Quantifying Understory Complexity in Unmanaged Forests Using TLS and Identifying Some of Its Major Drivers

Dominik Seidel,Katharina Willim,Martin Ehbrecht,Peter Annighöfer,Jan Bannister,Christian Ammer,Daniel P Soto

doi:10.3390/rs13081513

Dominik Seidel, Katharina Willim + Show 5 more

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https://doi.org/10.3390/rs13081513

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Abstract

The structural complexity of the understory layer of forests or shrub layer vegetation in open shrublands affects many ecosystem functions and services provided by these ecosystems. We investigated how the basal area of the overstory layer, annual and seasonal precipitation, annual mean temperature, as well as light availability affect the structural complexity of the understory layer along a gradient from closed forests to open shrubland with only scattered trees. Using terrestrial laser scanning data and the understory complexity index (UCI), we measured the structural complexity of sites across a wide range of precipitation and temperature, also covering a gradient in light availability and basal area. We found significant relationships between the UCI and tree basal area as well as canopy openness. Structural equation models (SEMs) confirmed significant direct effects of seasonal precipitation on the UCI without mediation through basal area or canopy openness. However, annual precipitation and temperature effects on the UCI are mediated through canopy openness and basal area, respectively. Understory complexity is, despite clear dependencies on the available light and overall stand density, significantly and directly driven by climatic parameters, particularly the amount of precipitation during the driest month.

Highlights

The understory of a forest, as well as vegetation in shrublands without a distinct overstory, are important contributors to several ecosystem functions and services, including flora and fauna diversity [1,2,3]
Mean annual temperature had a significant negative effect on the basal area, while precipitation during the driest month or mean annual precipitation showed no correlation with the basal area
We conclude that understory layer complexity, as determined by the understory complexity index, in unmanaged Chilean landscapes is strongly driven by climatic variables

Summary

Introduction

The understory of a forest, as well as vegetation in shrublands without a distinct overstory, are important contributors to several ecosystem functions and services, including flora and fauna diversity [1,2,3]. Shrubby vegetation affects nutrient cycling [4] and provides breeding and feeding grounds for large mammals [5]. In addition to these ecological functions, the understory layer determines the future species composition and structure of forests [6,7], which is of economic and ecological importance [8]. This is because juvenile trees—the so-called regeneration—are part of the understory layer. In shrublands with only scattered large trees, shrubby vegetation constitutes an important transitional habitat that results in high taxonomic and functional diversity [11]

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