Earlier springs decrease peak summer productivity in North American boreal forests
TL;DR: In this paper, the authors analyzed nearly three decades (1982?2008) of observational records and derived products, including satellite microwave and optical imagery as well as upscaled ecosystem flux observations, to better understand how shifts in seasonality impact hydrology and productivity in the North American boreal forests.
Abstract: In the northern high latitudes, alternative hypotheses with regards to how warming-related shifts in seasonality influence ecosystem productivity exist. Increased plant growth associated with a longer growing season may enhance ecosystem productivity, but shifts to earlier springs may also negatively influence soil moisture status and productivity during the peak of the growing season. Here, we analyzed nearly three decades (1982?2008) of observational records and derived products, including satellite microwave and optical imagery as well as upscaled ecosystem flux observations, to better understand how shifts in seasonality impact hydrology and productivity in the North American boreal forests. We identified a dominant adverse influence of earlier springs on peak summer forest greenness, actual evapotranspiration and productivity at interannual time scales across the drier western and central sections of the North American boreal forests. In the vast regions where this spring onset mechanism operates, ecosystem productivity gains from earlier springs during the early portion of the growing season are effectively cancelled through corresponding losses in the later portion. Our results also indicate that recent decadal shifts towards earlier springs and associated drying in the midst of the growing season over western North American boreal forests may have contributed to the reported declines in summer productivity and increases in tree mortality and fire activity. With projections of accelerated northern high-latitude warming and associated shifts to earlier springs, persistent soil moisture deficits in peak summer may be an effective mechanism for regional-scale boreal forest dieback through their strong influence on productivity, tree mortality and disturbance dynamics.
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TL;DR: In this paper, the authors quantitatively assessed the contributions of land cover composition, climate, and topography on the spatial and interannual variation in LSP throughout the 2002 Ponil Complex Fire in New Mexico, USA, using a machine learning approach of Boosted Regression Trees (BRT).
16 citations
TL;DR: In this article, the effects of climate change and anthropogenic-management practices on maize phenology (spring, summer, and intercropping maize) in China were distinguished based on historical meteorological and phenological data (1981-2010) of 114 stations using the first-order difference regression method.
14 citations
01 Dec 2019
TL;DR: A quantitative regional attribution of CO2 seasonal amplification over the past 4 decades is presented, using a tagged atmospheric transport model prescribed with observationally constrained fluxes and finds that seasonal flux changes in Siberian and temperate ecosystems together shape the increasing CO2 amplitude.
13 citations
TL;DR: The results suggest that the rate and spatial extent of plant colonization of unvegetated soils in mountainous areas experiencing climate change could depend on both growing season length and soil microbial community composition, with microbes potentially playing more important roles as growing seasons lengthen.
Abstract: As organisms shift their geographic distributions in response to climate change, biotic interactions have emerged as an important factor driving the rate and success of range expansions. Plant-microbe interactions are an understudied but potentially important factor governing plant range shifts. We studied the distribution and function of microbes present in high-elevation unvegetated soils, areas that plants are colonizing as climate warms, snow melts earlier, and the summer growing season lengthens. Using a manipulative snowpack and microbial inoculation transplant experiment, we tested the hypothesis that growing-season length and microbial community composition interact to control plant elevational range shifts. We predicted that a lengthening growing season combined with dispersal to patches of soils with more mutualistic microbes and fewer pathogenic microbes would facilitate plant survival and growth in previously unvegetated areas. We identified negative effects on survival of the common alpine bunchgrass Deschampsia cespitosa in both short and long growing seasons, suggesting an optimal growing-season length for plant survival in this system that balances time for growth with soil moisture levels. Importantly, growing-season length and microbes interacted to affect plant survival and growth, such that microbial community composition increased in importance in suboptimal growing-season lengths. Further, plants grown with microbes from unvegetated soils grew as well or better than plants grown with microbes from vegetated soils. These results suggest that the rate and spatial extent of plant colonization of unvegetated soils in mountainous areas experiencing climate change could depend on both growing-season length and soil microbial community composition, with microbes potentially playing more important roles as growing seasons lengthen.
13 citations
Dissertation•
01 May 2014
TL;DR: In this article, the authors investigated how boreal vegetation has responded to recent climate change, particularly to the lengthening of the growing season and changes in drought severity with warming, and found that earlier springs are associated with earlier onset of photosynthetic uptake of atmospheric CO2 by northern vegetation.
Abstract: The high northern latitudes have warmed faster than anywhere else in the globe during
the past few decades. Boreal ecosystems are responding to this rapid climatic change
in complex ways and some times contrary to expectations, with large implications for the
global climate system. This thesis investigates how boreal vegetation has responded to recent
climate change, particularly to the lengthening of the growing season and changes in
drought severity with warming. The links between the timing of the growing season and
the seasonal cycle of atmospheric CO2 are evaluated in detail to infer large-scale ecosystem
responses to changing seasonality and extended period of plant growth. The influence of
warming on summer drought severity is estimated at a regional scale for the first time using
improved data. The results show that ecosystem responses to warming and lengthening of
the growing season in autumn are opposite to those in spring. Earlier springs are associated
with earlier onset of photosynthetic uptake of atmospheric CO2 by northern vegetation,
whereas a delayed autumn, rather than being associated with prolonged photosynthetic uptake,
is associated with earlier ecosystem carbon release to the atmosphere. Moreover, the
photosynthetic growing season has closely tracked the pace of warming and extension of the
potential growing season in spring, but not in autumn. Rapid warming since the late 1980s
has increased evapotranspiration demand and consequently summer and autumn drought
severity, offsetting the effect of increasing cold-season precipitation. This is consistent with
ongoing amplification of the hydrological cycle and with model projections of summer drying
at northern latitudes in response to anthropogenic warming. However, changes in snow
dynamics (accumulation and melting) appear to be more important than increased evaporative
demand in controlling changes in summer soil moisture availability and vegetation
photosynthesis across extensive regions of the boreal zone, where vegetation growth is often
assumed to be dominantly temperature-limited. Snow-mediated moisture controls of vegetation
growth are particularly significant in northwestern North America. In this region,
a non-linear growth response of white spruce growth to recent warming at high elevations
was observed. Taken together, these results indicate that net observed responses of northern
ecosystems to warming involve significant seasonal contrasts, can be non-linear and are
mediated by moisture availability in about a third of the boreal zone.
12 citations
Cites background or methods or result from "Earlier springs decrease peak summe..."
...A number of studies have shown that summer warming and longer growing seasons are associated with reduced rather than increased plant productivity during recent years at mid to high northern latitudes because of increased drought stress on vegetation growth (Angert et al., 2005; Buermann et al., 2007; Zhang et al., 2008; Peng et al., 2011; Piao et al., 2011; Ma et al., 2012; Buermann et al., 2013)....
[...]
...The result of the lagged coupling between vegetation and seasonal snow dynamics is consistent with the hypothesis that spring productivity gains from earlier thaw and extension of the growing season could potentially be offset by drought-induced productivity losses later in the season (Angert et al., 2005; Bunn & Goetz, 2006; Zhang et al., 2008; Buermann et al., 2013)....
[...]
...offset productivity gains due to warmer springs and longer growing seasons (e.g., Angert et al., 2005; Trujillo et al., 2012; Buermann et al., 2013)....
[...]
...In other cases, comparisons have been made with simple meteorological drought indices that often neglect soil properties, snow dynamics and vegetation (e.g., Angert et al., 2005; Lotsch et al., 2005; Hogg et al., 2008; Buermann et al., 2013; Vicente-Serrano et al., 2013)....
[...]
...100 List of Figures xv 5.7 Illustration of the time-dependent association between interannual variability in summer NDVI and summer temperature in northern Canada and Siberia. . . . . 101 5.8 Linear trends in summer NDVI and dominant climate drivers since 1982. . . . . 103 5.9 Temporal and spatial patterns of the leading Maximum Covariance Analysis (MCA) mode between maximum annual SWE and summer NDVI fields computed over the period 1982–2011. . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 5.10 Temporal and spatial patterns of the leading MCA mode between summer tem- perature and summer NDVI fields computed over the period 1982–2011. . . . . ....
[...]
References
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01 Jan 2007
TL;DR: The first volume of the IPCC's Fourth Assessment Report as mentioned in this paper was published in 2007 and covers several topics including the extensive range of observations now available for the atmosphere and surface, changes in sea level, assesses the paleoclimatic perspective, climate change causes both natural and anthropogenic, and climate models for projections of global climate.
Abstract: This report is the first volume of the IPCC's Fourth Assessment Report. It covers several topics including the extensive range of observations now available for the atmosphere and surface, changes in sea level, assesses the paleoclimatic perspective, climate change causes both natural and anthropogenic, and climate models for projections of global climate.
32,826 citations
Book•
01 Jan 2007
TL;DR: In this article, the authors present a historical overview of climate change science, including changes in atmospheric constituents and radiative forcing, as well as changes in snow, ice, and frozen ground.
Abstract: Summary for policymakers -- Technical summary -- Historical overview of climate change science -- Changes in atmospheric constituents and radiative forcing -- Observations: atmospheric surface and climate change -- Observations: changes in snow, ice, and frozen ground -- Observations: ocean climate change and sea level -- Paleoclimate -- Coupling between changes in the climate system and biogeochemistry -- Climate models and their evaluation -- Understanding and attributing climate change -- Global climate projections -- Regional climate projections -- Annex I: Glossary -- Annex II: Contributors to the IPCC WGI Fourth Assessment Report -- Annex III: Reviewers of the IPCC WGI Fourth Assessment Report -- Annex IV: Acronyms.
7,738 citations
United States Geological Survey1, University of Arizona2, University of Batna3, Oregon State University4, Los Alamos National Laboratory5, Centre national de la recherche scientifique6, Swiss Federal Institute for Forest, Snow and Landscape Research7, Natural Resources Canada8, University of California, Berkeley9, University of Granada10, Northern Research Institute11, Forest Research Institute12, Food and Agriculture Organization13, University of Montana14, Northern Arizona University15
TL;DR: In this paper, the authors present the first global assessment of recent tree mortality attributed to drought and heat stress and identify key information gaps and scientific uncertainties that currently hinder our ability to predict tree mortality in response to climate change and emphasizes the need for a globally coordinated observation system.
5,811 citations
TL;DR: In this article, a new climatic drought index, the standardized precipitation evapotranspiration index (SPEI), is proposed, which combines multiscalar character with the capacity to include the effects of temperature variability on drought assessment.
Abstract: The authors propose a new climatic drought index: the standardized precipitation evapotranspiration index (SPEI). The SPEI is based on precipitation and temperature data, and it has the advantage of combining multiscalar character with the capacity to include the effects of temperature variability on drought assessment. The procedure to calculate the index is detailed and involves a climatic water balance, the accumulation of deficit/surplus at different time scales, and adjustment to a log-logistic probability distribution. Mathematically, the SPEI is similar to the standardized precipitation index (SPI), but it includes the role of temperature. Because the SPEI is based on a water balance, it can be compared to the self-calibrated Palmer drought severity index (sc-PDSI). Time series of the three indices were compared for a set of observatories with different climate characteristics, located in different parts of the world. Under global warming conditions, only the sc-PDSI and SPEI identified an...
5,088 citations