Productivity of Pinus radiata plantations in Spain in response to climate and soil

Pinus radiata D. Don is planted in Spain, in a wide range of soils and climatic conditions. We aimed to identify the main site factors that control the productivity of this species and determine to what extent its growth is limited by the soil quality and the climate. For this purpose, we selected 22 stands of P. radiata on the basis of parent material (nine substrates) and climate (Mediterranean and Atlantic). The highest levels of forest productivity were unexpectedly found in the lower rainfall Mediterranean area, while the lowest ones were found in the wet Atlantic area. Litterfall showed the highest correlation with site index. Soil depth combined with altitude was also significantly related to site index. Principal component analysis, performed using a set of selected soil and site fertility variables, showed a separation between the Atlantic and the Mediterranean sites, suggesting that the soil processes determining soil fertility differ in the two climates. Within each climatic zone, site environmental variables were clearly associated with site index. In the Mediterranean area, site index was strongly related to soil depth and to the amount of P in the organic layers, while in the Atlantic area it was mainly associated with site altitude and mineral soil CEC. According to our results, Mediterranean plantations are confined to deep soils and their quality is also related to the amount and concentration of nutrients in the organic layers. On the other hand, the Atlantic plantations grow faster at lower elevations and they are also sensitive to soil fertility as their site quality is affected by CEC. The intensive management of these plantations is likely to increase productivity mainly in areas not limited by temperature. (C) 2004 Elsevier B.V. All rights reserved.