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Academic Minute

Dr. Jason Fridley, Syracuse University – Autumn and Invasive Plants

In today’s Academic Minute, Dr. Jason Fridley of Syracuse University explains how and when many invasive plants outcompete indigenous species.

Jason Fridley is an associate professor of biology at Syracuse University where his research interests include plant ecology and geography, landscape ecology, invasive species, and biodiversity. His lab’s research is focused on understanding the ecology of plant communities, including their organization and distribution with respect to the environment. He holds a Ph.D. from the University of North Carolina at Chapel Hill.

About Dr. Fridley

Dr. Jason Fridley – Autumn and Invasive Plants

Ecologists use the term ‘phenology’ to describe the timing of natural events, such as when migratory birds reappear in spring or when fruit trees flower. Forest ecologists in particular have long been fascinated by the growth phenology of understory plants like shrubs and spring wildflowers, and how they often appear green early in the spring before being shaded by canopy trees. Because plants use the energy provided by sunlight to make food, and the leafing out of deciduous trees blocks sunlight during the summer, ecologists think understory species depend on this “spring niche” to survive.

This may be particularly important to invasive, weedy species in forests, which tend to be shrubs and vines from the Far East like Japanese honeysuckle and multiflora rose, and often appear green in the spring before many of our native forest species.

To test this idea, we set up an experimental garden containing 75 species of both native and invasive shrubs and vines, and erected a shade cloth mimicking a natural forest canopy from June through October.  For three years we measured when each plant leafed out in the spring, when they shed leaves in the autumn, and how much food they produced via photosynthesis over the growing season.  We expected the invasive plants to get more of their food in April and May, before summer shading, than natives. Instead, we were surprised to discover that the invaders produced much of their food in autumn, long after most native plants had lost their leaves. 

In fact the invaders extended the fall growing season by an average of four weeks, suggesting that part of their success is due to their inhabiting a previously empty “autumn niche”. It remains a mystery why our native plants lose their leaves so early, but we strongly suspect that this extended growing season is changing how our forests function.

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