The role of herbaceous understorey vegetation in forest landscape dynamics

1.    Light competition between overstorey and understorey vegetation

In most temperate forests, competition for light is the main interaction between the understorey and overstorey. On the one hand, understorey competes with juvenile trees for light and can thus act as a filter for tree establishment. On the other hand, shading from the overstorey determines understorey composition and biomass. We studied the long-term implications of this interaction for forest dynamics (external page Thrippleton et al. 2016). In particular we addressed the questions: (1) How strongly does the understorey delay forest succession? (2) Can strong understorey competition cause ‘arrested’ succession, where the ecosystem does not revert back to a closed-canopy forest? (3) How does the presence of a dense understorey affect the composition of tree species in the long term?

2.    Water competition between trees and the herbaceous layer

Herbaceous understorey vegetation can be an efficient competitor for soil water resources, particularly in open, Mediterranean-type forests. Water competition will not only affect tree regeneration, but potentially reduce the growth and increase the mortality of mature trees. By improving the simulation of water competition between herbs, sapling and trees in LandClim, this project investigated the implications of increased water competition by the herbaceous layer on current and future forest landscape dynamics.