Figure 7
From: Thermodynamic basis for the demarcation of Arctic and alpine treelines
Conceptual model for the existence of treelines as a result of self-organization of the thermal environment. Self-organized treelines are demonstrated through the balance of positive or negative feedback between the resulting temperature gradient and the work performed by various vegetation structures. The negative of the resultant temperature gradient is plotted on the x-axis. Thus, the positive x-axis refers to a negative temperature gradient such that larger values indicate stronger declines in temperature from the earth surface to the atmosphere. The negative x-axis indicates positive temperature gradients, or temperature inversions. The dotted line represents an ecosystem without vegetation (i.e., bare soil). The colored solid lines represent vegetation curves as defined in Table 1. Dissipation rates leading to negative (N1 or N2) or positive (P) feedback loops between temperature gradient and vegetation structure are shown as the vertical distance from the bare soil curve to the vegetation scenarios. The starred scenario on each plot represents the most advantageous viable vegetation structure for the given ecosystem. The plot on the left represents ecosystems in which both vegetation scenarios (X-For & X-Un) are viable options, and the X-For scenario is most advantageous. The plot on the right represents ecosystems in which one of the vegetation scenarios (X-Tr) is infeasible due to positive feedback loops that result in continued dissipation of heat during temperature inversions. Instead, the X-Alp/Arc scenario is the most advantageous viable vegetation structure.
