Use of understory vegetation in classifying soil moisture and nutrient regimes G. Geoff Wang * Department of Biology, University of Winnipeg, Winnipeg, Man., R3B 2E9 Canada Received 2 April 1999; accepted 13 April 1999 Abstract One-hundred-and-two white spruce [Picea glauca (Moench) Voss] stands sampled in the sub-boreal spruce biogeoclimatic zone of British Columbia were used to examine the role of understory vegetation in assessing soil moisture and nutrient regimes. Based on the existing knowledge, each species of indicator value was assigned into one of six indicator species groups for soil moisture and/or one of three indicator species groups for soil nitrogen. On each stand, the frequency of each indicator species group was calculated using % covers of all indicator species. Soil moisture and nutrient regimes were then classi®ed based on calculated frequencies following the criteria proposed in the study. As a result, 16 stands were classi®ed as moderately dry, 27 stands slightly dry, 25 stands fresh, 15 stands moist, 12 stands very moist, and 7 stands as wet; 10 stands were classi®ed as very poor, 20 stands poor, 41 stands medium, 24 stands rich, and 7 stands as very rich. These classi®cations compared favorably with the two soil-based classi®cations reported earlier for the same data, with 47-59% of stands in agreement and 38-46% of stands in disagreement in only one class. Testing the classi®cation against soil moisture and nutrient measures and white spruce foliage nitrogen and site index further supported the indicator plant approach to soil moisture and nutrient regime classi®cation. It is concluded that the indicator plant approach is a good alternative to the soil-based approaches that have been commonly applied in site classi®cation systems across Canada. # 2000 Elsevier Science B.V. All rights reserved. Keywords: Site classi®cation; Indicator plants; White spruce 1. Introduction In plant communities species grow, reproduce, and survive or thrive under certain ecological conditions. The ranges of these conditions de®ne the ecological amplitude of each species. Once the ecological ampli- tude of a species is known, its performance on a particular site can be predicted by knowing the site conditions (e.g. climate, soil moisture regime, soil nutrient regime). Conversely, if one knows the per- formance of each species at a particular site, it is possible to assess the site conditions. These ecological understandings form the basic premise for using plants as site indicators. Even though every species has its de®nite ecologi- cal amplitude, only those species with relatively nar- row ecological amplitudes are of indicator value. By considering the abundance of all indicator species at a given site, site attributes such as soil moisture and Forest Ecology and Management 129 (2000) 93±100 *Tel.: +1-204-786-9407; fax: +1-204-774-4134 E-mail address: wang@io.uwinnipeg.ca (G.G. Wang) 0378-1127/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved. PII:S0378-1127(99)00142-5