Nonrandom processes maintain diversity in tropical forests

An ecological community\u27s species diversity tends to erode through time as a result of stochastic extinction, competitive exclusion, and unstable host-enemy dynamics. This erosion of diversity can be prevented over the short term if recruits are highly diverse as a result of preferential recruitment of rare species or, alternatively, if rare species survive preferentially, which increases diversity as the ages of the individuals increase. Here, we present census data from seven New and Old World tropical forest dynamics plots that all show the latter pattern. Within local areas, the trees that survived were as a group more diverse than those that were recruited or those that died. The larger (and therefore on average older) survivors were more diverse within local areas than the smaller survivors. When species were rare in a local area, they had a higher survival rate than when they were common, resulting in enrichment for rare species and increasing diversity with age and size class in these complex ecosystems

Assessing Evidence for a Pervasive Alteration in Tropical Tree Communities

In Amazonian tropical forests, recent studies have reported increases in aboveground biomass and in primary productivity, as well as shifts in plant species composition favouring fast-growing species over slow-growing ones. This pervasive alteration of mature tropical forests was attributed to global environmental change, such as an increase in atmospheric CO2 concentration, nutrient deposition, temperature, drought frequency, and/or irradiance. We used standardized, repeated measurements of over 2 million trees in ten large (16–52 ha each) forest plots on three continents to evaluate the generality of these findings across tropical forests. Aboveground biomass increased at seven of our ten plots, significantly so at four plots, and showed a large decrease at a single plot. Carbon accumulation pooled across sites was significant (+0.24 MgC ha−1 y−1, 95% confidence intervals [0.07, 0.39] MgC ha−1 y−1), but lower than reported previously for Amazonia. At three sites for which we had data for multiple census intervals, we found no concerted increase in biomass gain, in conflict with the increased productivity hypothesis. Over all ten plots, the fastest-growing quartile of species gained biomass (+0.33 [0.09, 0.55] % y−1) compared with the tree community as a whole (+0.15 % y−1); however, this significant trend was due to a single plot. Biomass of slow-growing species increased significantly when calculated over all plots (+0.21 [0.02, 0.37] % y−1), and in half of our plots when calculated individually. Our results do not support the hypothesis that fast-growing species are consistently increasing in dominance in tropical tree communities. Instead, they suggest that our plots may be simultaneously recovering from past disturbances and affected by changes in resource availability. More long-term studies are necessary to clarify the contribution of global change to the functioning of tropical forests

Do current stem size distributions predict future population changes? An empirical test of intraspecific patterns in tropical trees at two spatial scales

It is critical to understand the responses of tropical tree species to ongoing anthropogenic disturbances. Given the longevity of large trees and the scarcity of appropriately long-term demographic data, standing size distributions are a potential tool for predicting species' responses to disturbances and resultant changes in population structure. Here we test the utility of several different measures of size distribution for predicting subsequent population changes at the intraspecific level using demographic records from two subsampled 50-ha tree plots in Malaysia (Pasoh and Lambir). Most measures of size distribution failed to successfully predict population change better than random; however, the ‘coefficient of skewness’ (a measure of the relative proportion of small vs. large stems in a population) was able to correctly predict the direction of population change for approximately three-quarters of species at both sites. At Pasoh, the magnitude of this relationship decreased with adult stature and rate of turnover, but was unrelated to sapling growth rates at either site. Finally, using data for species common at both forests, we found that size distributions were generally uninformative of subsequent differences in population change between sites (only median dbh correctly predicted the direction of change for more species than random). Based on these results we conclude that some measures of intraspecific differences in size distribution are potentially informative of population trends within forests but have limited utility across broader spatial scales

Data from: Species-specific flowering cues among general flowering Shorea species at the Pasoh Research Forest, Malaysia

1.In a unique phenomenon restricted to the ever wet forests of Southeast Asia, hundreds of species from dozens of plant families reproduce synchronously at irregular, multi-year intervals. The proximate environmental cues that synchronize these general flowering events have not been evaluated systematically because there have been no long-term, high temporal-resolution, species-level records from the region. 2.We present 13 years of weekly flowering records for five Shorea species as well as daily temperature and rainfall records from the Pasoh Forest Reserve, Peninsular Malaysia. We constructed models to evaluate hypothesized relationships between flowering and cool temperature, drought, and additive and synergistic effects of cool temperature and drought for each species. Model parameters include periods of time for floral cue accumulation and flower development and temperature and/or rainfall thresholds required for floral initiation. Parameters estimated using flowering observations from 2001–2011 were used to forecast flowering for 2011–2014. 3.We show that drought and cool temperatures acting synergistically best explain the timing of flowering events for all Shorea species in the section Mutica and forecast the largest general flowering event accurately. Periods estimated for signal accumulation ranged from 54 to 90 days among species. Periods estimated for flowers to develop ranged between 43 to 96 days and closely followed the interspecific sequence of flowering in the Shorea species. Drought and temperature thresholds also varied among species, with S. maxwelliana requiring the most severe drought and S. leprosula the lowest temperatures. 4.Synthesis. Our results indicate that cool temperatures and low rainfall occurring on seasonal time scales of about two to three months rather than brief cold snaps or brief droughts best explain general flowering in Shorea species at the Pasoh Forest Reserve. Low rainfall is equally likely in winter (December–February) and summer (July–August) and cool temperatures are most likely in winter at Pasoh, which explains why general flowering events are restricted to spring and fall, with more frequent and stronger flowering in spring. In addition, species-specific sensitivity to environmental cues suggests that future climate change will have differential impacts on the frequency of reproduction, with potential consequences for regeneration of these dominant species of lowland tropical forests

Forest use types of mammals in the Pasoh Forest Reserve and adjacent forest fragments

This study reports the works conducted in Pasoh Forest Reserve for determining how forest mammals use different forest types. Study have focused on the entire forest reserve which includes primary and secondary forest patches, and secondary forest fragments around agricultural fields, pastures, clearcuts, silviculture plantations, and residential areas. Samples were obtained from camera-trappings at selected locations in the forest reserve and adjacent fragment forests to reveal actual species composition of mammals in different forest types. Invasion of domestic animals and poaching are found remains high in the reserve

Data from: Seed size and the evolution of leaf defences

1. Leaf defences vary widely among tree species, affecting rates of herbivory, survival and reproduction. 2. Two contrasting hypotheses account for variation in leaf defences among species. The first predicts that a slow life history, which is characteristic of larger seeded species adapted to resource-limited environments, is associated with well-defended leaves. The second, apparency theory, predicts that elevated leaf defences are necessitated for species that are more detectable to herbivores. 3. Here we use comparative methods and a global data set to test (i) the relationship between seed size and leaf defences and (ii) the relationship between clumping (spatial apparency) and leaf defences. 4. We found that seed size was positively related to leaf fracture toughness, but not phenolics or tannin concentration and that spatial aggregation was unrelated to leaf defences. 5. Synthesis. Our results suggest that larger seed size and increased leaf toughness are correlated as part of a trait syndrome associated with a slow, resource-limited life history, not clumped dispersion and increased spatial apparency

Geographical Pattern and Environmental Correlates of Regional-Scale General Flowering in Peninsular Malaysia

<div><p>In South-East Asian dipterocarp forests, many trees synchronize their reproduction at the community level, but irregularly, in a phenomenon known as general flowering (GF). Several proximate cues have been proposed as triggers for the synchronization of Southeast Asian GF, but the debate continues, as many studies have not considered geographical variation in climate and flora. We hypothesized that the spatial pattern of GF forests is explained by previously proposed climatic cues if there are common cues for GF among regions. During the study, GF episodes occurred every year, but the spatial occurrence varied considerably from just a few forests to the whole of Peninsular Malaysia. In 2001, 2002 and 2005, minor and major GF occurred widely throughout Peninsular Malaysia (GF2001, GF2002, and GF2005), and the geographical patterns of GF varied between the episodes. In the three regional-scale GF episodes, most major events occurred in regions where prolonged drought (PD) had been recorded prior, and significant associations between GF scores and PD were found in GF2001 and GF2002. However, the frequency of PD was higher than that of GF throughout the peninsula. In contrast, low temperature (LT) was observed during the study period only before GF2002 and GF2005, but there was no clear spatial relationship between GF and LT in the regional-scale episodes. There was also no evidence that last GF condition influenced the magnitude of GF. Thus, our results suggest that PD would be essential to trigger regional-scale GF in the peninsula, but also that PD does not fully explain the spatial and temporal patterns of GF. The coarse relationships between GF and the proposed climatic cues may be due to the geographical variation in proximate cues for GF, and the climatic and floristic geographical variations should be considered to understand the proximate factors of GF.</p></div

Distribution patterns of major and minor GF (left), and meteorological stations with PD (centre) and LT (right) during the three regional-scale GF episodes.

<p>Plots show the presence or absence of PD and LT during the putative floral induction season: June–August (GF2001) or January–March (GF2002 and GF2005).</p