Temporal Changes In Species Composition Research Articles

Between-year weather differences and long-term environmental trends both contribute to observed vegetation changes in a plot resurvey study.

Repeated surveys of vegetation plots offer a viable tool to detect fine-scale responses of vegetation to environmental changes. In this study, our aim was to explore how the species composition and species richness of dry grasslands changed over a period of 17 years, how these changes relate to environmental changes and how the presence of spring ephemerals, which may react to short-term weather fluctuations rather than long-term climatic trends, may influence the results. A total of 95 plots was surveyed in 2005 and resurveyed in 2022 in dry grasslands of the Kiskunság Sand Ridge (Hungary, Eastern Central Europe), where there has been a significant increase in mean annual temperature during the last decades, while no trends in precipitation can be identified. Db-RDA was performed to reveal compositional changes. The changes in environmental conditions and naturalness state were assessed using ecological and naturalness indicator values. We also compared per-plot richness of all species, native species and non-native species of the old and the new relevés. All analyses were repeated after removing all spring ephemerals. We found clear temporal changes in species composition. Mean temperature indicator values increased, while mean soil moisture indicator values decreased during the 17 years. Also, decreasing per-plot richness was detected both for all species and for native species, while mean naturalness increased. After the removal of spring ephemerals, the compositional changes were less obvious although still significant. The increase in the temperature indicator values remained significant even without the spring ephemerals. However, the decrease in the moisture indicator values, the decrease in the number of all species and native species, as well as the increase in naturalness indicator values disappeared when spring ephemerals were excluded from the analyses. Our study demonstrates that between-year weather differences and long-term environmental trends both contribute to observed vegetation changes.

Meiofauna is an important, yet often overlooked, component of biodiversity in the ecosystem formed by Posidonia oceanica

AbstractThe ecosystem formed by the marine flowering plant Posidonia oceanica is a biodiversity reservoir and provides many ecosystem services in coastal Mediterranean regions. Marine meiofauna is also a major component of that biodiversity, and its study can be useful in addressing both theoretical and applied questions in ecology, evolution, and conservation. We review the meiofaunal diversity in the meadow ecosystem of P. oceanica by combining a literature review and a case study. First, we gathered records of 672 species from 71 published studies, as well as unpublished sources, highlighting 4 species exclusive to this ecosystem. Eighteen of those studies quantified the spatial and temporal changes in species composition, highlighting habitat‐specific assemblages that fluctuate following the annual changes experienced by these meadows. Hydrodynamics, habitat complexity, and food availability, all three inherently linked to the seagrass phenology, are recognized in the literature as the main factors shaping the complex distribution patterns of meiofauna in the meadows. These drivers have been identified mainly in studies of Copepoda and Nematoda, and their effect may depend ultimately on species‐specific preferences. Second, we tested the generality of these observations using marine mites as a model group, showing that similar ecological preferences might be found in other less abundant meiofaunal groups. Overall, our study highlights the high diversity of meiofauna in meadows of P. oceanica compared with algae and sessile macrofauna associated with this seagrass and shows the complexity of the interactions and habitat use by meiofauna associated with the seagrass.

Diagnostic Species Diversity Pattern Can Provide Key Information on Vegetation Change: An Insight into High Mountain Habitats in Central Apennines

High mountain ecosystems are hotspots of biodiversity that are highly vulnerable to climate warming and land use change. In Europe, high mountain habitats are included in the EC Directive 92/43/EEC (Habitats Directive) and the identification of practices facilitating effective monitoring is crucial for meeting HD goals. We analyzed the temporal changes in species composition and diversity on high mountain EU habitats and explored if the subgroup of diagnostic species was able to summarize the comprehensive information on plant community variations. We performed a re-visitation study, using a set of 30 georeferenced historical plots newly collected after 20 years on two EU habitats (Galium magellense community growing on screes (8120 EU) and Trifolium thalii community of snowbeds (6170 EU)) in the Maiella National Park (MNP), which is one of the most threatened Mediterranean mountains in Europe. The presence of several endangered species and the availability of a botanical garden, a seed bank, and a nursery, make the MNP an excellent training ground to explore in situ and ex situ conservation strategies. We compared overall and diagnostic species richness patterns over time by rarefaction curves and described the singular aspects of species diversity (e.g., richness, Shannon index, Simpson index, and Berger–Parker index), by Rènyi’s diversity profiles. Diversity values consistently varied over time and across EU habitat types, with increasing values on scree communities and decreasing values on snowbeds. These changes could be associated with both land use change, through the increase of grazing pressure of Apennine chamois (Rupicapra pyrenaica ornata), which determined a rise of nitrophilous species in the scree community, and an increase of grasses at the expense of forbs in snowbeds, and to climate change, which promoted a general expansion of thermophilous species. Despite the two opposite, ongoing processes on the two plant communities studied, our results evidenced that diagnostic species and overall species followed the same trend of variation, demonstrating the potential of diagnostics for EU habitat monitoring. Our observations suggested that the re-visitation of historical plots and the implementation of frequent monitoring campaigns on diagnostic species can provide important data on species abundance and distribution patterns in these vulnerable ecosystems, supporting optimized in situ and ex situ conservation actions.

Temporal stability of biomass in annual plant communities is driven by species diversity and asynchrony, but not dominance

AbstractAimsPrimary biomass production is a fundamental process for ecosystem functioning. Yet, little is known on the mechanisms driving temporal stability of biomass production in annual plant communities, particularly when subjected to highly variable environments and undergoing temporal changes in species composition. We aimed to disentangle the relative importance of biomass production, species diversity, dominance and asynchrony of species fluctuations as drivers of biomass stability in mediterranean and semi‐arid annual plant communities.LocationMediterranean (31°42′ N; 35°03′ E) and semi‐arid (31°23′ N; 34°54′ E) sites, Israel.MethodsAbove‐ground biomass and species abundance were monitored in 15 plots of 250 m2 per site during eight consecutive years. Relationships between stability drivers and community stability were studied at the regional (between sites) and local (within sites) spatial scales.ResultsCommunity biomass stability (mean biomass/SD) increased from the semi‐arid to the mediterranean site concomitantly with higher biomass production, richness, and evenness. Differences in stability between sites were due to opposite effects of site conditions on the mean and SD of community biomass, leading to higher stability in the mediterranean site. Within sites, species asynchrony was the key driver of stability at the local spatial scale. Richness and biomass production affected stability indirectly through asynchrony, but in different ways at each site. At the mediterranean site, these factors had indirect negative effects on stability by reducing asynchrony, but did not rescind a positive effect of asynchrony on community stability. At the semi‐arid site, biomass production had indirect positive effects on stability through asynchrony, while richness had no effect on asynchrony and stability. Stability was not driven by species evenness in either site.ConclusionsOur study provides new insights into the complex control of biomass stability in the dynamics of mediterranean and semi‐arid annual plant communities, with different mechanisms driving stability across the regional vs local spatial scales.

Effects of Disturbance on Understory Vegetation across Slovenian Forest Ecosystems

The herbaceous understory represents a key component of forest biodiversity across temperate forests of Europe. Here, we quantified changes in the diversity and composition of the forest understory layer in representative Slovenian forest ecosystems between 2004/05 and 2014/15. In total, 60 plots were placed across 10 different managed forest types, ranging from lowland deciduous and mid-altitude mesic mixed forests to mountain conifer forests. This network is part of an international network of sites launched within the ICP Forests Programme aimed to assess the condition of forests in Europe. To examine how disturbance influenced understory dynamics, we estimated the disturbance impacts considering both natural and/or anthropogenic disturbances that cause significant damage to trees and to ground-surface layers, including ground-vegetation layers and upper-soil layers. Species richness across 10 sites (gamma diversity) significantly decreased from 272 to 243 species during the study period, while mean species richness per site did not significantly change. The mean value of site level Shannon diversity indices and evenness significantly increased. The cover of most common plant species increased during the monitoring period. The mean value of disturbance estimates per site increased from 0.8% in 2004/05 (ranging from 0% to 2.5%) to 16.3% in 2014/15 (ranging from 5.0% to 38.8%), which corresponded to a reduction in total vegetation cover, including tree-layer cover. More disturbed sites showed larger temporal changes in species composition compared to less disturbed sites, suggesting that forest disturbances caused understory compositional shifts during the study period. Rather than observing an increase in plant diversity due to disturbance, our results suggest a short-term decrease in species number, likely driven by replacement of more specialized species with common species.

Temporal changes in species composition affect a ubiquitous species' use of habitat patches.

Across landscapes, shifts in species composition often co‐occur with shifts in structural or abiotic habitat features, making it difficult to disentangle the role of competitors and environment on assessments of patch quality. Using over two decades of rodent community data from a long‐term experiment, we show that a small, ubiquitous granivore (Chaetodipus penicillatus) shifted its use of different experimental treatments with the establishment of a novel competitor, C. baileyi. Shifts in residency, probability of movement between patches, and the arrival of new individuals in patches altered which treatment supported the highest abundances of C. penicillatus. Our results suggest that the establishment of a new species worsened the quality of the originally preferred treatment, likely by impacting resource availability. Paradoxically, the presence of the new species also increased C. penicillatus’ use of the less preferred treatment, potentially through shifts in the competitive network on those plots.

Disturbances amplify tree community responses to climate change in the temperate–boreal ecotone

AbstractAimClimate change causes major shifts in species distributions, reshuffling community composition and favouring warm‐adapted species (“thermophilization”). The tree community response is likely to be affected by major disturbances, such as fire and harvest. Here, we quantify the relative contributions of climate change and disturbances to temporal shifts in tree composition over the last decades and evaluate whether disturbances accelerate community thermophilization.LocationQuébec, Canada.Time period1970–2016.Taxa studiedTrees.MethodsUsing 6,281 forest inventory plots, we quantified temporal changes in species composition between a historical (1970–1980) and a contemporary period (2000–2016) by measuring temporal β‐diversity, gains and losses. The effects of climate and disturbances on temporal β‐diversity were quantified using multiple regressions and variation partitioning. We compared how community indices of species temperature preference (CTI) and shade tolerance (CSI) changed for forests that experienced different levels of disturbance. We quantified the contribution of species gains and losses to change in CTI.ResultsTemporal β‐diversity was mainly driven by disturbances, with historical harvesting as the most important predictor. Despite the prevailing influence of disturbances, we revealed a significant thermophilization (ΔCTI = +.03 °C/decade) throughout forests in Québec. However, this shift in community composition was weakly explained by climate change and considerably slower than the rate of warming (+.14 °C/decade). Importantly, thermophilization was amplified by moderate disturbances (+.044 °C/decade), almost a threefold increase compared with minor disturbances (+.015 °C/decade). The gains and losses of a few tree species contributed to this community‐level shift.ConclusionsOur study provides evidence that disturbances can strongly modify tree community responses to climate change. Moderate disturbances, such as harvesting, might reduce competition and facilitate gains of warm‐adapted species, which then accelerate thermophilization of tree communities under climate change. Although accelerated by disturbances, community thermophilization was driven by the gains and losses of a small number of species, notably gains of maples.

Spatial and temporal changes in species composition of submersed aquatic vegetation reveal effects of river restoration

We examined temporal changes in spatial patterns of submersed aquatic vegetation (SAV) in response to the restoration of geomorphic habitat in Navigation Pool 8 of the Upper Mississippi River from 1998 to 2016. The frequency of occurrence and species composition of SAV at sampling sites were spatially interpolated for each year to create annual maps. Linear models were fitted to temporal changes in SAV within each map pixel. The frequency of occurrence of SAV (across all species) increased over time in much of the impounded region of the pool, including areas near restored islands. However, impounded areas maintained a relatively consistent species composition over time, with species known to be tolerant of higher flow velocities (>0.10 m/second) and wind fetch distances (>1,000 m) (e.g. Vallisneria americana) being most abundant. In contrast, areas protected by newly constructed islands transitioned from V. americana to species found in other protected backwater habitats and known to be intolerant of high flow velocities and wind fetch distances (e.g. Ceratophyllum demersum). The results suggest that previously reported improvements in water clarity may have improved growing conditions for all SAV species, especially in the lower impounded portion of the pool, while island restoration created more backwater‐like habitats and facilitated changes in species composition. Assessing changes in SAV occurrence alone offers only a partial view of local‐scale river restoration (e.g. island building), while analyses of species composition are likely to be more indicative of the types of changes (i.e. reduced flow velocity and wind fetch) associated with restoring geomorphic habitat.

Partitioning beta diversity in a tropical karst seasonal rainforest in Southern China

Both deterministic and stochastic processes have been linked to forest community assembly; however, their contribution to beta diversity has not been properly explored, and no studies to date have investigated their impacts on sparse depleted soils in forests that contain widespread exposed limestone karst. We found that the pairwise differences in species composition between quadrates was determined by a balanced variation in abundance, whereby the individuals of some species at one site were substituted by an equivalent number of individuals of different species at another site. Both the total beta diversity and its balanced variation in abundance declined with increasing sampling grain size. Our research indicated that environmental differences exert a strong influence on beta diversity, particularly total beta diversity and its balanced abundance variation in larger grain sizes. It was evident that deterministic and stochastic processes worked together, and that deterministic processes were more important than stochastic processes in the regulation of beta diversity in this heterogeneous tropical karst seasonal rainforest of Southern China. However, in future research a functional trait based approach will be required to tease out the relative degree of deterministic and stochastic processes toward an assessment of the temporal changes in species composition.

Back into the past: Resurveying random plots to track community changes in Italian coastal dunes

Resurveying studies are commonly appreciated as a means to monitoring temporal changes in plant diversity. However, most of them still rely on phytosociological plots, which, although representing an invaluable source of data, can lead to biased estimates of vegetation changes. At the community-level, temporal changes can be quantified by means of beta-diversity measures. However, compositional variation can be the result of two different, often contrasting, processes: turnover and nestedness. In this context we test the effectiveness of resurveying approaches based on quasi-permanent plots in revealing temporal changes in herbaceous communities of Mediterranean coastal dune systems. Indeed, due to their being highly dynamic, coastal dunes can be considered ideal habitats for implementing such tools. In particular, we quantified temporal changes in species composition occurred over 10–15 years by calculating Sørensen index of dissimilarity and, in order to determine whether the change was really driven by species turnover, we partitioned Sørensen index into its two components of turnover and nestedness. At the same time, since diagnostic species are considered to be particularly sensitive to habitat modifications and helpful in assessing changes in the ecological structure of a community, we analyzed temporal changes in the occurrence and cover of diagnostic species of the investigated habitats. Results show that coastal dune communities of our study area underwent consistent changes during the analyzed time-span. Almost 25% of the historical plots disappeared. Major transformations, mainly driven by species turnover, involved upper beach communities, embryonic and mobile dunes, as revealed by the parallel analysis of beta diversity and diagnostic species. This work shows how resurveying approaches can efficiently reveal useful insights on vegetation dynamics, therefore providing a solid basis for the implementation of effective conservation strategies, especially in endangered habitats.

Turnover and nestedness in subtropical dung beetle assemblages along an elevational gradient

AbstractAimWe investigated changes in dung beetle β‐diversity components along a subtropical elevational gradient, to test whether turnover or nestedness‐related processes drive the dissimilarity of assemblages at spatial and temporal scales.LocationAn elevational gradient (200–1,600 m a.s.l.) of the Atlantic Forest in southern Brazil.MethodsWe investigated the extent to which β‐diversity varied along the elevational gradient (six elevations) at both spatial (among sites at different elevations) and temporal (different months at the same site) scales. We compared both the turnover and nestedness‐related dissimilarity of species and genera using multiple‐site or multiple‐month measures and tested whether these measurements were different from random expectations.ResultsA mid‐elevation peak in species richness along the elevational gradient was observed, and the lowest richness occurred at the highest elevations. We found two different groups of species, lowland and highland species, with a mixing of groups at intermediate elevations. The turnover component of β‐diversity was significantly higher for both spatial (i.e. elevational) and temporal changes in species composition. However, when the data for genera by site were considered, the elevational turnover value decreased in relative importance. Nestedness‐related processes are more important for temporal dissimilarity patterns at higher elevation sites.Main conclusionsSpatial and temporal turnover of dung beetle species is the most important component of β‐diversity along the elevational gradient. High‐elevation assemblages are not subsets of assemblages that inhabit lower elevations, but this relationship ceases when β‐diversity is measured at the generic level. Environmental changes across elevations may be the cause of the differential establishment of distinctive species, but these species typically belong to the same higher taxonomic rank. Conservation strategies should consider elevational gradients in case‐specific scenarios as they may contain distinct species assemblages in lowlands vs. highlands.

Temporal changes in species composition, diversity, and woody vegetation structure of savannas in the Cerrado-Amazon transition zone

ABSTRACT Vegetation in the transition between tropical forest and savanna is hyperdynamic and there is evidence that in the absence of fire, forest advances over savanna. Between 2008 and 2013 we evaluated changes in species composition and diversity and in the structure of the woody vegetation of savanna physiognomies in the transition between the Cerrado and Amazon biomes that were fire free for 11 years. The physiognomies form a gradient from savanna woodland (Typical Cerrado - TC), to low woodland (Dense Cerrado - DC), to woodland (locally called Cerradao - CO). We hypothesise that: 1) the more open physiognomies (TC and DC) are more dynamic compared to the closed physiognomy (CO); and 2) in the absence of fire vegetation tends to become more forested. We found that: 1) TC was more dynamic (e.g. greater increases in richness, diversity, and abundance of plants and basal area) than CO and DC; 2) The three physiognomies experienced an increase in basal area and abundance of individuals, but only certain key species contributed to these increases. These results indicate that the open physiognomies were more dynamic than the closed physiognomies, and in the absence of fire the savanna physiognomies became more forested and accumulated biomass.

Pelagic marine refugia and climatically sensitive areas in an eastern boundary current upwelling system.

Refugia are areas relatively buffered from contemporary climate change that enable the persistence of valued physical, ecological, or sociocultural resources. Spatially identifying refugia is important for conservation and applied management. Yet the concept of refugia has not been broadly extended to marine ecosystems. Here, we analyze data from a unique and long-term (1999-2015) standardized survey of pelagic marine and anadromous species off Oregon and Washington in the northern California Current to identify such refugia. We use quantitative approaches to assess locations with high species richness and community persistence relative to local and basin-scale environmental fluctuations. We have identified a potential climate change refugial zone along the continental shelf of Washington State in the Northeastern Pacific Ocean, characterized by a species-rich community with low interannual temporal community change. This region contrasts with adjacent areas to the south and offshore that have lower species richness, and higher temporal species community change. Also, using spatially variant generalized additive mixed models, we identify areas with species compositions that are more influenced by basin-scale climatic fluctuations than others. We propose that upwelling regions with retentive topographic features, such as wide continental shelves, can function as marine refugia for pelagic fauna, whereas offshore locations are potentially more climatically sensitive and experience high temporal change in species composition. Further identification of these marine refugia using insitu data for pelagic biodiversity and climatically sensitive areas can help guide management in the face of inevitable climatically driven change.

Vegetation development after a large scale restoration of species-rich grasslands in a Central European floodplain

Large scale restoration using local high-diversity seed mixture combined with turf transfer was applied on ex-arable land in the Morava River floodplain in the western Slovakia in the years 1999–2012. The post-restoration vegetation development was recorded during 12 years after the restoration using floristic records per restored polygons with cover estimation in simple 3-degree scale. Temporal changes in species composition were evaluated by gradient analysis and number of characteristic grassland and ruderal species on restored sites was analysed by general linear models. Species composition changed gradually towards the species composition typical for species-rich floodplain grasslands, but the trajectory was not straightforward and several irregularities were observed. They were probably induced by extreme weather events (drought, floods). The decrease in ruderal species and increase in the number of typical floodplain grassland species were observed, when floodplain grassland species permanently outcompeted ruderal species since 8th year after the restoration. However the development in large scale was slower, than expected from previous small-scale experiments, it is evident, that combination of local seed mixture sowing with a turf transfer is a feasible method for the restoration of species-rich floodplain grasslands from arable land.

Temporal changes in the structure of a plant-frugivore network are influenced by bird migration and fruit availability.

Background. Ecological communities are dynamic collections whose composition and structure change over time, making up complex interspecific interaction networks. Mutualistic plant–animal networks can be approached through complex network analysis; these networks are characterized by a nested structure consisting of a core of generalist species, which endows the network with stability and robustness against disturbance. Those mutualistic network structures can vary as a consequence of seasonal fluctuations and food availability, as well as the arrival of new species into the system that might disorder the mutualistic network structure (e.g., a decrease in nested pattern). However, there is no assessment on how the arrival of migratory species into seasonal tropical systems can modify such patterns. Emergent and fine structural temporal patterns are adressed here for the first time for plant-frugivorous bird networks in a highly seasonal tropical environment.Methods. In a plant-frugivorous bird community, we analyzed the temporal turnover of bird species comprising the network core and periphery of ten temporal interaction networks resulting from different bird migration periods. Additionally, we evaluated how fruit abundance and richness, as well as the arrival of migratory birds into the system, explained the temporal changes in network parameters such as network size, connectance, nestedness, specialization, interaction strength asymmetry and niche overlap. The analysis included data from 10 quantitative plant-frugivorous bird networks registered from November 2013 to November 2014.Results. We registered a total of 319 interactions between 42 plant species and 44 frugivorous bird species; only ten bird species were part of the network core. We witnessed a noteworthy turnover of the species comprising the network periphery during migration periods, as opposed to the network core, which did not show significant temporal changes in species composition. Our results revealed that migration and fruit richness explain the temporal variations in network size, connectance, nestedness and interaction strength asymmetry. On the other hand, fruit abundance only explained connectance and nestedness.Discussion. By means of a fine-resolution temporal analysis, we evidenced for the first time how temporal changes in the interaction network structure respond to the arrival of migratory species into the system and to fruit availability. Additionally, few migratory bird species are important links for structuring networks, while most of them were peripheral species. We showed the relevance of studying bird–plant interactions at fine temporal scales, considering changing scenarios of species composition with a quantitative network approach.

Temperature affects the partitioning of absorbed light energy in freshwater phytoplankton

Summary Temperature affects phytoplankton growth by altering the balance between light energy absorption and consumption. However, the way absorbed light energy (Qphar) is partitioned as a function of temperature has never been compared among phytoplankton groups. Accordingly, light‐energy partitioning in seven freshwater phytoplankton species acclimated to eight temperatures (7–35 °C) was quantified by photosynthetic and bio‐optical measurements. At low temperature, cyanobacteria and green algae received an excess of energy due to a decreased C‐fixation capacity. Consequently, Qphar partitioning was mainly directed towards dissipation mechanisms, such as non‐photochemical quenching and alternative electron pathways. The same photo‐protective mechanisms were stimulated in diatoms, but their ability to maintain stable C‐fixation capacities over the entire temperature range prevented the cells from experiencing excessive excitation pressure. At high temperatures, Qphar was preferentially invested in growth, showing a taxon‐specific positive correlation with growth rate. The cyanobacteria and a diatom required the lowest amount of energy to sustain their growth rate. The higher efficiency of these taxa in using light for growth is therefore a cellular trait that favours their dominance during summer. Our results are in line with literature reports showing temporal changes in species composition that can be attributed to temperature, and may help to explain the seasonal succession of species observed in nature.

Structural patterns of beech and silver fir suggest stability and resilience of the virgin forest Sinca in the Southern Carpathians, Romania

The structural patterns and dynamics of a primeval silver fir (Abies alba) – European beech (Fagus sylvatica) forest in the Southern Carpathians (Romania) were assessed to gain deeper insight into species interactions and mechanisms of coexistence, and to study the influence of species composition on forest structure. At 21 sample plots, each covering 0.123ha within an area of 240ha, all living and dead trees ⩾6cm dbh (diameter at breast height) were mapped and measured. Regeneration was assessed on four sub-plots per plot. Additionally, a 1-ha permanent plot established in 2003 was re-measured in 2013 to obtain information on stand dynamics. Point pattern analyses were conducted to study the spatial patterns and tree-to-tree interactions. The overall dbh distributions of beech and fir tended to indicate sustainable population structures. The share of beech varying from 24.8% to 95% (average 58%) in stand basal area did not influence stand parameters such as basal area or volume, nor the distribution of growing stock to different canopy layers. We found fir to dominate the lowest dbh classes in plots that were strongly dominated by beech in the top layer and vice versa, locally indicating species alternation. The regeneration density of fir was lower than of beech, although browsing by ungulates was negligible. In contrast to its share among living trees, fir contributed two-thirds to the deadwood volume. The 10-year changes in forest structure and mortality rate on the 1-ha plot were very small, suggesting the absence of recent intermediate or severe disturbances. The spatial patterns of the dead trees and of the living beech and fir in different canopy layers agreed with a disturbance regime dominated by stochastic small-scale events. Although the spatial patterns of beech and fir were similar, the tree-to-tree interactions indicated a higher intraspecific competition of beech than of fir and a higher shade tolerance of fir particularly in later stages of development. Both could be important factors for the coexistence of the two species. We conclude that the primeval fir–beech forest Sinca shows under the present small scale disturbance regime a high stability and structural resilience. Temporal changes in species composition only lead to small fluctuations in stand parameters and do not threaten the long-term coexistence of beech and fir. Forest managers may vary the species composition of fir–beech forests without substantially influencing the overall forest structure or productivity.

Patterns in species and functional dissimilarity: insights from periphytic algae in subtropical floodplain lakes

Understanding spatial and temporal changes in species composition has long demanded the attention of ecologists. However, only recently questionsrelatedtochangesinspecies functionaltraits have been investigated. We explored patterns of species andfunctionaldissimilarity ofperiphyticalgae at six lakes sampled over a year across a subtropical floodplain. We evaluated the importance of turnover and nestedness components across space and time; the influence of environmental dissimilarity, spatial dis- tance,andtimeonspecies andfunctionaldissimilarity; and whether functional dissimilarity results from non- stochastic assembly processes. We used six functional traits to describe 155 species. Functional dissimilarity was estimated by functional dendrograms, and stochasticity was evaluated using null models. The turnover component was greater than nestedness for species and functional dissimilarity. Environmental dissimilarity, spatial distance, or time did not signif- icantly explain species or functional dissimilarity. However, functional dissimilarity was significantly greater than expected given the observed species dissimilarity. The main finding of this study is that communityassemblywasdeterministicwithrespectto traits. Further, each lake contributed similarly to the overall species and traits pool. These results highlight the importance of comparing species and functional dissimilarities to reach a better understanding of the organization of periphytic algal communities.

Partial recovery of a tropical rain forest a half‐century after clear‐cut and selective logging

Summary The extent to which tropical rain forests recover tree species richness, composition and community structure after clear‐cutting or selective harvest is controversial. Thus, the conservation value of forests regenerated after harvest remains unclear, but critically important for biodiversity. We sampled trees from 164 25 × 25 m quadrats across a 160‐km2 tropical rain forest landscape on Hainan Island, China, which had been clear‐cut or selectively harvested and left to recover without management for up to 50 years. Species richness and species abundance distributions were compared among five successional categories to investigate changes in species richness and species abundance over time. Basal areas and three different species similarity indices were compared to reveal temporal changes in species composition and community structure. Species richness recovered faster than species composition and structure in both selectively logged and clear‐cut forests. Both total number of species and number of rare species tended to increase from younger harvested forests through older harvested forests to old‐growth intact forests. Within 20–40 years after harvest species composition of harvested forests tended towards that of old‐growth forests, community similarity between harvested and old‐growth forests decreased subsequently and basal area did not recover, given even a half‐century of succession undisturbed by anthropogenic forces. Shortly after harvest, pioneer species increased rapidly, but shade‐tolerant species required much more time to recover to former abundances. The shift from pioneer species to shade‐tolerant species indicates significant recovery of logged forests. Selectively logged forests recovered more quickly and had higher conservation values than clear‐cut forests. Synthesis and applications. Our findings indicate that logged tropical forests only partially recovered the characteristics of pre‐harvest, primary forest after a half‐century of succession. Recovery of the original tree biodiversity on such post‐harvest landscapes will be slow at best, if measured by species composition or stand structure. Our study amplifies the importance of conserving tropical forest integrity and developing harvest and management approaches that facilitate full recovery of logged tropical forests.

Vegetation resurvey is robust to plot location uncertainty.

Resurveys of historical vegetation plots are increasingly used for the assessment of decadal changes in plant species diversity and composition. However, historical plots are usually relocated only approximately. This potentially inflates temporal changes and undermines results. Temperate deciduous forests in Central Europe. To explore if robust conclusions can be drawn from resurvey studies despite location uncertainty, we compared temporal changes in species richness, frequency, composition and compositional heterogeneity between exactly and approximately relocated plots. We hypothesized that compositional changes should be lower and changes in species richness should be less variable on exactly relocated plots, because pseudo-turnover inflates temporal changes on approximately relocated plots. Temporal changes in species richness were not more variable and temporal changes in species composition and compositional heterogeneity were not higher on approximately relocated plots. Moreover, the frequency of individual species changed similarly on both plot types. The resurvey of historical vegetation plots is robust to uncertainty in original plot location and, when done properly, provides reliable evidence of decadal changes in plant communities. This provides important background for other resurvey studies and opens up the possibility for large-scale assessments of plant community change.