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Decline of Leaf Hydraulic Conductance with Dehydration: Relationship to Leaf Size and Venation Architecture
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Across plant species, leaves vary enormously in their size and their venation architecture, of which one major function is to replace water lost to transpiration. The leaf hydraulic conductance (Kleaf) represents the capacity of the transport system to deliver water, allowing stomata to remain open for photosynthesis. Previous studies showed that Kleaf relates to vein density (vein length per area). Additionally, venation architecture determines the sensitivity of Kleaf to damage; severing the midrib caused Kleaf and gas exchange to decline, with lesser impacts in leaves with higher major vein density that provided more numerous water flow pathways around the damaged vein. Because xylem embolism during dehydration also reduces Kleaf, we hypothesized that higher major vein density would also reduce hydraulic vulnerability. Smaller leaves, which generally have higher major vein density, would thus have lower hydraulic vulnerability. Tests using simulations with a spatially explicit model confirmed that smaller leaves with higher major vein density were more tolerant of major vein embolism. Additionally, for 10 species ranging strongly in drought tolerance, hydraulic vulnerability, determined as the leaf water potential at 50% and 80% loss of Kleaf, was lower with greater major vein density and smaller leaf size (|r| = 0.85–0.90; P , 0.01). These relationships were independent of other aspects of physiological and morphological drought tolerance. These findings point to a new functional role of venation architecture and small leaf size in drought tolerance, potentially contributing to well-known biogeographic trends in leaf size.
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Declining annual streamflow distributions in the Pacific Northwest United States, 1948–2006
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Much of the discussion on climate change and water in the western United States centers on decreased snowpack and earlier spring runoff. Although increasing variability in annual flows has been noted, the nature of those changes is largely unexplored. We tested for trends in the distribution of annual runoff using quantile regression at 43 gages in the Pacific Northwest. Seventy-two percent of the stations showed significant (a = 0.10) declines in the 25th percentile annual flow, with half of the stations exceeding a 29% decline and a maximum decline of 47% between 1948 and 2006. Fewer stations showed statistically significant declines in either median or mean annual flow, and only five had a significant change in the 75th percentile, demonstrating that increases in variance result primarily from a trend of increasing dryness in dry years. The asymmetric trends in streamflow distributions have implications for water management and ecology well beyond those of shifted timing alone, affect both rain and snow-dominated watersheds, and contribute to earlier timing trends in high- elevation watersheds.
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Defaunation in the Anthropocene
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We live amid a global wave of anthropogenically driven biodiversity loss: species
and population extirpations and, critically, declines in local species abundance.
Particularly, human impacts on animal biodiversity are an under-recognized form of
global environmental change. Among terrestrial vertebrates, 322 species have
become extinct since 1500, and populations of the remaining species show 25%
average decline in abundance. Invertebrate patterns are equally dire: 67% of
monitored populations show 45% mean abundance decline. Such animal declines
will cascade onto ecosystem functioning and human well-being. Much remains unknown
about this “Anthropocene defaunation”; these knowledge gaps hinder our capacity
to predict and limit defaunation impacts. Clearly, however, defaunation is both a
pervasive component of the planet’s sixth mass extinction and also a major driver of
global ecological change
25 JULY 2014 • VOL 345 ISSUE 6195
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Defenders Magazine Fall 2019
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Florida manatee numbers are up but so are the challenges they face.
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Defenders of Wildlife-Defenders Magazine
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Defenders of Wildlife
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Defenders works on the ground, in the courts, and on Capitol Hill to protect and restore imperiled wildlife across North America and around the world. Together, we can ensure a future for the wildlife and wild places we all love.
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Defenders of Wildlife-Defenders Magazine
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With engaging stories and spectacular photography, Defenders of Wildlife's magazine provides readers with a behind-the-scenes look at what biologists and conservationists are doing to protect imperiled wild animals and plants.
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Defenders of Wildlife-Defenders Magazine
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Delaware Water Gap_Jiashiang.jpg
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Delaware Water Gap_Jiashiang.jpg
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Climate Change Vulnerability Assessment Photo Gallery
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Delaware Water Gap_Jiashiang.jpg
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Delaware Water Gap_Jiashiang.jpg
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Assessing Vulnerability of Species and Habitats to Large-scale Impacts
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Species and Habitat Vulnerability Assessment Photo Gallery
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Delayed detection of climate mitigation benefits due to climate inertia and variability
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Climate change mitigation acts by reducing greenhouse gas emissions, and thus curbing, or even reversing, the increase in their atmospheric concentration. This reduces the associated anthropogenic radiative forcing, and hence the size of the warming. Because of the inertia and internal variability affecting the climate system and the global carbon cycle, it is unlikely that a reduction in warming would be immediately discernible. Here we use 21st century simulations from the latest ensemble of Earth System Model experiments to investigate and quantify when mitigation becomes clearly discernible. We use one of the scenarios as a reference for a strong mitigation strategy, Representative Concentration Pathway (RCP) 2.6 and compare its outcome with either RCP4.5 or RCP8.5, both of which are less severe mitigation pathways. We analyze global mean atmospheric CO2, and changes in annually and seasonally averaged surface temperature at global and regional scales. For global mean surface temperature, the median detection time of mitigation is about 25–30 y after RCP2.6 emissions depart from the higher emission trajectories. This translates into detection of a mitigation signal by 2035 or 2045, depending on whether the comparison is with RCP8.5 or RCP4.5, respectively. The detection of climate benefits of emission mitigation occurs later at regional scales, with a median detection time between 30 and 45 y after emission paths separate. Requiring a 95% confidence level induces a delay of several decades, bringing detection time toward the end of the 21st century.
regional climate change | climate variability | signal detection
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