Abstract:
Deforestation for gaining pastures and croplands is still advancing in the tropical Andes while vast agricultural areas are at the same time disused due to degradation (FAO 2011). In the research area in South Ecuador infestation by bracken (Pteridium spp.) plays an important role in this regard (Göttlicher et al. 2009), especially where fire is used for forest clearing or in pasture management (Hartig & Beck 2003, Roos et al. 2010).
The focus of our study was: (1) the analysis of the infestation rate of bracken on agricultural land, (2) to reconvert bracken-infested areas into useful pastures, and (3) to find a sustainable management for the rehabilitated pastures.
Bracken cover was analyzed using high resolution satellite data (QuickBird) on which bracken could be identified from the spectral reflection. Actually, almost 40% of the potential mountain pastures in the research area have been abandoned, because they are overgrown by the weed. An experiment extending over several years was conducted to reconvert these abandoned areas into pastures (Roos et al. 2011): A two-step strategy seemed to be successful. In a first step, the efficacy of 13 bracken control treatments was compared with the vegetation development in untreated plots. Two of the measures proved to be successful and at the same time affordable for the local farmers, namely periodical cutting of the weed with a machete or repeated spraying of a locally available herbicide ?Combo? (a mixture of metsulfuron methyl and picloram) (Figure 1A). However, due to brackens persistent rhizomes in various soil depths, only ponderable weakening of the weed could be achieved, but not complete eradication. In a next step, the common pasture grass Setaria sphacelata (a highly competitive C4-grass) was planted. About 1.5 years later, the grass had reached a cover of more than 70% suppressing the fern to a cover of less than 40% and grazing could start (Figure 1B). Growth of bracken and of Setaria was monitored monthly using cover and height of vegetation as variables. Different extensive and intensive management treatments (various grazing intensities in combination with fertilization regimes) were applied to the rehabilitated pasture plots, and the effects on biomass gain and protein content of Setaria were analyzed. Additionally, vegetation composition depending on the treatments was compared with existing pastures. Regrowing bracken fronds should be removed annually with the machete to maintain the weed on a low stage.
Following the described protocol, repasturisation requires about 2.5 years until the pastures can be used. Applying a balanced management of fertilization and grazing can lead into a sustainable reutilization of the abandoned areas and thus alleviate the pressure on the natural forests.
