A CONCEPTUAL-MODEL OF CHANGES IN ROOT COHESION IN RESPONSE TO VEGETATION MANAGEMENT

Cohesion contributed by plant root systems is an important factor in determining the stability of steep, vegetated slopes subject to shallow landslides. The effects of vegetation removal on root cohesion can be simulated by two functional relationships: (i) root deterioration as described by an exponential decay function and (ii) regrowth of newly planted or invading vegetation as described by a sigmoid relationship. The rates of these simultaneous functions determine the temporal changes in net rooting strength. The general root strength model developed in this paper is adapted to specific silvicultural systems such as clearcutting, partial cutting, shelterwood cutting, and thinning. The models simulate the long-term effects of vegetation management on root cohesion by overlaying the impacts of a prior vegetation removal on a more recent removal. Examples presented for specific silvicultural systems indicate that vegetation and site conditions that promote rapid root strength deterioration and slow regrowth may depress net rooting strength over several management rotations. Progressively shorter clearcut or partial cut rotations can cause a steady temporal decline in root strength. Longer intervals between initial and final shelterwood cuttings promote greater rooting strength than short intervals.