by Celina Osuna

The Global Drylands Center wishes to congratulate Executive Committee Member Enrique R. Vivoni on his latest publication this month in Agricultural and Forest Meteorology, “A micrometeorological flux perspective on brush management in a shrub-encroached Sonoran Desert grassland,” for which he is the first author. Vivoni is a professor in the School of Earth and Space Exploration and the School of Sustainable Engineering and the Built Environment. His research focuses on water, climate and ecosystem processes and interactions with sustainability and management, with a specific emphasis on semiarid and arid regions of North America.

The article is the result of over 7 years of work studying and comparing “ecosystem responses to brush management in an herbicide-treated site to an untreated, control location to explicitly account for pre-treatment differences” in the Santa Rita Experimental Range (SRER) of the Sonoran Desert, just under 30 miles south of Tucson. Its contribution is especially important with regard to brush management strategies, which “rarely account for site differences that might occur prior to treatment.”

Below is the abstract, and you can access the full article here:

Woody plant encroachment typically limits the forage productivity of managed rangelands and alters a panoply of semiarid ecosystem processes and services. Intervention strategies to reduce woody plant abundance, collectively termed “brush management”, often lack observations to quantify and interpret changes in ecosystem processes. Furthermore, comparative studies between treated and untreated areas should account for heterogeneity since plant composition, microclimate, topoedaphic factors, and historical land use can substantially vary over short distances in drylands. Here, we quantify ecosystem responses to brush management after a single aerial herbicide application on an 18 hectare shrub-encroached grassland (savanna) in southern Arizona, USA. We conducted a pre- and post-treatment comparison of a flux tower site in the treated area with that of a tower in a nearby control site. The comparison, spanning a seven year period, included: (1) ground, airborne, and satellite-based measurements of vegetation structure, and (2) eddy covariance measurements. The herbicide treatment defoliated the dominant shrub (velvet mesquite, Prosopis velutina) and led to a temporary reduction in summer greening, but full foliar recovery occurred within two years. Contrary to expectations, perennial grass cover decreased and bare soil cover increased on the treated site. Relative amounts of evapotranspiration were reduced, while carbon uptake increased during the 2 year post-treatment period at the treated site due to a higher water use efficiency in the following spring. During mesquite recovery, carbon uptake was enhanced by higher gross primary productivity and accompanied by a decrease in ecosystem respiration relative to the untreated site. Mesquite recovery was facilitated by access to deep soil water, carbohydrate reserves in rooting systems, and a lower competition from reduced perennial grass cover.