Effects of aspect and altitude on carbon cycling processes in a temperate mountain forest catchment

Johannes Kobler,Bernhard Zehetgruber,Andreas Schindlbacher,Thomas Dirnböck,Robert Jandl,Michael Mirtl

doi:10.1007/s10980-019-00769-z

Johannes Kobler, Bernhard Zehetgruber + Show 4 more

Open Access

https://doi.org/10.1007/s10980-019-00769-z

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Abstract

ContextVarying altitudes and aspects within small distances are typically found in mountainous areas. Such a complex topography complicates the accurate quantification of forest C dynamics at larger scales.ObjectivesWe determined the effects of altitude and aspect on forest C cycling in a typical, mountainous catchment in the Northern Limestone Alps.MethodsForest C pools and fluxes were measured along two altitudinal gradients (650–900 m a.s.l.) at south-west (SW) and north-east (NE) facing slopes. Net ecosystem production (NEP) was estimated using a biometric approach combining field measurements of aboveground biomass and soil CO2 efflux (SR) with allometric functions, root:shoot ratios and empirical SR modeling.ResultsNEP was higher at the SW facing slope (6.60 ± 3.01 t C ha−1 year−1), when compared to the NE facing slope (4.36 ± 2.61 t C ha−1 year−1). SR was higher at the SW facing slope too, balancing out any difference in NEP between aspects (NE: 1.30 ± 3.23 t C ha−1 year−1, SW: 1.65 ± 3.34 t C ha−1 year−1). Soil organic C stocks significantly decreased with altitude. Forest NPP and NEP did not show clear altitudinal trends within the catchment.ConclusionsUnder current climate conditions, altitude and aspect adversely affect C sequestering and releasing processes, resulting in a relatively uniform forest NEP in the catchment. Hence, including detailed climatic and soil conditions, which are driven by altitude and aspect, will unlikely improve forest NEP estimates at the scale of the studied catchment. In a future climate, however, shifts in temperature and precipitation may disproportionally affect forest C cycling at the southward slopes through increased water limitation.

Highlights

In complex mountain terrains, the topography, renders steep gradients in site parameters within small distances, thereby promoting gravity-related erosion processes (Konz et al 2010), creating site-specificclimatic conditions (Beniston 2005) and developing diverse soil (Haring et al 2012) and plant landscapes (Fischer et al 2014)
SR was higher at the SW facing slope too, balancing out any difference in Net ecosystem production (NEP) between aspects (NE: 1.30 ± 3.23 t C ha-1 year-1, SW: 1.65 ± 3.34 t C ha-1 year-1)
Soil organic C stocks significantly decreased with altitude

Summary

Introduction

The topography, renders steep gradients in site parameters within small distances, thereby promoting gravity-related erosion processes (Konz et al 2010), creating site-specific (micro-)climatic conditions (Beniston 2005) and developing diverse soil (Haring et al 2012) and plant landscapes (Fischer et al 2014). Together, this results in small-scaled and intermingled spatial ecological units, each characterized by a specific set of climatic, physical, chemical and biotic factors (Hansen et al 2000; Swetnam et al 2017). Forest soil organic C (SOC) stocks typically increase with altitude due to slow soil organic matter decomposition at the colder higher elevation sites (Schindlbacher et al 2010; Tashi et al 2016)

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