. The Canadian field-naturalist. 1982 Sullivan and Sullivan: Effects of Logging and Seeding on Shrews 459 >. 4- *- CO 3- c CD â o 2- ^ 1- CD ^ n CO U" -lJ, c CD -2^ CT c cc -3- ^ O -4- CLEARCUT 1600 400 Number 800 of seeds 1200 per ha 2000 X 10^ Figure 3. Responses of shrew populations over a range of Douglas-fir seed densities in cutover habitats. Each triangle represents the response in density of shrews on the control (A) and seeded (A) grid areas. Changes in shrew density reflect the difference between the minimum number captured in trapping periods before and after seeding. respon
. The Canadian field-naturalist. 1982 Sullivan and Sullivan: Effects of Logging and Seeding on Shrews 459 >. 4- *- CO 3- c CD â o 2- ^ 1- CD ^ n CO U" -lJ, c CD -2^ CT c cc -3- ^ O -4- CLEARCUT 1600 400 Number 800 of seeds 1200 per ha 2000 X 10^ Figure 3. Responses of shrew populations over a range of Douglas-fir seed densities in cutover habitats. Each triangle represents the response in density of shrews on the control (A) and seeded (A) grid areas. Changes in shrew density reflect the difference between the minimum number captured in trapping periods before and after seeding. response of shrews to seedings on burned versus unburned clearcuts. Removal experiments To determine the potential competitive effect of Deer Mice on shrews, all mice (and voles) were removed from some seeded grids. In these experi- ments the density of shrews increased in two of the three trials (A and B), while the density of shrews on seeded and unseeded controls decreased (Table 2). The extended removal of mice, voles, and shrews on the unburned clearcuts in 1977 (experiment D-August to October) and 1978 (experiment E- March to mid- April) indicated that the shrews were rather unaf- fected by the procedure and if anything, their densities were reduced. In the spring 1978 experiment, the den- sity of shrews decreased after seeding even though the numbers of shrews in both controls were increasing at this time. The most noticeable difference resulting from the extended removal experiments is the over- winter recovery and early spring densities on the rem- oval grid when compared with the control. Discussion Population Density The variable nature of the shrew densities observed on our trapping grids may result from two factors. Firstly, the majority of shrews caught either did not survive the overnight trapping or were removed alive from the areas. Thus, the number of shrews caught in subsequent trapping periods would be dependent upon immigrants from other areas with a higher den-
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