Comparing the recovery of richness,structure, and biomass in naturally regrowing and planted reforestation

The clearing of natural vegetation for agriculture has reduced the capacity of natural systems to provide ecosystem functions. Ecological restoration can restore desirable ecosystem functions, such as creating habitat for animal conservation and carbon sequestration as woody biomass. In order to maintain these beneficial ecosystem functions, restoration projects need to mature into self‐perpetuating communities. Here we compared the ecological attributes of two types of restoration, “active” tree plantings with “passive” natural forest regeneration (“natural regrowth”) to existing remnant vegetation in a cleared agricultural landscape. Specifically, we measured differences between forest categories in factors that may predict future restoration failure or ecosystem collapse: aboveground plant biomass and biomass accrual over time (for regrowing stands), plant density and size class distributions, and diversity of functional groups based on seed dispersal and growth strategy traits. We found that natural regrowth and planted forests were similar in many ecological characteristics, including biomass accrual. Despite this, planted stands contained fewer tree recruit and shrub individuals, which may be due to limited recruitment in plantings. If this continues, these forests may be at risk of collapsing into nonforest states after mature trees senesce. Lower shrub density and richness of mid‐story trees may lead to lower structural complexity in planting plots, and alongside lower richness of fleshy‐fruited plant species may reduce animal resources and animal use of the restored stand. In our study region, natural regrowth may result in restored woodland communities with greater conservation and carbon mitigation value.     

Pantropical geography of lightning‐caused disturbance and its implications for tropical forests

Lightning is a major agent of disturbance, but its ecological effects in the tropics are unquantified. Here we used ground and satellite sensors to quantify the geography of lightning strikes in terrestrial tropical ecosystems, and to evaluate whether spatial variation in lightning frequency is associated with variation in tropical forest structure and dynamics. Between 2013 and 2018, tropical terrestrial ecosystems received an average of 100.4 million lightning strikes per year, and the frequency of strikes was spatially autocorrelated at local‐to‐continental scales. Lightning strikes were more frequent in forests, savannas, and urban areas than in grasslands, shrublands, and croplands. Higher lightning frequency was positively associated with woody biomass turnover and negatively associated with aboveground biomass and the density of large trees (trees/ha) in forests across Africa, Asia, and the Americas. Extrapolating from the only tropical forest study that comprehensively assessed tree damage and mortality from lightning strikes, we estimate that lightning directly damages c. 832 million trees in tropical forests annually, of which c. 194 million die. The similarly high lightning frequency in tropical savannas suggests that lightning also influences savanna tree mortality rates and ecosystem processes. These patterns indicate that lightning‐caused disturbance plays a major and largely unappreciated role in pantropical ecosystem dynamics and global carbon cycling.     

Effects of forest fragmentation on species richness and composition of ground beetles (Coleoptera: Carabidae and Brachinidae) in urban landscapes

To clarify the effects of forest fragmentation in urban landscapes on the abundance, species richness, dominance, and species composition of ground beetles (Coleoptera: Carabidae and Brachinidae), we compared the beetles collected in 12 pitfall traps from April to July and from September to November between three continuous suburban forests and eight isolated urban forests (0.06–1.02 ha), most of which were in the precincts of shrines and temples in Hanshin District, Honshu, Japan. A total of 28 species and 4178 individuals of ground beetles were collected. Segregation of urban forests from continuous suburban forests has changed the species composition and resulted in the loss of some large‐sized forest species and the addition of some non‐forest species. Simpson's index of dominance (λ) also increased in the urban forests. The richness of forest species markedly decreased with the reduction in forest area but not with the distance from continuous forests, although the species richness of non‐forest species did not change with them. Also, species composition changed only with forest area. These findings indicate that continuous forests do not necessary serve as a “mainland” for urban forest species and that every urban habitat, however small in size, acts as a temporary reservoir of species. In comparison with populations of small‐sized species, populations of large‐sized forest species appeared to decline more readily during forest fragmentation.     

Biodiversity and climate determine the functioning of Neotropical forests

Aim

Tropical forests account for a quarter of the global carbon storage and a third of the terrestrial productivity. Few studies have teased apart the relative importance of environmental factors and forest attributes for ecosystem functioning, especially for the tropics. This study aims to relate aboveground biomass (AGB) and biomass dynamics (i.e., net biomass productivity and its underlying demographic drivers: biomass recruitment, growth and mortality) to forest attributes (tree diversity, community‐mean traits and stand basal area) and environmental conditions (water availability, soil fertility and disturbance).

Location

Neotropics.

Methods

We used data from 26 sites, 201 1‐ha plots and >92,000 trees distributed across the Neotropics. We quantified for each site water availability and soil total exchangeable bases and for each plot three key community‐weighted mean functional traits that are important for biomass stocks and productivity. We used structural equation models to test the hypothesis that all drivers have independent, positive effects on biomass stocks and dynamics.

Results

Of the relationships analysed, vegetation attributes were more frequently associated significantly with biomass stocks and dynamics than environmental conditions (in 67 vs. 33% of the relationships). High climatic water availability increased biomass growth and stocks, light disturbance increased biomass growth, and soil bases had no effect. Rarefied tree species richness had consistent positive relationships with biomass stocks and dynamics, probably because of niche complementarity, but was not related to net biomass productivity. Community‐mean traits were good predictors of biomass stocks and dynamics.

Main conclusions

Water availability has a strong positive effect on biomass stocks and growth, and a future predicted increase in (atmospheric) drought might, therefore, potentially reduce carbon storage. Forest attributes, including species diversity and community‐weighted mean traits, have independent and important relationships with AGB stocks, dynamics and ecosystem functioning, not only in relatively simple temperate systems, but also in structurally complex hyper‐diverse tropical forests.     

Water availability drives aboveground biomass and bird richness in forest restoration plantings to achieve carbon and biodiversity cobenefits

To combat global warming and biodiversity loss, we require effective forest restoration that encourages recovery of species diversity and ecosystem function to deliver essential ecosystem services, such as biomass accumulation. Further, understanding how and where to undertake restoration to achieve carbon sequestration and biodiversity conservation would provide an opportunity to finance ecosystem restoration under carbon markets. We surveyed 30 native mixed‐species plantings in subtropical forests and woodlands in Australia and used structural equation modeling to determine vegetation, soil, and climate variables most likely driving aboveground biomass accrual and bird richness and investigate the relationships between plant diversity, aboveground biomass accrual, and bird diversity. We focussed on woodland and forest‐dependent birds, and functional groups at risk of decline (insectivorous, understorey‐nesting, and small‐bodied birds). We found that mean moisture availability strongly limits aboveground biomass accrual and bird richness in restoration plantings, indicating potential synergies in choosing sites for carbon and biodiversity purposes. Counter to theory, woody plant richness was a poor direct predictor of aboveground biomass accrual, but was indirectly related via significant, positive effects of stand density. We also found no direct relationship between aboveground biomass accrual and bird richness, likely because of the strong effects of moisture availability on both variables. Instead, moisture availability and patch size strongly and positively influenced the richness of woodland and forest‐dependent birds. For understorey‐nesting birds, however, shrub cover and patch size predicted richness. Stand age or area of native vegetation surrounding the patch did not influence bird richness. Our results suggest that in subtropical biomes, planting larger patches to higher densities, ideally using a diversity of trees and shrubs (characteristics of ecological plantings) in more mesic locations will enhance the provision of carbon and biodiversity cobenefits. Further, ecological plantings will aid the rapid recovery of woodland and forest bird richness, with comparable aboveground biomass accrual to less diverse forestry plantations.     

Land use types influenced avian assemblage structure in a forest–agriculture landscape in Ghana

The conservation of biodiversity within tropical forest regions does not lie only in the maintenance of natural forest areas, but on conservation strategies directed toward agricultural land types within which they are embedded. This study investigated variations in bird assemblages of different functional groups of forest‐dependent birds in three agricultural land types, relative to distance from the interior of 34 tropical forest patches of varying sizes. Point counts were used to sample birds at each study site visited. Data from counts were used to estimate species richness, species evenness, and Simpson's diversity of birds. Mean species richness, evenness, and diversity were modeled as responses and as a function of agricultural land type, distance from the forest interior and three site‐scale vegetation covariates (density of large trees, fruiting trees, and patch size) using generalized linear mixed‐effect models. Mean observed species richness of birds varied significantly within habitat types. Mean observed species richness was highest in forest interior sites while sites located in farm centers recorded the lowest mean species richness. Species richness of forest specialists was strongly influenced by the type of agricultural land use. Fallow lands, density of large trees, and patch size strongly positively influenced forest specialists. Insectivorous and frugivorous birds were more species‐rich in fallow lands while monoculture plantations favored nectarivorous birds. Our results suggest that poor agricultural practices can lead to population declines of forest‐dependent birds particularly specialist species. Conservation actions should include proper land use management that ensures heterogeneity through retention of native tree species on farms in tropical forest‐agriculture landscapes.     

Recovery of mammal diversity in tropical forests: a functional approach to measuring restoration

Ecological restoration is increasingly applied in tropical forests to mitigate biodiversity loss and recover ecosystem functions. In restoration ecology, functional richness, rather than species richness, often determines community assembly, and measures of functional diversity provide a mechanistic link between diversity and ecological functioning of restored habitat. Vertebrate animals are important for ecosystem functioning. Here, we examine the functional diversity of small‐to‐medium sized mammals to evaluate the diversity and functional recovery of tropical rainforest. We assess how mammal species diversity and composition and functional diversity and composition, vary along a restoration chronosequence from degraded pasture to “old‐growth” tropical rainforest in the Wet Tropics of Australia. Species richness, diversity, evenness, and abundance did not vary, but total mammal biomass and mean species body mass increased with restoration age. Species composition in restoration forests converged on the composition of old‐growth rainforest and diverged from pasture with increasing restoration age. Functional metrics provided a clearer pattern of recovery than traditional species metrics, with most functional metrics significantly increasing with restoration age when taxonomic‐based metrics did not. Functional evenness and dispersion increased significantly with restoration age, suggesting that niche complementarity enhances species' abundances in restored sites. The change in community composition represented a functional shift from invasive, herbivorous, terrestrial habitat generalists and open environment specialists in pasture and young restoration sites, to predominantly endemic, folivorous, arboreal, and fossorial forest species in older restoration sites. This shift has positive implications for conservation and demonstrates the potential of tropical forest restoration to recover rainforest‐like, diverse faunal communities.     

Predicting dispersal of auto‐gyrating fruit in tropical trees: a case study from the Dipterocarpaceae

Seed dispersal governs the distribution of plant propagules in the landscape and hence forms the template on which density‐dependent processes act. Dispersal is therefore a vital component of many species coexistence and forest dynamics models and is of applied value in understanding forest regeneration. Research on the processes that facilitate forest regeneration and restoration is given further weight in the context of widespread loss and degradation of tropical forests, and provides impetus to improve estimates of seed dispersal for tropical forest trees. South‐East Asian lowland rainforests, which have been subject to severe degradation, are dominated by trees of the Dipterocarpaceae family which constitute over 40% of forest biomass. Dipterocarp dispersal is generally considered to be poor given their large, gyration‐dispersed fruits. However, there is wide variability in fruit size and morphology which we hypothesize mechanistically underpins dispersal potential through the lift provided to seeds mediated by the wings. We explored experimentally how the ratio of fruit wing area to mass (“inverse wing loading,” IWL) explains variation in seed dispersal kernels among 13 dipterocarp species by releasing fruit from a canopy tower. Horizontal seed dispersal distances increased with IWL, especially at high wind speeds. Seed dispersal of all species was predominantly local, with 90% of seed dispersing <10 m, although maximum dispersal distances varied widely among species. We present a generic seed dispersal model for dipterocarps based on attributes of seed morphology and provide modeled seed dispersal kernels for all dipterocarp species with IWLs of 1–50, representing 75% of species in Borneo.     

Structural characteristics and aboveground biomass of old‐growth spruce–fir stands in the eastern Carpathian mountains,Ukraine

Abstract

Temperate old‐growth forests are known to have ecological characteristics distinct from younger forests, but these have been poorly described for the remaining old‐growth Picea abies–Abies alba forests in the eastern Carpathian mountains. In addition, recent studies suggest that old‐growth forests may be more significant carbon sinks than previously recognized. This has stimulated interest in quantifying aboveground carbon stocks in primary forest systems. We investigated the structural attributes and aboveground biomass in two remnant old‐growth spruce–fir stands and compared these against a primary (never logged) mature reference stand. Our sites were located in the Gorgany Nature Reserve in western Ukraine. Overstory data were collected using variable radius plots; coarse woody debris was sampled along line intercept transects. Differences among sites were assessed using non‐parametric statistical analyses. Goodness‐of‐fit tests were used to evaluate the form of diameter distributions. The results strongly supported the hypothesis that old‐growth temperate spruce–fir forests have greater structural complexity compared to mature forests, including higher densities of large trees, more complex horizontal structure, and elevated aboveground biomass. The late‐successional sites we sampled exhibited rotated sigmoid diameter distributions; these may reflect natural disturbance dynamics. Old‐growth Carpathian spruce–fir forests store on average approximately 155–165 Mg ha^?1 of carbon in aboveground tree parts alone. This is approximately 50% higher than mature stands. Given the scarcity of primary spruce–fir forests in the Carpathian region, remaining stands have high conservation value, both as habitat for late‐successional species and as carbon storage reservoirs.     

Large‐sized rare tree species contribute disproportionately to functional diversity in resource acquisition in African tropical forest

Increasing evidence is available for a positive effect of biodiversity on ecosystem productivity and standing biomass, also in highly diverse systems as tropical forests. Biodiversity conservation could therefore be a critical aspect of climate mitigation policies. There is, however, limited understanding of the role of individual species for this relationship, which could aid in focusing conservation efforts and forest management planning. This study characterizes the functional specialization and redundancy for 95% of all tree species (basal area weighted percentage) in a diverse tropical forest in the central Congo Basin and relates this to species' abundance, contribution to aboveground carbon, and maximum size. Functional characterization is based on a set of traits related to resource acquisition (wood density, specific leaf area, leaf carbon, nitrogen and phosphorus content, and leaf stable carbon isotope composition). We show that within both mixed and monodominant tropical forest ecosystems, the highest functional specialization and lowest functional redundancy are solely found in rare tree species and significantly more in rare species holding large‐sized individuals. Rare species cover the entire range of low and high functional redundancy, contributing both unique and redundant functions. Loss of species supporting functional redundancy could be buffered by other species in the community, including more abundant species. This is not the case for species supporting high functional specialization and low functional redundancy, which would need specific conservation attention. In terms of tropical forest management planning, we argue that specific conservation of large‐sized trees is imperative for long‐term maintenance of ecosystem functioning.     

Logging impacts on avian species richness and composition differ across latitudes and foraging and breeding habitat preferences

Understanding the causes underlying changes in species diversity is a fundamental pursuit of ecology. Animal species richness and composition often change with decreased forest structural complexity associated with logging. Yet differences in latitude and forest type may strongly influence how species diversity responds to logging. We performed a meta‐analysis of logging effects on local species richness and composition of birds across the world and assessed responses by different guilds (nesting strata, foraging strata, diet, and body size). This approach allowed identification of species attributes that might underlie responses to this anthropogenic disturbance. We only examined studies that allowed forests to regrow naturally following logging, and accounted for logging intensity, spatial extent, successional regrowth after logging, and the change in species composition expected due to random assembly from regional species pools. Selective logging in the tropics and clearcut logging in temperate latitudes caused loss of species from nearly all forest strata (ground to canopy), leading to substantial declines in species richness (up to 27% of species). Few species were lost or gained following any intensity of logging in lower‐latitude temperate forests, but the relative abundances of these species changed substantially. Selective logging at higher‐temperate latitudes generally replaced late‐successional specialists with early‐successional specialists, leading to no net changes in species richness but large changes in species composition. Removing less basal area during logging mitigated the loss of avian species from all forests and, in some cases, increased diversity in temperate forests. This meta‐analysis provides insights into the important role of habitat specialization in determining differential responses of animal communities to logging across tropical and temperate latitudes.     

Global‐scale impacts of nitrogen deposition on tree carbon sequestration in tropical,temperate, and boreal forests: A meta‐analysis

Elevated nitrogen (N) deposition may increase net primary productivity in N‐limited terrestrial ecosystems and thus enhance the terrestrial carbon (C) sink. To assess the magnitude of this N‐induced C sink, we performed a meta‐analysis on data from forest fertilization experiments to estimate N‐induced C sequestration in aboveground tree woody biomass, a stable C pool with long turnover times. Our results show that boreal and temperate forests responded strongly to N addition and sequestered on average an additional 14 and 13 kg C per kg N in aboveground woody biomass, respectively. Tropical forests, however, did not respond significantly to N addition. The common hypothesis that tropical forests do not respond to N because they are phosphorus‐limited could not be confirmed, as we found no significant response to phosphorus addition in tropical forests. Across climate zones, we found that young forests responded more strongly to N addition, which is important as many previous meta‐analyses of N addition experiments rely heavily on data from experiments on seedlings and young trees. Furthermore, the C–N response (defined as additional mass unit of C sequestered per additional mass unit of N addition) was affected by forest productivity, experimental N addition rate, and rate of ambient N deposition. The estimated C–N responses from our meta‐analysis were generally lower that those derived with stoichiometric scaling, dynamic global vegetation models, and forest growth inventories along N deposition gradients. We estimated N‐induced global C sequestration in tree aboveground woody biomass by multiplying the C–N responses obtained from the meta‐analysis with N deposition estimates per biome. We thus derived an N‐induced global C sink of about 177 (112–243) Tg C/year in aboveground and belowground woody biomass, which would account for about 12% of the forest biomass C sink (1,400 Tg C/year).     

A Multi‐Taxa Assessment of Biodiversity Change After Single and Recurrent Wildfires in a Brazilian Amazon Forest

In the last decades, due to human land management that uses fire as a tool, and due to abnormal droughts, many tropical forests have become more susceptible to recurrent wildfires with negative consequences for biodiversity. Yet, studies are usually focused on few taxa and rarely compare different fire frequencies. We examined if the effects of single and recurrent fires are consistent for leaf litter ants, dung beetles, birds (sampled with point‐counts PC and mist net‐MN), saplings, and trees. Recurrent fires had a great effect on forest structure, reducing live tree biomass and number of lianas, and increasing canopy openness and numbers of saplings alive. Recurrent fires had consistently stronger effects on species richness and composition across all sample groups than single fires, except ants. Birds and plants were more grouped in the congruence analysis. The average dissimilarities between control and recurrent‐burned forest were higher than between control and once‐burned forest for all sample groups, furthermore birds and vegetation communities in recurrent‐burned forest are almost entirely dissimilar from the unburned forest. While beta diversity of ants, birds (MN), and trees was not affected by the frequency of fire, it changed for dung beetles, birds (PC), and saplings. Effects of fire on faunal community structure were more due to indirect effects, through vegetation, than through the fire itself. These results reinforce the effect of single and recurrent fires on tropical forests, and highlight the mechanisms acting behind them. Policy‐makers need to explicitly address protection of tropical forests from wildfires in conservation planning.     

Optimal climate for large trees at high elevations drives patterns of biomass in remote forests of Papua New Guinea

Our ability to model global carbon fluxes depends on understanding how terrestrial carbon stocks respond to varying environmental conditions. Tropical forests contain the bulk of the biosphere's carbon. However, there is a lack of consensus as to how gradients in environmental conditions affect tropical forest carbon. Papua New Guinea (PNG) lies within one of the largest areas of contiguous tropical forest and is characterized by environmental gradients driven by altitude; yet, the region has been grossly understudied. Here, we present the first field assessment of aboveground biomass (AGB) across three main forest types of PNG using 193 plots stratified across 3,100‐m elevation gradient. Unexpectedly, AGB had no direct relationship to rainfall, temperature, soil, or topography. Instead, natural disturbances explained most variation in AGB. While large trees (diameter at breast height > 50 cm) drove altitudinal patterns of AGB, resulting in a major peak in AGB (2,200–3,100 m) and some of the most carbon‐rich forests at these altitudes anywhere. Large trees were correlated to a set of climatic variables following a hump‐shaped curve. The set of “optimal” climatic conditions found in montane cloud forests is similar to that of maritime temperate areas that harbor the largest trees in the world: high ratio of precipitation to evapotranspiration (2.8), moderate mean annual temperature (13.7°C), and low intra‐annual temperature range (7.5°C). At extreme altitudes (2,800–3,100 m), where tree diversity elsewhere is usually low and large trees are generally rare or absent, specimens from 18 families had girths >70 cm diameter and maximum heights 20–41 m. These findings indicate that simple AGB‐climate‐edaphic models may not be suitable for estimating carbon storage in forests where optimal climate niches exist. Our study, conducted in a very remote area, suggests that tropical montane forests may contain greater AGB than previously thought and the importance of securing their future under a changing climate is therefore enhanced.     

Species and structural diversity of church forests in a fragmented Ethiopian Highland landscape

Question: Thousands of small isolated forest fragments remain around churches (“church forests”) in the almost completely deforested Ethiopian Highlands. We questioned how the forest structure and composition varied with altitude, forest area and human influence. Location: South Gondar, Amhara National Regional State, Northern Ethiopia. Methods: The structure and species composition was assessed for 810 plots in 28 church forests. All woody plants were inventoried, identified and measured (stem diameter) in seven to 56 10 m x 10‐m plots per forest. Results: In total, 168 woody species were recorded, of which 160 were indigeneous. The basal area decreased with tree harvest intensity; understorey and middle‐storey density (<5 cm DBH trees) decreased with grazing; overstorey density (>5 cm DBH trees) increased with altitude. The dominance of a small set of species increased with altitude and grazing intensity. Species richness decreased with altitude, mainly due to variation in the richness of the overstorey community. Moreover, species richness in the understorey decreased with grazing intensity. Conclusions: We show how tree harvesting intensity, grazing intensity and altitude contribute to observed variations in forest structure, composition and species richness. Species richness was, however, not related to forest area. Our study emphasizes the significant role played by the remaining church forests for conservation of woody plant species in North Ethiopian Highlands, and the need to protect these forests for plant species conservation purposes.     

Influence of Post‐Clearing Treatment on the Recovery of Herbaceous Plant Communities in Amazonian Secondary Forests

Secondary forests are an increasingly common feature in tropical landscapes worldwide and understanding their regeneration is necessary to design effective restoration strategies. It has previously been shown that the woody species community in secondary forests can follow different successional pathways according to the nature of past human activities in the area, yet little is known about patterns of herbaceous species diversity in secondary forests with different histories of land use. We compared the diversity and abundance of herbaceous plant communities in two types of Central Amazonian secondary forests—those regenerating on pastures created by felling and burning trees and those where trees were felled only. We also tested if plant density and species richness in secondary forests are related to proximity to primary forest. In comparison with primary forest sites, forests regenerating on non‐burned habitats had lower herbaceous plant density and species richness than those on burned ones. However, species composition and abundance in non‐burned stands were more similar to those of primary forest, whereas several secondary forest specialist species were found in burned stands. In both non‐burned and burned forests, distance from the forest edge was not related to herbaceous density and species richness. Overall, our results suggest that the natural regeneration of herbaceous species in secondary tropical forests is dependent on a site's post‐clearing treatment. We recommend evaluating the land history of a site prior to developing and implementing a restoration strategy, as this will influence the biological template on which restoration efforts are overlaid.     

The relationship between species richness and biomass changes from boreal to subtropical forests in China

Diversity‐manipulation experiments suggest a positive effect of biodiversity on ecosystem properties (EPs), but variable relationships between species richness and EPs have been reported in natural communities. An explanation for this discrepancy is that observed richness–EPs relationships in natural communities change with environment and species functional identities. But how the relationships change along broad‐scale climatic gradients has rarely been examined. In this paper, we sampled 848 plots of 20 × 30 m² from boreal to tropical forests across China. We examined plot biomass with respect to environmental factors, tree species richness and functional group identity (FGI, i.e. evergreen vs deciduous, and coniferous vs broadleaf). Variation partitioning was used to evaluate the relative effects of the three classes of factors. We found that, most of the ‘effects’ (percentage of variation explained) of richness and FGI on forest biomass were shared with environmental factors, but species richness and FGI still revealed significant effects in addition to environment for plots across China. Richness and FGI explained biomass mainly through their shared effects instead of independent effects, suggesting that the positive biodiversity effect is closely associated with a sampling effect. The relative effects of richness, FGI and environment varied latitudinally: the independent effects of environment and richness decreased from boreal to subtropical forests, whereas the total effect of FGI increased. We also found that the slope of richness–biomass relationship decreased monotonically from boreal to subtropical forests, possibly because of decreasing complementarity and increasing competition with increasing productivity. Our results suggest that while species richness does have significant effects on forest biomass it is less important than environmental gradients and other biotic factors in shaping large‐scale biomass patterns. We suggest that understanding how and why the diversity–EPs relationships change along climatic gradient would be helpful for a better understanding of real biodiversity effects in natural communities.     

Functional traits determine tree growth and ecosystem productivity of a tropical montane forest: Insights from a long‐term nutrient manipulation experiment

Trait‐response effects are critical to forecast community structure and biomass production in highly diverse tropical forests. Ecological theory and few observation studies indicate that trees with acquisitive functional traits would respond more strongly to higher resource availability than those with conservative traits. We assessed how long‐term tree growth in experimental nutrient addition plots (N, P, and N + P) varied as a function of morphological traits, tree size, and species identity. We also evaluated how trait‐based responses affected stand scale biomass production considering the community structure. We found that tree growth depended on interactions between functional traits and the type or combination of nutrients added. Common species with acquisitive functional traits responded more strongly to nutrient addition, mainly to N + P. Phosphorous enhanced the growth rates of species with acquisitive and conservative traits, had mostly positive effects on common species and neutral or negative effects in rare species. Moreover, trees receiving N + P grew faster irrespective of their initial size relative to trees in control or to trees in other treatment plots. Finally, species responses were highly idiosyncratic suggesting that community processes including competition and niche dimensionality may be altered under increased resource availability. We found no statistically significant effects of nutrient additions on aboveground biomass productivity because acquisitive species had a limited potential to increase their biomass, possibly due to their generally lower wood density. In contrast, P addition increased the growth rates of species characterized by more conservative resource strategies (with higher wood density) that were poorly represented in the plant community. We provide the first long‐term experimental evidence that trait‐based responses, community structure, and community processes modulate the effects of increased nutrient availability on biomass productivity in a tropical forest.     

Does plant diversity increase top–down control of herbivorous insects in tropical forest?

Higher trophic level interactions are key mediators of ecosystem functioning in tropical forests. A rich body of theory has been developed to predict the effects of plant diversity on communities at higher trophic levels and the mechanisms underlying such effects. The 'enemies hypothesis’ states that predators exert more effective top–down control of herbivorous insects with increasing plant diversity. Support for this hypothesis has been found in temperate forests and agroecosystems, but remains understudied in tropical forests. We compared incidence of attacks of different natural enemies using artificial caterpillars in a tropical forest landscape and investigated the role of plant community structure (i.e. species richness, composition and density), and the role of forest fragmentation (i.e. patch size, edge distance and canopy openness) on predation intensity. Plant community effects were tested with respect to three vegetation strata: trees, saplings and herbs. Observed predation was substantially due to ants. Predation rates increased with plant species richness for trees and herbs. Density of saplings, herb cover and herb species composition were important factors for predation. No significant patterns were found for fragmentation parameters, suggesting that forest fragmentation has not altered predation intensity. We conclude that in tropical forests, top–down control of herbivorous insects in the understory vegetation is affected by a combination of plant diversity, plant species composition and structural features of the plant community.     

Edge disturbance drives liana abundance increase and alteration of liana–host tree interactions in tropical forest fragments

Closed‐canopy forests are being rapidly fragmented across much of the tropical world. Determining the impacts of fragmentation on ecological processes enables better forest management and improves species‐conservation outcomes. Lianas are an integral part of tropical forests but can have detrimental and potentially complex interactions with their host trees. These effects can include reduced tree growth and fecundity, elevated tree mortality, alterations in tree‐species composition, degradation of forest succession, and a substantial decline in forest carbon storage. We examined the individual impacts of fragmentation and edge effects (0–100‐m transect from edge to forest interior) on the liana community and liana–host tree interactions in rainforests of the Atherton Tableland in north Queensland, Australia. We compared the liana and tree community, the traits of liana‐infested trees, and determinants of the rates of tree infestation within five forest fragments (23–58 ha in area) and five nearby intact‐forest sites. Fragmented forests experienced considerable disturbance‐induced degradation at their edges, resulting in a significant increase in liana abundance. This effect penetrated to significantly greater depths in forest fragments than in intact forests. The composition of the liana community in terms of climbing guilds was significantly different between fragmented and intact forests, likely because forest edges had more small‐sized trees favoring particular liana guilds which preferentially use these for climbing trellises. Sites that had higher liana abundances also exhibited higher infestation rates of trees, as did sites with the largest lianas. However, large lianas were associated with low‐disturbance forest sites. Our study shows that edge disturbance of forest fragments significantly altered the abundance and community composition of lianas and their ecological relationships with trees, with liana impacts on trees being elevated in fragments relative to intact forests. Consequently, effective control of lianas in forest fragments requires management practices which directly focus on minimizing forest edge disturbance.