Enhancing Garry Oak Seedling Performance in a Semiarid Environment

Abstract

Successful establishment of desired species is crucial for accelerating the development of functioning ecosystems. In the Pacific Northwest, Garry oak (Quercus garryana) woodlands are of significant conservation value as many have been lost or degraded due to anthropogenic factors. Restoration plantings are one strategy for reversing this loss and enhancing the resilience of wildlife habitats confronting climate change. We tested the effects of seedling age (1- vs. 3-years old at planting), plastic mulch, tree shelters, and first-year irrigation on the performance of Garry oak seedlings for three years after outplanting in the semiarid East Cascades of Washington state. Net survival was 33% after three years. Growth was minimal as basal area increment and height growth averaged 21 mm2 and 5 cm, respectively, over this period. Most mortality occurred early in the first growing season after planting and was related, in part, to stock quality; this obscured the effects seedling age might have had on performance. Survival and growth were enhanced primarily by plastic mulch and to a lesser extent by tree shelters. First-year irrigation enhanced survival but not growth. We highly recommend the use of plastic mulch, which is easily installed and inexpensive, when planting Garry oak in semiarid environments. Irrigation, while beneficial, is not feasible for many projects. Tree shelters were of limited utility, likely because browse pressure was low. Attention to stock quality and the use of post-planting treatments appropriate to local climatic and site conditions are essential for restoration plantings to be ecologically and economically effective.