Drivers of variability in transpiration and implications for stream flow in forests of western Oregon

I compared transpiration among different types of forest stands in the western Cascades of Oregon. The three major questions were: 1) How does transpiration compare between a young and old stand and why? 2) Does diversity of overstory trees affect transpiration? and 3) How is transpiration related to stream flow? Transpiration was quantified using thermal dissipation sap flow measurements scaled to a ground-area basis using sapwood surveys for periods during the summer months of 2000, 2001, and 2002, and in a subset of plots, for a full year. I found that a young, rapidly growing stand ([approximately] 40 years since disturbance) used 3.3 times more water during the growing season than an old-growth stand ([approximately] 450 years since disturbance) because the young stand had 2.3 times higher sap flow rates per unit sapwood in Douglas-fir, had a 21% greater total sapwood basal area, and had a larger component of hardwoods that use 1.41 times more water than conifers per unit sapwood. In two-species mixtures of Douglas-fir and red alder, I found evidence that mixtures are less productive and have lower annual transpiration than monocultures of these two species. The observed differences were probably due to altered biomass rather than diversity itself, but diversity likely played a role in altering biomass. Such stand age- and diversity-related differences in transpiration potentially impact stream flow. In a small watershed with a 450-yr-old forest, I examined the role of vegetation in stream flow patterns at hourly, daily, and storm scales. Transpiration apparently controlled stream flow during the summer at hourly scales with lags of at least five hours. In contrast, at daily and storm scales, soil water apparently controlled both stream flow and transpiration during the dry season, but there was no relationship during the wet season. These results indicate that forest management practices that reduce stand age and decrease diversity may lead to increased transpiration and consequently may reduce summer stream flow

Water-use dynamics of an invasive reed, Arundo donax, from leaf to stand

Abstract We investigated water use of an invasive riparian reed species, Arundo donax (L.), along moisture gradients to determine how extensively this plant might affect water resources. On an approximately 250 m stretch of the Lower Rio Grande in South Texas, we measured the gas exchange of water vapor at the leaf scale and structural characteristics, such as leaf area and shoot density, at the stand scale. To assess the effect of water availability, we used transects perpendicular to the edge of the river along a potential moisture gradient. Stands of A. donax used approximately 8.8±0.9 mm of water per day during the peak of the 2008 growing season; this rate of water use is at the high end of the spectrum for plants. Transpiration and leaf area index varied with water availability, which suggests this plant is sensitive to drought and declining water tables. This provides a baseline for future studies comparing water use between A. donax and other plant species, especially native species considered in riparian restoration efforts

Tracer-aided ecohydrological modelling across climate, land cover, and topographical gradients in the tropics

Funding Information: We thank the Leverhulme Trust funded ISOLAND (RPG‐2018‐375) project, the IAEA‐CRP F31005 contract 22904, the IAEA‐CRP F31006, and the IAEA‐CRP F31006 and UCR C1038 funded the IsoRSM project. We also acknowledge the many suggestions by two anonymous reviewers that improved this paper. Funding Information: We thank the Leverhulme Trust funded ISOLAND (RPG-2018-375) project, the IAEA-CRP F31005 contract 22904, the IAEA-CRP F31006, and the IAEA-CRP F31006 and UCR C1038 funded the IsoRSM project. We also acknowledge the many suggestions by two anonymous reviewers that improved this paper. Publisher Copyright: © 2023 The Authors. Hydrological Processes published by John Wiley & Sons Ltd.Peer reviewedPublisher PD

Global transpiration data from sap flow measurements : the SAPFLUXNET database

Plant transpiration links physiological responses of vegetation to water supply and demand with hydrological, energy, and carbon budgets at the land-atmosphere interface. However, despite being the main land evaporative flux at the global scale, transpiration and its response to environmental drivers are currently not well constrained by observations. Here we introduce the first global compilation of whole-plant transpiration data from sap flow measurements (SAPFLUXNET, https://sapfluxnet.creaf.cat/, last access: 8 June 2021). We harmonized and quality-controlled individual datasets supplied by contributors worldwide in a semi-automatic data workflow implemented in the R programming language. Datasets include sub-daily time series of sap flow and hydrometeorological drivers for one or more growing seasons, as well as metadata on the stand characteristics, plant attributes, and technical details of the measurements. SAPFLUXNET contains 202 globally distributed datasets with sap flow time series for 2714 plants, mostly trees, of 174 species. SAPFLUXNET has a broad bioclimatic coverage, with woodland/shrubland and temperate forest biomes especially well represented (80 % of the datasets). The measurements cover a wide variety of stand structural characteristics and plant sizes. The datasets encompass the period between 1995 and 2018, with 50 % of the datasets being at least 3 years long. Accompanying radiation and vapour pressure deficit data are available for most of the datasets, while on-site soil water content is available for 56 % of the datasets. Many datasets contain data for species that make up 90 % or more of the total stand basal area, allowing the estimation of stand transpiration in diverse ecological settings. SAPFLUXNET adds to existing plant trait datasets, ecosystem flux networks, and remote sensing products to help increase our understanding of plant water use, plant responses to drought, and ecohydrological processes. SAPFLUXNET version 0.1.5 is freely available from the Zenodo repository (https://doi.org/10.5281/zenodo.3971689; Poyatos et al., 2020a). The "sapfluxnetr" R package - designed to access, visualize, and process SAPFLUXNET data - is available from CRAN.Peer reviewe

A mesic maximum in biological water use demarcates biome sensitivity to aridity shifts

Biome function is largely governed by how efficiently available resources can be used and yet for water, the ratio of direct biological resource use (transpiration, ET) to total supply (annual precipitation, P) at ecosystem scales remains poorly charac- terized. Here, we synthesize field, remote sensing and ecohydrological modelling estimates to show that the biological water use fraction (ET/P) reaches a maximum under mesic conditions; that is, when evaporative demand (potential evapotranspira- tion, EP) slightly exceeds supplied precipitation. We estimate that this mesic maximum in ET/P occurs at an aridity index (defined as EP/P) between 1.3 and 1.9. The observed global average aridity of 1.8 falls within this range, suggesting that the biosphere is, on average, configured to transpire the largest possible fraction of global precipitation for the current climate. A unimodal ET/P distribution indicates that both dry regions subjected to increasing aridity and humid regions subjected to decreasing aridity will suffer declines in the fraction of precipitation that plants transpire for growth and metabolism. Given the uncertainties in the prediction of future biogeography, this framework provides a clear and concise determination of ecosystems' sensitivity to climatic shifts, as well as expected patterns in the amount of precipitation that ecosystems can effectively use

Does Shrub Removal Increase Groundwater Recharge in Southwestern Texas Semiarid Rangelands?

Evapotranspiration (ET) is a key component limiting groundwater recharge past the root zone in semiarid regions. Vegetation management may alter groundwater recharge if ET is altered due to changes in vegetation type or cover. This study quantifies changes in groundwater recharge following vegetation cover change from native woodland to pasture in a semiarid region of southwest Texas. The Carrizo-Wilcox aquifer is a valuable groundwater resource in this area, where overuse by dependent farming practices has lowered aquifer levels significantly in the last 85 yr. Combining data from short-term (30 mo) monitoring of the changes in soil moisture and long-term (5-30 yr) changes in total soil chloride indicated deep drainage increased slightly where land had been cleared of vegetation. Annual recharge rates below rooting depths (standardized to 155 cm) averaged only 0.72 +/- 0.2 mm yr-1 (mean 6 SE) in areas not cleared of woody vegetation, as estimated by chloride mass balance. Upon clearing, 72% of the total chloride naturally occurring in the soil profile was flushed away within 30 yr, leading to an estimated 2.59 +/- 1.7 mm yr-1 additional recharge. Deep soil moisture in recently cleared land increased by up to 17% during the growing season of wet years (double the average rainfall) but did not increase in dry or normal precipitation years, providing supporting evidence that more water penetrated below the roots under certain environmental conditions. These results demonstrate that brush management can increase recharge by modest, but measurable, amounts depending on site-specific soil characteristics and degree of reduction in vegetation./La evapotranspiración (ET) es un componente clave que limita la recarga de agua subterránea más allá de la zona radicular en regiones semiáridas. El manejo de la vegetación puede alterar la recarga de las aguas subterráneas si se altera la ET por los cambios en la cubierta o el tipo de vegetación. Este estudio midió los cambios de la recarga del agua subterránea después de los cambios en la cubierta de la vegetación de un bosque nativo a un pastizal en una región semiárida del suroeste de Texas. El acuífero de Carrizo–Wilcox es un recurso valioso de las aguas subterráneas en esta zona, donde el uso excesivo debido a las prácticas dependientes de la agricultura ha bajado significativamente los niveles acuíferos en los últimos 85 años. Combinando los datos de seguimiento a corto plazo (30 meses) de los cambios en la humedad del suelo y a largo plazo (5–30 años) en los cambios del total del cloruro de suelo indicaron que el drenaje profundo aumentó ligeramente en áreas donde la vegetación se había aclarado. Las tasas anuales de recarga debajo de la profundidad de la raíz (estandarizado a 155 cm) promedió sólo 0.72 +/- 0.2 mm año-1 en áreas no esclarecidas de vegetación leñosa, estimado por el balance de masa de cloruro. Después de la clareo el 72% del total del cloruro que ocurre naturalmente en el perfil del suelo fue removido entre 30 años, conduciendo aun a estimación de recarga adicional de 2.59 +/- 1.7 mm año-1. La humedad del suelo profundo en tierras recientemente aclaradas se incrementó hasta un 17% durante la estación de crecimiento en años húmedos (doble de la media de la precipitación) pero no aumentó durante años con precipitación normal o años secos, proporcionando pruebas que más agua penetró por debajo de la zona radicular bajo ciertas condiciones ambientales. Estos resultados demuestran que el manejo de arbustivas puede incrementar modestamente la recarga del agua, pero en cantidades medibles, dependiendo de las características especificas del sitio del suelo y el grado de reducción de la vegetación.The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202

Structural and compositional controls on transpiration

Summary Large areas of forests in the Pacific Northwest are being transformed to younger forests, yet little is known about the impact this may have on hydrological cycles. Previous work suggests that old trees use less water per unit leaf area or sapwood area than young mature trees of the same species in similar environments. Do old forests, therefore, use less water than young mature forests in similar environments, or are there other structural or compositional components in the forests that compensate for tree-level differences? We investigated the impacts of tree age, species composition and sapwood basal area on stand-level transpiration in adjacent watersheds at the H.J. Andrews Forest in the western Cascades of Oregon, one containing a young, mature (about 40 years since disturbance) conifer forest and the other an old growth (about 450 years since disturbance) forest. Sap flow measurements were used to evaluat

Modeling Profiles of Micrometeorological Variables in a Tropical Premontane Rainforest Using Multi‐Layered CLM (CLM‐ML)

Abstract This study updates the multi‐layered Community Land Model (CLM‐ml) for hillslopes and compares predictions from against observations collected in tropical montane rainforest, Costa Rica. Modifications are made in order to capture a wider array of vertical leaf area distributions, predict CO2 profiles, account for soil respiration, and adjust wind forcings for difficult topographic settings. Test results indicate that the modified multi‐layer CLM model can successfully replicate the shape of various micrometeorological profiles (humidity, CO2, temperature, and wind speed) under the canopy. In the single‐layer models (CLM4.5 and CLM5), excessive day‐to‐night differences in leaf temperature and leaf wetness were originally noted, but CLM‐ml significantly improved these issues, decreasing the amplitudes of diurnal cycles by 67% and 47%. Sub‐canopy considerations, such as canopy shapes and turbulent transfer parameters, also played a significant role in model performance. More importantly, unlike single layer models, the results that CLM‐ml produces can be compared to variables measured within the canopy to provide far more detailed diagnostic information. Further observations and model developments, aimed at reflecting surface heterogeneity, will be necessary to adequately capture the complexity and the features of the tropical montane rainforest

Ecohydrological drivers of neotropical vegetation in montane ecosystems

Montane ecosystems are known for their high numbers of endemic species, unique climate conditions, and wide variety of ecosystem services such as water supply and carbon storage. Although many ecohydrological and climatic studies of montane environments have been carried out in temperate and boreal regions, few have been done in Neotropical regions. Hence, the objective of this review is to synthesize the existing literature on the main factors (biotic and abiotic) that influence vegetation distribution, functional traits, and ecohydrological processes and feedbacks in tropical montane ecosystems (TME) and to identify key knowledge gaps. Most of the literature used includes work conducted in Neotropical montane rainforests, cloud forests, and grass/scrublands (eg, páramos, punas, and campos de altitude/rupestres). Fog is a major climatic attribute in tropical montane …Montane ecosystems are known for their high numbers of endemic species, unique climate conditions, and wide variety of ecosystem services such as water supply and carbon storage. Although many ecohydrological and climatic studies of montane environments have been carried out in temperate and boreal regions, few have been done in Neotropical regions. Hence, the objective of this review is to synthesize the existing literature on the main factors (biotic and abiotic) that influence vegetation distribution, functional traits, and ecohydrological processes and feedbacks in tropical montane ecosystems (TME) and to identify key knowledge gaps. Most of the literature used includes work conducted in Neotropical montane rainforests, cloud forests, and grass/scrublands (eg, páramos, punas, and campos de altitude/rupestres). Fog is a major climatic attribute in tropical montane