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USA - Parts of US's Southernmost States will “Tropicalize” as Climate Changes

Cold-sensitive plants, animals moving north due to fewer, weaker winter freezes

As climate change reduces the frequency and intensity of killing freezes, tropical plants and animals that once could survive in only a few parts of the U.S. mainland are expanding their ranges northward, a new U.S. Geological Survey-led study has found. The change is likely to result in some temperate zone plant and animal communities found today across the southern U.S. being replaced by tropical communities.

These changes will have complex economic, ecological and human health consequences, the study predicts. Some effects are potentially beneficial, such as expanding winter habitat for cold-sensitive manatees and sea turtles; others pose problems, such as the spread of insect-borne human diseases and destructive invasive species.

The researchers found that a number of tropical plant and animal species are enlarging their ranges to the north. They include insects, fish, reptiles, amphibians, mammals, grasses, shrubs and trees. Among them are species native to the U.S. such as mangroves, which are tropical salt-tolerant trees, and snook, a warm water coastal sport fish, and invasive species such as Burmese pythons and buffelgrass.

In the study published this month in Global Change Biology, a team of 16 scientists who have studied the effects of killing freezes describe how many cold-sensitive tropical plants and animals are kept in check by temperate zone winter cold snaps. Warming winters allow these organisms to spread north, especially into the eight subtropical U.S. mainland states: Florida, Alabama, Mississippi, Louisiana, Texas, New Mexico, Arizona and California.

Most climate change studies focus on changes in mean temperature rather than changes in the highest highs and lowest lows, so the powerful effects of extreme cold snaps on ecosystems are poorly understood, according to USGS research ecologist Michael Osland, the study’s lead author.

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