Geology topics

Alix A. Pfennigwerth

Publications and source records attributed to Alix A. Pfennigwerth.

4 recordsLinked to original sources

USGS2026

Selective mortality leads to competitive release of a foundational perennial grass in an aridifying grassland

Vegetation dynamics in dryland ecosystems are defined by competition for water, a limiting and increasingly variable resource. As aridification creates warmer and drier conditions, with more frequent and intense droughts, the nature of competitive relationships may be altered, leading to changes in community composition. Reduced water availability is expected to decrease the cover and abundance of cool-season C 3 grasses on the Colorado Plateau, with unknown impacts on other plant functional types, such as drought-tolerant C 4 species. Here, we explore the effects of competitive release on Pleuraphis jamesii , a dominant C 4 grass with rooting and photosynthetic traits that may enable it to capitalize on the mortality of less drought tolerant C 3 species. To accomplish this, we used herbicide to create three removal treatments (C 3 grass and forb removal, C 4 grass removal, and control (no removal)) surrounding P. jamesii focal individuals and measured the subsequent impacts on water availability and plant water relations and growth. The experimentally induced mortality resulted in greater water availability for focal individuals in the C 3 removal treatment. Increased water availability in C 3 removal plots translated to less water stress and greater biomass production of focal P. jamesii plants, suggesting that competitive release can serve as the basis for shifts in community composition towards drought tolerant C 4 plants observed regionally. These responses were not observed in the C 4 removal treatment despite removing roughly equivalent amounts of total plant cover. Our results suggest that reductions in C 3 competitors may benefit drought-tolerant C 4 species through increased resource availability. These findings contribute to a mechanistic understanding of competitive interactions in increasingly water-limited systems.

Utah↗

USGS2022

Decline in biological soil crust N-fixing lichens linked to increasing summertime temperatures

Across many global drylands, biocrusts form a protective barrier on the soil surface and fill many critical roles in these harsh yet fragile environments. Previous short-term research suggests that climate change and invasive plant introduction can damage and alter biocrust communities, yet few long-term observations exist. Using a globally unique long-term record of continuous biocrust surveys from a rare never-grazed, protected grassland on the US Colorado Plateau, we found lichen species diversity and cover to be negatively correlated with increasing summer air temperatures, while moss species showed more sensitivity to variation in precipitation and invasive grass cover. These results suggest that dryland systems may be at a critical tipping point where ongoing warming could result in biological soil crust degradation.

Proceedings of the National Academies of Science (↗

USGS2021

Drought resistance and resilience: The role of soil moisture–plant interactions and legacies in a dryland ecosystem

In many regions of the world, climate change is projected to reduce water availability through changes in the hydrological cycle, including more frequent and intense droughts, as well as seasonal shifts in precipitation. In water-limited ecosystems, such as drylands, lower soil water availability may exceed the adaptive capacity of many organisms, leading to cascading ecological effects during (concurrent effects) and after drought (legacy effects). The magnitude and duration of concurrent and legacy effects depends on drought intensity, duration and timing as well as the resistance and resilience of the ecosystem. Here, we investigated the effects of drought seasonality and plant community composition on two dominant perennial grasses, Achnatherum hymenoides (C 3 photosynthesis) and Pleuraphis jamesii (C 4 photosynthesis), in a dryland ecosystem. The experiment consisted of three precipitation treatments: control (ambient precipitation), cool-season drought (−66% ambient precipitation November–April) and warm-season drought (−66% ambient precipitation May–October), applied in two plant communities (perennial grasses with or without a large shrub, Ephedra viridis ) over a 3-year period. We examined the concurrent and legacy effects of seasonal drought on soil moisture, phenology and biomass. Drought treatments had strong concurrent and legacy effects on soil moisture, which impacted the phenology and biomass of the two grasses. Drought reduced growing season length by delaying green-up (cool-season drought) or advancing senescence (warm-season drought) and reduced biomass for both species. Biomass and phenology legacy effects from drought emerged in the second and third years of the experiment. While we observed differential sensitivity to drought legacies between the two grasses, we found limited evidence that shrub presence had interactive effects with the drought treatment. Synthesis . The results from this study highlight how abiotic and biotic legacies can develop and influence a community's resistance and resilience to subsequent droughts. When the frequency of repeated extreme events, such as recurring seasonal droughts, exceeds the capacity of organisms or ecosystems to recover (i.e. resilience), persistent drought legacies can reduce the resistance to subsequent drought events. Overall, these results highlight how drought legacies are a product of ecological resistance and resilience to past drought and can influence ecosystem vulnerability to future droughts.

Utah↗

USGS2019

Wind erosion and dust from US drylands: a review of causes, consequences, and solutions in a changing world

Erosion by wind is one of the principal processes associated with land degradation in drylands and is a signiﬁcant concern to land managers and policymakers globally. In the drylands of North America, millions of tons of soil are lost to wind erosion annually. Of the 60 million ha in the United States identiﬁed as most vulnerable to wind erosion (arid and dominated by ﬁne sandy soils), 64% are managed by federal agencies (37 million ha). Here we review the drivers and consequences of wind erosion and dust emissions on drylands in the United States, with an emphasis on actionable responses available to policymakers and practitioners. We ﬁnd that while dryland soils are often relatively stable when intact, disturbances includ-ing ﬁre, domestic livestock grazing, and off-highway vehicles can increase horizontal eolian ﬂux by an order of magnitude, in some cases as much as 40-fold. A growing body of literature documents the large-scale impacts of deposited dust changing the albedo of mountain snow cover and in some cases reducing regional water supplies by ~5%. Predicted future increases in aridity and extreme weather events, includ-ing drought, will likely increase wind erosion and consequent dust generation. Under a drier and more variable future climate, new and existing soil- and vegetation-disturbing practices may interact in synergis-tic ways, with dire consequences for environments and society that are unforeseen to many but fairly pre-dictable given current scientiﬁc understanding. Conventional restoration and reclamation approaches, which often entail surface disturbance and rely on adequate moisture to prevent erosion, also carry consid-erable erosion risk especially under drought conditions. Innovative approaches to dryland restoration that minimize surface disturbance may accomplish restoration or reclamation goals while limiting wind erosion risk. Finally, multidisciplinary and multijurisdictional approaches and perspectives are necessary to under-stand the complex processes driving dust emissions and provide timely, context-speciﬁc information for mitigating the drivers and impacts of wind erosion and dust.

Ecosphere↗