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1. Quantitative assessment of ecosystem services in diverse land uses within the forest-grassland transition zone of southern Great Plains, USA

   https://doi.org/10.1016/j.ecoser.2025.101697  

   Whiteis, Ally M; Zou, Chris B; Joshi, Omkar; Ferguson, Benedict; Roberts, Sophie (February 2025, Ecosystem Services)

   Ecosystem services, essential for supporting life, are increasingly being altered by anthropogenic activities. This study focuses on the Cross Timbers ecoregion of the southern Great Plains, USA, where oak woodland and grassland co-exist. However, grasslands are rapidly transitioning to woodlands through a process known as woody plant encroachment, or are being considered for switchgrass biofuel production. Our objectives were to quantify the supporting (plant biodiversity, aboveground net primary productivity), provisioning (water quantity, forage production), regulating (soil organic carbon, flood regulation), and cultural services (hunting-based recreation, aesthetics) of four land use types—tallgrass prairie, oak woodland, eastern redcedar woodland, and switchgrass biofuel production—using the Millennium Ecosystem Assessment Framework. We integrated these services into an ecosystem sustainability index. Results showed that tallgrass prairie provided balanced services and ranked highest in this index. Eastern redcedar and switchgrass exhibited an imbalance in services, while oak woodland’s ranking varied with normalization methods. Our results highlight the need for grassland conservation by curtailment of eastern redcedar expansion. While oak woodland ranks high in cultural services, its restoration is recommended to enhance multiple ecosystem services. This study provides a roadmap for quantitatively evaluating ecosystem services to inform management decisions for ecosystem transitions and promote regional sustainability. Future research should broaden stakeholder engagement and explore integrated land use strategies within large watersheds encompassing multiple land uses to enhance regional environmental sustainability. 

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2. Improved productivity, water yield, and water use efficiency by incorporating switchgrass cultivation and native ecosystems in an integrated biofuel feedstock system

   https://doi.org/10.1111/gcbb.12787  

   Schmidt, Kathryn_N; Zou, Chris_B; Kakani, Vijaya_Gopal; Zhong, Yu; Will, Rodney_E (December 2020, GCB Bioenergy)

   Abstract The southern Great Plains of the USA has great potential to produce biofuel feedstock while minimizing the dual stresses of woody plant encroachment and climate change. Switchgrass (Panicum virgatum) cultivation, woody biomass captured during removal of the encroaching eastern redcedar (Juniperus virginiana) to restore grasslands and thinning of the native oak forest can provide an integrated source of feedstock and improve ecosystem services. In north‐central Oklahoma, we quantified productivity and ecosystem water use of switchgrass stands and degraded ecosystems encroached by eastern redcedar and compared these to native oak forest and tallgrass prairie ecosystems. We measured aboveground net primary productivity (ANPP) using allometric equations (trees) and clip plots (herbaceous), and evapotranspiration (ET) using a water balance approach from gauged watersheds, and calculated water use efficiency (WUE = ANPP/ET) from 2016 to 2019. Among vegetation cover types, ANPP averaged 5.1, 5.4, 6.0, and 7.8 Mg ha⁻¹ year⁻¹for the prairie, oak, eastern redcedar, and switchgrass watersheds and was significantly greater for switchgrass in 2018 and 2019 (2 and 3 years post establishment) when it reached 8.6 Mg ha⁻¹ year⁻¹. Averaged across 2017–2019, ET was significantly greater in the forested watersheds than the grassland watersheds (1022 mm year⁻¹for eastern redcedar, 1025 mm year⁻¹for oak, 874 mm year⁻¹for prairie, and 828 mm year⁻¹for switchgrass). The mean WUE was significantly greater (9.47 kg ha⁻¹ mm⁻¹) for switchgrass than for the prairie, eastern redcedar, and oak cover types (6.03, 6.02, and 5.31 kg ha⁻¹ mm⁻¹). Switchgrass offered benefits of greater ANPP, less ET, and greater WUE. Our findings indicate that an integrated biofuel feedstock system that includes converting eastern redcedar encroached areas to switchgrass and thinning the oak forest can increase productivity, increase runoff to streams, and improve ecosystem services. 

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3. Shade is the most important factor limiting growth of a woody range expander

   https://doi.org/10.1371/journal.pone.0242003  

   Ward, David (December 2020, PLOS ONE)

   Gomory, Dusan (Ed.)

   The expansion of woody plants into grasslands and old fields is often ascribed to fire suppression and heavy grazing, especially by domestic livestock. However, it is also recognized that nutrient availability and interspecific competition with grasses and other woody plants play a role in certain habitats. I examined potential factors causing range- and niche expansion by the eastern redcedar Juniperus virginiana , the most widespread conifer in the eastern United States, in multifactorial experiments in a greenhouse. Historical records suggest that the eastern redcedar is a pioneer forest species, and may be replaced as the forest increases in tree density due to shading. Another possible factor that affects its distribution may be nutrient availability, which is higher in old fields and other disturbed lands than in undisturbed habitats. In its historic range, eastern redcedars are particularly abundant on limestone outcrops, often termed ‘cedar barrens’. However, the higher abundance on limestone could be due to reduced interspecific competition rather than a preference for high pH substrates. I manipulated shade, fertilization, lime, and interspecific competition with a common dominant tree, the post oak Quercus stellata . In a separate experiment, I manipulated fire and grass competition. I measured growth rates (height and diameter) and above- and belowground biomass at the end of both experiments. I also measured total non-structural carbohydrates and nitrogen in these plants. Shade was the most important factor limiting the growth rates and biomass of eastern redcedars. I also found that there were significant declines in nitrogen and non-structural carbohydrates when shaded. These results are consistent with the notion that the eastern redcedar is a pioneer forest species, and that shade is the reason that these redcedars are replaced by other tree species. In the second experiment, I found that a single fire had a negative effect on young trees. There was no significant effect of competition with grass, perhaps because the competitive effect was shading by grasses and not nutrient depletion. Overall, the effects of shade were far more apparent than the effects of fire. 

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4. Red maple tree root water uptake depths are influenced by neighboring tree species composition

   https://doi.org/10.1093/treephys/tpaf049  

   Sobota, Matthew; Li, Kevin; Knighton, James; Meinzer, ed., Frederick (April 2025, Tree Physiology)

   Abstract Understanding how mixed-species forests uptake subsurface water sources is critical to projecting future forest water use and stress. Variation in root water uptake (RWU) depths and volumes is common among trees but it is unclear how it is affected by species identity, local water availability or neighboring tree species compositions. We evaluated the hypothesis that RWU depths and the age of water (i.e., time since water entered soils as precipitation) taken up by red maples (Acer rubrum) varied significantly between two forested plots, both containing red maples, similar soils, topography and hydrologic conditions, but having different neighboring tree species. We measured soil moisture contents as well as stable isotopes (δ2H, δ18O) in plant xylem water and soil moisture across two years. These data were used to calibrate process-based stand-level ecohydrological models for each plot to estimate species-level RWU depths. Model calibration suggested significant differences in red maple tree RWU depths, transpiration rates and the ages of water taken up by maples across the two stands. Maple trees growing with ash and white spruce relied on significantly deeper and older water from the soil profile than maple trees growing with birch and oak. The drought risk profile experienced by maple trees differed between the plots as demonstrated by strong correlations between precipitation and model simulated transpiration on a weekly time scale for maples taking up shallow soil moisture and a monthly time scale for maples reliant on deeper soil moisture. These findings carry significant implications for our understanding of water competition in mixed-species forests and for the representation of forest rooting strategies in hydrologic and earth systems models. 

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5. An experimental comparison of stand management approaches to sudden oak death: prevention vs restoration

   https://doi.org/10.1139/cjfr-2022-0328  

   Quiroga, Gissella Betzavel; Simler-Williams, Allison B; Frangioso, Kerri M; Frankel, Susan; Rizzo, David M.; Cobb, Richard (January 2023, Canadian Journal of Forest Research)

   Many coastal forests stretching from central California to southwest Oregon are threatened or have been impacted by the invasive forest pathogen Phytophthora ramorum, cause of sudden oak death. We analyzed a set of stand-level forest treatments aimed at preventing or mitigating disease impacts on stand composition, biomass, and fuels, using a before-after-control-intervention experiment with a revaluation after five years. We compared the effects of restorative management in invaded stands to preventative treatments in uninvaded forests. The restorative treatments contrasted two approaches to mastication, hand-crew thinning, and thinning with pile burning with untreated controls (N=30) while the preventative treatments were limited to hand-crew thinning (N=10). Half of the restoration treatments had basal sprouts removed two- and four-years after treatment. All treatments significantly reduced stand density and increased average tree size without significantly decreasing total basal area both immediately and five years after treatments. Preventative treatments also significantly increased dominance of timber species not susceptible to P. ramorum. Follow-up basal sprout removal in the restoration experiment appears to maintain treatment benefits to average tree size and may be associated with small decreases in stand density five years after initial treatment. Our study demonstrates that for at least five years, a range of common stand management practices can improve forests threatened or impacted by sudden oak death. 

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