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1.
Heli M. Jutila 《植被学杂志》2001,12(5):729-738
Abstract. The objective of this study was to investigate the effects of flooding and draw‐down on the germination from the coastal grassland seed banks and to determine whether the effect of flooding varies between the delta and the seashore. Seed bank samples were collected from three shore transects in SW Finland, two on the shore of the Baltic Sea and one on the delta of River Kokemäenjoki. Samples were germinated in non‐flooded and flooded conditions for over a month, after which both treatments were maintained in non‐flooded conditions. A total of 9267 seedlings of 47 species germinated and mean density of seeds in the soil was ca. 84 000/m2. Most of the seedlings were monocots (98%) and perennials (98%). Ca. 30–40% of the species found in the above‐ground vegetation had a seed bank including the majority of the most abundant species. The number of seeds and species richness increased as the organic layer became thicker. The organic layer was thicker in the seashore samples and the seed bank was significantly larger than in the delta. The flooding and draw‐down treatment significantly increased the number of germinating seedlings in the seashore and also increased species richness in two transects, one in the delta and the other in the seashore. Two species, Schoenoplectus tabernaemontani and Typha latifolia, had significantly higher germination in the flooded treatment than in the non‐flooded. Apparently, many species in these coastal grasslands have adapted to flood disturbance and for seeds of some species flooding may work as a positive signal, possibly breaking dormancy. 相似文献
2.
Abstract. Semi‐natural grasslands are a threatened biotope type in many countries. Typical grassland plant species are adapted to continuous grazing or mowing that keeps the environment open. With the decline in grassland area, these species are ever more reliant on alternative habitats such as road verges. To find out whether plant communities comparable to those of semi‐natural grasslands can be maintained on modern road and railway sides, the vegetation of 92 grasslands and 90 road and railway verges was studied. These biotope types were compared with each other according to their community structure, total number of species, number of grassland species and restricted‐range diversity. Further study of the vegetation of road and railway verges was carried out in order to identify the treatments and environments which are most likely to support diverse plant communities. The species number and the restricted‐range diversity proved to be higher next to roads and railways than on grasslands. Grassland species were, however, most abundant on grasslands. Furthermore, the community structure of these biotope types was totally divergent. In their present state, road and railway verges are not a substitute for semi‐natural grasslands. Nevertheless, the occurrence of grassland species in verges may be enhanced by a suitable mowing regime, by giving up the use of de‐icing salt and herbicides and by allowing natural establishment of vegetation on the verges. 相似文献
3.
Abstract. This paper compares the regeneration by seeds of heath and meadow and studies relationships between the floristic composition of phases in the regeneration pathway. Seed densities in the seed rain and seed bank as well as the densities of emerged seedlings in gaps and in closed vegetation were greater in the meadow than in the heath. In the heath, environmental constraints hindered seedling emergence almost completely so seeds accumulated in the seed bank. In the meadow, the decrease in the seed bank was due to high seedling emergence. Within both plant communities, seedling emergence in gaps and in closed vegetation was comparable. In the meadow, the seed rain and seedling emergence in gaps, as well as the seed bank and seedling emergence in gaps were positively correlated. Differences in seed and adult plant sizes were reasons for the low correlation between the standing vegetation and the other phases. In DCA ordination the first axis separated the phase of seedling emergence in closed vegetation and seed bank. The second axis separated the standing vegetation from the other phases. The structure of the seed rain was more heterogeneous than that of other phases. In the heath, the standing vegetation and the seed rain were positively correlated. The ordination of these phases reflected the patchiness of standing vegetation and the ability of the diaspores of Betula nana to disperse over long distances. 相似文献
4.
Question: Which one of the two mainly used mowing regimes along road verges, mowing once or twice a year is a better option regarding flowering and seed‐producing success of grassland species and plant species in general? Location: Southeast Finland. Methods: Plant species composition, flowering and seed production success were studied in road verges (1) mown once in August and (2) mown at the end of June and August. Flowering shoots were counted and phenological phases were estimated four times during a growing season. Results: The numbers of flowering or seed‐producing species and shoots indicated that mowing once a year corresponding to the timing of traditional management was markedly better than mowing twice a year. The difference between the management groups was greatest at the end of July when the number of flowering species was 43% and the number of flowering and seed‐producing shoots 76% less after the first mowing than in the still unmown sites. The species avoided early cutting either through the timing of flowering or due to their growth form. Early season mowing had no effect on the occurrence and seed‐producing success of grassland species and the first flowering species. Seed production of grasses succeeded poorly in the verges mown twice. Conclusion: Mowing once in August resulted in higher seed production in general, but mowing twice a season might be a better way to manage young verges on nutrient‐rich soils. The useful qualities of the management options should be considered locally when planning road verge management. 相似文献
5.
Abstract. When management, in the form of cattle grazing and mowing, ceases the abundance of competitively superior plant species tends to increase in abandoned semi‐natural meadows. Litter accumulation elevates the soil nutrient levels and hinders seedling recruitment. We surveyed changes in plant cover and species composition of a formerly grazed meadow in permanent plots for six years. Some plots were unmown, while others were mown and raked annually in August. The cover of grasses decreased and herb cover remained unchanged regardless of the treatment. Mowing and raking significantly reduced litter accumulation and increased the number of ground layer species. The expected long‐term effects of abandonment and restorative mowing were studied by calculating the transition probabilities for unmown and mown plots and simulating the course of succession as projected by the transition matrices. During a simulation period of 30 yr, abandonment led to (1) a decrease in the cover of small herbs, (2) a slight increase in the cover of tall herbs and (3) a slight decrease in the cover of grasses. In contrast, the cover of small herbs on the mown plots remained unchanged or slightly increased during the course of simulation. These results suggest that mowing late in the season is primarily a management tool for the maintenance of the existing species diversity and composition. However, it may not be an effective restorative tool to induce overall changes in the resident vegetation of abandoned grass‐dominated meadows. Grazing or mowing early in the season may be more effective in this respect. Consequently, mowing early or, alternatively, late in the season may provide management strategies for the maintenance and restoration of species diversity, respectively. 相似文献
6.
Abstract. The deciduous Vaccinium myrtillus and the evergreen Vaccinium vitis‐idaea were subjected to five removal treatments of understorey layers: control, removal of the moss layer, removal of the field layer, removal of both moss and field layers and removal of moss, field and humus layers. A second factor, sowing, was included to investigate sexual reproduction after disturbance. Density of new ramets and seedlings and growth of annual shoots were studied for the first two growing seasons, whereas cover was measured for five growing seasons after disturbance treatment. Initially, vegetative production of new ramets and species cover increased rapidly in all disturbed plots, except for the most severe treatment, in which production of new ramets was virtually absent throughout the study. Full recovery following removal of the field layer only or both field and moss layers was reached after four years for V. myrtillus. V. vitis‐idaea recovered more quickly, after one year (removal of field layer only) and four years (removal of field and moss layers). The relative growth of V. myrtillus and V. vitis‐idaea increased in the latter treatment in terms of production of annual shoots and length of annual shoots, respectively. Seedling density increased after sowing in the most severe treatment. The results underscore the importance of vegetative growth for recovery of these species at moderate‐level disturbances. The high rate of sexual reproduction in the most severe treatment implies that strong mechanical disturbance is needed to enhance the establishment of new genotypes in these species. 相似文献
7.
P. Rautiainen T. Björnström M. Niemelä P. Arvola A. Degerman L. Erävuori P. Siikamäki A. Markkola J. Tuomi M. Hyvärinen 《应用植被学》2007,10(1):25-32
Question: Arctophila fulva var. pendulina, Primula nutans var. jokelae and Puccinellia phryganodes are threatened early successional species growing in the seashore meadows of the northern Baltic Sea. Patches formed by these species are destined to be replaced by other species during primary succession and in order to persist in the area they have to continuously colonize new areas. We studied whether the displacement of the species could be slowed down and their sexual and/or vegetative reproduction enhanced by management targeted to surrounding vegetation. Location: Bothnian Bay, Baltic Sea, W Finland. Methods: Vegetation surrounding patches of all study species was mown in four successional growing seasons. Moreover, the impact of additional soil turning on creating new favourable growing sites was tested for A. fulva. Results: Deterioration of suitable habitats of A. fulva and P. nutans was markedly slowed down by management and the vegetative and/or sexual reproduction of these species was enhanced. In the case of P. phryganodes, however, no positive response to management was obtained. Conclusions: In order to improve the long‐term persistence of these three species successional vegetation changes should be slowed down and their dispersal and colonization success improved by continuous management of the populations. We further suggest that the colonization of new areas should be aided by transplantations to the non‐vegetated islets, which have recently risen from the sea and cannot be reached by means of dispersal. 相似文献
8.
Abstract. The use of digital images in measuring plant species cover and species number in boreal forest vegetation was studied. Plant cover was estimated by manual delineation on photographs and subsequent digitized measurement of the areas. This value was regarded as the reference and compared with cover obtained by visual estimate, point frequency and automatic image analysis methods. The automatic image analysis was based on scanned photographs. Supervised image classification with ERDAS software was then used to distinguish between the covers of different plant species. When comparing the ability of the methods to detect species, the visual estimate method gave values similar to the reference. The study material was collected from three sites along a heavy‐metal pollution transect in western Finland. All four methods detected, in a similar manner, differences between the plant species abundances along the transect. Compared with the reference, the digital images underestimated the cover of the lichens Cladina spp. and Cetraria islandica, but gave similar estimates for the dwarf shrubs Empetrum nigrum and Vaccinium vitis‐idaea. The point frequency method overestimated the cover of all the species studied. The visual estimates of lichens were close to the reference, while the dwarf shrub covers were overestimated. The number of species detected using supervised image analysis and the point frequency method was lower than that with visual estimation. Visual estimation was faster, and the estimate closer to the reference cover values than the others. Digital images may be useful in detecting changes in some selected species in vegetation with a simple vertical structure but with taller, multilayered vegetation and a higher species number, the reliability of the cover estimates is lower. 相似文献
9.
Abstract. We studied tree regeneration, a key process for the existence of urban woodlands. We hypothesized that, besides the usual biological factors, anthropogenic ones (fragmentation, wear, pollution etc.) determine the regeneration success of tree species in urban woodlands. To test this hypothesis, within an observational setting, we collected data from 30 urban woodlands in the cities of Helsinki and Vantaa, Finland. We defined the number of living saplings (30–200 cm in height) as an indicator of regeneration success and used regression analysis to test different factors as independent variables. The results showed that different tree species responded differently to urban pressure. The regeneration of Picea abies decreased with increasing fragmentation of the forest landscape, whereas for the other most common (deciduous) species, regeneration increased. Wear, measured as total path area per study site, had a negative effect on regeneration success. An a posteriori examination of the data suggested that coarse woody debris might promote regeneration. We conclude that, although tree regeneration in general is not threatened in urban woodlands in the area we studied, the species composition may gradually change. We discuss some management implications for counteracting the urban pressures on tree regeneration. 相似文献
10.
Abstract. Wet dune slacks occur as small, naturally fragmented systems in the dune landscape, isolated from other slacks. We studied the effects of slack isolation and area on the rate and direction of primary succession in a chronosequence of dune slacks. The results indicate that important changes occur in community characteristics over a period of 50 yr. Total cover and number of species increase as a result of the endogenous succession process, during which organic matter and nutrients accumulate. Consequently, competitive interactions shift from competition for nutrients to competition for light. Local factors thus determine, at least partially, the community composition in the slack. However, differences in community composition with increasing age are smaller when the slack is more isolated or smaller, suggesting a slower succession rate and biomass accumulation. Together with a lower contribution of slow dispersing species in more isolated slacks, this indicates that species accumulation is dispersal limited and thus influenced by regional factors. The stochastic variation resulting from this dispersal limited species accumulation causes a divergent successional pathway. 相似文献
11.
12.
Abstract. The floristic effects of river‐borne litter that accumulates in riparian zones may vary in space and time depending on variations in mass and particle size of the deposited litter. To analyse the effects of litter mass and size we applied differentsized litter (natural uncut pieces and powder) to riparian vegetation at different quantities. Vegetation responses were analysed after one season at the community level (total biomass or richness for all species) and species traits (biomass or richness for groups of species). At the community level uncut litter, but not powder, reduced species richness and both uncut and ground litter reduced above‐ground biomass. At the species trait level uncut litter had a stronger effect than powder on species richness and biomass. The only positive effect of litter addition was that powder increased graminoid species richness. The topsoil conditions indicated that the major impact of deposited, river‐borne litter was that it acted as a physical barrier directly preventing established plants from penetrating the litter layer and reducing light and soil temperature. 相似文献
13.
Abstract. Data on floristic composition and environmental variables were collected in floristically homogeneous oligotrophic pine (Pinus sylvestris) forests with heath-like under- storey vegetation in eastern Fennoscandia, and ordinated by non-linear multidimensional scaling (NMDS) in order to study the effect of lichen grazing by reindeer on the understorey vegetation. The study sites included areas with varying grazing pressure, as well as 50-yr old grazing exclosures. Sites rich in respectively bryophytes and lichens were placed at opposite ends of the ordination axes, and heavily grazed sites were placed in between them. Reindeer grazing increased the abundance of bryophytes, especially Dicranum spp. and Pleurozium schreberi. Grazing changed the vegetation to the extent that it resembled more mesotrophic sites, but this did not show any relationship with tree volume or other site productivity indicators. This was observed both in the ordination and, in a more compelling way, when exclosures with adjacent grazed areas were compared. No such signs were evident at ungrazed sites, where especially Cladina spp. spatially replace Cladonia spp. and tiny bryophytes like Barbilophozia spp., Polytrichum spp. and Pohlia nutans during succession. Cladina stellaris had almost disappeared from the most intensively grazed sites. The soil at ungrazed sites was characterized by high Al and Fe concentrations and bryophyte-rich sites by high Mn concentrations. Shannon's diversity index, depth of humus layer and proportion of bare ground also increased in sites getting richer in bryophytes. 相似文献
14.
Abstract. Forest patches in central Belgium were inventoried twice for the presence or absence of forest plant species to study the effects of age and distance on species composition. All forests in the study area were subdivided based on their land use history. To avoid effects of autocorrelated environmental characteristics on species composition, habitat homogeneity was indirectly investigated using a TWINSPAN classification of the vegetation data. Two major habitats (alluvial and non‐alluvial forests) were distinguished and analysed separately. Patterns of species composition were investigated at the landscape level using Mantel tests. Species composition similarity measures were calculated between all pairs of fragments based on the floristic data. A highly significant correlation was found between species composition similarity and inter‐patch distance. Difference in age, which we used as a measure for habitat quality, was less important in explaining species composition patterns. The effects of spatial configuration became significant when difference in age was accounted for, and a partial correlation was calculated between inter‐patch distance and species composition similarity. Different results were found for alluvial and non‐alluvial forest types. Alluvial forests were more influenced by the spatial configuration than the non‐alluvial. For the non‐alluvial forest type effects measured with the difference in age between forest fragments obscured the effects of inter‐patch distance. Based on our findings we suggest that species composition is not only internally generated, but external processes such as differential colonization caused by varying degrees of isolation may be of overriding importance. 相似文献
15.
Mathieu Rouget David M. Richardson Sandra Lavorel Jordi Vayreda Carles Gracia Suzanne J. Milton 《植被学杂志》2001,12(4):491-502
Abstract. This study explores the determinants of distribution, abundance and regeneration of six Pinus species (P. halepensis, P. nigra, P. pinaster, P. pinea, P. sylvestris and P. uncinata) that occur naturally in Catalonia, northeastern Spain. The aim of this study was to generate accurate predictions of the distribution of each species using simple and readily available environmental variables. We used recursive partitioning and GIS analyses to relate the data base of 10 600 field plots from the Forestry Inventory of Catalonia with abiotic and biotic characteristics of each plot. We present general patterns of distribution, dominance and regeneration for the six species and then focus on P. halepensis, the most abundant pine species in the western Mediterranean Basin. For all six species, the models correctly classified more than 80% of the distribution using abiotic factors, mainly altitude and rainfall variability. Biotic factors such as the basal area of other pine species were necessary to accurately predict patterns of pine species dominance. Biotic factors, especially the basal area of evergreen species (mainly Quercus ilex), were of overriding importance when predicting patterns of seedling occurrence. Potentially important factors such as land use and fire history were of little significance for predicting distribution at the scale of our study. Our models failed to predict accurately which species (and in which numbers) co‐occur with P. halepensis. Factors not included in this study, such as stand age, disturbance (cutting, clearing) and other human‐induced factors, are probably the main determinants of co‐existence patterns. 相似文献
16.
Abstract. This is the first quantitative study of seed bank characteristics in North American alvar habitats. We assessed seed bank density, species richness, and species composition in 75 plots distributed among five alvar sites in Bruce Peninsula National Park, Ontario, Canada, each of which displayed areas of high and low vegetation cover within the alvar and a fully forested perimeter area. Forested habitats immediately adjacent to alvar patches contained minimal seed banks for species restricted to the alvar patches. Open alvars contained less than 1% seeds from woody forest species. This suggests that forest is not invading adjacent alvar habitat via seeds and that adjacent forest does not contain a reservoir of alvar seeds. When compared to areas on the alvar with high vascular plant cover, areas with low cover contained a slightly smaller viable seed bank, but seed banks from high and low vegetation cover plots had similar species composition and species richness. High vegetation cover plots had slightly higher mean and maximum soil depths compared with low cover plots, but no differences in other physical and chemical parameters. Thus, spatial heterogeneity in plant cover is associated only weakly with heterogeneity in below‐ground factors. Despite the availability of seed and soil resources, vegetation dynamics are constrained in areas with low plant cover, and thus alvar community development seems to respond non‐linearly to resource availability. 相似文献
17.
Abstract. An integrated analysis of the colonization patterns of forest plant species was carried out in a 34‐ha, mixed deciduous forest in northern Belgium. First, we sought to describe the relationships between land use history and environmental conditions. Land use history and soil type were related and negative correlations between pH and secondary forest age were found. The density of the shrub layer increases with secondary forest age. Litter quantity and cover of Urtica dioica were mainly indirectly influenced by land use history. Litter starts accumulating at low pH values and high shrub density and Urtica dioica grows vigorously on nutrient enriched soils where much light can reach the ground. Next, the importance of these human‐altered environmental conditions for the colonization of forest plant species was assessed relative to the importance of dispersal limitation. Therefore, the distribution of 16 forest species was mapped and species‐specific spatio‐temporal isolation measures were calculated. The analysis revealed that the colonization patterns of the slowly colonizing species (i.e. ‘ancient forest plant species’) are best explained by a combination of spatio‐temporal isolation, soil type, pH and the (non‐)cover of Urtica dioica. By contrast, spatio‐temporal isolation was never a limiting factor for good colonizing forest species. Our results suggest that colonization of ‘ancient forest plant species’ is hampered by a combination of dispersal‐ and recruitment limitation and that the relative importance of both factors is species‐specific. 相似文献
18.
Abstract. We studied the vegetation distribution in eight landscape types distinguished along an altitudinal gradient in the Trans‐Himalayan region of Ladakh, India. The point‐intercept method was used for vegetation sampling. Six plant communities were distinguished by cluster analysis. Of these 6 communities, three communities were dominated by shrub species. Table lands are the landscape type with the highest species diversity followed by undulating areas and river beds. Most plant species were restricted to one landscape type. 相似文献
19.
Raisa Mkip 《植被学杂志》1999,10(1):17-26
Abstract. The relationships between biomass of dwarf shrub species and nutrient gradients of forest soils was studied under field conditions in boreal forests. The biomass-response curves of Vaccinium myrtillus and V. vitis-idaea were fitted against soil nutrient gradients using Generalized Linear Models (GLM). Ecological niches of Vaccinium myrtillus and V. vitis-idaea were evaluated, and effects of nitrogen addition (manipulation of the nutrient gradient) on response function were tested. The Vaccinium species showed statistically significant Gaussian responses along soil nitrogen, phosphorus and calcium gradients, but not along other gradients (K and Mg). Furthermore, manipulation of the nitrogen gradient seemed to have a minor effect on response functions, i.e. addition of nitrogen did not change ecological niches of these species. Ecological optima of V. myrtillus and V. vitis-idaea on the nutrient gradients were about the same. This study suggests that differences in dominance between Vaccinium myrtillus and V. vitis-idaea in boreal forest is not determined by nutrient gradients, but may rather be explained by light conditions and/or moisture availability. 相似文献
20.
Abstract. Plant life‐form abundance along a 600 m altitudinal gradient (1600–2200 m a.s.l.) in the semi‐arid valley of Zapotitlán, México was correlated with soil characteristics and climatic variables. One mixed soil sample was taken and analysed for each of six elevations, temperature was estimated using a terrestrial thermal gradient, and precipitation using a linear regression between total annual precipitation and the elevation of the weather stations in the valley. Rosettes, microphanerophytes, therophytes and nanophanerophytes were well represented throughout the gradient. Columnar cacti were restricted to the 1600–1800 m range, and geophytes to the 1700–1800 m range. In general, abundance of life forms was inversely associated with altitude. Multiple regression analysis did not show parameters to significantly explain the abundance of rosettes, nanophanerophytes, epiphytes, geophytes and hemiparasites; altitude and nitrogen proved significant for columnar cacti, succulents and chamaephytes; altitude, pH, electrical conductivity and nitrogen were significant for globose cacti; pH was significant for therophytes; and altitude was significant for microphanerophytes. 相似文献