Argentinian Yungas Forest Fragmentation: Effects on Aboveground Biomass, Microclimate and Carbon Storage

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’s interesting to know if they constitute small-scale replicas of the forest from which they were detached. The objective of this study was to characterize 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.

The authors selected two size categories for fragments: 5 - 10 ha and 100 - 150 ha, located in the lower Yungas forest (LYF). They did sampling during the dry and wet seasons. As a result, in the larger fragments, the distance exerted 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 were 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 did not depend on the edge distance, but it was actually sunnier, drier and hotter than that of the forest. The soil had also lost organic carbon and humidity. These changes were 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 showed less density and trees of reduced dimensions (lower dbh and height). Fast-growing pioneer plant species and disturbance-loving lianas accompanied them. Edge plant composition presented notorious changes in the bigger fragments.

In conclusion, biomass and ecosystem processes such as carbon cycling, which had been modified into fragments, both were 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.

Article by Silvina Manrique, et al, from Argentina.

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Image by Andres Claros, from Flickr-cc.