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Cavities made by birds are an important microhabitat for many taxa in forests. Long-term dynamics of cavity patterns and the effect of forest management on cavities are, however, largely unknown. We studied cavity production, measured as nest cavity production rates (CPR = no. of new cavities/km2/year), of woodpeckers and tits in forests with different management intensity in southern Finland, based on a data from 37 years. Forests were divided into managed, seminatural and natural stands. The data covered 56 forest stands with the total area of 1690 ha. Stands were inventoried annually for new cavities. The total numbers of woodpecker and tit cavities were 2238 and 329, respectively. There were large differences in CPRs between forest stands with different management intensity. For woodpeckers, the CPR was highest in natural forests (5.7) and lowest in managed forests (1.5). For the tit species, the respective numbers were 0.9 and 0.3. The CPRs of different cavity-making bird species and cavity tree characteristics (e.g. tree condition and species) were consistent, suggesting that different cavity-makers benefit from similar forest and tree characteristics. The results also suggest that forests managed with currently prevailing methods limit the production of cavities. To promote cavities, the results from this and other studies suggest that managed forests should include more features of natural forests, such as more diverse tree species and within-stand structural variability distribution (tree-level heterogeneity), larger amount of decayed wood, more retention trees and snags and longer rotation periods. [ABSTRACT FROM AUTHOR]

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]

• Cavities had a median persistence time of 10 years. • Persistence of a cavity depended on both tree- and stand-level factors. • Cavities persisted longest in the largest trees, except in European aspens. • Cavities persisted longer in healthy and weakened, living trees than in dead trees. • There was significant spatial variation in the risk of cavity persistence. Tree cavities are microhabitats used by multiple taxa and are considered indicators of forest biodiversity. The factors that affect cavity occurrence and its dynamics are poorly known. We studied tree- and stand-level factors that affect cavity persistence in boreal forests. Cavities of Eurasian Three-toed Woodpeckers (Picoides tridactylus) (n = 654) were surveyed in a 170 km2 area in southern Finland for 31 years during 1987–2017. In total, 447 cavities were lost during the study period: 329 to tree fall or breakage, 72 to cavity damage, and 46 to logging. With the Kaplan-Meier method and Cox proportional hazards models, we analysed which tree- and stand-level factors affected the risk of a cavity to be damaged or lost due to tree fall. The median lifespan of cavities was 10 years, and both tree- and stand-level factors affected the persistence of cavities. Cavities in managed forest areas with low territory occupancy rates were more at risk of tree fall and cavity damage than in other types of forest areas. In all nest tree species, with the exception of European aspen (Populus tremula), the risk of cavity loss to tree fall declined with increasing tree diameter. Moreover, the risk of cavity loss to tree fall was higher in dead trees than in healthy and weakened trees. Cavities in deciduous tree species other than aspen were more at risk of damage than in other tree species. Furthermore, the risk of cavity damage was greater in cavities located lower in a tree. This study showed that factors like the tree species, and size and condition of a tree modify the persistence of woodpecker-made cavities. Consequently, it is likely that these factors influence the value of cavities as microhabitats and how these cavities can be used as indicators of forest biodiversity. Understanding the dynamics of cavities in forest habitats appears critical for the use of cavities as general biodiversity indicators. [ABSTRACT FROM AUTHOR]