Tree cavities in riverine forests: What determines their occurrence and use by hole-nesting passerines? |
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| Institution: | 1. Institute of Zoology and Hydrobiology, Centre of Basic and Applied Ecology, University of Tartu, Vanemuise 46, EE-51014 Tartu, Estonia;2. Institute of Geography, University of Tartu, Vanemuise 46, EE-51014 Tartu, Estonia;1. Department of Biological Sciences, Virginia Tech, 1405 Perry Street, 2125 Derring Hall, Blacksburg, VA 24061, USA;2. Department of Medical Microbiology & Immunology, University of Wisconsin-Madison, 1550 Linden Drive, Madison, WI 53706, USA;3. US Forest Service, Center for Forest Mycology Research, One Gifford Pinchot Drive, Madison, WI 53726, USA;1. Chair for Landscape Management, Institute of Earth and Environmental Sciences, Faculty of Environment and Natural Resources, University of Freiburg, Tennenbacher Str. 4, 79106 Freiburg, Germany;2. Department of Environmental Planning, Landscape Ecology and Nature Conservation, Environmental Protection Agency, City of Freiburg, Talstr. 4, 79102 Freiburg, Germany;1. INRA, UMR1201 DYNAFOR, Chemin de Borde Rouge, Auzeville, CS 52627, 31326 Castanet Tolosan Cedex, France;2. CNPF/IDF, Antenne de Toulouse, 7 chemin de la Lacade, 31320 Auzeville Tolosane, France;3. Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Zürcherstrasse 111, 8903 Birmensdorf, Switzerland;4. Irstea, UR EFNO, Domaine des Barres, 45290 Nogent-sur-Vernisson, France;5. Technische Universität Dresden, Pienner Str. 8, 01737 Tharandt, Germany;1. Instituto de Bio y Geociencias del NOA (IBIGEO-CONICET-UNSa), Av. 9 de Julio 14, Rosario de Lerma, Salta 4405, Argentina;2. Centre for Applied Conservation Research, Department of Forest and Conservation Sciences, University of British Columbia, 2424 Main Mall, Vancouver, BC V6T 1Z4, Canada;3. Proyecto Selva de Pino Paraná, Vélez Sarsfield y San Jurjo S/N, San Pedro, Misiones 3352, Argentina;4. Environment and Climate Change Canada, 5421 Robertson Road, RR1, Delta, BC V4K 3N2, Canada |
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| Abstract: | We assessed: (1) the relative importance of different macro- and microhabitat characteristics for explaining the occurrence of tree cavities and their occupancy by hole-nesting passerines and (2) the role of woodpeckers as keystone species in riverine aspen and birch stands in central Estonia. In 1999–2003, multiple surveys were carried out in 16 stands with a total area of 104 ha. Of the 713 tree-holes found, 483 were considered suitable for secondary cavity-nesters. The mean density was 4.1 ± 3.0 (S.D.) suitable cavities ha−1 (including 2.0 ± 1.3 suitable for hole-nesting passerines). Woodpeckers had excavated 88% of suitable cavities. The density of breeding woodpeckers explained 78% of variance in the density of woodpecker-excavated cavities (mean = 28 holes per pair) and 51% of natural cavities. Woodpecker-excavated and natural cavities occurred in very similar conditions, determined mostly by tree species, decay and size, stand type, as well as the vicinity of other cavities. Ninety-six of 161 occupancy cases of cavities were by passerines, which – probably to reduce the risk of nest predation or physical destruction – preferred small natural cavities in live trees. We conclude that riverine areas are important centres of cavity supply in forested regions and the value of woodpeckers as keystone species comes mostly from the large quantity, but not quality, of the cavities they provide. The results imply that: (1) for cavity-nesters, large (DBH > 30 cm) broadleaved trees, both live and dead, are the most important to retain during forestry operations in hemiboreal riverine forests and (2) woodpecker censuses may indicate cavity abundance, particularly if woodpecker-holes dominate among all cavities. |
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