MARIOLA - A MODEL FOR CALCULATING THE RESPONSE OF MEDITERRANEAN BUSH ECOSYSTEM TO CLIMATIC VARIATIONS

The paper summarizes the bush ecosystem model developed for assessing the effects of climatic change on the behaviour of mediterranean bushe s assuming that temperature, humidity and rain-fall are the basic dime nsions of the niche occupied by shrub species. In this context, change s in the monthly weather pattern serve only to outline the growth cond itions due to the nonlinearity of response of shrubs to climatic facto rs. The plant-soil-atmosphere system is described by means of ordinary non-linear differential equations for the state variables: green biom ass, woody biomass, the residues of green and woody biomasses, faecal detritus of mammals on the soil, and the total organic matter of the s oil. The behaviour of the flow variables is described by means of equa tions obtained from non-linear multiple regressions from the state var iables and the input variables. The model has been applied with succes s to the behaviour of Cistus albidus in two zones of the Province of A licante (Spain). The data base for the parametrical locations (zone 1) and validation (zone 2) is based upon measurements taken weekly over a 2-year period. The model is used to simulate the response of this sh rub to a decreasing tendency in precipitation combined with a simultan eous rise in temperature. A period of 10 years is simulated and it is observed that plants with woody biomass smaller than 85 g die between the first and the third month and other plants' biomass decreases duri ng this period, and strongly thereafter.