Predictors of Microhabitat Frequency and Diversity in Mixed Mountain Forests in South-Western Germany

Abstract

Tree-related microhabitats are an important determinant of forest biodiversity. Habitat trees, which typically provide many microhabitats such as hollows, crown dead wood, etc., are therefore selected to maintain those structural attributes within managed forests. To what extent the occurrence of microhabitats on potential habitat trees may be predicted from common tree attributes is a question of high practical relevance. Until now, most studies have attempted to predict the quantity of microhabitats at the tree or forest stand level. In our study, we aimed at explaining microhabitat occurrence from a qualitative perspective by considering their diversity. Tree diameter at breast height (dbh), tree species, and canopy class were useful predictors of microhabitat diversity. Microhabitat diversity on broadleaved trees was on average higher than in conifers of the same diameter. In contrast to microhabitat quantity, microhabitat diversity saturated towards higher dbh levels. Microhabitat diversity in beech trees of lower tree canopy classes was found to be surprisingly high. Habitat trees support not only more, but also more diverse, microhabitats in comparison to crop trees. Considering these findings on microhabitat distribution, the selection of habitat trees within Central European mixed mountain forests can be significantly improved.

Nothing else matters? Tree characteristics have more effects than biogeoclimatic context on microhabitat diversity and occurrence: a nationwide analysis

“…woodpecker feeding holes or bark characteristics). Previous studies comparing microhabitat number between living and dead trees almost all found higher microhabitats numbers on dead trees (see [17]). However, this difference varied across studies, from 1.2x more microhabitats in Mediterranean forest [15], 2x more in five forests in France [12], to 4x more on habitat trees in south-western Germany [31].…”

“…Finally, our models assumed – unrealistically – microhabitat number to increase exponentially with diameter. Recent studies [17], as well as ecological theory (e.g. species-area relationship), tend to rather show a saturated (e.g.…”

“…[12,39]). Depending on the studies, for a comparable increase in tree diameter (from 50 to 100cm), number of tree microhabitats was roughly multiplied by two in several studies [12,16,17], but can be multiplied by four [31] up to five [11] in certain cases. Our results showed magnitudes below the lower end of this range (the multiplication coefficient ranged from 1.2 to 1.4).…”

“…The relationships between microhabitats and tree characteristics have nevertheless been demonstrated on a limited number of tree species involving only a maximum of a few thousand observations at the tree level (e.g. [10-12]), and within a limited biogeographical range (see case studies in Mediterranean forests [15], the French Pyrénées [11] or in Germany [16,17]). As a consequence, the question still remains whether the observed relationships between tree characteristics and microhabitats are idiosyncratic or not.…”

Legacy forest structure increases bird diversity and abundance in aging young forests

“…Literature suggests the large trees act as keystone habitat features (DeMars, Rosenberg, & Fontaine, 2010). The rough, corrugated bark, and multiple microhabitats, like small places of rot, of larger trees host insects, providing rich and abundant forage for birds of multiple guilds (Großmann, Schultze, Bauhus, & Pyttel, 2018;Kozák et al, 2018;Larrieu & Cabanettes, 2012). Studies have tied specifically bark-foraging bird species to large-diameter trees (Pennington & Blair, 2011;Whelan & Maina, 2005).…”