Interactions between all pairs of neighboring trees in 16 forests worldwide reveal details of unique ecological processes in each forest, and provide windows into their evolutionary histories

When Darwin visited the Galapagos archipelago, he observed that, in spite of the islands’ physical similarity, members of species that had dispersed to them recently were beginning to diverge from each other. He postulated that these divergences must have resulted primarily from interactions with sets of other species that had also diverged across these otherwise similar islands. By extrapolation, if Darwin is correct, such complex interactions must be driving species divergences across all ecosystems. However, many current general ecological theories that predict observed distributions of species in ecosystems do not take the details of between-species interactions into account. Here we quantify, in sixteen forest diversity plots (FDPs) worldwide, highly significant negative density-dependent (NDD) components of both conspecific and heterospecific between-tree interactions that affect the trees’ distributions, growth, recruitment, and mortality. These interactions decline smoothly in significance with increasing physical distance between trees. They also tend to decline in significance with increasing phylogenetic distance between the trees, but each FDP exhibits its own unique pattern of exceptions to this overall decline. Unique patterns of between-species interactions in ecosystems, of the general type that Darwin postulated, are likely to have contributed to the exceptions. We test the power of our null-model method by using a deliberately modified data set, and show that the method easily identifies the modifications. We examine how some of the exceptions, at the Wind River (USA) FDP, reveal new details of a known allelopathic effect of one of the Wind River gymnosperm species. Finally, we explore how similar analyses can be used to investigate details of many types of interactions in these complex ecosystems, and can provide clues to the evolution of these interactions

Understanding High Altitude Reforestation in Mt. Apo, Philippines

Comparing the difference in forest community structure between a reforested area and a nearby old growth forest is one way to evaluate the ability of a disturbed forest to recover. Here, we show how a high altitude reforested area in Mt. Apo, Philippines is recovering relative to a nearby old growth forest. The species richness of understory vegetation in the old growth forest did not differ significantly from the 11 year-old reforested area, suggesting fast recovery in this aspect. However, the tree assemblage and sizes (i.e., Diameter at Breast Height) in the old growth forest had significantly higher tree diversity as well as larger trees than the reforested area, suggesting slower recovery in this aspect. In addition, the dominant species in terms of understory vegetation cover, tree abundance, and sizes differed significantly between the old growth forest and the 11 year-old reforested area. In general, the composition and structure of vegetation communities (understory and trees) in the old growth forest and the 11 year-old reforested area were about 13-29% similar. This means that, without management interventions (e.g., assisted recovery), it would probably take much longer time (than 11 years) for the reforested area to get to same condition as the nearby old growth forest. More importantly, results showed which aspects of the reforested area could be adjusted to potentially hasten its recovery towards the old growth forest status

Data from: 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

Twelve-year changes in palm populations from a tropical lowland forest in the Philippines

Arecaceae (Palmae) is an ecologically and economically important family characteristic of the vegetation in tropical and subtropical regions, with at least 125 species occurring in the Philippines, most of them endemics. We monitored changes in stem density, mortality and recruitment of palm populations for 12 years within a 16-ha Forest Dynamic Plot located in northern Luzon, the Philippines. We recorded a total of 4060 stems, dominated by Pinanga insignis (46%) and P. maculata (34%), followed by Caryota cumingii (19%), and a few stems (< 1%) of Orania decipiens and Areca whitfordii. Half (51%) of the initially recorded stems in the 2004 census died by the time of the 2016 census, while 1086 (36%) additional stems were recorded in the same period. Overall palm population declined with the decreasing populations of P. insignis and P. maculata due to higher mortality than recruitment during the 2004–2010 and 2010–2016 census intervals while C. cumingii population increased in the same period. Regarding topographic position, the stem density of P. maculata is higher in val- leys > midslopes > ridges across censuses, higher in valleys and midslopes than ridges for C. cumingii across censuses, and higher in midslopes than valleys for P. insignis during the 2016 census only. Mortality and recruitment were weakly observed along topographic positions between species and across censuses. Our result presents how palm population may change within 12 years with population trends differing between species, indicating the importance of palms in understanding the population dynamics of plant communities in a fast-changing environment

Ant_behavior_Raw_data

Ant behavior analysis. Number of interactions by interaction type according to experiments

Predation_and_variables_raw_data

Plasticine caterpillar predation rates, plant diversity data and environmental variables used in the analysis

Effects of forest fragmentation on nocturnal Asian birds: A case study from Xishuangbanna, China

Owls have the potential to be keystone species for conservation in fragmented landscapes, as the absence of these predators could profoundly change community structure. Yet few studies have examined how whole communities of owls respond to fragmentation, especially in the tropics. When evaluating the effect of factors related to fragmentation, such as fragment area and distance to the edge, on these birds, it is also important in heterogeneous landscapes to ask how ‘location factors’ such as the topography, vegetation and soil of the fragment predict their persistence. In Xishuangbanna, southwest China, we established 43 transects (200 m×60 m) within 20 forest fragments to sample nocturnal birds, both visually and aurally. We used a multimodel inference approach to identify the factors that influence owl species richness, and generalized linear mixed models to predict the occurrence probabilities of each species. We found that fragmentation factors dominated location factors, with larger fragments having more species, and four of eight species were significantly more likely to occur in large fragments. Given the potential importance of these birds on regulating small mammal and other animal populations, and thus indirectly affecting seed dispersal, we suggest further protection of large fragments and programs to increase their connectivity to the remaining smaller fragments