Aboveground Deadwood Biomass and Composition Along Elevation and Land-Use Gradients at Mount Kilimanjaro

Armin Komposch,Markus Fischer,Andreas Ensslin,Andreas Hemp

doi:10.3389/fevo.2021.732092

Abstract

Deadwood is an important structural and functional component of forest ecosystems and biodiversity. As deadwood can make up large portions of the total aboveground biomass, it plays an important role in the terrestrial carbon (C) cycle. Nevertheless, in tropical ecosystems and especially in Africa, quantitative studies on this topic remain scarce. We conducted an aboveground deadwood inventory along two environmental gradients—elevation and land use— at Mt. Kilimanjaro, Tanzania. We used a huge elevation gradient (3690 m) along the southern slope of the mountain to investigate how deadwood is accumulated across different climate and vegetation zones. We also compared habitats that differed from natural forsts in land-use intensity and disturbance history to assess anthropogenic influence on deadwood accumulation. In our inventory we distinguished coarse woody debris (CWD) from fine woody debris (FWD). Furthermore, we calculated the C and nitrogen (N) content of deadwood and how the C/N ratio varied with decomposition stages and elevation. Total amounts of aboveground deadwood ranged from 0.07 ± 0.04 to 73.78 ± 36.26 Mg ha–1 (Mean ± 1 SE). Across the elevation gradient, total deadwood accumulation was highest at mid-elevations and reached a near-zero minimum at very low and very high altitudes. This unimodal pattern was mainly driven by the corresponding amount of live aboveground biomass and the combined effects of decomposer communities and climate. Land-use conversion from natural forests into traditional homegardens and commercial plantations, in addition to frequent burning, significantly reduced deadwood biomass, but not past selective logging after 30 years of recovery time. Furthermore, we found that deadwood C content increased with altitude. Our study shows that environmental gradients, especially temperature and precipitation, as well as different anthropogenic disturbances can have considerable effects on both the quantity and composition of deadwood in tropical forests.

Highlights

Deadwood has many important key functions in forest ecosystems
The chemical composition (C and N content) of wood samples was measured for 274 coarse woody debris (CWD) samples and varied across different decomposition classes (Table 1) as well as elevation (Figure 2)
Percentage of both C and N in CWD samples increased with increasing decomposition (Table 1: R2 = 0.03, F4,269 = 3.01, P < 0.01, and R2 = 0.04, F4,269 = 4.21, P < 0.01, respectively)

Summary

Introduction

Deadwood has many important key functions in forest ecosystems. It provides resources and habitats for a wide range of plant and animal groups, including amphibians, reptiles, arthropods, birds, mammals, vascular plants, bryophytes, fungi and lichens, and is an important driver of biodiversity (Spetich et al, 1999). Deadwood currently stores about 8% of the global forest carbon stock (Pan et al, 2011) and 8.5% of atmospheric carbon (Friedlingstein et al, 2019). These sinks are offset by losses of C due to deforestation and forest degradation, in tropical regions (Pan et al, 2011; Baccini et al, 2017)

Methods

Results

Discussion

Conclusion