Pinus contorta invasion in Patagonia is influenced by resident vegetation and herbivory

Background/Question/Methods

Pine invasions have been well documented, especially in the southern hemisphere. Pinus contorta, one of the most aggressive pine species, represents a serious threat to the new environments where it has been introduced. Originally the species was introduced to the Chilean Patagonia almost forty years ago in order to control the erosion process caused by intense human-originated fires, but currently it is also planted with commercial purposes covering more than 6000 ha in the Aysén Region. Given its excellent adaptation, it is now invading anthropogenic grasslands, created by fires in previously forested areas, and the native Patagonian Steppe.  Our aim was to determine the spatial patterns of the invasion process and to identify the main influences of the resident vegetation and herbivory. Transects were established to determine spatial patterns at the local scale. A grid sampling was used to understand microsite interactions using point pattern analysis. Finally, a field experiment was conducted to test for the effects of substrate on survival and growth. 

Results/Conclusions

Pinus contorta invasion in the Chilean Patagonia is at an early stage, following the same patterns reported in other affected areas, and with sites still available for recruitment. When analyzing at a micro site scale, we realized that recruitment is determined by the presence of two native cover types, Baccharis magellanica and Tussock grasses. This interaction, seen as pine individuals clumped around the two cover types determines the spatial distribution of pines in the new environment. But when we looked at a smaller scale, experiments showed that this positive association does not occur only with those two cover types, and that those spatial patterns at a micro-site scale probably represent “safe” environmental conditions for pine establishment.  Herbivory on the other side, is limiting the invasion process. Browsed trees present wider crowns as the result of losing the main stem, giving it a shrubby aspect, and reducing the size of trees. Finally, P. contorta is interacting with the resident biota of the Patagonian steppe. Native plant could be enhancing its establishment whereas herbivores could be limiting its success.  

Funded by Fondecyt 1100792, ICM P05-002, and PFB-23.