Degradation of net primary production in a semiarid rangeland

Hasan Jackson, Stephen D. Prince
2016 Biogeosciences  
<p><strong>Abstract.</strong> Anthropogenic land degradation affects many biogeophysical processes, including reductions of net primary production (NPP). Degradation occurs at scales from small fields to continental and global. While measurement and monitoring of NPP in small areas is routine in some studies, for scales larger than 1<span class="thinspace"></span>km<sup>2</sup>, and certainly global, there is no regular monitoring and certainly no attempt to measure degradation. Quantitative
more » ... repeatable techniques to assess the extent of deleterious effects and monitor changes are needed to evaluate its effects on, for example, economic yields of primary products such as crops, lumber, and forage, and as a measure of land surface properties which are currently missing from dynamic global vegetation models, assessments of carbon sequestration, and land surface models of heat, water, and carbon exchanges. This study employed the local NPP scaling (LNS) approach to identify patterns of anthropogenic degradation of NPP in the Burdekin Dry Tropics (BDT) region of Queensland, Australia, from 2000 to 2013. The method starts with land classification based on the environmental factors presumed to control (NPP) to group pixels having similar potential NPP. Then, satellite remotely sensing data were used to compare actual NPP with its potential. The difference in units of mass of carbon and percentage loss were the measure of degradation. The entire BDT (7.45<span class="thinspace"></span> × <span class="thinspace"></span>10<sup>6</sup><span class="thinspace"></span>km<sup>2</sup>) was investigated at a spatial resolution of 250<span class="thinspace"></span> × <span class="thinspace"></span>250<span class="thinspace"></span>m. The average annual reduction in NPP due to anthropogenic land degradation in the entire BDT was −2.14<span class="thinspace"></span>MgC<span class="thinspace"></span>m<sup>−2</sup><span class="thinspace"></span>yr<sup>−1</sup>, or 17<span class="thinspace"></span>% of the non-degraded potential, and the total reduction was −214<span class="thinspace"></span>MgC<span class="thinspace"></span>yr<sup>−1</sup>. Extreme average annual losses of 524.8<span class="thinspace"></span>gC<span class="thinspace"></span>m<sup>−2</sup><span class="thinspace"></span>yr<sup>−1</sup> were detected. Approximately 20<span class="thinspace"></span>% of the BDT was classified as "degraded". Varying severities and rates of degradation were found among the river basins, of which the Belyando and Suttor were highest. Interannual, negative trends in reductions of NPP occurred in 7<span class="thinspace"></span>% of the entire region, indicating ongoing degradation. There was evidence of areas that were in a permanently degraded condition. The findings provide strong evidence and quantitative data for reductions in NPP related to anthropogenic land degradation in the BDT.</p>
doi:10.5194/bg-13-4721-2016 fatcat:tgk3jhthcffgbhe6j3rkr4mlfi