Abstract
Few studies exist that document how high-elevation Andean ecosystems recover naturally after the cessation of human activities and this can limit the implementation of cost-effective restoration actions. We assessed Andean forest (Polylepis stands) and páramo grassland recovery along an elevation gradient (3,600–4,350 m.a.s.l.) in the Yanacocha Reserve (Ecuador) where natural recovery has been allowed since 1995. Within the Yanacocha Reserve in 2012 and 2014 the aboveground biomass (AGB), aboveground necromass (AGN) and belowground biomass (BGB) carbon (C) stocks were measured and C sequestration rates calculated as proxy of ecosystem recovery. The soil organic carbon (SOC) stock to 36-cm depth was also quantified during the 2012 survey. To explore potential drivers of spatiotemporal variation of the forest and páramo C stocks they were related to abiotic and biotic variables. Andean forest C stocks were influenced mainly by disturbance history and tree-species composition. Páramo C stocks´ spatial variation were related to the elevation gradient; we found a positive significant trend in páramo AGB-C stocks with elevation, whereas we found a significant negative trend in AGN-C stocks. Likewise, significant temporal changes were found for AGB-C and AGN-C stocks. Net increases in AGB-C stocks were the largest in the Andean forest and páramo, 2.5 Mg C ha-1 year-1 and 1.5 Mg C ha-1 year-1 respectively. Carbon sequestration rates were partly explained by environmental variables. In the Andean forest, plots with low dominance of Baccharis padifolia were observed to present higher AGB-C and lower BGB-C sequestration rates. In the páramo, higher sequestration rates for AGB-C were found at higher elevations and associated with higher levels of growth-forms diversity. Temporal changes in BGB-C stocks on the contrary were non-significant. Our results indicated that terrestrial aboveground C sequestration rates might be an appropriate indicator for assessing Andean forest and páramo recovery after human disturbance.
Highlights
High-elevation tropical Andean ecosystems, such as woodlands dominated by the genus Polylepis and grass dominated paramo, are of paramount importance due to the economic and ecosystem services they provide [1,2,3]
In this paper we seek to improve the understanding of the natural recovery of terrestrial C stocks in both high-elevation Andean forest (> 3,700 m.a.s.l.) and paramo. To do this we provide a comprehensive assessment of aboveground biomass (AGB), Aboveground necromass (AGN), Belowground biomass (BGB), and soil organic carbon (SOC) stocks in Andean forest and paramo 23 years after grazing, firewood extraction and fire regimes ceased
We found an increase in the number of individuals recruited, and the total number of individuals, in each diameter at breast height (DBH) class of trees in 2014, except for the 2.5–4.9 and the 5–10.9 cm classes that experienced a subtle decrease in number of individuals (Table 1)
Summary
High-elevation tropical Andean ecosystems, such as woodlands dominated by the genus Polylepis (hereafter Andean forest) and grass dominated paramo, are of paramount importance due to the economic and ecosystem services they provide [1,2,3] These services include diverse and unique biodiversity [4, 5], carbon (C) storage [6,7,8,9,10,11], and water provision for direct human consumption, irrigation and hydropower generation [8]. Aerial and belowground C stocks vary greatly along the Andean forest and paramo gradient with the ratio between aboveground biomass (AGB) and soil organic carbon (SOC) decreasing at higher elevations. Grazing and burning may have effects on the SOC stock of both paramo and Andean forest ecosystems [1, 8, 14]
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