Scott Stark, MSU assistant professor in the Department of Forestry, and Marielle Smith, MSU research associate in the Department of Forestry, have each spent more than a decade studying the rainforest ecosystem in Brazil. A $1.12 million National Science Foundation grant —$839,000 for MSU — will now allow them to expand their research into the topic of tropical forest drought.
Most research on how drought impacts the Amazon has focused on upland "terra firme" regions of forest, which have deep water tables and regularly experience droughts. Up until this point, MSU researchers have not had the opportunity to study what Stark labels “the other side of drought.” Approximately one-third of Amazon forests have shallow water tables — effectively too much water in the soil for ideal tree growth conditions.
“Trees don’t want to be under water. They need oxygen to get to their roots,” Stark said. “When the soil is waterlogged, the trees can’t take in nutrients. It’s the other end of water stress.”
There have been studies on the impact of drought in upland areas, but none about how drought will affect the waterlogged areas. Stark and the research team suspect some aspects of drought in these waterlogged areas could be a positive thing.
“There is a totally different sensitivity to different levels of drought in these waterlogged forests,” Stark said. “It’s possible that moderate drought will make these forests grow more by creating more favorable root conditions. On the other hand, if these forests dry out in severe drought, it’s not clear if the trees that typically have shallow root systems can survive.”
The research will be gathered through a combination of methods employed at both upland and waterlogged sites. Ground-based lidar systems will be used to gather information on how the quantity and distribution of leaves changes seasonally within the different forests. Two new tower systems will be installed and a third repaired. These will house cameras that capture spectral images of the top of the forest canopy, providing information on how photosynthesis changes through the season and in response to changing soil water.
In addition to ground-based and forest-top levels, satellite data will be used to scale the results up to the level of the Amazon basin, a collaborative component with the University of Arizona. Satellite data will also give researchers a longer timescale to analyze drought cycles, allowing the comparison of data going back approximately 20 years.
“This can be used to analyze impacts of excessive rainfall — the higher highs and lower lows,” Stark said.
A unique aspect of the $1.12M grant is that it strengthens collaboration with Brazilian researchers. Core collaborators — Professors Flavia Costa of National Institute of Amazonian Research and Juliana Schietti of the Federal University of the Amazônas state — have been pioneers in this area of the Amazon.
They have championed work on waterlogged soil forest, spending the last 10 years setting up an immense forest plot network spanning almost 400 miles along the BR319 road that runs southwest from Manaus, offering unique access to forests of this type.
Without the collaboration of Costa and Schietti, the science objectives and practical challenges of this study would be nearly impossible to meet. Their work allows this study to incorporate forest surveys, environmental monitoring and measurements of forest impact on the atmosphere. These data are critical for understanding the contribution of the unique responses of waterlogged forests to climate change and drought.
This project will mark the first time there has been a network of canopy towers in waterlogged forests in the central Amazon, providing a new opportunity to link knowledge from field studies to satellite data.
“Hydrology is changing in many different ways. It’s not fair to only study upland forests,” Stark said.“We know these forests suffer severe water shortages when there is a drought and they respond in negative ways. In waterlogged forests, there is the possibility of some additional resilience to drought, but that resilience could be limited too. It's critical we come to understand this waterlogged (portion) of the Amazon. If waterlogged areas do respond positively to drought, they may provide a margin of resiliency for Amazon forests in the face of a drying climate to help reduce global warming.”