Small variations in climate and soil conditions may have greater influence on multitaxon species occurrences than past and present human activities in temperate mountain forests

Aim

Human activity is known to greatly influence species occurrences. In forest ecosystems, biodiversity is often believed to be influenced by two habitat characteristics: (1) forest continuity, related to a minimum length of time in a wooded state since a threshold date; and (2) stand maturity, related to the availability of late‐developmental‐forest attributes. In a context of ongoing global biodiversity loss, qualifying the effect of past and present human activity on forest ecosystems while taking into account variations in abiotic factors is of primary importance for conservation.

Location

Temperate mountain forests in the Northern Alps.

Method

Based upon a sampling design crossing forest continuity (ancient vs. Recent) and stand maturity (mature vs. overmature), and while controlling for the effect of two major environmental factors, soil and climate, we explored the individual response of saproxylic beetle, springtail, herbaceous plant and epiphytic macrolichen species to past and present human activity.

Results

Forest continuity influenced the occurrence of relatively few species, indicating that past land use had almost no legacy effect on the species occurring in the study forests today. In contrast, stand maturity had an overall positive effect on species occurrences. However, our results showed that species occurrences were more obviously influenced by abiotic conditions. Indeed, beyond the effect of continuity and maturity factors, the probability of presence of numerous species was best explained by climate and soil.

Main conclusions

Overall, we show that species occurrence was more influenced by stand maturity than by forest continuity, but also that site‐specific characteristics were of great importance in explaining the probability of presence for numerous species. In the ecological context of alpine forests, these findings emphasize the need to better control for climatic and edaphic conditions in order to (1) improve accuracy in predicting species occurrence and (2) better design areas of conservation interest.

     

Trait variation in juvenile plants from the soil seed bank of temperate forests in relation to macro- and microclimate

Aim

The soil seed bank is a key component of the biodiversity of plant communities, but various aspects of its functioning in temperate forest ecosystems are still unknown. We here adopted a trait-based approach to investigate the effects of macro- and microclimatic gradients on the juvenile plant communities from the realized seed bank of two types of European temperate forest.

Location

Oak-dominated forests in Italy and Belgium.

Methods

We analysed the variation of key functional traits (plant height, leaf area, leaf dry weight, specific leaf area and leaf number) of juvenile plants from the realised soil seed bank in relation to elevation (from 0 to 800 m a.s.l.), forest type (thinned and unthinned forest) and distance to the forest edge. We translocated soil samples from the forest core to the edge (and vice versa) and from high- to low-elevation forests to test the effects of edge and warming respectively.

Results

Taller communities developed at the forest edge due to higher light availability and warmer temperatures. The translocation from the core to the edge did not significantly modify mean trait values. Instead, the shadier and cooler microclimate of the forest core reduced the mean leaf area, mean dry weight, height and leaf number in the communities realised from the edge soil. The translocation from high- to lowland forests led to increased values for all traits (except specific leaf area). Edge vs core trait variation was more driven by intraspecific variability, whereas the translocation from high- to low-elevation forests caused trait changes mostly due to species turnover.

Conclusions

Global warming might result in a functional shift of the understorey due to both an early filtering effect on the seedlings from soil seed banks and their adaptive trait adjustments to temperature increase. Furthermore, our study underpins the importance of edge vs core microclimate in driving the functional composition of the realised soil seed bank.     

Bioindicators of edge effects within Atlantic Forest remnants: Conservation implications in a threatened biodiversity hotspot

Aim

Deforestation of the Atlantic Forest of eastern Paraguay has been recent but extensive, resulting in a fragmented landscape highly influenced by forest edges. We examined edge effects on multiple dimensions of small mammalian diversity.

Location

Forest fragments of eastern Paraguayan Atlantic Forest.

Methods

We trapped small mammal species at different distances from the forest edge (DTE) in reserves and estimated multiple dimensions of diversity per site. Similarity analysis identified species clusters that best described the patterns of diversity across reserves. Multivariate ordination and linear mixed models were used to determine the influence of DTE on various dimensions of small mammal diversity.

Results

There was an increase in richness and abundance along a DTE gradient, and remnants with higher edge:area ratios showed higher richness and abundance, independent of remnant size. Species at edges were generalists, open-habitat species or exotic species (spillover effect). We found higher phylogenetic diversity and functional richness and divergence towards forest edges. Spillover of non-forest and invasive species best explained richness, generalist forest species best explained total abundance, abundance of Hylaeamys megacephalus best explained diversity and evenness metrics and the presence of Marmosa paraguayana best explained various phylogenetic diversity models. None of the models that included megafauna or social factors were shown to be important in explaining patterns as a function of DTE.

Main Conclusions

We found strong support for a spillover effect and mixed support for complementary resource use and enhanced habitat resources associated with ecotones. Generalists characterized edge assemblages but not all generalists were equivalent. Edges showed more phylogenetically and functionally distinct assemblages than the interior of remnants. There was a conservation of functional diversity; however, open-habitat species, habitat generalists and exotic species boosted diversity near forest edges. Mechanisms governing diversity along forest edges are complex; disentangling those mechanisms necessitates the use of multiple dimensions of diversity.     

Identifying plant traits associated with topographic contrasts in a rugged and diverse region (Klamath‐Siskiyou Mts,OR, USA)

Rugged topography affects species distributions and community composition by creating contrasting mesic (cool, moist) and xeric (warm, dry) microclimates on adjacent slopes. This microclimatic heterogeneity is thought to have contributed to species survival during past climate fluctuations. Within a rugged and botanically rich region, we asked what functional, distributional, and/or biogeographic traits distinguished the species significantly associated with xeric or mesic microclimates. For each of 236 species in 4773 plots in the Klamath‐Siskiyou Mountains, we tested for significant associations with mesic or xeric topographic microclimates inferred from high‐resolution topographic variables. For the subset of species showing significant associations, we then compared their functional traits, biogeographic origins, and macroclimatic attributes to those of other species. We also tested the dependence of topographic associations on elevation, canopy cover, and soil type. Many species in the region (40%) showed significant tendencies to be found only in either mesic or xeric topography. ‘Mesic’ species tended to be of northern biogeographic origin and to have geographic ranges with higher mean precipitation; ‘xeric’ species had the opposite attributes. Species occurred more often in mesic microclimates when they occurred on low‐nutrient serpentine soils, and were more often found in xeric microclimates at high elevations. Functional traits such as specific leaf area were not significant predictors of species association with topographic microclimate. Biogeographic origins and the mean precipitation (rather than temperature) of species geographic ranges are the best indicators of species that are found in cool/moist northerly or hot/dry southerly microclimates.     

Topographic microclimates drive microhabitat associations at the range margin of a butterfly

The habitat associations of individuals underpin the dynamics of species distributions. Broad‐scale gradients in climate can alter habitat associations across species’ geographic ranges, but topographic heterogeneity creates local microclimates which could generate variation in habitat use at finer spatial scales. We examined the selection of microhabitats for egg‐laying by populations of a thermally‐constrained butterfly, the skipper Hesperia comma, across 16 sites with different regional temperatures and topographic microclimates. Using models of thermal microclimate, we examined how the association between eggs and warm bare ground microhabitats varied with ambient temperature, and predicted bare ground associations in 287 existing H. comma populations, to investigate the relative impacts of regional temperatures and topographic microclimates on microhabitat use. Eggs were most strongly associated with bare ground in relatively cool sites, indicating climate‐driven changes in microhabitat use. The majority of temperature variation between study sites was attributable to topographic microclimates rather than regional temperature differences, such that changes in microhabitat associations occurred principally between north‐ and south‐facing slopes within the same region. Predicted microhabitat associations across the UK distribution of H. comma showed that, due to the large temperature differences generated by topography, most of the between‐population variation in microhabitat use occurs locally within 5 km grid squares, with a smaller proportion occurring at a regional level between 5 km squares. Our findings show how microclimatic variation generated by topography alters the habitat associations of populations at fine spatial scales, suggesting that microclimate‐driven changes in habitat suitability could shape species’ distribution dynamics and their responses to environmental change.     

Micro‐climate determines oviposition site selection and abundance in the butterfly Pyrgus armoricanus at its northern range margin

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Body size and microclimate use in Neotropical granivorous ants

The stability of tropical microclimates has left microclimate use by tropical species little unexplored. At La Selva Costa Rica, I related foraging activity at seed baits to humidity in two forests types. I recorded 38 and 35 ant species at seed baits in closed and open canopy forest. The microclimate 5 cm above the forest floor in the younger, Open Forest was warmer, drier, more variable, and more sensitive to current weather than in the older Closed Forest. Ant species within both forests foraged at different Vapor Pressure Deficits (kPa), a measure of the drying power of the air. VPD use was not confounded with diel activity patterns. Body size explained 46% of the variance in mean VPD use among ant species. Small ant species tended to forage in moist microclimates; large species tended to be microclimate generalists. Larger species were also more active in the drier Open Forest. Foraging activity by these assemblages varies 4-fold, and peaks close to the mean VPD for each habitat. The behavior of these assemblages suggest that 1) small ant species at La Selva potentially compete with the entire range of ant body sizes, whereas large ants forage when and where small ants are inactive; and 2) seeds dispersed to the forest floor at dawn will be consumed or further dispersed by a larger suite of ants species than those falling in the heat of the tropical afternoon.     

Predicting effects of large‐scale reforestation on native and exotic birds

Aim

Ecological restoration is critical for recovering biodiversity and ecosystem services, yet designing interventions to achieve particular outcomes remains fraught with challenges. In the extensive regions where non‐native species are firmly established, it is unlikely that historical conditions can be fully reinstated. To what degree, and how rapidly, can human‐dominated areas be shifted via restoration into regimes that benefit target species, communities or processes?

Location

We explore this question in a >20‐year‐old reforestation effort underway at Hakalau Forest National Wildlife Refuge in montane Hawaii. This large‐scale planting of Acacia koa trees is designed to secure populations of globally threatened bird species by transitioning the site rapidly from pasture to native forest.

Methods

We surveyed all forest birds in multiple corridors of young planted trees, remnant corridors of mature trees along gulches and at sites within mature forest. Using a Bayesian hierarchical approach, we identified which factors (distance from forest, habitat type and surrounding tree cover) had the most important influence on native and exotic bird abundance in the reforestation area.

Results

We found that 90% of native and exotic bird species responded quickly, occupying corridors of native trees approximately a decade after planting. However, native and exotic forest birds responded to markedly different characteristics of the reforested area. Native bird abundance was strongly predicted by proximity to mature forest and remnant corridors; conversely, exotic bird abundance was best predicted by overall tree cover throughout the area reforested.

Main conclusions

Our results demonstrate that large‐scale tree planting in corridors adjacent to mature forest can catalyse rapid recovery (both increased abundance and expanded distribution) of forest birds and that it is possible to design reforestation to benefit native species in novel ecosystems.

     

Livestock grazing and forest structure regulate the assembly of ecological clusters within plant networks in eastern Australia

Questions

How do changes in grazing intensity by different herbivores and differences in forest structure affect the assembly of ecological clusters within plant ecological networks in dryland plant communities?

Location

Eastern Australia across an area of 0.4 million km².

Methods

We used correlation network analysis and structural equation modelling to examine how changes in grazing intensity, by different herbivores, and differences in forest structure (tree canopy cover, basal area and density) and soil fertility influenced the assembly of ecological clusters of plant communities (i.e. relative abundance of ecological clusters formed by co‐occurring plant species within an ecological network) in three forested communities from eastern Australia.

Results

Livestock grazing and forest structure regulated the relative abundance of ecological clusters within plant networks, but their effects on these plant assemblies were highly dependent on the ecological cluster and forest community type, with no single winner or loser across forest types, conditions or grazing intensities. Thus, the relative abundance of some ecological clusters increased under grazing while others declined, a response that was maintained across different forest structures. The relative importance of grazing, forest structure and soil fertility varied across forest community type. The two eucalypt communities exhibited mixed effects of grazing and forest structure (Eucalyptus largiflorens ) or forest structure only (Eucalyptus camaldulensis ). In the third (Callitris glaucophylla ) community, grazing played a larger role in controlling the plant community assembly. Soil fertility (soil C and P) effects were of a similar magnitude to grazing and forest structure, but the effects differed among clusters.

Conclusions

Livestock grazing and forest structure regulated the relative abundance of ecological clusters within networks of plant communities in forests in eastern Australia. Our study uses a novel approach of ecological clusters to show that differences in grazing and forest structure will always disadvantage some plant ecological clusters. Furthermore, changes in one cluster will ultimately affect other clusters. Any changes in management therefore will have varied effects on different ecological plant clusters.

     

Large-Scale Removal of Invasive Honeysuckle Decreases Mosquito and Avian Host Abundance

Invasive species rank second only to habitat destruction as a threat to native biodiversity. One consequence of biological invasions is altered risk of exposure to infectious diseases in human and animal populations. The distribution and prevalence of mosquito-borne diseases depend on the complex interactions between the vector, the pathogen, and the human or wildlife reservoir host. These interactions are highly susceptible to disturbance by invasive species, including terrestrial plants. We conducted a 2-year field experiment using a Before–After/Control–Impact design to examine how removal of invasive Amur honeysuckle (Lonicera maackii) in a forest fragment embedded within a residential neighborhood affects the abundance of mosquitoes, including two of the most important vectors of West Nile virus, Culex pipiens and Cx. restuans. We also assessed any potential changes in avian communities and local microclimate associated with Amur honeysuckle removal. We found that (1) removal of Amur honeysuckle reduces the abundance of both vector and non-vector mosquito species that commonly feed on human hosts, (2) the abundance and composition of avian hosts is altered by honeysuckle removal, and (3) areas invaded with honeysuckle support local microclimates that are favorable to mosquito survival. Collectively, our investigations demonstrate the role of a highly invasive understory shrub in determining the abundance and distribution of mosquitoes and suggest potential mechanisms underlying this pattern. Our results also give rise to additional questions regarding the general impact of invasive plants on vector-borne diseases and the spatial scale at which removal of invasive plants may be utilized to effect disease control.     

Hiding from the climate: Characterizing microrefugia for boreal forest understory species

Climate warming is likely to shift the range margins of species poleward, but fine‐scale temperature differences near the ground (microclimates) may modify these range shifts. For example, cold‐adapted species may survive in microrefugia when the climate gets warmer. However, it is still largely unknown to what extent cold microclimates govern the local persistence of populations at their warm range margin. We located 99 microrefugia, defined as sites with edge populations of 12 widespread boreal forest understory species (vascular plants, mosses, liverworts and lichens) in an area of ca. 24,000 km² along the species' southern range margin in central Sweden. Within each population, a logger measured temperature eight times per day during one full year. Using univariate and multivariate analyses, we examined the differences of the populations' microclimates with the mean and range of microclimates in the landscape, and identified the typical climate, vegetation and topographic features of these habitats. Comparison sites were drawn from another logger data set (n = 110), and from high‐resolution microclimate maps. The microrefugia were mainly places characterized by lower summer and autumn maximum temperatures, late snow melt dates and high climate stability. Microrefugia also had higher forest basal area and lower solar radiation in spring and autumn than the landscape average. Although there were common trends across northern species in how microrefugia differed from the landscape average, there were also interspecific differences and some species contributed more than others to the overall results. Our findings provide biologically meaningful criteria to locate and spatially predict potential climate microrefugia in the boreal forest. This opens up the opportunity to protect valuable sites, and adapt forest management, for example, by keeping old‐growth forests at topographically shaded sites. These measures may help to mitigate the loss of genetic and species diversity caused by rear‐edge contractions in a warmer climate.     

Climate change drives substantial decline of understorey species richness and abundance in Norway spruce forests during 32 years of vegetation monitoring

Questions

Observations in permanent forest vegetation plots in Norway and elsewhere indicate that complex changes have taken place over the period 1988–2020. These observations are summarised in the “climate-induced understorey change (CIUC)” hypothesis, i.e. that the understorey vegetation of old-growth boreal forests in Norway undergoes significant long-term changes and that these changes are consistent with the ongoing climate change as an important driver. Seven testable predictions were derived from the CIUC hypothesis.

Location

Norway.

Methods

Vegetation has been monitored in a total of 458 permanently marked plots, each 1 m², in nine old-growth forest sites dominated by Picea abies at intervals of 5–8 years over the 32-year study period. For each of the 52 combinations of site and year, we obtained response variables for the abundance of single species, abundance and species density of taxonomic–ecological species groups and two size classes of cryptogams, and site species richness. All of these variables were subjected to linear regression modelling with site and year as predictors.

Results

Mean annual temperature, growing-season length and the number of days with precipitation were higher in the study period than in the preceding ca. 30-year period, resulting in increasingly favourable conditions for bryophyte growth. Site species richness decreased by 13% over the 32-year study period. On average, group abundance of vascular plants decreased by 24% (decrease in forbs: 38%). Patterns of group abundance change differed among cryptogam groups: although peat-moss abundance increased by 39%, the abundance of mosses, hepatics and lichens decreased by 13%, 49% and 67%, respectively. Group abundance of small cryptogams decreased by 61%, whereas a 13% increase was found for large cryptogams. Of 61 single species tested for abundance change, a significant decrease was found for 43 species, whereas a significant increase was found only for 6 species.

Conclusions

The major patterns of change in species richness, group species density and group abundance observed over the 32-year study period accord with most predictions from the CIUC hypothesis and are interpreted as direct and indirect responses to climate change, partly mediated through changes in the population dynamics of microtine rodents. The more favourable climate for bryophyte growth explains the observed increase for a few large bryophyte species, whereas the decrease observed for small mosses and hepatics is interpreted as an indirect amensalistic effect, brought about by shading and burial in mats of larger species and accelerated by reduced fine-scale disturbance by microtine rodents. Indirect effects of a thicker moss mat most likely drive the vascular plant decline although long-term effects of tree-stand dynamics and former logging cannot be completely ruled out. Our results suggest that the ongoing climate change has extensive, cascading effects on boreal forest ecosystems. The importance of long time-series of permanent vegetation plots for detecting and understanding the effects of climate change on boreal forests is emphasised.     

Enough space in a warmer world? Microhabitat diversity and small‐scale distribution of alpine plants on mountain summits

Aim

Global warming is predicted to shift distributions of mountain species upwards, driven by a release from climatic restrictions at their upper distribution limit and increased biotic pressure at their lower distribution limit. In alpine ecosystems, which are characterized by large microclimatic diversity and sparse vegetation cover, the relative importance of abiotic and biotic drivers for species distribution is poorly understood. To disentangle abiotic and biotic mechanisms affecting distributions of alpine species, we investigated how alpine plant species with differing elevational ranges and frequency trends over the past century differ in their microhabitat distribution, and how they respond to neighbouring vegetation.

Location

A total of 11 summits (2635—3410 m a.s.l.) in SE‐Switzerland.

Methods

We quantified the microscale abundance of 12 species in relation to biogeographic (frequency trend, i.e., change in occurrences over the past century, and elevational range on summits) and local microhabitat characteristics (temperature, substrate type). We assessed species size traits in relation to neighbouring vegetation characteristics to investigate possible neighbour interactions.

Results

Species with increasing frequency on summits over the past century were most abundant on scree and warmer slopes. Species with negative or stable frequency trends on summits were more abundant on organic soil and colder slopes. The preferred microhabitats of the latter were rarest overall, decreased with increasing elevation, and had the most competitive neighbours. Size of one high‐alpine specialist, Ranunculus glacialis was negatively related to cover of neighbouring vegetation, whereas other species showed no response to neighbours.

Main conclusions

Long‐term frequency trends of species correlate with their microhabitat association. Species with most negative frequency trends show preferences for the rarest microhabitat conditions, where they likely experience higher competitive pressure in a warming climate. This finding emphasizes the importance of characterizing microhabitat associations and microclimatic diversity to assess present and future distributions of alpine plant species.

     

Are the assemblages of tree pollination modes being recovered by tropical forest restoration?

Questions

Do the assemblages of pollination modes in restored (tree plantings) and secondary (naturally regenerated) forests change in comparison to primary forests, and how do these assemblages relate to species turnover at regional scale?

Location

Southeast region of Brazil.

Methods

We classified tree species found in a total of 40 forest sites (18 primary, 11 restored, 11 secondary) according to pollination mode, based on the literature. We calculated and compared functional dissimilarity distances, amounts of species and accumulated abundance of pollination modes, and functional indices of richness and evenness between forest types.

Results

Functional dissimilarity distances were much smaller than species dissimilarity distances within forest types (mean <20%, >80%, respectively), indicating a small variation in pollination modes between sites. Functional indices of richness and evenness did not differ between forest types. However, significant changes were found in the species and abundance proportions of several pollination modes. Primary forests were characterized by the predominance of generalized insect‐pollinated species, followed by secondary proportions of bee, wind and moth pollination; other pollination modes were underrepresented. In restored forests, reductions were found in generalized insect, moth, wind, fly, pollen‐consuming insect and very‐small insect pollination, whereas the species pollinated by bees and bats more than doubled. Smaller changes were found among secondary forests, including reductions in moth, fly and fig‐wasp pollination, whereas there were incremental changes in bee, beetle, big animal and small insect pollination.

Conclusions

Our results indicate a rather stable assemblage of pollination modes and also high ecological redundancy among trees regardless of the species replacement at the regional scale. Major changes among restored forests are probably in response to larger disturbance effects and/or restoration practices conducted in these sites. In contrast, smaller changes among secondary forests could be in response to smaller disturbance effects and natural selection processes, and also seem to suggest that highly resilient degraded areas are more likely to recuperate their functional diversity through natural regeneration alone. In both cases, however, efforts to recover such patterns should be encouraged to avoid possible negative effects in plant–pollinator interactions.     

Vegetation cover of Brazil in the last 21 ka: New insights into the Amazonian refugia and Pleistocenic arc hypotheses

Aim

The two main hypotheses about the Neotropical palaeovegetation, namely that of Amazonian refugia by Haffer and of the Pleistocene arc by Prado and Gibbs, are still constantly debated. We offer new insights on this debate using ecological niche modelling with combined climate–soil predictors to test both hypotheses, reconstruct the palaeovegetation of the Last Glacial Maximum (LGM; 21 ka) and Mid‐Holocene (Mid‐H; 6 ka) and indicate the configuration of refugia areas.

Location

Brazil.

Time period

Last 21 ka.

Major taxa studied

Biomes.

Methods

We modelled the environmental space of the 10 most representative biomes with the RandomForest classifier, using climate predictors from three atmospheric general circulation models (CCSM4, MPI‐ESM‐P and MIROC‐ESM) and soil predictors, the same for the different situations. Based on the consensus among the models, we reconstructed the palaeovegetation cover for LGM and Mid‐H and used fossil pollen sites to validate the reconstructions in a direct comparison.

Results

The climate in the past was cooler and wetter throughout most of the territory. The Amazon basin region was the most affected by climate change in the last 21 ka, with equatorial rain forest retracting to refugia areas, while the tropical rain forest (with climatic preferences similar to the Atlantic forest) expanded in the basin. In southern Brazil, the mixed forest (Araucaria forest) shifted to lower latitudes, while the grasslands expanded. In most biomes, the greatest changes occurred in the ecotonal zones, supported by pollen fossils.

Main conclusions

With regard to Haffer's hypothesis, the forests of the Amazonian lowlands retreated to refugia areas, while the colder and wetter climate of the basin created a favourable niche for another type of forest, instead of savanna. The advance of dry vegetation was restricted to ecotonal conditions, preventing the formation of a continuous Pleistocene arc, predicted by Prado and Gibbs's hypothesis.     

Fragmentation Impairs the Microclimate Buffering Effect of Tropical Forests

Background

Tropical forest species are among the most sensitive to changing climatic conditions, and the forest they inhabit helps to buffer their microclimate from the variable climatic conditions outside the forest. However, habitat fragmentation and edge effects exposes vegetation to outside microclimatic conditions, thereby reducing the ability of the forest to buffer climatic variation. In this paper, we ask what proportion of forest in a fragmented ecosystem is impacted by altered microclimate conditions driven by edge effects, and extrapolate these results to the whole Atlantic Forest biome, one of the most disturbed biodiversity hotspots. To address these questions, we collected above and below ground temperature for a full year using temperature sensors placed in forest fragments of different sizes, and at different distances from the forest edge.

Principal Findings

In the Atlantic forests of Brazil, we found that the buffering effect of forests reduced maximum outside temperatures by one third or more at ground level within a forest, with the buffering effect being stronger below-ground than one metre above-ground. The temperature buffering effect of forests was, however, reduced near forest edges with the edge effect extending up to 20 m inside the forest. The heavily fragmented nature of the Brazilian Atlantic forest means that 12% of the remaining biome experiences altered microclimate conditions.

Conclusions

Our results add further information about the extent of edge effects in the Atlantic Forest, and we suggest that maintaining a low perimeter-to-area ratio may be a judicious method for minimizing the amount of forest area that experiences altered microclimatic conditions in this ecosystem.     

Successional shifts in tree demographic strategies in wet and dry Neotropical forests

Aim

Tropical forest succession and associated changes in community composition are driven by species demographic rates, but how demographic strategies shift during succession remains unclear. Our goal was to identify generalities in demographic trade-offs and successional shifts in demographic strategies across Neotropical forests that cover a large rainfall gradient and to test whether the current conceptual model of tropical forest succession applies to wet and dry forests.

Location

Mexico and Central America.

Time period

1985–2018.

Major taxa studied

Trees.

Methods

We used repeated forest inventory data from two wet and two dry forests to quantify demographic rates of 781 tree species. For each forest, we explored the main demographic trade-offs and assigned tree species to five demographic groups by performing a weighted principal components analysis to account for differences in sample size. We aggregated the basal area and abundance across demographic groups to identify successional shifts in demographic strategies over the entire successional gradient from very young (<5 years) to old-growth forests.

Results

Across all forests, we found two demographic trade-offs, namely the growth–survival trade-off and the stature–recruitment trade-off, enabling the data-driven assignment of species to five demographic strategies. Fast species dominated early in succession and were then replaced by long-lived pioneers in three forests. Intermediate and slow species increased in basal area over succession in all forests, but, in contrast to the current conceptual model, long-lived pioneers continued to dominate until the old-growth stage in all forests. The basal area of short-lived breeders was low across all successional stages.

Main conclusions

The current conceptual model of Neotropical forest succession should be revised to incorporate the dominance of long-lived pioneers in late-successional and old-growth forests. Moreover, the definition of consistent demographic strategies that show clear dominance shifts across succession substantially improves the mechanistic understanding and predictability of Neotropical forest succession.     

The complexity of forest borders determines the understorey vegetation

Questions

What are the most important drivers of plant species richness (gamma‐diversity) and species turnover (beta‐diversity) in the field layer of a forest edge? Does the tree and shrub species richness structure and complexity affect the richness of forest and grassland specialist species?

Location

Southeast Sweden.

Methods

We sampled 50 forest edges with different levels of structural complexity in agricultural landscapes. In each border we recorded trees, shrubs and herb layer species in a 50‐m transect parallel with the forest. We investigated species composition and species turnover in relation to the proportions of gaps in the border and the diversity of trees and shrubs.

Results

Total plant species richness in the field layer was mainly explained by the proportion of gaps to areas with full canopy cover and tree diversity. Increasing number of gaps promoted higher diversity of grassland specialist species within the field layer, resulting in open forest borders with the highest overall species richness. Gaps did however have a negative impact on forest species richness. Conversely, increasing forest species richness was positively related to tree diversity, but the number of grassland specialist species was negatively affected by tree diversity.

Conclusions

Managing forest borders, and therefore increasing the area of semi‐open habitats in fragmented agricultural landscapes, provides future opportunities to create a network of suitable habitats for both grassland and deciduous forest specialist species. Such measures therefore have the potential to increase functional connectivity and support dispersal of species in homogeneous forest/agricultural landscapes.     

Long-term field data and climate-habitat models show that orangutan persistence depends on effective forest management and greenhouse gas mitigation

Background

Southeast Asian deforestation rates are among the world’s highest and threaten to drive many forest-dependent species to extinction. Climate change is expected to interact with deforestation to amplify this risk. Here we examine whether regional incentives for sustainable forest management will be effective in improving threatened mammal conservation, in isolation and when combined with global climate change mitigation.

Methodology/Principal Findings

Using a long time-series of orangutan nest counts for Sabah (2000–10), Malaysian Borneo, we evaluated the effect of sustainable forest management and climate change scenarios, and their interaction, on orangutan spatial abundance patterns. By linking dynamic land-cover and downscaled global climate model projections, we determine the relative influence of these factors on orangutan spatial abundance and use the resulting statistical models to identify habitat crucial for their long-term conservation. We show that land-cover change the degradation of primary forest had the greatest influence on orangutan population size. Anticipated climate change was predicted to cause reductions in abundance in currently occupied populations due to decreased habitat suitability, but also to promote population growth in western Sabah by increasing the suitability of presently unoccupied regions.

Conclusions/Significance

We find strong quantitative support for the Sabah government’s proposal to implement sustainable forest management in all its forest reserves during the current decade; failure to do so could result in a 40 to 80 per cent regional decline in orangutan abundance by 2100. The Sabah orangutan is just one (albeit iconic) example of a forest-dependent species that stands to benefit from sustainable forest management, which promotes conservation of existing forests.     

Land use changes could modify future negative effects of climate change on old‐growth forest indicator species

Aim

Climate change is expected to have major impacts on terrestrial biodiversity at all ecosystem levels, including reductions in species‐level distribution and abundance. We aim to test the extent to which land use management, such as setting‐aside forest from production, could reduce climate‐induced biodiversity impacts for specialist species over large geographical gradients.

Location

Sweden.

Methods

We applied ensembles of species distribution models based on citizen science data for six species of red‐listed old‐forest indicator fungi confined to spruce dead wood. We tested the effect on species habitat suitabilities of alternative climate change scenarios and varying amounts of forest set‐aside from production over the coming century.

Results

With 3.6% of forest area set‐aside from production and assuming no climate change, overall habitat suitabilities for all six species were projected to increase in response to maturing spruce in set‐aside forest. However, overall habitat suitabilities for all six species were projected to decline under climate change scenario RCP4.5 (intermediate–low emissions), with even greater declines projected under RCP 8.5 (high emissions). Increasing the amount of forest set‐aside to 16% resulted in significant increases in overall habitat suitability, with one species showing an increase. A further increase to 32% forest set‐aside resulted in considerably more positive trends, with three of six species increasing.

Main conclusions

There is interspecific variation in the importance of future macroclimate and resource availability on species occurrence. However, large‐scale conservation measures, such as increasing resource availability through setting aside forest from production, could reduce future negative effects from climate change, and early investment in conservation is likely to reduce the future negative impacts of climate change on specialist species.