Dynamics of forests with Araucariaceae in the western Pacific

Abstract. Several species of Araucaria and Agathis (Araucariaceae) occur as canopy emergents in rain forests of the western pacific region, often representing major components of total stand biomass. New data from permanent forest plots (and other published work) for three species (Araucaria hunsteinii from New Guinea, A. laubenfelsii from New Caledonia, and Agathis australis from New Zealand) are used to test the validity of the temporal stand replacement model proposed by Ogden (1985) and Ogden & Stewart (1995) to explain the structural and compositional properties of New Zealand rain forests containing the conifer Agathis australis. Here we propose the model as a general one which explains the stand dynamics of rain forests with Araucariaceae across a range of sites and species in the western Pacific. Forest stands representing putative stages in the model were examined for changes through time in species recruitment, growth and survivorship, and stand richness, density and basal area. Support for the model was found on the basis of: 1. Evidence for a phase of massive conifer recruitment following landscape-scale disturbances (e.g. by fire at the Huapai site, New Zealand for Agathis australis); 2. Increasing species richness of angiosperm trees in the pole stage of forest stand development (i.e. as the initial cohort of conifers reach tree size; >10 cm DBH); 3. A high turnover rate for angiosperms (<100 yr), and low turnover for conifers (≥ 100 yr) in the pole stage, but similar turnover rates for both components (50–100 yr) as forests enter the mature to senescent phase for the initial conifer cohort; 4. Very low rates of recruitment for conifers within mature stands, and projected forest compositions which show increasing dominance by angiosperm tree species; 5. A low probability of conifer recruitment in large canopy gaps created by conifer tree falls during the initial cohort senescent phase, which could produce a second generation low density stand in the absence of landscape scale disturbance; 6. Evidence that each of the three species examined required open canopy conditions (canopy openness > 10 %) for successful recruitment. The evidence presented here supports the temporal stand replacement model, but more long-term supporting data are needed, especially for the phase immediately following landscape level disturbance.     

Beta-diversity in seasonally dry tropical forests (SDTF) in the Caatinga Biogeographic Domain, Brazil, and its implications for conservation

Tropical biomes are species rich, but some biomes such as seasonally dry tropical forests (SDTFs) are still inadequately studied compared to their co-occurring rain forest and savanna. SDTFs occur in areas of high environmental heterogeneity, resulting in high beta (β)-diversity or species turnover, but this has so far only been accessed using a single β-diversity measure, and at a spatial scale that is of limited applicability for reserve planning. The Caatinga Biogeographic Domain in Brazil contains the largest known extent of SDTF which are poorly studied and inadequately reserved. We therefore studied the variation in species richness and species turnover among SDTF between localities and between known floristic communities. From six localities within the Caatinga Biogeographic Domain we recorded all tree species with a circumference at breast height equaling or exceeding 10 cm within 106 400 m² survey plots. From the species presence/absence data we calculated three measures of β-diversity between pairs of study localities and between different floristic communities representing: (i) species similarity, (ii) differences between species richness, and (iii) species gain and loss. Our results confirm the high β-diversity of SDTFs and species turnover between localities and also between floristic communities. The three indices were also complementary to each other and can be used to maximize accuracy in β-diversity studies. The implications of our study for conservation and reserve planning of SDTFs are discussed.     

Structure and function in two tropical gallery forest communities: implications for forest conservation in fragmented systems

1. Composition, growth and turnover of trees in two species-rich tropical gallery forests were examined to evaluate what community reorganization may be needed to transform recently created tropical forest fragments into stable refugia for regional forest biotas.
2. Rates of tree growth and turnover over a 5-year interval were comparable to those recorded in continuous forests and in both communities there had been some tree species turnover in the measured stem size classes during the 5-year interval.
3. The more abundant tree species in both communities formed three functional groups along gradients between streams and forest edges: edge-concentrators, core-concentrators and generalists.
4. Soil fertility showed no consistent increase close to streams and neither tree growth nor recruitment rates were increased in this zone. In contrast, forest edge zones exhibited increased rates of tree growth and recruitment indicating that growth processes in these forests are light-limited rather than soil-limited, and that forest edge zones are generally favourable habitats for tree populations.
5. Both communities showed signs of past fire incursions, and the tendency of a subset of tree species to concentrate in the more growth-limited core habitats is attributed to their fire sensitivity.
6. Rapid development of an edge zone of fire-insensitive tree species is considered to be essential to the survival of forest community fragments in the fire-prone landscapes of the tropics, and the edges of gallery forests are recommended as potential sources of species with which to fashion these protective ecotones.
7. Preservation of a diverse forest biota in the fire-protected interiors of fragments will require natural or artificially enhanced immigration rates that are sufficient to offset local extinctions.     

Frequent,low‐amplitude disturbances drive high tree turnover rates on a remote,cyclone‐prone Polynesian island

Aim How important are frequent, low‐intensity disturbances to tree community dynamics of a cyclone‐prone forest? We tested the following hypotheses concerning the ‘inter‐cataclysm’ period on a remote Polynesian island: (1) tree turnover would be high and recruitment rates would be significantly higher than mortality; (2) low‐intensity disturbance would result in a marginal increase in tree mortality in the short term; (3) turnover would vary among species and would be associated with plant traits linked to differences in life history; and (4) mortality and recruitment events would be spatially non‐random. Location Tutuila, a volcanic island in the Samoan Archipelago, Polynesia. Methods We censused the tree (stem diameter ≥ 10 cm) community in 3.9 ha of tropical forest three times over a 10‐year period, 1998–2008. We calculated annual mortality, recruitment and turnover rates for 36 tree species. We tested for non‐random spatial patterns and predictors of mortality, and non‐random spatial patterns of tree recruitment. A 2004 cyclone passing within 400 km allowed us to measure the effects of a non‐cataclysmic disturbance on vital rates. Results Annual turnover was 2.8% and annual recruitment was 3.6%; these are some of the highest rates in the tropics, and likely to be a response to a cyclone that passed < 50 km from Tutuila in 1991. Species turnover rates over 10 years were negatively correlated with wood specific gravity, and positively correlated with annual stem diameter increment. Mortality was spatially aggregated, and a function of site, species and an individual’s growth rate. Recruitment was highest on ground with low slope. The low‐magnitude cyclone disturbance in 2004 defoliated 29% of all trees, but killed only 1.8% of trees immediately and increased annual mortality over 5 years by 0.7%. Main conclusions The inter‐cataclysm period on Tutuila is characterized by frequent, low‐amplitude disturbances that promote high rates of tree recruitment and create a dynamic, non‐equilibrium or disturbed island disequilibrium tree community. Species with low wood density and fast growth rates have enhanced opportunities for recruitment between cataclysms, but also higher probabilities of dying. Our results suggest that increases in the frequency of cyclone activity could shift relative abundances towards disturbance‐specialist species and new forest turnover rates.     

Long‐term tree fern dynamics linked to disturbance and shade tolerance

Question: Do New Zealand tree ferns have recognizable shade tolerance niches? Location: Lowland temperate rain forest of New Zealand (41°20′S, 174°58′E). Methods: Growth, death and recruitment of five tree fern species were estimated from a 38‐year record of stem heights, collected within a 2.25‐ha block of forest, and electron transport rates (ETR) of photosystem II of fronds were measured. Results: Two species of Cyathea were comparatively common (603 and 351 stems in total) and two were comparatively rare (155 and 17 stems in total) on the site. The common species had lower rates of growth, recruitment and mortality than the rare species, had skewed age distributions typical of shade‐tolerant species and were probably recruited soon after a catastrophic earthquake in 1855. The two rare species were failing to recruit under closed forests; their age distributions indicated that all had regenerated long after the earthquake. ETR were higher for faster‐growing than for the shade‐tolerant species. A tree fern that regenerates vegetatively from aerial buds, Dicksonia squarrosa, was common on the site (361 stems in total). Its age distribution suggested it was relatively shade tolerant, but its mortality and recruitment rates were much higher than those of the two shade‐tolerating Cyathea species, suggesting that this multi‐stemmed species functions differently from the monopodial Cyathea species. Conclusions: New Zealand Cyathea tree ferns occupy distinct niches along a shade tolerance spectrum and their relative abundances are strongly influenced by disturbance history. The study provides evidence that tree fern species differ strongly in their responses to canopy disturbance and are not ecologically equivalent.     

Forest turnover rates follow global and regional patterns of productivity

Using a global database, we found that forest turnover rates (the average of tree mortality and recruitment rates) parallel broad-scale patterns of net primary productivity. First, forest turnover was higher in tropical than in temperate forests. Second, as recently demonstrated by others, Amazonian forest turnover was higher on fertile than infertile soils. Third, within temperate latitudes, turnover was highest in angiosperm forests, intermediate in mixed forests, and lowest in gymnosperm forests. Finally, within a single forest physiognomic type, turnover declined sharply with elevation (hence with temperature). These patterns of turnover in populations of trees are broadly similar to the patterns of turnover in populations of plant organs (leaves and roots) found in other studies. Our findings suggest a link between forest mass balance and the population dynamics of trees, and have implications for understanding and predicting the effects of environmental changes on forest structure and terrestrial carbon dynamics.     

Elevational distribution of conifer-broadleaved hardwood forests on South Island,New Zealand

Constrained canonical correspondence analysis was used to compare the elevational distribution of conifer-broadleaved hardwood forests at nine localities on South Island, New Zealand. Elevations of individual species were compared using cover-weighted mean elevations and cover-weighted standard deviations of mean elevation. Mean elevations of floristically similar stands declined with latitude, but was also lower at a locality with a granite substrate than at an adjacent locality with a schist substrate. The mean elevation breadth of frequent species (those in >5% of stands) was greatest at a locality underlain by schist and least at a locality underlain by granite. This is consistent with wide habitat breadth for species in early successional stages, because forest underlain by schist is more frequently disturbed than forest underlain by granite. Elevation breadth of frequent species was less, and species' turnover greater, in South Island conifer-broadleaved hardwood forests than in conifer forests at similar latitudes in the Southern Rocky Mountains, USA.     

Demography of the long‐lived conifer Agathis ovata in maquis and rainforest,New Caledonia

Abstract. The endemic New Caledonian conifer Agathis ovata occurs as an emergent tree in fire‐prone shrublands (maquis), and fire‐sensitive rainforest. Growth, survivorship and recruitment over 5 yr were compared for populations from forest and maquis on ultramafic substrates in New Caledonia to investigate whether demographic behaviour varied in response to the strongly contrasting forest and shrubland environments. Growth of seedlings and of small (30–100 cm height) and large (100 cm height; 5 cm DBH) saplings was slow, but varied significantly among stages, site types and years. The greatest difference in growth rates was among stages, seedlings growing 0.34 cm.yr^?1, small saplings 1.06 cm.yr^?1 and large saplings 2.13 cm.yr^?1. Tree DBH increased by only 0.05 cm.yr^?1 and, based on these rates, individuals with DBH of 30 cm are estimated to be more than 700 yr old. Few trees (3.5%) produced cones in any year and seedling recruitment was low, but some recruitment was recorded each year in both maquis and forest. Rates of recruitment per parent were highest in forest (1.28.yr^?1, cf 0.78.yr^?1), but the higher density of trees in maquis meant that overall recruitment was greater there (92 ha^?1.yr^?1, cf 56 ha^?1.yr^?1). Seedling mortality ranged from 0.9 to 2.9% among years with no significant difference between maquis and forest. No sapling mortality was recorded, but annual tree mortality ranged from 0 to 1.4%. Evidence from a recently burned site indicated that while trees may survive fire, seedlings and saplings do not. Post‐fire seedling recruitment per ha from surviving trees was four times lower than in unburned sites, but growth rates were four times higher. Similar demographic attributes, including high survivorship, low growth rate and low rates of recruitment over a long reproductive life, characterize Agathis ovata populations in both maquis and rainforest in New Caledonia and are indicative of a broad tolerance of light environments that is unusual among tree species. These demographic attributes help to explain the long‐term persistence of the species in these strongly contrasting habitats.     

Dynamics,productivity and species richness of tropical rainforests along elevational and edaphic gradients on Mount Kinabalu,Borneo

We studied the dynamics of nine tropical rainforests on Mount Kinabalu, Borneo, at four elevations (700, 1,700, 2,700 and 3,100 m) on various edaphic conditions for four 2-year periods over 8 years (1995–2003), and examined the relationships with above-ground productivity. Mean growth rate of stem diameter, basal area turnover rate and estimated recruitment rate (using growth rate and size distribution) correlated with productivity among the nine forests in all periods. These rates based on growth rates of surviving stems appeared to be good measures of stand turnover. However, observed recruitment rate and mortality (and turnover rate as mean of these rates) based on direct observation of recruits and deaths did not correlate with productivity in some periods. These rates may not be useful as measures of stand turnover given small sample size and short census interval because they were highly influenced by stochastic fluctuation. A severe drought associated with the 1997–1998 El Niño event inflated mortality and depressed mean growth rate, recruitment rate and basal area turnover rate, but had little effect on the correlations between these rates (except mortality) and productivity. Across broad elevational and edaphic gradients on Mount Kinabalu, forest turnover, productivity and species richness correlated with each other, but the causal interpretation is difficult given the different histories and species pools among forests at different elevations.     

Spatial and temporal structure of diversity and demographic dynamics along a successional gradient of tropical forests in southern Brazil

1. Analysis of the structure, diversity, and demographic dynamics of tree assemblages in tropical forests is especially important in order to evaluate local and regional successional trajectories.
2. We conducted a long‐term study to investigate how the structure, species richness, and diversity of secondary tropical forests change over time. Trees (DBH ≥ 5 cm) in the Atlantic Forest of southern Brazil were sampled twice during a 10‐year period (2007 and 2017) in six stands (1 ha each) that varied in age from their last disturbance (25, 60, 75, 90, and more than 100 years). We compared forest structure (abundance and basal area), species richness, alpha diversity, demographic rates (mortality, recruitment, and loss or gain in basal area), species composition, spatial beta diversity, and temporal beta diversity (based on turnover and nestedness indices) among stand ages and study years.
3. Demographic rates recorded in a 10‐year interval indicate a rapid and dynamic process of species substitution and structural changes. Structural recovery occurred faster than beta diversity and species composition recovery. The successional gradient showed a pattern of species trade‐off over time, with less spatial dissimilarity and faster demographic rates in younger stands. As stands grow older, they show larger spatial turnover of species than younger stands, making them more stochastic in relation to species composition. Stands appear to split chronologically to some extent, but not across a straightforward linear axis, reflecting stochastic changes, providing evidence for the formation of a nonequilibrium community.
4. Policy implications. These results reiterate the complexity and variability in forest succession and serve as a reference for the evaluation and monitoring of local management and conservation actions and for defining regional strategies that consider the diversity of local successional trajectories to evaluate the effectiveness of restoration measures in secondary forests of the Atlantic Forest biome.

     

Tree diversity in primary forest and different land use systems in Central Sulawesi,Indonesia

We studied the tree communities in primary forest and three different land use systems (forest gardens, ca. 5-year-old secondary forests, cacao plantations) at 900–1200 m elevation in the environs of Lore Lindu National Park, Central Sulawesi. The primary forests had ca. 150 tree species 10 cm diameter at breast height (dbh) per hectare, which is unusually high for forests at this elevation in southeast Asia. Basal area in the primary forest was 140 m² ha^–1, one of the highest values ever recorded in tropical forests worldwide. Tree species richness declined gradually from primary forest to forest gardens, secondary forests, and cacao plantations. This decline was paralleled by shifts in tree family composition, with Lauraceae, Meliaceae, and Euphorbiaceae being predominant in primary forests, Euphorbiaceae, Rubiaceae and Myristicaeae dominating in the forest gardens and Euphorbiaceae, Urticaceae, and Ulmaceae in the secondary forests. Cacao plantations were composed almost exclusively of cacao trees and two species of legume shade trees. Forest gardens further differed from primary forests by a much lower density of understorey trees, while secondary forests had fewer species of commercial interest. Comparative studies of birds and butterflies demonstrated parallel declines of species richness, showing the importance of trees in structuring tropical forest habitats and in providing resources.     

Structure and dynamics of a tropical dry forest in Ghana

Forest under low rainfall (averaging 745 mm yr^-1) on the Shai Hills in S.E. Ghana has redeveloped following cessation of farming in the 1890s. Forest stature is low, with a canopy at about 11 m, principally of three species, Diospyros abyssinica, D. mespiliformis and Millettia thonningii. Drypetes parvifolia and Vepris heterophylla are common understorey trees. Twelve species of woody liane were recorded. Species of thicket vegetation in the area were also present at low density. Most species are evergreen.Tree mortality averaged 2.3% yr^-1 and exceeded recruitment (1.5% yr^-1). Differences between species in mortality and recruitment were pronounced: canopy species showed a small decline in density; understorey species increased markedly and the thicket species declined. Seed production was very variable, but seedling establishment was very poor for all species. Seedling mortality was high (11% yr^-1) especially for small seedlings. These population trends probably represent the latter stages of succession of forest regrowth after farming about 100 years ago.Compared with tropical rain forest, Shai Hills forest has similar relative tree diameter growth (1–3.5% yr^-1), mortality and recruitment rates, and small-litter fall (5.52 t ha^-1 yr^-1).Shai Hills forest differs from rain forest by its short stature, relatively few (evergreen) tree species, poor regeneration from seed, high soil nutrient status and low rainfall. Similar forests have been reported in east Africa and in parts of New Guinea.Abbreviations dbh diameter at breast height (1.3 m) - gbh girth at breast height died May 1984     

Seedling mortality and damage due to non‐trophic animal interactions in a northern New Zealand forest

Abstract The importance of non‐trophic animal damage (biting and uprooting without consumption) and mortality of canopy tree seedlings were investigated in a warm temperate forest, in northern New Zealand. Two hundred seedlings 10‐30 cm in height were monitored at 4‐6‐week intervals for 2 years. Non‐trophic animal damage accounted for more seedling mortality in the first year (37.5% of all mortalities) than any other cause. Of the seedlings damaged in non‐trophic animal interactions 73% were bitten off close to the ground and left uneaten and the remainder were uprooted. In the second year all non‐trophic animal damage and mortality ceased following the control of rabbits (Oryctolagus cuniculus), suggesting that rabbits were the major cause of this damage. Total annual mortality rates (6‐8%) were low. However, measured seedling growth rates indicated an average time for seedlings to grow from 10 to 30 cm of 37 years. Therefore, in the absence of rabbit control, mortality due to non‐trophic animal interactions (3% per year) can have an important cumulative effect. Non‐trophic animal damage found in the present study before rabbits were culled (5% per year) was similar to that reported for two tropical forests, but much less than that reported for some other tropical and temperate forests.     

Tropical dry forests in New Caledonia

Tropical dry forest is the most endangered major vegetation type in the New Caledonia biodiversity hotspot. Vegetation surveys following a transect method used by Gentry were undertaken in two tropical dry forest sites, Ouen-Toro and Pindai, in order to compare species richness, floristic composition, and structure. Pindai contained significantly higher species richness than Ouen-Toro, although there was little difference in forest structure. Tropical dry forest sites in New Caledonia were compared to seven other biodiversity hotspots with tropical dry forest where Gentry's transect method was employed. New Caledonia and other tropical dry forests on islands contain significantly lower species richness than mainland tropical dry forests in biodiversity hotspots. However, New Caledonia contained the highest number of threatened species based on IUCN global conservation categories. Tropical dry forest in New Caledonia appears to be the world's most endangered tropical dry forest based on the extent of forest, number of reserves, and threatened species. Management of tropical dry forests on private and community lands is absolutely imperative to the long-term persistence of this ecosystem.     

Diversity,composition, and structure of tropical dry forests in Central America

Tropical dry forests have been reduced to less than 0.1% of their original expanse on the Pacific side of Central America and are considered by some to be the most endangered ecosystem in the lowland tropics. Plots 1000 m² were established in seven tropical dry forests in Costa Rica and Nicaragua in order to compare levels of species richness to other Neotropical dry forest sites and to identify environmental variables associated with species richness and abundance. A total of 204 species and 1484 individuals 2.5 cm were encountered. Santa Rosa National Park was the richest site with the highest family (33), genera (69), and species (75) diversity of all sites. Species richness and forest structure were significantly different between sites. Fabaceae was the dominant tree and shrub family at most sites, but no species was repeatably dominant based on number of stems in all fragments of tropical dry forest. Central American dry forests had similar species richness when compared to other Neotropical forests. There was no correlation between forest cover within reserves, or precipitation and plant species richness. There was a significant correlation between anthropogenic disturbance (intensity and frequency of fire, wood collection, grazing) and total species richness, tree and shrub species richness, and liana abundance. These results suggest controlling levels on anthropogenic disturbance within reserves should be a high priority for resource managers in Central America. Further research in forest fragments which examine individual and a combination of disturbance agents would help clarify the importance of anthropogenic disturbance on species richness and abundance.     

Demographic Drivers of Aboveground Biomass Dynamics During Secondary Succession in Neotropical Dry and Wet Forests

The magnitude of the carbon sink in second-growth forests is expected to vary with successional biomass dynamics resulting from tree growth, recruitment, and mortality, and with the effects of climate on these dynamics. We compare aboveground biomass dynamics of dry and wet Neotropical forests, based on monitoring data gathered over 3–16 years in forests covering the first 25 years of succession. We estimated standing biomass, annual biomass change, and contributions of tree growth, recruitment, and mortality. We also evaluated tree species’ contributions to biomass dynamics. Absolute rates of biomass change were lower in dry forests, 2.3 and 1.9 Mg ha^?1 y^?1, after 5–15 and 15–25 years after abandonment, respectively, than in wet forests, with 4.7 and 6.1 Mg ha^?1 y^?1, in the same age classes. Biomass change was largely driven by tree growth, accounting for at least 48% of biomass change across forest types and age classes. Mortality also contributed strongly to biomass change in wet forests of 5–15 years, whereas its contribution became important later in succession in dry forests. Biomass dynamics tended to be dominated by fewer species in early-successional dry than wet forests, but dominance was strong in both forest types. Overall, our results indicate that biomass dynamics during succession are faster in Neotropical wet than dry forests, with high tree mortality earlier in succession in the wet forests. Long-term monitoring of second-growth tropical forest plots is crucial for improving estimates of annual biomass change, and for enhancing understanding of the underlying mechanisms and demographic drivers.     

Species diversity,susceptibility to disturbance and tree population dynamics in tropical rain forest

Abstract. In 1964 a census of all trees > 9.7 cm diameter at breast height (DBH) was conducted on 22 plots totalling 13.2 ha in lowland tropical evergreen rain forest on Kolombangara, Solomon Islands. Over the following 30 yr (1964–1994), populations of all individuals > 4.85 cm DBH of the 12 most common tree species and amounts of disturbance have been monitored on a declining number of these plots (in 1994, nine plots totalling 5.4 ha were still being recorded). Between November 1967 and April 1970, Kolombangara was struck by four cyclones, although only two of these caused substantial amounts of damage to the canopy structure. Multivariate analysis has identified six forest types on Kolombangara (Greig-Smith et al. 1967). The species richness and diversity of trees in the 1964 census, turnover rates of the populations monitored over 1964–1975, and the amount of disturbance sustained during a cyclone in 1970, were all positively correlated across five of the forest types. The sixth forest type was a consistent outlier in these analyses and is believed to have been seriously disturbed by humans about a century ago. The floristics, turnover and disturbance data support Connell's intermediate disturbance hypothesis. The most species-rich forest types contained a higher proportion of fast-growing individuals and species that are early-successional and which have low density timber. Properties of these species rendered them more susceptible to damage when struck by the 1970 cyclone. They showed higher turnover rates because disturbance-dependent species are also characterised by higher mortality and recruitment rates. Thus, periodic cyclones appear to favour the maintenance of differences in species diversity and composition between forest types.     

Why are there more arboreal ant species in primary than in secondary tropical forests?

1.?Species diversity of arboreal arthropods tends to increase during rainforest succession so that primary forest communities comprise more species than those from secondary vegetation, but it is not well understood why. Primary forests differ from secondary forests in a wide array of factors whose relative impacts on arthropod diversity have not yet been quantified. 2.?We assessed the effects of succession-related determinants on a keystone ecological group, arboreal ants, by conducting a complete census of 1332 ant nests from all trees with diameter at breast height?≥?5?cm occurring within two (unreplicated) 0·32-ha plots, one in primary and one in secondary lowland forest in New Guinea. Specifically, we used a novel rarefaction-based approach to match number, size distribution and taxonomic structure of trees in primary forest communities to those in secondary forest and compared the resulting numbers of ant species. 3.?In total, we recorded 80 nesting ant species from 389 trees in primary forest but only 42 species from 295 trees in secondary forest. The two habitats did not differ in the mean number of ant species per tree or in the relationship between ant diversity and tree size. However, the between-tree similarity of ant communities was higher in secondary forest than in primary forest, as was the between-tree nest site similarity, suggesting that secondary trees were more uniform in providing nesting microhabitats. 4.?Using our rarefaction method, the difference in ant species richness between two forest types was partitioned according to the effects of higher tree density (22·6%), larger tree size (15·5%) and higher taxonomic diversity of trees (14·3%) in primary than in secondary forest. The remaining difference (47·6%) was because of higher beta diversity of ant communities between primary forest trees. In contrast, difference in nest density was explained solely by difference in tree density. 5.?Our study shows that reduction in plant taxonomic diversity in secondary forests is not the main driver of the reduction in canopy ant species richness. We suggest that the majority of arboreal species losses in secondary tropical forests are attributable to simpler vegetation structure, combined with lower turnover of nesting microhabitats between trees.     

Can we predict carbon stocks in tropical ecosystems from tree diversity? Comparing species and functional diversity in a plantation and a natural forest

? Linking tree diversity to carbon storage can provide further motivation to conserve tropical forests and to design carbon-enriched plantations. Here, we examine the role of tree diversity and functional traits in determining carbon storage in a mixed-species plantation and in a natural tropical forest in Panama. ? We used species richness, functional trait diversity, species dominance and functional trait dominance to predict tree carbon storage across these two forests. Then we compared the species ranking based on wood density, maximum diameter, maximum height, and leaf mass per area (LMA) between sites to reveal how these values changed between different forests. ? Increased species richness, a higher proportion of nitrogen fixers and species with low LMA increased carbon storage in the mixed-species plantation, while a higher proportion of large trees and species with high LMA increased tree carbon storage in the natural forest. Furthermore, we found that tree species varied greatly in their absolute and relative values between study sites. ? Different results in different forests mean that we cannot easily predict carbon storage capacity in natural forests using data from experimental plantations. Managers should be cautious when applying functional traits measured in natural populations in the design of carbon-enriched plantations.     

A climate change‐induced threat to the ecological resilience of a subtropical monsoon evergreen broad‐leaved forest in Southern China

Recent studies have suggested that tropical forests may not be resilient against climate change in the long term, primarily owing to predicted reductions in rainfall and forest productivity, increased tree mortality, and declining forest biomass carbon sinks. These changes will be caused by drought‐induced water stress and ecosystem disturbances. Several recent studies have reported that climate change has increased tree mortality in temperate and boreal forests, or both mortality and recruitment rates in tropical forests. However, no study has yet examined these changes in the subtropical forests that account for the majority of China's forested land. In this study, we describe how the monsoon evergreen broad‐leaved forest has responded to global warming and drought stress using 32 years of data from forest observation plots. Due to an imbalance in mortality and recruitment, and changes in diameter growth rates between larger and smaller trees and among different functional groups, the average DBH of trees and forest biomass have decreased. Sap flow measurements also showed that larger trees were more stressed than smaller trees by the warming and drying environment. As a result, the monsoon evergreen broad‐leaved forest community is undergoing a transition from a forest dominated by a cohort of fewer and larger individuals to a forest dominated by a cohort of more and smaller individuals, with a different species composition, suggesting that subtropical forests are threatened by their lack of resilience against long‐term climate change.