Growth Pattern of European Black Pine outside Its Current Natural Range: A Case Study in Portugal

European Black Pine (Pinus nigra J.F. Arnold) is a fast-growing conifer, currently distributed in a fragmented pattern from western North Africa through Southern Europe to Asia Minor and is an economically important native conifer in Southern Europe. In Portugal, P. nigra populations are allochthonous, and were planted 50–90 years ago with plant material of unknown origin. This work intended to evaluate and investigate long-term radial growth characteristics of the species on the westernmost part of Europe, outside its natural range, in mainland Portugal. To achieve this objective, six planted stands located in the north and centre of the country were chosen, which were considered representative of the distribution of the species in the country and the most extreme south-western location in Europe. The height and diameter at breast height was measured and the general state of these stands was evaluated. Overall, no mortality was observed except in one site, where trees manifested poor growth. Sampling a set of 15 trees per site, was used to create a database for analysis of the radial development of the species. The 90 trees sampled, with ages ranging from 56–98 years, provided a database of 5308 observations of diameter-age pairs. The Schumacher function was tested for the description of radial growth and provided satisfying results in terms of the model fitness, allowing us to summarize general trends of diameter growth among sites. Complementary analysis of radial growth at a tree age of 50-yr was performed to assess for differences among populations. It was concluded that radial growth differs between sites, and two statistically different groups were identified, although no specific latitudinal or longitudinal gradients were found. The information on the identified growth patterns can be used for decision-making purposes when considering species selection in afforestation or reforestation procedures in the context of adaptive management.