Atlantic Forest meeting Cerrado: floristic, structure, and species distribution of an ecotonal tree community

We evaluated the floristic and structural composition of a tree community in an ecotone between Cerrado (cerradão) and Atlantic Forest (seasonal semideciduous forest) domains located in Porto Ferreira State Park (PFSP), southeastern Brazil. We compared the floristic relationships of this ecotone with those of previous surveys carried out on the same vegetation types and checked the species distribution among the Brazilian biomes. We sampled all living trees with PBH>10 cm in 64 10x10 m plots (0.64 ha), totaling 1,755 individuals belonging to 101 species and 37 families. The richest families were Myrtaceae (13 spp.) and Fabaceae (11 spp.), and Siparuna guianensis was the most abundant species (188 individuals). We reported two threatened species. A great number of species are widely distributed, occurring in different Brazilian biomes. Floristic similarity values were low among the selected studies, but our sampled community clustered with communities of cerradão and ecotone areas of previous surveys. Our results corroborate that ecotonal areas have great tree diversity and the predominance of widely distributed species. This fact, combined with the vegetation thickening verified through historical photographs, reinforces that the study area belongs to an under-changing ecotone.

A 40-year evaluation of drivers of African rainforest change

Background Tropical forests are repositories of much of the world’s biodiversity and are critical for mitigation of climate change. Yet, the drivers of forest dynamics are poorly understood. This is in large part due to the lack of long-term data on forest change and changes in drivers. Methodology We quantify changes in tree abundance, diversity, and stand structure along transects first enumerated in 1978 and resampled 2019 in Kibale National Park, Uganda. We tested five predictions. First, based on the purported role of seed dispersal and herbivory and our quantification of changes in the abundance of frugivores and herbivores, we tested two predictions of how faunal change could have influenced forest composition. Second, based on an evaluation of life history strategies, we tested two predictions concerning how the forest could have changed following disturbance that happened prior to written history. Finally, based on a 50-year climate record, we evaluate the possible influence of climate change on forest dynamics. Results More trees were present on the assessed transects in 2019 (508) than in 1978 (436), species richness remained similar, but diversity declined as the number of dominant species increased. Rainfall increased by only 3 mm over the 50 years but this had not significant effect on forest changes measured here. Annual average monthly maximum temperature increased significantly by 1.05 °C over 50 years. The abundance of frugivorous and folivorous primates and elephants increased over the 50 years of monitoring. Neither the prediction that an increase in abundance of seed dispersing frugivores increases the abundance of their preferred fruiting tree species, nor that as an increase in folivore abundance causes a decline in their preferred species were supported. As predicted, light-demanding species decreased in abundance while shade-tolerant species increased as expected from Kibale being disturbed prior to historical records. Finally, while temperature increased over the 50 years, we found no means to predict a priori how individual species would respond. Conclusions Our study revealed subtle changes in the tree community over 40 years, sizable increases in primate numbers, a substantial increase in the elephant population and an increase in local temperature. Yet, a clear picture of what set of interactions impact the change in the tree community remains elusive. Our data on tree life-history strategies and frugivore/herbivore foraging preferences suggest that trees species are under opposing pressures.

Landscape and tree community effects on the infestation of an endemic fungal pathogen in riparian forests were mediated by leaf traits

Background Plant pathogens are regarded as crucial agents shaping the dynamics of natural forest communities. Marssonina leaf spot of poplar is induced by an endemic pathogenic fungus Drepanopeziza populi, causing increased damage to riparian poplar stands in recent years. However, such endemic fungal diseases have received little attention at the landscape scale, despite the key role of landscape heterogeneity in the development and spread of emerging forest diseases. Moreover, most studies have insufficiently captured multiple ecological factors driving the infestation of an endemic pathogen acting at the landscape, community, and individual scales. Methods We measured pathogen load, disease prevalence, and disease severity of Marssonina leaf spot in poplars in riparian forests. We explored the direct and indirect effects of multiple ecological factors on pathogen infestation using a path analysis. Specifically, we first assessed the effects of landscape and community factors on leaf traits including leaf area, specific leaf area (SLA) and leaf dry matter content (LDMC), and then examined the role of these factors in shaping disease dynamics. Results Path analysis showed that landscape features had no direct impact on leaf traits and pathogen infestation, but directly affected tree community composition. Landscapes with higher forest cover resulted in higher host density and tree diversity. Host density was the most important factor of pathogen load, with higher host density resulting in more symptomatic leaves. Tree diversity had direct effects on disease prevalence, with poplars growing in mixed forest stands far less affected by pathogens than in pure stands. Moreover, disease prevalence was positively related to pathogen load. Tree diversity strongly reduced SLA, but increased LDMC. Higher SLA was found to increase pathogen load and disease severity, but higher LDMC was found to reduce both of them. Conclusions Our results show that the effects of landscape and tree community on Marssonina leaf spot disease are mediated by leaf traits. Disentangling the effects of biotic and abiotic factors affecting pathogen infestation contributes to reduce the overall impact of this disease, which can provide policy makers with sustainable management of endemic plant diseases in natural forests.

Environmental filters and biotic interactions drive species richness and composition in ecotone forests of the northern Brazilian Amazonia

The structure of tree communities in tropical forests depends on environmental filters and biotic interactions such as competition and facilitation. Many ecotone forests in Northern Amazonia are intriguingly populated by tree assemblages characterized by distinct abundances of a single species, Peltogyne gracilipes (Leguminosae). It is unclear whether this pattern solely reflects environmental filters or also antagonistic interactions among species with similar habitat requirements. The aim of this study was to determine the response of species richness and composition to environmental filters, and analyze the role of P. gracilipes in structuring tree communities in ecotone forest areas of the Northern Brazilian Amazonia. We sampled 129 permanent plots along a hydro-edaphic gradient. All arboreal individuals with stem diameter ≥10 cm were measured and identified. Multiple regressions were performed to test the effects of environmental filters, and abundance of P. gracilipes on the tree species richness and composition. Species richness and composition responded to the same filters which, in turn, affected species composition directly and indirectly, through the abundance of P. gracilipes. Our results indicate that both abiotic filters and biotic interactions shape the studied tree communities. P. gracilipes can be considered an indicator species of hydro-edaphic conditions, but also is itself a driver of tree community structure.