Résumé
Ecosystems provide goods and services that contribute to human welfare, and provide an environment in which ecological process take place. Economic theories predict that ecosystem goods and services for which there are inefficient markets, trend to be underrepresented in management decisions and their supply will be sub-optimal. Ecosystem Degradation not only has many negative impacts on economic condition, but also has many negative effects on future sustainable economic growth. One of the most important reasons for this degradation is lack of market for ecological goods and services. On the other hand, estimating the real value of these functions is an essential need for achieving the appropriate allocation of natural resources. Valuation can be effective in obtaining the social decisions, in the assessment of cost and benefit, accept or reject of the project, or determine appropriate and acceptable level of damages to the environment. Also in national income calculations in macro level, awareness of the value is required, because usually in the process of economic development ecosystem goods and services are not entered in the calculations and often results in wrong patient to provide statistics such as GDP indices. Knowing the values plays an effective role in people's and policy makers' attention to the environment. In fact, the fundamental point is that the value of ecosystem service is not the solely aim but it is a [decision support tool] to a better decision making in environmental filed. Forests as one of the most important terrestrial ecosystems provide the highest number of ecosystem services and there is no market to present their values. Among these non market services, gas regulation is the most important issue. Forests are carbon stores, and they are carbon dioxide sinks because plants absorb co[2] and use it in photosynthesis process. This process, in addition to producing plant biomass and releasing O[2], has an effective role in reducing the greenhouse effect. In the recent years there are a lot of concerns with this phenomena and it causes global warming with a lot of significant effects. Amongst the world forests, tropical forest stands the highest in carbon absorption. There is not a spatial similarity in co[2] absorption because of the difference in plant concentration, tropical situation, kinds of specious and the amount of plant annual growth per hectare. Therefore, spatial valuation can distinguish between these differences and shows the heterogeneity in these areas. In this study we introduce a pattern to achieve spatial distribution of co[2] absorption with geographical information system in a part of Caspian forests of Iran