Study Area
The Channel Islands have a coastal Mediterranean climate with rainy winters and dry summers and are made up of rocky coasts, grasslands, shrublands, and woody forests . The islands have historically been subject to disruption, principally by humans, through the introduction of livestock and other invasive animal and plant species. This in turn has heavily impacted native flora and fauna communities on the islands. Santa Cruz Island (250 km2, largest of the Channel Islands) and Santa Rosa Island (215 km2, second largest) are part of the northern Channel Island archipelago and separated by a 9.6 km wide channel. The two islands were once connected as a super island called Santarosae that was separated from the mainland until sea level rise separated them from one another approximately 10,000 years ago after the end of the Pleistocene epoch . Santa Cruz Island (SCZ) is characterized by two east-west mountain ranges that bound a central valley, and hosts a variety of habitat types including grassland, chaparral, coastal sage scrub, oak woodland, and pine forests . Santa Rosa Island (SRI) is characterized by a single mountain chain running east-west through the middle of the island, with relatively flat marine terraces bisected by canyons and dominated by grassland on the north side, and more rugged terrain dominated by sagebrush scrub on the south side. Small pockets of native island oak and pine woodland are present. Both islands support a number of similar habitat types; however, Santa Rosa Island is less rugged and less topographically and vegetatively diverse compared to Santa Cruz Island. Grazing livestock were removed from most of Santa Cruz Island by the late 1980s, while grazers persisted on Santa Rosa Island until 2011. Thus, the majority of Santa Cruz Island is further advanced in vegetative recovery than Santa Rosa Island.