Water use dynamics of young and mature apple trees planted in South African orchards: a case study of the Golden Delicious and Cripps’ Pink cultivars

Apple orchards have previously been bearing 60–80 t ha-1 at most. However in recent years yield has increased to more than 100 t ha-1. There is need to understand the water requirements of the high yielding orchards, given that high crop loads are associated with high water use rates. The aim of this study was to quantify the water requirements of young and mature unstressed apple orchards. We also assess the impact of climate variables on transpiration rates. Data was collected in 4 orchards in the Western Cape Province. The orchards comprised young non-bearing (< 3 years) and mature trees planted to the Golden Delicious and Cripps’ Pink cultivars, all under micro-sprinkler irrigation. Transpiration by the trees was measured using heat pulse velocity sap flow sensors hourly throughout the growing season (October–June). Weather was monitored using an automatic weather station. Tree transpiration was linearly related to the solar radiation, but the relationship with the vapour pressure deficit (VPD) was non-linear. There were no significant differences (p>0:05) in the sapflux density of the Golden Delicious and Cripp’s Pink cultivars. This suggests that these two cultivars have similar water use characteristics. Mature orchards transpired between 6000 to 8000m3 ha-1 season-1 while nonbearing orchards used between 2000 to 3000m3 ha-1 season-1

Estimates of the impacts of invasive alien plants on water flows in South Africa

The adverse impacts of alien plant invasions on water flows have been a prime motivation for South Africa’s Working for Water Programme. The approach used in this study builds on a previous national assessment in 1998 by incorporating factors that limit plant water-use, information from recent research and improved flow reduction models. The total reduction in flows is estimated to be 1 444 million m3·yr−1 or 2.9% of the naturalised mean annual runoff (MAR), less than half of the 3 300 million m3·yr−1 estimated in 1998. Two main factors account for this difference: (a) a decrease in the estimated unit-area flow reduction to 970 m3·ha−1·yr−1 compared with 1 900 m3·ha−1·yr−1 estimated in 1998, largely due to the new model being based on more representative reduction factors; and (b) the updated estimate of the condensed invaded area of 1.50 million ha (previously 1.76 million ha), although the taxa mapped for this assessment only accounted for 1.00 million of the 1.76 million ha reported in 1998. Reductions due to invasions in Lesotho are estimated to be about 161 million m3·yr−1 and those in Swaziland about 193 million m3·yr−1. The taxon with the greatest estimated impact was wattles (Acacia mearnsii, A. dealbata, A. decurrens) with 34.0% of the total reductions, followed by Pinus species (19.3%) and Eucalyptus species (15.8%). The revised estimate is considered on the low side largely because the extent and impacts of riparian invasions have been underestimated. If the current estimates that 4–6% of Acacia mearnsii, Eucalyptus, Populus and Salix invasions are riparian, are adjusted to a more representative 20%, 50%, 80% and 80%, respectively, the total reductions increase by nearly 70% to ~2 444 million m3·yr−1. Producing these estimates involved a number of assumptions and extrapolations, and further research is needed to provide more robust estimates of the impacts.Keywords: plant water-use, flow reduction, mean annual runoff, riparian invasions, Working for Water Programm

Estimating evapotranspiration in a semi-arid catchment: A comparison of hydrological modelling and remote-sensing approaches

Reliable spatial data of evapotranspiration (ET) in support of water resources management are limited. ET is a major component of the water&nbsp; balance, in many regions, and therefore it is critical that it be accurately quantified. To identify a product that accurately estimates spatially&nbsp; distributed ET for application in data-scarce regions, an inter-model comparison was conducted between the MOD16 ET dataset and the ET&nbsp; calculated with the calibrated and validated JAMS/J2000 hydrological model in the Sandspruit catchment (South Africa). Annual JAMS-ET and MOD16-ET data were generally consistent. Monthly JAMS-ET and MOD16-ET dynamics are influenced by the response of vegetation to precipitation as well as the atmospheric evaporative demand. The maximum correlation coefficient between JAMS-ET and MOD16-ET was 0.82 and it was evident at Lag 0, showing that both ET estimates are in phase when evaluated at the basin scale. The maximum correlation coefficients between the ET estimators and precipitation were 0.67 and 0.70 for JAMS-ET and MOD16-ET, respectively, and this was evident at Lag 2 (1 lag is 1 month) for both methods. This&nbsp; suggests that there is a 2-month delay in the maximum response of ET to precipitation. The models did not exhibit significant dependence on the seasonal distribution of precipitation. The complementary use of hydrological modelling and satellite-derived data may be greatly advantageous to water resources management, e.g., water allocation studies, ecological reserve determinations and vegetation water use studies. The results of the inter-model comparison also provide motivation for the use of the MOD16 ET dataset to estimate ET in data-scarce regions. Additionally, this study provides evidence for the potential use of validated satellite-based ET data as inputs in hydrological models. This may facilitate a more realistic representation of the catchment hydrological processes. Keywords: evapotranspiration hydrological modelling remote sensingJ2000 MOD16-E

Water use of Prosopis juliflora and its impacts on catchment water budget and rural livelihoods in Afar Region, Ethiopia

CITATION: Shiferaw, H. et al. 2021. Water use of Prosopis juliflora and its impacts on catchment water budget and rural livelihoods in Afar Region, Ethiopia. Scientific Reports, 11:2688,doi:10.1038/s41598-021-81776-6.The original publication is available at https://www.nature.comDense impenetrable thickets of invasive trees and shrubs compete with other water users and thus disrupt ecosystem functioning and services. This study assessed water use by the evergreen Prosopis juliflora, one of the dominant invasive tree species in semi-arid and arid ecosystems in the tropical regions of Eastern Africa. The objectives of the study were to (1) analyze the seasonal water use patterns of P. juliflora in various locations in Afar Region, Ethiopia, (2) up-scale the water use from individual tree transpiration and stand evapotranspiration (ET) to the entire invaded area, and 3) estimate the monetary value of water lost due to the invasion. The sap flow rates of individual P. juliflora trees were measured using the heat ratio method while stand ET was quantified using the eddy covariance method. Transpiration by individual trees ranged from 1–36 L/day, with an average of 7 L of water per tree per day. The daily average transpiration of a Prosopis tree was about 3.4 (± 0.5) mm and the daily average ET of a dense Prosopis stand was about 3.7 (± 1.6) mm. Using a fractional cover map of P. juliflora (over an area of 1.18 million ha), water use of P. juliflora in Afar Region was estimated to be approximately 3.1–3.3 billion m3/yr. This volume of water would be sufficient to irrigate about 460,000 ha of cotton or 330,000 ha of sugar cane, the main crops in the area, which would generate an estimated net benefit of approximately US$320 million and US$ 470 million per growing season from cotton and sugarcane, respectively. Hence, P. juliflora invasion in the Afar Region has serious impacts on water availability and on the provision of other ecosystem services and ultimately on rural livelihoods.https://www.nature.com/articles/s41598-021-81776-6Publisher's versio

Field quantification of the water footprint of an apple orchard, and extrapolation to watershed scale within a winter rainfall Mediterranean climate zone

Please read abstract in the article.The Water Research Commission (Projects K5/1770 and K5/2273), with additional funding from the Dept. Agriculture, Forestry and Fisheries, and the CSIR, South Africa.https://www.elsevier.com/locate/agrformet2020-06-15hj2019Plant Production and Soil Scienc

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

Stomatal Oscillations in Orange Trees under Natural Climatic Conditions

• Background and Aims Stomatal oscillations have been reported in many plant species, but they are usually induced by sudden step changes in the environment when plants are grown under constant conditions. This study shows that in navel orange trees (Citrus sinensis) pronounced stomatal oscillations occur and persist under natural climatic conditions