landscape change

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


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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A 100 m × 100 m monitoring area was established in March 2016. A prescribed fire was set to burn the monitoring area on March 10, 2016, the beginning of the windy season, to create the burned treatment. Within each (5 m × 5 m) sampling plot, 50 randomly distributed soil samples were collected from the top 5 cm of the soil profile. The coordinates of the sampling locations were randomly generated and a different set of sampling locations was used for each sampling period.

Data were collected during the following time periods:
2016/03/11 - 2016/03/13
2016/06/14 - 2016/06/16
2017/03/17 - 2017/03/19
2017/06/26 - 2017/06/28


Instrument Names: Meter stick, shovel, sampling bags, ball mill, element analyzer.

Manufacturer: ball mill (PBM-04 Planetary Ball Mill, RETSCH, Germany), element analyzer (FLASH 2000 OEA, Thermal Fisher Scientific, USA).

Model Number: PBM-04 Planetary Ball Mill, FLASH 2000 OEA

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Each sample was analyzed three times and the results were averaged.

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We greatly acknowledge the contributions of Jon Erz, Eric Krueger and Andy Lopez (FWS, SNWR), Scott Collins and Amaris Swan (Sevilleta LTER, New Mexico, USA), Julie McDonald and Bethany Theiling (The University of Tulsa) for their assistance in field work and laboratory analysis.

The site is a black grama (Bouteloua eriopoda) dominated grassland with creosote bush shrubs (Larrea tridentata), and the soil is primarily sandy loam. This sampling area is large enough to capture the heterogeneity in the landscape comprising of shrub, grass and bare soil microsites.

The soil TC and TN results of the same field site can be found in Guan et al., 2018. Ecosystems (Post-fire Redistribution of Soil Carbon and Nitrogen at a Grassland– Shrubland Ecotone).

Keystone species have large impacts on community and ecosystem properties, and create important ecological interactions with other species.  Prairie dogs (Cynomys spp.) and banner-tailed kangaroo rats (Dipodomys spectabilis) are considered keystone species of grassland ecosystems, and create a mosaic of unique habitats on the landscape.

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