Predictive approaches to forest site productivity: recent trends, challenges and future perspectives. Forestry 87, 109–128. doi:10.1093/forestry/cpt034

In the framework of sustainable forest management, measuring site quality and predicting site productivity remain a major forestry topic. Over the past years, it has been fostered by a number of site-growth modelling studies seeking to establish quantitative relationships between site index and explicit biophysical indicators. In addition, comparative modelling studies of site index and site productivity have highlighted limited accordance of their environmental determinism, questioning site index as a reliable indicator of site quality. Lastly, process-based modelling approaches have recently arisen as a means to predict site productivity over large regions. All these investigations have however drawn limited attention in recent syntheses. In this review,we provide an over-view of the literature on these site-growth studies. Concepts and vocabulary related to site productivity are intro-duced. Taking regional studies as a baseline, we first highlight recent progress regarding the geographic areas encompassed, and the major role played by NFI programmes and spatialized environmental information. A trade-off between model accuracy and geographic extent is suggested, pointing out potential deficiencies in the modelling of site-growth associations, insufficient accuracy or resolution in climatic data, or uncontrolled factors in site-growthmodels thatemergeonahigher spatial scale. Inappropriateuseofbiophysical classifications where environmental factors remain implicit is also emphasized. In a next step, we discuss early andmost recent indications on weaknesses of the site index concept when applied over large regions, including its differential re