Forest fragmentation and edge effects from deforestation and selective logging in the Brazilian Amazon

Forest fragmentation results from deforestation and disturbance, with subsequent edge effects extending deep into remaining forest areas. No study has quantified the effects of both deforestation and selective logging, separately and combined, on forest fragmentation and edge effects over large regions. The main objectives of this study were to: (1) quantify the rates and extent of forest fragmentation from deforestation and logging within the Brazilian Amazon, and (2) contextualize the spatio-temporal dynamics of this forest fragmentation through a literature review of potential ecological repercussions of edge creation. Using GIS and remote sensing, we quantified forest fragmentation - defined as both increases in the forest edge-to-area ratio and number of forest fragments - and edge-effected forest occurring from these activities across more than 1.1 million km² of the Brazilian Amazon from 1999 to 2002. Annually, deforestation and logging generated ∼32,000 and 38,000 km of new forest edge while increasing the edge-to-area ratio of remaining forest by 0.14 and 0.15, respectively. Combined deforestation and logging increased the edge-to-area ratio of remaining forest by 65% over our study period, while generating 5539 and 3383 new forest fragments, respectively. Although we found that 90% of individual forest fragments were smaller than 4 km², we also found that 50% of the remaining intact forests were located in contiguous forest areas greater than 35,000 km². We then conducted a literature review documenting 146 edge effects and found that these penetrated to a median distance of 100 m, a distance encompassing 6.4% of all remaining forests in our study region in the year 2002, while 53% of forests were located within two km of an edge. Annually deforestation and logging increased the proportion of edge-forest by 0.8% and 3.1%, respectively. As a result of both activities, the total proportion of edge-forest increased by 2.6% per year, while the proportion within 100-m increased by 0.5%. Over our study period, deforestation resulted in an additional ∼3000 km² of edge-forest, whereas logging generated ∼20,000 km², as it extended deep into intact forest areas. These results show the large extent and rapid expansion of previously unquantified soft-edges throughout the Amazon and highlight the need for greater research into their ecological impacts.     

Soil quality degradation processes along a deforestation chronosequence in the Ziwuling area, China

Accelerated erosion caused by deforestation and soil degradation has become the primary factor limiting sustainable utilization of soil resources on the Loess Plateau of Northwestern China. We studied the physical, chemical, and microbiological processes of soil degradation along a chronosequence of deforestation in the Ziwuling area of northwestern Shaanxi province. The results indicated that soil wet aggregate stability, mean aggregate diameter decreased with years following deforestation. Accelerated erosion resulted in soil nutrient loss, and a decrease in soil enzyme activities including notable losses of total soil N, organic C, alkaline phosphatase activity, and invertase activity. During the early time period, the rates of total soil N, organic C, alkaline phosphatase activity, and invertase activity decreasing were rapid and gradually decreased with deforestation years. Increased use of nitrogen fertilizers made determination of soil quality based on measured NO₃–N and NH₄–N inconclusive. The differences in measured parameters between the topsoil and subsoil horizons decreased with time since deforestation, and we concluded that soil erosion was the primary process responsible for the degradation of measured soil physical, chemical, and microbiological properties.     

Using remote sensing to inform conservation status assessment: Estimates of recent deforestation rates on New Britain and the impacts upon endemic birds

Remote sensing is increasingly used by policy-makers and conservationists to identify conservation priorities and changes in land cover. This is particularly important in the biodiverse tropics, where there are often few field data. Conservation action is often directed towards areas containing globally threatened species, but there have been few attempts to improve assessments of species’ extinction risk through remote sensing. Here, in a novel approach we use deforestation estimates, measured through satellite imagery, to assess the conservation status of an entire endemic avifauna, based on IUCN Red List criteria. The island of New Britain, east of New Guinea, is of very high global conservation importance, and home to 37 endemic or restricted-range bird species. Analysis suggests 12% of forest cover was lost between 1989 and 2000, including over 20% of forest under 100 m altitude, with substantial areas cleared for commercial oil palm plantations. Application of the IUCN Red List criteria to these new data on area of remaining forest and rates of deforestation indicates that many species are more threatened than previously realised, with the total number of threatened or near threatened species increasing from 12 to 21. Thus, this study highlights the urgency of establishing and effectively managing protected areas in suitable lowland forests of New Britain. More broadly, it demonstrates another potential of remote sensing to assist strategic conservation decisions.     

Habitat fragmentation and the desiccation of forest canopies: A case study from eastern Amazonia

Across the deforestation frontier in eastern Amazonia, we examined the relationship between edge-related forest desiccation and deforestation patterns using remote-sensing techniques. Canopy-moisture levels were estimated over an eight-year period in three study sites that encompassed ∼100,000 km² in area. We found four main effects of deforestation on dry-season canopy desiccation. First, intact forests showed no detectable change in canopy water content whereas forests adjacent to clearings showed significant water loss. Second, the distance to which edge-related desiccation penetrated into forest interiors varied among landscapes with differing forest loss and fragmentation. In moderately fragmented landscapes (with 65% and 51% remaining forest cover), canopy desiccation extended 1-1.5 km into forest interiors, whereas in heavily fragmented landscapes (20% forest cover) desiccation penetrated up to 2.7 km into forests. Third, the magnitude of edge-related desiccation varied among landscapes with differing fragmentation. Moderately fragmented landscapes exhibited a greater magnitude of change in canopy-water loss over the first 1 km from an edge than did heavily fragmented landscapes. Finally, forest desiccation penetrated further into forests over time in the moderately fragmented landscapes, but not in the heavily fragmented landscape, where edge-related desiccation had evidently ‘saturated’ remaining forests. We conclude that protracted dry seasons will have far more serious effects on fragmented than intact rainforests, with the former becoming highly vulnerable to destructive fires. With ∼30,000 km of new forest edge being created annually in Brazilian Amazonia, these finding have serious implications for forest conservation.