The Influence of Forest Management on the Spatial and Temporal Ecology of Squirrels (completed 2003)

Amanda Lloyd

Thesis abstract: Red and grey squirrel populations (Sciurus vulgaris and S. carolinensis respectively) and the influence of forest management were studied in Kielder forest, Northumberland and Creech forest, Hampshire between 1998 and 2001. The majority of the work was carried out in Kielder, an upland conifer plantation consisting primarily of Sitka spruce (Picea sitchensis), a non-native conifer species. The site at Creech was an ancient/semi-natural wood with large areas of Corsican pine (Pinus nigra).

Hairtube and live capture trapping were used to investigate the presence-absence of red squirrels in Kielder forest. Regression of hairtubes use against trapping in habitat- specific types allowed the prediction of the number of red squirrels using hairtubes in mixed conifer crops in upland habitats. The utility by red squirrels of mixed-species crops was higher than pure crops with the level of use changing on a yearly but not a seasonal basis. Hairtubes were used to collect presence-absence data from two forest blocks in Northumberland and the Borders in order to investigate the influence of habitat features of the spatial and temporal distribution of red squirrels. The data was modelled using logistic regression and linear relationships were found to exist between the utility of the hairtubes and the distance to clear fells for both of the forest sites along with the year of the survey. The effect of the clear fell distance on the utility of hairtubes is discussed with relation to food, habitat and fragmentation effects on squirrels.

Tree seed predictability, squirrel cone selection and seed morphometrics were investigated using a number of approaches including large-scale Forest research cone surveys, coneline data, and bomb calorimetry. Overall squirrels showed the least preference for Sitka spruce cones. There was differential selection for cones within the forest stands with peaks for production and consumption at 4 m and 10 m into the stands. Norway spruce seeds had the heaviest seed weight and calorific value, whilst Sitka spruce seeds had the lowest for both variables.

The impact of coning on a red squirrel population was investigated using an existing Spatially Explicit Population Model incorporating the observed seed energy data. The modelled squirrel population did not fluctuate in response to changes in seed energy. The scenario that made every year a good mast year, had an effect by doubling the population and density from 1 squirrel per 5.69ha to 1 squirrel per 3.42ha. The possible reasons behind this and future recommendations are discussed.

The effects of clear felling on a population of grey squirrels was investigated in Creech (Hants). Of the original 6 individuals, 3 either died or left the study area during the period of fieldwork, therefore only a sufficient amount of data for 3 squirrels was collected. Of these 3 squirrels, the home ranges were 25% smaller than grey squirrels in similar habitat consisting of semi-natural/Corsican pine woodland, suggesting a higher density population (~1 squirrel per ha) than Smith’s (1999) findings. On average these home ranges decreased in size after the clear felling had ceased, however 2 of the squirrels increased their core areas. At least 1 of the squirrels was pregnant during the month prior to felling, which may explain some of the ranging behaviour observed. It was however more likely that the squirrels were shifting their ranges in response to food availability rather than as a response to the impacts of clear felling.

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