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Effects of forest connectivity on ecological processes : using spruce grouse as a model system Harrison, Scott

Abstract

I considered the question: Does forest connectivity affect the ecological processes of animals? I addressed this question within the contexts of theoretical and applied ecology by 1) examining ecological processes, 2) collecting empirical field data from comparative treatments, and 3) conducting research at a spatial scale relevant to human land-use in forested landscapes. I compared data on the natality, movement, dispersal, and survival rates in 8, 100-ha connectivity treatment units. I studied spruce grouse as a model system for animals that are associated with structurally complex forests and that use the landscape at a spatial scale relevant to industrial logging. I captured 302 spruce grouse and radio-tagged 253 in 4 low- and 4 medium-connectivity treatment units dispersed throughout a 4,160-km study area. The connectivity treatment units were structurally complex forests that have never been logged in a matrix of 10 to 25-year-old clear-cuts. Population densities were not different in low- and medium-connectivity treatment units, but there were differences in age-specific survival rates. Adults that remained in the connectivity treatment units had lower, but not statistically different, survival rates in low connectivity (0.39 + 0.22) than in medium connectivity (0.67 ± 0.43). Juveniles that remained in the connectivity treatment units had significantly lower survival rates in low connectivity (0.13 ± 0.06) than in medium connectivity (0.60 ± 0.29). The contrast between the population densities and the age specific survival rates reveals the value of examining process, in contrast to pattern, for determining the effect of connectivity on population dynamics. I collected data on breeding and natal dispersal and compared survival between spruce grouse that remained within the connectivity treatment units and spruce grouse that "left" the connectivity treatment units. This comparison enabled me to differentiate the within-patch effects from the beyond-patch effects associated with moving beyond the 100-ha, connectivity treatment units. The median maximum movement distance for adults that left the connectivity treatment units was 3832 m (95th percentile: 150-13673) from low and 547 m (95th percentile: 130-5352) from medium connectivity. Adults that left low-connectivity treatment units had lower, but not statistically different, survival rates (0.63 ± 0.20) than did adults that left the medium-connectivity units (0.70 ± 0.24). The median maximum movement distances for juvenile spruce grouse that undertook natal dispersal and left the connectivity treatment units were not significantly different at 2043 m (95th percentile: 483-6728) from low and 2411m (95th percentile: 131-6410) from medium connectivity. However, the survival rates were significantly lower for juveniles that attempted natal dispersal and left low-connectivity treatment units (0.36 + 0.12) than for juveniles that left medium-connectivity treatment units (0.74 ± 0.19). The natal dispersal data indicate that the distance of natal dispersal provides little information about the effect of connectivity on juvenile survival. Instead, the configuration of the forest through which a juvenile moves is more important to juvenile survival than the distance that the juvenile moves. The landscape units surrounding both low- and medium-connectivity treatment units had similar forest:matrix ratios. Therefore, the differences between low and medium connectivity suggest that the effects of the configuration of the forest landscape that remains after logging is as important as the effects of the amount of forest loss on the ecological processes of animals.

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