Arboreal elements of the agricultural matrix as structural connecting devices in fragmented landscapes – A case study in the Los Tuxtlas Biosphere Reserve

Abstract

Agriculture is one of the main drivers of deforestation worldwide, generating highly fragmented landscapes that severely limit the mobility of forest species. Knowledge of the state of previously forested landscapes, taking into account all of its arboreal elements (including isolated trees, living fences, riparian corridors, and others) is a necessary first step to gaining a better understanding of the ecological dynamics of anthropic landscapes, and for designing conservation and management plans that enhance functional connectivity within these landscapes. We used high-resolution images (2.5 m/pixel) to identify all of the arboreal elements—from single tree crowns up to large forest fragments—for 40,000 ha of the Los Tuxtlas Biosphere Reserve. We included isolated trees, usually ignored in most inventories of fragmented landscapes, but which together with the other arboreal elements play an important role as landscape connectors and extra habitat for many species. Using a graph theory approach, we assessed landscape connectivity at six inter-patch distances across open areas (from 50 to 500 m), and propose two strategies for improving landscape connectivity: the creation of woodland islets and the widening of forested riparian corridors in the agricultural matrix. The main arboreal elements that influenced connectivity were old-growth forest fragments and widespread treed living fences, each increasing connectivity by up to 57% (depending on the threshold distance), while riparian corridors and isolated trees contributed 38% and 6%, respectively. Isolated trees in pastures substantially increased the number of effective connections at all distances (>85%). The GIS-simulated restoration proposals to establish circular woodland islets (10 m radius) in the middle of open agricultural areas increased connectivity by 26%, while widening riparian corridors by up to 10 m per riverside increased it by 11%. Increasing the number of arboreal elements within the agricultural matrix at key sites would enhance landscape connectivity considerably, benefiting the organisms that live in forest remnants in the study area without the need to stop agricultural activities.