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The encroachment of woody shrubs into grasslands is a phenomenon that has been occurring in the Chihuahuan Desert since the 1800s. Research shows that extensive livestock grazing and increased drought levels have acted as the main drivers of the grassland-to-shrubland transition. Very few studies have considered the impacts of such vegetation changes on microbial communities. Microbes play important ecosystem roles in nutrient cycling and carbon sequestration but also have the potential to act as pathogens. As the role of microbes in ecosystems is so important, it is crucial to understand the potential impacts of shrub encroachment on microbes and vice versa. Additionally, dryland microbes in general are understudied and as drylands cover over 40% of Earth’s land, understanding these microbes is of great ecological importance. The goal of this study was to assess microbial communities in shrub encroached systems in the Chihuahuan Desert to improve understanding of the ecological impacts of encroachment and increase general knowledge of dryland microbes. To conduct this study, soil samples were collected from sites dominated by black grama grass (Bouteloua eriopoda), sites dominated by honey mesquite shrubs (Prosopis glandulosa), and transition sites with both black grama and mesquite. DNA from soil samples was sequenced for bacteria (16S) and fungi (ITS2). Soil sampling was conducted through five sampling periods across a 10-month range to assess any potential seasonal variation in the microbial communities. In addition to DNA sequencing, microbial biomass and other environmental variables were collected. Statistical analyses were conducted to assess potential differences in microbial communities between vegetation types and seasons. Analyses included assessments of alpha and beta diversity, co-occurrence networks, and differential abundance analyses. Results show that there are significant changes in the microbial communities across vegetation types and seasons. Unique fungal and bacterial communities were identified in association with the different vegetation types, demonstrating that differences in vegetation influence microbial communities. Additionally, findings show that microbial communities are strongly impacted by seasons, showing decreases in biomass and changes to community composition in warm summer months compared to cooler months. Additionally, results show higher proportions of fungal pathogens in grass sites compared to other sites. Overall, this study demonstrates that microbial communities are influenced by shrub encroachment. As dryland microbial communities are often understudied, these findings can provide valuable insight into the ecology of dryland microbes and shrub-encroached systems.
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Effects of Fire Intensity and Abiotic Factors on Persistence of an Encroaching Woody Species
Over the past century, rangelands worldwide have experienced changes in vegetation cover and structure, many transitioning from grass-dominated to shrub-dominated systems (Archer et al. 2017; Fuhlendorf et al. 2017). In North America, such transitions are primarily a consequence of livestock management and fire exclusion practices of Euro-American settlers (Bray 1904; Archer 1989; Fuhlendorf and Smeins 1997). These shrub-dominated systems are often less productive for wildlife and livestock and may have crossed a threshold which cannot be reversed via common restoration practices such as prescribed fire (Ansley and Castellano 2006; Ratajczak et al. 2016). Oftentimes, the inability of prescribed fire to succeed at crossing this threshold is the result of insufficient fuel loading or inadequate fire intensity due to prescription parameters (Havstad and James 2010; Twidwell et al. 2016). However, recent work has demonstrated that burning under more extreme conditions (e.g. higher temperatures, lower fine fuel moisture) can slow or change the course of encroachment (Twidwell et al. 2013; Twidwell et al. 2016). Many encroaching shrub species are capable of persisting after fire via resprouting from protected buds (Bond and Midgley 2001). Such mechanisms pose challenges for land managers, particularly because resprouting often results in a higher number of stems per individual plant. Mesquite (Prosopis spp.) shrubs are well-known for their ability to persist to varying degrees following disturbance due to fire, chemical, and mechanical treatments. Due to historical livestock management and fire suppression practices, honey mesquite (Prosopis glandulosa) has increased in dominance and abundance in the southern Great Plains since the beginning of Euro-American settlement (Bray 1904; Archer 1989). Although prescribed fire has increased in acceptance as a method to reduce encroachment of mesquite, low-intensity fires performed during the dormant season rarely cause mortality (Wright and Bailey 1980; Ansley et al. 1998), especially when they are performed as a single treatment rather than as part of a comprehensive management plan. However, recent studies have demonstrated that more intense fires conducted outside the dormant season are capable of reducing resprouters (including mesquite), particularly during periods of drought (Twidwell et al. 2016). We evaluated impacts of fire intensity and abiotic factors on persistence of honey mesquite, a species of concern for managers in the southern Great Plains.
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- PAR ID:
- 10139334
- Date Published:
- Journal Name:
- Proceedings of the Albuquerque Fire Behavior and Fuels Conference
- Page Range / eLocation ID:
- 1-6
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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