Validating the Use of Coefficients of Conservatism to Assess Forest Herbaceous Layer Quality in Upland Mesic Forests

• Published in: Natural areas journal 2018-01, Vol.38 (1), p.6-14
• Main Authors: Mabry, Cathy, Golay, Michaeleen E. Gerken, Lock, Dennis, Thompson, Janette R
• Format: Article
• Language: English
• Subjects: anthropogenic disturbance; Floristic Quality Assessment; forest monitoring; forest understory; habitat specialist species; RESEARCH ARTICLE
• ISSN: 0885-8608; 2162-4399
• DOI: 10.3375/043.038.0103

Monitoring is a key activity in management and restoration, yet practitioners' choices among methods may be limited by available resources. Coefficients of Conservatism (C values) have been widely used among practitioners because they are easy to apply. To determine C, expert botanists assign species in a flora to one of 11 categories, from 0 to 10, with “0” assigned to species most tolerant of human disturbance, and “10” to species of highest-quality native habitats. Although first proposed over 30 y ago, C values are criticized as subjective, creating a need for external validation using independently derived metrics. Our study corroborates earlier validations of C values for forest understory species. Our work was made possible by consistent collection of herbaceous layer data from 126 plots at 38 sites across Iowa, USA, spanning five types of forests common in the Midwest: secondary, grazed, urban, managed (timber), and preserved. We used PCA to develop an independent metric of human disturbance (LHi) based on five plant attributes (exotic, annual, biennial, closed-canopy specialist, mesic-site specialist, and fern) that are determined apart from species' C values. We found high correlation between mean C and LHi (r = 0.837) and an identical pattern of means for these indices between the five forest types, with secondary forests having lowest and preserved forests highest values. This evidence supports earlier assertions that mean C provides a valid, simple, and inexpensive means to assess qualitative differences in the forest herbaceous layer of upland mesic forests due to human disturbance.