“Thicketized oak woodlands reduce groundwater recharge” @prairiefiresci @oakfirescience

“Thicketized oak woodlands reduce groundwater recharge”

Article available online Dec. 2022 in Science of the Total Environment. Access the article via the permanent web address (DOI). (https://doi.org/10.1016/j.scitotenv.2022.160811)

Highlights

• Woodland thicketization is a common phenomenon across the oak savannas (USA) with possible implications for groundwater recharge.
• Chloride and soil moisture were measured under different vegetation covers in a woodland pasture in Post Oak Savanna, Texas.
• Both sets of measurements showed substantial deep drainage in the open areas and no deep drainage in the thicketized woodland.
• Our results strongly suggest that thicketization is greatly reducing recharge in the Post Oak Savannas and the underlying Carrizo-Wilcox aquifer.

Abstract

Woodlands and pastures across the Post Oak Savannas (POS) in Texas have been undergoing thicketization over the last century via encroachment by understory shrubs such as Yaupon (Ilex decidua, Ilex vomitoria) and expansion of eastern redcedar (Juniperus virginiana). Because a large part of POS overlies the Carrizo-Wilcox (CW) aquifer – the third most important aquifer in Texas, there is a strong incentive to identify opportunities to increase groundwater recharge through land management.

The purpose of this research is to evaluate the influence of thicketization of post oak (Quercus stellata) stands on deep drainage (DD) in POS. We achieved this by, a) applying chloride mass balance on soil cores, and b) simultaneously monitoring soil moisture in a woodland pasture setting in POS. Four sites representing different vegetation covers were identified for sampling: 1) a thicketized oak woodland paired with an adjacent open site, 2) a woodland mosaic, 3) a pasture and 4) a pine-oak stand paired with an adjacent open site. A total of 24 soil cores to the depth of 260 cm were collected and (soil) pore water chloride concentrations at multiple depths were measured. Soil moisture was monitored at 21 locations, to the depth of 140–260 cm using a neutron moisture meter.

Negligible DD was estimated in the thicketized woodland, whereas most open locations recorded 3–18 cm/year and the woodland mosaic 0–1 cm of DD. Soil moisture data, collected from Jul-2020 to Jun-2021 also suggested higher deep drainage fluxes under open areas – with occurrence of sub-surface saturation only under the open areas and never under the woodlands. These results suggest that the thicketization in oak savannas is substantially reducing groundwater recharge.

Given the extent of thicketized oak savannas across United States, this could be impacting water budgets and groundwater recharge rates on regional scales.

Keywords: Woody plant encroachment; Ecohydrology; Chloride mass balance; Carrizo–Wilcox aquifer; Thicketization

Citation

Basant, Shishir, Bradford P. Wilcox, Chelsea Parada, Briana M. Wyatt, and Brent D. Newman. "Thicketized oak woodlands reduce groundwater recharge." Science of The Total Environment 862 (2023): 160811.

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“Impact of Eastern Redcedar encroachment on water resources in the Nebraska Sandhills” #rxfire #nitrate #hydrology @gpfirescience @prairiefiresci

“Impact of Eastern Redcedar encroachment on water resources in the Nebraska Sandhills”

This article was published Oct. 24, 2022, in Science of the Total Environment. Access the article via the permanent web address (DOI). (https://doi.org/10.1016/j.scitotenv.2022.159696)

Highlights

• Streamflow reduced by 46 % compared to historical flows for 100 % redcedar encroachment.
• Encroachment increases atrazine by 4 to 30 % compared to historical concentrations.
• Nitrate increases from 0.89–0.94 mg/L to 0.98–1.02 mg/L for 100 % encroachment.

Abstract

Worldwide, tree or shrub dominated woodlands have encroached into herbaceous dominated grasslands. While very few studies have evaluated the impact of Eastern Redcedar (redcedar) encroachment on the water budget, none have analyzed the impact on water quality.

In this study, we evaluated the impact of redcedar encroachment on the water budget in the Nebraska Sand Hills and how the decreased streamflow would increase nitrate and atrazine concentrations in the Platte River. We calibrated a Soil and Water Assessment Tool (SWAT model) for streamflow, recharge, and evapotranspiration. Using a moving window with a dilate morphological filter, encroachment scenarios of 11.9 %, 16.1 %, 28.0 %, 40.6 %, 57.5 %, 72.5 % and 100 % were developed and simulated by the calibrated model.

At 11.9 % and 100 % encroachment, streamflow was reduced by 4.6 % and 45.5 %, respectively in the Upper Middle Loup River, a tributary to the Platte River. Percolation and deep aquifer recharge increased by 27 % and 26 % at 100 % encroachment. Streamflow in the Platte River, a major water source for Omaha and Lincoln, would decrease by 2.6 %, 5.5 % and 10.5 % for 28 %, 57.5 %, and 100 % encroachment of the Loup River watershed, respectively. This reduction in streamflow could increase nitrate and atrazine concentrations in the Platte River by 4 to 15 % and 4 to 30 %, respectively.

While the density of redcedar is minimal, it is important to manage their encroachment to prevent reductions in streamflow and potential increases in pollutant concentrations.

Keywords: Soil and Water Assessment Tool; Loup River Platte River; Atrazine; Baseflow-dominated watershed

Citation

Kishawi, Yaser, Aaron R. Mittelstet, Troy E. Gilmore, Dirac Twidwell, Tirthankar Roy, and Nawaraj Shrestha. "Impact of Eastern Redcedar encroachment on water resources in the Nebraska Sandhills." Science of The Total Environment 858 (2023): 159696.

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“Trajectories and state changes of a grassland stream and riparian zone after a decade of woody vegetation removal”

“Trajectories and state changes of a grassland stream and riparian zone after a decade of woody vegetation removal”

Published online March 2, 2023, in Ecological Applications. Access online via the permanent web address (DOI). (https://doi.org/10.1002/eap.2830)

Abstract

Riparian zones and the streams they border provide vital habitat for organisms, water quality protection, and other important ecosystem services. These areas are under pressures from local (land use/ land cover change) to global (climate change) processes. Woody vegetation is expanding in grassland riparian zones worldwide.

Here, we report on a decade-long watershed-scale mechanical removal of woody riparian vegetation along 4.5 km of stream channel in a before-after control impact experiment. Prior to this removal, woody plants had expanded into grassy riparian areas, which was associated with a decline in streamflow, loss of grassy plant species, and other ecosystem-scale impacts.

We confirmed some expected responses, including rapid increases in stream nutrients and sediments, disappearance of stream mosses, and decreased organic inputs to streams via riparian leaves. We were surprised that nutrient and sediment increases were transient for three years, that there was no recovery of stream discharge, and that areas with woody removal did not shift back to a grassland state, even when re-seeded with grassland species. Rapid expansion of shrubs (Cornus drummondii, Prunus americana) in the areas where trees were removed allowed woody vegetation to remain dominant despite repeating the cutting every two years. Our results suggest woody expansion can fundamentally alter terrestrial and aquatic habitat connections in grasslands resulting in inexorable movement toward a new ecosystem state. Human pressures such as climate change, atmospheric CO2 increases, and elevated atmospheric nitrogen deposition could continue to push the ecosystem along a trajectory that is difficult to change.

Our results suggest that predicting relationships between riparian zones and the streams they border could be difficult in the face of global change in all biomes, even in well-studied sites.

Keywords: alternative states; nutrients; riparian zone; stream discharge; thresholds; water quality; woody vegetation

Citation

Dodds, Walter K., Zak Ratajczak, Rachel M. Keen, Jesse B. Nippert, Bartosz Grudzinski, Allison Veach, Jeffery H. Taylor, and Amanda Kuhl. "Trajectories and state changes of a grassland stream and riparian zone after a decade of woody vegetation removal." Ecological Applications (2023): e2830.

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“Heterogeneity of Kentucky Bluegrass (Poa pratensis L.) Seed Germination After Controlled Burning” @prairiefiresci @gpfirescience @rangelands

“Heterogeneity of Kentucky Bluegrass (Poa pratensis L.) Seed Germination After Controlled Burning”

Available online May 7, 2022 in Rangeland Ecology and Management. Access the article via the permanent web address (DOI). (https://doi.org/10.1016/j.rama.2022.04.001)

Abstract

Prescribed burning is sometimes advocated as a means for controlling Kentucky bluegrass (POPR) in invaded grazing lands. However, little is known about the effects of fire on POPR seed survival.

We exposed seeds of POPR (c.v. Kenblue), placed in shallow metal dishes, at ground level to prescribed burns while monitoring temperature at the soil surface and at 10 cm above ground with thermocouples and assessed subsequent seed germinability.

Maximum surface temperatures during the test burns averaged 271°C ± 23°C but varied widely (range 41°C–509°C) while maximum temperature at 10 cm above ground was slightly higher (301°C ± 25°C). Burning inhibited seed survival or the ability to germinate (Kolmogorov-Smirnov P < .0001). Germination of the POPR seeds in the control dishes averaged 93% ± 1%. Average germination for burned locations was 37% ± 7% and was distributed bimodally; it was absent or strongly inhibited in 59% of the samples but much less affected (≥ 60% normal germination) in the remaining 41% of locations. Germination success was similar in burned plots previously managed with both grazing and fire (35% ± 10%) or previously managed by fire alone (38% ± 11%), but it was significantly and inversely correlated to maximum surface temperature during the burn (Spearman r = −0.49, P < 0.005). However, we observed a binary pattern of high and low seed germination response across the entire gradient of recorded surface temperatures, including instances of highly disparate values for seed survival in samples located within 60 cm of each other.

Such extreme variability may result from unburned or superficially affected safe sites that originate from heterogeneity of fire impacts.This study suggests prescribed burning can kill POPR seeds near the soil surface, especially those located in standing litter and dry thatch. However, some seeds under these layers and closer to the mineral soil surface may be less impacted.

Citation

Halvorson, Jonathan J., David Toledo, and John R. Hendrickson. "Heterogeneity of Kentucky Bluegrass (Poa pratensis L.) Seed Germination After Controlled Burning." Rangeland Ecology & Management 83 (2022): 112-116.

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“Cattle Graze Central US Milkweeds at Least as Much as Grasses, Even Under Patch-Burn-Grazing Management” @gpfirescience @rangelands @helzerprairie

“Cattle Graze Central US Milkweeds at Least as Much as Grasses, Even Under Patch-Burn-Grazing Management”

This article was published Jan. 26, 2023 in Rangeland Ecology and Management. Access the article via the permanent web address (DOI). (https://doi.org/10.1016/j.rama.2023.01.001)

Abstract

Most researchers assume cattle avoid milkweeds due to toxic compounds. However, observations suggest cattle graze common milkweed (Asclepias syriaca L.), an important summer host plant for monarch butterflies (Danaus plexippus L.) east of the Rocky Mountains, as well as showy milkweed (Asclepias speciosa Torr.). This directly relates to efforts to add over 1 billion stems of milkweed for monarch butterfly conservation.

We sampled whether cattle regularly graze common/showy milkweed in a central Nebraska restored prairie patch-burn-grazing system with patches burned in the year of the main study (2018) or previous years (2017–2016). We also sampled burned control grasslands without livestock. This sampling therefore compared three different types of burn-graze management. Cow-calf pairs were put onto the grasslands in April, and we sampled every 2 wk through September.

We found that wild grazers (e.g., deer) were not grazing common/showy milkweed stems in control grasslands, whereas by August > 73% of stems had been grazed in the patch-burn-grazed grasslands—with no noticeable negative effects on cattle. Also, cattle grazing of common/showy milkweed did not differ significantly in different patches, even though big bluestem grass (Andropogon gerardii Vitman) was grazed significantly more in patches burned in 2018. Finally, milkweed abundance in control grasslands ranged from 34- to 185-fold higher than the average milkweed abundance in patch-burn-grazed grasslands.

These results suggest that cattle regularly graze common/showy milkweed and that patch-burn-grazing does not increase milkweed abundance when cattle begin grazing in April. The good news of these results is that cattle safely grazed low amounts of common/showy milkweed, suggesting control efforts for these milkweeds are often unnecessary. Future work should examine how to increase milkweed abundance without affecting cattle weight gain, possibly by deferring grazing in some areas during critical milkweed growth periods.

Citation

Dickson, Timothy L., Brittany Poynor, and Christopher J. Helzer. "Cattle Graze Central US Milkweeds at Least as Much as Grasses, Even Under Patch-Burn-Grazing Management." Rangeland Ecology & Management 87 (2023): 158-166.

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“Pre-Columbian red pine (Pinus resinosa Ait.) fire regimes of north-central Pennsylvania, USA” @prairiefiresci @oakfirescience @usfs_nrs

“Pre-Columbian red pine (Pinus resinosa Ait.) fire regimes of north-central Pennsylvania, USA”

Published June 28, 2022 in Fire Ecology. Access the article via the USDA Treesearch database. (https://www.nrs.fs.usda.gov/pubs/64570)

Abstract

Background

Fire-dependent vegetation communities in the northeastern USA have undergone significant transitions since social and ecological disruptions associated with Euro-American colonization of North America. There is much interest, though little information available, about historical fire regimes of fire-adapted vegetation communities in the northeastern USA in pre-Columbian times (i.e., pre-1492 CE).

We intensively investigated a red pine (Pinus resinosa Ait.)—oak (Quercus spp.) forested landscape in north-central Pennsylvania, USA, for exceptionally old red pine remnants (stumps, snags) where previous research had suggested the potential to develop fire-scar and tree-ring chronologies which extend to time periods prior to 1492.

Results

Tree-ring and fire-scar chronologies recovered from red pine trees extend back to 1370 and 1402, respectively. Red pine trees were broadly distributed across this landscape (34.4 km2 area) prior to 1492, and frequent fire (i.e., mean fire return intervals of 4.1 years at landscape scale, 9.7–11.7 years at smaller spatial scales (0.5–7.1 km2)) was observed in the time period prior to sustained contact between Indigenous peoples and Euro-American colonizers circa 1609.

Conclusions

This study resulted in the longest fire-scar record in eastern North America and offers unique foundational ecological information regarding pre-Columbian fire regimes of northeastern USA fire-adapted forest communities. Fire scars provide physical evidence that fire was an important ecological component of this landscape before and after 1492 and that the current period of reduced fire activity is unprecedented in the 500 years prior to fire exclusion practices that were widely adopted circa 1915. Beyond fire scars, the spatial and temporal extent of the red pine tree-ring record provides evidence that red pine, a fire-dependent species, was historically a more important component of this landscape than it is today. The conservation of red pine vegetation communities will require incorporating recurring fire into management plans, for the successful regeneration and perpetuation of red pine, and to sustain associated flora and fauna of conservation concern.

Keywords: Fire regimes; Northeastern USA; Pennsylvania; Pre-Columbian; Red pine

Citation

Marschall, Joseph M.; Stambaugh, Michael C.; Abadir, Erin R.; Dey, Daniel C.; Brose, Patrick H.; Bearer, Scott L.; Jones, Benjamin C. 2022. Pre-Columbian red pine (Pinus resinosa Ait.) fire regimes of north-central Pennsylvania, USA. Fire Ecology. 18(1): Article 11. 19 p. https://doi.org/10.1186/s42408-022-00135-6.

“Savanna fire regimes depend on grass trait diversity” @kim_1801 @SallyArchibald @sheffieldplants @prairiefiresci

“Savanna fire regimes depend on grass trait diversity”

Published September 2022 in Trends In Ecology and Evolution. Access the article via the permanent web address (DOI). (https://doi.org/10.1016/j.tree.2022.04.010)

Highlights

Most fires on Earth occur in savannas, but vary considerably in their extent, frequency, and intensity. These patterns cannot fully be explained by climate or land management.

An important ‘missing-piece’ in explaining the variation in savanna fire regimes is the diversity of grasses that fuel fires and whose traits strongly influence fire behaviour. The major differences in savanna fire behaviour across continents may lie in the contrasting species and trait assemblages in savanna grass communities.

Fire regimes change significantly when savanna grass communities or traits are altered by the introduction of invasive species and climatic changes.

Improved representation of grass trait diversity in fire models will be essential for reliable forecasts of the behaviour and impacts of the majority of fires on Earth.

Grasses fuel most fires on Earth and strongly influence local fire behaviour through traits that determine how flammable they are. Therefore, grass communities that differ in their species and trait compositions give rise to significant spatial variation in savanna fire regimes across the world, which cannot be otherwise explained. Likewise, fire regimes are continuously modified by alterations to savanna grass community traits, through species introductions and climatic changes. However, current representation of grassy fuels in global fire models misses important variation and therefore limits predictive power. The inclusion of grass trait diversity in models, using remotely sensed trait proxies, for example, will greatly improve our ability to understand and project savanna fires and their roles in the Earth system.

Keywords: fire regimes; flammability; functional traits; grasses; Poaceae; savannas

Citation

Simpson, Kimberley J., Sally Archibald, and Colin P. Osborne. "Savanna fire regimes depend on grass trait diversity." Trends in Ecology & Evolution (2022).

“Fire effects on the persistence of soil organic matter and long-term carbon storage” @eco_pelle @prairiefiresci @gpfirescience @nafse @apfirescience @sefirescience

"Fire effects on the persistence of soil organic matter and long-term carbon storage"

This review article was published Dec. 23, 2021, in Nature Geoscience. Access the article via the permanent web address (DOI). (https://doi.org/10.1038/s41561-021-00867-1)

Abstract

One paradigm in biogeochemistry is that frequent disturbance tends to deplete carbon (C) in soil organic matter (SOM) by reducing biomass inputs and promoting losses. However, disturbance by fire has challenged this paradigm because soil C responses to frequent and/or intense fires are highly variable, despite observed declines in biomass inputs.

Here, we review recent advances to illustrate that fire-driven changes in decomposition, mediated by altered SOM stability, are an important compensatory process offsetting declines in aboveground biomass pools. Fire alters the stability of SOM by affecting both the physicochemical properties of the SOM and the environmental drivers of decomposition, potentially offsetting C lost via combustion, but the mechanisms affecting the SOM stability differ across ecosystems. Thus, shifting our focus from a top-down view of fire impacting C cycling via changes in plant biomass to a bottom-up view of changes in decomposition may help to elucidate counterintuitive trends in the response of SOM to burning.

Given that 70% of global topsoil C is in fire-prone regions, using fire to promote SOM stability may be an important nature-based climate solution to increase C storage.

Keywords: Carbon cycle; Fire ecology; Forest ecology; Natural hazards

Citation

Pellegrini, Adam FA, Jennifer Harden, Katerina Georgiou, Kyle S. Hemes, Avni Malhotra, Connor J. Nolan, and Robert B. Jackson. "Fire effects on the persistence of soil organic matter and long-term carbon storage." Nature Geoscience 15, no. 1 (2022): 5-13.

“Goat browse selectivity during conservation grazing in an invaded eastern oak-hickory forest” @prairiefiresci @oakfirescience @savannainst

“Goat browse selectivity during conservation grazing in an invaded eastern oak-hickory forest”

Published January 25, 2023, in Agroforestry Systems. Access the article via the permanent web address (DOI). (https://doi.org/10.1007/s10457-023-00810-w)

Abstract

Oak and hickory (Quercus spp. and Carya spp.) recruitment in forests of eastern North America is adversely impacted by woody invasive species. Conservation grazing, the use of livestock for restoration or biodiversity promotion, has been used to control invasive plants. The efficacy of such grazing and its ecological tradeoffs in oak-hickory forests, however, is unknown.

We aimed to fill this gap by investigating browsing intake and preference by goats. To support this, nineteen experimental plots were established in an invaded forest, and their species composition and biomass quantified. Twelve plots were browsed under high (1019 goat-days ha−1) and low (509 goat-days ha−1) browsing pressure regimes with direct observations of forage intake and selection. Leaves of commonly browsed species were assessed for nutritional composition.

Goats generally selected for native spicebush (Lindera benzoin) over invasive multiflora rose (Rosa multiflora), however, selection of the latter increased with time. Both species identity and browsing pressure were good predictors of browse intake. For greater biomass reduction of invasive species, the use of high browsing pressure is recommended.

This research showed that conservation grazing can be an effective tool to reduce biomass of invasive species such as multiflora rose, privet (Ligustrum spp.), and oriental bittersweet (Celastrus orbiculatus) in oak-hickory forests when high browsing pressure is implemented, nevertheless goats may initially target their preferred species (e.g., spicebush).

Keywords: Ecological restoration; Feeding behavior; Forest management; Browse quality; Invasive species; Deciduous forest

Citation

Novais, Wanderson, Benjamin A. Wenner, Jeremy A. Block, Simon C. Power, Elizabeth Porteus, and G. Matt Davies. "Goat browse selectivity during conservation grazing in an invaded eastern oak-hickory forest." Agroforestry Systems (2023): 1-12.

“Organizational capacity and ecological restoration” @SERestoration @UMNFWCB @prairiefiresci

“Organizational capacity and ecological restoration”

This open access review article was first published June 30, 2022, in Restoration Ecology. Access the article via the permanent web address (DOI). (https://doi.org/10.1111/rec.13757)

Abstract

Organizations entrusted with responsibilities and resources to repair ecosystems have for many decades pursued their defining purpose against long odds created by a host of inherent challenges, notably the long time frames required for ecological recovery and landscape-level stressors. Global change compounds these challenges, increasing shocks to the operating environments of these organizations. Interest in assessing organizational capacity to respond to system shocks (i.e. resilience) productively has been strong in many fields, though not in the restoration arena.

The objectives of this paper are to build awareness of the importance of organizations for achieving the aims of restoration and to spur organizational research to strengthen the restoration sector. I summarize research on organizations relevant to the restoration sector and with this foundation propose a framework for assessing the capacity of restoration organizations. The proposed framework is an adaptation of models used in other sectors, based on five critical capacities:

1. situation awareness
2. governance and leadership
3. internal resources
4. external relations, and
5. change readiness.

We can assess the extent to which an organization possesses each capacity by eliciting feedback about functions linked to each capacity. Devising assessment tools from this framework requires attention to key realities of the restoration sector including prevalence of short-term funding, effect of externalities on restoration outcomes, dependence on partnerships of multiple organizations for complex and large restorations.

Exploration into assessment approaches for restoration organizations highlights a major knowledge gap that, if addressed, could enhance the reliability of restoration as a global and local strategy for improving ecosystems services.

Implications for Practice

• The capacity of people (i.e. organization) undertaking a restoration greatly affects what can be accomplished with available resources and support. Yet, there has been little exploration of how to assess organizational deficiencies so these can be addressed, potentially improving outcomes of their restoration.
• Using precedents from other sectors, a framework to assess restoration organizations' capacity is proposed here. Assessments of organizational capacity can be undertaken for an individual organization or as an external assessment of multiple organizations.
• Because many restoration organizations depend on external support to pursue projects, expectations linked to funding decisions can accelerate the adoption of organizational capacity assessments.

Keywords: conservation organizations; ecosystem restoration; organizational functions; organizational resilience; strategic planning

Citation

Galatowitsch, Susan. "Organizational capacity and ecological restoration." Restoration Ecology (2022): e13757.