Understory specialists in southern Chile

The simplification of forest structural complexity, caused by
anthropogenic land-use practices, is one of the main threats to understory
specialist birds. We examined the association of both single structural
attributes and structural complexity, with the density of four understory
bird species in the Global Biodiversity Hotspot “Chilean Winter
Rainfall-Valdivian Forests” of South America. Between 2011 and 2013, we
surveyed habitat attributes and conducted bird point counts in 505 plots
in Andean temperate ecosystems in Chile. In each habitat plot, we measured
understory density, volume of coarse woody debris (CWD), number of snags,
diameter at breast height (DBH) of trees, and leaf litter depth. With
these attributes, we developed an index of stand structural complexity
(ISC). On average, old-growth forests had higher values ​​for understory
density, CWD volume, DBH, and litter depth than secondary forests and open
fields, and thus greater values of ISC. The density of understory birds
was positively correlated with the ISC for the Rhinocryptidae Pteroptochos
tarnii, Scelorchilus rubecula, and Scytalopus magellanicus. We also found
a positive association between understory density and litter depth, with
the density of the Furnariidae Sylviorthorhynchus desmursii. However, this
latter species showed a negative association with the density of snags.
Our results suggest the utility of using an index of structural
complexity, rather than single or even additive habitat attributes, for
determining the density of understory specialist birds. We recommend that
management plans should promote the retention of habitat attributes that
contribute to the structural complexity of temperate forests of South
America and beyond.