Lichens are a major component of biological soil crusts, also known as “biocrusts”, communities of organisms on the soil surface that perform important ecological roles and can affect rangeland function, health, and resilience. Biocrusts consist of an assortment of drought-tolerant organisms, including cyanobacteria, algae, fungi, bacteria, lichens, bryophytes, and microarthropods that occur in the top few centimeters of the soil surface. Biological soil crusts can constitute up to 75% ground cover in drylands (Ferrenberg et al. 2017), such as Alberta’s grasslands, and have important roles in these ecosystems, including soil formation and stabilization (Belnap and Budel 2016); influence over the hydrologic cycle (Chamizo et al. 2016); regulating seed establishment and germination (Li et al. 2005, Pyle 2018), and enhancement of soil fertility (Belnap 2003). Biocrusts make major contributions to global biogeochemical carbon and nitrogen cycles (Poulter et al. 2014, Porada et al. 2014), and some models suggest that up to 49% of global terrestrial nitrogen fixation and 7% of global carbon fixation are carried out by biocrust communities (Elbert et al. 2012). Biocrust cover and community composition have the potential to be altered dramatically by anthropogenically-induced climate change and land-use intensification (Ferrenberg et al. 2015) resulting in decreased net CO2 uptake and fixation (Maestre et al. 2015), suggesting that degradation of these communities could have detrimental global impacts (Elbert et al. 2012, Porada et al. 2014, Reed et al. 2016, Ferrenberg et al. 2017).
Biocrust communities in other regions of the world have been found to be highly sensitive to climate change and physical disturbance. Grazing, and more specifically, trampling, can reduce biocrust cover and alter species composition (Marble and Harper 1989, Muscha and Hild 2006), triggering subsequent effects on diversity, biomass, and nutrient cycling (Dettweiler-Robinson et al. 2013). Some biocrust organisms possess adaptations that allow them to survive harsh UV radiation and extended precipitation free periods. Biocrust organisms like mosses and lichen are poikilohydric, meaning that their internal water balance equilibrates with their surrounding environment. After prolonged periods of dehydration, they are able to take advantage of small water pulses to recover photosynthetic activity. However, it is these same drought-adaptive traits that may heighten biocrust vulnerability to climate change. Small water pulses cause individuals to break dormancy more often, making them prone to resource exhaustion and carbon starvation. Coupled with increased evaporation rates from warmer temperatures, periods of hydration are shortened, thus shortening active photosynthesis, decreasing survivorship, and having impacts on biocrust function – namely hydrology, soil stability, and nutrient cycling (Coe et al. 2012). Modelling efforts have proposed that within the next 65 years, biocrust cover could decrease by 25-40% globally due to anthropogenically-induced climate change and land use intensification (Rodriguez-Caballero et al. 2018), despite the drought-tolerant adaptations of biocrust organisms.
Understanding of biocrust community composition response to disturbance and drought has important implications for land management and conservation approaches. Globally, temperate grasslands were identified as the most endangered ecosystem, with over 40% of temperate grasslands being converted from their indigenous state (IUCN 2008) and were found to be the global biome with the greatest biodiversity impacts from land-use pressures (Newbold et al. 2016). Grass and pasturelands provide 80% of the feed used in Canadian beef production (Petty and Cecava 1995), and the value of forage produced by native prairie in Alberta is estimated to be $200 million (ABMI 2018a), highlighting the economic importance of productive and functional rangeland systems. A fundamental challenge of land management in these areas is how to allow for a variety of land uses while balancing the conservation of biodiversity and other factors important to long-term sustainability of the landscape. Maintaining the resiliency and productive capability of rangelands is critical for producers who rely on rangelands for their livelihoods, and for global societies that rely on the wide range of ecosystem services that rangelands provide (Teague et al 2013). This study aims to understand the impacts of drought on biocrust communities under different grazing management strategies in Alberta's rangelands to help inform land management and conservation practices into the future.
Research Objectives.
The goal of this study is to characterize biocrust lichen community response to grazing and drought in Alberta’s grasslands. The research questions of this study include:
Do drought and grazing affect biocrust community composition?
Which environmental variables contribute to differences in species composition between treatments?
Are certain biocrust species more sensitive to drought and grazing than others?
Expected Results.
It is predicted that a 40% reduction of precipitation during summer months will have negative effects on biocrust cover and species richness. Moderate grazing under a no-drought scenario may improve biocrust cover and richness due to decreased litter deposition and increased access to light, whereas no grazing may be actually be detrimental to biocrusts due to decreased access to light as well as litter buildup.
Disclaimer: This website was created for a class project for RENR 690 at the University of Alberta. Results presented are based on a randomly generated dataset.