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Category: Ecological Research

Title: Fact Sheet: Increasing Evidence That Thinning and Burning Treatments Help Restore Understory Plant Communities in Ponderosa Pine Forests

Author: * Strahan, R.T.

Subject: Understory Plant Communities, Thinning

Abstract: There is a general consensus that throughout their range, contemporary ponderosa pine forests exist outside of their natural range of variability in terms of overstory structure such as tree density (trees ac-1) and basal area (ft2 ac-1). As a result these ecosystems are increasingly susceptible to landscape-scale, high-intensity wildfires. Over the last century, a number of factors—particularly intensive livestock grazing, selective logging, and fire suppres-sion—have combined to favor pine establishment at the expense of understory diversity and productivity. This has given rise to uncharacteristically high tree densities with closed canopies, lower light availability, and deeper forest floor litter and duff layers (Covington and Moore 1994). A major consequence of this has been the degra-dation of understory integrity, including declines in understory cover, productivity, and diversity. Restoration techniques for mitigating these changes include mechanical thinning, prescribed fire, or a combina-tion of the two. Empirical studies assessing treatment success have shown that a combination of mechanical thin-ning plus prescribed fire is most successful at reaching overstory restoration targets (Fulé et al. 2002; Roccaforte et al. 2015). Yet consensus on meeting understory objectives remains mixed and few studies have defined quanti-tative targets to assess understory response (Laughlin et al. 2006). Therefore, developing more specific restoration objectives for the understory plant community represents an under-developed and challenging area of research. However, a primary goal of ecological restoration for understory plant response following treatments is to max-imize cover and diversity of native vegetation. Our first objective in this study was to evaluated understory response to alternative restoration treatments. We measured understory cover and species richness five years after treatments in the Mineral Ecosystem Manage-ment Area (Mineral) located in east-central Arizona and part of the Ecological Restoration Institute’s Long-term Ecological Assessment and Restoration Network (LEARN). An untreated control (Untreated) was used for com-parison of two alternative restoration treatments 1) thinning followed by prescribed fire (Thin + Burn) and 2) pre-scribed fire only (Burn-only). Our second objective was to compare the understory response patterns we observed at Mineral with those following similar treatments at other LEARN sites. To make comparisons we quantified a range of variability associated with understory cover and species richness to restoration using three comparison LEARN sites located in ponderosa pine forests of northern Arizona: Fort Valley (FV), Mount Trumbull (MT), and Grandview (GV). All three sites are located across a gradient of precipitation and soil types, representing a broad range of ponderosa pine forest types with characteristic differences in the contribution of species and func-tional groups to understory cover and diversity.

Date: 2016

Type: Fact Sheet

Source: ERI - Fact Sheet

Identifier: 2p.

Publisher: Ecological Restoration Institute

Format: PDF

Language: English