Temporal dynamics of mast and small mammals: Short-term responses to silviculture

Kenneth F Kellner, Purdue University

Abstract

Oaks (Quercus) are a keystone species in eastern deciduous forests. One of their most important functions is the production of hard mast (acorns), a crucial food resource for many wildlife species. Oaks are relatively shade-intolerant and have been maintained as a dominant overstory species in many forests through a cycle of disturbance including fire and land clearing for agriculture. Recently, changing disturbance regimes have resulted in oak regeneration failure. Eventually, oak-dominated stands may instead be dominated by other tree species, such as maple (Acer). This shift may have important negative consequences for other forest species that rely on oak, especially those that consume hard mast. Forest managers have begun to use silviculture (i.e., timber harvest) as an artificial disturbance mechanism in an effort to promote oak regeneration and maintain oak dominance in deciduous forests, with mixed results. Understanding the effects of timber harvest on wildlife species is an important corollary to these efforts, particularly in the case of wildlife species that themselves affect successful oak regeneration (e.g., small mammals and acorn weevils (Curculio)). In this thesis, I examined the impact of two groups of acorn predators, small mammals and acorn weevils, on the survival of acorns prior to the implementation of timber harvest (Chapter 2). I then studied the effect of several methods of silviculture on common small mammal species, two of which (the white-footed mouse, Peromyscus leucopus, and the eastern chipmunk, Tamius straitus) are consumers of acorns (Chapters 3-4). I used two recently developed statistical techniques, an N-mixture model of abundance and a multi-species occupancy model, to make inferences about small mammal responses to harvest. Both models explicitly incorporated variability in detection probability, which if ignored can be a significant source of bias. I found that acorn mortality due to both weevils and removal by small mammals was maximized when mast production was lowest, reflecting the scarcity of this crucial food resource. In years when mast was abundant, small mammal predators preferred to remove more valuable acorns (e.g., acorns that were undamaged). Not surprisingly, abundance of granivorous small mammals were closely linked to mast availability throughout the study. Of the common small mammals that were the focus of the second portion of this thesis, one (the eastern chipmunk) generally responded positively to the creation of openings through timber harvest. A second, the generalist white-footed mouse, generally did not respond strongly to any type of silviculture. In contrast, the short-tailed shrew (Blarina brevicauda) and the pine vole (Microtus pinetorum) generally responded negatively to the creation of openings via harvest. In general, small mammals did not respond strongly to the first stage of a shelterwood harvest. Some of these shifts may have been due to changes in habitat variables following harvest; notably, the eastern chipmunk was associated with areas containing a large amount of coarse woody debris, which increased following the creation of openings. The results of this thesis will be useful in furthering our understanding of how silviculture affects insects and wildlife that play important roles in the oak life cycle. Successful oak regeneration depends on proper implementation of silviculture, but also on ensuring that potential sources of oak mortality, such as small mammals and weevils, do not create a bottleneck in the oak life cycle. My results lay the groundwork for future studies that examine the effects of animals and insects on the entire life cycle of oak in managed forests.

Degree

M.S.

Advisors

Swihart, Purdue University.

Subject Area

Plant biology|Ecology|Zoology|Forestry

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