Current and Past Research Projects
Fuels treatment effects on understory vegetation structure and function in Northern Rocky Mountain forests
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After a century of exclusion and suppression, fire-prone western US conifer forests have become increasingly reliant on fuel treatments to mitigate wildfire hazard and restore historical ecosystem conditions. The US Forest Service is preparing to significantly expand the area targeted for thinning and prescribed fire to reduce fuel hazard and reestablish historical fire regimes. Despite a wealth of literature and a general consensus on the benefits of fuel treatments for forest structure and fuel reduction, there remains greater uncertainty and geographic variability regarding the response of understory plant communities to fuels treatments.
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Forest understory communities are crucial components of conifer forest ecosystems, as they harbor high plant biodiversity, provide wildlife habitat, and play a key role in essential ecosystem services such as nutrient and carbon cycling. Despite the vital roles played by the understory, only a few studies have systematically addressed the long-term effects of fuel treatments on understory vegetation beyond the initial short-term response. Previous studies on understory response to fuels treatments have rarely extended past three years of observation and have primarily focused on plant functional types as opposed to species level response. Importantly, there is a lack of research evaluating the potential ecological tradeoffs associated with fuel treatments on understory plant community dynamics. These tradeoffs include risks of plant invasion, changes in nutrient cycling and availability, and impacts to carbon cycling. Moreover, our understanding of understory response to fuels treatments is likely to be influenced by recent human-driven environmental changes, such as climate change and increased human disturbances. These changes have altered environmental conditions, which may override the current inertia of understory communities and favor the establishment of plant communities with traits better suited to the modified conditions.
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Reducing fuel hazard and controlling invasive species are critical needs in many of our nation’s forests and these two issues have been identified by the Forest Service as among the top four threats to our National Forests. Thus, the main objective of this project is to determine how understory vegetation responds to fuel treatments and to better understand how local, landscape, and human factors influence the vegetative response, with a focus on nonnative species dynamics.
Figure 1. Our field crew out installing a vegetation monitoring plots in a mixed conifer stand in the Upper Blackfoot River region of western MT.
Nitrogen cycling in tropical montane forests​
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This work addresses a question that is fundamental to understanding how global tropical forests function and how they are represented in earth system models—how does climate affect forest nutrient cycling and carbon storage?
Tropical mountains give rise to some of the most striking climatic and ecological gradients on Earth. Over relatively small distances, elevational gradients in tropical mountains recapitulate latitudinal shifts in temperature and thus provide a natural laboratory for understanding environmental control of ecosystem function and effects of global change. In this study, we use multiple lines of evidence to conclude that tropical montane forest soils hold a large pool of nitrogen that is highly sensitive to warming
Through the use of forest elevational gradients across tropical regions we 1. quantify the distribution of forest soil N across tropical mountains 2. assess the topographical and climatic controls over surface soil N and δ15N (a proxy for N availability and long-term N cycling).
We find a globally consistent pattern of increasing soil N concentrations and decreasing δ15N with increasing elevation that is driven primarily by temperature constraints on microbial N mineralization and denitrification that result in lower ecosystem-level gaseous N losses. Moreover, we show that montane forests account for an outsized proportion of the tropical forest soil N pool and that these pools exceed previous global estimates by nearly two-fold (!).
Taken together, our results identify a large and potentially vulnerable pool of soil nitrogen to future climate warming in tropical latitudes. Moving forward, I am working on evaluating the extent montane tropical forests have warmed over the last 25 years and how this has impacted tropical forest productivity.
Figure 1. Global tropical mountain distribution (Row 1 green shaded), soil nitrogen pool (row 2) and δ15N (row 3). From Gay et al. 2022.
Biogeochemical dynamics of woody plant expansion and prescribed fire in the Northern Great Plains​
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Woody plant expansion (WPE) into grasslands is a well-documented phenomenon, yet the effects on ecosystem biogeochemical cycling remain poorly understood. Recently observed trends in the increase of WPE and ecosystem productivity in the Northern Great Plains (NGP, Currey et al. 2022, Brookshire et al. 2020) have important considerations for 1. determining the trajectory of ecosystem carbon storage, 2. constraints on further WPE, and 3. effects on future nitrogen availability. Yet, many questions remains on how fire regime shifts will interact with WPE in these ecosystems.
One hypothesis my work explores is that the expansion of trees into grasslands increases fire severity and thus increases nitrogen loss (volatile and runoff) from the ecosystem. Yet, it is unknown how this increased tree driven N loss affects ecosystem function compared to previous grassland conditions. Thus, the confluence of the recent widespread fire suppression in the NGP and expanding conifer trees into grassland has likely had biogeochemical consequences that have been relatively unexplored at the ecosystem scale.
Taken together, I am interested in understanding how the introduction of prescribed fire to these landscapes has interacted with the recent WPE of conifer species (ponderosa and juniper) and their synergistic effects on the C and N cycles. Furthermore, I am evaluating how the pyrolysis of different plant species (with unique biochemical profiles) and soil organic matter will affect future biogeochemical processes (e.g. SOC accumulation and nutrient availability). Specifically, I am working towards quantifying pyrogenic-C production under WPE conditions and its impact on soil fertility, greenhouse gas production, and the long-lasting potential of these systems as C-sinks.
The field site is located in the Musselshell-Missouri River Breaks, Petroleum County, MT.
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Disentangling how soil disturbance and climate change impact subalpine grassland community structure and biogeochemical function in the northern Rocky Mountains
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We have leveraged a 30 year long-term ecological monitoring (founded by MSU emeritus Professor Dr. Tad Weaver) site in a subalpine grassland in the Bangtail Mountains of SW Montana to experimentally understand how climate change and soil disturbance regimes have shaped the plant community structure and biogeochemical functioning of natural montane grassland ecosystems.
We are pursuing questions about how the frequency of soil disturbance alters grassland community succession and the associated effects on soil carbon storage and greenhouse gas fluxes. We are also interested in how climate perturbations have influenced community trajectories and biogeochemical processes.
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The field site is located in the Bangtail Mountains northeast of Bozeman, MT.
Perennial grass agroecosystem C and N dynamics in semi-arid climates
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An important but relatively unexplored question in western semi-arid bioenergy systems is whether the functional importance of regional crop selection dictates soil processes - namely, soil carbon sequestration and greenhouse gas emissions. This work aimed to increases our understanding of the biogeochemical implications and trade-offs of pairing alternative bioenergy crops and bio-fertilizers in western semi-arid agroecosystems. Specifically, we are examining shifts in carbon (C) and nitrogen (N) fluxes associated with experimental C4 and C3 perennial systems, switchgrass (P. virgatum), and tall-wheatgrass (T. ponticum), under conventional-synthetic (urea) and bio-fertilizer (cyanobacteria) based N-fertilizer treatments.
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The field site was located at the Arthur H. Post Research Farm in Bozeman, Montana
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We recently (2022) published this work in Global Change Biology: Bioenergy. Check out a short outreach clip that GCBB put together on youtube!