In the coniferous forests of the Pacific Northwest, canopy gaps created by the death of large trees within mature forests are hypothesized to determine the species composition and future development of those forests. In 1990, the investigators established experimental canopy gaps of different sizes within two conifer forests of different age. The main objectives have been to determine the influence of the composition and abundance of vegetation and the availability of resources (e.g. light and moisture) prior to and immediately after gap formation on the pattern of development in old growth forests. The investigators will continue their long-term measurements of plant diversity and abundance, and of light and soil moisture levels, in the experimental gaps. Recent plans for management of federal lands in the Pacific Northwest emphasize managing young forests to encourage a greater diversity of species and structure that is characteristic of old-growth forests. Allowing stands to age naturally may accomplish this goal, but selective tree harvest has also been proposed as a way to achieve structural complexity more rapidly while allowing some commodity extraction. This study will aid in understanding how canopy gaps influence development of old-growth forests, how long it might take for old-growth structure to develop naturally, and whether selective harvest of different sizes of openings can mimic this process. This study will also provide new information on the most appropriate gap size for the establishment and growth of different tree and understory plant species, and the effect of existing vegetation on tree survival and growth.
