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1.
Abstract. The composition of the bryophyte diaspore bank in an old-growth Picea abies forest was studied before and after experimental disturbance of forest-floor patches. 40 species, both hepatics and mosses, emerged from spores, and probably also from gemmae and moss fragments, in greenhouse cultivations of soil samples. The three most abundant taxa were Pohlia nutans, Sphagnum spp. and Polytrichum commune/longisetum. Initially, the number of species from the diaspore bank in mineral soil, 9.9 species/sample, was higher than that in humus, 6.6. Four years after the disturbance took place, the reverse was found. Several species that are typical colonisers of disturbed soil were very common in the diaspore bank. By contrast, some of the most abundant forest floor species appeared to be absent. The diaspore bank of bryophytes appears to play a role similar to that of the seed bank in vascular plants: (1) it allows species to survive unfavourable periods (temporal dispersal); (2) it facilitates rapid colonisation after disturbance; (3) it influences the post-disturbance species composition and diversity. The results emphasise that the understanding of vegetation succession patterns is, to a large extent, dependent on quantitative data on the relative importance of spatial and temporal dispersal.  相似文献   

2.
It has been proposed that the interaction between life–history attributes of different organisms and distrbance characteristics play an important role in determining the successional pattern following a disturbance event. We compared the responses of vascular plants and bryophytes (mosses and hepatics) to variation in disturbance size and severity in an old-growth boreal forest during a four–year period. The experiment included two patch sizes (0.25 and 2.5 m2) and two levels of severity: humus patches (removal of vegetation) and mineral soil patches (removal of both vegetation and humus layer). Treatments were chosen to reflect some aspects of disturbance by uprooting. Species richness was significantly affected by both disturbance size and severity but the response differed among plant groups. In vascular plants, species numbers were highest in humus patches while mosses were more numerous in mineral soil patches, the most severe disturbance. In contrast, severity had no effect on hepatics. Plant recovery was more rapid in bryophytes than in vascular plants. Species richness of bryophytes had exceeded that of adjacent, undisturbed vegetation after 2-3 yr. We attribute the contrasting response of the plant groups to differences in regeneration strategies. As a group, bryophytes had a greater variety of regeneration methods than vascular plants, with several types of asexual propagules and abundant production of spores in some species. In contrast, clonal ingrowth dominated in vascular plants while seedlings were rare. Thus, our analysis supports the view that plant response to patchy disturbance is strongly dependent on the interplay among disturbance traits and specific attribtites of different plant groups.  相似文献   

3.
Revegetation is described for a portion of a Taxodium distichum-Nyssa aquatica (bald cypress-water tupelo) forested wetland in South Carolina. Thermal effluent from nuclear production reactors from 1954 to 1968 eliminated most of the original vegetation from the study area. Vegetation in disturbed and adjacent undisturbed areas was sampled in 1981 and 1985 using permanent plots. Herbs invaded rapidly throughout the disturbed portion of the wetland after thermal discharge ceased. Shrubs (Salix spp. and Cephalanthus occidentalis) followed soon thereafter, and have gradually occupied more of the area. Taxodium and Nyssa regeneration is rare because of the inability of seedlings of these species to compete with the dense cover of herbs and shrubs. Species composition is correlated with water depth, substrate type, and severity of disturbance. Because of substrate diversity, several successional mechanisms may account for the revegetation patterns.Abbreviation DCA Detrended Correspondence Analysis  相似文献   

4.
The effects of trampling and burrowing by streaked shearwaters were studied on thePersea thunbergii forest in Kanmurijima Is. The vegetation data were analysed using both the phytosociological tabulation method and principal component analysis (PCA). The vegetation ordination on the first axis reflected the environmental gradient from light to heavy disturbance by the streaked shearwater, and the vegetation ordination on the second axis represented the gradient from the latter phase of forest succession to retrogressive succession. The position of the three vegetation groups in the ordination diagram successfully explained the relation between the habitat and the species composition. The disturbance caused by activities of the streaked shearwater such as burrowing and trampling causes a decrease of species, especially character species of Camellietea japonicae, and also causes retrogressive succession: patches ofMallotus japonicus develop and many heliophytes occur.  相似文献   

5.
The effects of soil disturbance caused by the uprooting of a single or a few canopy trees on species richness and composition of vascular plant species and bryophytes were examined in a temperate beech forest (Fagus sylvatica) in northern Germany. We recorded the vegetation in 57 pairs of disturbed and adjacent undisturbed plots and established a chronosequence of mound ages to study the effect of time since microsite formation on plant species richness and composition. We found significant differences in plant species richness and composition between disturbed and adjacent undisturbed plots. Species richness of both vascular plants and bryophytes was higher in the disturbed than in the undisturbed plots, but these differences were more pronounced for bryophytes. We suggest that three main factors are responsible for this differential response. The availability of microsites on the forest floor that are suitable for the recruitment of bryophytes is lower than for vascular plants. Establishment of bryophytes in disturbed microsites is favoured by a greater abundance of propagules in the close vicinity and in the soil of the disturbed microsites, as well as by a greater variety of regeneration strategies in bryophytes than in vascular plants. Time since mound formation was a major factor determining plant species richness and composition. A significant decrease in the mean number of species was found from young mounds to intermediate and old mounds. However, differences were observed between vascular plants and bryophytes in the course of changes through time in species richness and composition. A large number of exclusive and infrequent vascular plant species was observed on young mounds, among them several disturbance specialists. We suggest that the establishment of many vascular plant species was infrequent and short-lived due to unfavourable light conditions and a low abundance of propagules. By contrast, the development of a litter layer was the main reason for the decreased mean number of bryophytes on old mounds. Our study supports the view that groups of species differing in important life history traits exhibit different responses to soil disturbance.  相似文献   

6.
Severity is recognized as an important attribute of disturbance in many plant communities. However, the effects of disturbances of different severity on patterns of regeneration in oligohaline marsh vegetation have not been experimentally examined. In these communities, a critical difference in the effects of disturbance severity may be whether the vegetation dies as a result of the disturbance or is merely damaged and hence capable of resprouting. We described the regeneration of vegetation in two Louisiana marsh community types, one dominated by Sagittaria lancifolia L. and the other by Spartina patens (Ait.) Muhl., following three levels of disturbance: no disturbance, a nonlethal disturbance, and a lethal disturbance. In the nonlethal disturbance, aboveground vegetation was clipped to simulate common disturbances such as fire and herbivory that remove aboveground vegetation but leave rhizomes intact. In the lethal disturbance vegetation was killed using herbicide to simulate disturbances causing plant mortality such as wrack deposition, sedimentation, scouring, and flooding following fire or herbivory. Regeneration was assessed over a 2-year period by measuring plant species richness, relative abundance, relative dominance, cover, and final biomass. To elucidate mechanisms for observed responses of vegetation, the species composition of the seed bank, light penetration, water level, salinity, and soil redox potential were evaluated. Despite differences in the structure of undisturbed vegetation in the two community types, they exhibited the same overall pattern of regeneration. Following nonlethal disturbance, the dominant species resprouted and quickly reestablished the structure of the vegetation. In contrast, recolonization following lethal disturbance occurred primarily via seedling recruitment, which resulted in marked shifts in community structure that persisted throughout the study. While the two communities responded similarly overall to disturbance, the response of individual species was not uniform; abundance, dominance, biomass, or cover increased for some species but decreased for others in response to disturbance. Seed bank species occurred in the vegetation following lethal disturbance in the Spartina community and in both disturbed and undisturbed plots in the Sagittaria community, indicating that the seed bank is a source of propagules for regeneration and maintenance of oligohaline marshes. Of the environmental variables measured, light level was most closely related to the effect of disturbance severity on community structure. Our results suggest that lethal and nonlethal disturbances have differential effects on regeneration of vegetation that can create pattern in oligohaline marshes communities. Received: 29 September 1997 / Accepted: 12 May 1998  相似文献   

7.
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   

8.
Abstract. Successional processes within northern Swedish boreal forest are investigated for the last 2000 years by analysis of pollen, charcoal fragments and insect remains preserved in a deep mor humus layer on a small island in a large lake. Frequent disturbances by fire, blow-down, insect attack and flood have been the chief influence on vegetation dynamics. The gradual climatically induced replacement of Betula pubescens by Picea abies is superimposed on the disturbance dynamics. Picea first became established during the Little Ice Age, which was the longest period without fire in the record. A thin layer of volcanic ash from Iceland confirms the chronology at the onset of the Little Ice Age. The present importance of Pinus sylvestris and Ericaceae on the island is a product of a recent increase in disturbance frequency. The disturbance regime ensures that the communities stay in equilibrium with prevailing climate.  相似文献   

9.
10.
In boreal spruce forests that rarely experience extensive disturbances, fine-scale vegetation gaps are important for succession dynamics and species diversity. We examined the community implications of fine-scale gap disturbances by selective removal of vegetation layers in a pristine boreal spruce forest in Northern Finland. The aim was to investigate how the speed of recovery depends on the type of disturbance and the species growth form. We also wanted to know if there appeared changes in species composition after disturbance. Five different treatments were applied in the study: Control, removal of the ground layer (bryophytes and lichens), removal of the understorey layer (dwarf shrubs, herbs and graminoids), removal of both the ground and understorey layers, and complete removal of the vegetation and humus layers above the mineral soil. The vegetation recovery was monitored in terms of cover and species numbers over a 5-year period. Understorey layer cover, composed mainly of clonal dwarf shrubs, recovered completely in 4 years in treatments where the humus layer remained intact, whereas ground layer cover did not reach the control level in plots from where bryophytes and lichens were removed. Recovery was faster in terms of species number than species cover. Bryophytes, graminoids and dominant dwarf shrubs appeared in all disturbed plots quickly after disturbance. Seedlings of trees appeared exclusively in disturbed plots. Graminoids dominated after the removal of humus layer. The results indicate that the regeneration of forest floor after small gap disturbance occurs mainly by re-establishment of the dominant species. Although destruction of the humus layer leaves a long-lasting scar to the forest floor, exposing of mineral soil may enhance the sexual reproduction of dominant species and the colonization of weaker competitors.  相似文献   

11.
All over the world forests and woodlands are damaged or reset to initial stages by fire, insect outbreaks or storms. In Central Europe storm events are the most important natural disturbances affecting stand structures of both natural and managed forests and yet only a few studies exist on long-term forest development following the destruction of the tree layer by a storm. This paper presents a permanent plot study established in 1988 in the Bavarian Forest National Park (SE Germany) on areas, where the tree layer had been destructed by a storm on August 1, 1983. The records concerning (1) floristic composition (spermatophytes, pteridophytes, bryophytes, lichens) and cover degree, (2) location and shape of each tree higher than 1 meter (height, diameter at breast height) including position of fallen trees and (3) number of seedlings and saplings were taken in 1988, 1993 and 1998. Two windfall areas, situated next to each other in the same broad and flat valley bottom on wet soils under local cold climate conditions (potential as well as recent vegetation:Calamagrostio villosae-Piceetum bazzanietosum) were analyzed, one of them with completely free development after the storm event (“untouched”), the other with dead wood cleared off after the event, but thereafter with free development (“cleared”). The vegetation analysis separated two major trends in vegetation dynamics: (1) On the cleared plots with intensive soil-surface disturbance (removal of the damaged wood) the species composition changed towards pioneer herb vegetation (Rubus sp.), and pioneer forest species (here: birch,Betula pendula and/orB. pubescens) established. Subsequently, vegetation dynamics leading towards clusters of forest ground-layer species composition took place. (2) In untouched stands, where soil-surface disturbances were restricted to pit-and-mound-system created by uprooted trees, the patchiness of forest vegetation increased and a regeneration of mainly terminal tree species (here: Norway spruce,Picea abies) started. Stand development for the next 100 years was simulated using the model FORSKA-M. The model is individual-based and includes competition for light, soil water, and nutrients. The simulations suggest that floristic structures of cleared and untouched plots, respectively, will remain different for several decades, but within one century, the floristic structure becomes rather similar. Major processes in forest ecosystems which can be used to improve forest management and nature conservation practices have been identified based on the results of the case study.  相似文献   

12.
Abstract

We investigated the community ecology and autecology of chasmophytes in the Karst (southwest Slovenia). An unusually massive occurrence of chasmophytes on settled screes and rock falls was detected in some of the collapse dolines of ?kocjan Caves and surroundings, building floristically and physiognomically homogenous plant communities. At first sight, no significant floristic distinctions in vascular plants were observed between scree and rock crevice stands, despite striking differences in habitats. A detailed floristic survey of stands, including vascular plants and bryophytes, as well as ecological parameters, revealed four distinct vegetation types. Floristically, bryophytes proved to differentiate groups of stands excellently but, in contrast to vascular plants, their presence and abundance only poorly reflected site conditions. Among chasmophytes, which, in terms of the Braun-Blanquet approach in phytosociology, are assigned to the class Asplenietea trichomanes (sensu Braun-Blanquet and Oberdorfer), only Saxifraga petraea and Saxifraga tridactylites prefer rock crevices and artificial walls, respectively, while others, e.g., Saxifraga crustata, Primula auricula and Athamanta turbith, prefer screes and their habitat selection is governed by different ecological parameters, shaped primarily by the phenomenon of temperature inversion in collapse dolines.  相似文献   

13.
Aims and Methods Disturbance is supposed to play an important role for biodiversity and ecosystem stability as described by the intermediate disturbance hypothesis (IDH), which predicts highest species richness at intermediate levels of disturbances. In this study, we tested the effects of artificial soil disturbances on diversity of annual and perennial vascular plants and bryophytes in a field experiment in 86 agricultural grasslands differing in land use in two regions of Germany. On each grassland, we implemented four treatments: three treatments differing in application time of soil disturbances and one control. One year after experimental disturbance, we recorded vegetation and measured biomass productivity and bare ground. We analysed the disturbance response taking effects of region and land-use-accompanied disturbance regimes into account.Important findings Region and land-use type strongly determined plant species richness. Experimental disturbances had small positive effects on the species richness of annuals, but none on perennials or bryophytes. Bare ground was positively related to species richness of bryophytes. However, exceeding the creation of 12% bare ground further disturbance had a detrimental effect on bryophyte species richness, which corresponds to the IDH. As biomass productivity was unaffected by disturbance our results indicate that the disturbance effect on species richness of annuals was not due to decreased overall productivity, but rather due to short-term lowered inter- and intraspecific competition at the newly created microsites. Generally, our results highlight the importance of soil disturbances for species richness of annual plants and bryophytes in agricultural grasslands. However, most grasslands were disturbed naturally or by land-use practices and our additional experimental soil disturbances only had a small short-term effect. Overall, total plant diversity in grasslands seemed to be more limited by the availability of propagules rather than by suitable microsites for germination. Thus, nature conservation efforts to increase grassland diversity should focus on overcoming propagule limitation, for instance by additional sowing of seeds, while the creation of additional open patches by disturbance might only be appropriate where natural disturbances are scarce.  相似文献   

14.
Abstract. The vegetation of anthropogenically disturbed sites on the Chukotka Peninsula was investigated in 1986 and 1990. 102 sites had been bulldozed free of vegetation and soil between 2 and 20 yr ago and revegetated. Anthropogenic vegetation differs considerably from natural tundra. The total plant cover decreases, lichens are absent, moss composition changes, and graminoids predominate. A floristic classification was developed in order to describe the diversity of anthropogenic communities formed on these sites. Four associations were distinguished, all belonging to the alliance Poion glaucomalacanthae. An additional alliance characterized by Alopecurus alpinus is suggested for colder sites, but it has not yet been described. There is a correspondence of associations to substrate types. The association Phippsietum algidae was found only on loam substrate. The Artemisietum glomeratae and Saxifragetum punctatae are connected with rubble or gravel. The graminoid association Arctagrostietum arundinaceae is generally widespread in disturbed habitats and occurs on a variety of substrate types.  相似文献   

15.
Abstract. Humus profiles were sampled along an altitudinal gradient in the Macot‐La‐Plagne Forest (France, northern Alps) to investigate variation occurring under carpets of Vaccinium myrtillus present within Picea abies forests. The vertical distribution of subterranean organs of V. myrtillus was compared with (1) that of P. abies roots and other accompanying vegetation and (2) other components of humus profiles, in particular humified organic matter mainly consisting of animal faeces. It was shown that V. myrtillus roots were mostly concentrated in mineral horizons, while P. abies roots and V. myrtillus rhizomes occupied litter horizons. This was interpreted in terms of competition for nutrient capture between P. abies and V. myrtillus. The effects of altitude were (1) a change in the vegetation accompanying V. myrtillus in dense V. myrtillus carpets, bryophytes at the montane level being replaced by forbs at the sub‐alpine level and (2) a decrease in the thickness of ecto‐organic horizons. This was interpreted as a shift from a moder system characterized by recalcitrant litter (moss) processed by an active faunal community (stabilized in the form of animal faeces) to a mor system characterized by low animal abundance but with litter of better quality which is easily leached in the absence of prominent faunal activity.  相似文献   

16.
Over two vegetation cycles we compared the recovery of macrophytes from flood disturbances that occured at different seasons (July vs December) on patches of a former channel of the Rhône River, France. Some patches were disturbed twice; others were disturbed either in summer or in winter; others were never disturbed and were used as controls.The recovery rate of the vegetation was estimated from the duration of recolonization of the disturbed areas and of growth of the recolonizing species. The influence of the summer disturbance appeared to be strong because the disturbance occurred when the development of the vegetation was maximum. The influence of the winter disturbance was apparently much lower since most species had already declined at this time because of their phenology. The repetition of the two disturbances on the same patch had little influence on the vegetation community.In all cases, the recovery of the vegetation occurred rapidly, both for total vegetation cover and species richness. By the following spring, no significant differences appeared between disturbed and reference patches. The effect of the disturbances varied according to the phenology of the plants, and the macrophyte community studied was more sensitive in summer than in winter.  相似文献   

17.
Eight forest types varying in disturbance frequencies were identified along an elevational gradient in Uttaranchal, central Himalaya. Low elevation forests were close to human habitation and had high disturbance frequency, while high elevation forests were situated far from the human habitation and had low disturbance. The dominant tree species at low elevation were Pinus roxburghii and Quercus leucotrichophora, while Q. floribunda and Q. semecarpifolia dominated the high elevation forests. Pyracantha crenulata was the shrub present in all the forests except in Q. semecarpifolia forest and Anaphalis contorta, a herb species, was present in all the forests. Disturbance decreased the dominance of single species and increased the plant biodiversity by mixing species of different successional status. Species richness and diversity for all the vegetation layers were higher in low elevation–high disturbance forests. Mean tree density decreased from high to moderate and increased in low disturbance. The shrub density decreased from high to low disturbance while the reverse occured for herbs. High proportion of early successional species in disturbed forests indicated that disturbance induces succession. The mean number of young individuals increasing from high to low disturbance indicates that disturbance adversely affects regeneration. But, however, the high number of young individuals of Coriaria nepalensis, a small non-leguminous nitrogen fixing tree, in disturbed forests shows that the forest is regenerating. This species could be helpful in the re-establishment of original vegetation through triggering the regeneration of these forests. High elevation–low disturbed forests separated from low elevation–high disturbed forests. Forest type and elevation may have more influence on tree richness while shrub and herb richness may be more sensitive to disturbance and forest types.  相似文献   

18.
Question: What were the temporal patterns and rates of tree mortality in a recent episodic tree mortality event? Have similar events occurred in the past, and does climatic variability play a role in the disturbance regime? Location: Intact Picea abies‐dominated taiga in the Arkhangelsk region, northwestern Russia. Methods: We reconstructed the past tree mortality and disturbance history by applying dendroecological methods in five forest stands and related these to climatic data. The role of other potential causes of tree mortality was assessed in a field inventory. Results: The recent episode lasted from 1999 to 2004, influenced all stands studied, and killed on average 21% of trees with a diameter of over 10 cm at 1.3‐m height. The annual tree mortality rate in the decades preceding this episode was 0.49%. During the past 200 years, the stands have experienced chronic small‐scale disturbances, with several irregular disturbances of moderate severity. The recent episode was associated with abundant signs of the bark beetle Ips typographus. Furthermore, the timing of both the recent tree mortality episode and the past disturbance events was associated with dry summers. Conclusion: The results indicate a connection between climatic variability and forest dynamics, the likely driving factors being droughts and bark beetles. In the context of the past 200 years, the recent episode was potentially at the higher end of the range of disturbance variability in terms of severity and spatial extent. This has ecological implications in a changing climate, potentially influencing ecosystem structure and long‐term dynamics.  相似文献   

19.
The influence of thermal disturbance and site characteristics on distribution of herbs was studied in portions of a 3020 ha wetland in the southeastern USA. Presence-absence of 52 species in 130 0.25 m2 plots was determined from four sites with different disturbance histories and from an undisturbed site. Data from the four disturbed sites were ordinated by detrended correspondence analysis. Differences in species composition among sites (coarse scale) were associated with water depth, light, and substrate type. Within a site (at a fine scale), correlation of environmental variables with ordination scores at a chronically disturbed site was weakly correlated with light (r=0.50). At two sites with episodic disturbance, species composition correlated significantly and positively with substrate and water depth. At a recovering site, vegetation patterns were moderately correlated with water depth (r=?0.52). Species richness was correlated with substrate type along the disturbance gradient. Our results are consistent the intermediate disturbance hypothesis and the subsidy-stress gradient concept.  相似文献   

20.
Questions: Does stand age influence the direction and rate of post‐fire successional dynamics in coastal Calluna heaths and can old degraded heath vegetation be restored through reintroduction of fire? Location: Coastal heaths in the Tarva archipelago, central Norway. Methods: We investigated revegetation dynamics after experimental fires set in young (8 years since last fire) and old (>50 years since last fire) grazed heath stands. A repeated measures design was used, with floristic data recorded in permanent plots in the post‐fire successions (n=12) over a 7‐year period. The data were analysed using multivariate ordination techniques (PCA, RDA and PRC) and mixed effects models. Results: The age of Calluna stands strongly influenced post‐fire succession, different trends due to age explained 10.4% of variation in floristic data. Young heath showed faster succession towards pre‐fire community composition than old heath, and this could partially be explained by succession‐related factors: young heath had lower cover of mosses and lichens in the pre‐burned vegetation, and lower cover of litter early in succession. Young heath had a less pronounced overall community response to fire than old heath. Vegetative regeneration of C. vulgaris was absent in both old and young heath, but Calluna still re‐established as the dominant species within 5–7 years in both young and old stands. Regeneration dynamics were also affected by habitat conditions, different trends due to habitat explained 6% of variation. Conclusions: Our study demonstrates that old stands do develop characteristic heathland vegetation and structure after fire, and while potential invasives into the system such as trees and rhizomatous species are present, they do not impair Calluna regeneration or vegetation development towards the target heathland community composition and structure. Further, as our young stands are only in their second fire rotation after restoration, we suggest that characteristic dynamics of managed heathlands can re‐establish relatively rapidly, even in severely degenerated sites (>50 years since last fire). Site‐specific factors also need to be considered. We conclude that there is restoration potential in old heaths, despite slow dynamics in the first rotation.  相似文献   

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