HEIGHT OF WHITE-FLOWERED TRILLIUM (TRILLIUM-GRANDIFLORUM) AS AN INDEX OF DEER BROWSING INTENSITY

The height of white-flowered trillium (Trillium grandiflorum) is a useful indicator of deer browsing intensity. In their foraging activities deer select larger plants over smaller plants. Because flowering plants are larger than nonflowering plants, the number of plants in flower decreases with increasing browsing intensity. As browsing intensity increases, the height of the Trillium becomes shorter in successive growing seasons, presumably due to the loss of photosynthetic capacity and reduction in belowground resources. Tillium stem height was positively correlated with reproductive output by perennial herbaceous plants and negatively correlated with the percent of the herbaceous understory that is browsed. This indicates change in stem height is an indication of the general status of the herbaceous flora as influenced by deer browsing. Based on deer population densities associated with study sites supporting Trillium populations with stable stem heights and flowering plants, maintenance of deer densities of 4-6 individuals/km(2) is recommended for deciduous forests in northeastern Illinois. In eastern United States, research workers who assume they are studying relatively undisturbed sites should be aware that intense deer browsing may have imposed an alteration on their study sites.