An official website of the United States government
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.
more »
« less
Multi‐Year Tracing of Spatial and Temporal Dynamics of Post‐Fire Aeolian Sediment Transport Using Rare Earth Elements Provide Insights Into Grassland Management
Aeolian sediment transport occurs as a function of, and with feedback to ecosystem changes and disturbances. Many desert grasslands are undergoing rapid changes in vegetation, including the encroachment of woody plants, which alters fire regimes and in turn can change the spatial and temporal patterns of aeolian sediment transport. We investigated aeolian sediment transport and spatial distribution of sediment in the surface soil for 7 years following a prescribed fire using a multiple rare earth element (REE) tracer‐based approach in a shrub‐encroached desert grassland in the northern Chihuahuan desert. Results indicate that even though the aeolian horizontal sediment mass flux increased approximately three‐fold in the first windy season in the burned areas compared to control areas, there were no significant differences after three windy seasons. The soil surface of bare microsites was the major contributor of aeolian sediments in unburned areas (87%), while the shrub microsites contributed the least (<2%) during the observation period. However, after the prescribed fire, the contribution of aeolian sediments from shrub microsites increased considerably (∼40%), indicating post‐fire microsite‐scale sediment redistribution. The findings of this study, which is the first to use multiple REE tracers for multi‐year analysis of the spatial and temporal dynamics of aeolian sediment transport, illustrate how disturbance by prescribed fire can influence aeolian processes and alters dryland soil geomorphology in which distinct soils develop over time at very fine spatial scales of individual plants.
more »
« less
- Award ID(s):
- 1655499
- PAR ID:
- 10510283
- Publisher / Repository:
- American Geophysical Union
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Earth Surface
- Volume:
- 128
- Issue:
- 11
- ISSN:
- 2169-9003
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Vegetation change in drylands can influence wind erosion and sand and dust storms (SDS) with far‐reaching consequences for Earth systems and society. Although vegetation is recognized as an important control on wind erosion and SDS, the interactions are not well described at the landscape level or in the context of dryland ecosystem change. The transition of sites from one ecological state to another (e.g., grassland to shrubland) is typically associated with changes in the composition, cover, and structure of vegetation, which influence drag partitioning and wind shear velocities that drive aeolian sediment transport. Here, we quantify the magnitude and direction of aeolian sediment transport responses to ecological state change in the northern Chihuahuan Desert and identify thresholds associated with state transitions. Our results show aeolian sediment mass flux (Q) increased from ∼1 to 10 g m−1 d−1in historical grassland with scattered shrubs to ∼10–100 g m−1 d−1following shrub invasion and decline in perennial grass cover to ∼100–10,000 g m−1 d−1in shrubland following complete grass loss. The magnitude shifts were associated with critical perennial grass cover thresholds governing nonlinear increases inQacross ecological state transitions. Grass recovery in shrubland reducedQto rates similar to those in historical grasslands—a multiple order of magnitude reduction. Our results show that crossing degradation and restoration thresholds between alternative ecological states can have a profound effect on the magnitude and spatiotemporal variability of aeolian sediment transport and primacy in determining patterns of wind erosion and dust emissions in vegetated drylands.more » « less
-
Dryland environments are experiencing shifting ecogeomorphic patterns due to climatic changes and anthropogenic activities, resulting in a shift from grasslands to shrub-dominated landscapes. This dissertation investigates the effects from increasingly variable monsoonal precipitation and ecogeomorphic connectivity on perennial grass growth, litter distribution, and soil organic matter in drylands, with a focus on grass-shrub ecotones. Field experiments were conducted in the Chihuahuan Desert at the Jornada Basin Long-Term Ecological Research (LTER) site using a precipitation manipulation system and connectivity modifiers (ConMods) to assess their effects on plant productivity, recruitment, and soil nutrient distribution. Results show that reducing connectivity, combined with increased monsoonal precipitation, can enhance perennial grass productivity and recruitment, and affect the distribution of soil organic matter and non-photosynthetic vegetation. These findings contribute to our understanding of how aeolian processes and shifting precipitation regimes will shape vegetation patterns and soil properties in dryland environments under future climate scenarios. This research provides insights into potential mitigation strategies for combating shrub encroachment and promoting the sustainability of dryland ecosystems.more » « less
-
Disturbance from fire can affect the abundance and distribution of shrubs and grasses in arid ecosystems. In particular, fire may increase grass and forb production while hindering shrub encroachment. Therefore, prescribed fires are a common management tool for maintaining grassland habitats in the southwest. However, Bouteloua eriopoda (black grama), a dominant species in Chihuahuan Desert grassland, is highly susceptible to fire resulting in death followed by slow recovery rates. A prescribed fire on the Sevilleta National Wildlife refuge in central New Mexico in 2003 provided the opportunity to study the effects of infrequent fires on vegetation in this region. This study was conducted along a transition zone where creosote bushes (Larrea tridentata) are encroaching on a black grama grassland. Before and after the fire, above ground plant productivity and composition were monitored from 2003 to present. Following the prescribed fire, there were fewer individual grass clumps and less above ground grass cover in burned areas compared to unburned areas. This decrease in productivity was primarily from a loss of B. eriopoda. Specifically, B. eriopoda density and cover were significantly lower following the fire with a slow recovery rate in the five years following the fire. Other grasses showed no such adverse response to burning. Data were collected from 2004-2013 and 2018. Data were not collected for 2014-2017.more » « less
-
Redox reactions underlie several biogeochemical processes and are typically spatiotemporally heterogeneous in soils and sediments. However, redox heterogeneity has yet to be incorporated into mainstream conceptualizations and modeling of soil biogeochemistry. Anoxic microsites, a defining feature of soil redox heterogeneity, are non-majority oxygen depleted zones in otherwise oxic environments. Neglecting to account for anoxic microsites can generate major uncertainties in quantitative assessments of greenhouse gas emissions, C sequestration, as well as nutrient and contaminant cycling at the ecosystem to global scales. However, only a few studies have observed/characterized anoxic microsites in undisturbed soils, primarily, because soil is opaque and microsites require µm-cm scale resolution over cm-m scales. Consequently, our current understanding of microsite characteristics does not support model parameterization. To resolve this knowledge gap, we demonstrate through this proof-of-concept study that X-ray fluorescence (XRF) 2D mapping can reliably detect, quantify, and provide basic redox characterization of anoxic microsites using solid phase “forensic” evidence. First, we tested and developed a systematic data processing approach to eliminate false positive redox microsites,i.e., artefacts, detected from synchrotron-based multiple-energy XRF 2D mapping of Fe (as a proxy of redox-sensitive elements) in Fe-“rich” sediment cores with artificially injected microsites. Then, spatial distribution of FeIIand FeIIIspecies from full, natural soil core slices (over cm-m lengths/widths) were mapped at 1–100 µm resolution. These investigations revealed direct evidence of anoxic microsites in predominantly oxic soils such as from an oak savanna and toeslope soil of a mountainous watershed, where anaerobicity would typically not be expected. We also revealed preferential spatial distribution of redox microsites inside aggregates from oak savanna soils. We anticipate that this approach will advance our understanding of soil biogeochemistry and help resolve “anomalous” occurrences of reduced products in nominally oxic soils.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1029/2023JF007274
