Sviluppo di un modello dinamico ecologico-forestale per foreste a struttura complessa

Forests are important both for socio-economic and for environmental aspects. Forests changes affect a delicate balance that involves not only vegetation components but also bio-geochemical cycles and global climate and they play an important role in biodiversity conservation. Hence the knowledge of the amount of Carbon sequestered for carbon cycle by forests, represents precious information for their sustainable management in the framework of climate changes. The aim of the present work is the development of a forest dynamic model, generic, hybrid on ecosystem spatial scale able to obtain useful predictive information for the knowledge of the process at the base of forest dynamic and forest management using ecophysiological parameters easy to be assessed and to be measured. The 3D-CMCC Forest Model is based on light use efficiency (LUE) approach at the canopy level. It's well documented that the mutual interaction of forest growth and light conditions cause vertical and horizontal differentiation in the natural forest mosaic. Only eco- physiological parameters which can be either directly measured or estimates with reasonable certainty, are used. The model has been created considering a tri-dimensional cell structure with different vertical layers depending on the forest type that has to be simulated. The 3D-CMCC Forest Model is able to work on multi-layer and multi-species forests type from one hectare cell resolution and at monthly time-step for the typical Italian forest species. The multi-layer version is the result of the implementation and development of Lambert-Beer law for the estimation of intercepted, absorbed and transmitted light through different storeys of the forest in a new logic structure. It is possible estimates, for each storey, a PAR value (Photosynthetic Active Radiation) through Leaf Area Index (LAI), Light Extinction Coefficient and cell Canopy Cover using a "Big Leaf" approach and the evapotraspiration rate, itself closely linked to the light intercepted, for each layer and the evaporation from soil. Hence, the presence of a cohort in a storey determines the amount of light received for the photosynthetic processes. The population density (numbers of trees per cell) represents a good competition index for determining the tree crown structure and tree crown dimension within a forest population. The model assesses the structure of the tree crown both vertically and horizontally on the base of the population density and it upscale the result to the whole stand. The canopy depth and the percentage of horizontal coverage determines moreover a crowding competition index that lead to a specific biomass partitioning-allocation ratio among the different tree components (foliage, roots, stem and fruits) and especially for the stem affecting Height-Diameter (at breast height) ratio hence modeling the forest dynamic. In this model, Height- Diameter ratio is used as an alternative competition index in determining the vigour and the strength of competition on free growth status of trees. The forest dominant vegetative cover affects moreover the presence of a dominated layer, it influences its yield and its carbon stocking capacity and thereby the forest ecosystem CO 2 carbon balance. Using this model it is possible to simulate the impact of climate change on forests as a result of productivity decrement or in some cases increment as well as the feedback of one or more dominated layers in terms of CO 2 uptake in a forest stand and the effects of forest management activities for the next years. The model has been applied in an explanatory investigation to compute the medium-term (10 years) development of a multi-layer, multi-age and multi-species turkey oak forest (Q. cerris L.). The results obtained agree with measured data.