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

Kobler  Johannes  Zehetgruber  Bernhard  Dirnböck  Thomas  Jandl  Robert  Mirtl  Michael  Schindlbacher  Andreas 《Landscape Ecology》2019,34(2):325-340

Context

Varying 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.

Objectives

We determined the effects of altitude and aspect on forest C cycling in a typical, mountainous catchment in the Northern Limestone Alps.

Methods

Forest 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.

Results

NEP 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.

Conclusions

Under 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.

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Nitrogen Leaching of Two Forest Ecosystems in a Karst Watershed     

Georg Jost  Thomas Dirnb?ck  Maria-Theresia Grabner  Michael Mirtl 《Water, air, and soil pollution》2011,218(1-4):633-649

Karst watersheds are a major source of drinking water in the European Alps. These watersheds exhibit quick response times and low residence times, which might make karst aquifers more vulnerable to elevated nitrogen (N) deposition than non-karst watersheds. We summarize 13 years of monitoring NO ₃ ^? , NH ₄ ⁺ , and total N in two forest ecosystems, a Norway spruce (Picea abies (L.) Karst.) forest on Cambisols/Stagnosols (IP I) and a mixed beech (Fagus sylvatica L.) spruce forest on Leptosols (IP II). N fluxes are calculated by multiplying concentrations, measured in biweekly intervals, with hydrological fluxes predicted from a hydrological model. The total N deposition in the throughfall amounts to 26.8 and 21.1 kg/ha/year in IP I and IP II, respectively, which is high compared to depositions found in other European forest ecosystems. While the shallow Leptosols at IP II accumulated on average 9.2 kg/ha/year of N between 1999 and 2006, the N budgets of the Cambisols/Stagnosols at IP I were equaled over the study period but show high inter-annual variation. Between 1999 and 2006, on average, 9 kg/ha/year of DON and 20 kg/ha/year of DIN were output with seepage water of IP I but only 4.5 kg/ha/year of DON and 7.7 kg/ha/year of DIN at IP II. Despite high DIN leaching, neither IP I nor IP II showed further signs of N saturation in their organic layer C/N ratios, N mineralization, or leaf N content. The N budget over all years was dominated by a few extreme output events. Nitrate leaching rates at both forest ecosystems correlated the most with years of above average snow accumulation (but only for IP I this correlation is statistically significant). Both snow melt and total annual precipitation were most important drivers of DON leaching. IP I and IP II showed comparable temporal patterns of both concentrations and flux rates but exhibited differences in magnitudes: DON, NO ₃ ^? , and NH ₄ ⁺ inputs peak in spring, NH ₄ ⁺ showed an additional peak in autumn; the bulk of the annual NO ₃ ^? and DON output occurred in spring; DON, NO ₃ ^? , and NH ₄ ⁺ output rates during winter months were low. The high DIN leaching at IP I was related to snow cover effects on N mineralization and soil hydrology. From the year 2004 onwards, disproportional NO ₃ ^? leaching occurred at both plots. This was possibly caused by the exceptionally dry year 2003 and a small-scale bark beetle infestation (at IP I), in addition to snow cover effects. This study shows that both forest ecosystems at Zöbelboden are still N limited. N leaching pulses, particularly during spring, dictate not only annual but also the long-term N budgets. The overall magnitude of N leaching to the karst aquifer differs substantially between forest and soil types, which are found in close proximity in the karstified areas of the Northern Limestone Alps in Austria.  相似文献   

Effects of stand patchiness due to windthrow and bark beetle abatement measures on soil CO2 efflux and net ecosystem productivity of a managed temperate mountain forest     

Johannes Kobler  Robert Jandl  Thomas Dirnböck  Michael Mirtl  Andreas Schindlbacher 《European Journal of Forest Research》2015,134(4):683-692

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