On the growth performance of two competing species in an Andean pasture of southern Ecuador - monitoring and simulations
The megadiverse tropical mountain forests in the southeastern Andes of Ecuador, including their biodiversity and ecosystem services, are severely threatened due to climate warming and the clearing of forests to produce pasture land. The common local practice of recurrent burning for pasture rejuvena...
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|Summary:||The megadiverse tropical mountain forests in the southeastern Andes of Ecuador, including their biodiversity and ecosystem services, are severely threatened due to climate warming and the clearing of forests to produce pasture land. The common local practice of recurrent burning for pasture rejuvenation has proven to be non-sustainable, since it enables bracken fern to invade pastures, causing farmers to abandon heavily infested pastures and instead clear new tracts of natural forest. No quantitative information on the growth potential of pasture grass and bracken fern under current and future environmental conditions has yet been available for the Andes of Ecuador. The scientific basis required to understand bracken invasion has yet to be established. This scientific basis would enable the development of sustainable pasture management strategies. Such strategies would, in turn, help protect the remnants of natural forest. Consequently, the present work aims at investigating the growth potential of two competing species under current and future climate conditions. Outcomes provide new knowledge and methodological developments concerning pasture invasion by bracken fern in southern Ecuador. The method entails the development of a new model, the Southern Bracken Competition Model (SoBraCoMo), realistically parameterized and validated. The model code is based on existing Soil Vegetation Atmosphere Transfer (SVAT) and vegetation dynamic models to calculate the potential growth of two main competitors, the southern bracken fern (Pteridium arachnoideum) and the pasture grass (Setaria sphacelata). Extensive field measurements and proper meteorological forcing delivered new site and species-specific parameters for realistic productivity simulations of both species. An experimental site was established to observe pasture and bracken fern development under the practice of recurrent burning, and to provide atmospheric data for a realistic forcing of the developed model. A novel balloon-borne monitoring system was developed to detect species cover and provided new insights into post-fire canopy recovery. The main results demonstrate that, under current environmental conditions, Setaria has a slightly higher competitive growth potential under undisturbed conditions (no grazing, trampling, or light competition). Furthermore, this growth advantage of Setaria should most likely increase due to global warming. Because field observations show bracken infestation, however, other factors than those investigated should be responsible for the bracken fern’s current success. The most likely cause of bracken success to be investigated in the future is cattle browsing; although browsing continuously removes aboveground biomass, this disruption of the upper soil does not affect deep roots and rhizomes of bracken plants. The newly developed SoBraCoMo can now provide an excellent basis to implement new mechanisms like browsing for future simulations.|