The three-toed woodpecker: an important biodiversity indicator and model species for the conservation of biodiversity in boreal forests.

Abstract

The use of biodiversity indicators have been proposed as a comprehensive method for assessing conservation values at the stand scale. In the boreal biome, the three-toed woodpecker have been proposed as an indicator for high species richness of co-occurring forest birds. However, to be able to fully understand the potential of biodiversity indicators it is necessary to understand when indicators are valid indicators, as natural dynamics within boreal forest systems can effect bird communities and thus indicator values of species. To assess the impact of natural disturbances we collected data within a large-scale field experiment where we assessed the short term (4-5 years) impact of two restoration treatments mimicking natural disturbances − prescribed burning (n=10) and gap cutting (n=10), using continuous cover stands (n=20) as references − on boreal breeding bird assemblages. We performed detailed bird inventories, through territory mapping and additionally we collected data of local stand characteristics. In this study, we confirmed that the three-toed woodpecker belong to the best indicators of high species richness and abundance within resident forest birds occurring in middle and northern boreal forests. However, the three-toed woodpecker lost its indicator value after prescribed burning; in these stands the goldcrest was the best biodiversity indicator. Based on habitat associations we found that the three-toed woodpeckers is closely associated with structural complexity within forest stands, similar to co-occurring species. Thus structural complexity at such may influence species richness. Still the three-toed woodpecker can be used for conservation planning if their habitats/resource requirements are set as quantitative targets. To accommodate managers with management recommendation regarding these quantitative targets, we quantified refined habitat thresholds and related this with their foraging substrate selection. We found resource requirement thresholds by a 0.9 probability of occurrence of 1.5 m2/ha freshly dead spruce and 0.07 m2/ha dying spruce. By focal bird observations we were able to confirm that indeed modeled resources matched with important foraging substrates for three-toed woodpecker in mature forest areas. This suggest that proposed resource thresholds can be used to plan forest management concerning three-toed woodpeckers population. However, we need to consider additional habitat structures when we planning forest management aiming to conserve biodiversity.