1 December, 2023
by Nico Arcilla and Māris Strazds
An American migratory species that nests in temperate and boreal forests, Wilson’s Warbler (Cardellina pusilla) has declined by 57% since 1970. Photo by Dan Marks.
Most of the world’s natural forests are subject to logging operations, many of which are highly detrimental to forest birds and other wildlife, and demand for timber is expected to continue to grow. Europe has the highest proportion of the world’s forests dedicated to the production of wood and other commodities, and logging operations have also changed North American forests and bird communities. In recent decades, many European resident and American migratory bird species that nest in forests have exhibited population declines related to logging. We investigated relevant research to synthesize 10 principles of bird-friendly forestry that forest managers may apply to improve the bird conservation value of logged forests, which we briefly summarize below.
1. Practice Uneven-Aged Silviculture
Old-growth forests harbor high structural complexity and habitat heterogeneity that may be diminished by logging operations. By avoiding cutting all of the largest, most valuable trees in a single rotation, foresters can practice uneven-aged silviculture, allowing forests to maintain a full range of development stages after logging, including old-growth trees.
A European forest resident that nests in tree cavities, the Crested Tit (Lophophanes cristatus), has declined by 53% since 1980. Photo by Nils-Fredrik Nilsson.
2. Leave Dead and Dying Trees
Large snags (standing dead or dying trees) and coarse woody debris (fallen dead or dying trees and tree remnants) provide important habitat features and food resources for many birds. Historically, standing dead wood in unlogged European forests could comprise 20–50% of standing trees. Avoiding disturbance to standing and fallen dead wood may allow a higher proportion of resident species to persist. For example, an increase in standing dead wood to 3.2% of the total standing trees in Swiss forests was correlated with an increase in Middle Spotted Woodpeckers (Dendrocopos medius).
3. Maintain Residual Large, Green Trees
Retaining large (> 55 cm dbh) mature trees in production forests improves habitat for arthropods and birds in regenerating stands. Conserving legacy trees and allowing regeneration of longer-lived species partially emulates the natural successional pattern following logging operations. For example, most Black Storks (Ciconia nigra) nest in trees that are over twice as old as the age when most trees of their species are logged (41–101 years). Particular tree species, such as large oaks (Quercus spp.), may be important for particular bird species, such as jays and woodpeckers.
Migratory birds that depend on large, mature trees for nesting in Europe, the Black Stork (Ciconia nigra) has been extirpated from Scandinavia and is now critically endangered in Latvia. Photo by Māris Maskalāns.
4. Establish and Maintain Uncut Reserves and Corridors
Old-growth stands serve as crucial breeding, nesting, and foraging habitat for many bird taxa, including woodpeckers, raptors, storks, and grouse, with larger reserves benefiting more species. Leaving uncut reserves for species that prefer or require mature, closed-canopy forests provides a refuge from logging operations and mitigates the landscape-scale effects of logging on birds. These and other forest protected areas play an essential role in conservation, and many forest-nesting birds appear better able to adapt to changing climatic conditions in protected areas than outside them.
5. Maximize Forest Interior through Retaining Large Contiguous Forest Tracts
Forest interior species tend to increase in abundance at distances greater than 200–400 m from forest edge. Maintaining large areas of contiguous forest increases the amount of forest interior and mitigates the effects of forest fragmentation. In Germany’s Black Forest, bird species richness and diversity in 1 ha forest patches increased with increasing proximity to other forest patches, highlighting the importance that landscape configuration has for bird conservation.
A European forest resident that is negatively affected by logging operations, the Lesser Spotted Woodpecker (Dryobates minor) has declined by 80% in boreal forests since 1980. Photo by Nico Arcilla.
6. Maintain Buffers around Streams, Rivers, Wetlands, and Known Nesting Areas
Many forest breeding species require riparian buffers in order to nest successfully, and foresters can allow them to do so by maintaining such buffers where logging operations take place. Buffer sizes will depend on the conservation needs of focal species. For example, Louisiana Waterthrush (Parkesia motacilla), Neotropical migratory birds that nest in southeastern forests of the United States, require > 40 m buffers of closed-canopy forest along contiguous > 1.5 km stream networks to breed successfully.
7. Maintain Horizontal Stand Structure and Enhance Vegetation Diversity in Canopy Gaps
Bird species richness, diversity, and abundance benefit from natural disturbances that create light gaps, which are associated with higher species richness, diversity, and breeding bird abundance compared with closed forests. Silvicultural practices that create small gaps appear to benefit many forest species without negatively influencing others, and can be used to enhance forest composition and structure.
8. Extend the Temporal Scale of Logging Cycles through Prolonged Rotations
Increasing the cutting age of retention trees benefits many bird species, particularly those that require mature trees for nesting and foraging. For example, Black Storks in Latvia would benefit from extending logging rotation periods of mature trees used for nesting, as well as surrounding forest within at least 500 m of nesting trees.
An American migratory species that requires mature temperate and boreal forests for nesting, Townsend’s Warbler (Setophaga townsendi) has declined by 15% since 1970 in North America. Photo by Dan Marks.
9. Minimize Disturbance to Forests after Logging and during the Breeding Season
Whereas natural disturbances such as forest fires are typically followed by ecological succession without human disturbance, logging operations may be followed by high intensity of human activities, such as uncontrolled hunting, that drive declines in bird populations that could otherwise recover over time. Protecting forests from detrimental human activities and avoiding logging during the main bird breeding season can reduce negative impacts, including allowing nesting birds to successfully fledge young. For example, forest landowners in Finland have voluntarily avoided logging during the bird breeding season to protect nesting raptors including European Honey Buzzards (Pernis apivorus), Common Buzzards (Buteo buteo), and Northern Goshawks (Accipiter gentilis).
10. Manage for Focal Species and Guilds
Conservation strategies should focus on birds that decline in response to logging, including many ground-nesting, cavity-nesting, canopy-nesting, predatory, and insectivorous species, such as many gamebirds, raptors, woodpeckers, hornbills, and songbirds, among others. Forest management plans targeting conservation priority focal species or guilds would be expected to benefit many other bird taxa with similar life histories.
Conclusion
Any or all of the principles we present here may serve as a starting point toward developing bird-friendly forest management plans. To improve the bird conservation value of production forests, conservation strategies and focal species must be area-specific, clearly articulated, and have measurable objectives. In this way, bird-friendly forestry can make important contributions to conservation.
A North American forest resident species, Red-headed Woodpecker (Melanerpes erythrocephalus) has declined by 67% since 1970 in eastern temperate forests. Photo by Nico Arcilla.
More information: Nico Arcilla and Māris Strazds, Ten Principles for Bird-Friendly Forestry: Conservation Approaches in Natural Forests Used for Timber Production. Birds (2023), 245-261; https://doi.org/10.3390/birds4020021
About the authors: Nico Arcilla is affiliated with the International Bird Conservation Partnership and and the University of Nebraska-Lincoln, USA; she earned her PhD from the University of Georgia. Māris Strazds is affiliated with the Laboratory of Ornithology, Institute of Biology, University of Latvia, where he also earned his PhD.
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