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Old Trees: Extraction, Conservation Can Coexist
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BECAUSE LARGE OLD TREES ARE ESSENTIAL FOR FOREST ECOSYSTEM INTEGRITY AND BIODIVERsity,
timber extraction in managed forests should preferentially be concentrated where large old
trees are least likely to develop (“Global decline in large old trees,” D. B. Lindenmayer et al.,
Perspectives, 7 December 2012, p. 1305). However, timber extraction and the conservation of
large old trees are not necessarily mutually exclusive.
Current forest policy and management practices in Flanders, Belgium, aim to convert
even-aged stands (areas in which trees are all the same age) to stands with trees of varying
ages in an effort to increase forest ecosystem stability and resilience and to allow trees to
grow old. As part of their ecologically sustainable forest management, public forest managers
have adopted a large-tree retention approach [see also (1, 2)]. Tree islands within
stands managed for production of high-quality timber are reserved for conservation, and
trees within these islands will never be extracted. Large old trees of commercially valuable
species that have grown beyond the commercially optimal dimensions will
not be logged either. And no tree beyond a threshold diameter [currently set at
dbh (diameter at breast height) of more than 102 cm] will ever be logged. The
strip-shelterwood system (in which trees are cut in linear strips and surrounding
trees are given time to grow old) and the coppice-with-standards system
(in which some trees are left to grow while others around them are cut) are
two examples of forest management that allows the combination of sustainable
forest exploitation and conservation of large old trees
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Simultaneously Mitigating Near-Term Climate Change and Improving Human Health and Food Security
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Tropospheric ozone and black carbon (BC) contribute to both degraded air quality and global
warming. We considered ~400 emission control measures to reduce these pollutants by using
current technology and experience. We identified 14 measures targeting methane and BC
emissions that reduce projected global mean warming ~0.5°C by 2050. This strategy avoids 0.7
to 4.7 million annual premature deaths from outdoor air pollution and increases annual crop
yields by 30 to 135 million metric tons due to ozone reductions in 2030 and beyond. Benefits
of methane emissions reductions are valued at $700 to $5000 per metric ton, which is well
above typical marginal abatement costs (less than $250). The selected controls target different
sources and influence climate on shorter time scales than those of carbon dioxide–reduction
measures. Implementing both substantially reduces the risks of crossing the 2°C threshold.
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Financial Costs of Meeting Global Biodiversity Conservation Targets: Current Spending and Unmet Needs
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World governments have committed to halting human-induced extinctions and safeguarding
important sites for biodiversity by 2020, but the financial costs of meeting these targets are
largely unknown. We estimate the cost of reducing the extinction risk of all globally threatened
bird species (by ≥1 International Union for Conservation of Nature Red List category) to be
U.S. $0.875 to $1.23 billion annually over the next decade, of which 12% is currently funded.
Incorporating threatened nonavian species increases this total to U.S. $3.41 to $4.76 billion
annually. We estimate that protecting and effectively managing all terrestrial sites of global
avian conservation significance (11,731 Important Bird Areas) would cost U.S. $65.1 billion
annually. Adding sites for other taxa increases this to U.S. $76.1 billion annually. Meeting
these targets will require conservation funding to increase by at least an order of magnitude.
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Plant Species Richness and Ecosystem Multifunctionality in Global Drylands
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Experiments suggest that biodiversity enhances the ability of ecosystems to maintain multiple
functions, such as carbon storage, productivity, and the buildup of nutrient pools (multifunctionality).
However, the relationship between biodiversity and multifunctionality has never been assessed globally
in natural ecosystems. We report here on a global empirical study relating plant species richness and
abiotic factors to multifunctionality in drylands, which collectively cover 41% of Earth’s land surface
and support over 38% of the human population. Multifunctionality was positively and significantly
related to species richness. The best-fitting models accounted for over 55% of the variation in
multifunctionality and always included species richness as a predictor variable. Our results suggest
that the preservation of plant biodiversity is crucial to buffer negative effects of climate change and
desertification in drylands.
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The Greenhouse Is Making the Water-Poor Even Poorer
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How bad will global warming get? The question
has long been cast in terms of how hot
the world will get. But perhaps more important
to the planet’s inhabitants will be how
much rising greenhouse gases crank up the
water cycle. Theory and models predict that
a strengthening greenhouse will increase
precipitation where it is already relatively
high—tropical rain forests, for example—
and decrease it where it is already low, as in
the subtropics.
SCIENCE VOL 336 27 APRIL 2012
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Ocean Salinities Reveal Strong Global Water Cycle Intensification During 1950 to 2000
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Fundamental thermodynamics and climate models suggest that dry regions will become drier
and wet regions will become wetter in response to warming. Efforts to detect this long-term
response in sparse surface observations of rainfall and evaporation remain ambiguous. We show
that ocean salinity patterns express an identifiable fingerprint of an intensifying water cycle.
Our 50-year observed global surface salinity changes, combined with changes from global climate
models, present robust evidence of an intensified global water cycle at a rate of 8 T 5% per degree
of surface warming. This rate is double the response projected by current-generation climate
models and suggests that a substantial (16 to 24%) intensification of the global water cycle will
occur in a future 2° to 3° warmer world.
SCIENCE VOL 336
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Generic Indicators for Loss of Resilience Before a Tipping Point Leading to Population Collapse
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Theory predicts that the approach of catastrophic thresholds in natural systems (e.g., ecosystems,
the climate) may result in an increasingly slow recovery from small perturbations, a phenomenon
called critical slowing down. We used replicate laboratory populations of the budding yeast
Saccharomyces cerevisiae for direct observation of critical slowing down before population
collapse. We mapped the bifurcation diagram experimentally and found that the populations
became more vulnerable to disturbance closer to the tipping point. Fluctuations of population
density increased in size and duration near the tipping point, in agreement with the theory.
Our results suggest that indicators of critical slowing down can provide advance warning of
catastrophic thresholds and loss of resilience in a variety of dynamical systems.
SCIENCE VOL 336 1
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Impacts of Biodiversity Loss
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How much diversity is needed to maintain
the productivity of ecosystems?
VOL 336 SCIENCE
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Navigating the Anthropocene: Improving Earth System Governance
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The United Nations conference in Rio de
Janeiro in June is an important opportunity
to improve the institutional framework
for sustainable development.
VOL 335 SCIENCE
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The Global Extent and Determinants of Savanna and Forest as Alternative Biome States
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Theoretically, fire–tree cover feedbacks can maintain savanna and forest as alternative stable states.
However, the global extent of fire-driven discontinuities in tree cover is unknown, especially accounting
for seasonality and soils. We use tree cover, climate, fire, and soils data sets to show that tree cover is
globally discontinuous. Climate influences tree cover globally but, at intermediate rainfall (1000 to
2500 millimeters) with mild seasonality (less than 7 months), tree cover is bimodal, and only fire
differentiates between savanna and forest. These may be alternative states over large areas, including
parts of Amazonia and the Congo. Changes in biome distributions, whether at the cost of savanna (due to
fragmentation) or forest (due to climate), will be neither smooth nor easily reversible.
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