SUMMARYStudies investigating associations between air pollution exposure and health outcomes benefit from the estimation of exposures at the individual level, but explicit consideration of the spatio-temporal variation in exposure is relatively new in air pollution epidemiology. We address the problem of estimating spatially and temporally varying particulate matter concentrations (black smoke = BS = PM 4 ) using data routinely collected from 20 monitoring stations in Newcastle-upon-Tyne between 1961 and 1992. We propose a two-stage strategy for modelling BS levels. In the first stage, we use a dynamic linear model to describe the long-term trend and seasonal variation in area-wide average BS levels. In the second stage, we account for the spatio-temporal variation between monitors around the area-wide average in a linear model that incorporates a range of spatio-temporal covariates available throughout the study area, and test for evidence of residual spatio-temporal correlation. We then use the model to assign time-aggregated predictions of BS exposure, with associated prediction variances, to each singleton pregnancy that occurred in the study area during this period, guided by dates of conception and birth and mothers' residential locations. In work to be reported separately, these exposure estimates will be used to investigate relationships between maternal exposure to BS during pregnancy and a range of birth outcomes. Our analysis demonstrates how suitable covariates can be used to explain residual spatio-temporal variation in individual-level exposure, thereby reducing the need to model the residual spatio-temporal correlation explicitly.

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The native Eurasian red squirrel is considered endangered in the UK and is under strict legal protection. Long-term management of its habitat is a key goal of the UK conservation strategy. Current selection criteria of reserves and subsequent management mainly consider species composition and food availability. However, there exists a critical gap in understanding and quantifying the relationship between squirrel abundance, their habitat use and forest structural characteristics. This has partly resulted from the limited availability of structural data along with costefficient data collection methods. This study investigated the relationship between squirrel feeding activity and structural characteristics of Scots pine forests. Field data were collected from two study areas: Abernethy and Aberfoyle Forests. Canopy closure, diameter at breast height, height and number of trees were measured in 56 plots. Abundance of squirrel feeding signs was used as an index of habitat use. A GLM was used to model the response of cones stripped by squirrels in relation to the field collected structural variables. Results show that forest structural characteristics are significant predictors of feeding sign presence, with canopy closure, number of trees and tree height explaining 43% of the variation in stripped cones. The GLM was also implemented using LiDAR data to assess at wider scales the number of cones stripped by squirrels. The use of remote sensing-in particular Light Detection and Ranging (LiDAR)-enables cost efficient assessments of forest structure at large scales and can be used to retrieve the three variables explored in this study; canopy cover, tree height and number of trees, that relate to red squirrel feeding behaviour. Correlation between field-predicted and LiDAR-predicted number of stripped cones was performed to assess LiDAR-based model performance. LiDAR data acquired at Aberfoyle and Abernethy Forests had different characteristics (in particular pulse density), which influences the accuracy of LiDAR derived metrics. Therefore correlations between field predicted and LiDAR predicted number of cones (LSC) were assessed for each study area separately. Strong correlations (r s =0.59 for Abernethy and 0.54 for Aberfoyle) suggest that LiDAR-based model performed relatively well over the study areas. The LiDAR-based model was not expected to

SummaryThis paper describes the use of a spatially explicit population model (SEPM) to investigate the effects of different forest management strategies on a red squirrel conservation area. The study was based in woodland managed by Forest Enterprise, which manages 75 000 ha of woodlands in Northumberland, Co. Durham, Tyne and Wear, and east Cumbria. The forests contain the largest remaining red squirrel populations in northern England and the area of the study, Kidland Forest, is one of five key areas or refuges where red squirrel conservation is a priority. The SEPM integrates expert knowledge on red and grey squirrels, based on 10 years of fieldwork in the area and information from the scientific literature. We investigated the current tree species composition, distribution and proposed felling plans as well as the future restocking for Kidland Forest, an area of 2050 ha of predominantly conifer species. The assessment also included a proposed planting of 15 ha of oak and its likely consequences on grey squirrel population viability. These results were then applied to develop a forest design plan to ensure red squirrel persistence over the next rotation. Results indicated that red squirrels were at risk of extinction due to a drastic reduction in the availability of suitable habitats through clear-felling. Furthermore the proposed planting of 15 ha of oak could lead to a substantial grey squirrel population at Kidland once the trees matured and assuming that grey squirrels colonize the area. The felling profile was therefore revised, allocating a proportion of the tree crop on more wind-firm sites to long-term retentions. The approach adopted at Kidland illustrates how geographical information systems, expert knowledge on the threatened species and spatially explicit models can be integrated to assist forest managers in assessing the suitability of a site for red squirrel conservation.

Seasonal body weight changes were investigated in red and grey squirrels in spruce-dominated conifer plantations in the north of England. Annual seed food availability, particularly in the spruce plantations, varies markedly and is characterized by years with large cone crops (`mast crops') followed by several years of intermediate or low crops. The last mast crop in Kielder Forest District occurred in 1991 and we studied the two squirrel species when food availability was intermediate and low between 1992 and 1999. Neither red nor grey squirrels in the conifer plantations signi®cantly increased their body weight for the autumn or winter. The responses of red and grey squirrels to the different foraging conditions in deciduous and conifer woodlands and the accumulation of seasonal fat stores may have to be seen in the context of habitat type and the pattern and predictability of seed availability. Our ®ndings suggest that fat accumulation is likely to be less pronounced in conifer habitats where autumn and winter food supplies are more predictable, and manoeuvrability to feed on cones in the canopy is important.

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