120-foot tower in coastal forest adding to understanding of global climate change
GEORGETOWN — The pines and the climate are talking to each other on Hobcaw Barony, and Clemson University scientist Thomas O’Halloran is using a 120-foot tower to eavesdrop on their “conversations.”
Eddy covariance, or eddy flux, is an atmospheric measuring technique and statistical method used to determine exchange rates of trace gases over natural ecosystems — in this case, the longleaf pine forest at Clemson’s Belle W. Baruch Institute of Coastal Ecology and Forest Sciences.
“Everybody knows climate and weather make trees grow, but maybe it’s less obvious that what trees are doing also affects the climate — their growth determines how much carbon dioxide they take out of the atmosphere,” said O’Halloran, an assistant professor in the department of forestry and environmental conservation. “In turn, how much CO2 is in the atmosphere is affecting the climate. These things are coupled. They talk to each other.”
The instruments on O’Halloran’s tower measure the amount of carbon dioxide the pine trees are absorbing from the atmosphere and by studying the data over an extended time period will allow for the development of statistical relationships between the variables that affect the trees’ growth.
“What that means is it helps you to develop tools to understand what makes forests grow, and that’s useful for foresters who want to know what makes trees grow and how to make them grow better,” he said.
Making trees grow better is good news for South Carolina’s forestry industry.
A 2017 analysis by Clemson professors measured the contribution of the forestry sector to the state’s economy at more than $21 billion and 84,000 jobs, making it South Carolina’s No. 1 manufacturing sector in terms of jobs and labor income ($4.5 billion).
The environmental science at work in O’Halloran’s research is significant in terms of an even bigger picture as the data gleaned will also aid in understanding the ecosystem’s carbon balance — and in turn, the Earth’s.
“Climate change is being driven by putting too much carbon dioxide in the air from burning fossil fuels,” he said. “Carbon dioxide is a greenhouse gas that traps energy in the air and it heats the planet. Well, a huge part of what keeps carbon dioxide out of the atmosphere is forests. That is a tremendous ecosystem service that forests provide to the planet.”
While the tower is measuring the magnitude of that service at the Baruch Institute, it also represents a new data point in the measurement of carbon balance in the U.S. and internationally.
The Hobcaw Barony Mature Longleaf Pine tower is one of 337 sites registered as part of AmeriFlux, a network of principal investigator-managed sites measuring ecosystem CO2, water and energy fluxes in North, Central and South America. It was established to connect research on field sites representing major climate and ecological biomes, including tundra, grasslands, savanna and crops; and conifer, deciduous and tropical forests.
O’Halloran also recently returned from a meeting in Norway where he shared insights gained from his tower-based research in the southeastern U.S. with members of the Integrated Carbon Observation Systems (ICOS) network — a European infrastructure with similarities to AmeriFlux.
AmeriFlux is among the U.S. Department of Energy Office of Biological and Environmental Research’s most highly regarded brands in climate and ecological research. Its datasets, and the understanding derived from them, provide crucial linkages between terrestrial ecosystem processes and climate-relevant responses at landscape, regional and continental scales.
Because of the need to build a thorough body of datasets across the spectrum of ecosystems, O’Halloran’s site fills a critical void in the AmeriFlux network: a mature longleaf pine forest near the ocean.
“It is a very unique site, focused on the influence of fire in a needle-leaved evergreen forest, so it fills an important niche in the AmeriFlux network and in FLUXNET,” said Trevor Keenan, an assistant professor at the University of California Berkeley who serves on AmeriFlux Management Projects Data and Outreach Teams.
O’Halloran added: “For this science to work, we need to represent all the different plant types, all the forest types, all the climates. We need them in deserts, we need them in rainforests, we need them on mountaintops — and we need them in the Lowcountry. We need them at low elevation where our climate is very much defined by being close to the ocean.”
Flux tower research helps scientists understand how forests as a whole, rather than individual trees, respond to climate, weather, pests, controlled burns and other events, according to Baruch Institute director Skip Van Bloem, who said O’Halloran’s work is at “the leading edge of research” on interactions between forests and the atmosphere.
“It connects the Baruch Institute to AmeriFlux, a national network of research sites focused on plant-atmosphere feedbacks,” Van Bloem said. “At the same time, his research will provide important data to forest managers as they seek to understand how to respond to increasing frequency of extreme weather events like floods, drought and storms.”
Van Bloem said O’Halloran’s research will also help to quantify how much carbon and heat is absorbed by the forest, which are non-commercial benefits of forests.
“Understanding the role of forests in South Carolina’s Lowcountry landscape ecology is a priority of the Baruch Institute as we seek to provide scientific data to help manage the Lowcountry sustainably,” he said.
The nonprofit Belle W. Baruch Foundation owns and manages Hobcaw Barony, a 16,000-acre property dedicated to research and education, meaning that it also makes decisions on when and where to conduct prescribed burns on its pine forests.
George Chastain, executive director of the Belle W. Baruch Foundation, said O’Halloran’s work brings a new dimension to the traditional forestry research conducted at Hobcaw Barony.
“Society has long valued forests for the products they produce and the wildlife habitat they provide,” Chastain said. “Now our larger society is beginning to realize the role forests play in providing clean air, clean water and, yes, in sequestering carbon from the atmosphere.”
Chastain said by developing new methods to understand the carbon balance, O’Halloran is helping to provide a means to quantify yet another way forests benefit society.
“We believe his work, along with the work of others at the institute, will help value forest carbon in a way to benefit forest landowners,” he said.
By coordinating forest management activities with the Baruch Foundation, O’Halloran’s tower will allow him to study the role of fire in affecting longleaf pine carbon and water cycling, which will serve as invaluable research and data for South Carolina’s forestry industry.
The tower is powered by solar panels and fitted with cell phone modems to allow for remote monitoring of its data. Undergraduate and graduate students studying at Baruch will assist O’Halloran in taking frequent measurements on the ground to track the growth of understory, or plant life beneath the forest canopy.
“Part of our study is to analyze the effect of those burns on the water and carbon,” he said. “We’ll collect data for a few years, then they’ll burn it and we’ll see how that changes everything. We’ll see if that changes the water balance; we’ll see if that changes photosynthesis. And then the understory will grow back up for a few years, and then they’ll burn it again. This will allow us to determine things such as the optimal frequency of burning for controlling the water budget or for controlling the photosynthesis.”
Traditional methods of gathering data would mean measuring the trees once a year to track growth or working to understand photosynthesis at the chemical level inside the leaf, while O’Halloran’s tower will allow his team to measure and compile data at the landscape level.
“The tower is measuring all the trees within a couple hundred meters in the forest — several acres,” he said. “So we’re getting kind of an average picture of how that forest breathes, how it responds to changing weather and changing climate and things like that. That’s the big picture. How do these forests behave, how do they respond to climate and how are they part of the carbon budget? Because as we’ve started to recognize, this issue with too much carbon in the atmosphere is what causes climate change.”