Browsing by Subject "Ecohydrology"

Now showing 1 - 3 of 3

Evaluating abnormalities in daily transpiration patterns across tree species in a semi-arid climate
(2022-05-09) McLaughlin, Jack Riley; Matheny, Ashley M.
Climate change causes shifts in precipitation, temperature, shifting climate zones and more, thus affecting the ecology and hydrologic feedbacks of many environments, specifically those existing in already warm, arid climates. Vegetation affects the local hydrologic cycle, as it promotes multiple feedback mechanisms, such as the extraction of soil water via roots, the re-wetting of the atmospheric boundary layer and lowering temperatures through transpiration. This study focuses on transpiration patters in a hot semi-arid environment, which is defined as having a total annual precipitation between one-fifth and one-half of potential evapotranspiration and an annual mean temperature above 18°C. Meteorological conditions, sap flow, leaf water potential, carbon assimilation, and stomatal conductance were all recorded during 2021 in order to observe the drivers of transpiration among ashe juniper, lacey oak and pinyon pines, along with abnormalities in their diurnal sap flow patterns, where the majority of sap flow occurs at dawn and dusk instead of midday. Sap flow was shown to increase in magnitude (up to 350% in pinyon pines’ case) when environmental conditions such as vapor pressure deficit (VPD), temperature and soil water potential (SWP) are favorable. Ashe juniper was found to have a weak relationship between leaf water potential (LWP) and VPD, along with a stronger relationship between LWP and SWP. Oaks were found to have a very strong relationship between LWP and VPD, while pines were found to have a weak relationship between LWP and VPD. Of the three species, only the oaks were found to have a relationship between carbon assimilation rates and VPD, carbon assimilation rates and SWP, and stomatal conductance and SWP. This makes oaks the most vulnerable of the three species to future climate change and shifting climate zones. Better understanding of plant responses to stressful climatic conditions and in arid environments will provide insight in plant durability and adaptations to a warming climate, all of which are important as our global and local climates continue to change
Evaluating biomass water storage and sap flux in three semi-arid tree species in central Texas
(2022-05-05) Beaman, Lillian Brown; Matheny, Ashley M.; Chuchla, Richard J. (Richard Julian); Rempe, Daniella
This study explores how semi-arid forests respond to drought and the potential impact of climate change. It provides novel information to guide political decision-making concerning climate change, water use, and land use with respect to juniper tree clearing. We used sap flux observations as a proxy for transpiration and capacitance-style FDR sensors installed directly into trees as a means to assess wood water storage. We also recorded meteorological conditions at the field site including atmospheric vapor pressure deficit (VPD), temperature, precipitation, and soil moisture. Our results indicate sap flux can either use internal wood water storage for daily transpiration (an inverse relationship) or be used to recharge the wood water storage (a parallel relationship) depending on environmental conditions. During stressful environmental conditions, sap flux is typically well below 10 [gH₂0]/[m²] /sapwood/s and used to refill wood water storage rather than for transpiration. During non-stressful times with moderate temperatures, VPD, and ample soil moisture, sap flux is typically above 10 [gH₂0]/[m²] /sapwood/s and is used for transpiration. On an individual tree scale, we found junipers are neither transpiring at higher rates nor storing more wood water than either oak or pine. Current policies suggest removal of woody brush such as juniper, will lead to an increase in water yield. Our results show that this may only be the case in certain circumstances. Our study showed daily wood water storage and withdrawal is highly dependent on VPD (water demand) and soil water potential (water supply). As the effects of climate change intensify, VPD will likely increase while soil water potential will further decline. This is expected to have a large effect on internal wood water storage and ultimately lead to an increase in cavitation and tree mortality. Stakeholders of the Texas Hill Country must realize as climate change intensifies, the ecosystem will change, and water availability for both plants and people will decrease. Juniper brush management may be a potential solution due to the prolific spreading but not the all-encompassing remedy for the issue of the area’s water availability as previously stated in Texas policy.
Modeling of soil moisture dynamics of grasslands in response to CO₂ and biodiversity manipulations at BioCON
(2014-12) Flinker, Raquel Henriques; Cardenas, Meinhard Bayani, 1977-; Caldwell, Todd G.
Increasing atmospheric carbon dioxide (CO₂) leads to global warming. This can have several impacts on climate and on plant biodiversity, and has been the topic of many studies. The objective of this thesis was to understand the effects of higher atmospheric CO₂ on soil moisture dynamics in the grasslands of central Minnesota using detailed hydrologic modeling to explain previous experimental observations at the BioCON site, a free-air CO₂ enrichment experiment. The hydraulic properties and texture of soils collected from BioCON were determined in the laboratory through grainsize analysis and continuous evaporative drying to determine soil moisture retention curves and hydraulic conductivities. These results were used as input for numerical soil water flow and energy balance models. The models showed that vegetation presence and atmospheric CO₂ concentrations significantly affected the soil moisture dynamics. Summer evapotranspiration (ET) had a higher variation for bare plots than for vegetated plots. This likely occurred because the vegetation provided a buffer against the variations in weather conditions. Vegetation not only retains part of the precipitation on its leaves, it also retains water in its structure and transpires while carrying out photosynthesis. Higher water content was also seen for the bare plots than for the vegetated soils. For some vegetated plots, there were differences between simulated and observed soil moisture. This could have been caused by a difference in plant composition and could suggest that different plant species can respond differently to varying CO₂ atmospheric concentrations leading to different soil moisture dynamics. In addition to this, smaller ET values and higher soil water content values at vegetated elevated CO₂ conditions than at ambient CO₂ conditions were simulated. This was expected, as higher atmospheric CO₂ is linked to higher plant water efficiency and larger biomass. For the simulations, higher values for stomatal resistance and higher plant and plant residue biomass were used. If increasing CO₂ conditions in fact decreases ET, regional weather patterns could be affected as less ET could delay the speed that water flows through the water cycle.