Planting trees is commonly suggested as a method to combat climate change, yet a new study has demonstrated how forestry can negatively impact birds of open landscapes.
Lowland Iceland is one such place being targeted by widespread afforestation projects, in part encouraged by the suggestion of its benefits for the climate. However, Iceland is also internationally important for a range of breeding waders that rely on undisturbed open ground in which to reproduce successfully.
To quantify the effects of plantation forests on the abundance and distribution of ground-nesting birds, Aldís E Pálsdóttir and colleagues from the University of East Anglia (UK) and the University of Aveiro (Portugal) conducted surveys on 161 transects (surrounding 118 plantations) perpendicular to forest edges throughout Iceland.
Whimbrel breeds in internationally important numbers in Iceland (Darran Rickards).
The resulting variation in density with distance from plantation was used to estimate the likely changes in bird numbers resulting from future afforestation plans, and to explore the potential effects of different planting configuration (size and number of forest patches) scenarios.
More than 3,700 individuals of 30 bird species were recorded on the transects, with the most common breeding species being seven waders (European Golden Plover, Eurasian Oystercatcher, Dunlin, Common Snipe, Whimbrel, Black-tailed Godwit and Common Redshank) and two passerines (Redwing and Meadow Pipit), with these nine species account for almost 90% of all birds recorded.
Densities of five of the seven waders (European Golden Plover, Eurasian Oystercatcher, Dunlin, Whimbrel and Black-tailed Godwit) were found to be lower within 200 m of a plantation than further away (up to 700 m). Dunlin and oystercatcher showed the largest differences (~15% increase in density per 50 m away from a plantation), with Whimbrel (12%) just behind, followed by Black-tailed Godwit (7%) and European Golden Plover (4%).
Common Redshank did not show a notable relationship with distance from plantation edges, other than nest densities were at their lowest ≤150 m from a plantation edge.
Common Snipe was the only 'winner', with densities 50% higher within 50 m of a plantation than further away (51-700 m).
Black-tailed Godwit was one of several breeding wader species impacted by the plantation of forestry in lowland Iceland (Carl Corbidge).
In Iceland, forestry is typically planted in small blocks across the landscape. Further analysis by the researcher showed that if trees were planted in one block of 1,000 ha instead of 1,000 blocks of 1 ha, the impact on nearby breeding waders would be nine times smaller, as overall there would be less forestry edge for waders to be nesting within the vicinity of on a single, large block of trees.
The scientists concluded that planting forests in open landscapes can have severe impacts on populations of ground-nesting birds, which emphasises the need for strategic planning of tree-planting schemes. Considering Iceland's statutory commitments to species protection and the huge contribution of Iceland to global migratory bird flyways, these are challenges that must be addressed quickly, before population-level impacts are observed across migratory ranges.
Reference
Pálsdóttir, A E, Gill, J A, Alves, J A, P, S, Méndez, V, Ewing, H, & Gunnarsson, T G. 2022. Subarctic afforestation: effects of forest plantations on ground-nesting birds in lowland Iceland. Journal of Applied Ecology. DOI: https://doi.org/10.1111/1365-2664.14238
