scispace - formally typeset
Search or ask a question
Journal ArticleDOI

Earlier springs decrease peak summer productivity in North American boreal forests

01 Jun 2013-Environmental Research Letters (Institute of Physics)-Vol. 8, Iss: 2, pp 024027
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.

Content maybe subject to copyright    Report

Citations
More filters
Journal ArticleDOI
02 Apr 2020
TL;DR: In this article, the effects of warmer temperatures on boreal forest productivity are not uniformly positive and water stress is already negatively affecting the productivity of these forests, while increased temperatures appear beneficial in northern and wetter regions, while warmer temperatures mostly reduce forest productivity in southern and drier areas.
Abstract: Boreal forests are warming twice as fast as the rest of the planet. Do the benefits of higher temperatures and longer growing seasons for forest productivity exceed the negative effects of more frequent dry spells and heat waves, shifting precipitation patterns and higher evaporative demands? And are the effects uniformly distributed geographically? To answer to these questions, we use NDVI as a proxy of forest productivity and explore, via Partial Least Square (PLS) regression analyses, the relation between climatic variables and forest productivity at the regional scale. We focus on Northern Europe, a region for which contrasting findings on the effects of warming have been reported and that has so far been overlooked by systematic large-scale explorations of the linkages between boreal forest productivity and climatic conditions. Our results show that the effects of warmer temperatures on boreal forest productivity are not uniformly positive and that water stress is already negatively affecting the productivity of these forests. Indeed, increased temperatures appear beneficial in northern and wetter regions, while warmer temperatures mostly reduce forest productivity in southern and drier areas. These results are suggestive of already existing limitations due to water availability and warm temperatures, even in mesic regions like Northern Europe. These conditions are expected to become more frequent and intense in the future, potentially reducing the ability of boreal forests to provide their essential ecosystem services unless forest management practices are adapted to the new conditions.

28 citations

Journal ArticleDOI
TL;DR: In this article, the authors analyzed the interannual variation of summer net carbon uptake derived from atmospheric CO2 measurements and satellite vegetation indices in relation to surface meteorology from regional observational records.
Abstract: Increased photosynthetic activity and enhanced seasonal CO2 exchange of northern ecosystems have been observed from a variety of sources including satellite vegetation indices (such as the Normalized Difference Vegetation Index; NDVI) and atmospheric CO2 measurements. Most of these changes have been attributed to strong warming trends in the northern high latitudes (greater than or equal to 50N). Here we analyze the interannual variation of summer net carbon uptake derived from atmospheric CO2 measurements and satellite NDVI in relation to surface meteorology from regional observational records. We find that increases in spring precipitation and snow pack promote summer net carbon uptake of northern ecosystems independent of air temperature effects. However, satellite NDVI measurements still show an overall benefit of summer photosynthetic activity from regional warming and limited impact of spring precipitation. This discrepancy is attributed to a similar response of photosynthesis and respiration to warming and thus reduced sensitivity of net ecosystem carbon uptake to temperature. Further analysis of boreal tower eddy covariance CO2 flux measurements indicates that summer net carbon uptake is positively correlated with early growing-season surface soil moisture, which is also strongly affected by spring precipitation and snow pack based on analysis of satellite soil moisture retrievals. This is attributed to strong regulation of spring hydrology on soil respiration in relatively wet boreal and arctic ecosystems. These results document the important role of spring hydrology in determining summer net carbon uptake and contrast with prevailing assumptions of dominant cold temperature limitations to high-latitude ecosystems. Our results indicate potentially stronger coupling of boreal/arctic water and carbon cycles with continued regional warming trends.

28 citations

Journal ArticleDOI
TL;DR: In this paper, the authors examined a well-characterized eddy covariance site in a drought-prone temperate deciduous broadleaf forest combining tower measurements and satellite observations and found that an increase in spring temperature usually leads to enhanced spring gross primary production (GPP), but a GPP reduction in late growing season due to water limitation.
Abstract: The understanding and modeling of photosynthetic dynamics affected by climate variability can be highly uncertain. In this paper, we examined a well‐characterized eddy covariance site in a drought‐prone temperate deciduous broadleaf forest combining tower measurements and satellite observations. We find that an increase in spring temperature usually leads to enhanced spring gross primary production (GPP), but a GPP reduction in late growing season due to water limitation. We evaluated how well a coupled fluorescence‐photosynthesis model (SCOPE) and satellite data sets track the interannual and seasonal variations of tower GPP from 2007 to 2016. In SCOPE, a simple stress factor scaling of Vcmax as a linear function of observed predawn leaf water potential (ψ_(pd)) shows a good agreement between modeled and measured interannual variations in both GPP and solar‐induced chlorophyll fluorescence (SIF) from the Global Ozone Monitoring Experiment‐2 (GOME‐2). The modeled and satellite‐observed changes in SIF_(yield) are ~30% smaller than corresponding changes in light use efficiency (LUE) under severe stress, for which a common linear SIF to GPP scaling would underestimate the stress reduction in GPP. Overall, GOME‐2 SIF tracks interannual tower GPP variations better than satellite vegetations indices (VIs) representing canopy “greenness.” However, it is still challenging to attribute observed SIF variations unequivocally to greenness or physiological changes due to large GOME‐2 footprint. Higher‐resolution SIF data sets (e.g., TROPOMI) already show the potential to well capture the downregulation of late‐season GPP and could pave the way to better disentangle canopy structural and physiological changes in the future.

26 citations


Cites background from "Earlier springs decrease peak summe..."

  • ...A warmer spring would lengthen the photosynthetically active period and thus increase annual GPP (Buermann et al., 2013; Grippa et al., 2005; Keenan et al., 2014; Richardson et al., 2013; Sippel et al., 2017)....

    [...]

Journal ArticleDOI
TL;DR: In this paper, the authors examined how climate change will alter the vernal window and thereby impact basic hydrology during this transitional period and found that over the 21st century, the window will lengthen by +15 to +28 days in northeastern North America.
Abstract: The vernal window, or the winter-to-spring transition, is a key period for seasonally snow-covered, forested ecosystems. The events that open and close the vernal window shape the unique characteristics of spring hydrology that, in turn, influence both terrestrial and aquatic ecosystem processes. Few studies have examined how climate change will alter the vernal window and thereby impact basic hydrology during this transitional period. We project that over the 21st century the vernal window will lengthen by +15 to +28 days in northeastern North America. Loss of snow cover under a high forcing scenario eliminates the vernal window across 59% of the study domain, removing snow's influence on spring runoff in those areas. Spring runoff timing where the vernal window lengthens but does not disappear becomes similar to the southern, snow-free region where precipitation drives winter runoff, indicating a fundamental change in the hydrologic character of northeastern forested ecosystems.

26 citations

Journal ArticleDOI

25 citations


Cites background from "Earlier springs decrease peak summe..."

  • ...The advancement of spring onset would facilitate vegetation growth and consume more moisture in the earlier stage, which may cause summer droughts, productivity reduction, and earlier leaf senescence at later phases (Buermann et al., 2013; Keenan and Richardson, 2015)....

    [...]

References
More filters
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

Journal ArticleDOI
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

Journal ArticleDOI
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

Related Papers (5)