Understorey Vegetation Research Articles

Climate and soil differentially affect species, trait and diversity patterns of woody overstorey and fern understorey in a subtropical forest along an elevation gradient in Taiwan

AbstractQuestionsAlthough the relative importance of climate in abiotic filtering is higher for woody than for herbaceous species assemblages, it is unclear whether this pattern is also reflected between the woody overstorey and herbaceous understorey of forests. The understorey might respond more to small‐scale soil variation, next to experiencing additional abiotic filtering through overstorey effects on light and litter quality. We explored the proportional importance of climate and soil on the species, trait and (functional) diversity patterns of both the forest overstorey and fern and lycophyte understorey.LocationSubtropical forest along an elevational gradient from 850 to 2100 m a.s.l. in northern Taiwan.MethodsWe measured nine functional traits expected to respond to soil nutrient or climatic stress for woody overstorey species and understorey ferns and lycophytes. Next, we performed parallel constrained ordinations on over‐ and understorey species and trait composition, and multiple regression for species and functional diversity, using measured climate proxies and soil variables as predictors.ResultsClimate was more important than soil in predicting the species composition of both vegetation layers and trait composition of the understorey. The stronger than expected effect of climate for the understorey was likely due to fern and lycophytes’ higher vulnerability to drought, while the higher importance of soil for the overstorey trait composition seemed driven by deciduous species. The environmental drivers affected different response traits in both vegetation layers, and the overstorey had additional effects on understorey traits, resuling in a disconnection of community‐level trait values across layers. Interestingly, species and functional diversity patterns could be almost exclusively explained by climate effects for both layers.ConclusionsThis study illustrates that abiotic filtering can differentially affect species, trait and diversity patterns and can be highly divergent for forest overstorey and fern understorey vegetation, and should consequently not be extrapolated across vegetation layers.

Shift in tree species changes the belowground biota of boreal forests.

Summary The replacement of native birch with Norway spruce has been initiated in Norway to increase long‐term carbon storage in forests. However, there is limited knowledge on the impacts that aboveground changes will have on the belowground microbiota.We examined which effects a tree species shift from birch to spruce stands has on belowground microbial communities, soil fungal biomass and relationships with vegetation biomass and soil organic carbon (SOC).Replacement of birch with spruce negatively influenced soil bacterial and fungal richness and strongly altered microbial community composition in the forest floor layer, most strikingly for fungi. Tree species‐mediated variation in soil properties was a major factor explaining variation in bacterial communities. For fungi, both soil chemistry and understorey vegetation were important community structuring factors, particularly for ectomycorrhizal fungi. The relative abundance of ectomycorrhizal fungi and the ectomycorrhizal : saprotrophic fungal ratio were higher in spruce compared to birch stands, particularly in the deeper mineral soil layers, and vice versa for saprotrophs.The positive relationship between ergosterol (fungal biomass) and SOC stock in the forest floor layer suggests higher carbon sequestration potential in spruce forest soil, alternatively, that the larger carbon stock leads to an increase in soil fungal biomass.

No evidence for trade‐offs between bird diversity, yield and water table depth on oil palm smallholdings: Implications for tropical peatland landscape restoration

Abstract Tropical peat swamp forests retain large carbon stocks and support unique biodiversity, but clearance and drainage for agriculture have resulted in fires, carbon emissions and biodiversity losses. Initiatives to re‐wet cultivated peatlands may benefit biodiversity if this protects remaining forests from fire and agricultural encroachment, but there are concerns that re‐wetting could reduce yields and damage livelihoods, as relationships between drainage, on‐farm biodiversity, and crop yields have not been studied. We examined oil palm fruit yields and bird diversity on 41 smallholder farms in Jambi (Sumatra, Indonesia), which varied in drainage intensity (12‐month mean water table per plot from August 2018 to August 2019: −52 to −3 cm below‐ground). We also compared farm bird diversity with a neighbouring area of protected peat swamp forest (11,000 ha, 21 plots; mean water table per plot −3 to +15 cm). Bird species richness (3–18 species per plot), species composition and oil palm yields (4.5–19.2 t fresh fruit bunch ha−1 year−1) varied among farms, but were not detectably affected by water table depth, although ground‐level vegetation was more complex on wetter farms. Bird richness in oil palm (mean = 10.3 species per plot) was <50% of that in forest (26 species per plot), and only 3 of 35 conservation‐priority species found in forest were recorded in oil palm. Synthesis and applications. Tropical peatlands in Indonesia have been drained to allow farmer access and improve farm yields, but we found no trade‐offs between drainage depth, yields and bird diversity on smallholder oil palm farms in our study landscape within the studied range of drainage depths. Current restoration initiatives to re‐wet peat may benefit farmers by reducing fire risk, without affecting yields. Wetter farms had increased understorey vegetation complexity, but this did not affect bird diversity, so we find no evidence that re‐wetting improves on‐farm biodiversity. However, on‐farm fire reduction efforts in cultivated peatlands, including re‐wetting, will be vital for reducing the risk of fires escaping into nearby forests, which contain unique and diverse bird species assemblages. Protection of remaining peatland forests from fire and clearance is key for biodiversity conservation, and for providing a source of seed dispersers and genetic material for future forest and landscape restoration efforts. Restoration of more biodiversity‐friendly land covers will improve landscape permeability and help conserve species and the ecosystem services they deliver.

Which Factors Favour Biodiversity in Iberian Dehesas?

Dehesas or montados are man-made systems whose conservation interest as a Mediterranean landscape or agroforestry system has been highlighted in the scientific literature due to their high levels of biodiversity. The understanding of how management practices influence the biodiversity of the dehesa requires a comprehensive approach that considers the broad spectrum of biological components (i.e., fungi, lichens, vascular plants, macroinvertebrates, and vertebrates) that make the dehesa an ecosystem. We have reviewed around seventy publications compiled through Scopus and other specialized bibliographic sources not included in Scopus that study the impact of land use and land cover on the biodiversity of Iberian dehesas. The most significant results have been organized and summarized into a group of factors related to habitat structure and management practices. The conclusion to be drawn from the scientific studies is that not all biological components respond in the same way to land-cover and human practices, and the maintenance of a high overall diversity in dehesas depends on a complex understorey vegetation and habitat heterogeneity.

The dynamics of the carbon storage and fluxes in Scots pine (Pinus sylvestris) chronosequence

To evaluate the impact of stand age on the ecosystem's C budget, as well as the post-harvest recovery of the C storages and fluxes, a chronosequence of Scots pine stands from the clear-cut stage up to the age of 110 years was studied. An age-related trend of net primary production (NPP) demonstrated effective C accumulation in the young and middle-aged stands and their levelling out thereafter.The understorey vegetation contributed 8–46% to total NPP, being lower in the pole and middle-aged stands, but without a clear age related trend. Annual cumulative soil heterotrophic respiration (Rh) demonstrated stable values along the chronosequence, varying between 3.8 and 5.4 t C ha−1 yr−1. The Rh flux of 2.9 t C ha−1 yr−1 at the clear–cut site did not exceed the corresponding value for stands. The NEP along the chronosequence followed the dynamics of the annual biomass production of the trees, peaking at the middle-aged stage and decreasing in the older stands; the NPP of the trees was the main driver directing the dynamics of NEP.There was no significant correlation between Rh and dynamics of aboveground litter or fine root production, which can partly explain why no relationship was established between annual Rh and stand age.The total ecosystem C stocks followed the same trend as cumulative tree biomass, peaking in the older stands, however, the soil C stocks varied along the chronosequence irrespective of stand age.The post-harvest C compensation point was reached at the age of 7-years and C payback occurred at a stand age of 11–12 years. Stands acted as C accumulating ecosystems and average annual C accumulation was around 2.5 t C ha−1 yr−1, except for the youngest stand and the clear-cut area which acted as C sources. In the oldest stand C budget was almost balanced, with a modest annual accumulation of 0.12 t C ha−1 yr−1.

Intra- and inter-specific leaf trait responses of understorey species to changes in forest maturity

Coppice forest management impacts understorey vegetation. This is particularly true for habitat specialists (priority elements in conservation) who prefer closed canopy conditions associated with mature forests. Most trait-based studies of forest understorey focus on interspecific differences, which neglect the role of intraspecific variability. Here, we tackled this issue by examining how leaf traits respond (intra- and inter-specifically) to different stages of stand maturity for habitat specialist and generalist species. We measured the leaf area (LA), leaf dry matter content (LDMC) and specific leaf area (SLA) for 1,932 individuals belonging to 71 understorey species in 18 beech coppice forests grouped in three stages of stand maturity (i.e., post-logging, n = 5; recovering, n = 5; old stands, n = 8). We assessed leaf trait variation across stages of forest maturity for the entire community, and for specialists and generalists separately using monotonic trend tests. Then, we disentangled the proportion of variation attributable to intraspecific variability and interspecific differences of specialists and generalists using variance decomposition. We found significant positive trends in community-level SLA and negative ones in LDMC with increasing stand maturity. Beech forest understorey specialists (but not generalists) explained these patterns. The contribution of intra- and inter-specific components was dependent upon the trait under consideration and habitat specialization. For specialists, intraspecific variability was significant for all leaf traits and could explain 15.2% of model variance for SLA, 4.2% for LA and 3.1% for LDMC along the stand maturity gradient. Interspecific differences were significant for LDMC (29.8% of variance explained) and SLA (7.6%). For generalists, intraspecific variability was not significant; interspecific differences were significant for LA and explained 26.2 % of variability along the stand maturity gradient. We revealed that the maturity of coppice stands have different effects on generalist and specialist species. Habitat specialists are responsive to subtle changes in forest stand age both intra- and interspecifically, with their prevalence being function- and trait-dependent. Interspecific differences explained most of the LDMC (resource conservation) variance, while intraspecific variability accounted most of the SLA (light capture) variance. Generalists contribute to community-level trait variation, yet these species were less responsive to changes in forest stand age. To assess the impact of forest management on understories and refine the effectiveness of monitoring plans, we recommend focusing on habitat specialists, ideally including both trait variability within- and among-species.

Modelling fuel loads of understorey vegetation and forest floor components in pine stands in NW Spain

Modelling fuel loads of understorey vegetation and forest floor components in pine stands in NW Spain

Fuel loads and fuel structure in Austrian coniferous forests

Understanding fires in temperate European coniferous forests is hindered by a lack of reliable field observations on fuel load and structure. Fuel load influences the spread, intensity and spotting distance of a surface fire, torching likelihood and potential carbon emissions. We quantified fuel load and structure for Austrian coniferous forests using 93 sample plots across Austria. We compared Austrian fuel types with fuels collected in other regions and biomes. We found significant differences among regions and forest types. Fuel load was more dependent on region and forest type than on age class. Highest fuel load was found in Picea abies stands, lowest in Pinus nigra forests. Dead fuel loads were positively correlated with basal area, while live fuels were negatively correlated, suggesting that basal area drives accumulation of dead fuels and suppresses growth of understorey vegetation. Fuel loads in Austria are similar to published data for other temperate forests. The large variation in observed fuel loads and lack of previous studies highlight the need to further develop fuel models for mixed conifer–broadleaf forests. This pilot study underpins that consistent terminology and fuel classification are important to interpret differences between regions and forest types.

Complementary allometric model of understory tree biomass in the semi-deciduous rainforest of Cameroon

Forest understorey contains remarkable plant diversity, contributing to the heterogeneous environments for other biotic gatherings and soil supplement aggregations. Nonetheless, the biomass of the understorey vegetation is neglected because of the lack of appropriate allometric equations without which there are uncertainties in biomass estimation. This study was aimed at developing multispecies allometric equations that will be used to estimate the aboveground biomass of different compartments (trunk, crown, and leaves) of understorey trees in the semi-deciduous rainforest of Cameroon. Understorey tree diameter (1.0-10.0 cm), height, and crown diameter were measured on 1023 trees as biomass predictors. The results showed that the fit of the model improves with more predictive variables, four of which were considered in all studied compartments (trunk, crown, and leaves). Existing specific and pantropic allometries based on diameter tend to overestimate the aboveground biomass of understorey trees when compared to the allometry developed in this study. This study highlighted the importance of a specific aboveground biomass allometric equation for understorey trees. Furthermore, the multispecies allometric equation developed for understorey trees complements those recently developed for overstorey trees, thereby contributing to the total aboveground woody biomass estimation in semi-deciduous forest in the Congo Basin.

Broadleaved Trees Enhance Biodiversity of the Understorey Vegetation in Boreal Forests

Broadleaved Trees Enhance Biodiversity of the Understorey Vegetation in Boreal Forests

Restored river-floodplain connectivity promotes riparian tree maintenance and recruitment

Riparian forest loss and degradation due to river-floodplain disconnection is a global problem. Prospects for the maintenance and recruitment of riparian trees via restored flooding can be uncertain, in part due to competition from understorey vegetation and limited availability of tree propagules. In a field-based trial, we assessed the response of a keystone riparian tree to restored flooding, reduced competition and seed addition.We built diversion weirs to reconnect floodplains supporting riparian forest. Using a multiple control-intervention-reference study design with two restored flooding (intervention) sites, two naturally-engaged (reference) and two dry (control) sites, we assessed seedling recruitment of the dominant tree, Eucalyptus camphora, with and without clearance of understorey vegetation and with and without seed addition. We also assessed the growth of extant trees using dendrometers and seedfall using funnel traps at all six sites.Our weirs resulted in extensive flooding of the adjacent floodplain, while control sites remained dry. Flooding increased seed germination, seedling establishment, tree growth and seedfall. However, seed germination benefits were only realised where understorey vegetation was cleared and seed was added. Seedling establishment was also limited by dry summer conditions, except where flooding duration was longest (∼6 months cf. < 3 months).Restored flooding via river-floodplain reconnection is likely to promote the rehabilitation of riparian forests degraded by flow regulation or stream modification through benefits at multiple tree life-history stages. However, widespread tree recruitment may require complementary works that reduce competition via clearing of understorey vegetation and alleviate seed limitation by direct seeding or planting.

Stretching the Habitat Envelope: Insectivorous Bat Guilds Can Use Rubber Plantations, but Need Understorey Vegetation and Forest Buffers

Effects of land-cover change on insectivorous bat activity can be negative, neutral or positive, depending on foraging strategies of bats. In tropical agroforestry systems with high bat diversity, these effects can be complex to assess. We investigated foraging habitat use by three insectivorous bat guilds in forests and rubber plantations in the southern Western Ghats of India. Specifically, we monitored acoustic activity of bats in relation to (1) land-cover types and vegetation structure, and (2) plantation management practices. We hypothesized that activity of open-space aerial (OSA) and edge-space aerial (ESA) bat guilds would not differ; but narrow-space, flutter-detecting (NSFD) bat guild activity would be higher, in structurally heterogeneous forest habitats than monoculture rubber plantations. We found that bat activity of all guilds was highest in areas with high forest cover and lowest in rubber plantations. Higher bat activity was associated with understorey vegetation in forests and plantations, which was expected for NSFD bats, but was a surprise finding for OSA and ESA bats. Within land-cover types, open areas and edge-habitats had higher OSA and ESA activity respectively, while NSFD bats completely avoided open habitats. In terms of management practices, intensively managed rubber plantations with regular removal of understorey vegetation had the lowest bat activity for all guilds. Intensive management can undermine potential ecosystem services of insectivorous bats (e.g., insect pest-control in rubber plantations and surrounding agro-ecosystems), and magnify threats to bats from human disturbances. Low-intensity management and maintenance of forest buffers around plantations can enable persistence of insectivorous bats in tropical forest-plantation landscapes.

Variations of the Oxidative Ratio across Ecosystem Components and Seasons in a Managed Temperate Beech Forest (Leinefelde, Germany)

The oxidative ratio (OR) of organic material integrates the ratio of CO2 sequestered in biomass vs. O2 produced over longer timescales, but the temporal and spatial variability within a single ecosystem has received very limited attention. Between October 2017 and October 2019, we repeatedly sampled leaves, twigs, bark, outer stem wood, understorey vegetation and litter in a temperate beech forest close to Leinefelde (Germany) for OR measurements across a seasonal and spatial gradient. Plant component OR ranged from 1.004 ± 0.010 for fine roots to 1.089 ± 0.002 for leaves. Inter- and intra-annual differences for leaf and twig OR exist, but we found no correlation with sampling height within the canopy. Leaf OR had the highest temporal variability (minimum 1.069 ± 0.007, maximum 1.098 ± 0.002). This was expected, since leaf biomass of deciduous trees only represents the signal of the current growing season, while twig, stem and litter layer OR integrate multiple years. The sampling years 2018 and 2019 were unusually hot and dry, with low water availability in the summer, which could especially affect the August leaf OR. Total above-ground OR is dominated by the extremely stable stem OR and shows little variation (1.070 ± 0.02) throughout the two sampling years, even when facing extreme events.

Variation in fine root traits with thinning intensity in a Chinese fir plantation insights from branching order and functional groups

Thinning is a widely used practice in forest management, but the acclimation mechanisms of fine roots to forest thinning are still unclear. We examined the variations in fine root traits of different branching orders and functional groups along a thinning intensity gradient in a 26-year-old Chinese fir (Cunninghamia lanceolata) plantation. With increasing thinning intensity, the root C concentration (RCC), root N concentration (RNC), specific root area (SRA), and specific root length (SRL) of the absorptive roots (the first two orders) significantly decreased, while root abundance (root biomass and root length density) and root tissue density (RTD) significantly increased. Fifty-four percent of the variation in the absorptive root traits could be explained by the soil N concentration and the biomass and diversity of the understorey vegetation. Conversely, transport root (third- and higher-order) traits did not vary significantly among different thinning intensities. The covariation of absorptive root traits across thinning intensities regarding two dimensions was as follows: the first dimension (46% of the total variation) represented changes in root abundance and chemical traits (related to RCC, RNC), belonging to an extensive foraging strategy; the second dimension (41% of the total variation) represented variations in root morphological traits (related to RTD, SRL and SRA), which is an intensive foraging strategy (i.e., root economic spectrum). These results suggested that the absorptive roots of Chinese fir adopt two-dimensional strategies to acclimate to the altered surroundings after thinning.

Influence of fuel structure derived from terrestrial laser scanning (TLS) on wildfire severity in logged forests

ContextLogging and wildfire can reduce the height of the forest canopy and the distance to the understorey vegetation below. These conditions may increase the likelihood of high severity wildfire (canopy scorch or consumption), which may explain the greater prevalence of high severity wildfire in some recently logged or burnt forests. However, the effects of these structural characteristics on wildfire severity have not clearly been demonstrated. ObjectivesWe aimed to assess how the structure of forests affected by logging and wildfire influence the probability of high severity wildfire. MethodsWe used terrestrial laser scanning to measure the connectivity of canopy and understorey vegetation in forests at various stages of recovery after logging and wildfire (approximately 0–80 years since disturbance). These sites were subsequently burnt by mixed severity wildfire during the 2019–20 ‘Black Summer’ fire season in south-eastern Australia. We assessed how these forest structure metrics affected the probability of high severity wildfire. ResultsThe probability of high severity fire decreased as the canopy base height increased, and the distance between the canopy base and understorey increased. High severity wildfire was less likely in forests with taller understoreys and greater canopy or understorey cover, but these effects were not considered causal. Fire weather was the strongest driver of wildfire severity, which was also affected by topography. ConclusionsThese findings demonstrate a link between forest structure characteristics, that are strongly shaped by antecedent logging and fire, and fire severity. They also indicate that vertical fuel structure should be incorporated into assessments of fire risk.

Fire Regime Has a Greater Impact Than Selective Timber Harvesting on Vegetation in a Sub-Tropical Australian Eucalypt Forest

We compared selectively harvested and unharvested areas located among treatments of annual burning since 1952, triennial burning since 1973 and an area that had received no prescribed burning, but with a single wildfire in 2006 (one fire in 72 years), in a dry sclerophyll eucalypt forest, south-eastern Queensland, Australia. Historic fire regime, rather than low-intensity, selective timber harvesting (17% to 37% live tree basal area removed) had a greater impact on a range of vegetation and soil attributes. Plant taxa composition was influenced more by historic fire regime than recent harvesting; of the 25.5% of the variation in taxa composition explained, fire treatments alone accounted for 96.4% of the explained variation and harvesting alone accounted for just 4.8%. Selective harvesting of timber had a predictable influence associated with removal of tree cover and physical impacts associated with extraction of logs. In harvested areas there were increases (p &lt; 0.05) in bare-ground cover and in coarse woody debris volumes and decreases in understorey vegetation height, particularly where woody understorey was present. However, overall, the combined effects of timber harvesting and fire regime were relatively minor. These sub-tropical dry eucalypt forests appear to be resilient to the impacts of combined, but low-intensity disturbances.

Climate and Management Factors Underlying Changes in Beech Forest Herbaceous Layer Plant Communities in the Polish Eastern Carpathians

The herbaceous vegetation and forest stand characteristics in European beech forests growing in the Polish part of the Eastern Carpathians have changed over the last 40 years. This has been influenced by many factors, including land-use change, forest management and climate change. This study investigates changes in forest cover and structure and the associated changes in herbaceous layer plant communities and seeks to elucidate whether and how beech forest herbaceous layer communities have been affected by climate change. The study used information from archival and current land cover maps, semi-permanent sampling plots, forest management plans for the Forest Districts of Brzozów, Lesko and Ustrzyki Dolne and meteorological weather station data compiled for three study periods of herbaceous vegetation (1970s, 2000s, 2010s). In the study area, the regular shelterwood system was changed to an irregular shelterwood system that produces stands with a complex overstorey structure. The results revealed the important role of light availability in shaping the species composition of the herbaceous layer in semi-natural Carpathian beech forests, which was strongly related to the course of management activities. An overall decrease in the number of species during the 2010s is linked to the ageing of beech forests, increased intensity of management activities in ageing stands, competition from understorey vegetation and lower soil moisture that can be linked to climate change. Our study partially supports the existing findings that more manipulative forest management systems can play an important role in countering the current and expected effects of climate change on the forest ecosystem because of the low degree of spatial differentiation of the stand’s structure (developmental stages). Therefore, foresters managing the structure of stands should strive to create a forest structure with high variability of developmental stages on a regional scale.

Climate Change is Driving Greening Trend Whereas Tree Cover is Declining in The Western Himalaya of Pakistan

Recent studies suggest that two factors including climate change (especially precipitation) and human land use management (HLUM) are primarily driving greening trend around the world. However, studies targeting the impact of both factors on different vegetation layers (i.e. herbs, shrubs and tree layers) are lacking. This study hypothesize that precipitation relatively influence the under-storey vegetation cover more quickly, and HLUM (say afforestation/reforestation, deforestation) is more important towards top-storey layer. To investigate this, 13 randomly selected permanent stations in the wild natural west Himalayan coniferous forests of Sudhan Gali, Pakistan were explored from 2000-2016 to collect vegetation health data by two ways; Ground data (i.e. cover estimation of three layers), and indirect remote sensing (RS) data (i.e. MODIS NDVI/EVI 16-days-time series). Deforestation and grazing pressure as HLUM were measured by using some new and more intuitive mathematical operations, and climatic data (1979-2018) was also collected and compared. The results depicted that there is an overall greening trend in the study area coupled with significant increase in average herbaceous cover, NDVI, EVI and precipitation during 2009-2016. Contrastingly, high elevation microhabitats are facing maximum cover loss (especially top-storey), and have negative seasonal Sen’s slope values of the studied time series. The distance-based Redundancy Analysis (db-RDA) results confirmed that variations in RS-data were significantly explained by precipitation and herbaceous cover only. This study concluded that overall greening trend was driven by precipitation, and not remarkably by HLUM by supporting under-storey vegetation, whereas, top-storey tree layer is still declining, and need immediate attention.

Interplay of above‐ and belowground resource limitations: a competition–facilitation shift maintains species coexistence

Forest ecosystems are commonly characterised by a hierarchy of resources. During a disturbance of a forest community, increased light availability in the understorey can support competitive interactions at the expense of facilitation. This may overwhelm the role of belowground resource heterogeneity in maintaining species coexistence and so result in biotic homogenisation of a site. We re‐surveyed species composition while estimating interspecific interactions along a microtopographic (moisture) gradient of a temperate swamp forest after increasing the availability of light into the undergrowth. We measured temporal changes in species diversity, compositional dissimilarity measures and functional traits, while belowground resource heterogeneity remained unchanged over time. To explain observed changes in terms of prevailing interspecific interactions, we evaluated temporal changes in the competition–facilitation balance. The productivity of understorey vegetation increased strongly over the five years of the study. This was accompanied by an increase in species diversity and the maintenance of compositional dissimilarity. The relative importance of competitive and facilitative interactions along the microtopographic gradient did not change over time. Rather than an overall biotic homogenisation of a site, we observed a spread of resource acquisitive species within the resource‐rich sites and of stress‐tolerant species within the resource‐limited sites. We have shown that the temporary increase in productivity did not mitigate the effects of belowground resource heterogeneity on plant species turnover, which is likely maintained by contrasting interspecific interactions prevalent in different parts of the resource gradient. This suggests contrasting community assembly processes maintain diversity and productivity even in a local community.

Contrasting responses of saproxylic beetles and plants to non-native tree invasion reveal feedback mechanisms between trophic levels

Invasive, alien trees threaten native biodiversity, but detailed information about the patterns and mechanisms of diversity loss remain unknown. We explored the impact of an invasive tree on vascular plants and saproxylic beetles. We compared their species richness, community composition, and selected biological characteristics between stands of invasive black locust (Robinia pseudoacacia), a nitrogen-fixing clonal tree, and native oak-dominated, broadleaf forests in the SE Czech Republic and W Slovakia.Compared to native forests, R. pseudoacia stands were characterised by low canopy cover, high light and soil nutrient availability, and similar deadwood volumes. R. pseudoacacia had species-poor, dense understorey vegetation composed of tall, nitrophilous herbs. Saproxylic beetles, on the other hand, were similarly diverse and abundant in both R. pseudoacacia stands and native forests. Their communities were mainly shaped by forest structure, as overall beetle diversity and guilds exploiting more decayed wood benefited from the open canopies and high deadwood volumes. Richness and abundance of threatened plants and beetles requiring fresh wood, together with total richness of threatened beetles were, however, substantially lower in R. pseudoacacia stands.The adverse impacts of R. pseudoacacia on plants partly contrasted with its much less pronounced effects on saproxylic beetles. In intensively exploited landscapes, R. pseudoacacia stands can offer refuge to saproxylic beetles. However their lower diversity and lower incidence of threatened species show that R. pseudoacacia contributes to homogenization and impoverishment of plant and insect assemblages. Robinia stands thus should be eliminated from protected areas and minimalised wherever biodiversity conservation is of concern.