Vertical and Horizontal Vegetation Structure across Natural and Modified Habitat Types at Mount Kilimanjaro.

Markus Fischer,Andreas Ensslin,Andreas Hemp,Gemma Rutten

doi:10.1371/journal.pone.0138822

Abstract

In most habitats, vegetation provides the main structure of the environment. This complexity can facilitate biodiversity and ecosystem services. Therefore, measures of vegetation structure can serve as indicators in ecosystem management. However, many structural measures are laborious and require expert knowledge. Here, we used consistent and convenient measures to assess vegetation structure over an exceptionally broad elevation gradient of 866–4550m above sea level at Mount Kilimanjaro, Tanzania. Additionally, we compared (human)-modified habitats, including maize fields, traditionally managed home gardens, grasslands, commercial coffee farms and logged and burned forests with natural habitats along this elevation gradient. We distinguished vertical and horizontal vegetation structure to account for habitat complexity and heterogeneity. Vertical vegetation structure (assessed as number, width and density of vegetation layers, maximum canopy height, leaf area index and vegetation cover) displayed a unimodal elevation pattern, peaking at intermediate elevations in montane forests, whereas horizontal structure (assessed as coefficient of variation of number, width and density of vegetation layers, maximum canopy height, leaf area index and vegetation cover) was lowest at intermediate altitudes. Overall, vertical structure was consistently lower in modified than in natural habitat types, whereas horizontal structure was inconsistently different in modified than in natural habitat types, depending on the specific structural measure and habitat type. Our study shows how vertical and horizontal vegetation structure can be assessed efficiently in various habitat types in tropical mountain regions, and we suggest to apply this as a tool for informing future biodiversity and ecosystem service studies.

Highlights

In most habitats, vegetation provides the main structure of the environment
All six vertical vegetation structure variables showed a unimodal pattern along the elevation gradient peaking at intermediate elevations (Table 2; Fig 2)
Elevation explained between 45% and 75% of the variation in vertical vegetation structure

Summary

Introduction

Vegetation provides the main structure of the environment. This complexity can facilitate biodiversity [1] and provide ecosystem services. Plants are important ecosystem engineers that generate habitat niches, such as light patches in canopies and understory, and more complex vegetation structure utilized by other organisms, for example birds [9], reptiles and small mammals [10]. In this context, distinguishing horizontal (variation of structure across a horizontal space) from vertical vegetation structure (variation in structure across a vertical space) is important, as some taxa, e.g. birds or bees may depend more on strong changes in horizontal structures (e.g. trees for nesting and open area for foraging) than other taxa [4]

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Discussion

Conclusion