Abstract
Montane ecosystems occur throughout the world, and harbor many endemic species. They also provide key ecological services, including the catchment of water resources and the storage of organic carbon. These ecosystems are vulnerable to global climate change and increasing human pressures, including forestry and their conversion to arable land. In the extensive and biodiverse Mexican montane regions, ongoing deforestation and conversion to arable lands has led to diminished ecosystem health and services. Here, we undertook a comprehensive evaluation of carbon stocks within Mexican montane habitats in the Flora and Fauna Conservation Area of Nevado de Toluca. This aimed to integrate these habitats into Mexican and global census of forest carbon, the first step needed to convert on carbon credit markets to incentivize conservation of this region by local communities. Our study evaluated both, living biomass and belowground soil organic carbon in sites within forests, alpine grasslands and converted arable land. We addressed the following questions: (1) What are the organic carbon stocks, including the soil component, of our studied montane habitats? (2) What are the avoided CO emissions from maintaining natural forests and preventing conversion to arable land? And (3) Within our study area, are organic carbon stocks in the soil correlated to carbon stocks in aboveground living biomass? We found whole ecosystem organic carbon stocks ranged from 68 Mg OC ha in unburnt alpine grasslands to 668 Mg OC ha in Abies religiosa forests. By avoiding conversion of the A. religiosa forests to arable lands, we show that emissions of 1,122 to 1,671 Mg CO ha are avoided. Notably, the belowground soil organic carbon stock comprised ≥ 40% of the total ecosystem organic carbon stock. We recommend soil organic carbon stocks should be included within Mexican and global forestry carbon stock inventories, and should be considered within voluntary carbon-credit markets used to incentivize the conservation of Mexican montane habitats.
Highlights
The highland slopes of mountains are covered by montane ecosystems, including forests and alpine grasslands
Conversion from forestry to arable land within the Nevado de Toluca Conservation Area is likely to occur in the few years if conservation incentives are not placed
We found that the A. religiosa forests exhibited the highest whole ecosystem organic carbon (OC) stocks with values of 633 ± 102 and 668 ± 163 Mg OC ha−1 respectively, intermediate values of whole ecosystem OC stocks were found in the P. montezumae, A. religiosa, and P. pseudostrobus and A. religiosa forests with mean values ranging from 304 to 466 Mg OC ha−1 (Figure 2 and Table 6)
Summary
The highland slopes of mountains are covered by montane ecosystems, including forests and alpine grasslands. This notably includes the catchment, storage and provision of water, as montane habitats can store snow and ice that is released as water run-off within basins and rivers during warm periods (Keith et al, 2009; Ariza et al, 2013; Schermer et al, 2016). Montane forests typically reside in bands below the alpine zone and are characterized by temperate to cold climates, due to the high elevations that mountains reach. Due to this restricted distribution, montane habitats are vulnerable to rising temperatures from global climate change which can reduce their resilience and functions (e.g., Nogués-Bravo et al, 2007; Koörner and Ohsawa, 2005). Montane ecosystems themselves store organic carbon (OC) within soils and vegetation that provides soil stability (Ward et al, 2014)
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