UMaine researchers incorporate “chemical phenology” into their studies of the effects of climate change on forest ecosystems.
Phenology is the study of the timing of when things happen in nature, usually focusing on plant and animal life as it relates to seasons and a changing climate. A parallel question is if climate change alters the chemical composition of leaves in a forest, particularly the timing of changes in nutrient concentrations? Can we use measurements of the chemical composition of forest foliage to monitor climate change effects on nutrient cycling in forests? Can this help us identify significant change in forests, and possibly prepare for damage to the forest ecosystem?
That is the questionthat UMaine professor Ivan J. Fernandez and graduate student Erin Redding tested in the Bear Brook Watershed in eastern Maine. Much like Signs of the Seasons observers monitor the timing of seasonal biological events for a variety of plant and animal species (i.e. phenology), Fernandez and Redding set out to study “chemical phenology”, which they define as the timing of changes in the chemical composition of leaves during the growing season. Just like every gardener knows the early leaves are succulent and light green, but get darker and thicker as they age, so too does the concentrations of nutrients like nitrogen and phosphorus change over the life of the leaf. The timing of those changes could be considered to represent “chemical phenology.”
Fernandez has spent nearly 30 years studying the response of ecosystems to perturbations, or abrupt changes that set a system out of equilibrium. He has been involved with the Bear Brook Watershed project since the late 1980’s when experiments conducted there helped guide policy decisions related to the reauthorization of the Clean Air Act of 1990. Since then, the West Bear watershed has been treated with bimonthly nutrient additions to mimic chronic acid rain deposition, while the East Bear serves as a reference. Acid rain results when the gases sulfur dioxide (SO2) and nitric oxides (NOx) react with water and oxygen in the atmosphere to form dilute sulfuric and nitric acids that fall to ground with precipitation. This acid deposition impacts lakes, streams, and groundwaters, and can harm the plants and animals that live in or rely on that water. Though there are natural sources of SO2 and NOx, a significant contribution comes from the burning of fossil fuels. Fernandez has used this experimental watershed to identify the effects of acid rain by looking for signals in the chemistry of the ecosystem before significant damage is done biologically. When thinking about the effects of climate change, he wanted to take the same approach. Phenology, the study of how annual biological events were influenced by changes in physical phenomena such as temperature, moisture, and photoperiod (the daily exposure to light), could be extended to look at biogeochemical changes in the ecosystem. However in nature there are often effects that work in opposition to each other. Carbon dioxide causes rising temperature, but it also stimulates the growth of forests. Acid rain can damage forests, but the nitrogen in acid rain is also an important nutrient for forests. As Fernandez puts it, climate change is a
“a really complex, modern perturbation of ecosystems [which] can have [both] positive and negative effects. Sorting that out at the ecosystem level, and then at a the global scale, is an immense challenge.”
Fernandez and Redding set out to ask three questions:
1) Does the concentration of nitrogen or other nutrients in the leaves change over time, and what is the typical pattern of change (i.e. chemical phenology)?
2) Do trees of the same species from the East and West Bear have different chemical compositions that would indicate the nutrient additions in the West Bear had caused a change in “chemical phenology?
3) Was there any evidence that the nutrient additions to the West Bear affected phenological events, such as the timing of bud burst or leaf fall?
On a monthly basis from March to October 2010 they observed red and sugar maple trees in both the East and West Bear forests for the timing of budburst, flowering, leaf unfolding, fall color change and leaf fall. Similarly, the red spruce trees were monitored for budburst, needle emergence and needle elongation. Leaf samples were collected and analyzed for concentrations of various nutrients and metals.
They found no significant differences in the timing of phenophase events between the East and West Bear watersheds, indicating the nutrient treatments in the West Bear watershed did not have a detectable effect on things like the timing of bud break or leaf fall.
They were able to document distinct changes in nutrient concentrations within the leaves over time, as Fernandez summarizes,
“Percent nitrogen and phosphorous showed a clear pattern of decline throughout the growing season. Calcium and magnesium, which tend to be more structural materials in leaves, increased during the growing season, which is consistent with them building thicker cell walls and more structural material as the leaves age.”
These patterns in nutrient concentrations were slightly different for each species. While these patterns are not a surprise, they were not well documented at Bear Brook before this study, and there is limited data on patterns of foliar nutrient concentrations in forest species in the scientific literature.
Was there a difference in the pattern of nutrient concentrations between the West Bear and East Bear watershed trees of the same species, indicating a response to the nutrient additions? The answer was yes. The decrease in nitrogen concentration in the spring for the maple trees in the West Bear was more dramatic than that in the East Bear. The difference was slight, but it was still an indication of a change in chemical phenology.
Fernandez hopes to continue this study of how nutrient ratios (“stoichiometry”) may be altered with changing climate. These initial observations provide a baseline for future studies, which are needed to capture phenophase changes that often happen quickly. That would require a longer-term study incorporating a more frequent sampling schedule
Why pursue this research? Who cares? Since nitrogen is the limiting nutrient for Maine forests, it is important to know how plants are responding to changes in nutrient concentrations. As Fernandez summarizes,
“There may be information in those differences [in chemical phenology] that allow us to determine how vulnerable plant and ecosystem health is to environmental change. That would be the practical implication of these findings. There may be situations where the plant starts growing earlier and, depending on the character of the chemical phenology, we could determine how vulnerable to change plants are or will be in the future. “
Dr. Fernandez’s background information from interview:
I am Professor of Soil Science at the University of Maine, and the Forest Soils faculty member at the University and the Maine Agricultural and Forest Experiment Station. My appointment is in the School of Forest Resources and the Climate Change Institute. As Maine’s Land Grant institution in a heavily forested state, of course, it is logical to have this kind of faculty position. I have been there for almost 30 years now.
My research over the years has included a wide variety of environmental issues having to do with air pollution impacts on forests (primarily acid deposition and climate change), biosolids and metals effects on forests, and biogeochemical cycling in forests. We often look at biogeochemical cycling or nutrient cycling in a watershed context. This allows us to study a closed system where we can measure inputs, outputs and everything that goes on “inside the box”. Most of my work is about everything that goes on in that box; that is, the mechanisms of ecosystem function. I also teach soil science. I have taught a number of different classes in forest soils and related to climate change over the years. I teach the basic soil science class that most students in natural science majors take at the University. I have had over 2400 students in the basic soil science class so far, and I’m not done yet!
For the past two decades my outreach efforts have increasingly been focused on the extension of our ecosystem work to issues of climate change and adaptation. We did the climate change assessment for the State of Maine, “Maine’s Climate Future”(http://climatechange.umaine.edu/research/publications/climate-future), in 2009. I was involved with the subsequent state adaptation efforts, although official state programs led by Maine DEP are no longer active. However, I continue to work to see how the University can be a catalyst and resource for adaptation concerns relevant to climate across a range of natural resource based economic sectors for Maine.
Image Description: Picture of Prof. Ivan Fernandez collecting data in the woods