ABSTRACT
The Argentinian Yungas ecosystem, the more extensive of the two richest biodiversity ecoregions of the country, is subject to rapid deforestation and fragmentation. Because these fragments are the future biodiversity reserves of this ecosystem, it was interesting to know if they constitute small-scale replicas of the forest from which they were detached. Our objective was to characterise the fragments and compare them with sectors of continuous forest by studying the aboveground tree biomass (for the five most representative forest species), microclimate (three variables) and edaphic factors (three) as a function of distance from forest edge at 15, 25, 50, 100 and 200 meters. We selected two size categories for fragments: 5 - 10 ha and 100 - 150 ha, located in the lower Yungas forest (LYF). We did sampling during the dry and wet seasons. As a result, in the larger fragments, the distance exerts a significant effect on the records of the microclimate and edaphic variables, gradually modifying them from the edge to the interior (up to at least 100 meters). The variations are more evident in the wet season. Solar radiation and relative humidity were two of the factors with greater response (Spearman r= -0.89; p < 0.001 and r = 0.58; p < 0.001, in the dry season, respectively). The microclimate of small fragments does not depend on the edge distance, but it is actually sunnier, drier and hotter than that of the forest. The soil has also lost organic carbon and humidity. These changes are accompanied by a lower AGB in the fragments with respect to the forest (6% and 60% of 162 ± 26.02 t·ha-1, for small and big fragments, respectively). The five species studied show less density and trees of reduced dimensions (lower dbh and height). Fast-growing pioneer plant species and disturbance-loving lianas accompany them. Edge plant composition presents notorious changes in the bigger fragments. Biomass and ecosystem processes such as carbon cycling, which have been modified into fragments, both are directly associated with the structure and functioning in LYF remnants. The human and animal intervention detected in the area could be interacting synergistically with the microclimate and biological changes observed and potentiate the effects of degradation in the fragments, creating conditions of greater threat to LYF’s biodiversity. However, the management of the LYF ecosystem within an adequate land use scheme could conserve and even encourage the recovery of the fragments ensuring a natural legacy of great importance for the country. Financing opportunities and globally assumed responsibilities in the context of climate change could constitute a favorable framework for the implementation of strategies to safeguard these forests.