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Ecologist Melany Fisk on climate change research and predicting changes in ecosystems

12/06/2012

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Melany Fisk, left, and Lynn Christenson, assistant professor of biology, Vassar College, sampling soil in the Hubbard Brook Experimental Forest in New Hampshire's White Mountains (photo courtesy Melany Fisk)

Miami University ecologist Melany Fisk is part of a study recently published in BioScience that shows current climate change models don't account for real life surprises that take place in forests.

Read more about that study.

Here, she describes some of the complexities and surprises of climate change in forest ecosystems:

“Understanding or predicting changes in ecosystems that are associated with climate can be confounded by the gradual and small rates of climate change relative to the backdrop of highly variable weather, and also heterogeneity of geology, soils, and vegetation in the landscape.

To learn about some of the unanticipated and complex consequences of changing climates, we need long-term records and also a focus on very local contexts in the landscape.

We have taken advantage of our long-term records at the Hubbard Brook Experimental Forest to identify some of those complexities that are less apparent at broader spatial and temporal scales, but that are essential for interpreting ecosystem change.

Vegetation change is one example. Climate models that run at broad spatial and temporal scales predict a transition to tree species that are more competitive at warmer temperatures. But it is not likely to be a gradual change that we will see unfolding over time.

Melany Fisk (right) and Sharon Santangelo, Miami '09, former Research Experience for Undergraduate (REU) student, sampling at Hubbard Brook (photo courtesy Melany Fisk)

Long-lived organisms like trees have to die before there are openings in the forest that allow the regeneration necessary for species to change.

That means we have to consider other factors that influence survival, and how those factors operate in a changing climate.

For instance, other stressors such as acid deposition and ice storms have interacted to accelerate tree death in specific elevation zones of the landscape. Where this has occurred, vegetation regeneration and changes in species composition respond to climate much more rapidly compared to surrounding areas.

Vegetation change must also be considered in the context of land-use, with past histories of forest harvest, agriculture or fire differentially influencing present species composition, productivity, and susceptibility to other stressors.

Timing is so critical to ecological interactions, and changes in climate are throwing off the timing of organisms' activities relative to their environment or to each other, especially at transitional times like changes in the seasons.

Luisa Quitalo, master's student, Institute for the Environment and Sustainability, and Hannah Clark, research assistant, Vassar College

Changes in growing season length, or in how long the ground is snow covered, can disrupt close interactions between trees and the soil organisms that make essential nutrients available, because the soil organisms are more rapidly responsive than trees to this change.

As a consequence we see the potential for losses of essential plant nutrients during the spring transition period, when earlier snowmelt means that soils are now warming up about a week before trees leaf out and begin taking up nutrients.

In the northern hardwood forest in winter, soils are protected from freezing air temperatures by a thick insulating snowpack. This over-winter climate buffering of the soil environment promotes nutrient recycling and retention activities by soil organisms.

The depth of this snowpack has declined over the past 50 years as the winter season has shortened and temperatures have warmed. Timing again is critical here. Soils are more likely to freeze when snowpack accumulates later in the season, and this disrupts interactions between plants and soil organisms causing losses of plant nutrients from the ecosystem during the summer.”