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1.
Leaving small patches of forest intact at harvesting is now a standard procedure to mitigate negative effects on biodiversity. One purpose of the patches is to “life-boat” species over the forest regeneration phase, although the capacity of small forest fragments to do so is very uncertain. We investigated the survival of red-listed and indicator species of bryophytes and lichens in 74 retention patches in boreal Sweden. The patches were between 0.01 and 0.5 ha in size and of six different types with respect to tree species composition and location on the harvested area. Species presence and abundance were recorded shortly after harvest in transects covering the whole patches, and an identical inventory was carried out 6 years after the first. During this time, bryophytes generally decreased, most pronounced for liverworts. The largest decreases were found in buffer zones to streams and lakes and the smallest in tree groups dominated by deciduous trees. By contrast, among the lichens some species decreased while others increased, and there was no difference between retention patch types. Among the species abundant enough to be analyzed individually, the lichens Calicium parvum and Micarea globulosella decreased less in larger patches and the bryophyte Hylocomiastrum umbratum decreased more in patches of irregular shape. The results imply that retention patches of this size might be too small to function as refugia for sensitive bryophytes and lichens until the surrounding forest regenerates, but that some lichens appear to persist or even increase. Retention harvesting is still a young management practice and further studies on its long-term conservation benefits will be valuable.  相似文献   

2.
An inventory of the understory forest epiphyte and epiphyllous bryophyte floras was carried out in eight Atlantic rain forest fragments. The fragments were between 7 and 500 ha in size and belonged to two areas (lowland and submontane) of the state of Pernambuco, northeastern Brazil. The aim of this study was to investigate the effect of habitat fragmentation and changes in the natural landscape on community structure (composition, richness, diversity, and abundance). Although the influence of altitude was noted in this study by increasing richness, diversity, and abundance, it was clear that in some fragments the influence of fragment size and isolation can be more important than this positive environmental factor. Fragment size and isolation affect both communities but the last one seems to be a stronger threatening factor for the epiphylls. The least isolated and the largest fragments housed the richest floras - especially in relation to the epiphylls - and had the greatest proportion of shade species. Habitat fragmentation negatively affected epiphytic and epiphyllous bryophytes and increased the representation of species with larger niches (generalists) while decreasing the representation of species with smaller niches (typically found in shady or in sunny areas). The results suggests that the critical fragment size necessary for bryophyte preservation must be correlated with insularity levels; for epiphytes, however, it is likely that low levels of isolation cannot compensate borderline effects as with the epiphyllous bryophytes.  相似文献   

3.
The combined effects of rapid habitat loss, fragmentation and disturbance on tropical forest avifaunas have not been examined to date. The southern Amazonian ‘arc of deforestation’ marks the boundary of the most aggressive agricultural frontier in tropical forests worldwide. We sampled 21 disturbed and undisturbed primary forest patches, ranging in size from 1.2 to 14,476 ha, to elucidate the synergistic effects of both forest disturbance and fragmentation on bird community structure, and pinpoint which species were the “winners” and “losers” from this process. A number of forest patch metrics, derived from an independent remote sensing approach, explained much of the resulting presence/absence matrix. The bird community exhibited a highly nested structure, with small patches being most dissimilar from one another. Bird species differed in their response to both forest patch size and forest canopy perforation according to their dependence on closed-canopy primary forest. Forest patch geometry, which clearly modulated the shape of species-area relationships accounted for 83-96% of the variation in species richness, but forest habitat quality resulting from logging and surface-fire disturbance was also a significant predictor of species richness for the most forest-dependent taxa.  相似文献   

4.
Tall-grass prairies are a critically endangered ecosystem in North America. Our objectives were to evaluate potential roles of prairie patch structure (defined in terms of prairie patch area, matrix type, and edge effects) in explaining changes in number, size, and quality of northern tall-grass prairies over time. In 2006, we evaluated changes in remnant tall-grass prairies at the most northern extent of the tall-grass prairie range, by resurveying plant communities in 65 remnant patches in Manitoba, Canada, that were previously surveyed in 1987 or 1988. In 2007 and 2008 we conducted more detailed surveys of vegetation structure and composition at 580, 0.2 × 0.5 m quadrats distributed within 24 remnant patches of northern tall-grass prairie. Our findings suggest remnant northern tall-grass prairies continue to suffer from serious threats: 37% of the patches surveyed in 1987 or 1988 had changed to other habitat types by 2006; patches smaller than 21 ha tended to decrease in size, while larger patches increased in size; and most patches, particularly smaller ones, declined in quality. Both native and alien species responded more strongly to distance to edge than to patch size or matrix type. Edge effects may explain why prairie quality is lower and more likely to decline in smaller remnants. Richness of native plants was negatively correlated with cover and richness of alien species, suggesting that alien species may displace native species. Few existing northern tall-grass prairies are likely to be self-sustaining, and immediate active management is required to prevent further loss of remnant northern tall-grass prairies.  相似文献   

5.
We asked if short-term changes in bryophyte communities in response to clear-cutting of boreal stream-side forests are persistent and whether species with low resilience may survive in narrow riparian buffer strips. To assess short-term changes and the function of buffer strips we compared the bryophyte community in permanent 0.1 ha plots of mature forest before and after clear-cutting. Persistent changes were inferred by pair-wise comparisons of 0.1 ha plots of mature forests with carefully matched 0.1 ha plots in stands established after clear-cutting 30-50 years earlier. Total bryophyte species richness did not respond significantly to clear-cutting. However, richness changed in many subgroups defined by phylogenetic, habitat or substrate affinity. Numbers of both liverwort and forest species were significantly reduced on clear-cuts and these differences remained significant, although smaller, 30-50 years after clear-cutting. In contrast, there were short-term increases in richness of mosses and of species growing on disturbed mineral soil, but these species numbers returned to mature-forest levels in the young stands. Number of species associated with convex substrates, especially woody debris species, was strongly reduced by clear-cutting and showed no significant recovery after 30-50 years. Hence, most of the negative effects of clear-cutting on bryophyte species persist almost halfway into the next forestry rotation period. However, narrow buffer strips (10 m on each side) prevented most of the short-term extirpations of species with low resilience on clear-cuts. Buffer strips may thus be effective in conserving the bryophyte flora of stream-side forests, but their long-term function as refugia and their contribution to population recovery in other parts of the landscape need further evaluation.  相似文献   

6.
In highly-modified agricultural landscapes, regrowth (secondary) forest on abandoned farmland offers the potential for passive landscape restoration for biodiversity conservation. While numerous studies have investigated the ecological values of regrowth for fauna recovery at the local-level (1-10 ha), there is a dearth of studies quantifying the contribution of regrowth forest at the landscape-level (100-1000s ha). To address this critical knowledge gap we question how the age and amount of regrowth forest in the landscape influence species richness and abundance of mature forest dependent species? Using woodland dependent birds in fragmented sub-tropical brigalow landscapes in southern Queensland, Australia, we applied model averaging and hierarchical partitioning analyses to test and rank the relative importance of the amount of regrowth forest in the landscape in three age classes (<15, 15-30, and >30 years) compared to local (grazing disturbance, abundance of aggressive miners, mistletoe abundance and patch age) and landscape measures of habitat (amount of mature forest and number of mature forest patches). Response variables included the species richness of woodland dependent birds and sub-groupings of foraging guilds, and the abundance of selected individual species. The importance of explanatory variables differed considerably among response groups. Local attributes, such as patch age and the abundance of mistletoe plants, had the strongest influences on woodland dependent birds. However, we found that the amount of regrowth forest, particularly >30 years, also had a strong influence on both species richness and abundance. This study confirms that regrowth, especially older regrowth, can make an important contribution to landscape restoration in highly-modified agricultural landscapes.  相似文献   

7.
Management of forest for timber values presents potential threats for forest floor bryophytes, as localized disturbances are applied across landscapes. Dispersal limitation may exacerbate local extirpation, by preventing recolonization within a cut-block rotation period. Populations of forest floor bryophytes that persist under those patches of tree canopy remaining after clear-cutting could reduce dispersal distances and thereby contribute to conservation of species across the landscape. We examined bryophyte guilds (liverworts, forest-habitat mosses and colonist-pioneer mosses) and community composition in relation to habitat quality (microclimate and substrate) in five treatment classes in New Brunswick Acadian forest, 4 years after harvest. Four potential refugium classes with intact substrate were examined: three were characterized by remnant canopy height, one was treeless. These were compared to clear-cut areas with substrate disturbance. Microclimate (temperature, total daily photosynthetically active radiation and vapour pressure deficit) differed significantly between areas with and without remnant canopy, but differed little among refugium classes. This suggests that any remnant canopy moderates microhabitat relative to treeless areas. Liverworts and forest-habitat mosses were more frequent under remnant canopy than in open and clear-cut areas, with 25 species present only under remnant canopy. Environmental variation explained approximately 24% of bryophyte pattern, highlighting the potential influence of the pre-harvest community, which we could not document. In the absence of substrate disturbance, patches of remnant canopy provide potential refugia for some forest-habitat bryophytes. Characteristics of effective refugia (size and shape) should be determined by assessments of their impacts on: (i) change in bryophyte communities in refugia relative to natural dynamics and (ii) recolonization of adjacent areas.  相似文献   

8.
Saproxylic organisms are among the most threatened species in Europe and constitute a major conservation problem because they depend on the most important forestry product - dead wood. Diversity of fungal and bryophyte communities occurring on dead beech trees was analyzed in five European countries (Slovenia, Hungary, The Netherlands, Belgium and Denmark) considering tree level species richness (TLSR), country level species richness (CLSR), frequency distributions of species, occurrence of threatened species and relations between TLSR and decay stage, tree size and countries. Altogether 1009 trees were inventoried in 19 beech dominated forest reserves.The number of fungi in the full dataset was approximately three times larger (456 versus 161 species) and the proportion of low frequent species was higher than among bryophytes. The species richness of bryophytes and fungi was significantly different among countries considering both TLSR and CLSR. In addition the diversity patterns deviated considerably between the two groups of organisms. Slovenian sites appeared to be biodiversity hotspots for bryophytes characterized by high TLSR and CLSR and a high fraction of threatened species. Hungarian sites had somewhat lower bryophyte diversity, while the Atlantic region had deteriorated assemblages. Fungal species richness was very high in Denmark, but the Hungarian and Slovenian sites were richer in threatened and low frequency species. Tree size was better able to explain variation in TLSR in both organism groups than decay stage. TLSR was found to vary significantly between countries but the difference was most considerable in the case of bryophytes.The diversity patterns of both organism groups along the investigated geographical gradient appear to be influenced by both climatic and management related factors (forest history, dead wood availability and continuity, habitat fragmentation). There is no doubt that an increase in the abundance of dead wood in European beech forests will benefit diversity of saproxylic fungi and bryophytes, especially if a continuous presence of large diameter logs are secured within individual stands.  相似文献   

9.
The effect of tree species, stand structure, landscape and historical variables was studied on the species composition, species richness and cover of epiphytic bryophyte assemblages in mixed deciduous-coniferous forests of Western Hungary. Stand and tree level assemblages were analyzed by ordinations and generalized linear modeling in 35 70-110 year old stands of different management regimes.Bryophytes showed a considerable preference to different host trees, so that stand level diversity of bryophyte assemblages was determined mainly by tree species diversity, and their composition by tree species composition. Cover and diversity of epiphytic bryophytes were the highest on oaks (Quercus petraea and Quercus robur), and the lowest on Scotch pine (Pinus sylvestris). The presence of sapling (shrub) layer increased, whereas a large number of medium sized trees decreased bryophyte species richness in this study. Tree size was much less influential which is explained by the lack of large, veteran trees. Forest management maintaining tree species diversity, structural heterogeneity and temporal continuity of the stands could considerably contribute to the conservation of this organism group. Selective cutting is more appropriate for these conservational purposes than shelterwood management system.  相似文献   

10.
We studied the importance of fragment size and structural and functional connectivity on the occurrence and abundance of seven Atlantic Forest bird species in 13 patches (13-275 ha) and three sites within a continuous forest (10,000 ha). We sampled birds with point counts and evaluated structural connectivity considering the presence of corridors and the degree of isolation. We defined functional connectivity by analyzing species movements using playbacks in forest corridors between fragments and in the surrounding matrix. Species differed in their responses to fragmentation. For the frugivorous species, Trogon surrucura, Carpornis cucullatus and Triclaria malachitacea, patch size was the main factor determining abundance. Two understory insectivorous species, Basileuterus leucoblepharus and Pyriglena leucoptera, were more affected by the degree of patch connectivity, the former by the presence of corridors and the latter by the distance between patches. The capacity of P. leucoptera to use corridors and open areas (i.e. functional connectivity) shaped its abundance pattern. Fragmentation had no effect on the abundance of Chiroxiphia caudata and had a positive effect on Batara cinerea. This study emphasizes the importance of considering species’ perceptions of landscape, especially functional connectivity, in understanding the effects of habitat fragmentation.  相似文献   

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