An Examination of Stand Attributes and the Presence of English holly in a Pacific Northwest Forest, Grays Harbor County, Wash.

摘要

English holly (Ilex aquifolium) is an ornamental favored by people who appreciate its wildlife benefits and traditional significance. Since its introduction into the Pacific Northwest over one hundred years ago, Ilex has escaped from cultivation and is increasingly found in natural areas such as national parks and forests that are far from an urban-rural interface. The presence of Ilex within these natural areas is disconcerting to natural resource managers and organizations because the plant is observed to out-compete native vegetation and resists attempts at its removal. While there are piecemeal efforts of identifying Ilex 's habitat, there has not been a systematic collection of data focused on that purpose. The purpose of this study was to identify the forest conditions under which Ilex is found and to determine if there are significant differences between plots where Ilex is present (Ilex-present plots) and where it is absent ( Ilexabsent plots). The research site is located in Grays Harbor County in Washington State, and data collection occurred from June 2011–November 2012, on 200 plots placed throughout the stand stages found on the landscape. The results yielded a significant difference in basal area and the number of shrubby understory vegetation species between the Ilex-absent and Ilex-present plots. Downed woody debris (DWD) (0.5-1.9" in diameter) also proved significantly different between the two conditions, and the stand stages identified as being significant DWD were Understory Reinitiation and Late Initiation. The presence of reed canary grass and native grass could serve as an indicator for the absence of Ilex while other common PNW species such as sword fern or cascara serve as indicators of a favorable habitat. Ilex's growth pattern of upright single stalk and multiple stalks upright and lying down was also found to be affected by SDI. While was found to Ilex appear in any stand stage, being linked with a high basal area this means that mature forests are particularly vulnerable to Ilex entering the stand and becoming established because this stage has combination of a high SDI and light-rich conditions capable of supporting diverse understory vegetative species.