We are comparing spatially explicit process-model based estimates of the terrestrial carbon balance and its components over Africa and confront them with remote sensing based proxies of vegetation productivity and atmospheric inversions of land-atmosphere net carbon exchange. Particular emphasis is on characterizing the patterns of interannual variability of carbon fluxes and analyzing the factors and processes responsible for it. For this purpose simulations with the terrestrial biosphere models ORCHIDEE, LPJ-DGVM, LPJ-Guess and JULES have been performed using a standardized modeling protocol and a uniform set of corrected climate forcing data. While the models differ concerning the absolute magnitude of carbon fluxes, we find several robust patterns of interannual variability among the models. Models exhibit largest interannual variability in southern and eastern Africa, regions which are primarily covered by herbaceous vegetation. Interannual variability of the net carbon balance appears to be more strongly influenced by gross primary production than by ecosystem respiration. A principal component analysis indicates that moisture is the main driving factor of interannual gross primary production variability for those regions. On the contrary in a large part of the inner tropics radiation appears to be limiting in two models. These patterns are corroborated by remotely sensed vegetation properties from the SeaWiFS satellite sensor. Inverse atmospheric modeling estimates of surface carbon fluxes are less conclusive at this point, implying the need for a denser network of observation stations over Africa.

A large-scale regional event of springtime bark-splitting in Acer pseudoplatanus was observed in Germany in May 2018, where bark dissected from the wood. In young trees, an average of about 30% of the circumference was affected by cracks that were up to 8 m long. The damage occurred on the south-facing side of the trees after a warm period in March, followed by an extreme cold spell and warm temperatures. In this study, we investigated the possible causes of this damage. The damage occurred in the expanding xylem with cambial cells remaining in the bark. These cells-initiated growths of new, bark-based stems. The unprotected xylem was attacked by several fungi and wood-boring bark beetles. The mode of damage-recovery suggested that this event will eventually lead to a frost-scar-like structure in the future that will not totally heal, because the new stems attached to the old bark were in the process of forming new bark. Due to the increase in variation of springtime temperatures observed over the past 40 years, such damage may become more common in the future.