Allometric variability of Haloxylon species in Central Asia

Abstract

The Haloxylon vegetation in Central Asia has undergone vast changes throughout the last century, which has lead to a strong degradation and desertification of the desert ecosystems in Kazakhstan, Uzbekistan, and Turkmenistan. In terms of combating desertification and restoration of ecosystems, two pilot-projects recently are aiming at the reforestation of Haloxylon ecosystems. Hereby, two of the internationally discussed climate change mitigation activities may be of higher relevance: (I) to sequester CO2 through afforestation and reforestation and (II) to substitute fossil fuels by sustainable utilization of regenerative bio-fuels. With particular focus on Central Asian desert ecosystems, the questions arose: (I) to which extent Haloxylon species – the dominant shrub species – sequester CO2, (II) what the recent carbon pool related to Haloxylon ecosystems is, and (III) in which magnitude the existing and/or reforested ecosystems could be utilized for bio-fuels sustainably. Therefore, this study aims at the derivation of allometric models including carbon contents for the two Haloxylon species in Central Asian desert ecosystems. A first application to measured transect data across Central Asia is carried out to reflect the recent biomass variability of the two study species. We found, that above- and below-ground biomass for both species is best modeled when taking growth height, basal area, and canopy area of shrubs into account (0.87<r2<0.97 for the top-models). Regarding the transect data, Haloxylon aphyllum showed a significantly higher variability of measured and modeled variables as well as higher maximum and average biomass estimates when compared to Haloxylon persicum. As our study sites partly include regions with moderate to strong human impact, the observed biomass variability represents differing ecological conditions as well as anthropogenic effects, with the latter also being reflected in the observed shrub species compositions.