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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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What Does Zero Deforestation Mean?
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Ambiguous defi nitions and metrics create risks
for forest conservation and accountability.
SCIENCE VOL 342
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Physical Laws Shape Biology
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IN THE PERSPECTIVE “A DYNAMICAL-SYSTEMS VIEW OF STEM CELL
biology” (12 October 2012, p. 215), C. Furusawa and K. Kaneko discuss
the relevance of dynamic systems biology approaches and the
concept of “attractors” to understand cell differentiation and proliferation.
We share their excitement in using computational models that
apply physical laws to cell fate decision.
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Water in the Balance
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Satellite data may enable improved management of regional groundwater reserves.
VOL 340 SCIENCE
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Enhanced Seasonal Exchange of CO2 by Northern Ecosystems Since 1960
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Seasonal variations of atmospheric carbon dioxide (CO2) in the Northern Hemisphere have increased since the 1950s, but sparse observations have prevented a clear assessment of the patterns of long-term change and the underlying mechanisms. We compare recent aircraft-based observations of CO2 above the North Pacific and Arctic Oceans to earlier data from 1958 to 1961 and find that the seasonal amplitude at altitudes of 3 to 6 km increased by 50% for 45° to 90°N but by less than 25% for 10° to 45°N. An increase of 30 to 60% in the seasonal exchange of CO2 by northern extratropical land ecosystems, focused on boreal forests, is implicated, substantially more than simulated by current land ecosystem models. The observations appear
to signal large ecological changes in northern forests and a major shift in the global carbon cycle.
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Pathways for Conservation
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NEXT WEEK, CONSERVATION SCIENTISTS WILL GATHER AT THE INTERNATIONAL CONGRESS FOR
Conservation Biology (ICCB) in Baltimore, Maryland, to grapple with the challenges of
preserving our natural world in the face of a growing and increasingly consumptive human
population. The natural world provides countless services, such as clean water, protection
from fl ooding, and carbon sequestration, while offering opportunities for new medicines,
foods, and energy production. Yet these valuable services and opportunities are disappearing
along with the species and natural areas that supply them. The needs of a growing human
population must be met while conserving the planet’s natural systems. Accomplishing both
will depend on making clearer connections between scientifi c results regarding issues such
as biodiversity loss and the critical decisions that must be made about conditions that underlie
change, such as greenhouse gas emissions and freshwater availability. The good news is
that today’s conservation scientists are developing innovative tools
and strategies.
SCIENCE VOL 341
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A Reconstruction of Regional and Global Temperature for the Past 11,300 Years
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Surface temperature reconstructions of the past 1500 years suggest that recent warming is
unprecedented in that time. Here we provide a broader perspective by reconstructing regional
and global temperature anomalies for the past 11,300 years from 73 globally distributed
records. Early Holocene (10,000 to 5000 years ago) warmth is followed by ~0.7°C cooling
through the middle to late Holocene (<5000 years ago), culminating in the coolest temperatures
of the Holocene during the Little Ice Age, about 200 years ago. This cooling is largely
associated with ~2°C change in the North Atlantic. Current global temperatures of the past
decade have not yet exceeded peak interglacial values but are warmer than during ~75% of
the Holocene temperature history. Intergovernmental Panel on Climate Change model projections
for 2100 exceed the full distribution of Holocene temperature under all plausible greenhouse
gas emission scenarios.
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Is Embracing Change Our Best Bet?
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Restoration ecology and conservation
biology are both under pressure to
adapt to accelerated anthropogenic
global change. Pristine areas free from human
infl uence no longer exist and, arguably, have
not for thousands of years ( 1). Major landcover
transformations for agriculture affected
vast territories more than 3000 years ago ( 2).
Large mammal extinctions in the late Pleistocene
(circa 12,000 years ago) were related to
human expansion ( 3). And relocation of nowwidespread
naturalized species was already
happening 4230 years ago, when domestic
dogs (dingos) were introduced into Australia
by way of southeast Asia ( 4). Thus, humansculpted
landscapes are what we have been
mostly managing for millennia. Because the
rate of alteration has dramatically increased
over the past 200 years, those ancient localized
impacts now affect most of the world.
Additionally, other indirect impacts act at a
planetary scale—e.g., increased carbon dioxide
concentration and nitrogen deposition
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Hell and High Water: PracticeRelevant Adaptation Science
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Adaptation requires science that analyzes decisions, identifies vulnerabilities, improves foresight, and develops options
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Marine Taxa Track Local Climate Velocities
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Organisms are expected to adapt or move in response to climate change, but observed
distribution shifts span a wide range of directions and rates. Explanations often emphasize
biological distinctions among species, but general mechanisms have been elusive. We tested an
alternative hypothesis: that differences in climate velocity—the rate and direction that climate
shifts across the landscape—can explain observed species shifts. We compiled a database of
coastal surveys around North America from 1968 to 2011, sampling 128 million individuals
across 360 marine taxa. Climate velocity explained the magnitude and direction of shifts in
latitude and depth much more effectively than did species characteristics. Our results demonstrate
that marine species shift at different rates and directions because they closely track the complex
mosaic of local climate velocities.
SCIENCE VOL 341 13 SEPTEMBER 2013
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