Crown plasticity in Scots pine (Pinus sylvestris L.) as a strategy of adaptation to competition and environmental factors

Competition for canopy space is a major ecological process in forest dynamics and some tree species are able to shift their crowns away from competition pressure to improve light capture. As a result canopy structure is an expression of the spatial pattern of resource acquisition. A novel combination of spatial analysis, tessellations and computer simulations of crown movements allowed us to disentangle the main processes that govern crown movements in Pinus sylvestris L. forests. By applying spatial point process statistics to three sets of coordinates (stem, crown and tessellation centre points), we analysed and modelled the interaction between individuals along different tree-crown development stages in Valsain forest, Sierra of Guadarrama (Spain). Overall we found that Scots pine trees were able to respond to the presence of neighbours in monospecific stands. The trees involved tended to avoid competition by shifting their crowns towards empty spaces. Mature trees showed more crown displacement than smaller trees and made an effective use of canopy space. The efficient use of space in older stands was indicated by more regular crown patterns compared to those of younger stands, which usually were more clustered. We also found that crown asymmetry was often a combination of some minor abiotic and biotic ecological processes. In our study, wind and slope did not have a big effect on crown displacement, while biotic interactions showed a strong effect on canopy structure causing trees to be regularly distributed and thus using canopy space more efficiently.