Betula Nana) in Communities Dominated by Ledum Palustre and Vaccinium Uliginosum

Home , Betula glandulosa, Betula nana, Betula pubescens

Biologia 65/2: 248—253, 2010 Section Botany DOI: 10.2478/s11756-010-0007-9

Demographic variation of dwarf birch (Betula nana) in communities dominated by Ledum palustre and Vaccinium uliginosum

Wo jciech Ejankowski

Department of Botany and Hydrobiology, The John Paul II Catholic University of Lublin, Konstantynów 1H, PL-20-708 Lublin, Poland; e-mail: [email protected]

Abstract: The structure and demographic processes were compared in shrub communities to test the effects of vegetation succession on population growth, fecundity and abundance of the dwarf birch (Betula nana L.), which is a rare and endangered plant species in Poland and a glacial relict in Central Europe. The effects of Ledum palustre L. and Vaccinium uliginosum L. were studied in the Linje nature reserve in Chelmińskie Lake District (northern Poland), in three permanent plots on a peat bog. Vegetative growth and reproduction of B. nana were lower in plant communities dominated by L. palustre and V. uliginosum, than in a reference site. Fecundity was also lower, despite the fact that the percentage share of potentially fertile age groups was similar in all study sites. Mortality of ramets was independent of vegetation, both for juvenile and mature stages. The results confirm that B. nana is intolerant of shade, and it is more abundant in vegetation without competitors. Light limitation can lead to its decline, primarily by a decrease in vegetative growth. Sexual reproduction may be negatively affected by shade, but it plays only small role in population growth. Butterfly larvae can destroy inflorescences, and thus contribute to low effectiveness of sexual reproduction. Increasing density of shrubs and trees in peat bogs can reduce the abundance of dwarf birch, and can lead to the extinction of its local populations. Key words: clonal plant; competition; glacial relict; peat bog; vegetative growth

Introduction ascending shoots (de Groot et al. 1997; Jonsell 2000). It has a circumpolar distribution, spreading from western Peat-bogs belong to the ecosystems most endangered coastal regions of Greenland and Iceland across North- by human activity. The majority of them have been de- ern Europe and Siberia to North America. In central stroyed in past decades, and their area has decreased Europe it occurs in isolated localities, e.g. in the Alps, throughout Europe due to desiccation, peat extraction Swiss Jura, Ardennes and Sudety Mts and only rarely and agricultural land use. Drainages of these wetlands, in the lowlands (Jalas & Suominen 1976). It is included caused by economic utilization, has important ecolog- in the Red Books and Red Lists of Plants of Poland, ical consequences, namely mineralisation of peat soils Germany, Bohemia, Lithuania and Belarus, and is en- and subsidence of peat deposits (Brag et al. 2003). dangered and strictly protected in Poland. Currently, Drawdown of ground-water table induces vegetation it occurs in this country in three localities: two in the succession, i.e., development of shrubs and forests in- Sudety Mts and one in the Pomeranian region. stead open bog communities (Laine et al. 1995; Frankl Dwarf birch is intolerant of waterlogging (Ejan- & Schmeidl 2000; Pellerin & Lavoie 2003). kowski 2008). It grows mainly in dry sites in arctic Changes of vegetation due to environmental condi- and subalpine tundra and at elevated hummocks of the tions influence microhabitats within plant communities, mires where it commonly forms dense cushions (Vir- e.g. light availability and light quality, soil temperature tanen & Oksanen 1999; Jonsell 2000). It is a charac- and moisture; and vegetation cover can have an imme- teristic species of open bogs and understorey of open diate influence on plant populations (Breshears et al. tree stands with widely dispersed trees, but not under 1997, 1998). The alterations in habitats can lead to the closed canopies. It is intolerant of shade and afforesta- decline and even local extinction of highly specialised tion (Hutchinson 1966; Laine et al. 1995). plant species. In this study the geographically isolated Conservation of threatened species requires knowl- glacial relict inhabiting peat bogs were taken into con- edge of the effects of the environment on demographic sideration (Gostyńska-Jakuszewska & Lekavičius 1989). processes and the viability of a population. This knowl- The dwarf birch, Betula nana L., is a glacial relict edge may be helpful for predicting population changes in the flora of Poland. It is a richly branched clonal in the future. Many studies have been carried out on shrub growing up to 1 m in height, forming prostrate to the ecology of B. nana in the tundra (Bret-Harte et al.

c 2010 Institute of Botany, Slovak Academy of Sciences Demograﬁc variation of Betule nana in shrub communities 249

2001; van Wijk et al. 2003). Relatively little is known 160 2002

-2 140 about its responses to the succession proceeding in peat 2003 bogs. 120 Variation in demography in different environmen- 100 tal conditions and successional stages have been found 80 for a few plant species in mires (Gunnarsson & Rydin 60 1998; Nordbakken et al. 2004). The objective of this 40 20 study was to test the influence of plant communities Number of ramets m on the demographic processes in B. nana,andtoeval- 0 uate the consequences of vegetation succession on its Site A Site B Site R abundance, distribution and fecundity. Fig. 1. Vegetative reproduction of Betula nana in Sites A, B, and referenceSite(R)intheLinjepeat-bog. Material and methods The study sites were chosen in the Linje nature reserve in south-western part of Chelmno Lake District in northern of ramets of Stages 1–4 in permanent plots in consecutive Poland (Kondracki 1998). The mire of ca. 6 ha is situated years. Fertile ramets and female catkins were also counted, in moraine landscape, which originated from the late glacial and the number of fruits produced at each Site was deter- period (Nory´skiewicz 2005). Shrubs and open bog commu- mined on the ground for twenty cones. The probability of nities belonging to the class Oxycocco-Sphagnetea currently transition from vegetative to the reproductive state, and dominate in the area. This raised bog vegetation is sur- the inverse switching, were additionally assessed using fifty rounded by transitional bog communities, and partly by marked ramets. bushes and forests of the classAlnetea glutinosae.Themireis Age and size measurements of fifty ramets at each site surrounded by mixed forests with Scots pine. The area was were carried out in October and November 2001. Age was drained in the 2nd half of 19th century, and hence strong determined by counting annual growth rings, and cross sec- changes were induced in the vegetation cover (Ejankowski tions of wood were dyed with Lugol’s solution in order to & Kunz 2006). make the vessels more visible and to distinguish the growth Study plots were staked out randomly in three homo- rings. geneous plant communities, dominated in the shrub layer Normality of the data was initially analysed by scatter in Site A by labrador tea Ledum palustre L. (80.5% of per- plots and the Levene test, and homogeneity of variances centage cover) and in Site B byVaccinium uliginosum L. was tested by the Shapiro-Wilk test. Since the data did (65%). The reference Site R was composed mainly of Betula not fit the assumptions of normality and homogeneity, non- nana in the shrub layer (62.2%) with a scarcity of the above parametric statistical tests were used according to Sokal & mentioned shrubs. The permanent plots were delimited as Rohlf (1995). Calculations were carried out with Statistica rectangles five meters long and two meters wide, and each of 8.0 software. them was systematically divided into ten one-meter squares in 2001. In 2002–2003 each plot was subdivided into 160 Results smaller squares of 0.0625 m2 to facilitate counting of plants. In this study a ramet (sensu Harper 1977) was treated as a unit. During the course of the study no seedlings of Betula According to morphological criteria, ramification, num- nana were observed in the peat bog. Reproduction pro- ber of shoot scars, and development of bark, the following ceeded only by vegetative growth. The density of one- −2 stages of ramets were distinguished and counted separately: year old ramets in Sites A, B and R averaged 124 m , Stage 1 – one-year old unbranched, Stage 2 – two-year old 33.5 m−2 and 84.5 m−2, respectively (Fig. 1). Generally, unbranched, Stage 3 – two-year old branched, Stage 4 – the multiplication of ramets in the period 2001–2003 branched ramets that were three or more years old. was associated with vegetation types. The number of The effects of sexual and vegetative reproduction on new ramets was limited only in Site B, where Vaccinium the dynamics of B. nana were studied. The number of first- uliginosum was dominant in the shrub layer (Table 1). year-old ramets originating from vegetative growth was fol- lowed in 2001–2003 at each plot. The length of 500 one-year- There was no significant effect of Ledum palustre on old long shoots was also measured in each plot. The mor- vegetative reproduction in Site A. tality of juvenile unbranched ramets, and mature branched Another indicator of vegetative growth, the annual ramets, were assessed separately by comparing the number increase in lateral shoot length, was also affected by veg-

Table 1. Z-values of Mann-Whitney test of the eﬀect of Ledum palustre (Site A) and Vaccinium uliginosum (Site B) on vegetative reproduction, annual increase, leaf number on long shoots, ramet density, ramet size and age of Betula nana.Signatures:*p < 0.05, ** p < 0.01, *** p < 0.001.

vegetative annual increase Eﬀect reproduction of long shoot leaf number ramet density ramet size ramet age

Site A 1.53 −11.8*** 11.8** −2.87**–−4.14*** −2.4* 0.12 Site B −4.99*** −13.89*** 13.89** −3.71***–−11.84*** 0.14 0.12 250 W. Ejankowski

160 Site A J 768 140 744 V 80 727 120 R 100 60 80 60 40 292 40 205 174 20 20 Lenght [mm]

0 Share of ramets [%] 0 -20 Mean 200120022003 -40 Mean ± SD Mean ± 1.96 SD Years -60 Site A Site B Site R

Fig. 2. Annual long shoot growth in Betula nana in Sites A, B, Site B and reference Site (R) in Linje peat-bog. 211 J 80 199 195 V R 60 etation. Elongation growth of long shoots was the most 40 64 intensive in reference site R (Fig. 2), and growth rate 60 63 20 was limited in sites A and B (Table 1). The develop- Share of ramets [%] 1 2 0 ment of B. nana in Site A was higher than in Site B (U 0 test, Z = −2.18, p < 0.05). 2001 2002 2003 Years In accordance with the seasonal increase in B. nana, the number of leaves on long shoots was also influenced by vegetation (Table 1), and the leaf num- Site R 1252 ber on these shoots was lower in Sites A (6.1) and B J 80 1338 1156 (6.5) compared with the reference site (8.1). The small V R difference in leaf number between Sites A and B was 60 − . < important (U-test, Z = 2 41, p 0.05). 40 The vegetative phase was dominant in ramets in all 395 288 20 of the study sites (Fig. 3). Generally for A, B and R, the 26 62 149 45 (598) (561) (0) percentage share was approximately 80%, whereas the Share of ramets [%] 0 share of juvenile stage was ca. 20%. Generative ramets 2001 2002 2003 were in the minority in Site R (1–4%), and only ac- Years counted for 0.4–0.8% in Site B. The proportion of ram- Fig. 3. Population structure of Betula nana in juvenile (J), and ets switching from a vegetative stage to a generative mature: vegetative (V), and reproductive (R) stages in Sites A, phase averaged 0.4% in Site B and 2.4% in Site R. The B, and reference Site (R) in Linje peat-bog. Included are percent- inversed transition from generative phase to vegetative ages of ramets for 2001–2003, number of ramets (above bars) and number of fruits (in brackets). stage was 48.9% in Site R. In Site B all fertile ramets switched between years. No inversion was observed and no generative ramets were present in Site A. Flowering was limited in Site B in 2002 (χ2 = 6.34, p < 0.05), ble 1). The number of ramets in the permanent plots and in 2003 (χ2 = 7.11, p < 0.01), and the effect was fluctuated considerably in 2000–2003. Changes were non-significant in 2001 (χ2 = 1.45, p > 0.05). generally positive – 13.2 % in Site A, 58.9 % in Site The fecundity of B. nana was strongly and nega- B, and 7.5 in the reference site, although the number tively associated with L. palustre and V. uliginosum,it of ramets strongly declined in the period 2001–2003 – had fruits only in reference Site R, although fertile ram- 7.6 % in Site A, 4.8 % in Site B, 17.8 % in Site R. ets also occurred in Site B. Number of nuts per ramet The ramet size of B. nana was associated with the in Site R were similar in 2001 (0.34) and 2002 (0.37), type of vegetation (Table 1), and their length was sim- and there were 23 and 9 fruits per ramet in the gen- ilar in Site B (54.5 cm) and Site R (55.2 cm). They erative phase in 2001 and 2002, respectively. In 2003 were smaller in Site A (42.87 cm) compared with the no fruits were observed, although fertile ramets were reference site. present. This is because catkins were damaged during Mean ramet age varied from 7.0 in Sites B and their development, and fruit production was strongly R to 7.6 in Site A, but there were no differences be- reduced by the larvae of butterflies, Erannis defoliaria tween the Sites (Table 1). In Sites A and B the range and Pandemis cerasana. of ages was relatively extensive, and the proportion of Ramet density was limited in Site A (in average old ramets was high (Fig. 4). Ramets in age group of 97 ramet m−2) and Site B (25.8 ramet m−2)compared 1–4 years were the most frequent in Site A. In Site B with Site R (155 ramet m−2). The differences between one-year old ramets were lacking, and 2-year old ones Sites in all years were significant, and the effect of veg- were weakly represented. In both cases the contribution etation on abundance of B. nana was confirmed (Ta- of age classes was quite uniform, whereas 5 and 8 year- Demografic variation of Betule nana in shrub communities 251

Table 2. Percentage values of mortality in juvenal and mature ramets of Betula nana in vegetation dominated by Ledum palustre (Site A) and Vaccinium uliginosum (Site B) and reference Site R in the Linje peat-bog in 2001–2003.

Site juvenal stage mature stage

2001–2002 2002–2003 2001–2002 2002–2003

Site A 33.3 <0.1 19.9 19.8 Site B 25 11.7 11.2 19.9 Site R 30.9 <0.1 9 22.7

14 Site A Discussion 12 10 In the study area Betula nana grows mainly in open bog 8 and in shrub communities consisting of Ledum palus- 6 tre L. and Vaccinium uliginosum L., belonging to the 4 class Oxycocco-Sphagnetea. In the succession of vegeta- 2 tion these scrubs precede development of forest on peat Share of ramets [%] bogs, and according to Jasnowski et al. (1968) vegeta- 0

1 3 5 7 9 tion dominated by L. palustre is an initial successional 11 13 15 Age [year] stage of the drying process of the bog. Plant communities with V. uliginosum usually occur in more shaded 14 Site B sites, and are the next stage in the transition to swampy 12 pine forest. 10 The dominance of several species in the shrub layer 8 in peat-bogs appears to be related to soil moisture (Jas- 6 nowski et al. 1968). Low light intensity is therefore an 4 indirect eﬀect of the hydrological conditions (Kotowski 2 Share of ramets [%] et al. 2001). High level of ground water may locally 0

1 3 5 7 9 eliminate species sensitive to waterlogging, such as L. 11 13 15 Age [year] palustre and V. uliginosum. This effect reduces competition from these plants and enables stronger develop- 14 Site R ment of B. nana due to the improved light conditions. 12 Similarly, survival of wetland narrow endemics may rely 10 on tolerance to stressful soils, combined with hydrope- 8 riod and relaxation of competition (Knox 1997). 6 Peat bog vegetation can considerably influence en- 4 vironmental conditions. Soil temperature was generally 2 lower and light was less available in vegetation domi- Share of ramets [%] 0 nated by L. palustre and V. uliginosum than in areas 1 3 5 7 9 11 13 15 without these species (data not shown). The differences Age [year] in microhabitats may be a cause of demographic variation of B. nana. Atmospheric and microclimatic fac- Fig. 4. Age of ramets in Betula nana in Sites A, B, and reference tors can also determine demographic processes in other Site (R) in Linje peat-bog. perennial and annual plant species (Wilkoń-Michalska 1976; Symonides 1978). Many ecological studies have shown variation in demography including reproductive strategy, and habitat conditions in different plant com- old ramets were the most frequent in the reference site, munities (Falińska 1979a, 1979b). and extreme groups were rare. Those in the middle age The effects of plant communities on population group (9–13 years) amounted to approximately 21% in structure and demographic processes of B. nana were Site A and 35% in Site B, but did not differ signifi- interesting due to the vegetation dynamics in the Linje cantly in comparison with the reference Site R, where reserve. The development of P. sylvestris L., originally the percentage share was 32% (χ2 =1.47andχ2 =0.08 open mire and its subsequent retreat from the peat bog respectively, in both cases p > 0.05). was revealed. A strong increase of shrubs and trees of No effects of vegetation on the viability of juvenile Betula pubescens Ehrh. has been also observed in recent and mature ramets were found (Table 2). The estimated last decades (Ejankowski & Kunz 2006). mortality rate averaged 16.8% in the juvenile and 17.1% In this study vegetative growth and ramet den- in the mature stage, and was higher in the period 2001– sity of B. nana was generally lower in the communities 2002 (20.8% and 29.7%) than in the next period – 13.4% dominated by V. uliginosum and L. palustre compared and 3.9%, in the matures and juveniles, respectively. with the reference site. The data show that the species 252 W. Ejankowski is intolerant of shade. The confirmation of this phe- carbohydrates within the clonal plant (Stuefer et al. nomenon is that dwarf birch grows in open bogs and 1994). Redistribution of resources may eliminate differ- understorey of open tree stands, with widely dispersed ences in survivorship of life stages. The other reason trees of P. sylvestris and B. pubescens, but not under may be that the stages identified in this study were not closed canopies (Hutchinson 1966; Laine et al. 1995). homogenous, and they included ramets of various age The negative effects of shade on vegetative growth groups and of different mortality rates. have also been observed in other plants. The weakness In this study we detected no effect of water level is related to light intensity, rather than to light quality on population structure of B. nana. Ramet age and (Steufer & Huber 1998; Huber et al. 1999). The de- size were relatively high, and the proportion of ramets velopment of branches, in terms of growth intensity of in middle age 9–13 years, which are potentially fertile, long shoots can play an important role in competition was similar in all Sites (Ejankowski 2008). between shrubs (Bret-Harte et al. 2001). Butterfly larvae inhabit and damage inflorescences, Shade intolerance may also explain lower vegeta- and limit fruit production in dwarf birch. Two mi- tive reproduction and abundance of B. nana in vegeta- nor butterfly species, Erannis defoliaria and Pandemis tion dominated by V. uliginosum, than in communities cerasana, live in the leaf blades of the genus Betula, with L. palustre. On the other hand the stand of P. commonly in the region of the lower Vistula River sylvestris, which occurred in the peat-bog, could nega- (Buszko 1990). Insects feeding on plant tissues can tively influence the abundance of B. nana due to com- damage leaves, flowers and inflorescences, and there- petition (Laine et al. 1995). Low ramet number in Site fore limit the number of seeds and the emergence of B, compared to other sites, is caused by limitation in seedlings (Pilson 2000; Poveda et al. 2003). vegetative reproduction, and not by enhanced mortal- The present study refers to ramet demography, and ity. does not explain if, and how, genets may respond to Although herb plants in wetlands depend mainly changes in vegetation. The results suggest that the ap- on light availability, and immediately on soil moisture, pearance of new individuals by recruitment from seeds woody plant species are generally sensitive to hydrol- is probably very slow, and the pattern of number dy- ogy, and can increase in abundance due to the effect of namics of ramets and genets in populations varies in the ground water table (Kozlowski 1997; Kotowski et clonal species (Falińska 1990). Reduced sexual recruit- al. 2001; Pellerin & Lavoie 2003). These water level fluc- ment in clonally propagating plants in unfavorable en- tuations, due to precipitation, may affect demographic vironments may lead to monoclonal populations of the processes of plants, depending on heterogeneity of habi- species, and imply negative consequences for popula- tats. tion persistence (Honnay & Bossuyt 2005). It is not clear why B. nana in Linje mire varied The lack of effective generative reproduction of B. in ramet density between years. The explanation of its nana is in agreement with the classification performed simultaneous decline in all study sites may be meteo- by Silvertown et al. (1993). On the basis of Ebert & rological conditions, because precipitation in 2001 ex- Ebert (1989) Betula nana is classified as belonging to ceeded the average value by 21%. Rising water level the group of shrubs and trees of open communities, in in the peat bog could also affect the abundance of which population growth rate is influenced by vegeta- B. nana by increasing mortality (Ejankowski 2008). In tive reproduction, and not by seedling recruitment. The fact, its mortality was generally higher in 2001–2002, seed bank also plays an insignificant role in the finite than 2002–2003. rate increase in the group of woody plant species men- The pattern of ramet age was different from that tioned (Silvertown et al. 1993). of ramet size: age was similar in the Sites, whereas the The role of vegetative reproduction is a typical length varied in different vegetation types. This is be- strategy of plants from arctic and alpine environments. cause the relationship between age and size in B. nana In sites with dense vegetation canopy and deep litter is curvilinear (data not shown). Ramet length grows layer the development of seedlings is hampered, whereas proportionally with age only in the first age groups, vegetative reproduction is promoted (Grime 2001). On then it tends to stabilize. Otherwise, ramet architecture the other hand, the lack of seedling germination and and ramet size may depend on light conditions (Steufer the low investment in generative reproduction may not & Huber 1998; Huber et al. 1999). only be an effect of life strategy, but also an effect of Limited number of flowering ramets of B. nana is stress (Ejankowski 2008). Sexual reproduction may be caused by shade induced by dense vegetation, consisting also important strategy in some long-lived clonal plants, of L. palustre and V. uliginosum. Low light availability and establishment from seeds can contribute in popu- also diminishes fertilisation and generative reproduc- lation growth in favourable years (Weppler et al. 2006). tion of many other plants in moist habitats (Falińska In conclusion, long-term changes in vegetation due 1979b; Knox 1997). to alterations in habitat conditions can affect the de- There was no difference in mortality in dwarf birch mographic processes and survival of plant populations. between juvenile and mature stages, although mortal- The increasing presence of shrubs and trees in peat ity is generally size dependent in other peat bog species bogs threaten the abundance of B. nana,andcancause (Nordbakken et al. 2004). This is probably because the extinction of its local populations. In the localities physiological integration of ramets allows them to share of B. nana in Poland this relates to the accompany- Demografic variation of Betule nana in shrub communities 253 ing species, particularly Betula pubescens Ehrh., Pinus Hutchinson T.C. 1966. The occurrence of living and subfossil re- mugo Turra and P. × rhaetica Brügger. The overgrowth mains of Betula nana L. in Upper Teesdale. New Phytologist 65: 351–357. of peat-bogs by bushes and forests lead to a decrease Jalas J. & Suominen J. eds 1976. Atlas Florae Europaeae 3: in the vegetative growth of B. nana. In shaded sites Salicaceae to Balanophoraceae. Committee for Mapping the sexual reproduction may be also influenced, but it gen- Flora of Europe, and Socieda Biologica Fennica Vanamo, Helsinki, 128 pp. erally plays only small role in population growth. Jasnowski M., Jasnowska J. & Markowski S. 1968. Gin˛ace tor- fowiska wysokie i przej´sciowe w pasie nadbaltyckim Polski. Ochr. Przyr. 33: 69–123. Acknowledgements Jonsell B. 2000. Betula L. In: Jonsell B. (ed.), Flora Nordica 1. The Royal Swedish Academy of Science, Stockholm, pp. 197– We wish to express our thanks to Prof. Jaroslaw Buszko for 203. Knox J.S. 1997. A nine year demographic study of Helenium identification of the butterfly larvae. The study was financed virginicum (Asteraceae), a narrow endemic seasonal wetland by the State Committee for Scientific Research (grant No. plant. J. Torr. Bot. Soc. 124: 236–245. 3 PO4F 063 22). Kondracki J. 1998. Geografia regionalna Polski. Wyd. Nauk. PWN, Warszawa, 441 pp. Kotowski W., van Andel J., van Diggelen R. & Hogendorf J. 2001. References Responses of fen plant species to groundwater level and light intensity. Plant Ecol. 155: 147–156. Kozlowski T.T. 1997. Responses of woody plants to flooding and Brag O., Lindsay R., Risager M., Silvius M. & Zingstra H. 2003 salinity. Tree Physiol. Monogr. 1. Heron Publishing, Victoria, (eds). Strategy and action plan for mire and peatland conser- pp. 1–29. vation in Central Europe. Wetl. Intern. Publ. 18: 1–94. Laine J., Vasander H. & Laiho R. 1995. Long-term effects of water Breshears D.D., Nyhan J.W., Heil C.E. & Wilcox B.P. 1998. Ef- level drawdown on the vegetation of drained pine mires in fects of woody plants on microclimate in a semiarid woodland: southern Finland. J. Appl. Ecol. 32: 785–802. soil temperature and evaporation in canopy and intercanopy 159: Nordbakken J.-F., Rydgren K. & Økland R.H. 2004. Demography patches. Int. J. Plant Sci. 1010–1017. and population dynamics of Drosera anglica and D. rotundi- Breshears D.D., Rich P.M., Barnes F.J. & Campbell K. 1997. folia.J.Ecol.92: 110–121. Overstory-imposed heterogeneity in solar radiation and soil 7: Nory´skiewicz A.M. 2005. Preliminary results of study on vege- moisture in a semiarid woodland. Ecol. Appl. 1201–1215. tation history in the Linje mire region using pollen analysis. Bret-Harte M.S., Shaver G.G., Zoerner J.P., Johnstone J.F., Monogr. Bot. 94: 117–133. Wagner J.L., Chavez A.S., Gunkelman IV R.F., Lippert S.C. Pellerin S. & Lavoie C. 2003. Reconstructing the recent dynamics & Laundre J.A. 2001. Developmental plasticity allows Betula of mires using a multitechnique approach. J. Ecol. 91: 1008– nana to dominate tundra subjected to an altered environ- 82: 1021. ment. Ecology 18–32. Pilson D. 2000. Herbivory and natural selection on flowering phe- Buszko J. 1990. Struktura i dynamika zasi˛egów motyli minuj˛a- nology in wild sunflower, Helianthus annuus. Oecologia 122: cych (Lepidoptera) na obszarze Doliny Dolnej Wisly. Wyd. 72–82. UMK, Toruń, 166 pp. Poveda K., Dewenter I.S., Scheu S. & Tscharntke T. 2003. Ef- de Groot W.J., Thomas P.A. & Wein R.W. 1997. Biological flora fects of below- and above-ground herbivores on plant growth, of the British Isles Betula nana L. and Betula glandulosa flower visitation and seed set. Oecologia 135: 601–605. 85: Michx. J. Ecol. 241–264. Silvertown J., Franco M., Pisanty I. & Mendoza A. 1993. Com- Ebert T.A. & Ebert C.A. 1989. A method for studying vegeta- parative plant demography – relative importance of life-cycle tion dynamics when there are no obvious individuals: Virtual components to the finite rate of increase in woody and herba- population analysis applied to the tundra shrub Betula nana ceous perennials. J. Ecol. 81: 465–476. 85: L. Vegetatio 33–44. Sokal R.R. & Rohlf F.J. 1995. Biometry. W.H. Freeman and Com- Ejankowski W. & Kunz M. 2006. Reconstruction of vegetation pany, New York, 887 pp. dynamics in “Linje” peat-bog (N Poland) using remote sens- Steufer J.F. & Huber H. 1998. Differential effect of light quantity 1–2: ing method. Biodiv. Res. Conserv. 111–113. and spectral light quality on growth, morphology and de- Ejankowski W. 2008. Effect of waterlogging on regeneration in velopment of two stoloniferous Potentilla species. Oecologia 63: the dwarf birch (Betula nana). Biologia 670–676. 117: 1–8. Falińska K. 1979a. Experimental studies of the reproductive Steufer J.F., During H.J. & de Kroon H. 1994. High benefits of strategy of Caltha palustris L. populations. Ecol. pol. 27: clonal integration in two stoloniferous species, in response to 527–543. heterogeneous light environments. J. Ecol. 82: 511–518. Falińska K. 1979b. Modifications of plant populations in forest Symonides E. 1978. Effect of population density on the phenolog- ecosystems and their ecotones. Pol. Ecol. Stud. 5: 89–150. ical development of individuals of annual plant species. Ekol. Falińska K. 1990. Osobnik, populacja, fitocenoza. PWN, Warsza- pol. 26: 273–286. wa, 309 pp. van Wijk M.T., Klemmensen K.E., Shaver G.R., Williams R., Frankl R. & Schmeidl H. 2000. Vegetation change in South Ger- Callaghan T.V., Chapin III F.S., Cornelissen J.H.C., Gough man raised bog: Ecosystem engineering by plant species, veg- L., Hobbie S.E., Jonasson S., Lee J.A., Michelsen A., Press etation switch or ecosystem level feedback mechanisms? Flora M.C., Richardson S.J. & Rueth H. 2003. Long-term ecosys- 195: 267–276. tem level experiment at Toolik Lake, Alaska, and at Abisko, Gostyńska-Jakuszewska M. & Lekavičius A. 1989. Selected Bo- Northern Sweden: generalizations and differences in ecosys- real and Subboreal species in the flora of Poland and the tem and plant type responses to global change. Glob. Change Lithuanian SSR. Part I. Fragm. Flor. Geobot. 34: 299–314. Biol. 10: 105–123. Grime J.P. 2001. Plant Strategies, Vegetation Processes, and Virtanen R. & Oksanen L. 1999. Topographic and regional pat- Ecosystem Properties. John Wiley & Sons, Chichester, 417 terns of tundra heath vegetation from northern Fennoscandia pp. to the Taimyr Peninsula. Acta Bot. Fenn. 167: 29–70. Gunnarsson U. & Rydin H. 1998. Demography and recruitment of Weppler T., Stoll P. & Stöcklin J. 2006. The relative importance Scots pine on raised bogs in eastern Sweden and relationships of sexual and clonal reproduction for population growth in to microhabitat differentiation. Wetlands 18: 133–141. the long-lived alpine plant Geum reptans.J.Ecol.94: 869– Harper J.L. 1977. Population Biology of Plants. Acad. Press, Lon- 879. don, 857 pp. Wilkoń-Michalska J. 1976. Struktura i dynamika populacji Sali- Honnay O. & Bossuyt B. 2005. Prolonged clonal growth: escape cornia patula Duval-Jouve. Rozprawy UMK, Toruń: pp. 1– route or route to extinction? Oikos 108: 427–432. 156. Huber H., Lukács S. & Watson M.A. 1999. Spatial structure of stoloniferous herbs: an interplay between structural blue- Received February 25, 2008 print, ontogeny and phenotypic plasticity. Plant Ecol. 141: Accepted January 12, 2009 107–115.