New analysis offers important forest health information
Colorful mushrooms that pop up in forests around the world are much more than decorative baubles. Much more than realized, fungi are key components of forest ecosystems, helping to regulate the carbon cycle and driving the nutrient exchange between soil and trees.
One recent study showed the the recent bark beetle epidemic across the western U.S. may have wiped out crucial fungi that are critical to forest regrowth, and other research shows they helped stabilize global climate during low-C02 eras.
Scientists are still struggling to understand the role of fungi on a large scale, but a new analysis of satellite data from the Smithsonian’s Forest Global Earth Observatory is starting to unlock some of those secrets. The satellite images help show whether forests have healthy diets and give information about the trees’ access to nutrients based on its relationships with two different types of underground fungi.
The researchers involved in the study say the data will help them measure ecosystem productivity and responses to environmental change on vast scales.
“Every tree species has a distinct spectral signal, a kind of measurable aura,” said Sean McMahon, temperate program coordinator of the ForestGEO network. “Now we can tell who their underground friends are, an indicator of their nutrient status, from the sky.”
Fnngi and trees live in mutually beneficial relationships. The underground web of fungal hyphae intertwine with plant roots, helping them gather water and nutrients in exchange for sugars made by the trees’ photosynthesis.
Joshua Fisher from NASA’s Jet Propulsion Laboratory and UCLA and his colleagues developed a way to detect and map the associations between forests and fungi by comparing radiance data from Landsat satellites with traditional data about fungal associations of different species across several forest monitoring sites in Virginia, Wisconsin and Missourie.
“We discovered that groups of tree species associating with one type of fungi were spectrally distinct from groups of species associating with other types of fungi,” Fisher said.
The data showed whether trees are matched up with ectomycorrhizal fungi that only grow on and around root cells, or arbuscular mycorrhizal fungi, which penetrate the cells. Scientists knew which tree species associate with which fungi, but would have been impossible to map every single tree across landscapes or continents by hand.
Fungal associations indicate complex processes that are much harder to get a handle on. The researchers explained the differences in a release:
AM-associated trees usually have higher leaf phosphorus content, leaf out earlier and quickly decomposing leaf litter, resulting in faster nutrient cycling. ECM-associated trees are usually characterized by slower nutrient cycling. AM-associated trees are more common in the tropics, and ECM trees in boreal forests, but temperate forests have a mix of both. The mycorrhizal association also depends on land-use history.
Maples, tulip poplars and white ashes are all unique species with unique spectral signatures, and they all only associate with AM fungi. Oaks, American beeches, and hickories only associate with ECM fungi. Fisher and colleagues asked whether there are spectral signatures in common among the first group that differ from spectral signatures in common among the second group. Based on their observations they were able to predict 77 percent of the variation in mycorrhizal distribution within the forest plots.
The 30-year-old ForestGEO network has enabled researchers to compile an enormous amount of knowledge from forests around the world. In addition to studying the relationship between tree species and fungi, they map and measure more than six million individual trees at five-year intervals, take data on seasonal changes and measure leaf spectral properties using canopy cranes and drones, airplanes equipped with LiDAR technology and other tools that allow information to be integrated from local scales up to global scales.