It is well established that atmospheric carbon dioxide (CO2) (a greenhouse gas) is increasing in large part due to human activities such as the burning of fossil fuels. The atmospheric concentration of CO2 is reported to have increased from about 280 to 370 parts per million (ppm) during the past 200 years. Some experts predict the global climate change will alter landscapes appreciably as CO2 doubles over the next 50 to 100 years. The effects of increasing CO2 on plants are well known: increased photosynthesis, reduced water loss, and more efficient use of nutrients and other resources. These effects lead to more growth, particularly in roots, and this adds carbon to the soil and stimulates microbial activity.

Forest ecosystems are responsible for large amounts of carbon flux in the atmosphere, and forest productivity is expected to increase with the projected rise in concentration of atmospheric CO2. Land management practices at Kennedy Space Center and Merritt Island National Wildlife Refuge include the use of controlled burning for fuels management to reduce wildfires and also the reintroduction of natural fire return cycles into ecosystems that historically have fire as an integral part of their dynamic processes. With expected increases in forest productivity and with the relative uncertainty regarding the effects of elevated CO2 on forest ecosystem processes, Kennedy Space Center is currently embarked on a partnership with the Smithsonian Environmental Research Center (SERC) and the Department of Energy to understand the long-term effects of elevated atmospheric carbon dioxide on Florida scrub oak ecosystem processes. Understanding carbon storage or release by fire-driven ecosystems is central to predicting long-term trends in ecosystem carbon change and the resultant impact on processes critical to the maintenance of habitat of threatened and endangered species. This is important to the long-term operation and land stewardship programs of the KSC Spaceport.

Currently, there are two research efforts underway at KSC to understand the carbon cycle and other ecosystem processes that may be influenced by increasing atmospheric CO2. Both open-top chambers and eddy flux towers are used in the studies. The project unites researchers from SERC, KSC, and several national and international universities performing experiments in a natural Florida scrub oak ecosystem. The study is designed to gain insight into the effects of increased carbon dioxide on natural vegetation growth and structure, soils, nutrient cycling, and water relations among several attributes that are important to ecosystem processes. The experiment features a 4-acre site just north of the Launch Complex 39 area with 16 open-top chambers (19 cubic meters in volume measure 3.6 meters across and 2.3 meters high encompassing a surface area of 10 square meters) placed over areas dominated by naturally occurring Florida scrub oaks and other associated species. The Florida scrub oak was chosen for study in part because it is small in stature and woody and has the attributes of much larger forest ecosystems. Elevated amounts of carbon dioxide (ambient plus 350-ppm CO2) are piped into 8 of the 16 open-top chambers to simulate the expected doubling of atmospheric CO2. Eight chambers are maintained at ambient atmospheric CO2 concentration (about 360 ppm) and 8 sites without chambers are maintained as part of the experimental treatment. The results of the research are being published in the open literature, and the site has become recognized as one of the most important native ecosystem sites in the world.

Studies with the open-top chambers have some “chamber effects” limitations, such as elevated temperatures in the chambers, shielding from ambient rainfall, some light blockage from the Mylar used to construct the chamber walls, restrictions of normal movement of insects (grazers) and other wildlife essential to ecosystem processes, and restrictions of normal atmospheric movement in the plant canopy. The study sites also have to be small due to intense maintenance required for each chamber. Over the past year, another technique for measuring ecosystem carbon flux has been employed in concert with the chambers. That technique uses an eddy flux tower, which allows for continuous measurement of carbon flux between the ecosystem and atmosphere. The results show good agreement between values of carbon flux measured with the tower and those values obtained from the chambers. Thus, the tower system provides for an unchambered technique estimating the flux (uptake and/or storage) of carbon between the vegetation and the atmosphere. This tower approach takes advantage of a high-precision multidimensional anemometer system to establish precision estimates of vegetation canopy air flow, which, when coupled with measurements of atmospheric CO2 can be used to predict carbon flux between an ecosystem and the atmosphere.

The resultant modeling allows for the estimation of unit area carbon flux within the area of the tower and can be used to estimate carbon uptake and/or storage. Two eddy flux towers are in operation at KSC and expand the spatial footprint of the chamber studies. One tower is in place near the current CO2 site (for comparative purposes), and another tower is located in the Pine Flatwoods area (TEL-4) to collect data that will allow landscape-scale projections of carbon flux.

Key accomplishments:

The results of the project to date have demonstrated some significant responses to elevated CO2 in the Florida scrub oak since the project started in 1996. The overall results indicate that interactions between the effects of elevated atmospheric CO2 on carbon metabolism, ecosystem nutrient cycling, and water relations have resulted in stimulation of carbon accumulation that has been sustained for over 5 years. The large increases in photosynthesis coupled with smaller effects on respiration have resulted in increased aboveground biomass, total leaf area, and greater fine root production in areas exposed to higher CO2. There are large yearly variations in these carbon pools, which make it difficult to conclusively determine patterns in partitioning of carbon within the system, particularly for the belowground portion. Total nitrogen has increased in the shoot and root portion of the biomass pool under elevated CO2 because of the greater biomass produced under elevated CO2 in the pools. The additional demand for nutrients with increased growth under elevated CO2 has reduced soil nitrogen and phosphorous levels. Soil water content in surface soils has increased under elevated conditions due in part to reduced loss of water from leaves, which have lower stomatal conductance and greater shading in denser canopies.

Key milestones:

Current funding from the Department of Energy will support the site for 2 more years, at which time renewal proposals will be submitted. The study as planned will continue until the site has at least 8 to 10 years of growth since the last controlled burn. The site will be burned again and the study will continue for a number of years to look at system responses under elevated CO2 immediately after fire and during early recovery. An additional eddy flux tower is planned to allow for carbon flux studies in other sites of the same ecosystem type and also in different ecosystems. This new eddy flux tower will be designed as a portable unit to allow for short-term monitoring of carbon flux dynamics related to events such as controlled burns or wildfire.

Contact: Dr. J.C. Sager (John.Sager-1@ksc.nasa.gov), YA-E4, (321) 476-4270
Participating Organizations: SERC (Dr. B.G. Drake, Dr. G. Hymus, and D. Johnson), National Research Council (Dr. S. Dore), and Dynamac Corporation (Dr. C.R. Hinkle)