Testing an optimality-based model of rooting zone water storage capacity in temperate forests

Abstract

Abstract. Rooting zone water storage capacity ! is a crucial parameter in models of hydrology, ecosystem gas exchange 10 and vegetation dynamics. Despite its importance, this parameter is still poorly constrained and subject to high uncertainty.We tested the analytical, optimality-based model of effective rooting depth proposed by Guswa (2010) with regard to its applicability for parameterizing ! in temperate forests. The model assumes that plants dimension their rooting systems in order to maximize net carbon gain. Results from this model were compared against values obtained by calibrating a local water balance model against latent heat flux and soil moisture observations from 15 eddy covariance sites. To increase the 15 applicability of the rooting depth model, we provide a numerical approximation of its underlying probabilistic soil moisture model.The calibration and validation of the local water balance model showed that the concept of a single rooting zone storage capacity was appropriate at most temperate and cold sites, but not at Mediterranean sites and for very coarse soils. At a majority of sites, the estimates of ! are generally in good agreement. However, mismatches were found in stands dominated 20 by Norway spruce, especially at high elevations. These mismatches were attributed to the fact that the model does not consider rooting depth limitations due to oxygen stress and low soil temperature. Also, it is not clear whether the rooting behavior of pines on coarse soils is captured properly. Nevertheless, the overall good agreement suggests that this model may be useful for generating estimates of rooting zone storage capacity for both hydrological and ecological applications.Another potential use is the dynamic parameterization of the rooting zone in process-based models, which greatly increases 25 the reliability of transient climate-impact assessment studies.

Modeling the effect of rockfall on forest development in a dynamic forest landscape model

“…However, along with water availability, nutrients may be limited and thus impede recolonization of the highly disturbed areas. This implies that a more complex deterministic model of soil generation, water and nutrient availability (e.g., Speich et al, 2018), and its effect on regeneration would be necessary to satisfactorily represent the rockfall-forest feedback. The fast recolonization could also be related to a general overestimation of Larix biomass and overshooting effects in the first 50 years.…”