| 1. |
- Hasper, Thomas Berg, et al.
(författare)
-
Water use by Swedish boreal forests in a changing climate
- 2016
-
Ingår i: Functional Ecology. - : Wiley. - 0269-8463 .- 1365-2435. ; 30:5, s. 690-699
-
Tidskriftsartikel (refereegranskat)abstract
- The rising levels of atmospheric carbon dioxide concentration ([CO2]) and temperature have the potential to substantially affect the terrestrial water and energy balance by altering the stomatal conductance and transpiration of trees. Many models assume decreases in stomatal conductance and plant water use under rising [CO2], which has been used as a plausible explanation for the positive global trend in river run-off over the past century. Plant water use is, however, also affected by changes in temperature, precipitation and land use, and there is yet no consensus about the contribution of different drivers to temporal trends of evapotranspiration (ET) and river run-off. In this study, we assessed water-use responses to climate change by using both long-term monitoring and experimental data in Swedish boreal forests. Historical trends and patterns in ET of large-scale boreal landscapes were determined using climate and run-off data from the past 50 years, while explicit tree water-use responses to elevated [CO2] and/or air temperature were examined in a whole-tree chamber experiment using mature Norway spruce (Picea abies (L.) Karst.) trees. The results demonstrated that ET estimated from water budgets at the catchment scale increased by 18% over the past 50 years while run-off did not significantly change. The increase in ET was related to increasing precipitation and a steady increase in forest standing biomass over time. The whole-tree chamber experiment showed that Norway spruce trees did not save water under elevated [CO2] and that experimentally elevated air temperature did not increase transpiration as decreased stomatal conductance cancelled the effect of higher vapour pressure deficit in warmed air. Our findings have important implications for projections of future water use of European boreal coniferous forests, indicating that changes in precipitation and standing biomass are more important than the effects of elevated [CO2] or temperature on transpiration rates.
|
|
| 2. |
- Jaramillo, Fernando, et al.
(författare)
-
Dominant effect of increasing forest biomass on evapotranspiration: Interpretations of movement in Budyko space
- 2018
-
Ingår i: Hydrology and Earth System Sciences. - : Copernicus GmbH. - 1027-5606 .- 1607-7938. ; 22, s. 567-580
-
Tidskriftsartikel (refereegranskat)abstract
- During the last 6 decades, forest biomass has increased in Sweden mainly due to forest management, with a possible increasing effect on evapotranspiration. However, increasing global CO 2 concentrations may also trigger physiological water-saving responses in broadleaf tree species, and to a lesser degree in some needleleaf conifer species, inducing an opposite effect. Additionally, changes in other forest attributes may also affect evapotranspiration. In this study, we aimed to detect the dominating effect(s) of forest change on evapotranspiration by studying changes in the ratio of actual evapotranspiration to precipitation, known as the evaporative ratio, during the period 1961-2012. We first used the Budyko framework of water and energy availability at the basin scale to study the hydroclimatic movements in Budyko space of 65 temperate and boreal basins during this period. We found that movements in Budyko space could not be explained by climatic changes in precipitation and potential evapotranspiration in 60% of these basins, suggesting the existence of other dominant drivers of hydroclimatic change. In both the temperate and boreal basin groups studied, a negative climatic effect on the evaporative ratio was counteracted by a positive residual effect. The positive residual effect occurred along with increasing standing forest biomass in the temperate and boreal basin groups, increasing forest cover in the temperate basin group and no apparent changes in forest species composition in any group. From the three forest attributes, standing forest biomass was the one that could explain most of the variance of the residual effect in both basin groups. These results further suggest that the water-saving response to increasing CO 2 in these forests is either negligible or overridden by the opposite effect of the increasing forest biomass. Thus, we conclude that increasing standing forest biomass is the dominant driver of long-term and large-scale evapotranspiration changes in Swedish forests.
|
|
| 3. |
- Mills, Gina, 1959, et al.
(författare)
-
Ozone pollution will compromise efforts to increase global wheat production
- 2018
-
Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 24:8, s. 3560-3574
-
Tidskriftsartikel (refereegranskat)abstract
- Introduction of high-performing crop cultivars and crop/soil water management practices that increase the stomatal uptake of carbon dioxide and photosynthesis will be instrumental in realizing the United Nations Sustainable Development Goal (SDG) of achieving food security. To date, however, global assessments of how to increase crop yield have failed to consider the negative effects of tropospheric ozone, a gaseous pollutant that enters the leaf stomatal pores of plants along with carbon dioxide, and is increasing in concentration globally, particularly in rapidly developing countries. Earlier studies have simply estimated that the largest effects are in the areas with the highest ozone concentrations. Using a modelling method that accounts for the effects of soil moisture deficit and meteorological factors on the stomatal uptake of ozone, we show for the first time that ozone impacts on wheat yield are particularly large in humid rain-fed and irrigated areas of major wheat-producing countries (e.g. United States, France, India, China and Russia). Averaged over 2010-2012, we estimate that ozone reduces wheat yields by a mean 9.9% in the northern hemisphere and 6.2% in the southern hemisphere, corresponding to some 85 Tg (million tonnes) of lost grain. Total production losses in developing countries receiving Official Development Assistance are 50% higher than those in developed countries, potentially reducing the possibility of achieving UN SDG2. Crucially, our analysis shows that ozone could reduce the potential yield benefits of increasing irrigation usage in response to climate change because added irrigation increases the uptake and subsequent negative effects of the pollutant. We show that mitigation of air pollution in a changing climate could play a vital role in achieving the above-mentioned UN SDG, while also contributing to other SDGs related to human health and well-being, ecosystems and climate change.
|
|
