Background/Question/Methods In temperate forests, small mammals are voracious consumers of tree seed and can strongly reduce seed survival. However, it is not known if seedling recruitment is enhanced in the absence of seed predators. In the summer of 1994 we established 36 1m x 2m small mammal exclosures within two forest stands in northwestern Connecticut, USA. We monitored seed rain in 1994, 1995, and 1996, and seedling recruitment both within and outside of exclosures in 1995, 1996 and 1997.
Results/Conclusions
Overall, significantly more seedlings established within the exclosures (within: 43.218 ± 8.47 SEM vs outside: 20.139 ± 2.65 SEM; t=2.599, p=0.01), and locations with the highest seed rain had increased seedling recruitment (F = 29.312, p<0.001), independent of treatment and year. However, the effect of exclosure varied by year. In 1995, the year following a high seed rain year (1994) that caused large populations of small mammals, exclosures had an average of 80 ± 14.65 seedlings while there were only 33 ± 5.4 outside (t=2.975, p=0.004), and only seedling recruitment in exclosures was correlated with the amount of seed rain (F=7.093, p=0.012) – indicating that when their densities are high, small mammals have a large effect on seed survival and therefore seedling establishment. However, in 1996, after a poor seed year of 1995 caused low small mammal densities, there were only 14 seedlings established both within and outside of exclosures (t=0.15, p=0.881), independent of the amount of seed rain – indicating that small mammals may have little influence on seed survival, and therefore seedling recruitment, following poor to average seed years. This effect may also be species-specific – in 1997 there was not a significant effect of exclosure on seedling recruitment, but locations with high red maple seed rain had increased red maple seedling recruitment, both inside (F=6.323, p=0.019) and outside (F=14.248, p=0.001) of exclosures – indicating that seed predators may have less of an effect on less preferred seed species when small mammal densities are moderate. Thus, seedling recruitment in temperate deciduous forests is temporally variable and influenced primarily by the amount of seed produced. Seed predators can influence patterns of seedling recruitment, but only in post-mast years when small mammal densities are highest.
