Stand structure and breeding birds in managed Scots pine forests: Some likely long-term implications for continuous cover forestry

Continuous cover forestry (CCF) systems are increasingly advocated for stand management, with biodiversity among the ecosystem services perceived to benefit. However, long term (>100 years) influences of such silvicultural systems on biodiversity in managed forests are poorly understood. Timed point counts in Scots pine forests in Scotland were used to quantify associations between species richness, diversity and abundance of breeding birds and different forest structures provided by CCF. Managed forests with old growth features (some including particularly old pines and snags) were considered surrogates for long term CCF stands. A stand category with an understorey of young trees (understorey reinitiation) was the most species rich (other categories in descending order were old growth, commercially maturing stands with no regenerating understorey and exclusively pre canopy-closure young growth stage) but differences were small and marginally non-significant. Heterogeneity in canopy layer structure at a scale typical of many song bird territories (ca 1 ha) and the occurrence of old growth features were associated with greater abundance in a number of individual bird species but many associations were species-specific. Knowledge of species-specific responses to forest structure can inform management for the benefit of species of conservation concern and other priority species but requires better understanding of optimal structural mosaics including frequencies of old trees and snags for those species and groups. Bird distributions can change in response to extrinsic factors within the expected long-term plans for CCF managed forests; the contribution of structural mosaics to the resilience of forests in supporting a changing avifauna deserves further attention.

A New Approach to Modelling the Relationship Between Annual Population Abundance Indices and Weather Data

Weather has often been associated with fluctuations in population sizes of species; however, it can be difficult to estimate the effects satisfactorily because population size is naturally measured by annual abundance indices whilst weather varies on much shorter timescales. We describe a novel method for estimating the effects of a temporal sequence of a weather variable (such as mean temperatures from successive months) on annual species abundance indices. The model we use has a separate regression coefficient for each covariate in the temporal sequence, and over-fitting is avoided by constraining the regression coefficients to lie on a curve defined by a small number of parameters. The constrained curve is the product of a periodic function, reflecting assumptions that associations with weather will vary smoothly throughout the year and tend to be repetitive across years, and an exponentially decaying term, reflecting an assumption that the weather from the most recent year will tend to have the greatest effect on the current population and that the effect of weather in previous years tends to diminish as the time lag increases. We have used this approach to model 501 species abundance indices from Great Britain and present detailed results for two contrasting species alongside an overall impression of the results across all species. We believe this approach provides an important advance to the challenge of robustly modelling relationships between weather and species population size.

A bird's eye view: using circuit theory to study urban landscape connectivity for birds

ContextConnectivity is fundamental to understanding how landscape form influences ecological function. However, uncertainties persist due to the difficulty and expense of gathering empirical data to drive or to validate connectivity models, especially in urban areas, where relationships are multifaceted and the habitat matrix cannot be considered to be binary.ObjectivesThis research used circuit theory to model urban bird flows (i.e. ‘current’), and compared results to observed abundance. The aims were to explore the ability of this approach to predict wildlife flows and to test relationships between modelled connectivity and variation in abundance.MethodsCircuitscape was used to model functional connectivity in Bedford, Luton/Dunstable, and Milton Keynes, UK, for great tits (Parus major) and blue tits (Cyanistes caeruleus), drawing parameters from published studies of woodland bird flows in urban environments. Model performance was then tested against observed abundance data.ResultsModelled current showed a weak yet positive agreement with combined abundance for P. majorand C. caeruleus. Weaker correlations were found for other woodland species, suggesting the approach may be expandable if re-parameterised.ConclusionsTrees provide suitable habitat for urban woodland bird species, but their location in large, contiguous patches and corridors along barriers also facilitates connectivity networks throughout the urban matrix. Urban connectivity studies are well-served by the advantages of circuit theory approaches, and benefit from the empirical study of wildlife flows in these landscapes to parameterise this type of modelling more explicitly. Such results can prove informative and beneficial in designing urban green space and new developments.

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What are the forthcoming legislative issues of interest to ecologists and conservationists in 2012?

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Sample size required to characterize area use of tracked seabirds

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