Availability of tree cavities in a sal forest of Nepal

Tree cavities are important structural elements of forest ecosystem that host numerous birds, mammals and other cavity-dependent organisms. Pattern of cavity distribution in temperate and boreal forests are relatively well studied, yet little is known about cavities in tropical and subtropical forests. We compared cavity availability in relation to tree condition (living tree and snag), tree species and DBH class between two different sites in a subtropical deciduous sal forest in Nepal: the Chitwan National Park Forest (the park site) and the Khorsor Buffer Zone Forest (the buffer site). Surveys for tree cavities were conducted in 2013 on 50 circular sample plots of size 0.1 ha. We recorded 40 cavity trees in the park site and 31 cavity trees in the buffer site. Density of cavities was on average 22.4 ha-1 in the park site and 19.2 ha-1 in the buffer site. Cavities occurred mostly in living trees (85.9% cavity trees) and were formed mostly by damage and decay (natural cavities: 74%) or by woodpecker activity (excavated cavities: 26%). Most were observed on three tree species: Shorea robusta, Dillenia pentagyna and Syzygium operculatum, with a mean diameter of 43 cm (range: 12-111 cm). S. operculatum, Myrsine semiserrata and Semecarpus anacardium were overrepresented among tree species with cavities. In snags, 25.0% of all cavities were found in the park site and 8.3% in the buffer site, while snags represented 4.2% and 2.2% of all trees in the two sites, respectively. Statistical anaysis indicated that tree species, tree condition and particularly diameter (DBH) were important variables for the prediction of cavity presence. We recommend cavity-bearing tree species to be better protected by forest management in order to help maintain the community of cavity dwellers