuwen, 1998). For this thedensity of each pollen type within the sedimentand the rate of sedimentation expressed as theIn biostratigraphical studies pollen analysis is anumber of pollen grains settling on a given areawidely applied method for describing past vegeta-of surface sediment (cm2) in a given time (yr) istion changes in terms of increases or declines inneeded. Hicks (1994) found that pollen influx ispercentage values of certain pollen types. Duringmore informative in the cases when the changes inthe last decades attention has been focused onthe vegetation are studied in unforested landscapesobtaining precise information on absolute fluctua-where also the pollen productivity of the localtions of pollen abundance with time, that is, pollenvegetation is rather low or when considerableinflux (Pennington and Bonny, 1970; Tolonen,changes had occurred in forest edge dynamics. The1978; Huttunen, 1980). Use of this method allowsinflux reflects changes in species abundance orfor a more precise history of individual tree taxadensity, only one must be sure that the influx(Hicks, 1992), including density of the forestcalculations themselves are reliable and not(Odgaard, 1994) and range of tree limits (Van deraffected by changes in the sedimentation rate.

The main problem in the use of pollen data in* Corresponding author. Tel.: +372-2-451-634;palaeoecological and geographical studies is thefax: +372-2-453-748.

E-mail address: [email protected] (T. Koff ) establishment of the pollen source area. The pollen

0034-6667/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved.PII: S0034-6667 ( 00 ) 00013-0

20 T. Koff et al. / Review of Palaeobotany and Palynology 111 (2000) 19–29

source area of a site is a composite concept and, The main aims of the current research were: (1)to estimate the relationship between pollen influxin reality, each taxon in the diagram will have itsand the size of the lake; and (2) to determine theown pollen source area according to its pollenpotential limits of detecting the disturbances in theproduction and dispersal abilities, depending atvegetation on the catchment on the basis of pollenthe same time on the size of the site. The natureinflux values.of pollen representation has been subject of much

For these purposes four lakes in different partsdiscussion over several decades (Tauber, 1965;of Estonia with different sizes and disturbanceAndersen, 1970; Janssen, 1973; Kabailene, 1979)regimes but with quite similar catchments andwhich has provided material for different modelsfeeding types were selected.(Jacobson and Bradshaw, 1981; Bradshaw and

Webb, 1985; Prentice, 1985; Jackson 1990; Sugita,1994, 1998) for establishing the pollen source area.

There have been numerous theoretical studies 2. Study sitesbut comparatively little empirical data with whichto evaluate the models. Many models have been All the lakes selected (Table 1) are dystrophiccalculated in regions with a homogeneous forest or semidystrophic closed lakes situated in forestedcomposition in rather densely forested areas. landscapes (Fig. 1) where, according to historicalEstonia provides good possibilities to test these data, only small disturbances (with the exceptionresults in a mosaic of vegetation types. The need of Lake Tanavjarv) have occurred influencing thefor such studies has increased because it is not lake and its surroundings. In the case of Lakeenough just to determine the broad regional trends Matsimae the disturbances include some agricul-in vegetation development. Changes at a local level tural activity and clear-cutting in the forest whenare more important for predicting the resistance a gravel quarry was established in the vicinity ofand resilience of the ecosystem under different the lake. In the case of Lake Odre clear-cutting of

forest occurred at various distances from the lakeloads and therefore it is important to estimate theand in the case of lakes Tanavjarv and Mustjarvlimits of pollen analysis in investigations of thatforest fires were present. The studied sedimentkind. Natural and human disturbances are impor-sequences were formed during the 20th Century intant factors affecting the development of eco-a rather even accumulation. Lithologically all thesystems. Fossil pollen can potentially providestudied sediments were homogeneous brownishcrucial empirical data over thousands of years andgyttja.the study of the history of human impact based

on pollen data is important. However, to interpretfossil pollen records connected with a disturbance 2.1. Lake Tanavjarvwe have to know the effect of the lake size, itscatchment area and the size of the disturbed patch Lake Tanavjarv (59°10∞N, 23°48∞E) (Fig. 1b;

Table 1) is situated in western Estonia. The lakeon the pollen representation of the disturbance.

Table 1Characterisation of the study sites

Characteristic Odre Matsimae Tanavjarv Mustjarv

Elevation (m a.s.l.) 95 77 19 19Length (m) 260 340 2300 300Width (m) 140 230 830 270Area (ha) 3.0 5.5 136.9 4.8Maximum depth (m) 9.1 8.1 2.5 2.7

21T. Koff et al. / Review of Palaeobotany and Palynology 111 (2000) 19–29

Fig. 1. Location of study sites (a), main vegetation units and disturbances around the studied lakes: (b) lakes Tanavjarv and Mustjarv;(c) Lake Matsimae; (d) Lake Odre. In (b) the areas disturbed by forest fires in 1952 (—), 1980, 1992 and 1997 ( · · · ) are shown.

is elongated in the northeastern–southwestern sance and forestry maps we determined thatthe surroundings of the lake have suffered fromdirection. The lake is semidystrophic and precipita-

tion-fed with no inlets or noteworthy outlets. The several forest fires during the last century. Thelast fire was in 1997 destroying the forest neareastern and western shores of the lake are sandy.

The lake is surrounded by a big mire system and the northern shore of the lake. In the same area(within a radius of 10 km) fires have also occurredthe main vegetation type here is the pine forest.

Around the lake sandy soils, poor in nutrients due to the very flammable and dry pine forest;in 1992 ca. 460 ha was burnt and in 1980 ca.predominate presenting favourable conditions

only for Pinus sylvestris. Betula spp. also grows 100 ha. The most extensive fire occurred in 1952when an area of ca. 2000 ha of the forest wason the shores of the lake. The nearest settled

areas and fields are located ca. 7–8 km to the burnt. A fire can last for months because of thepeat cover.NW and SW from the lake. Using air reconnais-


2.2. Lake Mustjarv the southeastern and northwestern swampy shoresbirch grows. The main economic activity in thearea is forestry and thus the main disturbanceLake Mustjarv (59°10∞N, 23°48∞E) (Fig. 1b;

Table 1) is situated only 800 m to the south of affecting the vegetation around the lake could beclear-cutting of the forest. On forestry maps it wasLake Tanavjarv and therefore the surrounding

vegetation of both lakes is rather similar. The lake possible to distinguish that a mature pine foresthad stood around the lake before 1953. On thehas swampy shores, surrounded with pine trees

and birches towards the north and west with an map from 1963 this area is marked as a youngpine forest, indicating that in the meantime largeopen mire landscape towards the east. There is no

historical evidence of any fire in the immediate areas of the forest had been cut down. After theestablishment of a National Park in 1979 clear-vicinity of the lake. The distance to the biggest

forest fire area close to Lake Tanavjarv is 2.5 km cutting ceased. The nearest agriculturally used areais situated 1–2 km to the south from the lake.to the north.

2.3. Lake Matsimae3. Methods

Lake Matsimae (59°04∞N, 25°31∞E) (Fig. 1c;Table 1) is situated in central Estonia. The lake is Cores (50–60 cm) from the upper unconsoli-

dated surface of sediment were taken using aalmost circular in shape. Sediments are evenlydistributed in its deeper central part and close to modified Livingstone–Vallentyne piston corer

(diameter 7 cm) in the deepest part of the lake.the eastern shore. The lake is surrounded by anopen stretch of bog where Pinus sylvestris grows. The lithology of the sediment was described

directly at the study site. Sampling was continuous,Along the western shore is an esker covered withBetula pendula, Alnus glutinosa and Picea abies. with the sampled layer 1 cm thick. Samples were

kept in the refrigerator prior to analysis. SamplesWithin a distance of ca. 10 km from the lake largebogs and swamps unsuitable for agricultural activi- were dried at 105°C. From the same sample

different analyses were performed for the upperties predominate. Favourable places for farmingare found only on some eskers on the limnoglacial 25 cm part of the cores, which covered approxi-

mately the last 90–100 years.plain. On one esker, close to the western shore ofthe lake, a single farm with a garden and a fallow For pollen analysis a 50 mg dried sample from

the sediment core was boiled in 10% KOH andfield is located. Older maps give evidence of fieldsca. 20 ha in size at the end of the 19th Century. treated according to standard acetolysis (Moore

and Webb, 1978). Three to six tablets with aFor 5 yr from 1961 onward, the esker was exca-vated as a gravel quarry (covering 8.2 ha). Use of known content of Lycopodium spores were added

to each sample at the beginning of laboratoryland for agricultural purposes ceased and later P.sylvestris was planted on the quarry. At the end treatment to calculate the pollen concentration

(Stockmarr, 1971). In general, at least 500 arborealof the 1950s a swimming pool was built in the lakeand since then the lake has been intensively used pollen (AP) grains were identified under the micro-

scope. From all the pollen slides also charcoalfor recreational purposes.pieces �100 mm2 were counted, and their concen-tration and total surface were calculated.2.4. Lake Odre

For age estimation various methods were used.The core from Lake Matsimae was dated in theLake Odre (57°45∞N, 26°27∞E) (Fig. 1d;

Table 1) is situated in southern Estonia, in the most detailed way. Here we applied the 210Pbmethod and as the reference levels the layers withnorthern part of the Karula National Park. It is a

typical woodland lake, shaped by the mosaic hills maximum 137Cs activity (ref. yr=1986) were sepa-rated. The appearance of spherical fly-ash particles(105–110 m a.s.l.) of the Karula Upland. The main

vegetation type around the lake is pine forest; on (SFAP) was correlated with the year 1945.


Considering the history of high temperature com- where P number of pollen grains counted frombustion of fossil fuels in Europe, the sediment the sample, LYC total number of addedlayers with a significant increase in the concen- Lycopodium spores, lyc number of Lycopodiumtration of SFAP must have accumulated at the spores counted, M dry weight of the whole sampleend of the 1940s. The age of individual layers and (g), m dry weight of the analysed sample (g), Sthe deposition rate were calculated on the basis of surface area of the sample (cm−2) and A time ofthe mean annual sedimentation rate between their the formation of the layer (yr).reference layer and the sediment surface and usingthe measured dry matter content in individuallayers (Punning and Alliksaar, 2000). The cores 4. Resultsfrom the other lakes were dated using SFAPdistribution and in the case of Lakes Tanavjarv The content of dry matter in the studied coresand Mustjarv charcoal maximums were also used. (Fig. 2) was the lowest in Lake Odre where itTo reconstruct the impact history we used histori- varied from 0.01 g cm−3 on the surface up tocal sources such as old forestry maps, land-use 0.03 g cm−3 at a depth of 18 cm and then increasedmaps, as well as oral information. rapidly. The dry matter content records from lakes

For the calculation of the pollen influx I (pollen Matsimae, Tanavjarv and Mustjarv are quite sim-grains cm−2 yr−1) the following equation was ilar (Fig. 2). No increase in the dry matter contentused: was observed in Lake Matsimae sediment due to

the erosional processes caused by the exploitationof the quarry. In Lake Tanavjarv the dry matterI=

P×LYC×M

lyc×m×S×A

Fig. 2. Dry matter content (g cm−3) (a) and age–depth curve of the studied lake sediments (b). +, Lake Odre; —, Lake Matsimae;- - -, Lake Tanavjarv; $, Lake Mustjarv.


Fig. 3. Pollen influx (grains cm−2 yr−1) curves in the studied lake sediments: +, Lake Odre; —, Lake Matsimae; - - -, Lake Tanavjarv;$, Lake Mustjarv.


content has a peak at a depth of 9 cm, which is grains cm−2 yr−1 over the last century with a shortperiod of decrease in the 1960–1970s when themost probably caused by an increase in minero-

genic matter due to wind erosion from nearby minimum values fell to 5700 pollengrains cm−2 yr−1 (Table 2). In Lake Mustjarv thesandy dunes after a big forest fire. The top 5 cm

of the lake deposits in all lakes is a loose flocculent AP influx has on average greater values than thosein lakes Odre and Matsimae with a tendencylayer. According to the age–depth curve (Fig. 2)

the mean accumulation rate in different lakes varies towards decrease in the 1960s. The greatest APvalues and their variation were established in thefrom 1.7 (in Lake Matsimae) to 2.7 mm yr−1 (in

Lake Mustjarv). Lake Tanavjarv core. Here a sharp decrease in theinflux started around the 1930s (Fig. 3) and thisThe pollen influx values of selected pollen types

for the studied lakes are given from the beginning trend continued practically till the 1950s when theinflux was similar to that of Lake Mustjarv. Sinceof the 20th Century until the present and are

presented in Fig. 3 and Table 2. The average AP the 1970s the Lake Tanavjarv core shows sharpfluctuations until present day.influx values as well as the influxes of individual

pollen types in the studied lakes differ greatly. The Pinus is the dominant type in the pollen spectrain all the studied lakes, comprising on average ca.average of AP influxes was the lowest in Lake

Odre — 7200 pollen grains cm−2 yr−1 (Table 2). 44% of the AP (Table 2). The maximum relativevalues of the Pinus content within the lakes investi-The curve is almost vertical (and therefore most

stable) up to the 1970s (Fig. 3) followed by a slight gated are rather even. However, the minimumpercentage content shows some differences betweentrend towards an increase. In Lake Matsimae the

average AP influx values are 10 700 pollen the sites. The relative content of Pinus (as well as

Table 2The minimum, maximum and average values of the pollen influx (pollen grains cm−2 yr−1) and percentages of main pollen types inthe total AP in the analysed sediment sequences of different lakes

Odre Matsimae Mustjarv Tanavjarv

Influx % Influx % Influx % Influx %

APMinimum 3800 5700 18700 8500Average 7200 10700 24400 47800Maximum 12900 14000 35700 176600

PinusMinimum 900 19 2300 20 6800 34 1200 14Average 3300 45 4400 44 11400 45 20300 42Maximum 6000 64 6600 68 16000 61 79500 58

BetulaMinimum 1400 26 1400 18 3700 20 5900 17Average 2500 35 3200 39 7500 31 15800 33Maximum 3900 64 5200 74 13600 39 50900 72

AlnusMinimum 400 6 200 2 1800 11 700 9Average 1200 15 2300 19 3700 16 8200 17Maximum 3000 25 3300 27 7700 24 32900 27

PiceaMinimum 60 1 300 2 600 3 200 1Average 300 4 700 7 1400 6 2700 6Maximum 900 10 1200 20 1900 8 8800 11


of other pollen types) is the most stable in the 5. DiscussionLake Mustjarv core. In the case of lakes Matsimae,

There are several problematical points in theOdre and Mustjarv the fluctuations in the absolutedetermination and interpretation of the pollen(influx) as well in the relative (percentages) valuesinflux values. Dating accuracy is the most crucialof different pollen types have significantly lowerissue for the calculation of pollen influx values.frequencies than in the Lake Tanavjarve core.Also the geomorphological location of a lake in aThe relative average content of Betula and Alnuslandscape causes differences in pollen distributionpollen in the total AP was 34 and 17%, respectively.and redeposition. Openness of the landscape canBetula and Alnus grow mainly close to the shorescontribute to an increase in the share of long-of the lakes and therefore their impact on thedistance transported pollen. Also important is theinflux is quite direct and depends notably on theage structure of the forest and its closeness to thevariation of the humidity regime, fluctuation ofwater table. In addition, differences in the pollenthe water level and disturbances along the lakeproductivity of different species and the fluctuationshore. This statement is verified by more essentialof the most productive flowering periods connectedvariations in the content of Betula and Alnus pollenwith climatic variations should be considered.in the diagrams for lakes Matsimae and Tanavjarv.

The predominant local pollen source is theIn these lakes the influxes of both these pollenvegetation in an area within some 200 m aroundtypes started to decrease around the 1940s andthe lake, as most authors have demonstratedhad a continuous trend till present day with maxi-(Jackson and Wong, 1992; Sugita, 1994; Punningmum values in the 1950s (Fig. 3).and Koff, 1997). Van der Knaap and Van LeeuwenThe influxes of Picea pollen are much lower(1998) observed that pollen of trees growing withinthan those of Betula and Alnus in all the studied0.3 km from the shore is several times morelakes. The average proportion of Picea in the APstrongly over-represented in pollen spectra thanis ca. 6% (Table 2). In Lake Matsimae a sharpthat of trees growing outside this range. As the

decrease can be observed around the 1970slake area (Sl) increases, also the area coverage of

(Fig. 3). In the case of Lake Tanavjarv a strong the vegetation band (Sb) around the lake willtrend can be observed from the 1940s (Table 2). increase, but its area coverage relative to the lakeOnly in Lake Odre the Picea influx record shows area will decrease (when expressed as a percentagea continuous increasing trend from the beginning of this) (Fig. 4). Thus, the proportion of the influxof the 20th Century to the present time (Fig. 3). of local pollen (from the source area Sb) into the

The differences in the influxes of the pollen of lake should fall as the lake area increases. At thebroad-leaved trees (Quercus, Tilia, Ulmus) in thelakes investigated are great (Fig. 3). The pollen ofTilia and Quercus is transported from a distanceof at least 7–8 km where a few trees are growingnear old farmhouses. Due to the small number ofpollen of these taxa in the counted samples thestatistical uncertainty is higher and thus we shouldbe very careful in interpreting these influx values.The same tendencies of high variation wereobserved also in the influxes of pollen consideredas indicators of human impact. However, note

Fig. 4. Changes in pollen source areas in dependence of the lakethat for example Cerealia-type pollen is present insize. If we presume that the dominating local pollen source areaall the studied cores irrespective of whether the(Sb) consists of ca. 200–300 m around the lake and/or openingnearest fields are located 1–2 ( lakes Matsimae and area (Sl), the proportion of this local pollen will decrease with

Odre) or 7–8 km (lakes Tanavjarv and Mustjarv) increasing of Sl. Thus, the proportion of local pollen influx intothe lake should fall as the lake area increases.from the lake.


same time we should consider not only the size of is the impact of the edge effect on pollen influx.Because of the edge effect the greatest amount ofthe lake but also the size of the ‘opening in the

forest’. A lake surrounded by a treeless mire will pollen is deposited directly at the edge of theforest. If the forest reaches the shores of a lake,act like a bigger lake in the sense of Jacobson and

Bradshaw (1981) with the mire area effectively pollen may be deposited also directly into the lake.If, however, the forest edge moves for some reasonincreasing the ‘lake’ area Sl. In catchment terms it

is the distance from the sampling point to the further from the shoreline, this deforested area willbe seemingly added to the area of the water table.forest edge that is significant.

The ratio of the pollen source area and depos- Though the approach shown above is ratherapproximate, our calculations demonstrated thatition area obtained by a geometrical approach

should be the measure of the proportion of local in the case of the small lakes — lakes Matsimae,Mustjarv and Odre (surface area 3–6 ha) — thepollen in the total influx. This approach should

help specify the approximate disturbed area to influx values were mainly determined by the vege-tation in their immediate vicinity and only distur-understand signals in the influx curves. Using the

obtained influx values it is possible to calculate bances in that area could be detected. The LakeMatsimae records show clearly a marked decreasethe approximate amount of pollen produced by

the vegetation in Sb. The ratio Sb/Sl for Lake Odre in the influx of Betula, Alnus and Picea aroundthe 1960s (Fig. 3). The esker near Lake Matsimaeis 8.3, for Lake Mustjarv 5.9, Lake Matsimae 5.5

and Lake Tanavjarv 0.7. Naturally, such assump- was and is also nowadays a suitable habitat forPicea. The establishment of the gravel quarry ledtions are correct only if the distribution of pollen

deposition is even all over the lake surface and the to the clear-cutting of the forest on the esker andconsequently to a decrease in the local pollenwidth of the Sb ‘zone’ is always some 200 m. As

our earlier sediment trap experiment on Lake source area, which is reflected, for example, in a6–8-fold decline of the Picea, Betula and AlnusMatsimae showed, in real situations the pollen

concentrations near the shores are higher than pollen influxes. As Pinus is growing on ca. 75% ofthe area of the bog surrounding Lake Matsimaethose in the central part of a lake (Koff, 1998).

When comparing the sedimentation rate of dry the influence of quarrying on the western shoreof the lake was not as important on its pollenmatter and pollen grains calculated from sediment

traps with those of sediment cores, the effect of influx.The close dependence of the influx data onfocusing, that is, accumulation into a smaller

deposition zone than the lake area must be taken disturbances in the vegetation and changes in thequantity and density of trees growing around theinto account. Hurley and Armstrong (1991)

showed that the ratio of the surface area to that lake is vividly documented also in the influxrecords of Lake Odre. Here the increase in theof the sediment depositional area in lakes similar

to such lakes as lakes Matsimae, Mustjarv and total AP and in the pollen of single types from the1960s onwards reflects a halt in clear-cuttingOdre is 0.6–0.7. In the case of Lake Tanavjarv,

where post-depositional migration of sediments is around the lake and the growing number anddensity of trees. Correlation of the decrease in theof great importance (Saarse et al., 1989), the

overall focusing correction factor might be smaller. influx of pollen from Betula and Alnus (growingmainly on the shores of the lakes) with those ofThe shoreline coefficient, K, which reflects the

shape of the lake, must also be taken into account. the total AP and Pinus in the case of LakeTanavjarv indicates that some part of the pollenK is the ratio of the shoreline length to the

circumference of the circle with an area equal to of these taxa originates from a local (some hundredmetres from the lake) source. Comparison of thethat of the lake. Lakes Matsimae and Odre, which

are almost circular in shape (K=1.05) compared influx values with the area of Lake Tanavjarvshowed, that in the case of large lakes a majorto a K value of 1.23 for Lake Mustjarv. The

elongated shape of Lake Tanavjarv increases its K part of the pollen influx originates from outsidethe 200 m vegetation band around the lake. Thisvalue to 1.38. The higher the K value, the greater


suggests that a disturbance covering a much larger ( Koff et al., 1998). The pollen of Quercus, Tiliaand Ulmus in the studied cores originates fullyarea ought to be detectable. Changes in the influx

values of different pollen types are the most from outside the immediate vicinity of the lakes.These species can be found around farms some 7–remarkable in the case of Lake Tanavjarv. As the

time of forest fires and their extent are well docu- 8 km from all the studied lakes. Thus it seems thatthere is some background value of broad-leavedmented [Fig. 1(b)], it is possible to draw some

conclusions about the spatial extent of a detectable tree pollen in the atmosphere and fluctuations inthe pollen spectra from the upper part of sedimentdisturbance around the lake.

In detecting disturbances Sugita et al. (1997) cores reflect more statistical uncertainties thanthose in the forest composition.regarded a value of 10% change in the pollen

loading or percentage after the disturbance as the Direct indicators of long-distance transporta-tion of pollen are also Cerealia-type pollen, whichthreshold for detectable change. Proceeding from

this value they concluded that disturbances of any was found in all the studied sites. This is clearevidence of the presence of long-transported pollensize only 100 m away from a lake of 3 ha in area

do not create detectable changes in the pollen as the studied lakes are situated rather far fromthe nearest fields ( lakes Tanavjarv and Mustjarvloading of any of the taxa. Our data show that a

disturbance patch covering ca. 30% of the area 7–8 km, lakes Odre and Matsimae 1–2 km). Theinflux of long-transported pollen to a certain lakewithin a 100 m wide band around a lake of ca

6 ha (Lake Matsimae) in area is detectable in (especially larger than 3–6 ha) of course alsodepends greatly on the openness of the landscape,pollen influx. When a disturbance occurred outside

this distance (Lake Odre, Lake Mustjarv) the dominant atmospheric circulation mechanisms,aboveground turbulence, etc.changes in the influxes could not be determined

unambiguously. In the case of a sufficiently large Statistically irregular fluctuations in the long-transported (not closer than 7–8 km) pollen oflake, a detectable disturbance must embrace a

much larger area, depending on the distance from broad-leaved trees and Cerealia-type pollen and acomparison of the influx data from the cores ofthe lake. When very large disturbances (forest fires

affecting up to 2000 ha) occurred in the vicinity of lakes Tanavjarv and Mustjarv show that pollendiagrams allow for a reliable detection of humanLake Tanavjarv, the decline in the pollen loading

was up to a factor of 10. According to Sugita impact in the immediate vicinity of lakes if thesedisturbances embraced some 25–30% of a 100–(1998), such a disturbance will cause less than a

10% decline in the pollen loading when it occurs 200 m band area.only 100 m or a few hundred meters away fromthe lake. At the same time there was no detectableimpact of these fires on the influx into Lake 6. ConclusionsMustjarv situated only ca. 800 m from LakeTanavjarv. It is clear that in the case of a small The obtained results demonstrate how complex

the reconstruction of the history of vegetationlake the main pollen source area is situated in itsimmediate vicinity and a disturbance outside this disturbance is. Pollen influx data seem to provide

a promising tool for this. In practical work abelt, even when it embraces a large area, does notshow a significant record in the pollen spectra. correct selection of study objects relevant to that

aim is very important. The threshold of detectionThis example shows that in the case of small lakesthe detection of a disturbance is possible only, if is lower if the disturbance concerns a small lake

(some 3–6 ha). In the influx curves of significantlyit occurred in the vicinity of the lake and covereda sizeable part of the pollen source area. larger lakes (such as in this study Lake Tanavjarv,

area 136 ha) only disturbances (forest fires) thatA disturbance that increases the openness ofthe landscape around the lake creates more possi- took place repeatedly and embraced large territo-

ries (up to 2000 ha) close to the lake are recorded.bilities for an increase in ‘long-transported’ pollen.This has been demonstrated in some earlier studies The distance from the disturbance to the accumula-


for the Reconstruction of the Palaeovegetation. Proc. Inst.tion area ( lake) is of great importance as is sug-Geol, Vilnius. in Russian with English summary.gested by the absence of practically any

Koff, T., 1998. Pollen influx in lake Matsimae and its catchment.disturbance signals in the sediments of Lake Proc. Estonian Acad. Sci. Biol. Ecol. 47, 247–258.Mustjarv, located 800 m away from Lake Koff, T., Punning, J.-M., Yli-Halla, M., 1998. Human impact

on a paludified landscape in northern Estonia. LandscapeTanavjarv.Urban Plann. 41, 263–272.

Moore, P., Webb, J.A., 1978. An Illustrated Guide to PollenAnalysis. Hodder and Stoughton, London.

Odgaard, B., 1994. The Holocene vegetation history of northernAcknowledgements West Jutland, Denmark. Opera Bot. 123, 1–171.

Pennington, W., Bonny, A.P., 1970. Absolute pollen diagramsfrom the British late-glacial. Nature 226, 871–872.The research was supported by the Estonian

Prentice, I.C., 1985. Pollen representation, source area andScience Foundation Grants Nos 2873 and 3773basin size: toward a unified theory of pollen analysis. Quat.

and Research Project 8/97-2. The authors thank Res. 23, 76–86.Dr S. Hicks and Professor R. Janssen for valuable Punning, J.-M., Alliksaar, T., 2000. Comparative spherical fly-

ash particle and 210Pb geochronologies of sediments in somecomments on an earlier draft of the manuscript.Estonian lakes. J. Paleolimnol. (in press).

Punning, J.-M., Koff, T., 1997. The landscape factor in theformation of pollen records in lake sediments. J. Paleolim-nol. 18, 33–44.

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