Poster from 2006 Cascades student poster session.Small mammal populations are vital to the Metolius Forest Preserve. The forest preserve is undergoing selective thinning, which may affect small mammal populations in the forest. Our null hypothesis is that small mammal populations are not affected by the treatment of the forest. In addition to the null hypothesis, we have predicted that there are short-term effects that will contribute to a rise in the numbers of small mammals in the treated sites when compared to data that is obtained in identical future surveys. To test the null hypothesis, small mammal traps were set up on 9 experimental plots. Two plots were set up for four non-consecutive nights, and an additional control plot was set up in an un-logged area in the same forest. Four deer mice (Peromyscus maniculatus) were caught in untreated areas only. In conclusion, small mammal populations are probably effected by the thinning of the Metolius Forest Preserve.