Subarctic afforestation: effects of forest plantations on ground-nesting birds in lowland Iceland

Planting forests is a commonly suggested measure to mitigate climate
change. The resulting changes in habitat structure can greatly influence
the diversity and abundance of pre-existing wildlife. Understanding these
consequences is key for avoiding unintended impacts of afforestation on
habitats and populations of conservation concern. Afforestation in lowland
Iceland has been gaining momentum in recent years and further increases
are planned. Iceland supports internationally important breeding
populations of several ground-nesting, migratory bird species that mostly
breed in open habitats. If afforestation impacts the distribution and
abundance of these species, the consequences may be apparent throughout
their non-breeding ranges across Europe and Africa. To quantify the
effects of plantation forests on the abundance and distribution of
ground-nesting birds (in particular waders, Charadriiformes), surveys were
conducted on 161 transects (surrounding 118 plantations) perpendicular to
forest edges throughout Iceland. 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. Of seven wader species, densities of five
(golden plover (Pluvialis apricaria), whimbrel (Numenius phaeopus),
oystercatcher (Haematopus ostralegus), dunlin (Calidris alpina) and
black-tailed godwit (Limosa limosa)) in the 200 m surrounding plantations
were just over half of those further away (up to 700 m). Redshank (Tringa
totanus) densities were lowest <150 m from the plantation edge
while snipe (Gallinago gallinago) densities were 50% higher close to
plantations (0-50 m) than further away (51-700 m), and no consistent
effects of plantation height, diameter, density or type were identified.
Plantations are typically small and widespread, and simulated scenarios
indicated that total declines in bird abundance resulting from planting
trees in one large block (1000 ha) could result in only ~11% of the
declines predicted from planting multiple small blocks (1 ha) in similar
habitats. Synthesis and application: The severe impact that planting
forests in open landscapes can have on populations of ground-nesting birds
emphasises the need for strategic planning of tree-planting schemes. Given
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.