Anthropogenic forcing increases the water‐use efficiency of African trees

Wils, Tommy H. G.; Robertson, Iain; Woodborne, Stephan; Hall, Grant; Koprowski, Marcin; Eshetu, Zewdu

doi:10.1002/jqs.2865

Cited by 13 publications

(9 citation statements)

References 49 publications

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“…Although admittedly reflecting an initial stage, our results on the iWUE are in good accordance to existing studies from the Tibetan Plateau dealing with Pinus and Abies species, where similar positive trends in iWUE were reported for the last decades [28,58]. In addition, on a global scale, such responses can be observed in various tree species, e.g., from the tropics [59,60] or more temperate zones [53,[61][62][63][64][65][66]. We are aware that substantial ecophysiological investigations on and interpretations of iWUE need more knowledge about the corresponding changes in controlling plant physiological and environmental factors (e.g., c i , c a , and the carbon isotope discrimination ∆).…”

Section: Long-term Trends In Carbon Isotope Ratios and Their Implicatsupporting

confidence: 92%

A Dual Stable Isotope Approach Unravels Common Climate Signals and Species-Specific Responses to Environmental Change Stored in Multi-Century Tree-Ring Series from the Tibetan Plateau

et al. 2019

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Tree-rings are recorders of environmental signals and are therefore often used to reconstruct past environmental conditions. In this paper, we present four annually resolved, multi-centennial tree-ring isotope series from the southeastern Tibetan plateau. The investigation site, where juniper and spruce trees jointly occur, is one of the highest known tree-stands in the world. Tree ring cellulose oxygen (δ18O) and carbon (δ13C) isotopes were analyzed for a common period of 1685–2007 AD to investigate climate–isotope relationships. Therefore, various climate parameters from a local meteorological station and from the CRU 4.02 dataset were used. Tree-ring δ18O of both species revealed highly significant sensitivities with a high degree of coherence to hydroclimate variables during the growing season. The obtained δ18O–climate relationships can even be retained using a species mean. In contrast, the individual δ13C series indicated a weaker and non-uniform response to the tested variables. Underlying species-specific responses and adaptations to the long-term trend in atmospheric CO2 bias even after a trend correction identified dominant environmental factors triggering the tree-ring δ13C at our site. However, analysis of individual intrinsic water-use efficiency in juniper and spruce trees indicated a species-specific adaptation strategy to climate change.

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Section: Long-term Trends In Carbon Isotope Ratios and Their Implicatsupporting

confidence: 92%

A Dual Stable Isotope Approach Unravels Common Climate Signals and Species-Specific Responses to Environmental Change Stored in Multi-Century Tree-Ring Series from the Tibetan Plateau

et al. 2019

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“…CO 2 fertilization generally enhances water use efficiency, possibly lengthening the growing season [70]. This increased water use efficiency has been recently shown for African trees in drier areas [76].…”

Section: Evidence Of Biomass Increment and Carbon Sinkmentioning

confidence: 87%

Carbon sink despite large deforestation in African tropical dry forests (miombo woodlands)

Pelletier

Paquette

Mbindo³

et al. 2018

Environ. Res. Lett.

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Direct and indirect human impacts may be causing widespread vegetation changes African tropical dry forests (TDFs). This study provides the first field-based large-scale assessment of vegetation changes for the miombo region, using nation-wide re-measured permanent plots for the Republic of Zambia. Using path analysis, a technique used to describe and quantify causal relationships, we investigated the drivers of change for the 2006-2014 period, under different land-use and productivity trajectories. We assessed the change in vegetation metrics representing stand structure and tree diversity, identified causal factors for species richness, basal area, and productivity and compared the biomass change of different species. We assessed carbon emissions and absorptions from forestlands and used error propagation and sensitivity analysis to quantify uncertainty. Our results suggest that Zambia's TDFs are resilient in the face of human activities, with significant biomass gains observed in the re-measured plots over the country. However, the proximity to roads, fragmentation by other land uses, and to a lesser extent fire occurrence were found to negatively affect productivity. We found that biomass gains were concentrated in several dominant species, mostly belonging to a single subfamily of non-nodulating legumes (Fabaceae, subfamily Caesalpinioideae) characteristic of the region. Our results indicate that Zambia's TDFs have been acting as an overall carbon sink, despite large carbon emissions from land-cover change. Decline in biomass for certain dominant species signal a risk of over-exploitation. We also identified important differences in plant diversity and functional traits between miombo woodlands and other types of African savanna vegetation, signaling differences in ecological processes at play. These results illustrate the ecological complexity and diversity of Africa's vegetation, and caution against overgeneralizations of ecological processes in the context of global change and carbon management. Future research should focus on understanding the observed species-specific biomass gain and identifying its potential drivers.

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“…60••, 78,86]. Water dynamics are also important on their own as determinants of downstream water flows [54,55], which is important for the prediction of future water availability and infrastructure needs for the regulation of water flows [e.g. 87].…”

Section: Discussionmentioning

confidence: 99%

Warming and Elevated CO2 Have Opposing Influences on Transpiration. Which is more Important?

Kirschbaum

McMillan

2018

Curr Forestry Rep

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Plant transpiration is a key component of the terrestrial water cycle, and it is important to understand whether rates are likely to increase or decrease in the future. Plant transpiration rates are affected by biophysical factors, such as air temperature, vapour pressure deficits and net radiation, and by plant factors, such as canopy leaf area and stomatal conductance. Under future climate change, global temperature increases, and associated increases in vapour pressure deficits, will act to increase canopy transpiration rates. Increasing atmospheric CO 2 concentrations, however, is likely to lead to some reduction in stomatal conductance, which will reduce canopy transpiration rates. The objective of the present paper was to quantitatively compare the importance of these opposing driving forces. First, we reviewed the existing literature and list a large range of observations of the extent of decreasing stomatal conductance with increasing CO 2 concentrations. We considered observations ranging from short-term laboratory-based experiments with plants grown under different CO 2 concentrations to studies of plants exposed to the naturally increasing atmospheric CO 2 concentrations. Using these empirical observations of plant responses, and a set of well-tested biophysical relationships, we then estimated the net effect of the opposing influences of warming and CO 2 concentration on transpiration rates. As specific cases studies, we explored expected changes in greater detail for six specific representative locations, covering the range from tropical to boreal forests. For most locations investigated, we calculated reductions in daily transpiration rates over the twenty-first century that became stronger under higher atmospheric CO 2 concentrations. It showed that the effect of CO 2 -induced reduction of stomatal conductance would have a stronger transpiration-depressing effect than the stimulatory effect of future warming. For currently cold regions, global warming would, however, lengthen the growing seasons so that annual sums of transpiration could increase in those regions despite reductions in daily transpiration rates over the summer months.

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Anthropogenic forcing increases the water‐use efficiency of African trees

Cited by 13 publications

References 49 publications

A Dual Stable Isotope Approach Unravels Common Climate Signals and Species-Specific Responses to Environmental Change Stored in Multi-Century Tree-Ring Series from the Tibetan Plateau

A Dual Stable Isotope Approach Unravels Common Climate Signals and Species-Specific Responses to Environmental Change Stored in Multi-Century Tree-Ring Series from the Tibetan Plateau

Carbon sink despite large deforestation in African tropical dry forests (miombo woodlands)

Warming and Elevated CO2 Have Opposing Influences on Transpiration. Which is more Important?

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