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  • 1
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    Vegetation plays an important role in mediating future water resources (2016)
    Institute of Physics (IOP)
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    Publication Date: 2016-09-15
    Description: Future environmental change is expected to modify the global hydrological cycle, with consequences for the regional distribution of freshwater supplies. Regional precipitation projections, however, differ largely between models, making future water resource projections highly uncertain. Using two representative concentration pathways and nine climate models, we estimate 21st century water resources across Australia, employing both a process-based dynamic vegetation model and a simple hydrological framework commonly used in water resource studies to separate the effects of climate and vegetation on water resources. We show surprisingly robust, pathway-independent regional patterns of change in water resources despite large uncertainties in precipitation projections. Increasing plant water use efficiency (due to the changing atmospheric CO 2 ) and reduced green vegetation cover (due to the changing climate) relieve pressure on water resources for the highly populated, hum...
    Print ISSN: 1748-9318
    Electronic ISSN: 1748-9326
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering
    Published by Institute of Physics (IOP)
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  • 2
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    Phenology: Spring greening in a warming world (2015)
    Nature Publishing Group (NPG)
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    Publication Date: 2015-09-30
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Keenan, Trevor F -- England -- Nature. 2015 Oct 1;526(7571):48-9. doi: 10.1038/nature15633. Epub 2015 Sep 23.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Biological Sciences, Macquarie University, Sydney, New South Wales 2109, Australia.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26416739" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 3
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    Increase in forest water-use efficiency as atmospheric carbon dioxide concentrations rise (2013)
    Nature Publishing Group (NPG)
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    Publication Date: 2013-07-12
    Description: Terrestrial plants remove CO2 from the atmosphere through photosynthesis, a process that is accompanied by the loss of water vapour from leaves. The ratio of water loss to carbon gain, or water-use efficiency, is a key characteristic of ecosystem function that is central to the global cycles of water, energy and carbon. Here we analyse direct, long-term measurements of whole-ecosystem carbon and water exchange. We find a substantial increase in water-use efficiency in temperate and boreal forests of the Northern Hemisphere over the past two decades. We systematically assess various competing hypotheses to explain this trend, and find that the observed increase is most consistent with a strong CO2 fertilization effect. The results suggest a partial closure of stomata-small pores on the leaf surface that regulate gas exchange-to maintain a near-constant concentration of CO2 inside the leaf even under continually increasing atmospheric CO2 levels. The observed increase in forest water-use efficiency is larger than that predicted by existing theory and 13 terrestrial biosphere models. The increase is associated with trends of increasing ecosystem-level photosynthesis and net carbon uptake, and decreasing evapotranspiration. Our findings suggest a shift in the carbon- and water-based economics of terrestrial vegetation, which may require a reassessment of the role of stomatal control in regulating interactions between forests and climate change, and a re-evaluation of coupled vegetation-climate models.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Keenan, Trevor F -- Hollinger, David Y -- Bohrer, Gil -- Dragoni, Danilo -- Munger, J William -- Schmid, Hans Peter -- Richardson, Andrew D -- England -- Nature. 2013 Jul 18;499(7458):324-7. doi: 10.1038/nature12291. Epub 2013 Jul 10.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138, USA. tkeenan@oeb.harvard.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23842499" target="_blank"〉PubMed〈/a〉
    Keywords: Atmosphere/chemistry ; Carbon Dioxide/*analysis ; *Ecosystem ; Plant Leaves/chemistry ; Trees/*chemistry ; Water/*analysis
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 4
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    Keenan et al. reply (2014)
    Nature Publishing Group (NPG)
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    Publication Date: 2014-03-14
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Keenan, Trevor F -- Hollinger, David Y -- Bohrer, Gil -- Dragoni, Danilo -- Munger, J William -- Schmid, Hans Peter -- Richardson, Andrew D -- England -- Nature. 2014 Mar 13;507(7491):E2-3. doi: 10.1038/nature13114.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Biological Sciences, Macquarie University, North Ryde, New South Wales 2109, Australia. ; USDA Forest Service, Northern Research Station, Durham, New Hamphire 03824, USA. ; Department of Civil, Environmental and Geodetic Engineering, The Ohio State University, Columbus, Ohio 43210, USA. ; Department of Geography, Indiana University, Bloomington, Indiana 47405, USA. ; School of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138, USA. ; Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology, IMK-IFU, Garmisch-Partenkirchen 82467, Germany. ; Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24622207" target="_blank"〉PubMed〈/a〉
    Keywords: Carbon Dioxide/*analysis ; *Ecosystem ; Trees/*chemistry ; Water/*analysis
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 5
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    Greening of the land surface in the world’s cold regions consistent with recent warming (2018)
    Springer Nature
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    Publication Date: 2018-08-21
    Description: Greening of the land surface in the world’s cold regions consistent with recent warming Greening of the land surface in the world’s cold regions consistent with recent warming, Published online: 20 August 2018; doi:10.1038/s41558-018-0258-y The period 1982 to 2012 has seen a 16% decline in the area of vegetation limited by temperature. This rapid observed and expected decline in temperature limitation will facilitate further global greening subject to other limitations to growth in cold regions.
    Print ISSN: 1758-678X
    Electronic ISSN: 1758-6798
    Topics: Geosciences
    Published by Springer Nature
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  • 6
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    Warm spring reduced impact of summer drought [Sustainability Science] (2016)
    National Academy of Sciences
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    Publication Date: 2016-05-25
    Description: The global terrestrial carbon sink offsets one-third of the world’s fossil fuel emissions, but the strength of this sink is highly sensitive to large-scale extreme events. In 2012, the contiguous United States experienced exceptionally warm temperatures and the most severe drought since the Dust Bowl era of the 1930s, resulting...
    Keywords: Sustainability Science
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 7
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    Tracking forest phenology and seasonal physiology using digital repeat photography: a critical assessment (2014)
    Wiley
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    Publication Date: 2014-09-01
    Description: Digital repeat photography is becoming widely used for near-surface remote sensing of vegetation. Canopy greenness, which has been used extensively for phenological applications, can be readily quantified from camera images. Important questions remain, however, as to whether the observed changes in canopy greenness are directly related to changes in leaf-level traits, changes in canopy structure, or some combination thereof. We investigated relationships between canopy greenness and various metrics of canopy structure and function, using five years (2008?2012) of automated digital imagery, ground observations of phenological transitions, leaf area index (LAI) measurements, and eddy covariance estimates of gross ecosystem photosynthesis from the Harvard Forest, a temperate deciduous forest in the northeastern United States. Additionally, we sampled canopy sunlit leaves on a weekly basis throughout the growing season of 2011. We measured physiological and morphological traits including leaf size, mass (wet/dry), nitrogen content, chlorophyll fluorescence, and spectral reflectance and characterized individual leaf color with flatbed scanner imagery. Our results show that observed spring and autumn phenological transition dates are well captured by information extracted from digital repeat photography. However, spring development of both LAI and the measured physiological and morphological traits are shown to lag behind spring increases in canopy greenness, which rises very quickly to its maximum value before leaves are even half their final size. Based on the hypothesis that changes in canopy greenness represent the aggregate effect of changes in both leaf-level properties (specifically, leaf color) and changes in canopy structure (specifically, LAI), we developed a two end-member mixing model. With just a single free parameter, the model was able to reproduce the observed seasonal trajectory of canopy greenness. This analysis shows that canopy greenness is relatively insensitive to changes in LAI at high LAI levels, which we further demonstrate by assessing the impact of an ice storm on both LAI and canopy greenness. Our study provides new insights into the mechanisms driving seasonal changes in canopy greenness retrieved from digital camera imagery. The nonlinear relationship between canopy greenness and canopy LAI has important implications both for phenological research applications and for assessing responses of vegetation to disturbances. # doi:10.1890/13-0652.1
    Print ISSN: 1051-0761
    Electronic ISSN: 1939-5582
    Topics: Biology
    Published by Wiley on behalf of The Ecological Society of America (ESA).
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  • 8
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    Contrasting regional carbon cycle responses to seasonal climate anomalies across the east‐west divide of temperate North America (2020)
    American Geophysical Union
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    Publication Date: 2020-10-17
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
    Published by American Geophysical Union
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  • 9
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    On the uncertainty of phenological responses to climate change and its implication for terrestrial biosphere models (2012)
    Copernicus
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    Publication Date: 2012-01-20
    Description: Phenology, the timing of recurring life cycle events, controls numerous land surface feedbacks to the climate systems through the regulation of exchanges of carbon, water and energy between the biosphere and atmosphere. Land surface models, however, are known to have systematic errors in the simulation of spring phenology, which potentially could propagate to uncertainty in modeled responses to future climate change. Here, we analyzed the Harvard Forest phenology record to investigate and characterize the sources of uncertainty in phenological forecasts and the subsequent impacts on model forecasts of carbon and water cycling in the future. Using a model-data fusion approach, we combined information from 20 yr of phenological observations of 11 North American woody species with 12 phenological models of different complexity to predict leaf bud-burst. The evaluation of different phenological models indicated support for spring warming models with photoperiod limitations and, though to a lesser extent, to chilling models based on the alternating model structure. We assessed three different sources of uncertainty in phenological forecasts: parameter uncertainty, model uncertainty, and driver uncertainty. The latter was characterized running the models to 2099 using 2 different IPCC climate scenarios (A1fi vs. B1, i.e. high CO2 emissions vs. low CO2 emissions scenario). Parameter uncertainty was the smallest (average 95% CI: 2.4 day century−1 for scenario B1 and 4.5 day century−1 for A1fi), whereas driver uncertainty was the largest (up to 8.4 day century−1 in the simulated trends). The uncertainty related to model structure is also large and the predicted bud-burst trends as well as the shape of the smoothed projections varied somewhat among models (±7.7 day century−1 for A1fi, ±3.6 day century−1 for B1). The forecast sensitivity of bud-burst to temperature (i.e. days bud-burst advanced per degree of warming) varied between 2.2 day °C−1 and 5.2 day °C−1 depending on model structure. We quantified the impact of uncertainties in bud-burst forecasts on simulated carbon and water fluxes using a process-based terrestrial biosphere model. Uncertainty in phenology model structure led to uncertainty in the description of the seasonality of processes, which accumulated to uncertainty in annual model estimates of gross primary productivity (GPP) and evapotranspiration (ET) of 9.6% and 2.9% respectively. A sensitivity analysis shows that a variation of ±10 days in bud-burst dates led to a variation of ±5.0% for annual GPP and about ±2.0% for ET. For phenology models, differences among future climate scenarios represent the largest source of uncertainty, followed by uncertainties related to model structure, and finally, uncertainties related to model parameterization. The uncertainties we have quantified will affect the description of the seasonality of processes and in particular the simulation of carbon uptake by forest ecosystems, with a larger impact of uncertainties related to phenology model structure, followed by uncertainties related to phenological model parameterization.
    Print ISSN: 1810-6277
    Electronic ISSN: 1810-6285
    Topics: Biology , Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 10
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    Greening of the land surface in the world’s cold regions consistent with recent warming (2018)
    Springer Nature
    Details
    Publication Date: 2018-08-20
    Print ISSN: 1758-678X
    Electronic ISSN: 1758-6798
    Topics: Geosciences
    Published by Springer Nature
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