Experimental habitat restoration for conserved species using ecosystem engineers and vegetation management

We experimentally address the theoretical potential for managing ecosystem engineer species to support suites of species in degraded habitats. Historically, the ecosystem engineer California ground squirrel Otospermophilus beecheyi supported a grassland food web through widespread burrowing activity. Currently, ground squirrels are not a threatened species, but like many other ecosystem engineers, they exist at densities too low to fulfill their engineering role in many locations. Our objective was to implement short-term treatments, including squirrel translocation, to re-establish key ecological processes on protected reserve lands. We manipulated vegetation and squirrels in a replicated, large-scale field experiment for 2 years, and monitored through a third year. Vegetation mowing and soil decompaction treatments reduced grass density and thatch depth. Squirrel translocation accelerated squirrel settlement and activity in target sites. Of the more than 1000 burrow entrances remaining through the third year, nearly all burrows were concentrated in the plots that received squirrel translocation. We found significant additive effects of squirrel translocation and vegetation management on the spatial footprint of squirrel activity. Noteworthy and persistent engineering effects were achieved through squirrel activity, and both vegetation management and squirrel re-establishment were needed to stimulate squirrel activity. The overarching goal of this experiment was to provide conservation managers with a cost-effective tool for restoring degraded habitats to a hybrid ecosystem state with improved suitability for species of conservation concern, in this case, the western burrowing owl Athene cunicularia hypugaea.