Recovery of paramo vegetation after agricultural disturbance in the Colombian oriental cordillera

Abstract

The old field succession after potato crop abandonment, that takes place in a paramo situated in the Eastern Cordillera of the Colombian Andes, was studied. The aim was to analyse the dynamics of vegetation restoration and to estimate the optimal length of the fallow period that allows the restoration of paramo richness, diversity and structure. Six successional fallow periods were sampled: 10 months, 3 years, 6-8 years, 8-12 years, 12-15 years and natural paramo without evidence of recent use. The successional change in species richness and biodiversity was analysed as well as the abundance of the different life forms. The floristic turnover and floristic distance between plots with consecutives ages were calculated as two indicators of the rate of succession. The results show that the species richness increases linearly along the succession, reaching its maximum in the restored páramo. The rate of floristic turnover is high and constant along the succession but the floristic distance decreases progressively, indicating a community structure more and more close to the regenerated paramo. The sequence of species along the succession is very clear, with pioneer species (such as Rumex acetosella and Agrostis humboldtiana), intermediate successional species (like Paspalum hirtum and Espeletia argentea) and late successional species (such as Calamagrostis effusa and Espeletia grandifolia). The successional increase in structural complexity is also evidenced by the success of an increasing number of life-forms. Rhizomatous herbs and bunch grasses dominated the beginning of the succession, and progressively giant rosettes, bunch grasses and low shrubs become codominants. At the beginning of the succession most of the plant cover corresponds to introduced species, such as Rumex acetosella and Anthoxanthum odoratum, but during the succession their abundance decreases until their almost complete disappearance after 12 years. A TWINSPAN analysis classified the plots in five groups, which match well with the successional ages of the plots. The minimum time required to restore a significant part of the paramo vegetation is approximately 12 years, when more than 90% of the natural paramo species richness is attained