correlations with SMI are positive between 47° and
49°N and become negative above 50°N. As for
precipitation, the majority of the significant correlations are negative above 51° to 52°N (Fig.
3B). To summarize, all three climate variables point
toward a low-temperature constraint in black
spruce forests north of approximately 49°N. The
average MAT of forests sampled at this latitude is
1.1 ± 0.7°C (SD) and may be a threshold of MAT
below which the growth of black spruce trees is
constrained by low temperatures (Fig. 3C). In
contrast to typical climate envelope models, which
use species distribution data to estimate their
climatic niche, our approach uses the climate sensitivity of thousands of black spruce trees.
According to median temperature projections
for a low- and a high-emission scenario (4.5 and
8.5 W m–2) for 2041–2070, 63 to 80% of the territory
from 49° to 52°N should still be subject to MAT
associated with positive temperature responses
(Fig. 3C). Considering that (i) increasing growth
rates are being reported at the species treeline
[55° to 58°N (18)] and (ii) the species is already
dominant at these latitudes although at lower
density, we see no major constraint against a shift
of the refugium into the open-crown forests located
north of the study area, despite the presence of less
fertile soils. We acknowledge that there is a potential warming threshold when the region would
lose its capacity to favor black spruce growth.
The essentially monotypic black spruce boreal
forest dominating at latitudes from 49°to 52°N
has a largely positive growth response to the combined increase in temperature and decrease in
precipitation, thus supporting the hypothesis that
low temperatures are the dominant climatic growth
constraint. Conversely, growth reductions associated with increases in temperature and decreases
in precipitation and SMI are mostly found south
of 49°N. This conclusion agrees well with (i)
satellite-derived observations of recent increases
in photosynthetic activity in high-latitude forests
of NENA (12, 13, 33), (ii) ground-based reports of
a recent increase in black spruce growth in the
northern forest-tundra of NENA (18), and (iii)
predictive growth models for boreal tree species
of NENA (17). The poor adaptation of black spruce
to warm temperatures (6) that is responsible for
its lower relative abundance south of 49°N (fig.
S1), coupled with the higher water requirements
of the denser, taller, and more productive forest
stands found at these latitudes, may contribute
to the observed response gradient. Being mainly
driven by temperature, this gradient is likely to
also affect other boreal species of NENA, although
species-specific adaptations at the scale of this
study are unknown.
In contrast to the moisture-sensitive boreal
forests of central and western North America,
results from this heavily replicated network indicate that eastern black spruce populations north
of 49°N show no sign of a negative response to
climate warming and instead respond positively
to increased temperature and reduced precipitation.
Although these conclusions do not take into account the predicted changes in biotic and abiotic
disturbances (2), they do suggest that the higher
NENA water availability could allow boreal tree
species such as black spruce to better withstand
a warmer climate in NENA than in the central
and western portions of North America. Outside
of the potential for extreme disturbance events,
NENA may act as a refugium for the boreal forest.
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We gratefully acknowledge the staff of the Ministère des Forêts, de
la Faune et des Parcs du Québec (MFFP) for the meticulous work
related to tree core sampling, preparation, and measurements;
M.-C. Lambert, who generated meteorological data with the BioSim
software; R. Ouimet for graciously sharing tree-ring chronologies
from the Réseau d’Etude et de Surveillance des Ecosystèmes
Forestiers; J. Noël for the vegetation and climate maps; and the
anonymous referees for improving the manuscript with their
thoughtful comments. Climate scenarios used were from the NEX-GDDP data set, prepared by the Climate Analytics Group and the
NASA Ames Research Center, using the NASA Earth Exchange,
distributed by the NASA Center for Climate Simulation and
transformed by T. Logan at Ouranos. Data are available at the
Dryad Digital Repository, at http://dx.doi.org/10.5061/dryad.
785cv. This work was made possible by a NSERC scholarship to
L.D’O. as well as funding provided by the MFFP and Le Fond Vert
du Ministère du Développement Durable, de l’Environnement et de
la Lutte contre les Changements Climatiques du Québec within
the framework of Action Plan 2013-2018 on climate change. The
authors declare that they have no conflicts of interest.
Materials and Methods
Figs. S1 and S2
18 February 2016; accepted 19 May 2016
Improvements in ecosystem services
from investments in natural capital
Zhiyun Ouyang,1 Hua Zheng,1 Yi Xiao,1 Stephen Polasky,2 Jianguo Liu,3 Weihua Xu,1
Qiao Wang,4 Lu Zhang,1 Yang Xiao,1 Enming Rao,1 Ling Jiang,1 Fei Lu,1 Xiaoke Wang,1
Guangbin Yang,5 Shihan Gong,1 Bingfang Wu,6 Yuan Zeng,6
Wu Yang,7 Gretchen C. Daily8*
In response to ecosystem degradation from rapid economic development, China began investing
heavily in protecting and restoring natural capital starting in 2000. We report on China’s first
national ecosystem assessment (2000–2010), designed to quantify and help manage change in
ecosystem services, including food production, carbon sequestration, soil retention, sandstorm
prevention, water retention, flood mitigation, and provision of habitat for biodiversity. Overall,
ecosystem services improved from 2000 to 2010, apart from habitat provision. China’s national
conservation policies contributed significantly to the increases in those ecosystem services.
Through pursuit of rapid economic develop- ment, China has become the second largest economy in the world and has lifted hun- dreds of millions of people out of poverty since the “reform and opening up,” begun in the 1970s. Yet the costs of this success are re- flected in high levels of environmental degradation. In 1998, massive deforestation and erosion contrib- uted to severe flooding along the Yangtze River, killing thousands of people, rendering 13.2 million