The Amazon has lost almost 20% of its forest cover in the last 50 years. High levels of deforestation have left much of the area a patchwork of agriculture mixed with small, remnant forest patches. These forest patches contain numerous riparian corridors, which act to maintain overall landscape connectivity and safeguard critical water resources.
In a move that exacerbates the fragmentation, recent legislative changes in Brazil have relaxed a mandate requiring landowners to keep certain levels of riparian forests intact, resulting in a less connected landscape and a more open matrix. Given these changes, it’s important to know how remnant riparian corridors compare to more continuous riparian patches, and if these remnants are enough to support biodiversity in such an altered landscape.
A recent study in the heavily fragmented northern state of Mato Grasso looks at mammal use of riparian corridors within both intact and highly fragmented forests across a 16,000 km2 landscape that’s part of the Amazon’s “arc of deforestation.” The region has lost almost half of its original forest cover and includes a human-dominated matrix that consists primarily of extensively managed livestock pastures.
Camera traps captured over 4,000 records of 25 unique terrestrial mammal species and showed that there was high mammal community overlap between wide, high-quality riparian corridors in remnant forests and corridors in (relatively) continuous forests. Wider corridors also had higher species richness of forest specialists.
Increasingly isolated corridors were visited more frequently by species that are most tolerant of an open matrix, such as nine-banded armadillos and tapirs. This lack of connectivity between riparian habitats also favors non-forest species such as native capybaras. In addition, scale mattered for what conclusions can be drawn: corridor width was important for forest-dependent species at the scale of whole corridors, whereas forest degradation dominated the effects of forest width within corridors.
The overall message is that new legislation that permits narrower, more isolated riparian corridors will likely be insufficient to maintain high diversity for mammals, in part because of how lenient regulations are when it comes to environmental quality and integrity of preserved riparian fragments. Two management policies could be effective in helping riparian corridors remain functional: 1. promoting and maintaining wider corridors (at least 100m wide) and 2. minimizing disturbance from logging, cattle, wildfires, and hunting. With landscape-scale planning that aggressively preserves wide riparian corridors, landscape connectivity may still be maintained in the face of such large-scale destruction.
Zimbres, B., C. A. Peres, and R. B. Machado. 2017. Terrestrial mammal responses to habitat structure and quality of remnant riparian forests in and Amazonian cattle-ranching landscape. Biological Conservation 206: 283-292.