Floristic Quality Assessment: a critique, a defense, and a primer

Abstract

Floristic Quality Assessment (FQA) measures have become extraordinarily influential ecological metrics in North America over the past 20 yr. Government agencies, conservation organizations, land managers, and researchers alike utilize this plant-based measure to evaluate habitat conservation value, ecological integrity, and naturalness. Its relative uniqueness, utility, and ease of use, among vegetation measures, portend the continued popularity of FQA going forward. FQA's use and influence far exceeds its study-where the literature addressing questions and criticisms regarding its methodology and ecological meaning has not kept pace with reliance upon it. Furthermore, the lack of literature review has led to disorder and confusion among its users. This review addresses these issues in three parts. First, it concisely explains the metrics and their methods, and most importantly, it synthesizes the often-misinterpreted conceptual basis behind FQA. The bulk of the review then tackles common questions from researchers and non-technical users alike regarding the measures. It does this with two lists. The first list reviews FQA's most common criticisms and summarizes evidence for and against them. The second list confronts the most common mistakes surrounding FQA, regarding both its application and misunderstanding in the literature. In each instance, straightforward guidelines and answers to uncertainties are emphasized.

Dramatic long-term restoration of an oak woodland due to multiple, sustained management treatments

“…They caution that species with inherently larger growth forms or high population densities could unduly influence abundance-weighted measures. Conversely, other authors question whether such measures de-value species that are inherently rare in plant communities [ 71 ]. Some studies of abundance-weighted FQA measures have found little or no improvement over non-weighted measures [ 72 , 73 ] or improvement only in a small subset of habitats [ 74 ].…”

Using lichen communities as indicators of forest stand age and conservation value

“…The coefficient of conservation, an index for vascular plants that is similar to the lichen conservation index we present here, has a long history of use by botanists and land managers but has also been criticized at times (Spyreas 2019). Because values are assigned by experts, rather than based on field data, some researchers have suggested that they may be biased.…”

“…Land managers around the globe are tasked with conserving biodiversity, and must evaluate the conservation value of ecological communities to develop conservation plans. Managers frequently seek to identify the extent to which communities contain species with affinities for undisturbed, late-successional habitats, since these are often the most imperiled species in contemporary landscapes that have largely been altered by anthropogenic activities (Veldman et al 2015, Spyreas 2019. Identifying communities that contain late successional species can allow managers to evaluate the results of management practices and may facilitate the comparison of different areas or land parcels.…”

“…Other indices seek to represent the extent to which communities have been altered by anthropogenic activities, or the degree to which they are associated with late-successional habitats. The "coefficient of conservatism" has been widely used to represent the conservation value of vascular plant communities in recent decades, particularly in central and eastern North America (Spyreas 2019). Coefficient of conservatism values are assigned by experts rather than based on quantitative field data, and much empirical evidence suggests that plant coefficient of conservatism rankings capture real ecological differences among species (Matthews et al 2015, Bauer et al 2018, Bried et al 2018; reviewed by Spyreas 2019).…”

“…We then use a large forest survey data set to explore how the lichen conservation index corresponds to forest stand age and other environmental variables. The lichen conservation index that we present represents a lichen analog to the coefficient of conservatism index that is widely used for plant communities in central and eastern North America (Spyreas 2019). Using lichens for this purpose is appropriate because lichens exhibit a spectrum of ecological affinities, ranging from species that thrive under certain types of anthropogenic disturbance (e.g., nitrophiles that become especially abundant in nutrient enriched agricultural landscapes) to species that are very sensitive to most anthropogenic disturbance (e.g., species that are restricted to old-growth forests; McMullin and Wiersma, 2019).…”