Growth patterns of native and introduced conifers when both coexist: Implications for invasion process

RELVA, M.A.; SUAREZ, ML; GRISSINO-MAYER, H.

Congreso; . First IUFRO Landscape Ecology Latin-American and Second IALE Latin- American Congress; 2016

The invasion by woody plants is matter of concern amongst scientists, conservationists and environmental managers as it has a serious ecological and economic impact worldwide. In the last 40 years extensive conifer plantations, mainly fast-growing Pinaceae, highly invasive elsewhere, have been established in forests, shrublands and grasslands in Chile and Argentina. Problems derived from plantations include increased fire frequency and severity, reduction of biodiversity, and replacement of plant communities. Overall, tree invasion in forests occur comparatively at slower rate than in treeless and disturbed areas. In this study we investigate the competitive interaction of both native and exotic conifers (Austrocedrus chilensis and Pseudotsuga menziesii, respectively) as a mechanism explaining the slow process of conifer invasion observed in a pristine native forest in northern Patagonia, Argentina. In 2012, on Isla Victoria (Nahuel Huapi National Park), we collected tree core samples from native and exotic trees growing in a native forest close to the main plantation (n= 18 patches). We applied dendrochronological methods to assess growth patterns and changes in Basal Area Index (BAI) for both species. Contrary to expected, the results indicate a major competitive ability of exotic over native species. BAI patterns indicate that, despite both species grow well since its establishment, according time pass the presence of exotic impact negatively on the growth of native. This decreasing trend in growth could be in relation with the moment when the exotic surpass the native in terms of diameter and height. Negative interaction is also demonstrated as 70% of native trees show strong release in growth when exotic trees were removed through logging activities. As invasion is a complex process with multiple drivers interacting, others factors than competition, may be explaining the slow process of invasion in this pristine forests.However, the higher growth of exotic compared to the native would confer a competitive advantage in case of major disturbances occur, with a likely acceleration of the invasion.