Areas covered by cactus (Opuntia spp.) and methods to assess their biomass and carbon sequestration – A review

Increasing carbon sequestration in terrestrial systems is one potential solution to mitigate global warming. Cactus can withstand drought to produce biomass, making it an important carbon sink. Accurately estimating carbon stocks is crucial for identifying and promoting cactus production systems with the highest capacity for carbon sequestration. Although several methods for estimating biomass and carbon stocks are available in the literature, their application in cacti is still limited due to their unique structural characteristics, which require modified approaches. This review presents diverse cactus land uses and their potential to sequester carbon. We also provide the available methods for estimating carbon stocks and sequestration applied to cactus and future considerations. Typical land uses of cactus include fruit orchards, intensive systems for fodder, and rangelands. Aboveground biomass in cactus is mostly estimated using destructive methods and allometric equations. The use of remote sensing techniques is still limited and needs to be fully leveraged, given its robustness in covering vast areas such as those in rangelands. The Eddy covariance towers can also provide long-term ecosystem measurements of carbon fluxes, including carbon sequestration rates. Soil organic carbon can be estimated using the chronosequence technique and repeated measurements. However, the rate and extent of soil organic carbon can be determined using the fine root input, mean residence time, and root turnover methods. Although the reviewed methods have great application in cactus, developing a standardized methodological framework will enable more accurate projections of carbon sequestration potential under different land uses and management approaches. Similarly, future research actions are necessary to validate these methods under different land uses.