Temporal variation and controlling factors of tree water consumption in the thornbush savanna

Blécourt, Marleen de; Gröngröft, Alexander; Thomsen, Simon; Eschenbach, Annette

doi:10.1016/j.jaridenv.2021.104500

Cited by 4 publications

(7 citation statements)

References 34 publications

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“…For S. mellifera, soil moisture at 50 cm depth has no significant effect on sap flow. This finding contradicts the results of deBlécourt et al (2021), who report a strong correlation between soil moisture at a depth of 80 cm and daily sap flow over a two-year study period on sandy clay loam to sandy loam. We assume that this discrepancy may be attributed to the time and duration of our study, which covered only a period of 5 weeks in total, during which changes in soil moisture in deeper layers are not as pronounced as those occurring within two complete annual cycles.…”

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confidence: 99%

“…On the other hand, de Blécourt et al. (2021) also found that sap flow in S. mellifera in a semi‐arid savanna in central Namibia exhibits a minor response to VPD, while being more influenced by solar radiation. This is consistent with our study, where sap flow densities in S. mellifera did not decline with solar radiation larger than 2000 μmol m −2 s −1 as it was the case in C. mopane and C. alexandri .…”

Section: Discussionmentioning

confidence: 99%

“…While several studies have widened our knowledge of the effect of bush encroachment and climate change on savanna ecohydrology and the underlying feedbacks between water balances, vegetation, and climate (de Blécourt et al., 2021; Eldridge et al., 2011; Geißler et al., 2019; Huxman et al., 2005; Irob et al., 2023), the potential impact of browsers as a critical additional ecohydrological driver is still unresolved. Moreover, improved knowledge of species‐specific water use strategies in response to water scarcity can provide a more accurate understanding of ecosystem dynamics and can improve future predictions.…”

Section: Introductionmentioning

confidence: 99%

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Hungry herbivores and thirsty plants: Browsing wildlife shape savanna tree transpiration independently of water use strategies

Herkenrath,

Blaum,

Roth

et al. 2024

Functional Ecology

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Plant transpiration is a key component of the hydrological cycle that moves water from the soil through plants to the atmosphere and is largely determined by environmental conditions. The challenges of highly variable climatic conditions and water scarcity in the semi‐arid savannas of southern Africa drive trees to exhibit different water use strategies. An additional challenge for savanna trees arises from the browsing of large mammals, and its potential impact on transpiration has largely been overlooked. To assess water use strategies and the impact of browsing on transpiration in three common savanna woody species (Colophospermum mopane, Catophractes alexandri, Senegalia mellifera), we conducted an extensive field experiment in a wildlife reserve in Namibia. We established a browsing gradient ranging from 0% to 100% leaf removal to disentangle complex relationships, and we measured sap flow representing whole‐tree transpiration, stomatal conductance as a proxy for leaf level transpiration, and environmental factors including soil moisture, solar radiation, air temperature and air humidity. We discovered a unimodal relationship between browsing intensity and sap flow, consistent across all species, and peaking at low to moderate browsing levels equivalent to approximately 30% leaf removal. This universal pattern is remarkable since we found water use strategies to differ among species: Colophospermum mopane and C. alexandri exhibit a water‐saving behaviour to reduce water loss under unfavourable conditions while S. mellifera demonstrates water‐spending characteristics. The deviation from a negative linear effect of browsing does not meet the functional expectation when browsing is translated into a simple leaf area reduction. Instead, it can be attributed to stomatal adjustments that partially compensate for transpiratory surface loss. We propose that this conceptual mechanism can be generalised to other woody species and various ecosystems. In addition, common transpiration models relying solely on leaf area indices and abiotic factors can be improved by including a non‐linear relationship to reproduce the effect of browsing accurately. Our findings highlight the role of herbivores in shaping the connection between the Earth's spheres and improve our understanding of ecohydrological and vegetation dynamics in Southern African savannas. Read the free Plain Language Summary for this article on the Journal blog.

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confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Hungry herbivores and thirsty plants: Browsing wildlife shape savanna tree transpiration independently of water use strategies

Herkenrath,

Blaum,

Roth

et al. 2024

Functional Ecology

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“…Following this, the sap flow decreases or even stops [68]. The soil water content, including the deep soil water and the shallow soil water, is crucial to sap flow [28,[35][36][37].…”

Section: Dimensionality Reduction Methods Based On Factory Analysismentioning

confidence: 99%

“…Liu et al compared sap flow patterns and their relationships with environmental factors, and results show that the sap flow density was significantly correlated with Ta, VPD, and PAR [34]. Blécourt et al investigated the responses of global radiation, VPD and soil water availability to water consumption, indicating that soil water availability and global radiation are important factors influencing the water consumption of S. mellifera [35]. Hayat et al studied the nighttime sap flow dynamics by changing biophysical variables of Salix psammophila, and results show that temperature and soil water content (SWC) were important factors influencing night sap flow [36].…”

Section: Introductionmentioning

confidence: 99%

An Improved Sap Flow Prediction Model Based on CNN-GRU-BiLSTM and Factor Analysis of Historical Environmental Variables

Guo

Wang

et al. 2023

Forests

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Sap flow is widely used to estimate the transpiration and water consumption of canopies and to manage water resources. In this paper, an improved time series prediction model was proposed by integrating three basic networks—CNN, GRU and BiLSTM—to assess sap flow with historical environment variables. A dataset with 17,569 records of each, including 9 environment variables and 1 sap flow, was applied from a public database of SAPFLUXNET. After normalization, the environment variables were analyzed and composed with the factor analysis method. After the CNN-GRU-BiLSTM structure was designed, N records of three main factors were computed from environment variables, which were measured at N previous moments, and the sap flow was measured at the current moment, and they were applied for each training, validation, and testing cycle. To improve and compare the CNN-GRU-BiLSTM-based model, nine other models, using the methods of multiple linear regression, support vector regression, random forest, LSTM, GRU, BiLSTM, CNN-GRU, CNN-BiLSTM, and CNN-GRU-LSTM, were constructed in this study, respectively. Results show that the performance of the CNN-GRU-BiLSTM-based model has more accuracy than the other nine models we built in this paper, with the mean absolute error, mean squared error, mean absolute percentage error, and coefficient of determination (R2) being 0.0410, 0.0029, 0.2708 and 0.9329, respectively. Furthermore, for a comparison of the descending dimension method of factor analysis, principal component analysis (PCA) and singular value decomposition (SVD) methods were applied and compared, respectively. Results show that the performance of the factor analysis-based model is better than the PCA- or SVD-based model, with the R2 results of the factor analysis-based model being higher than the PCA- and SVD-based models by 5.06% and 10.63%, respectively. This study indicates that the CNN-GRU-BiLSTM-based sap flow prediction model established with a factor analysis of historical environmental variables has optimistic applications for analyzing the transpiration of trees and evaluating water consumption.

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The Potential Impact of Woody Encroachment on Evapotranspiration Losses in South Africa's Savannas: A combined Systematic Review and meta-Analysis Approach

Aldworth,

Toucher,

Clulow

2024

Ecohydrology & Hydrobiology

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Temporal variation and controlling factors of tree water consumption in the thornbush savanna

Cited by 4 publications

References 34 publications

Hungry herbivores and thirsty plants: Browsing wildlife shape savanna tree transpiration independently of water use strategies

Hungry herbivores and thirsty plants: Browsing wildlife shape savanna tree transpiration independently of water use strategies

An Improved Sap Flow Prediction Model Based on CNN-GRU-BiLSTM and Factor Analysis of Historical Environmental Variables

The Potential Impact of Woody Encroachment on Evapotranspiration Losses in South Africa's Savannas: A combined Systematic Review and meta-Analysis Approach

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