Two new studies examine the impact on climate change on plants in the Northern Hemisphere, with the first looking at a broad level indicator.
A multinational team led by the Department of Energy’s Oak Ridge National Laboratory Climate Change Science Institute has found the first positive correlation between human activity and enhanced vegetation growth.
The research team, led by Jiafu Mao of the Ecosystem Simulation Science group in the Environmental Sciences Division, used new environmental data and strict statistical methods to discover a significant human-vegetation interaction in the northern extratropical latitudes, the section of the planet spanning 30 to 75 degrees north, roughly between the Tropic of Cancer and the North Frigid Zone above the Arctic Circle.
“This is the first clear evidence of a discernible human fingerprint on physiological vegetation changes at the continental scale,” Mao said.
With the absence of long-term observational records and suitable Earth system model (ESM) simulations, the human “touch” on northern latitude greening had not been previously identified. The team used two recently available 30-year-long leaf area index data sets, 19 ESM simulations and a formal “detection and attribution” statistical algorithm to positively attribute changes in vegetation activity in the extratropical Northern Hemisphere to anthropogenic forcings, or human-induced climate inputs such as well-mixed greenhouse gas emissions.
Leaf area index – the ratio of leaf surface area to ground area – is an indicator of vegetation growth and productivity derived from satellite imaging. The remote-sensing-based LAI datasets and ESM simulations showed a significant “greening” trend over the northern extratropical latitudes vegetated area between 1982 and 2011, indicating increased vegetative productivity.
When Mao and his colleagues accounted for internal climate variability and responses to natural forcings such as volcanic eruptions and incoming solar radiation, it was clear that the greening was inconsistent with simulations of purely natural factors and could only be explained by anthropogenic greenhouse gas forcings, particularly elevated carbon dioxide concentrations.
This anthropogenic greening effect has the potential to alter natural processes on a planetary scale. Continent-wide changes in vegetative productivity, such as those in the study, impact energy exchanges, water use and carbon budgets, accelerating or slowing the pace of climate change.
Accurate detection and attribution of changes in vegetation growth patterns are essential for strategic decision-making in ecosystem management, agricultural applications and sustainable development and conservation. This is the first time the detection and attribution algorithm has been applied to terrestrial ecosystem changes such as leaf area index trends, as it is typically used to study physical climate data such as extreme events and variations in temperature or precipitation.
Mao would like to see these long-term regional- and global-scale observational data sets used in similar studies as they become available. He says the detection and attribution algorithm could be applied to study broad-scale terrestrial ecosystem dynamics, and the framework developed for this study could be used to identify and correct potential errors in next-generation ESM simulations.
The study and its results are reported in the article “Human-induced greening of the northern extratropical land surface” [$32 to read and print — esnl] in Nature Climate Change. Other ORNL participants and coauthors were Xiaoying Shi, Peter Thornton, Dan Ricciuto and Forrest Hoffman.
The impact of climate change on a single plant species
The second study looks at the impact of climate change on one plant species.
From the University of California, Irvine:
For the valerian plant, higher elevations in the Colorado Rocky Mountains are becoming much more co-ed. And the primary reason appears to be climate change.
In a study [$30 to download — esnl] appearing July 1 in Science, University of California, Irvine environmental biologists Kailen Mooney and Will Petry and colleagues report that an altering climate over the past four decades has significantly changed the growth patterns of male and female Valeriana edulis over elevation. Their work is the first to fully explain sex-specific species responses to climate change.
Read the rest, after the jump. . .
Valerian is dioecious, meaning individuals are either male or female. Unlike the majority of flowering plants, these cannot self-fertilize. Other well-known dioecious species include asparagus, ginko, papaya, holly, spinach, pistachio, willow and aspen.
In the Colorado Rockies, the sex ratio of valerian populations traditionally changed with climate from low elevation (50 percent male), where it’s hot and dry, to high elevation (only 20 percent male), where it’s cool and wet. At the highest elevations, the rarity of pollen-releasing males reduces the number of seeds produced by female plants.
Now all that’s changing. Over the past 40 years, tests conducted through the Rocky Mountain Biological Laboratory in Crested Butte, Colo., have revealed the region to be warming and drying to such a degree that each valerian population across the elevation gradient is now experiencing a climate that was historically found at a much lower elevation.
Mooney and Petry said their study shows that as the drier, warmer climate moves “up slope,” so do the arid-adapted males, shifting the sex ratios. Because of this, populations in which males were formerly rare now experience less mate limitation, enabling females to successfully produce more seed.
“Nearly all animals and many plants have separate males and females, and they almost always differ in characteristics that affect how they interact with the environment,” said Petry, who earned a Ph.D. in ecology & evolutionary biology at UCI this spring. “Understanding the responses of both sexes is important, because each sex must find mates of the opposite sex to reproduce, and no past work has connected ecological differences between males and females to their responses to climate change and the subsequent consequences for populations.”
These elevation-based patterns of sex ratio change are due, at least in part, to a physiological difference in how males and females use water.
While the increase in males has led to flourishing valerian growth at higher altitudes, an excess of males at low elevations may ultimately result in population declines. In this way, the plants’ sex-specific responses to climate change may cause the species to shift to higher elevations.
Furthermore, fluctuations in the relative abundance of valerian males and females may also have repercussions for species associated with this plant, as the two sexes support different communities of insects.
“Most past work documenting ecological responses to climate change has focused on range shifts of whole species,” said Mooney, an associate professor of ecology & evolutionary biology. “In our study, we instead looked at a species characteristic – the population sex ratio. We’re discovering that males and females respond to climate change differently and that the pace at which this species characteristic responds to climate change is unprecedentedly fast – about 10 times the average rate that species ranges are moving in response to a changing climate.”