Are bird density, species richness and community structure similar between native woodlands and non-native plantations in an area with a generalist bird fauna?

Abstract

This study compared the bird assemblages of native semi-natural woodlands and non-native Sitka spruce (Picea sitchensis) plantations in Ireland to identify what vegetation variables most influenced birds and to identify management targets in plantations to maximise future bird conservation. Point counts were conducted in 10 Oak (Quercus spp.) and 10 Ash (Fraxinus excelsior) native woodlands and in five Mid-rotation (20-30 years old) and five Mature (30-50 years old) Sitka spruce plantations. Ordination was used to characterise woodland types according to their constituent bird species. Total bird density (calculated using Distance software) and species richness were assessed for the different woodland types. Oak and Ash woodland bird assemblages were separated from Mid-rotation and Mature plantations by the ordination. There was no difference in total bird density between any of the woodland types. Oak woodlands had significantly higher species richness than either Mid-rotation or Mature Sitka spruce plantations. Ash had higher species richness than Mature Sitka spruce plantations. Understorey vegetation was negatively associated with total bird density, which also varied with survey year. Understorey vegetation was positively associated with species richness. Reasons for the relationships between vegetation and bird assemblages are discussed. Management should seek to increase shrub and understorey vegetation in the Mid-rotation phase to improve the contribution of plantations to bird conservation.

The value of plantation forests for plant, invertebrate and bird diversity and the potential for cross-taxon surrogacy

“…The understory of conifer plantations is typically less structurally complex than in natural woodlands (Aubin et al 2008) where higher light levels can contribute to increased plant diversity and understory structure (Riegel et al 1995). This, in turn, is important for the diversity of many species, particularly invertebrates and birds (Hardtle et al 2003;Messier et al 1998;Sweeney et al 2010;Purchart et al 2013). For many taxa in the current study species richness values in Norway spruce-dominated commercial plantations showed greater similarities to those of native woodlands than those in Sitka spruce-dominated forest plantations.…”

“…The lack of forest specialist beetles in Ireland may be the reason for this lack of distinction. For birds there was clear separation between native woodlands and spruce plantations, which was probably related to the lower structural diversity of plantations, as well as differences in the diet preferences of certain species (Sweeney et al 2010). …”

“…However, in countries where the extent of naturally occurring forests is limited, plantation forests may provide habitat for forest associated species and enhance overall landscape biodiversity, (Stephens and Wagner 2007;Brockerhoff et al 2008;Pawson et al 2008;Sweeney et al 2010;Coote et al 2012). Several studies have also suggested that plantation forests have the potential to benefit native diversity even where the planted tree species are nonnative conifer species (Bremer and Farley 2010;O'Hanlon and Harrrington 2012;Humphrey 2005).…”

Influences of forest type and habitat structure on bird assemblages of oak (Quercus spp.) and pine (Pinus spp.) stands in southwestern Turkey

“…Managed plantations, especially those comprising exotic tree species, are usually considered less hospitable for most forest organisms (Hartley, 2002). Sweeney et al, (2010a) suggested that the differences in bird species richness demonstrated between native broadleaved forests and exotic conifer plantations could be explained by a lower carrying capacity of conifer plantations. In the case of southwestern Turkey, where both pine and oak stands are native in origin but have been influenced by different management regimes, these differences -if at all present -do not seem to be prominent.…”

“…Managed stands of broadleaved and coniferous trees located in the same region have been found to support different assemblages of bird species (e.g. Díaz, 2006;Sweeney et al, 2010a), potentially reflecting differences in resource distribution. To what degree any of these factors explain differences in bird richness and species composition is poorly studied, particularly in the eastern Mediterranean basin, but constitutes a key aspect for successful management of forest stands.…”