Biological controls on net primary productivity: An example from the Chihuahua Desert

Steven Lee and Scott Ferrenberg, Department of Biology, New Mexico State University, Las Cruces, NM, Samuel Jordan, School of Life Sciences, Arizona State University, Tempe, AZ

Background/Question/Methods
Assessments of above ground annual net primary production (ANPP) often utilize the physical parameters of precipitation (e.g, mean annual precipitation, MAT) and temperature (e.g., mean annual temperature, MAT). In arid and semi-arid systems these parameters are often the defining limitation for carbon fixation. However, within region variability of ANPP can remain high, and more nuanced factors, such as interactions between biological organisms, can play a large role in the variation in ANPP observed across a landscape. Here we present an example from the Chihuahua Desert of ANPP estimates of Honey Mesquite (Prosopis glandulosa) and the influence of the native- cerambycid mesquite, twig girdling beetle (Oncideres rhodosticta). In 2019 and continuing through 2020, a large outbreak of O. rhodosticta was observed across much of the northern range of P. glandulosa. We developed allometric models to estimate the amount of biomass annually (2019-2020) killed by O. rhodosticta and total shrub (n=100) biomass at study sites located at the USDA Jornada Experimental Range
Results/Conclusions
Overall, we found stem girdling to reduce total living shrub biomass by about 4% in 2019 and 2% for the 2020 growing season. These numbers were similar to the 4% mean change in ANPP observed for P. glandulosa for the region. Annual estimates of ANPP are essential for understanding temporal dynamics of primary productivity and monitoring change in terrestrial systems. However, it is important to think beyond just broad physical limitations. Common biological processes, such as natural enemy impacts—in this case, twig girdling can cause as much variation in ANPP as climate.