Variation in the role of tree decay to promote cavity nester biodiversity in the World Wide Cavity Nest Web
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Date
2014
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Abstract
From a biodiversity perspective, much of the world is chronically short of tree decay, especiallyin human-influenced ecosystems. Yet over 1000 bird species globally depend on decay processesto form tree cavities to provide the critical nesting and roosting sites. Cavities can form slowlyover centuries with the presence of tree decay or physical processes or they may form relativelyquickly when avian excavators penetrate the outer sapwood and remove the decayed heartwood.We examine the role of tree decay dynamics in structuring cavity-using vertebrate communitiesin Nest Webs (i.e., interdependent assemblages of cavity consumers and/or producers instructured-nidic guilds) across continents in temperate and tropical systems in the Americas andAfrica. In the Nest Webs of North-America, woodpeckers function as keystone species as theyexcavate over 90% of the holes used by secondary cavity nesting (non-excavating) vertebrates.In South-America, 69-80% of secondary cavity nesters use cavities formed by decay or externaldamage, even when woodpeckers are present. The abundance and diversity of cavity-usingvertebrates is often positively associated with cavity availability that in turn depends on rates ofhole formation and persistence. To maintain biodiversity it is critical to understand the role oftree decay and excavators as structuring agents in wildlife communities. In North America, thisinvolves retaining the tree types and conditions (e.g., hard deciduous trees with soft spots ofdecay) that are suitable for woodpeckers to excavate. In forest ecosystems with decay-based nestwebs (South-America, Africa), it is important to retain a supply of large live trees with decayed branches and large and small dead-standing trees to maintain a diversity and abundance ofcavity-using birds.