A reference-based approach for estimating leaf area and cover in the forest herbaceous layer

Abstract

Cover data are used to assess vegetative response to a variety of ecological factors. Estimating cover in the herbaceous layer of forests presents a problem because the communities are structurally complex and rich in species. The currently employed techniques for estimating cover are less than optimal for measuring such rich understories because they are inaccurate, slow, or impracticable. A reference-based approach to estimating cover is presented that compares the area of foliar surfaces to the area of an observer's hand. While this technique has been used to estimate cover in prior studies, its accuracy has not been tested. We tested this hand-area method at the individual plant, population, and community scales in a deciduous forest herbaceous layer, and in a separate farm experiment. The precision, accuracy, observer bias, and species bias of the method were tested by comparing the hand-estimated leaf area index values with actual leaf area index, measured using a leaf area meter. The hand-area method was very precise when regressed against actual leaf area index at the plant, population, and community scales (R(2) of 0.97, 0.93, and 0.87). Among the deciduous sites, the hand-area method overestimated leaf area index consistently by 39.1% at all scales. There was no observer bias detected at any scale, but plant overestimation bias was detected in one species at the population scale. The hand-area method is a rapid and reliable technique for estimating leaf area index or cover in the forest herbaceous layer and should be useful to field ecologists interested in answering questions at the plant, population, or community level.

Excess Nitrogen in Temperate Forest Ecosystems Decreases Herbaceous Layer Diversity and Shifts Control from Soil to Canopy Structure

“…The herbaceous layer was sampled in five circular 1 m 2 sub-plots within each of seven circular 0.04 ha permanent sample plots using methods described in Gilliam et al [24]. Briefly, all vascular plants ≤1 m in height in each subplot were identified to species (sometimes to genus) and visually estimated for cover (%); see Walter et al [28] for detailed description of this method. This was carried out in the first week of July each of the sample years 1991,1992,1994,2003, and annually from 2009 to 2014, for a total of 10 sample years over a 24-year period representing 26 years of N treatment on WS3.…”

Twenty‐five‐year response of the herbaceous layer of a temperate hardwood forest to elevated nitrogen deposition

“…The herbaceous layer was sampled within seven circular 400‐m 2 sample plots in each of WS3 and WS4 (representing the full range of elevation and slope aspect) by identifying and visually estimating cover (%) of all vascular plants ≤1 m in height within five 1‐m 2 circular sub‐plots in each sample plot (Walter et al. ), for a total of 70 1‐m 2 sub‐plots. Sub‐plots were located within sample plots using a stratified‐random polar coordinates method, which was employed to avoid over‐sampling the center region of circular plots (Gaiser ).…”

The utility of visual estimation of cover for rapid assessment of graminoid abundance in forest and grassland habitats in studies of animal foraging

“…We found that visually estimated cover, which does not suffer from these drawbacks, was a good proxy for biomass of individual food species, as well as total graminoid biomass, in complex forest habitats. Such estimation of individual species or portions of the vegetation (in our study area, herbs are more abundant than graminoids) is not feasible with other non-destructive methods (discussed in Radloff and Mucina 2007, Redjadj et al 2012, Walter et al 2015). An objection to the visual estimation of species covers had been that the “sum of species covers” as a measure of total cover would give “non-sense number”s that exceeded 100% (Wilson 2011).…”