Annual litterfall dynamics and nutrient deposition depending on elevation and land use at Mt. Kilimanjaro

J. Becker,J. Mnyonga,Y. Kuzyakov,H. Pabst

doi:10.5194/bg-12-5635-2015

J. Becker, J. Mnyonga + Show 2 more

Open Access

https://doi.org/10.5194/bg-12-5635-2015

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Abstract

Abstract. Litterfall is one of the major pathways connecting above- and below-ground processes. The effects of climate and land-use change on carbon (C) and nutrient inputs by litterfall are poorly known. We quantified and analyzed annual patterns of C and nutrient deposition via litterfall in natural forests and agroforestry systems along the unique elevation gradient of Mt. Kilimanjaro. Tree litter in three natural (lower montane, Ocotea and Podocarpus forests), two sustainably used (homegardens) and one intensively managed (shaded coffee plantation) ecosystems was collected on a biweekly basis from May 2012 to July 2013. Leaves, branches and remaining residues were separated and analyzed for C and nutrient contents. The annual pattern of litterfall was closely related to rainfall seasonality, exhibiting a large peak towards the end of the dry season (August–October). This peak decreased at higher elevations with decreasing rainfall seasonality. Macronutrients (N, P, K) in leaf litter increased at mid elevation (2100 m a.s.l.) and with land-use intensity. Carbon content and micronutrients (Al, Fe, Mn, Na) however, were unaffected or decreased with land-use intensity. While leaf litterfall decreased with elevation, total annual input was independent of climate. Compared to natural forests, the nutrient cycles in agroforestry ecosystems were accelerated by fertilization and the associated changes in dominant tree species.

Highlights

With their high biodiversity and importance for the global carbon (C) cycle, tropical forests are often highlighted as ecosystems of specific research interest (Brown, 1993; Sayer et al, 2011)
The annual amount of total litterfall was independent of land use and elevation, whereas the amount of leaf litter in natural forests decreased with elevation (Fig. 1)
Kilimanjaro, the annual pattern of litterfall depends on seasonal climatic conditions

Summary

Introduction

With their high biodiversity and importance for the global carbon (C) cycle, tropical forests are often highlighted as ecosystems of specific research interest (Brown, 1993; Sayer et al, 2011). Tropical forest ecosystems account for one third of the terrestrial net primary production (NPP) (Saugier et al, 2001) and contain more than half of the world’s terrestrial species (Groombridge and Jenkins, 2002). Tropical forests act as a net sink for CO2 (FAO, 2010) and contain roughly 25 % of the terrestrial biosphere C (Bonan, 2008). Tree litterfall is one of the major pathways in C and nutrient cycles that connect above- and below-ground processes (Vitousek and Sanford, 1986). Litterfall varies considerably between ecosystems, depending on climate, tree species composition, stand structure and soil fertility (Vitousek and Sanford, 1986). The effect of elevation on litterfall is an important indicator for estimating future changes in ecosystem cycles

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