Benefits for Plants Living in Densely Populated Communities May Outweigh Disadvantages, According to Study Led by Bard College Biology Professor
ANNANDALE-ON-HUDSON, N.Y. – Organisms living close to each other compete for a limited set of resources: this extends from plant communities to human communities. Densely packed cities, like New York, can house many more people, but the space available for each person is limited. Competition for space is intense. Past research has shown that the same is true of plants—densely packed communities of plants usually compete with each other for resources such as space, water, and nutrients. However, a new study led by Bard College biology professor Alexandra Wright and published today in the Journal of Ecology suggests that these competitive disadvantages may be outweighed by benefits gained during severe weather conditions such as droughts and heat waves.
The two-year study of juvenile oak seedlings, which took place at BioCON—an ongoing ecological experiment at the Cedar Creek Ecosystem Science Reserve in central Minnesota—found that an increase in both the density and diversity of neighboring plants resulted in greater competition for resources on cool, humid days, but that the impact was reversed on hot, dry days, when the evaporative cooling effect of neighboring plants helped the seedlings maintain normal activity.
“We have never seen such rapidly changing interactions before—one day plants might be competing for resources and the very next day, the same plants might be benefiting each other,” says lead author Wright, visiting assistant professor of biology at Bard. “These interactions tend to happen more intensely on extremely hot and dry days—something we will expect more in a changing climate.”
When a plant has sufficient water it will open pores in the surface of its leaves, initiate photosynthesis, and consequently lose water over the course of the day. This water loss can cool and humidify the air around the plants leaves—think of the evaporative cooling effect that results from your own sweat evaporating off your skin—and create benefits for plant neighbors. When temperature and humidity become stress factors for plants on particularly hot, dry days, the small change in temperature and humidity provided by neighbors may be enough to help them maintain normal activity. When weather conditions are mild (cool, humid days) this type of “air conditioning” becomes less important, and plants resume their intense competition for space, water, and nutrients below ground.
Stefan Schnitzer at the University of Wisconsin–Milwaukee and Peter Reich at the University of Minnesota were partners in the study.
Wright says future work will focus on the details of this “air conditioning” effect. It appears to occur more often in higher-diversity ecosystems. It also may be more important during extreme weather events, such as those expected in a rapidly changing climate. In the future, we may be able to use this to our advantage to help buffer against the negative effects that climate change has on ecosystems.
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