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Woodpeckers are important species in forest ecosystems because they make tree cavities that are microhabitats for several other taxa. However, even in boreal areas where most tree cavities are made by woodpeckers, the properties of woodpeckers' nest trees and cavities are poorly known. We studied nest tree characteristics of the Grey-headed Woodpecker (Picus canus) in a 170-km2 forest-dominated area in southern Finland during 1987-2019. The data included 76 nest trees with 80 nest cavities in five different tree species. During the study period, 44% of all nesting attempts were in old cavities. Nestswere found in four forest types, but the proportions ofnest tree species differed between them. In all, aspen (Populus tremula) with 70% ofnest trees, and with 71% ofnest cavities was the dominant cavity tree species. Mostnesttrees (85%) were dead or decaying, and most cavities (70%) were excavatedat visible trunk injury spots. The mean diameterofanest tree atbreastheight(DBH)was 37.2 cm and the meanheightofacavityhole was 7.8 m; these were significantly positively correlated. The results highlight the importance of large aspens as nest cavity sites for the species. Conservation and retention of group s of large aspens in main habitats, including clear-cuts, are important for continuous availability of nest trees. This applies particularly to managed boreal forest landscapes where scarcity of suitable trees may be a limiting factor for the species. [ABSTRACT FROM AUTHOR]

Tree cavities, and especially cavities made by woodpeckers, are important microhabitats in forest ecosystems. However, the properties of woodpecker nest trees and cavities are poorly known even in boreal areas wheremost tree cavities aremade by woodpeckers. We studied the nest tree characteristics of the Lesser SpottedWoodpecker (Dendrocopos minor) in a 170-km² forest-dominated area in southern Finland during 1987-2018. The data included 97 nest trees with 106 nest cavities in five deciduous tree species. During the study period, more than one nest cavity (2-3) was excavated in 7% of all cavity trees. Nestswere found in three forest types, but the proportions of nest tree species differed between them. Birch (Betula spp.) was the most common nest tree species with 40% of nests. Nest trees were either dead (79%) or decaying (21%), and themajority (69%) had a broken top. Themean diameter at breast height (DBH) of a nest tree was 24.7 cmand the mean height of a cavity hole was 3.3m; size and height were significantly positively correlated. The mean ratio of cavity height in relation to the respective nest tree height was 0.49, and did not depend on the nest tree condition. The results highlight the importance of dead and decaying deciduous trees as nest cavity sites for this small woodpecker species. Provision of suitable cavity trees during forestmanagement is important tomaintain breeding and cavity building opportunities for theLesser SpottedWoodpecker inmanaged forests. [ABSTRACT FROM AUTHOR]

The Three-toed Woodpecker Picoides tridactylus is a mature and old-growth forest specialist but how the species uses trees for nesting in its breeding sites and whether cavity trees are a critical habitat feature is poorly known. We studied the nest tree characteristics of the species in a 170-km2 area in southern Finland during 1987-2016. The data included 538 nest trees of eight different species and 665 nest cavities in 86 territory areas. Norway spruce Picea abies was the predominant nest tree comprising 71% of all nest trees. portionally, deciduous nest trees were more common in moist forests on mineral soils and conifer nest trees more common in spruce swamps. The majority of nest trees (85%) were dead or decaying trees; higher numbers of dead deciduous nest trees were recorded than dead conifer trees. The mean diameter of a nest tree at diameter at breast height (DBH) was 29.4 cm and the mean height of a cavity hole was 5.1m; size and height were signifi-cantly positively correlated. The proportion of deciduous nest trees was significantly higher (45%) in natural forests compared with other areas subjected to variable amounts of forest management, where the respective proportion was only 9-17%. In addition, cavity holes were significantly higher in natural forests than in managed ones. In general, the results highlight the substantial flexibility in nest tree use but also the importance of large dead and decaying trees (including deciduous trees) as nest cavity sites for the species. Spruce swamps can be considered as key nesting habitats in managed forest landscapes. [ABSTRACT FROM AUTHOR]