Pinus contorta, with a native range in North America, has been registered as invasive in many parts of the world. Its invasiveness, as in other pine species, is given by a short juvenile period, short time period between large sees crops and the small size of the seeds. In Chile, the species has been recorded as invasive in the Araucanía Region (38° S) and in the Aysén Region (45°S). Invasions are relatively new (ca. 10-20 years for oldest individuals) and occur in anthropogenic grasslands, the Patagonian steppe and alpine environments. This pine invasion provides a unique opportunity to test several basic assumptions about tree invasions such as their dispersal spatial array and the existence of positive or negative spatial interactions with native plant species. We have studied Pinus contorta invasion in the steppe of Coyhaique Alto, of the Aysén Region. We have measured the extent of the invasion, the spatial arrangement of the invading pines at multiple scales and the association between pines and native plants. In addition to standard statistics, we have used point pattern analyses to test whether there is aggregation or repulsion between pines and native plants.
Results/Conclusions
Pine density was 3,100 trees per hectare at 50 m from the plantation decreased to 2,800 trees per hectare at 90 m from it and down to 900 at 100 m. Pine cover was also higher closer to the plantation. The most common cover type in both plots was bare ground, followed by grass tussocks and Baccharis magellanica. Univariate analyses show clumping for all cover types in both plots. B. magellanica and Oreopolus glacialis showed the most significant associations. Bivariate analyses show that B. magellanica is aggregated to pines up to a distance of 4.75 m. Pines showed intra-specific aggregation only for individuals in smaller height classes (<80cm). Our results indicate that the spatial distribution of the invasive pine is the result of positive and negative interactions with native species, but also depends on the strength of this interaction, driven by the disturbance level.