Response of red squirrels and feeding damage to variable stand density in young lodgepole pine forest

This study was designed to test the hypothesis that large-scale habitat alteration by stand thinning would reduce red squirrel (Tamiasciurus hudsonicus) populations and feeding damage in young lodgepole pine (Pinus contorta) forest. An additional objective included integration of stand protection with an optimum thinning regime for growth rates of crop trees. Study areas were located near Penticton, Kamloops, and Prince George in south-central British Columbia, Canada. Each study area had three stands thinned to densities of $\approx 500$ (low), 1000 (medium), and 2000 (high) stems/ha, with an unthinned, juvenile pine stand and old-growth pine stand for comparison. Squirrel populations were sampled intensively in the thinned stands from 1989 to 1991; feeding damage was assessed annually from 1989 to 1993. Five-year diameter and height increments of crop trees were measured in the thinned stands at Penticton and Prince George, and 4-yr increments in these stands at Kamloops. Red squirrel populations were significantly reduced in the low-density stand compared with either the medium- or high-density stands at Penticton and Prince George. Squirrels were less abundant in both the low- and medium-density stands at Kamloops. Squirrel populations in the unthinned and old-growth stands were similar or lower in abundance than those in the thinned stands. There were significantly higher numbers of red squirrel first captures in the medium- and high-density stands than in the low-density stand. There were no consistent significant differences between stands in proportion of squirrels breeding, recruitment, mean survival over summer and winter periods, or mean body mass. More trees per hectare were damaged in the high than in either low- or medium-density stands at all study areas. Mean diameter increments of trees in the low-density stands were significantly higher than those in the medium- and high-density stands at all study areas. Trees grew significantly faster in height in the high- than in the low-density stands at Penticton and Prince George; the converse was true at Kamloops. Manipulation of stand density on an operational basis in young lodgepole pine has clearly indicated that both stand protection from squirrel feeding damage and productivity of crop trees are enhanced by reducing the number of stems per hectare. This result has been achieved in replicated study areas covering three different forest ecological zones.