Environmental, Structural, and Disturbance Influences over Forest Floor Components in Interior Douglas-Fir Forests of the Intermountain West, USA

Andrew Giunta,John Shaw

doi:10.3390/f9080503

Abstract

Downed woody material (DWM) is a key component in forest ecosystems with age, structure, and disturbance described as primary factors that influence DWM dynamics. In particular, much emphasis is placed on large coarse woody debris (CWD). Fine woody debris (FWD) (less than 7.62 cm diameter), duff, and litter also contribute to carbon stocks, provide habitat, add to nutrient cycling, and are often the most available fuels for fire, yet are regularly overlooked in studies describing the forest floor. Throughout the middle montane zone within the Intermountain West region USA, interior Douglas-fir (Pseudotsuga menziesii var. glauca Mirb. Franco) is a predominant forest type, yet little is known about the forest floor complex in these forests. We used a chronosequence approach to compare DWM patterns over the course of stand development among stands with different disturbance histories. Using classification and regression trees, we also evaluated an assemblage of environmental, structural, and disturbance variables to determine factors of most importance for estimating loading for DWM, duff, and litter. We found CWD resembled a U-shaped pattern of buildup while FWD components remained stable over the course of stand development regardless of disturbance history. Our results indicate that large DWM components are most closely associated with the amount of standing dead material in a stand, primarily the density and basal area of snags. Fine woody material was more aligned with live stand components, while duff and litter were more influenced by disturbance.

Highlights

Downed woody material (DWM) is an integral structural component within forest ecosystems [1,2]which includes any dead wood from large tree boles [3,4] to small branches and twigs [5]
Throughout the literature, coarse woody debris (CWD) has been defined by a minimal diameter class ranging from as low as 2.5 cm diameter [6] to the more common 7.62 cm and greater [7], while fine woody debris (FWD) often consists of pieces less than 7.62 cm diameter
The majority of interior Douglas-fir stands sampled had no evidence of major disturbance associated with stand history (71%), followed by stands affected by fire (17%) and insects (12%)

Summary

Introduction

Downed woody material (DWM) is an integral structural component within forest ecosystems [1,2]which includes any dead wood from large tree boles [3,4] to small branches and twigs [5]. Coarse woody debris provides a critical habitat for wildlife [8,9,10], substrate for plant regeneration [11,12], and shading and protection of seedlings [1,7]; stabilizes soils and acts as erosion control [13]; and is intrinsically tied to forest nutrient cycling processes [14,15] It is important in forest carbon budgets acting as both a source and a sink [16], and when incorporated into riparian habitats, provides nutrients for aquatic life and refuge for fish [17]. The importance of FWD is Forests 2018, 9, 503; doi:10.3390/f9080503 www.mdpi.com/journal/forests

Objectives

Methods

Results

Conclusion