Tree cavities and cavity users in two caldén forests of Argentina managed as a protected area or for cattle ranching

Animal populations that require tree cavities can be either limited or structured depending on the quality and availability of tree cavities in their ecosystems. Over the last century, the Caldén forest of Argentina has experienced severe habitat degradation due to anthropogenic activities. Here, we report the density and characteristics of cavities and their vertebrate users in areas of the Caldén forest with two different types of management: a protected area and an area with cattle ranching. The average density of cavities was 16.1 cavities/ha. However, the reserve's cavity density was four times higher than the ranch's (19.5 vs. 5.8 cavities/ha). The characteristics of the cavities and their support trees showed significant variations, but they were generally similar between sites. Forty-four vertebrate species use or may use tree cavities. The proportion of recorded species using cavities in the reserve was higher (30/41 vs. 6/32; p < 0.01). While most cavity users in the semi-arid forest are not threatened, this ecosystem has been dramatically fragmented, with only 11% of its original area remaining. If anthropogenic activities continue to alter this fragile ecosystem, it is possible that in the future, many species, including tree cavity nesters, will suffer a decline in their populations.