The effects of windthrow on plant species richness in a Central European beech forest

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.     

Revegetation following experimental disturbance in a boreal old-growth Picea abies forest

Abstract. We studied revegetation patterns after experimental fine-scale disturbance (e.g. uprooting) in an old-growth Picea abies forest in southeastern Norway. An experimental severity gradient was established by manipulation of the depth of soil disturbance; two types of disturbed areas were used. Species recovery was recorded in the disturbed patches in three successive years after disturbance. The cover of vascular plants and, even more so the cover of bryophytes and lichens, recovered slowly after disturbance. The least severe treatments (removal of vegetation and removal of vegetation and the litter layer) was followed by the fastest recovery. The mean number of vascular plant species was usually higher three years after disturbance than before disturbance, while the opposite was true for bryophytes. Several vascular plant species that were abundant in intact forest floor vegetation (Vaccinium myrtillus, V. vitis-idaea and Deschampsia flexuosa) recovered during a three-year period primarily by resprouting from intact rhizomes and clonal in-growth. Other important recovery mechanisms included germination from a soil-buried propagule bank (e.g. Luzula pilosa, Plagiothecium laetum agg., Pohlia nutans and Polytrichum spp.) and dispersal of propagules into the disturbed patches (e.g. Betula pubescens and Picea abies). Microsite limitation seemed to occur in several species that were abundant in the soil propagule bank (e.g. the ferns Athyrium filix-femina, Gymnocarpium dryopteris and Phegopteris connectilis) but which did not appear in disturbed patches. Disturbance severity influenced revegetation patterns, recorded both as trajectories of vegetation composition in a DCA ordination space and as change in floristic dissimilarity. The length of the successional path (compositional change measured in β-diversity units) increased with increasing disturbance severity, and was also influenced by the area of the disturbed patch and the distance to intact vegetation. The rate of succession depended on the method by which it was measured; decreasing year by year in floristic space, while first decreasing and then increasing in ordination space. The reason for this difference is explained.     

Influence of experimental soil disturbances on the diversity of plants in agricultural grasslands

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.     

Recovery of pristine boreal forest floor community after selective removal of understorey, ground and humus layers

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.     

The bryophyte diaspore bank and its role after small-scale disturbance in a boreal forest

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.     

Species richness of vascular plants, bryophytes and lichens in dry grasslands: The effects of environment, landscape structure and competition

We studied the relative importance of local habitat conditions and landscape structure for species richness of vascular plants, bryophytes and lichens in dry grasslands on the Baltic island of Öland (Sweden). In addition, we tested whether relationships between species richness and vegetation cover indicate that competition within and between the studied taxonomic groups is important. We recorded species numbers of vascular plants, bryophytes and lichens in 4 m² plots (n=452), distributed over dry grassland patches differing in size and degree of isolation. Structural and environmental data were collected for each plot. We tested effects of local environmental conditions, landscape structure and vegetation cover on species richness using generalized linear mixed models. Different environmental variables explained species richness of vascular plants, bryophytes and lichens. Environmental effects, particularly soil pH, were more important than landscape structure. Interaction effects of soil pH with other environmental variables were significant in vascular plants. Plot heterogeneity enhanced species richness. Size and degree of isolation of dry grassland patches significantly affected bryophyte and lichen species richness, but not that of vascular plants. We observed negative relationships between bryophyte and lichen species richness and the cover of vascular plants. To conclude, effects of single environmental variables on species richness depend both on the taxonomic group and on the combination of environmental factors on a whole. Dispersal limitation in bryophytes and lichens confined to dry grasslands may be more common than is often assumed. Our study further suggests that competition between vascular plants and cryptogams is rather asymmetric.     

Disturbance effects on diversity of epiphytes and moths in a montane forest in Ecuador

We sampled the diversity of epiphytes (lichens, bryophytes, vascular plants) and moths (Geometridae, Arctiidae) in mature and recovering forest and in open vegetation in the montane belt in Ecuador. No uniform pattern of change in species richness was detected among the different taxonomic groups with increasing disturbance. Species richness of epiphytic bryophytes and vascular plants declined significantly from mature forest towards open vegetation. In contrast, species richness of epiphytic lichens did not change with increasing forest alteration, while that of geometrid moths was significantly higher in recovering forest compared with mature forest and open habitats. Arctiidae were significantly more species-rich in recovering forest and open vegetation than mature forest. Hence, for some organisms, modified habitats may play an important role for biodiversity conservation in the Andes, whereas others suffer from habitat disturbance. However, trends of changes in species composition following deforestation were surprisingly concordant across most studied epiphyte and moth taxa.     

Different responses of plants and herbivore insects to a gradient of vegetation height: an indicator of the vertebrate grazing intensity and successional age

Empirical studies have suggested that species richness of grassland insects usually decreases under grazing management. By contrast, grazing has been shown to increase the species density and richness of vascular plants, especially on productive soils. In order to test the suggested differences in response to management between plants and insects, we simultaneously studied species richness of vascular plants and their insect herbivores, butterflies and moths, in 68 semi-natural grasslands with varying grazing intensity and frequency in SW Finland. Species richness of plants and insects was for the first time related to a quantitative measure of disturbance intensity and successional age, mean vegetation height, by using generalized additive models (GAM). The effects of soil nutrients on vegetation height were accounted for by using phosphorus concentration as a productivity surrogate.
The results showed that species richness of butterflies and moths peaked in taller vegetation compared with vascular plants, corresponding to a lower disturbance intensity and increasing time since abandonment. These patterns are discussed in the light of two hypotheses, the "structural diversity hypothesis" and "dynamic equilibrium model" of Huston, both suggesting a weaker disturbance tolerance of insects compared with plants. Butterflies and moths which are specialists in their larval host-plant use (monophagous and oligophagous species) preferred lower vegetation (higher disturbances) compared with generalists (polyphagous species), as predicted by Huston's model. This difference indicates a stronger relationship with plant species richness for specialist than for generalist butterflies and moths. Our results support the application of regionally and temporally varying grazing intensities in grassland conservation management.     

Bryophyte colonisation in experimental microcosms: the role of nutrients, defoliation and vascular vegetation

A three-year multi-factorial microcosm experiment simulating fertilisation, defoliation and the composition of vascular vegetation in a dry grassland succession was used to test four hypotheses concerning the establishment and survival of bryophytes in grassland vegetation. H₁: bryophyte cover may be used to predict bryophyte species richness. H₂: bryophyte richness is suppressed at high nutrient levels and promoted by defoliation of vascular plants. H₃: species richness of bryophytes is influenced by the species composition of the vascular vegetation. H₄: bryophyte species richness is negatively correlated with vascular plant biomass.
The relationship between bryophyte richness and bryophyte cover was found to follow the classical species-area richness curve. Bryophyte species richness responded positively to defoliation and negatively to fertilisation. The species composition of vascular vegetation had no significant effect on bryophyte richness. Bryophyte species richness was lower at high vascular plant biomass and vascular plant dry weight above 400 g m⁻² appeared fatal to bryophytes. At high nutrient levels, defoliation increased bryophyte richness, but defoliation did not fully compensate for the negative effect of fertilisation. The study reinforces the concern for short lived shuttle bryophytes in the agricultural landscape.     

苔藓植物对植物天然更新的影响

种子是天然更新的基础,幼苗和幼树的生长是天然更新过程中最敏感的阶段。苔藓植物作为许多生态系统的主要地被物,在维管植物天然更新过程中发挥着不容忽视的作用。在许多植被类型中,都有发育良好的苔藓群落,大量的研究证明它们的存在影响到维管植物的萌发、建成和生长,并且可能进一步影响到物种的共生,有一些种类甚至可能指示树种的更新。本文就苔藓植物对物种更新早期阶段的作用和影响进行了综述。包括苔藓植物的生理特性造成的微气候变化;苔藓群落对种子传播、萌发及幼苗建成的影响。并讨论了苔藓植物与更新物种的种间关系及其对幼苗生长的化感作用。     

Environmental relations of the bryophytic and vascular components of a talus slope plant community

The environmental factors correlating with community structure of vegetation on talus slopes of the 785 km long Niagara Escarpment, southern Ontario, Canada, were studied using canonical correspondence and regression analysis. The bryophytes and higher vascular plants were analysed separately to see if their responses were similar or different. Both vascular plants and bryophytes responded similarly to the environmental variables that were measured. For both vegetation components, location from north to south explained most of the variance. When species richness was plotted against location for the complete vegetation and for the two components separately, the results showed that vascular plant species richness decreased with increasing latitude, while bryophyte richness increased. The magnitude of both of these trends was slight but consistent with the hypothesis that available environmental energy governs a significant amount of the variance in species richness. Since separate components of the talus vegetation were shown to respond differently to the same environmental variable, groups of taxa should not be excluded from community level studies without a consideration of the possible consequences of this bias.     

Soil Disturbance as a Grassland Restoration Measure—Effects on Plant Species Composition and Plant Functional Traits

Soil disturbance is recognized as an important driver of biodiversity in dry grasslands, and can therefore be implemented as a restoration measure. However, because community re-assembly following disturbance includes stochastic processes, a focus only on species richness or establishment success of particular species will not inform on how plant communities respond ecologically to disturbance. We therefore evaluated vegetation development following disturbance by quantifying species richness, species composition and functional trait composition. Degraded calcareous sandy grassland was subjected to experimental disturbance treatments (ploughing or rotavation), and the vegetation was surveyed during four subsequent years of succession. Treated plots were compared with control plots representing untreated grassland, as well as nearby plots characterized by plant communities representing the restoration target.Species richness and functional diversity both increased in response to soil disturbance, and rotavation, but not ploughing, had a persistent positive effect on the occurrence of specialist species of calcareous sandy grassland. However, no type of soil disturbance caused the plant species composition to develop towards the target vegetation. The disturbance had an immediate and large impact on the vegetation, but the vegetation developed rapidly back towards the control sites. Plant functional composition analysis indicated that the treatments created habitats different both from control sites and target sites. Community-weighted mean Ellenberg indicator values suggested that the observed plant community response was at least partially due to an increase in nitrogen and water availability following disturbance. This study shows that a mild type of disturbance, such as rotavation, may be most successful in promoting specialist species in calcareous sandy grassland, but that further treatments are needed to reduce nutrient availability. We conclude that a functional trait based analysis provides additional information of the vegetation response and the abiotic conditions created, complementing the information from the species composition.     

Do vascular plants and bryophytes respond differently to coniferous invasion of coastal heathlands?

Invasion by non-native conifers may pose a threat to local biodiversity, but knowledge about introduced conifer effects on Northern Hemisphere ecosystems is scarce. The coastal heathlands of north-west Europe are threatened by invasion of native and introduced tree species. We assess how spread of the introduced conifer Sitka spruce (Picea sitchensis (Bong.) Carr.) into European coastal heathlands affect two major functional groups; vascular plants and bryophytes, and how these effects relate to the environmental changes imposed by the developing tree canopies. We compared the impact of introduced Sitka spruce and native Scots pine (Pinus sylvestris L.) by analysing effects on species richness and turnover of vascular plants and bryophytes along fine-scale transects from individual tree stems into open heathland vegetation. Environmental impacts were assessed by measured environmental variables, and the responses of the two species groups were assessed by calculating changes in their respective mean Ellenberg indicator values. Species richness decreased beneath both conifers, related to decreased light and increased nitrogen and pH. Whereas vascular plants responded negatively to poor light conditions beneath dense and low Sitka spruce canopies, bryophytes were more negatively affected by the warmer and drier microclimates beneath Scots pine. Introduced Sitka spruce impacts the sub-canopy environment differently from the native Scots pine, and the two functional plant groups responded differently to these impacts. This suggests that future forests are likely to differ in species richness and composition, depending on whether succession is based on native or introduced coniferous trees.     

Species richness of vascular plants,bryophytes, and lichens along an altitudinal gradient in western Norway

Species richness patterns of ground-dwelling vascular plants, bryophytes, and lichens were compared along an altitudinal gradient (310–1135 m a.s.l.), in western Norway. Total species richness peaked at intermediate altitudes, vascular plant species richness peaked immediately above the forest limit (at 600–700 m a.s.l.), bryophyte species richness had no statistically significant trend, whereas lichen richness increased from the lowest point and up to the forest limit, with no trend above. It is proposed that the pattern in vascular plant species richness is enhanced by an ecotone effect. Bryophyte species richness responds to local scale factors whereas the lichen species richness may be responding to the shading from the forest trees.     

Partial restoration of fungal and plant species diversity by removal of litter and humus layers in stands of Scots pine in the Netherlands

A field experiment was set up in five mature Scots pine (Pinus sylvestris) stands in the Netherlands in order to study the effects of removal of litter and humus on ectomycorrhizal fungi and vegetation of higher plants, bryophytes, and lichens. Lime was also applied as a countermeasure to the removal of surplus cations. Application of lime did not have significant effects on mycorrhizal fungi. Removal of ectorganic material increased species richness of ectomycorrhizal fungi. The number of fruit bodies was also higher in the sod-cut plots, but the difference compared with the controls was not significant in all years. A major effect of removal of the ectorganic layer was a reversion of ectomycorrhizal succession to earlier stages. Liming increased the number and cover of ruderal, nitrophilous plant species. Sod-cutting caused a reversion of the green vegetation to earlier successional stages.     

Susceptibility of burned black spruce (Picea mariana) forests to non-native plant invasions in interior Alaska

As climate rapidly warms at high-latitudes, the boreal forest faces the simultaneous threats of increasing invasive plant abundances and increasing area burned by wildfire. Highly flammable and widespread black spruce (Picea mariana) forest represents a boreal habitat that may be increasingly susceptible to non-native plant invasion. This study assess the role of burn severity, site moisture and time elapsed since burning in determining the invisibility of black spruce forests. We conducted field surveys for presence of non-native plants at 99 burned black spruce forest sites burned in 2004 in three regions of interior Alaska that spanned a gradient of burn severities and site moisture levels, and a chronosequence of sites in a single region that had burned in 1987, 1994, and 1999. We also conducted a greenhouse experiment where we grew invasive plants in vegetation and soil cores taken from a subset of these sites. In both our field survey and the greenhouse experiment, regional differences in soils and vegetation between burn complexes outweighed local burn severity or site moisture in determining the invasibility of burned black spruce sites. In the greenhouse experiments using cores from the 2004 burns, we found that the invasive focal species grew better in cores with soil and vegetation properties characteristic of low severity burns. Invasive plant growth in the greenhouse was greater in cores from the chronosequence burns with higher soil water holding capacity or lower native vascular biomass. We concluded that there are differences in susceptibility to non-native plant invasions between different regions of boreal Alaska based on native species regeneration. Re-establishment of native ground cover vegetation, including rapidly colonizing bryophytes, appear to offer burned areas a level of resistance to invasive plant establishment.     

The effect of canopy disturbance on species richness in a central Himalayan oak forest

Non-epiphytic species richness was studied in different disturbance classes within a Quercus semecarpifolia forest. Nine disturbance classes were defined according to the degree of biomass removal (lopping) and their spatial mixture. Six of these were observed in the study area. The species were divided into three functional groups: climbers, phanerophytes, and field-layer plants. The primary aim was to test if there is an elevated species richness under an intermediate disturbed canopy for (i) all vascular plants, (ii) lianas, (iii) phanerophytes and (iv) field-layer species. The richness of the different plant groups and all species were fitted against the disturbance gradient by means of Generalized Linear Models (GLM). Other environmental variables such as altitude, potential solar radiation, light intensity, canopy cover and soil parameters were also evaluated as predictors. Disturbance classes, canopy cover and light intensity were combined into a new variable, disturbance-complex, using Principal Component Analyses.Phanerophytes did not respond to any variable. Climbers were mostly related to pH and canopy cover, and were the only group related to altitude, nitrogen and loss-on-ignition. Herbaceous plants and total species richness showed a unimodal response to disturbance classes and the complex disturbance gradient, which supports the intermediate disturbance hypothesis. Relative radiation and slope also supported a unimodal response in herbaceous plants, but disturbance had a significant additional contribution to this pattern. The most significant predictor for these two groups was pH. The responses to organic carbon and phosphorus were not significant for any of the subsets.The results indicate that a small-scale lopping regime will enhance species richness of vascular plants; only a few species in the intermediate disturbed forest are weedy ruderals. In such a situation, the conservation policy may accept small-scale human impact as part of the forest landscape.     

Frequent fire promotes diversity and cover of biological soil crusts in a derived temperate grassland

The intermediate disturbance hypothesis (IDH) predicts that species diversity is maximized at moderate disturbance levels. This model is often applied to grassy ecosystems, where disturbance can be important for maintaining vascular plant composition and diversity. However, effects of disturbance type and frequency on cover and diversity of non-vascular plants comprising biological soil crusts are poorly known, despite their potentially important role in ecosystem function. We established replicated disturbance regimes of different type (fire vs. mowing) and frequency (2, 4, 8 yearly and unburnt) in a high-quality, representative Themeda australis–Poa sieberiana derived grassland in south-eastern Australia. Effects on soil crust bryophytes and lichens (hereafter cryptogams) were measured after 12 years. Consistent with expectations under IDH, cryptogam richness and abundance declined under no disturbance, likely due to competitive exclusion by vascular plants as well as high soil turnover by soil invertebrates beneath thick grass. Disturbance type was also significant, with burning enhancing richness and abundance more than mowing. Contrary to expectations, however, cryptogam richness increased most dramatically under our most frequent and recent (2 year) burning regime, even when changes in abundance were accounted for by rarefaction analysis. Thus, from the perspective of cryptogams, 2-year burning was not an adequately severe disturbance regime to reduce diversity, highlighting the difficulty associated with expression of disturbance gradients in the application of IDH. Indeed, significant correlations with grassland structure suggest that cryptogam abundance and diversity in this relatively mesic (600 mm annual rainfall) grassland is maximised by frequent fires that reduce vegetation and litter cover, providing light, open areas and stable soil surfaces for colonisation. This contrasts with detrimental effects of 2-year burning on native perennial grasses, indicating that this proliferation of cryptogams has potentially high functional significance for situations where vegetation cover is depleted, particularly for reducing soil erosion.     

Effects of Retention Felling on Epixylic Species in Boreal Spruce Forests in Southern Finland

We studied the effects of patch retention felling and soil scarification by harrowing on the coverage and species richness of epixylic species in boreal Norway spruce (Picea abies) forests in Southern Finland. The epixylics were investigated from both the retention tree groups (RTGs) and the surrounding felling areas before and after fellings and after scarification on consecutive years. The cover percentage of all included species groups was shown to decrease after the felling, especially in the felling areas (vascular plants, ?0.4%; mosses, ?27.8%; liverworts, ?4.0%; and lichens,?2.1%). The decrease was considerable also in the RTGs. The amount of dead moss increased in both the areas indicating microclimatic changes. Species richness also declined rapidly after the first year, especially in the felling areas (vascular plants, ?2.2%; mosses, ?27.3%; liverworts, ?30.3%; and lichens, ?22.9%). Scarification also decreases covers and species richness of bryophytes. After the second year, the covers of the species groups generally started to regain, especially in the untreated RTGs. The size of RTG was in positive correlation with the total species number. Another main result indicates that it is possible to maintain much higher initial vegetation abundance and diversity in the RTGs than in the felling areas. Coarse woody debris formed by the frequent tree uprootings may also enhance the long‐term survival of epixylics over forest regeneration period. RTGs should be at least 10 times larger than the size used in current Finnish forestry, so that they could function as species refugia.     

茂县土地岭植被恢复过程中物种多样性动态特征

植被恢复是退化生态系统重建的重要途径,植被恢复过程物种多样性的变化反映了植被的恢复程度.通过群落调查和多样性分析,研究了岷江上游土地岭植被恢复过程中群落物种多样性特征.结果表明： 恢复过程中6类不同类型群落分别表现其对于不同环境特征、干扰及更新方式等的响应;森林是较灌丛更适合当地环境状况的植被类型;人工恢复无干扰和轻度干扰群落的多样性相对较高,是较好的恢复模式.重度干扰使得1年生植物与地下芽植物比例增加,其它口食性较好的多年生草本减少.较强的干扰是群落无法更新、长期处于灌丛阶段且多样性较低的重要原因.本地区人工恢复群落在更新进程和多样性维持上优于自然更新群落,种植华山松加速了本地区植被演替进程.建议以适合恢复区域的多种恢复配置方式进行造林,并避免较强干扰,可以加速群落演替进程并保持恢复群落较高的物种丰富度与多样性.