Anthropogenic disturbance in tropical forests can double biodiversity loss from deforestation.

Concerted political attention has focused on reducing deforestation, and this remains the cornerstone of most biodiversity conservation strategies. However, maintaining forest cover may not reduce anthropogenic forest disturbances, which are rarely considered in conservation programmes. These disturbances occur both within forests, including selective logging and wildfires, and at the landscape level, through edge, area and isolation effects. Until now, the combined effect of anthropogenic disturbance on the conservation value of remnant primary forests has remained unknown, making it impossible to assess the relative importance of forest disturbance and forest loss. Here we address these knowledge gaps using a large data set of plants, birds and dung beetles (1,538, 460 and 156 species, respectively) sampled in 36 catchments in the Brazilian state of Pará. Catchments retaining more than 69­80% forest cover lost more conservation value from disturbance than from forest loss. For example, a 20% loss of primary forest, the maximum level of deforestation allowed on Amazonian properties under Brazil's Forest Code, resulted in a 39­54% loss of conservation value: 96­171% more than expected without considering disturbance effects. We extrapolated the disturbance-mediated loss of conservation value throughout Pará, which covers 25% of the Brazilian Amazon. Although disturbed forests retained considerable conservation value compared with deforested areas, the toll of disturbance outside Pará's strictly protected areas is equivalent to the loss of 92,000­139,000 km2 of primary forest. Even this lowest estimate is greater than the area deforested across the entire Brazilian Amazon between 2006 and 2015 (ref. 10). Species distribution models showed that both landscape and within-forest disturbances contributed to biodiversity loss, with the greatest negative effects on species of high conservation and functional value. These results demonstrate an urgent need for policy interventions that go beyond the maintenance of forest cover to safeguard the hyper-diversity of tropical forest ecosystems.

Native forest cover safeguards stream water quality under a changing climate.

Ensuring a sufficient and adequate supply of water for humans and ecosystems is a pressing environmental challenge. The expansion of agricultural and urban lands has jeopardized watershed ecosystem services and a changing climate poses additional risks for regional water supply. We used stream water quality data collected between 2000 and 2014, coupled with detailed precipitation and land cover information, to investigate the effects of landscape composition and short-term precipitation variability on the quality of water resources in the state of São Paulo, Brazil. The state is home to over 45 million people and has a long history of human landscape modification. A severe drought in 2014-2015 led to a major water crisis and highlighted the fragility of the regional water supply system. We found that human-dominated watersheds had lower overall water quality when compared to forested watersheds, with urban cover showing the most detrimental impacts on water quality. Forest cover was associated with a better overall water quality across the studied watersheds, with forested watersheds having low turbidity and high dissolved oxygen. High precipitation led to increased turbidity and fecal coliforms levels and lower dissolved oxygen in streams but these effects depended on watershed land cover. High precipitation diluted concentrations of nitrogen and dissolved solids in highly urbanized watersheds but exacerbated turbidity in pasture-dominated watersheds. Given the high costs of water treatment in densely populated regions, there is a pressing need to plan and manage landscapes in order to ensure adequate water resources. In tropical regions, maintaining or restoring native vegetation cover is a promising intervention to sustain adequate water quality.

Thresholds of species loss in Amazonian deforestation frontier landscapes.

In the Brazilian Amazon, private land accounts for the majority of remaining native vegetation. Understanding how land-use change affects the composition and distribution of biodiversity in farmlands is critical for improving conservation strategies in the face of rapid agricultural expansion. Working across an area exceeding 3 million ha in the southwestern state of Rondônia, we assessed how the extent and configuration of remnant forest in replicate 10,000-ha landscapes has affected the occurrence of a suite of Amazonian mammals and birds. In each of 31 landscapes, we used field sampling and semistructured interviews with landowners to determine the presence of 28 large and medium sized mammals and birds, as well as a further 7 understory birds. We then combined results of field surveys and interviews with a probabilistic model of deforestation. We found strong evidence for a threshold response of sampled biodiversity to landscape level forest cover; landscapes with <30-40% forest cover hosted markedly fewer species. Results from field surveys and interviews yielded similar thresholds. These results imply that in partially deforested landscapes many species are susceptible to extirpation following relatively small additional reductions in forest area. In the model of deforestation by 2030 the number of 10,000-ha landscapes under a conservative threshold of 43% forest cover almost doubled, such that only 22% of landscapes would likely to be able to sustain at least 75% of the 35 focal species we sampled. Brazilian law requires rural property owners in the Amazon to retain 80% forest cover, although this is rarely achieved. Prioritizing efforts to ensure that entire landscapes, rather than individual farms, retain at least 50% forest cover may help safeguard native biodiversity in private forest reserves in the Amazon.

Large woody debris input and its influence on channel structure in agricultural lands of Southeast Brazil.

Riparian forests are important for the structure and functioning of stream ecosystems, providing structural components such as large woody debris (LWD). Changes in these forests will cause modifications in the LWD input to streams, affecting their structure. In order to assess the influence of riparian forests changes in LWD supply, 15 catchments (third and fourth order) with riparian forests at different conservation levels were selected for sampling. In each catchment we quantified the abundance, volume and diameter of LWD in stream channels; the number, area and volume of pools formed by LWD and basal area and tree diameter of riparian forest. We found that riparian forests were at a secondary successional stage with predominantly young trees (diameter at breast height <10 cm) in all studied streams. Results showed that basal area and diameter of riparian forest differed between the stream groups (forested and non-forested), but tree density did not differ between groups. Differences were also observed in LWD abundance, volume, frequency of LWD pools with subunits and area and volume of LWD pools. LWD diameter, LWD that form pools diameter and frequency of LWD pools without subunits did not differ between stream groups. Regression analyses showed that LWD abundance and volume, and frequency of LWD pools (with and without subunits) were positively related with the proportion of riparian forest. LWD diameter was not correlated to riparian tree diameter. The frequency of LWD pools was correlated to the abundance and volume of LWD, but characteristics of these pools (area and volume) were not correlated to the diameter of LWD that formed the pools. These results show that alterations in riparian forest cause modifications in the LWD abundance and volume in the stream channel, affecting mainly the structural complexity of these ecosystems (reduction in the number and structural characteristics of LWD pools). Our results also demonstrate that riparian forest conservation actions must consider not only its extension, but also successional stage to guarantee the quantity and quality of LWD necessary to enable the structuring of stream channels.

Impacts of converting low-intensity pastureland to high-intensity bioenergy cropland on the water quality of tropical streams in Brazil.

In Brazil, the cultivation of bioenergy crops is expanding at an accelerated rate. Most of this expansion has occurred over low-intensity pasture and is considered sustainable because it does not involve deforestation of natural vegetation. However, the impacts on the water quality of headwater streams are poorly understood, especially with regard to the influence of land use patterns in the watershed. In this study, we investigated the effects of land-use conversion on the water quality of streams draining sugarcane fields and examined whether the preservation of forested areas at the top of the headwaters would help mitigate the negative impacts of intensive agriculture. Water samples were collected in two paired catchments in southeastern Brazil, which is one of the largest sugarcane production regions in the world. Our results show significant differences in the water quality of streams predominantly draining the pasture or the sugarcane field. Several parameters commonly used to indicate water quality, such as the concentrations of nitrate and suspended solids, were significantly higher in the sugarcane than in the pasture stream. Differences in water quality between the streams draining predominantly pasture or sugarcane fields were accentuated during the wet season. The preservation of forests surrounding the headwater streams was associated with overall better water quality conditions, such as lower nitrate concentrations and temperature of the stream water. We concluded that forest conservation in the headwater agricultural catchments is an important factor preventing water quality degradation in tropical streams. Therefore, we strongly recommend the preservation of robust riparian forests in the headwaters of tropical watersheds with intensive agriculture. More studies on the effects of best agricultural practices in bioenergy crops can greatly improve our capacity to prevent the degradation of water quality in the tropical waterways as intensive agriculture continues to expand in this region of the world.

A social and ecological assessment of tropical land uses at multiple scales: the Sustainable Amazon Network.

Science has a critical role to play in guiding more sustainable development trajectories. Here, we present the Sustainable Amazon Network (Rede Amazônia Sustentável, RAS): a multidisciplinary research initiative involving more than 30 partner organizations working to assess both social and ecological dimensions of land-use sustainability in eastern Brazilian Amazonia. The research approach adopted by RAS offers three advantages for addressing land-use sustainability problems: (i) the collection of synchronized and co-located ecological and socioeconomic data across broad gradients of past and present human use; (ii) a nested sampling design to aid comparison of ecological and socioeconomic conditions associated with different land uses across local, landscape and regional scales; and (iii) a strong engagement with a wide variety of actors and non-research institutions. Here, we elaborate on these key features, and identify the ways in which RAS can help in highlighting those problems in most urgent need of attention, and in guiding improvements in land-use sustainability in Amazonia and elsewhere in the tropics. We also discuss some of the practical lessons, limitations and realities faced during the development of the RAS initiative so far.

Past and present land use influences on tropical riparian zones: an isotopic assessment with implications for riparian forest width determination / Influências pretéritas e presentes do uso da terra sobre zonas ripárias tropicais: uma avaliação isotópica com implicações para a determinação da largura de florestas ripárias

Abstract In this article, by using carbon stable isotopes, we assessed the past and present land use influences that riparian areas are subject within agricultural landscapes. Emphasis is given to the understanding of the effects of the 2012 Brazilian Forest Act on such areas. We selected five riparian areas within a highly C4 dominated agricultural landscape. Three of them had 30 meters native riparian forest buffer (NRFB) and two of them had 8 meter and no NRFB. We used three 100 meter-transects located 5, 15 and 30 meters relative to stream channel to obtain soil samples (0 - 10 cm). All riparian areas presented soil carbon isotopic signatures that are not C3 (native forests) irrespective of having or not 30 meters NRFB. Two cases presenting less than 30 meters NRFB had higher C4 derived carbon contribution. All of the other three areas that followed the 30 meters NRFB presented, to some degree, C4 derived carbon, which was attributed to C4 organic matter deposition originated from cultivated areas and, in one case, to the persistence of former exotic grasses. With the 2012 Forest Act allowing narrower buffers (< 30 meters), we expect C4 contributions to soil organic matter to remain high in riparian areas and streams within agricultural landscapes dominated by C4 plants where 30 meter NRFB is no longer required. Such contributions will likely continue to have detrimental effects on stream water quality and biota.

Resumo Neste artigo, ao utilizar isótopos estáveis de carbono, nós avaliamos as influências presentes e pretéritas do uso da terra a que as áreas ripárias estão sujeitas quando situadas dentro de paisagens agrícolas. Ênfase é dada ao entendimento dos efeitos do Código Florestal de 2012 em tais áreas. Nós selecionamos cinco áreas ripárias em uma paisagem agrícola altamente dominada por plantas C4. Três delas apresentam faixa ripária de floresta nativa (FRFN) de 30 metros de largura e as outras duas apresentam FRFN de 8 e 0 m (i.e. sem FRFN). Nós utilizamos três transectos de 100 metros localizados a 5, 15 e 30 metros de distância do canal fluvial para obter amostras de solo (0 - 10 cm). Todas as áreas ripárias apresentaram assinaturas isotópicas do carbono do solo que não são C3 (floresta nativa) independentemente de apresentarem ou não FRFN de 30 metros. Os dois casos em que FRFN era menor que 30 m apresentaram maior contribuição de carbono oriundo de plantas C4. Todas as outras três áreas com FRFN de 30 m também apresentaram, em algum grau, carbono oriundo de plantas C4. Todas as outras três áreas com FRFN de 30 m também apresentaram, em algum grau, carbono oriundo de plantas C4 que foi atribuído è deposição de matéria orgânica de plantas C4 originada das áreas cultivadas e, em um caso, è persistência de gramíneas exóticas pré-existentes. Com o Código Florestal de 2012 permitindo FRFN mais estreitas (< 30 metros), nós esperamos que a contribuição de plantas C4 para a matéria orgânica permaneça alta em áreas ripárias e rios dentro de paisagens agrícolas dominadas por plantas C4 onde a FRFN de 30 m não é mais uma obrigação. Tais contribuições irão, provavelmente, continuar a ter efeitos prejudiciais è qualidade de água dos rios e à sua biota.