Effect of small-scale woodland clearing and thinning on vertebrate fauna in a largely intact tropical savanna mosaic

Abstract

Context.Habitat degradation and fragmentation of vegetation can transform and deplete local wildlife populations, and is a key threatening process globally. In northern Australian tropical savannas, clearing is relatively rare across the biome, although it is slowly intensifying as a result of increasing agricultural development. However, the terrestrial vertebrates in these largely intact landscapes are undergoing current population declines because of a variety of land-management changes, one of which is increasing land clearing; therefore, there is a need to understand the relative effect of small-scale land clearing the fauna.Aims. The present study examined the variation in abundance of birds, mammals and reptiles in intact, thinned and cleared Eucalyptus woodlands in a tropical savanna bioregion.Methods. The vertebrate fauna were sampled in 88 sites over two general geographic locations within the Desert Uplands in 2005 and 2006. Standardised 1-ha surveys were employed in a single vegetation type and across three treatments. As two discrete locations were examined, linear mixed models were used in the analysis.Key results. The fauna composition varied significantly across the intact, thinned and cleared sites. Bird species richness reduced from intact to thinned and cleared sites, and reptile richness and abundance declined in cleared sites, but was largely unaffected by thinning. Seventeen bird species recorded significant variation in abundance across the three vegetation structural types, with 12 most abundant in the intact sites. Mammals on the whole were recorded in very low abundances and in few sites. For reptiles, two were most abundant in thinned sites and three in intact sites.Conclusions. In the present study, we have demonstrated that small-scale clearing and vegetation manipulation via thinning, even within largely intact tropical savanna woodland, can cause localised depletion of some species, although most notably where the vegetation disruption was most severe (i.e. clearing). Birds are most affected, and many species that declined in abundance are the same as those that suffered severe population reductions as a result of broad-scale clearing in south-eastern Australia.Implications. The proposed increase in the intensity of agricultural land use in northern Australia will result in incremental landscape change as a result of clearing. Understanding how the gradual reduction of vegetation cover and habitat will change the faun assemblage is important for pre-emptive conservation planning. This is vital to avoid the mistakes of extensive landscape change in southern Australia that has left a legacy of a permanently depleted fauna.

The hegemony of the ‘despots’: the control of avifaunas over vast continental areas

“…In the tropical and subtropical region of the distribution of the yellow‐throated miner, spatial and temporal changes in woody and ground vegetation (Price et al ., ), small‐scale clearing (Kutt et al ., ) and over‐grazing by domestic cattle (Ward & Kutt, ) have been linked to negative changes in the abundance and richness of bird assemblages. There is some evidence of increases in the abundance of the yellow‐throated miner in response to land‐use change (Kutt & Fisher, ), small‐scale peri‐urban fragmentation (Rankmore & Price, ) and that increased abundances of the yellow‐throated miner affect small passerine species (Kutt et al ., ), but there have been no explicit links between the land‐use change, increase in the abundance of the yellow‐throated miner and concomitant decline in other species until current study.…”

“…These four observers had mutually standardized their bird observation techniques in several studies (e.g. Kutt et al ., ,b; Perry et al ., ). Each observer had > 15 years of experience in bird surveys.…”

Long term thinning and logging in Australian cypress pine forest: Changes in habitat attributes and response of fauna

“…C. pectoralis), on the other hand, were much less abundant in thinned and unlogged stands, and appeared to prefer habitat with increased cover from tall shrubs and litter cover, as typical of unthinned/unlogged sites and thinned/logged sites. Shading from dense vegetation cover can reduce thermoregulatory options for small terrestrial skinks (Valentine, 2006), but also provides protection from predation (Martín and Lopez, 2002;Kutt et al, 2012a), and leaf litter provides thermal heterogeneity and refuge from predation (Singh et al, 2002;Valentine et al, 2007;Andersson et al, 2010). In our study area, the combination of habitat features in the unthinned/unlogged and thinned/logged sites must provide optimal thermoregulatory, anti-predation and foraging options for small terrestrial skinks.…”

“…However, the interaction between both management activities influenced assemblages and the abundance of terrestrial reptiles in particular; responses reflecting the variation in the thermal environment due to changed vegetation cover (Kutt et al, 2012a). Increased canopy cover from large cypress trees but low tall shrub and litter cover characterised habitat of thinned and unlogged sites preferred by larger terrestrial skinks (e.g.…”

Vulnerability of Australian tropical savanna birds to climate change

“…Further detailed analyses of extinction risk require understanding of the full range of extrinsic threatening processes and how these currently interact to impact species (Kutt & Fisher ; Kutt et al . 2012b,c). The combination of high vulnerability to climate change and high exposure to extrinsic threats will likely determine their long‐term persistence (Kutt et al .…”