Avian responses to vegetation changes from post oak savanna restoration efforts in eastern Texas

Abstract

Once covering approximately 46 million hectares of the Midwestern United States extending from southern Wisconsin southward into Texas, canopy cover of oak savannas ranged from 10% to 70%, and were dominated by fire-resistant oak species such as bur oak Quercus macrocarpa and post oak Quercus stellata, with a well-developed, diverse herbaceous layer dominated by fire-adapted grasses and forbs. In response to the loss and degradation of oak savannas, associated wildlife populations have experienced long-term declines. For example, 70% of disturbance-dependent bird species in the United States have experienced declines, with most of these species being associated with grasslands, oak savannas, and open forest communities. Few studies have documented the success of restoration in post oak savanna systems in regard to breeding bird assemblages. Our objective was to quantify avian abundance, density, species richness, and assemblage structure under three site conditions (reference, restored, and partially restored [aka unrestored]) within post oak savannas at Gus Engeling Wildlife Management Area in eastern Texas. We conducted vegetation and avian transect surveys postrestoration (2016-2017) and compared our results with prerestoration baseline surveys conducted in 2009. Restoration initiated in 2010 was partially successful, with vegetation changes that closely resemble presettlement characteristics, with the appearance of obligate grassland species. Specifically, prerestoration, one dickcissel Spiza americana and no lark sparrows Chondestes grammacus were detected. By 2017, dickcissel density in the restored sites was similar to densities recorded on tallgrass prairie and other high-quality habitat in the southern portion of its range. Lark sparrows were also detected, but at low densities. We also observed the persistence and increase of several woodland and open woodland species over time. These patterns are likely attributed to the creation of a mosaic of microhabitats selected by these species, such as the persistence of mottes, as well as their increased edge-to-area ratios. Restoration sites that are larger in size and in closer proximity to other restored or remnant savannas should have a higher priority to increase their likelihood of recolonization by target species. Restoration efforts may still be successful in more isolated areas, such as Gus Engeling Wildlife Management Area, but conducting postrestoration monitoring will further elucidate site-specific restoration dynamics.