Catastrophes in Exploited Forests

Gatto, M. & Rinaldi, S. (1984). Catastrophes in Exploited Forests. IIASA Working Paper. IIASA, Laxenburg, Austria: WP-84-078

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Abstract

(1) This paper shows why small variations of the human exploitation of a natural forest can give rise to dramatic changes in forest biomass.

(2) Two simple mechanisms for catastrophes, already pointed out for other ecosystems, are briefly discussed at the beginning of the paper. The first occurs when depensation phenomena are present in the forest growth curve, while the second is due to the concavity of the harvesting function, which can be interpreted as the functional response of the forest exploiters. In both cases a small increase in the exploitation can lead to the collapse of the forest.

(3) A more interesting mechanism for catastrophes is then presented. It is based on the dynamics of the soil nutrient and the fact that tree mortality may become very high when soil acidity exceeds a threshold.

(4) In particular, it is shown that an increase of the exploitation may give rise to a catastrophic collapse of the forest if the exogenous nutrient inflow (i.e., acidic deposition) is sufficiently high. Moreover, such a catastrophe is irreversible, i.e., reforestation is not possible, if the nutrient inflow is too high.

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