Tree Mortality may Drive Landscape Formation: Comparative Study from Ten Temperate Forests
Tree mortality can fundamentally affect soils, which in turn shape forest regeneration and dynamics. Here, we quantify the dynamics of soil volumes associated with tree mortality, parsing effects by mode of tree death (broken vs uprooted) and species. The concept of ecosystem biogeomorphic succession was also tested. We used repeated tree censuses carried out in ten European and North American forests, differing in species composition, climate, and disturbance regimes. Development of more than 172,000 individual trees was recorded over periods of up to 48 years, during which more than one-third of the trees died. Biogeomorphic impact of deaths was modeled using allometry and field measurements. Tree uprooting-related soil volumes accounted annually for 0.01–13.5 m3ha−1, reaching maximum values on sites with infrequent strong windstorms (European mountains). The redistribution of soils related to trees that died standing ranged annually between 0.17 and 20.7 m3ha−1 and were highest in the presence of non-stand-replacing fire (Yosemite National Park, USA). Comparison of the results with known long-term erosion rates suggests that on certain sites over the last few millennia, tree uprooting may represent a significant driver of landscape erosion. Despite the key role of severe disturbances, the data showed potential for future increases in the intensity of biogeomorphic processes. The high biogeomorphic potential in some USA sites that has not yet been realized can be activated by external changes in the disturbance regime. Forests in Central Europe, on the other hand, are more sensitive to changes in biogeomorphic processes due to species turnover.