Global gross primary productivity and water use efficiency changes under drought stress

Drought can affect the structure, composition and function of terrestrial ecosystems, yet drought impacts and post-drought recovery potentials of different land cover types have not been extensively studied at a global scale. We evaluated drought impacts on gross primary productivity (GPP), evapotranspiration (ET), and water use efficiency (WUE) of different global terrestrial ecosystems, as well as the drought-resilience of each ecosystem type during the period of 2000 to 2011. Using GPP as biome vitality indicator against drought stress, we developed a model to examine ecosystem resilience represented by the length of recovery days (LRD). LRD presented an evident gradient of high (\u3e60 days) in mid-latitude region and low (\u3c60 days) in low (tropical area) and high (boreal area) latitude regions. As average GPP increased, the LRD showed a significantly decreasing trend, indicating readiness to recover after drought, across various land cover types (R 2 = 0.68, p \u3c 0.0001). Moreover, zonal analysis revealed that the most dramatic reduction of the drought-induced GPP was found in the mid-latitude region of the Northern Hemisphere (48% reduction), followed by the low-latitude region of the Southern Hemisphere (13% reduction). In contrast, a slightly enhanced GPP (10%) was evident in the tropical region under drought impact. Additionally, the highest drought-induced reduction of ET was found in the Mediterranean area, followed by Africa. Water use efficiency, however, showed a pattern of decreasing in the Northern Hemisphere and increasing in the Southern Hemisphere. Drought induced reductions of WUE ranged from 0.96% to 27.67% in most of the land cover types, while the increases of WUE found in Evergreen Broadleaf Forest and savanna were about 7.09% and 9.88%, respectively. These increases of GPP and WUE detected during drought periods could either be due to water-stress induced responses or data uncertainties, which require further investigation

Research on HOV Lane Priority Dynamic Control under Connected Vehicle Environment

The optimization of high-occupancy vehicle (HOV) lane management can better improve the efficiency of road resources. This paper first summarized the current research on HOV lane implementation and analyzed and identifies the threshold of setting road HOV lane dynamic control under the connected vehicle environment. Then, the HOV lane priority dynamic control process was determined, and the operating efficiency and energy consumption evaluation method was proposed. Moreover, a case study in Wuxi City, China, was carried out. The results showed that, after implementing the HOV lane priority dynamic control, the total mileage of road network vehicles was saved by 4.93%, the average travel time per capita was reduced by 4.27%, and the total energy-saving rate of road network travel was 21.96%

Assessing the Impact of Forest Change and Climate Variability on Dry Season Runoff by an Improved Single Watershed Approach: A Comparative Study in Two Large Watersheds, China

Extensive studies on hydrological responses to forest change have been published for centuries, yet partitioning the hydrological effects of forest change, climate variability and other factors in a large watershed remains a challenge. In this study, we developed a single watershed approach combining the modified double mass curve (MDMC) and the time series multivariate autoregressive integrated moving average model (ARIMAX) to separate the impact of forest change, climate variability and other factors on dry season runoff variation in two large watersheds in China. The Zagunao watershed was examined for the deforestation effect, while the Meijiang watershed was examined to study the hydrological impact of reforestation. The key findings are: (1) both deforestation and reforestation led to significant reductions in dry season runoff, while climate variability yielded positive effects in the studied watersheds; (2) the hydrological response to forest change varied over time due to changes in soil infiltration and evapotranspiration after vegetation regeneration; (3) changes of subalpine natural forests produced greater impact on dry season runoff than alteration of planted forests. These findings are beneficial to water resource and forest management under climate change and highlight a better planning of forest operations and management incorporated trade-off between carbon and water in different forests

Global gross primary productivity and water use efficiency changes under drought stress

Drought can affect the structure, composition and function of terrestrial ecosystems, yet drought impacts and post-drought recovery potentials of different land cover types have not been extensively studied at a global scale. We evaluated drought impacts on gross primary productivity (GPP), evapotranspiration (ET), and water use efficiency (WUE) of different global terrestrial ecosystems, as well as the drought-resilience of each ecosystem type during the period of 2000 to 2011. Using GPP as biome vitality indicator against drought stress, we developed a model to examine ecosystem resilience represented by the length of recovery days (LRD). LRD presented an evident gradient of high (>60 days) in mid-latitude region and low (This article is published as Yu, Z.*, J. Wang, S. Liu, J.S. Rentch, P. Sun, and C. Lu. 2017. Global gross primary productivity and water use efficiency changes under drought stress. Environmental Research Letters, 12(1), p.014016. Doi: 10.1088/1748-9326/aa5258. </p

Decrease in winter respiration explains 25% of the annual northern forest carbon sink enhancement over the last 30 years

International audienc

Relationships between relative water content (RWC) and (a) photosynthesis (<i>A</i>) (r² = 0.742, <i>P</i> = 0.008), (b) stomatal conductance (<i>g</i>_s, ^____) (r² = 0.667, <i>P</i> = 0.005), mesophyll conductance (<i>g</i>_m, ----) (r² = 0.748, <i>P</i> = 0.003) and total conductance (<i>g</i>_t, ^…..) (r² = 0.653, <i>P</i><0.02), and (c) photochemical reflectance index (PRI) (r² = 0.935, <i>P</i><0.001), and between PRI and (d) <i>A</i> (r² = 0.762, <i>P</i> = 0.001, (e) <i>g</i>_m (r² = 0.844, <i>P</i><0.001), and (f) <i>g</i>_t (r² = 0.725, <i>P</i> = 0.002) in olive saplings grown during and after the drought cycle.

<p>Relationships between relative water content (RWC) and (a) photosynthesis (<i>A</i>) (r² = 0.742, <i>P</i> = 0.008), (b) stomatal conductance (<i>g</i>_s, ^____) (r² = 0.667, <i>P</i> = 0.005), mesophyll conductance (<i>g</i>_m, ----) (r² = 0.748, <i>P</i> = 0.003) and total conductance (<i>g</i>_t, ^…..) (r² = 0.653, <i>P</i><0.02), and (c) photochemical reflectance index (PRI) (r² = 0.935, <i>P</i><0.001), and between PRI and (d) <i>A</i> (r² = 0.762, <i>P</i> = 0.001, (e) <i>g</i>_m (r² = 0.844, <i>P</i><0.001), and (f) <i>g</i>_t (r² = 0.725, <i>P</i> = 0.002) in olive saplings grown during and after the drought cycle.</p

On the Use of Leaf Spectral Indices to Assess Water Status and Photosynthetic Limitations in <i>Olea europaea</i> L. during Water-Stress and Recovery

<div><p>Diffusional limitations to photosynthesis, relative water content (RWC), pigment concentrations and their association with reflectance indices were studied in olive (<i>Olea europaea</i>) saplings subjected to water-stress and re-watering. RWC decreased sharply as drought progressed. Following rewatering, RWC gradually increased to pre-stress values. Photosynthesis (<i>A</i>), stomatal conductance (<i>g</i>_s), mesophyll conductance (<i>g</i>_m), total conductance (<i>g</i>_t), photochemical reflectance index (PRI), water index (WI) and relative depth index (RDI) closely followed RWC. In contrast, carotenoid concentration, the carotenoid to chlorophyll ratio, water content reflectance index (WCRI) and structural independent pigment index (SIPI) showed an opposite trend to that of RWC. Photosynthesis scaled linearly with leaf conductance to CO₂; however, <i>A</i> measured under non-photorespiratory conditions (<i>A</i>_1%O2) was approximately two times greater than <i>A</i> measured at 21% [O₂], indicating that photorespiration likely increased in response to drought. <i>A</i>_1%O2 also significantly correlated with leaf conductance parameters. These relationships were apparent in saturation type curves, indicating that under non-photorespiratory conditions, CO₂ conductance was not the major limitations to <i>A</i>. PRI was significant correlated with RWC. PRI was also very sensitive to pigment concentrations and photosynthesis, and significantly tracked all CO₂ conductance parameters. WI, RDI and WCRI were all significantly correlated with RWC, and most notably to leaf transpiration. Overall, PRI correlated more closely with carotenoid concentration than SIPI; whereas WI tracked leaf transpiration more effectively than RDI and WCRI. This study clearly demonstrates that PRI and WI can be used for the fast detection of physiological traits of olive trees subjected to water-stress.</p></div

The Hydrological Impact of Extreme Weather-Induced Forest Disturbances in a Tropical Experimental Watershed in South China

Tropical forests are frequently disturbed by extreme weather events including tropical cyclones and cold waves, which can not only yield direct impact on hydrological processes but also produce indirect effect on hydrology by disturbing growth and structures of tropical forests. However, the hydrological response to extreme weather-induced forest disturbances especially in tropical forested watersheds has been less evaluated. In this study, a tropical experimental watershed in Hainan Province, China, was selected to investigate the hydrological responses to extreme weather-induced forest disturbances by use of a single watershed approach and the paired-year approach. Key results are: (1) extreme weather-induced forest disturbances (e.g., typhoon and cold wave) generally had a positive effect on streamflow in the study watershed, while climate variability either yielded a negative effect or a positive effect in different periods; (2) the response of low flows to forest discussion was more pronounced; (3) the relative contribution of forest disturbances to annual streamflow (48.6%) was higher than that of climate variability (43.0%) from 1995 to 2005. Given the increasing extreme weather with climate change and their possible catastrophic effects on tropical forests and hydrology in recent decades, these findings are essential for future adaptive water resources and forest management in the tropical forested watersheds.Arts and Sciences, Irving K. Barber School of (Okanagan)Non UBCEarth, Environmental and Geographic Sciences, Department of (Okanagan)ReviewedFacult

Consensus Forecasting of Species Distributions: The Effects of Niche Model Performance and Niche Properties

<div><p>Ensemble forecasting is advocated as a way of reducing uncertainty in species distribution modeling (SDM). This is because it is expected to balance accuracy and robustness of SDM models. However, there are little available data regarding the spatial similarity of the combined distribution maps generated by different consensus approaches. Here, using eight niche-based models, nine split-sample calibration bouts (or nine random model-training subsets), and nine climate change scenarios, the distributions of 32 forest tree species in China were simulated under current and future climate conditions. The forecasting ensembles were combined to determine final consensual prediction maps for target species using three simple consensus approaches (average, frequency, and median [PCA]). Species’ geographic ranges changed (area change and shifting distance) in response to climate change, but the three consensual projections did not differ significantly with respect to how much or in which direction, but they did differ with respect to the spatial similarity of the three consensual predictions. Incongruent areas were observed primarily at the edges of species’ ranges. Multiple stepwise regression models showed the three factors (niche marginality and specialization, and niche model accuracy) to be related to the observed variations in consensual prediction maps among consensus approaches. Spatial correspondence among prediction maps was the highest when niche model accuracy was high and marginality and specialization were low. The difference in spatial predictions suggested that more attention should be paid to the range of spatial uncertainty before any decisions regarding specialist species can be made based on map outputs. The niche properties and single-model predictive performance provide promising insights that may further understanding of uncertainties in SDM.</p></div

Relationships of photosynthesis (<i>A</i>), measured in ambient air (a, b, c) and in air with 1% [O₂] (<i>A</i>1%O2) (d, e, f), and (a, d) stomatal conductance (<i>g</i>_s), (b, e) mesophyll conductance (<i>g</i>_m), and (c, f) total conductance (<i>g</i>_t) in olive saplings grown during and after the drought cycle.

<p>Relationships of photosynthesis (<i>A</i>), measured in ambient air (a, b, c) and in air with 1% [O₂] (<i>A</i>1%O2) (d, e, f), and (a, d) stomatal conductance (<i>g</i>_s), (b, e) mesophyll conductance (<i>g</i>_m), and (c, f) total conductance (<i>g</i>_t) in olive saplings grown during and after the drought cycle.</p