Clear-Cut experiments

Forests are an important economic resource and thus subject to intense logging. Logging operations often clear-cut large stretches of forest. Thus, the first experiment we performed on the SORTIE model is a simple, one-time clear-cut. Clear-cuts are implemented by cutting 35% of the landscape 100 years into the simulation. The forest is left undisturbed after this single cut. We implement three different clear-cut regimes: one large cut with 10% seedling survival (partial cut), one large cut with no seedling survival (complete cut), and four simultaneous small cuts with no seedling survival.

Forest Age	Partial clear-cut 10% Seedlings remain	Complete clear-cut No seedlings survive	Small clear-cuts No seedlings survive
100 Years (cut)
500 Years
1000 Years	Animation	Animation	Animation

Clear-cuts are implemented 100 years into the simulation. The clear-cuts, which cover the same total area, remove all adult trees and most or all of the seedlings.

The results of the three clear-cuts are diverse and striking. In the partial clear-cut, yellow birch seedlings colonize the open space and are interspersed with seedlings of other species left behind in the cut. Over time, beech and hemlock outcompete yellow birch, driving the forest toward the base-line state. In contrast, the dense patch of yellow birch that colonizes the complete clear-cut is extremely stable through time. Although hemlock and beech are superior competitors in undisturbed forests, they have limited dispersal and are unable to displace the large, dense patch of yellow birch. The small cuts are intermediate in behavior: yellow birch is dominant in the areas that are cut, but the smaller size of each patch allows greater intrusion of the superior competitors, beech and hemlock.

The presence of a small number of seedlings from these competitively superior species in the partial clear-cut leads to the yellow birch steadily losing area to hemlock and beech. Essentially, these few seedlings serve as seed sources for the dispersal limited species. Smaller cuts enhance the ability of the dispersal-limited species to encroach upon the yellow birch patches but are not as effective as leaving a few seedlings in the cut itself.

Base-line without disturbance	Base-line with disturbance	Small clear-cut no seedlings

The effect of these clear-cuts is similar to the base-line runs with disturbance. In all runs, yellow birch is able to quickly colonize newly opened space but unable to maintain itself in direct competition with beech and hemlock. The relative balance of power and the subsequent speed of competitive exclusion of yellow birch is strongly influenced by the size of the cut and the survival of even a few seedlings within the cut.

Implementing Clear-Cuts