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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. 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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3. Comparison of Field Sampling- and Airborne Laser Scanning-Derived Stand-Level Inventories in a Mixed Conifer Forest and Volume Validation Using Log Scaling Data

   https://doi.org/10.3390/f16050784  

   Sparks, Aaron M; Corrao, Mark V; Keefe, Robert F; Armstrong, Ryan; Smith, Alistair_M S (May 2025, Forests)

   Forest managers need stand-level forest inventories to make operational decisions and model growth and yield to inform long-term planning. However, few studies have quantified errors in field sampling- and airborne laser scanning (ALS)-derived inventories at the stand level, particularly in species-diverse and structurally diverse mixed conifer forests. In this study, we compared stand-level metrics derived from field cruise measurements of a forest-wide stratified sample of variable-radius plots, an ALS-derived area-based approach (ABA) trained and tested using an independent sample of fixed-area stem-mapped plots, and two ALS-derived individual tree approaches. Inventory volume estimates were validated using the gross volume of harvested logs from multi-stand harvest data, tracked by load and location and scaled at the processing mill. Results show that the ABA and individual tree approaches produced stand-level volume estimates with similar errors (−8 to 6%) to the cruise estimated volume (−16 to 6%) when compared with scaled volume. Across the entire forest, regression-based equivalence tests showed that merchantable and total stand volume estimates between the cruise and ALS-derived individual tree methods were more similar than between cruise and ABA methods, potentially due to underestimation of trees by both cruise and individual tree methods in some areas of the study area. Our results also highlight important differences between conventional cruise inventories and ALS-derived inventories, such as the spatial variability of within-stand attributes that ALS inventories provide. Overall, this study improves our understanding of the limitations and advantages of conventional and ALS-derived stand-level inventories in mixed conifer, structurally diverse forests. 

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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 (May 2025, Tree Physiology)

   Meinzer, Frederick (Ed.)

   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. Complex trajectories of tree growth in the southwestern United States after severe drought

   https://doi.org/10.1002/ecs2.70514  

   Zenes, Nicole; Anderegg, Leander_D L; Ogle, Kiona; Peltier, Drew_M P; Anderegg, William_R L (March 2026, Ecosphere)

   Abstract Climate change driven extreme droughts have major impacts on forest ecosystems, including large‐scale mortality and reduced primary production, which feedback to affect the global carbon cycle. The long‐term impacts of extreme drought events on forest mortality, ecosystem responses, and recovery/post‐drought trajectories are poorly understood. In this study, we combine annual tree ring widths of five major species occurring in the southwestern United States and data obtained from long‐term forest inventory and monitoring plots to study the effect of an extreme drought event in 2002 on subsequent tree growth. We quantified the extent to which trees that survived the drought had increased growth due to potential increases in resources from reduced stand density or reduced growth due to lingering impacts of drought stress. We found diverse patterns of post‐drought growth trajectories across species, with drastic increases in growth in some species such as trembling aspen (Populus tremuloides) and clear growth suppression in other species such as ponderosa pine (Pinus ponderosa), reflecting notable drought legacy effects. Total basal area was the best predictor of post‐drought growth responses, though the regression effect (positive or negative) varied by species; for example, ponderosa pine showed less growth than predicted in higher density stands while spruce had greater growth than expected in the higher density stands. Climatic water deficit and stand age also emerged as important drivers of post‐drought growth trajectories for multiple species. The results of this study can help to elucidate how different forest types in the southwestern United States will respond to future drought events and the ramifications for carbon cycling in this region. 

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