Space-time modeling of changes in the abundance and distribution of tree species

Land use change and global warming are important drivers in the distribution of tree species. The Mediterranean mountain forest ecosystems can be severely affected by climate change since an increment in temperature has been observed. The main aim of this work was to analyze shifts in the distribution and changes in the abundance of Pyrenean oak (Quercus pyrenaica Willd.) and Scots pine (Pinus sylvestris L.) in Mediterranean mountains over a period of 47 years (1965-2012) by using data from the National Forest Inventories, extending the Universal Kriging/Cokriging models to the space-time case for long-term forest inventory data analysis including climatic variables. Our results indicated that both the distribution and the abundance of Scots pine remained quite constant during the study period. Pyrenean oak increased its presence by 42% whereas its abundance doubled between 1965 and 2012. This movement took place towards both higher and lower altitudes. With regard to climatic factors, the kriging models showed a negative association between the presence of Scots pine and the temperature. However, we found a quadratic relationship between the Pyrenean oak and temperature, pointing to the occurrence of at intermediate altitudes. Additionally, we found significant relationships between the rainfall and the abundance of both species. Rainfall was positively related to the abundance of Scots pine and negatively to that of Pyrenean oak. Our results indicate that there has been a threefold increase in the area covered by mixed stands. However, successive land use changes as well as forest policies related to conservation have played an important role in the distribution of both species and therefore are taken into account in the discussion of these results. (C) 2016 Elsevier B.V. All rights reserved.