Secondary Succession after Slash-and-Burn Cultivation in Papuan Lowland Forest, Indonesia

Papuan forests have been subjected to shifting cultivation for centuries by indigenous people affecting the ecological processes therein; during secondary succession, fallow forests recover naturally. However, the information on ecological succession after swidden practices remains poorly understood in Papuan lowland forests. This study aimed to examine the plant species richness and density of different plant lifeforms in fallows of increasing time after slash-and-burn cultivation along with basic edaphic factors. We performed data collection in the northern part of the lowland evergreen tropical forest near Manokwari, West Papua, Indonesia. The sampling consisted of 26 plots distributed in the primary forest (n = 6) and in secondary/fallow forests 2-, 4-, 7-, and 9-years after cultivation (n = 5 for each age class). The plant community in primary forest clearly differed from the secondary forests. The plant species richness was about twice as high in primary compared to secondary forests. The density of trees and shrubs increased during succession whereas that of lianas declined. The soil fertility declined in secondary forests, although soil organic matter was greatest two years after swidden and then decreased gradually over time. This research underlined that indigenous swidden practices alter ecological conditions and that secondary forests will take a long time to fully recover to resemble primary forest. Hence, the monitoring of vegetation during the process is necessary to inform conservation programs

From earthquakes to island area: multi-scale effects upon local diversity

Tropical forests occupy small coral atolls to the vast Amazon basin. They occur across bioregions with different geological and climatic history. Differences in area and bioregional history shape species immigration, extinction and diversification. How this effects local diversity is unclear. The Indonesian archipelago hosts thousands of tree species whose coexistence should depend upon these factors. Using a novel dataset of 215 Indonesian forest plots, across fifteen islands ranging in area from 120 to 785 000 km2, we apply Gaussian mixed effects models to examine the simultaneous effects of environment, earthquake proximity, island area and bioregion upon tree diversity for trees ≥ 10 cm diameter at breast height. We find that tree diversity declines with precipitation seasonality and increases with island area. Accounting for the effects of environment and island area we show that the westernmost bioregion Sunda has greater local diversity than Wallacea, which in turn has greater local diversity than easternmost Sahul. However, when the model includes geological activity (here proximity to major earthquakes), bioregion differences are reduced. Overall, results indicate that multi-scale, current and historic effects dictate tree diversity. These multi-scale drivers should not be ignored when studying biodiversity gradients and their impacts upon ecosystem function

Co-limitation towards lower latitudes shapes global forest diversity gradients

The latitudinal diversity gradient (LDG) is one of the most recognized global patterns of species richness exhibited across a wide range of taxa. Numerous hypotheses have been proposed in the past two centuries to explain LDG, but rigorous tests of the drivers of LDGs have been limited by a lack of high-quality global species richness data. Here we produce a high-resolution (0.025° × 0.025°) map of local tree species richness using a global forest inventory database with individual tree information and local biophysical characteristics from ~1.3 million sample plots. We then quantify drivers of local tree species richness patterns across latitudes. Generally, annual mean temperature was a dominant predictor of tree species richness, which is most consistent with the metabolic theory of biodiversity (MTB). However, MTB underestimated LDG in the tropics, where high species richness was also moderated by topographic, soil and anthropogenic factors operating at local scales. Given that local landscape variables operate synergistically with bioclimatic factors in shaping the global LDG pattern, we suggest that MTB be extended to account for co-limitation by subordinate drivers