Abstract
Forests play an important role in climate regulation due to carbon sequestration. However, a deeper understanding of forest carbon flux dynamics is often missing due to a lack of information about forest structure and species composition, especially for non-even-aged and species-mixed forests. In this study, we integrated field inventory data of a species-mixed deciduous forest in Germany into an individual-based forest model to investigate daily carbon fluxes and to examine the role of tree size and species composition for stand productivity. This approach enables to reproduce daily carbon fluxes derived from eddy covariance measurements (R2 of 0.82 for gross primary productivity and 0.77 for ecosystem respiration). While medium-sized trees (stem diameter 30–60 cm) account for the largest share (66%) of total productivity at the study site, small (0–30 cm) and large trees (>60 cm) contribute less with 8.3% and 25.5% respectively. Simulation experiments indicate that vertical stand structure and shading influence forest productivity more than species composition. Hence, it is important to incorporate small-scale information about forest stand structure into modelling studies to decrease uncertainties of carbon dynamic predictions.
Highlights
Forests mitigate the effects of climate change through carbon sequestration [1]
These multiple drivers of carbon dynamics lead to high uncertainties regarding the quantification of carbon fluxes, especially in mixed deciduous forests
Simulation results in this study show an increase of productivity with tree size from small- to medium-size trees, while the productivity of large tress (>60 cm) decreases
Summary
Forests mitigate the effects of climate change through carbon sequestration [1]. Globally, forests store about 45% of terrestrial carbon [2] and account for an annual net sink of2.4 Pg C [3]. Stand age, and management practices as well as site characteristics such as soil properties and climate can influence local carbon stocks and fluxes [9,10,11,12,13]. A study in Belgium revealed that carbon accumulation in the soil increases with rising precipitation, lower temperature, and higher clay content [14]. These multiple drivers of carbon dynamics lead to high uncertainties regarding the quantification of carbon fluxes, especially in mixed (species-mixed) deciduous forests. EC measurements are representative for areas extending some hundreds of metres in length [16,17]
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