Design and management of linkage areas across headwater drainages to conserve biodiversity in forest ecosystems

Biota in managed forest landscapes may be at risk from habitat fragmentation that prevents dispersal among subpopulations. Management provisions to provide connectivity are often considered independently for aquatic and terrestrial species. Of increasing concern is that dichotomous approaches are economically inefficient and may fragment populations that rely on both water and land. To provide habitat connectivity over ridgelines for such populations, which include many species of amphibians and arthropods, we propose designation of headwater “linkage areas.” Essentially, we propose that headwater ridgelines be managed as important “linkage areas” to retain forested areas for species dispersal. Our process of linkage area planning, as demonstrated for headwater streams in the Coast Range of Oregon, USA, includes considerations at three spatial scales: landscape, drainage basin, and forest stand. At the landscape scale, linking headwater drainages across 7th-code hydrologic units (HUs) is a practical design regarding landscape connectivity for headwater species. In the Coast Range, each 7th-code HU adjoins an average of six 7th-code HUs. If each of these were linked via extending buffers or alternative forest management practices, about 5000 linkage areas would be provided in the 2.3-million ha landscape. We propose that the layout of such links considers site-to-landscape scale factors including known locations of target species, existing protections, land ownership patterns, dispersal capability of species of concern, climate change predictions, and the natural disturbance regime, such as landslide prone areas for managing wood and sediment inputs to streams. Although the proposed linkage areas target sensitive headwater species by design, the resulting web of connection across the landscape can be expected to benefit a host of forest-dependent species.