Douglas Sheil

The Potential for Species Conservation in Tropical Secondary Forests

In the wake of widespread loss of old-growth forests throughout the tropics, secondary forests will likely play a growing role in the conservation of forest biodiversity. We considered a complex hierarchy of factors that interact in space and time to determine the conservation potential of tropical secondary forests. Beyond the characteristics of local forest patches, spatial and temporal landscape dynamics influence the establishment, species composition, and persistence of secondary forests. Prospects for conservation of old-growth species in secondary forests are maximized in regions where the ratio of secondary to old-growth forest area is relatively low, older secondary forests have persisted, anthropogenic disturbance after abandonment is relatively low, seed-dispersing fauna are present, and old-growth forests are close to abandoned sites. The conservation value of a secondary forest is expected to increase over time, as species arriving from remaining old-growth forest patches accumulate. Many studies are poorly replicated, which limits robust assessments of the number and abundance of old-growth species present in secondary forests. Older secondary forests are not often studied and few long-term studies are conducted in secondary forests. Available data indicate that both old-growth and second-growth forests are important to the persistence of forest species in tropical, human-modified landscapes.

The intermediate disturbance hypothesis applies to tropical forests, but disturbance contributes little to tree diversity

The intermediate disturbance hypothesis (IDH) predicts local species diversity to be maximal at an intermediate level of disturbance. Developed to explain species maintenance and diversity patterns in species-rich ecosystems such as tropical forests, tests of IDH in tropical forest remain scarce, small-scale and contentious. We use an unprecedented large-scale dataset (2504 one-hectare plots and 331,567 trees) to examine whether IDH explains tree diversity variation within wet, moist and dry tropical forests, and we analyse the underlying mechanism by determining responses within functional species groups. We find that disturbance explains more variation in diversity of dry than wet tropical forests. Pioneer species numbers increase with disturbance, shade-tolerant species decrease and intermediate species are indifferent. While diversity indeed peaks at intermediate disturbance levels little variation is explained outside dry forests, and disturbance is less important for species richness patterns in wet tropical rain forests than previously thought.

Maintaining ecosystem function and services in logged tropical forests

Vast expanses of tropical forests worldwide are being impacted by selective logging. We evaluate the environmental impacts of such logging and conclude that natural timber-production forests typically retain most of their biodiversity and associated ecosystem functions, as well as their carbon, climatic, and soil-hydrological ecosystem services. Unfortunately, the value of production forests is often overlooked, leaving them vulnerable to further degradation including post-logging clearing, fires, and hunting. Because logged tropical forests are extensive, functionally diverse, and provide many ecosystem services, efforts to expand their role in conservation strategies are urgently needed. Key priorities include improving harvest practices to reduce negative impacts on ecosystem functions and services, and preventing the rapid conversion and loss of logged forests.

Evaluating the success of conservation actions in safeguarding tropical forest biodiversity.

We reviewed the evidence on the extent and efficacy of conservation of tropical forest biodiversity for each of the classes of conservation action defined by the new International Union for Conservation of Nature (IUCN) classification. Protected areas are the most tested conservation approach, and a number of studies show they are generally effective in slowing deforestation. There is some documentation of the extent of sustainable timber management in tropical forest, but little information on other landscape-conservation tactics. The extent and effectiveness of ex situ species conservation is quite well known. Forty-one tropical-forest species now survive only in captivity. Other single-species conservation actions are not as well documented. The potential of policy mechanisms, such as international conventions and provision of funds, to slow extinctions in tropical forests is considerable, but the effects of policy are difficult to measure. Finally, interventions to promote tropical conservation by supporting education and livelihoods, providing incentives, and furthering capacity building are all thought to be important, but their extent and effectiveness remain poorly known. For birds, the best studied taxon, the sum of such conservation actions has averted one-fifth of the extinctions that would otherwise have occurred over the last century. Clearly, tropical forest conservation works, but more is needed, as is critical assessment of what works in what circumstances, if mass extinction is to be averted.

The persistence and conservation of Borneo's mammals in lowland rain forests managed for timber: observations, overviews and opportunities.

Lowland rainforests on Borneo are being degraded and lost at an alarming rate. Studies on mammals report species responding in various ways to habitat changes that occur in commercial forestry concessions. Here we draw together information on the relationship between the ecological, evolutionary, and biogeographic characteristics of selected Bornean non-volant mammals, and their response to timber harvesting and related impacts. Only a minority of species show markedly reduced densities after timber harvesting. Nonetheless there are many grounds for concern as various processes can, and often do, reduce the viability of wildlife populations. Our review of what we know, and of current understanding, helps predict mammalian dynamics and subsequent mammal-induced ecosystem changes in logged forests. We identify groups of mammal species that, although largely unstudied, are unlikely to tolerate the impacts associated with timber harvesting. On a positive note we find and suggest many relatively simple and low-cost ways in which concession management practices might be modified so as to improve the value of managed forests for wildlife conservation. Improving forest management can play a vital role in maintaining the rich biodiversity of Borneo’s tropical rain forests.

Standardized Assessment of Biodiversity Trends in Tropical Forest Protected Areas: The End Is Not in Sight

Extinction rates in the Anthropocene are three orders of magnitude higher than background and disproportionately occur in the tropics, home of half the world’s species. Despite global efforts to combat tropical species extinctions, lack of high-quality, objective information on tropical biodiversity has hampered quantitative evaluation of conservation strategies. In particular, the scarcity of population-level monitoring in tropical forests has stymied assessment of biodiversity outcomes, such as the status and trends of animal populations in protected areas. Here, we evaluate occupancy trends for 511 populations of terrestrial mammals and birds, representing 244 species from 15 tropical forest protected areas on three continents. For the first time to our knowledge, we use annual surveys from tropical forests worldwide that employ a standardized camera trapping protocol, and we compute data analytics that correct for imperfect detection. We found that occupancy declined in 22%, increased in 17%, and exhibited no change in 22% of populations during the last 3–8 years, while 39% of populations were detected too infrequently to assess occupancy changes. Despite extensive variability in occupancy trends, these 15 tropical protected areas have not exhibited systematic declines in biodiversity (i.e., occupancy, richness, or evenness) at the community level. Our results differ from reports of widespread biodiversity declines based on aggregated secondary data and expert opinion and suggest less extreme deterioration in tropical forest protected areas. We simultaneously fill an important conservation data gap and demonstrate the value of large-scale monitoring infrastructure and powerful analytics, which can be scaled to incorporate additional sites, ecosystems, and monitoring methods. In an era of catastrophic biodiversity loss, robust indicators produced from standardized monitoring infrastructure are critical to accurately assess population outcomes and identify conservation strategies that can avert biodiversity collapse.

How plants water our planet: advances and imperatives

Most life on land depends on water from rain, but much of the rain on land may also depend on life. Recent studies indicate that vegetation, especially tree cover, influences rain and rainfall patterns to a greater extent than is generally assumed. Here, I briefly highlight some of these findings to show that vegetation sciences will have an increasing role in understanding climate and its vulnerability to changes in land cover.

Spread of the invasive alien species Piper aduncum via logging roads in Borneo.

We examine how spiked pepper (Piper aduncum L., Piperaceae), a shade intolerant, animal-dispersed Neotropical tree, is spreading in the interior of Borneo. Concerned that logging roads might be facilitating this spread, we made a series of observations, relating tree distribution, location and road history, in a concession in East Kalimantan. These roads will connect West Kutai and Malinau Districts and may allow alien plants to disperse from one to the other. We observed that P. aduncum was already well established on the oldest, southern portions of the logging road network, but was absent on the newest roads to the north. A few scattered individuals occur on the roadside as much as 150 km beyond the main areas dominated by P. aduncum, suggesting an occasional ability to achieve long-hop dispersal. Rivers of 30 m width are not a barrier to P. aduncums spread. Based on road age, we estimate a minimum rate of spread between five and seven km per year. We infer that logging roads are assisting P. aduncum to spread and the tree will become widely established in Malinau District. Prevention of this spread would require urgent, intensive and coordinated control over the length of the road network and, more generally, major restrictions on how such roads are located and managed.

Carbon isotopic signatures of soil organic matter correlate with leaf area index across woody biomes

Leaf area index (LAI), a measure of canopy density, is a key variable for modelling and understanding primary productivity, and also water use and energy exchange in forest ecosystems. However, LAI varies considerably with phenology and disturbance patterns, so alternative approaches to quantifying stand-level processes should be considered. The carbon isotope composition of soil organic matter (C-13(SOM)) provides a time-integrated, productivity-weighted measure of physiological and stand-level processes, reflecting biomass deposition from seasonal to decadal time scales. Our primary aim was to explore how well LAI correlates with C-13(SOM) across biomes. Using a global data set spanning large environmental gradients in tropical, temperate and boreal forest and woodland, we assess the strength of the correlation between LAI and C-13(SOM); we also assess climatic variables derived from the WorldClim database. We found that LAI was strongly correlated with C-13(SOM), but was also correlated with Mean Temperature of the Wettest Quarter, Mean Precipitation of Warmest Quarter and Annual Solar Radiation across and within biomes.Synthesis. Our results demonstrate that C-13(SOM) values can provide spatially explicit estimates of leaf area index (LAI) and could therefore serve as a surrogate for productivity and water use. While C-13(SOM) has traditionally been used to reconstruct the relative abundance of C-3 versus C-4 species, the results of this study demonstrate that within stable C-3- or C-4-dominated biomes, C-13(SOM) can provide additional insights. The fact that LAI is strongly correlated to C-13(SOM) may allow for a more nuanced interpretation of ecosystem properties of palaeoecosystems based on palaeosol C-13 values.

Oil-Palm Plantations in the Context of Biodiversity Conservation

A native from western Africa, oil palm is one of the most rapidly expanding and cheap tropical plant species. It produces more oil per unit area than any other vegetable oil crop. Widespread planting has been at the expense of other tropical vegetation, notably including species-rich tropical rain forests. Even though planted oil palm provides habitat to some species, species diversity in oil palm is much lower than in most tropical rain forest and even timber concessions and timber plantations. Although oil-palm plantations have a negative impact on local biodiversity, their ultimate global impact depends on considering the impacts of alternative oil crops with greater land requirements.