Abstract. Rooting zone water storage capacity Sr is a crucial parameter for
modeling hydrology, ecosystem gas exchange 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 (2008, 2010) with regard to its
applicability for parameterizing Sr in temperate forests. The
model assumes that plants dimension their rooting systems 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. Then, the effect of
optimality-based Sr estimates on the performance of local water
balance predictions was assessed during model validation. The agreement between calibrated and optimality-based Sr varied
greatly across climates and forest types. At a majority of cold and temperate
sites, the Sr estimates were similar for both methods, and the
water balance model performed equally well when parameterized with calibrated
and with optimality-based Sr. At spruce-dominated sites,
optimality-based Sr were much larger than calibrated values.
However, this did not affect the performance of the water balance model. On
the other hand, at the Mediterranean sites considered in this study,
optimality-based Sr were consistently much smaller than
calibrated values. The same was the case at pine-dominated sites on sandy
soils. Accordingly, performance of the water balance model was much worse at
these sites when optimality-based Sr were used. This rooting
depth parameterization might be used in dynamic (eco)hydrological models
under cold and temperate conditions, either to estimate Sr
without calibration or as a model component. This could greatly increase the
reliability of transient climate-impact assessment studies. On the other
hand, the results from this study do not warrant the application of this
model to Mediterranean climates or on very coarse soils. While the cause of
these mismatches cannot be determined with certainty, it is possible that
trees under these conditions follow rooting strategies that differ from the
carbon budget optimization assumed by the model.
Testing an optimality-based model of rooting zone water storage capacity in temperate forests
