colonization capacity of herb woodland species in fertile, recent alder woods adjacent to ancient...

Anna ORCZEWSKA

Department of Ecology, Faculty of Biology and Environmental Protection, University of Silesia

Bankowa 9, 40–007 Katowice, Poland, e-mail: [email protected]

COLONIZATION CAPACITY OF HERB WOODLAND SPECIES

IN FERTILE, RECENT ALDER WOODS ADJACENT

TO ANCIENT FOREST SITES

POLISH JOURNAL OF ECOLOGY

(Pol. J. Ecol.)

58 2 297–310 2010

Regular research paper

ABSTRACT: The herb layer recovery in post-agricultural woods adjacent to ancient for-ests has not yet been studied for the wettest Euro-pean woodlands, like those with black alders (Al-nus glutinosa L. (Gaertn.)). Therefore, the studies aimed at: I. checking which herbs from the Polish list of ancient woodland species that are present in the alder woods show an association with these woods (AAWS=Ancient Alder Woodland Spe-cies); II. presenting their ecological profile (spec-tra of life forms, life strategies, dispersal modes, phytosociological affinity, and Ellenberg indicator values), and III. comparing the dispersal potential and other traits of species recorded more often in ancient woods (AAWS) vs the Polish ancient woodland indicators frequently present in ancient and recent alder woods (OAWS = Other Ancient Woodland Species).

The survey was carried out in Alnus glutinosa-dominated woodlands, located in south-western Poland. The study sites are located within large forest complexes, where they occupy either peri-odically waterlogged sites or other places with a high level of groundwater. In the case of ancient woods, wet types of an oak-hornbeam commu-nity (Tilio-Carpinetum Tracz. 1962 or Galio-Car-pinetum Oberd. 1957) (11 sites), alder-ash carrs (Fraxino-Alnetum W. Mat. 1952) (12 sites) and typical wet alder woods (Ribeso nigri-Alnetum Sol.-Górn. (1975) 1987) (10 sites) were investi-gated. The ancient woodland sites varied in size from 0.73 ha to 15.54 ha. Recent woods, adjacent

to these sites, included black alder stands planted on former meadows. The area of their patches ranged from 0.72 ha to 8.6 ha. Post-agricultural woods represented the following age classes: up to 10 years, 11–20, 21–30, 31–40, and 41–50 years. The process of colonization of recent woods by woodland flora was investigated in 33 transects, approximately 80 m in length by 4 m in width, consisting of 10–12 quadrates, 16 m2 each, laid out at intervals of 4 m, perpendicularly across the ancient-recent border. In total 131 quadrates in the ancient wood, 198 in the recent woodland, and 34 in the ecotone zone were investigated. The migration rates (m yr-1) based on the occur-rence of the farthest individuals, were calculated for over 50 woodland species. The original lists of species obtained from the transects were com-pleted after detailed inspections of the whole area of adjacent forest sectors where the studies on the colonization process were undertaken. Then, the frequency of herb layer species in ancient and re-cent woods was compared (Fisher exact probabil-ity test). The mean migration rates of species from the AAWS and OAWS groups were calculated.

Although 62 herbs from the group of ancient woodland indicators for Poland were recorded in the course of the studies, only 21 of them occurred significantly more often in alder woods. The mean migration rate for herbs from AAWS was signifi-cantly lower (0.68 m yr-1) than in the case of the OAWS group (1.54 m yr-1). This indicates that true woodland herbs differ distinctively in their

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dispersal potential. Species from those two sets also showed some differences in their ecological requirements. Such results allow a conclusion to be reached that in wet and fertile recent forests adjacent to ancient source woods, recolonization of the herbaceous layer by typical woodland flora proceeds faster than in other, less fertile and dri-er habitats. This in turn explains why many true woodland species do not occur in ancient wood-land sites exclusively. They are often recorded in recent woods, as they are able to colonize such sites reasonably fast.

KEY WORDS: true woodland indicator spe-cies, forest recovery, recent woods, life-history traits, species migration

1. INTRODUCTION

Since 1974, when a method for using an-cient woodland indicator species in the as-sessment of the conservation value of wood-lands was proposed by Peterken (1974), lists of herbs strictly associated with wood-land conditions for many parts of north-western and central Europe have been com-piled (Peterken and Game 1984, Wulf 1997, Rose 1999, Dzwonko and Loster 2001, and others – for a detailed review see Hermy et al. 1999). Regardless of the indi-vidual differences in species sets, herbs from such lists show a similar ecological behav-iour typical for interior forest species. This differentiates them from other plant species occurring in forests (for a detailed ecologi-cal profile of ancient woodland indicators see Hermy et al. 1999). A wide range of life his-tory adaptations of true woodland herbs that have evolved over a long period of time allow such species to persist in a woodland envi-ronment (Bierzychudek 1982, Whigham 2004). Among these specific features a very poor or no effective colonizing ability of woodland species is stressed by all the au-thors. Such species’ attributes as the length of seed persistence in the soil, dispersule weight and seed dispersal mode are responsible for their poor migration capacity (Graae and Sunde 2000). This in turn allows them to be treated as indicators of natural diversity in forests. However, the high representation of species from such lists, in an attempt to establish woodland age and origin, is in it-self not sufficient. In such situations, spe-

cies’ presence should be used in combination with cartographic, historical, archaeologi-cal and topographical evidence (Peterken 1974, Rose 1999). Species’ lists in ancient woodlands are particularly important in as-sessing the woodland history and diversity in fragmented landscapes. In such conditions the migration of herbs from ancient to re-cent woodlands is an extremely difficult and long-lasting process documented for cen-turies – 350 years (Fa l iński 1986) to 800 years (Peterken 1977). Thus, in landscapes with a very fragmented forest cover, ancient woodland species are particularly vulner-able to the effects of fragmentation and are prone to extinction (Hermy et al. 1999). Restoration of the herb layer in recent woods adjacent to ancient ones by true woodland species is a distinctively faster process, al-though it still lasts for a few decades or even a century (Brunet and von Oheimb 1998, B ossuyt et al. 1999, Dzwonko 2001). In such circumstances, effective colonizers have a chance to migrate and become established in recent woods. By contrast, other species do not take advantage of the direct proxim-ity of a recent wood, but persist in ancient woodlands or migrate very slowly to recent ones. Those species are of particular inter-est in assessing the conservation value of such woods. However, many herbs with a poor colonizing capacity may eventually ap-pear in recent woodland (Peterken 1974, Dzwonko and Gawroński 1994, Rose 1999), although the pace of their migration depends on local habitat conditions. In gen-eral this process proceeds faster in moist soils rich in nutrients. The recovery of the herb layer in post-agricultural woods has been studied in mesotrophic deciduous forests of moderate humidity and fertility (Dzwonko and Gawroński 1994, Mat lack 1994, Brunet and von Oheimb 1998, B ossuyt et al. 1999) whereas little is known about the recovery of woodland flora in the wettest, azonal types of European woodlands, such as those with stands dominated by black alders.

As a consequence of the drainage of sites designated for agricultural purposes or to more productive, fast-growing timber for-ests, wetland ecosystems including periodi-cally waterlogged forests have almost entirely disappeared from the landscape of western

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Europe or are endangered. That process has contributed to a decrease in the abundance of plant indicators of moist and wet soils, or even to their extinction. Forest ecosystems that develop in wet habitats are rich in vas-cular plant species and contain many repre-sentatives of stenotopic woodland flora. The large species richness and diversity of such forests is of critical functional significance in forest ecosystem processes, especially in the colonization by woodland flora of adjoining recent, post-agricultural woods. The aims of the research were:

• to ascertain which species can be re-garded as recorded more often in an-cient alder woods and to what extent this group of herbs differs from or overlaps with the lists of reliable in-dicators for broadleaved forests on a European scale;

• to check whether all of the ancient woodland indicator species for Po-land that occurred in the alder woods studied show an association with these woods, bearing in mind the fact that in more fertile and wetter forest conditions the pace of herb layer res-toration on post-agricultural sites is faster than in poorer and drier wood-lands;

• to compare the migration potential of species recorded significantly more often in ancient alder woods (AAWS) with those Polish ancient wood-land indicators which did not exclu-sively occur in ancient alder woods (OAWS);

• to compare the ecological features of the flora of the AAWS and OAWS groups.

2. STUDY AREA

The data on the herb layer composition were collected in Alnus glutinosa-dominated woodlands located within two neighbour-ing geographical regions of south-west-ern Poland: the Oleśnica Plain (5104N; 1743E), Opole Silesia and the Żmigród Val-ley (5128N; 1654E), Lower Silesia. These regions are characterized by both a high proportion of well-preserved ancient wood-lands (77%, and 70% of the overall forested

cover, respectively; Orczewska 2009a) and by a good representation of recent woods of a post-agricultural origin. Within these for-est categories, woodlands with stands domi-nated by black alders are well represented. In the case of ancient woods, wet types of oak-hornbeam community (Tilio-Carpinetum Tracz. 1962 or Galio-Carpinetum Oberd. 1957) (11 sites), alder-ash carrs (Fraxino-Alnetum W. Mat. 1952) (12 sites) and typical wet alder woods (Ribeso nigri-Alnetum Sol.-Górn. (1975) 1987) (10 sites) were studied. By contrast, recent woods adjacent to these sites included black alder stands planted on former meadows, from the Molinietalia and Arrhenatheretalia orders. The status of an-cient woodland sites was confirmed using cartographic evidence originating from 1780, 1880, and 1980 due to the detailed studies. According to these sources the continuity of these woods has lasted for the last 230 years (Orczewska 2009a). Post-agricultural woods represented the following age classes: up to 10 years, 11–20, 21–30, 31–40, and 41–50 years. The study sites were scattered within extensive forest complexes where they occu-pied either places with periodically stagnat-ing water or were distributed along small for-est streams and other localities with a high level of groundwater. Survey patches in an-cient woods varied in size from 0.73 ha to 15.54 ha with 4.66 ha being the average area. Out of the 33 ancient woods 14 ranged in size from 2 to 4 ha. Recent stands ranged in size from 0.72 ha to 8.6 ha. The mean size of re-cent patches was 3.9 ha. Eight recent wood-land sites were 4–5 ha in size, whereas anoth-er seven patches were 1–2 ha. Despite the fact that the number of woodland species in re-cent alder woods depends on their age (Or-czewska 2009b), all post-agricultural alder woods were grouped together and compared with ancient woodland sites. This approach is by way of simplification. Nevertheless, in the case of dividing recent woods into sepa-rate age classes, only subjective comparisons could be made, since the statistical sample would have been too small.

In the woodlands studied meso- and eu-trophic soils on moist, wet and periodically waterlogged sites predominate, including mainly a wide spectrum of gleysols (Orcze-wska 2009c).

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3. MATERIAL AND METHODS

Detailed research on the process of colo-nization of the herb layer of alder woods by forest plant species was carried out in April and June between 2002–2006, on all 33 study sites. In order to estimate the pace of migra-tion of the woodland species into recent alder stands, vegetation was surveyed in transects located perpendicularly across the ancient-recent border. Each transect was approxi-mately 80 m in length and consisted of 10 quadrates of 16 m2, laid out at intervals of 4 m. Four sample plots (28 meters in length) were located in the ancient woodland, and six (44 m) in the recent wood. In total 131 quad-rates in the ancient wood, 198 in the recent woodland, and 34 in the ecotone zone were surveyed. Calculations of the migration rates (MR) followed the procedure proposed by Mat lack (1994) and applied by successive authors (Brunet and von Oheimb 1998, Dzwonko 2001). These calculations were based on the occurrence of the farthest indi-vidual since many species were present in re-cent woods with a minimal cover. In order to allow for comparisons of all the woods stud-ied, regardless of the age of the recent wood-land stand, standardized distances (calculated by dividing the distance of each plot from the ancient forest by the age of the recent forest) were taken into account:

MR = dfi

× a-1 (1)

where dfi is the occurrence of the farthest

individual in meters, and a is the age of the re-cent forest in years. The migration rates were calculated for each transect where the spe-cies was present, and then the mean rates for a species on all study sites were counted (for more details of the procedure see Orczew-ska 2009b). This resulted in the calculation of migration rates of over 50 woodland spe-cies into post-agricultural woods, the results of which were presented in a separate paper (Orczewska 2009b).

In order to fully reflect the species pools in all the ancient and recent woods, original lists of species obtained from transects were completed after detailed inspections of the whole area of adjacent forest sections where transects were located. Thus, 33 species lists

for ancient and 33 for recent woodlands were complied.

As the next step, the frequency of herb layer species in ancient and recent woodlands was compared using the Fisher exact prob-ability test (Statistica 8.0 package). Then, the performance of species occurring predomi-nantly in ancient alder woods was studied by comparing the published data on their be-haviour in other selected European countries, which sufficiently represent the gradient of deciduous forests of north-western and cen-tral Europe (Hermy et al. 1999, Dzwonko and Loster 2001).

Woodland species present in alder woods were divided into two groups. The first in-cluded those which were more frequent in ancient alder woods and have a status of ancient woodland indicators for Poland, ac-cording to Dzwonko and Loster’s list (2001) (AAWS = Ancient Alder Woodland Species; N = 31). The second group consisted of spe-cies regarded as ancient woodland indicators for Poland but which did not occur more often in the case of the ancient alder woods studied (OAWS = Other Ancient Woodland Species; N = 28). Then, the ecological attri-butes of the species from those two lists were given. For these characteristics the spectra of Raunkiaer life forms, Grime life strategies (Grime et al. 1996), and dispersal modes (Mül ler-S chneider 1986, Gr ime et al. 1996) were compared. The phytosociologi-cal behaviour of species (Matuszkiewicz 2001) was also given. In addition, the species’ ecological requirements were defined using Ellenberg’s indicator values (moisture – F, soil reaction – R, nitrogen content – N, and light conditions – L) (E l lenberg et al. 1992).

As a final step the mean migration rates (m yr-1) of species from the AAWS and OAWS were compared (Mann-Whitney test, Statis-tica 8.0 package).

4. RESULTS

In total, in both woodland types, there were 313 species recorded within all of the 33 study sites (in transects, 299 species were present). Ancient and post-agricultural alder forests differed in the herb layer composition despite their direct proximity. These differ-ences were also reflected in the lists of herbs

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Table 1. Species present significantly more often in ancient alder woods (AAWS) and the data on their dispersal mode, migration rate, and the status for ancient woodlands, according to different sources (MR = d

fi × a-1; where d

fi is the occurrence of the farthest individual in meters and a is the age of the

recent forest in years). Data on species’ migration rates were obtained from 33 transects, 80 m in length by 4 m in width, consisting on 10–12 quadrates, 16 m2 each, laid out perpendicularly across the ancient-recent border. Species’ frequency is based on the species’ lists (N = 33 in ancient forests; N = 33 in recent forests) obtained from the whole area of forest sections where transects were located (see Materials and methods for details).

SpeciesDispersal

mode

Number of occur-rences

P levelMean migration rate

(m yr- 1 ) in alder woods studied

H et al. 1999

D & L 2001Ancient

N=33RecentN=33

Asarum europaeum L. Myrm 11 3 0.0163 0.34 × ×

Athyrium filix-femina (L.) Roth An1

27 15 0.0022 1.17 × ×

Campanula trachelium L. An2

7 0 0.0055 Absent in transects × ×

Carex sylvatica Huds. Myrm 11 1 0.0014 0.30 × ×

Corylus avellana L. Baro 13 5 0.0257 0.82 × -

Crataegus monogyna Jacq. Endo 12 5 0.0448 1.12 - -

Equisetum sylvaticum L. An1

13 4 0.013 0.07 × ×

Euonymus europaea L. Endo 25 17 0.0361 1.35 × -

Fagus sylvatica L. Baro 13 4 0.0113 1.50 - -

Gagea lutea (L.) Ker Gawl. Myrm 4 0 0.0568 (*) 0.00 × ×

Galeobdolon luteum Huds. Myrm 20 7 0.0012 0.27 × ×

Galium odoratum (L.) Scop. Epi 8 2 0.0412 0.45 × ×

Geranium robertianum L. Auto 27 19 0.0297 0.95 - -

Hepatica nobilis Schreb. Myrm 10 1 0.0030 0.00 × ×

Iris pseudacorus L. Hy 25 14 0.0058 0.99 - -

Lathyrus vernus (L.) Bernh. Auto 5 0 0.0266 Absent in transects × ×

Lysimachia vulgaris L. Hy/An2

29 19 0.0058 1.31 × ×

Maianthemum bifolium (L.) F. W. Schmidt

Endo 21 5 0.0001 1.33 × ×

Melica nutans L. Myrm 4 0 0.0568 (*) 0.00 × ×

Mercurialis perennis L. Myrm 15 7 0.0332 0.43 × ×

Mycelis muralis (L.) Dumort. An2

6 0 0.0122 0.00 - ×

Oxalis acetosella L. Auto 29 21 0.0212 0.85 × ×

Paris quadrifolia L. Endo 17 9 0.0385 0.85 × ×

Polygonatum multiflorum (L.) All.

Endo 13 2 0.0012 0.94 × ×

Pulmonaria obscura Dumort. Myrm 7 0 0.0055 0.00 × ×

Rorippa amphibia (L.) Besser Hy 4 0 0.0568 (*) Absent in transects - -

Rubus caesius L. Endo 17 9 0.0385 1.52 - -

Sanicula europaea L. Epi 6 0 0.0122 0.00 × ×

Scutellaria galericulata L. Hy 23 12 0.0065 1.55 - -

Tilia cordata Mill. An2

8 2 0.0412 Absent in transects × -

Viola reichenbachiana Jord. ex Boreau

Myrm 15 1 0.0000 0.15 × ×

H et al. 1999 – Hermy et al. 1999; D & L 2001 – Dzwonko and Loster 2001. Symbols: ‘×’ – listed as associated with ancient woodland; (*) – significance level between 0.05 and 0.1

Myrm – myrmecochores; Auto – autochores; Baro – barochores; Epi – epizoochores; Endo – endo-zoochores; An

1 – unwinged anemochores with small diaspores; An

2 – anemochores with diaspores with

pappus or wings; Hy – hydrochores.

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Table 2. Ancient woodland indicator herbaceous species for Poland (after Dzwonko and Loster 2001), which did not reach such a status in the alder woods studied (OAWS) and the data on their dis-persal modes and migration rates (MR = d

fi × a-1; where d

f is the occurrence of the farthest individual in

meters and a is the age of the recent forest in years). For the explanations on the calculations of species’ migration rates and frequency see Table 1 and Materials and Methods).

Species occurring in both forest types with a similar frequency

Dispersal mode

Number of occurrences in ancient

woods N=33

Number of occurrences

in recent woods N=33

Mean migra-tion rate (m yr-1) in alder woods

studied

Adoxa moschatellina L. Endo 23 18 1.40

Aegopodium podagraria L. Baro 23 20 0.79

Ajuga reptans L. Myrm 17 21 2.38

Anemone nemorosa L. Myrm 27 23 1.73

Anthriscus nitida (Wahlenb.) Hazsl. Epi 14 15 1.44

Brachypodium sylvaticum (Huds.) P. Beauv.

Epi 19 18 1.12

Carex elongata L. Hy 18 14 2.68

Carex remota L. Hy 9 7 0.31

Chrysosplenium alternifolium L. Hy 19 22 1.52

Circaea lutetiana L. Epi 21 19 1.77

Convallaria majalis L. Endo 6 2absent in transects

Dryopteris carthusiana (Vill.) H. P. Fuchs

An1

31 30 1.57

Dryopteris filix-mas (L.) Schott An1

9 5 0.69

Festuca gigantea (L.) Vill. Epi 31 28 3.70

Ficaria verna Huds. Myrm 32 32 1.44

Geum urbanum L. Epi 28 27 1.87

Impatiens noli-tangere L. Auto 32 30 1.83

Milium effusum L. An2

28 24 0.91

Moehringia trinervia (L.) Clairv. Myrm 32 29 1.75

Ranunculus auricomus L. s. l. Myrm 23 26 2.44

Ranunculus lanuginosus L. Epi 9 7 1.50

Ribes nigrum L. Endo 9 4 0.67

Ribes spicatum E. Robson Endo 3 7 0.99

Rumex sanguineus L. An2

22 24 1.94

Scrophularia nodosa L. An1

20 15 1.70

Stachys sylvatica L. Epi 17 12 1.38

Stellaria holostea L. Baro 13 9 0.71

Stellaria nemorum L. Hy 11 12 1.24

Species with low frequency in ancient woods or either with low frequency or absent in recent woods

Anemone ranunculoides L. Myrm 5 3

Bromus benekenii (Lange) Trimen Epi 0 1

Circaea intermedia Ehrh. Epi 1 2

Daphne mezereum L. Endo 2 0

Dentaria bulbifera L. Baro 1 1

Epilobium montanum L. An2

1 3

Galium sylvaticum L. An2

2 0

Listera ovata (L.) R. Br. An1

2 3

Luzula pilosa (L.) Willd. Myrm 3 0

Melampyrum nemorosum L. Myrm 2 0

Melica uniflora Retz. Myrm 3 0

Poa nemoralis L. An2

5 1

Myrm – myrmecochores; Auto – autochores; Baro – barochores; Epi – epizoochores; Endo – endozoochores; An1 – unwinged

anemochores with small diaspores; An2 – anemochores with diaspores with pappus or wings; Hy – hydrochores.

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with a significantly higher frequency in either ancient or recent woods. From the group of herbs having the status of ancient woodland indicators for Poland, 62 species were record-ed on the sites studied. However, only one third of them occurred predominantly in an-cient alder woods (AAWS) (Table 1), whereas the other 40 (OAWS) did not. Among those 40 species 12 had either a low frequency or were absent in recent woods. For these rea-sons they were not taken into account when the mean migration rate was calculated. The remaining 28 species occurred in both forest types with a similar frequency (Table 2). The migration rates of most of them exceeded 1.5 m yr-1, and in the case of Ajuga reptans L., Carex elongata L., Ranunculus auricomus

L. s. l., and Festuca gigantea (L.) Vill. even 2 or 3 m yr-1.

Groups of species occurring predomi-nantly in ancient alder woodlands consisted of 31 herbs (Table 1), whereas the group of plants significantly more frequent in recent alder woods included 30 species (Table 3). Among the herbs more often recorded in ancient alder woods, some species occurred exclusively (Campanula trachelium L., Ga-gea lutea (L.) Ker Gawl., Lathyrus vernus (L.) Bernh., Melica nutans L., Mycelis muralis (L.) Dumort., Pulmonaria obscura Dumort., Ror-ippa amphibia (L.) Besser, and Sanicula euro-paea L.) or almost exclusively (Carex sylvatica Huds., Galium odoratum (L.) Scop., Hepatica nobilis Schreb., Polygonatum multiflorum

Table 3. Species present significantly more often in recent alder woods. For the explanations on the calculation of species’ frequency see Table 1 and Materials and methods.

SpeciesNumber of occurrences

P level Ancient N = 33 Recent N = 33

Agrostis capillaris L. 2 8 0.0412

Alopecurus pratensis L. 2 9 0.0220

Anthoxanthum odoratum L. s. str. 2 10 0.0113

Arrhenatherum elatius (L.) P. Beauv. Ex J. Presl & C. Presl 0 7 0.0055

Cardamine pratensis L. s. str. 9 23 0.0006

Carex hirta L. 3 13 0.0042

Carex vesicaria L. 2 8 0.0412

Cirsium rivulare (Jacq.) All. 1 12 0.0006

Deschampsia caespitosa (L.) P. Beauv. 29 33 0.0568 (*)

Dryopteris dilatata (Hoffm.) A. Gray 10 17 0.0662 (*)

Festuca rubra L. s. str. 2 9 0.0220

Filipendula ulmaria (L.) Maxim. 15 23 0.0402

Galeopsis tetrahit L. 11 21 0.0130

Holcus lanatus L. 7 18 0.0052

Lapsana communis L. s. str. 2 8 0.0412

Lychnis flos-cuculi L. 21 29 0.0212

Lysimachia nummularia L. 22 31 0.0056

Molinia caerulea (L.) Moench s. str. 2 11 0.0056

Poa angustifolia L. 1 6 0.0524 (*)

Potentilla erecta (L.) Raeusch. 0 7 0.0055

Potentilla reptans L. 6 14 0.0297

Prunella vulgaris L. 4 12 0.0212

Ranunculus acris L. s. str. 2 8 0.0412

Ranunculus repens L. 25 31 0.0412

Rumex acetosa L. 5 15 0.0166

Stellaria graminea L. 1 6 0.0524 (*)

Stellaria palustris Retz. 0 7 0.0055

Trifolium repens L. 0 4 0.0568 (*)

Veronica chamaedrys L. s. str. 10 22 0.0032

Vicia cracca L. 3 9 0.0540 (*)

* significance level between 0.05 and 0.1

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(L.) All., and Viola reichenbachiana Jord. ex Boreau) in these woods. An unexpected result was the more frequent presence of Dryopteris dilatata (Hoffm.) A. Gray, an ancient wood-land indicator species for Poland, in recent alder woods (Table 3).

The different ecological requirements of the ancient alder woodland species (AAWS) and other woodland species (OAWS) were confirmed when their ecological spectra were compared. Among ancient woodland herbs, geophytes reached a much higher number

Fig. 1. Distribution of species from AAWS (Ancient Alder Woodland Species) and OAWS (Other An-cient Woodland Species) groups in relation to their life forms. Species’ sets based on the species’ lists obtained from 33 patches of ancient forests (varied in size from 0.73 ha to 15.54 ha), and 33 patches in recent woods (varied in size from 0.72 ha to 8.6 ha ) (see Materials and methods for details). Ph – phanerophytes; CH – chamaephytes; H – hemicryptophytes; G – geophytes; Hy – hydrophytes; T – therophytes.

Fig. 2. Distribution of species from AAWS and OAWS groups (for codes see Fig. 1) in relation to their life strategies. For the explanations on species’ sets see Fig. 1. and Materials and methods.c – competitors; s – stress tolerators; r – ruderals; cr – competitive ruderals; sr – stress-tolerant ruderals, cs – stress-tolerant competitors; csr – competitor-stress tolerator-ruderals, ? – strategy not specified.

Ph

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than in the other group. In the second group there were two therophytes, which were ab-sent among the ancient alder woodland spe-cies group (Fig. 1).

Differences were also noted in the spec-tra of life strategies; since there were twice as

many species with the ability to tolerate stress (s strategy) in the AAWS group than in the OAWS set. In contrast to the AAWS group, the OAWS set contained many species able to tolerate disturbances (sr and cr strategies) (Fig. 2).

Fig. 3. Distribution of species from AAWS and OAWS groups (for codes see Fig. 1) in relation to their dispersal modes. For the explanations on species’ sets see Fig. 1. and Materials and methods.Myrm – myrmecochores; Auto – autochores; Baro – barochores; Epi – epizoochores; Endo – endo-zoochores; An

1 – unwinged anemochores with small diaspores; An

2 – anemochores with diaspores with

pappus or wings; Hy – hydrochores.

Fig. 4. Phytosociological distribution of species from AAWS and OAWS groups (for codes see Fig. 1). For the explanations on species’ sets see Fig. 1 and Materials and methods.

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The dispersal modes of almost half of the ancient alder wood species belonged to those which were ineffective, namely myrme-cochorous, autochorous, and barochorous. Herbs with diaspores adapted to short dis-tance dispersal were very poorly represented among the other woodland species group where anemochores, epizoochores and endo-zoochores predominated (Fig. 3).

The phytosociological behaviour of species from the AAWS and OAWS sets also differed; there were more herbs characteristic of Fageta-lia order, and Alno-Ulmion alliance among the OAWS than in the case of AAWS. By contrast, among the species which occurred significant-ly more often in ancient alder woods, there was a high representation of herbs associated with wetlands (for example Magnocaricion, Phrag-mition, and Filipendulion alliances), which were absent in the other group, as well as more species from the Querco-Fagetea class (Fig. 4).

Further differences between AAWS and OAWS groups were observed when their ecological responses to abiotic factors were compared. Within the OAWS set there was a

higher number of species confined to slightly acidic and slightly alkaline soils (R = 5–7) (Fig. 5a), a higher number of herbs of semi-shaded (L = 5) or intermediate between shad-ed and semi-shaded sites (L = 4) (Fig. 5c), and more species preferring moist soils (F = 6–8) (Fig. 5d) than in the AAWS group. On the other hand, among the group occurring pre-dominantly in ancient alder woodlands there were more species which prefer soils with a low or an average nitrogen content (N = 3–5) but fewer of those demanding soils rich in ni-trogen (N = 7–8) (Fig. 5b).

The mean migration rate for species that were recorded more often in ancient alder woodlands was significantly lower than for the other species group (AAWS = 0.68 m yr –1, OAWS = 1.54 m yr –1; P = 0.000027).

5. DISCUSSION AND CONCLUSIONS

The studies show that species from the Polish list of ancient woodland indicators which were recorded in alder woods differ in their performance. Although some of them

Fig. 5. Distribution of species from AAWS and OAWS groups (for codes see Fig. 1) in relation to El-lenberg indicator values: a) R – soil reaction; b) N – nitrogen; c) L – light intensity; d) F – moisture. For the explanations on species’ sets see Fig. 1. and Materials and method.

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were associated with ancient woodland sites (AAWS), other species occurred in both for-est types with a similar frequency (OAWS). Simple ecological species’ attributes such as life forms, life strategies, dispersal modes and phytosociological affinity appeared to be very effective in confirming differences in the ecological behaviour of species from the AAWS and OAWS groups. Most herbs which occurred predominantly in ancient alder woodlands showed the features characteristic of true woodland species, typical for forest interiors and of ancient woodland indicator species sensu Peterken (1974). Thus, they include: a high representation of geophytes, stress-tolerant species with limited disper-sal abilities (ant-dispersed, barochorous and autochorous). These differences and the fact that the mean migration rate of species more frequent in ancient alder woods was signifi-cantly lower than in the case of OAWS prove that species from those two sets differ in their colonization and establishment potential. The above-mentioned features of the AAWS group are in accordance with the ecological profile of ancient woodland indicator spe-cies of Polish (Dzwonko and Loster 2001) and other European broadleaved forests (Hermy et al. 1999). By contrast, the group of species which occurred with a similar fre-quency in ancient and recent alder woods contained therophytes, species able to toler-ate disturbance (absent among the AAWS), and more species capable of dispersal over long distances (epi- and anemochores). Fur-thermore, the different behaviour of species from the AAWS and OAWS sets is consistent with the observations of other authors who have reported that in the situation of direct proximity to ancient and recent woodland sites, recolonization of the herb layer in post-agricultural woods takes place and that many true woodland species, even poor colonizers, eventually migrate into such sites (Peterken 1974, Dzwonko and Gawroński 1994, Rose 1999). Many herbs from the country list of ancient woodland indicators were re-corded in both the ancient and recent alder woods with a similar frequency. In the situa-tion of a lack of the spatial isolation of post-agricultural woods from the ancient source woodlands many woodland plants are able to colonize recent sites and establish there

successfully. In the particular case of alder woods the direct proximity of both woodland types is of utmost importance in the migra-tion of woodland flora. In addition, the lack of preference for ancient woodland sites by many forest species may be due to the fact that in more fertile and wetter forest condi-tions the pace of herb layer recovery in recent woods proceeds faster than in poorer and drier habitats (Dzwonko and Gawroński 1994, Orczewska 2009b). The migration rates of many woodland species in such con-ditions are higher (Orczewska 2009b) than in other deciduous forests in Europe. How-ever, species differ in their colonizing capac-ity; many true woodland herbs still migrate more slowly into alder woods (AAWS) than others (OAWS). Those species which migrate very slowly or do not colonize recent alder woods seem to be the best indicators of an-cient woodland sites and probably, as forest specialists, also the most endangered in de-ciduous forest habitats. Among species from that group, Campanula trachelium, Galium odoratum, Oxalis acetosella, Paris quadrifolia, Sanicula europaea, and Viola reichenbachiana were classified as highly associated with pri-mary or primary and ancient woodlands in England (Peterken 1974), and as ancient woodland site indicators in many other parts of Europe (Wulf 1997, Hermy et al. 1999), including Poland (Dzwonko and Loster 2001). Moreover, Carex sylvatica and Polygo-natum multiflorum, the two species almost exclusively occurring in ancient alder woods, together with Galeobdolon luteum and Mai-anthemum bifolium, also seem to be good indicators of ancient forests on a European scale (Table 1). Among the 11 true woodland species which were either unable to colonize recent alder woods or showed very poor colo-nizing potential more than half are dispersed by ants or autochorous. This group includes: Carex sylvatica, Gagea lutea, Hepatica nobilis, Lathyrus vernus, Melica nutans, Pulmonaria obscura, and Viola reichenbachiana. The re-maining four species are either anemochor-ous (Campanula trachelium and Mycelis mu-ralis), epizoochorous (Sanicula europaea) or hydrochorous (Rorippa amphibia) (Table 1). Thus, dispersal mode is one of the key spe-cies traits responsible for their poor coloniz-ing capacity of recent woods. As Graae and

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Sunde (2000) indicate traits related to colo-nization and establishment are among the most important ones to many forest plants.

In situations like those studied where all of the secondary woods are close to ancient ones, there are opportunities for poor colo-nizers to migrate into the herb layer of recent woodland sites. However, there are other plants which colonize recent woods very ef-ficiently. Aegopodium podagraria, Geum urbanum, Moehringia trinervia, Rumex san-guineus, and Stachys sylvatica are among that group. They are all reported as associated with ancient woods in Poland (Dzwonko and Loster 2001), and some of them also in England (Rose 1999) or north-eastern Germany (Wulf 2003). However, they were recorded with a similar frequency in both forest types in alder woods. Furthermore, in England (Peterken and Game 1984) all of them were clearly associated with recent woods. Such results confirm that all these species can be described as effective coloniz-ers of recent, post-agricultural, fertile wood-land sites. These observations are in accor-dance with the reports of other authors, for example Wulf (2004), who among other herbs classified Adoxa moschatellina, Geum urbanum, Milium effusum, and Stachys syl-vatica as species with good colonizing ca-pacity. In alder woods they were grouped in OAWS. However, contrary to Wulf ’s (2004) results, such species as Athyrium filix-femina, Corylus avellana, Maianthemum bifolium, Oxalis acetosella, Paris quadrifolia, and Po-lygonatum multiflorum did not belong to fast colonizers in alder woods. On the other hand, similarly to Peterken (1974), Dryopteris dilatata was recorded more often in recent al-der wood, although it is on the list of ancient woodland indicators for Poland (Dzwonko and Loster 2001). Similar differences are reported for Dryopteris carthusiana, which belonged to OAWS. Although it is listed as an ancient woodland indicator for Poland, in some cases it can be classified as an effec-tive colonizer of recent woods (Dzwonko and Loster 1992). Undoubtedly, very small spores of the fern species, easily dispersed by wind, facilitate their effective colonization of recent woodland sites.

Some species seem to be reliable univer-sal ancient woodland indicators for most de-

ciduous European forests. However, in such a specific site situation as the one studied where recent woods are not spatially isolated from ancient woods but are located in their direct proximity, application of the lists of woodland indicators is limited. In such cases, as Mabr y and Fraterr igo (2009) suggest, simple spe-cies traits, reflecting a species’ behaviour and a level of its specialization to woodland con-ditions, may be good predictors of forest herb layer response to a different management his-tory and a forest’s existence in the landscape. The migration potential of woodland vascular plants is among its most important features. This in turn should have implications for na-ture conservation, allowing those forests with the richest biodiversity to be protected. Due to the knowledge of forest species behaviour, maintenance of conditions needed for their long-term persistence in temperate European woodlands is possible (Hermy et al. 1999). Habitat specialization, which is stressed by Mabr y and Fraterr igo (2009) is a good way of tracking the impact of past manage-ment and a “general predictor of change in response to future human intervention’. Habi-tat specialization therefore is a relatively quick and simple way to classify plant species. Thus, it has the potential to identify groups of species most likely to decline as human disturbances intensify and to target species for conservation and restoration”.

The studies in alder woodlands allowed only a small group of herbs not given by other authors to be distinguished, occurring more often in such habitats. Most of these plants (Iris pseudacorus, Rorippa amphibia, and Scutel-laria galericulata) are specialist hygromorphic species, and therefore, are adapted to a high groundwater level. Other species which were more frequent in ancient alder woodland sites have similar ecological requirements to those species listed previously by different authors as ancient woodland indicators. However, many true specialist woodland species given on a European (Hermy et al. 1999) or Polish list (Dzwonko and Loster 2001) of indica-tors of ancient woodland sites did not occur predominantly in ancient alder woods. Most of them possessed effective modes of seed dispersal and migrated at a faster pace than the species which were either restricted to or recorded more often in ancient alder woods.

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Thus, the study indicates that the colonization capacity of many specialist woodland herbs is enhanced by the high fertility and humidity of these sites. Combined with the direct proxim-ity of ancient and recent woods, compared to the poorer and drier habitats, a relatively fast restoration of the herbaceous layer in alder woodlands is possible.

ACKNOWLEDGMENTS: I would like to express my gratitude to John Parker † (formerly with Forestry Commission, UK) for his great support at every stage of the work, to Iza Szwarc, Adriana Strzelczyk, Sabina Słomian, and Paweł Góras for their technical assistance and help in the field work, and to Patricia Thomas (Univer-sity of Białystok, Poland) and Michele L. Simmons (BA, English Language Centre, University of Sile-sia, Katowice) for making linguistic corrections to the previous version of the manuscript. Much gratitude is also to Zbigniew Dzwonko for valu-able comments on the manuscript. The project was supported by the Polish Ministry of Science, Grant No. 2P04F 059 29, between 2005 and 2007

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Received after revision February 2010

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