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1. Press-pulse interactions and long-term community dynamics in a Chihuahuan Desert grassland

   Scott L Collins, Y. Anny (October 2020, Journal of vegetation science)

   Questions: Reordering of dominant species is an important mechanism of community response to global environmental change. We asked how wildfire (a pulse event) interacts with directional changes in climate (environmental presses) to affect plant community dynamics in a Chihuahuan Desert grassland. Location: Sevilleta National Wildlife Refuge, Socorro County, New Mexico, USA Methods: Vegetation cover by species was measured twice each year from 1989 to 2019 along two permanently located 400 m long line intercept transects, one in Chihuahuan Desert grassland, and the second in the ecotone between Chihuahuan Desert and Great Plains grasslands. Trends in community structure were plotted over time, and climate sensitivity functions were used to predict how changes in the Pacific Decadal Oscillation (PDO) affected vegetation dynamics. Results: Community composition was undergoing gradual change in the absence of disturbance in the ecotone and desert grassland. These changes were related to the reordering of abundances between two foundation grasses, Bouteloua eriopoda and B. gracilis, that together account for >80% of aboveground primary production. However, reordering varied over time in response to wildfire (a pulse) and changes in the PDO (a press). Community dynamics were initially related to the warm and cool phases of the PDO, but in the ecotone these relationships changed following wildfire, which reset the system. Conclusions: Species reordering is an important component of community dynamics in response to ecological presses. However, reordering is a complex, non-linear process in response to ecological presses that may change over time and interact with pulse disturbances. 

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2. Warming-El Nino-Nitrogen Deposition Experiment (WENNDEx): Soil Nitrogen Data from the Sevilleta National Wildlife Refuge, New Mexico (2006 - 2020)

   https://doi.org/10.6073/pasta/2b7ab47e8e3bfab993e80cdae1c887f5  

   Collins, Scott; Pockman, William (January 2020, Environmental Data Initiative)

   Humans are creating significant global environmental change, including shifts in climate, increased nitrogen (N) deposition, and the facilitation of species invasions. A multi-factorial field experiment is being performed in an arid grassland within the Sevilleta National Wildlife Refuge (NWR) to simulate increased nighttime temperature, higher N deposition, and heightened El Niño frequency (which increases winter precipitation by an average of 50%). The purpose of the experiment is to better understand the potential effects of environmental drivers on grassland community composition, aboveground net primary production and soil respiration. The focus is on the response of two dominant grasses (Bouteloua gracilis and B eriopoda), in an ecotone near their range margins and thus these species may be particularly susceptible to global environmental change. It is hypothesized that warmer summer temperatures and increased evaporation will favor growth of black grama (Bouteloua eriopoda), a desert grass, but that increased winter precipitation and/or available nitrogen will favor the growth of blue grama (Bouteloua gracilis), a shortgrass prairie species. Treatment effects on limiting resources (soil moisture, nitrogen availability, species abundance, and net primary production (NPP) are all being measured to determine the interactive effects of key global change drivers on arid grassland plant community dynamics and ecosystem processes. On 4 August 2009 lightning ignited a ~3300 ha wildfire that burned through the experiment and its surroundings. Because desert grassland fires are patchy, not all of the replicate plots burned in the wildfire. Therefore, seven days after the wildfire was extinguished, the Sevilleta NWR Fire Crew thoroughly burned the remaining plots allowing us to assess experimentally the effects of interactions among multiple global change presses and a pulse disturbance on post-fire grassland dynamics. This data set provides soil N availability in each plot of the warming experiment for the monsoon season (also see SEV176). 

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3. Warming-El Nino-Nitrogen Deposition Experiment (WENNDEx): Soil Temperature, Moisture, and Carbon Dioxide Data from the Sevilleta National Wildlife Refuge, New Mexico

   https://doi.org/10.6073/pasta/9e9f235128c82a46bb073589d91c6989  

   Collins, Scott (January 2021, Environmental Data Initiative)

   Humans are creating significant global environmental change, including shifts in climate, increased nitrogen (N) deposition, and the facilitation of species invasions. A multi-factorial field experiment is being performed in an arid grassland within the Sevilleta National Wildlife Refuge (NWR) to simulate increased nighttime temperature, higher N deposition, and heightened El Nino frequency (which increases winter precipitation by an average of 50%). The purpose of the experiment is to better understand the potential effects of environmental drivers on grassland community composition, aboveground net primary production and soil respiration. The focus is on the response of two dominant grasses (Bouteloua gracilis and B eriopoda), in an ecotone near their range margins and thus these species may be particularly susceptible to global environmental change. It is hypothesized that warmer summer temperatures and increased evaporation will favor growth of black grama (Bouteloua eriopoda), a desert grass, but that increased winter precipitation and/or available nitrogen will favor the growth of blue grama (Bouteloua gracilis), a shortgrass prairie species. Treatment effects on limiting resources (soil moisture, nitrogen availability, species abundance, and net primary production (NPP) are all being measured to determine the interactive effects of key global change drivers on arid grassland plant community dynamics and ecosystem processes. This dataset shows values of soil moisture, soil temperature, and the CO2 flux of the amount of CO2 that has moved from soil to air. On 4 August 2009 lightning ignited a ~3300 ha wildfire that burned through the experiment and its surroundings. Because desert grassland fires are patchy, not all of the replicate plots burned in the wildfire. Therefore, seven days after the wildfire was extinguished, the Sevilleta NWR Fire Crew thoroughly burned the remaining plots allowing us to assess experimentally the effects of interactions among multiple global change presses and a pulse disturbance on post-fire grassland dynamics. 

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4. Post-fire SOC and delta-13C at different types of microsite at a grassland-shrubland ecotone

   https://doi.org/10.6073/pasta/993cd7029af115ee4508c2a688af7bf9  

   Wang, Guan (January 2018, Environmental Data Initiative)

   Woody plant encroachment of grassland ecosystems is a geographically extensive phenomenon that can lead to rapid land degradation and significantly alter global biogeochemical cycles, and this ecosystem change has been particularly well documented in the desert grassland of the southwestern United States. Fires are known to decrease vegetation cover and increase soil erodibility, and the shifts in wildfire regimes are currently occurring in Chihuahuan Desert. It is generally recognized that the invasion of woody vegetation into grasslands and savannas will increase the carbon stored in arid ecosystems. However, carbon storage may be complicated by disturbance such as wildfire, which alters the distribution and amount of C pools in the drylands. The relative distribution of each vegetation type to the soil C pool and its variability after fires are not well-understood in this ecosystem. This research will investigate the variations of SOC and its vegetation source partition at microsite scale in the woody shrub encroached grassland after the occurrence of fire, which will provide further information on wildfire’s influence on soil C pool dynamics in arid and semiarid lands. The post-fire changes of the spatial pattern of SOC and vegetation contributions in the shrub encroached grassland will be analyzed using a geostatistical method outlined in Guan et al. (2018). Overall, understanding the post-fire redistribution and sources of SOC may provide insights on the important role played by fire, aeolian processes and vegetation in the dynamics of desert grassland ecosystems. 

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5. Small Mammal Exclosure Study (SMES) Vegetation Data from the Chihuahuan Desert Grassland and Shrubland at the Sevilleta National Wildlife Refuge, New Mexico (1995-2009)

   https://doi.org/10.6073/pasta/84841a70dd8cc89b9a5716e3511cc3a4  

   Lightfoot, David; Rudgers, Jennifer A (January 2021, Environmental Data Initiative)

   This is data for vegetation canopy cover measured from each of the SMES study plots. Vegetation canopy cover was measured from each of the 36 one-meter2 quadrats twice each year. Animal consumers have important roles in ecosystems, determining plant species composition and structure, regulating rates of plant production and nutrient, and altering soil structure and chemistry. The purpose of this study is to determine whether or not the activities of small mammals regulate plant community structure, plant species diversity, and spatial vegetation patterns in Chihuahuan Desert shrublands and grasslands. The purpose of this study is to determine whether or not the activities of small mammals regulate plant community structure, plant species diversity, and spatial vegetation patterns in Chihuahuan Desert shrublands and grasslands. What role if any do indigenous small mammal consumers have in maintaining desertified landscapes in the Chihuahuan Desert? Additionally, how do the effects of small mammals interact with changing climate to affect vegetation patterns over time? This study will provide long-term experimental tests of the roles of consumers on ecosystem pattern and process across a latitudinal climate gradient. The following questions or hypotheses will be addressed. 1) Do small mammals influence patterns of plant species composition and diversity, vegetation structure, and spatial patterns of vegetation canopy cover and biomass in Chihuahuan Desert shrublands and grasslands? Are small mammals keystone species that determine plant species composition and physiognomy of Chihuahuan Desert communities? Do small mammals have a significant role in maintaining the existence of shrub islands and spatial heterogeneity of creosotebush shrub communities? 2) Do small mammals affect the taxonomic composition and spatial pattern of vegetation similarly or differently in grassland communities as compared to shrub communities? How do patterns compare between grassland and shrubland sites, and how do these relatively small scale patterns relate to overall landscape vegetation patterns? 3) Do small mammals interact with short-term (annual) and long-term (decades) climate change to affect temporal changes in vegetation spatial patterns and species composition? 4) Do small mammals interact with other herbivore and granivore consumers enough to affect the species composition and abundances of other consumers such as ants and grasshoppers? 

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