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ABSTRACT Woody encroachment—the expansion of woody shrubs into grasslands—is a widely documented phenomenon with global significance for the water cycle. However, its effects on watershed hydrology, including streamflow and groundwater recharge, remain poorly understood. A key challenge is the limited understanding of how changes to root abundance, size and distribution across soil depths influence infiltration and preferential flow. We hypothesised that woody shrubs would increase and deepen coarse‐root abundance and effective soil porosity, thus promoting deeper soil water infiltration and increasing soil water flow velocities. To test this hypothesis, we conducted a study at the Konza Prairie Biological Station in Kansas, where roughleaf dogwood (Cornus drummondii) is the predominant woody shrub encroaching into native tallgrass prairie. We quantified the distribution of coarse and fine roots and leveraged soil moisture time series and electrical resistivity imaging to analyse soil water flow beneath shrubs and grasses. We observed a greater fraction of coarse roots beneath shrubs compared to grasses, which was concurrent with greater saturated hydraulic conductivity and effective porosity. Half‐hourly rainfall and soil moisture data show that the average soil water flow through macropores was 135% greater beneath shrubs than grasses at the deepest B horizon, consistent with greater saturated hydraulic conductivity. Soil‐moisture time series and electrical resistivity imaging also indicated that large rainfall events and greater antecedent wetness promoted more flow in the deeper layers beneath shrubs than beneath grasses. These findings suggest that woody encroachment alters soil hydrologic processes with cascading consequences for ecohydrological processes, including increased vertical connectivity and potential groundwater recharge.
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Effects of post oak (Quercus stellata) and smooth brome (Bromus inermis) competition on water uptake and root partitioning of eastern redcedar (Juniperus virginiana)
Eastern redcedar Juniperus virginiana is encroaching into new habitats, which will affect native ecosystems as this species competes with other plants for available resources, including water. We designed a greenhouse experiment to investigate changes in soil moisture content and rooting depths of two-year-old J . virginiana saplings growing with or without competition. We had four competition treatments: 1) none, 2) with a native tree ( Quercus stellata ), 3) with an invasive grass ( Bromus inermis ), and 4) with both Q . stellata and B . inermis . We measured soil moisture content over two years as well as root length, total biomass, relative water content, midday water potential, and mortality at the end of the experiment. When J . virginiana and B . inermis grew together, water depletion occurred at both 30–40 cm and 10–20 cm. Combined with root length results, we can infer that J . virginiana most likely took up water from the deeper layers whereas B . inermis used water from the top layers. We found a similar pattern of water depletion and uptake when J . virginiana grew with Q . stellata , indicating that J . virginiana took up water from the deeper layers and Q . stellata used water mostly from the top soil layers. When the three species grew together, we found root overlap between J . virginiana and Q . stellata . Despite the root overlap, our relative water content and water potential indicate that J . virginiana was not water stressed in any of the plant combinations. Regardless, J . virginiana saplings had less total biomass in treatments with B . inermis and we recorded a significantly higher mortality when J . virginiana grew with both competitors. Root overlap and partitioning can affect how J . virginiana perform and adapt to new competitors and can allow their co-existence with grasses and other woody species, which can facilitate J . virginiana encroachment into grasslands and woodlands. Our data also show that competition with both Q . stellata and B . inermis could limit establishment, regardless of water availability.
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- Award ID(s):
- 1915908
- PAR ID:
- 10412175
- Editor(s):
- Guo, Xiao
- Date Published:
- Journal Name:
- PLOS ONE
- Volume:
- 18
- Issue:
- 2
- ISSN:
- 1932-6203
- Page Range / eLocation ID:
- e0280100
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1371/journal.pone.0280100
