Eastern red-cedar (Juniperus virginiana L.) is becoming a problem in Oklahoma and adjacent states, invading old fields, pastures and oak (Quercus sp. L.) woodland, creating fire hazards and competing with grasses and forage plants. Most stands are less than sixty years old, suggesting that something changed in the last sixty years to facilitate their spread.
Oklahoma’s last severe drought was the 1950s Drought which lasted 77 months from 1950 to 1957, based on negative PDSI values. No drought since then has lasted that long nor have any been as dry. Is Oklahoma’s climate changing? Could a climate change be behind the eastern red-cedar invasion?
To find out, we calculated 30-year running averages for both temperature and rainfall in each of Oklahoma’s nine climate divisions from 1904 through 2018 and compared these results with records of cedar coverage.
Results/Conclusions
Temperatures rose between 0.59°C and 1.06°C. All divisions showed 30-year average temperatures increasing about 1.11°C from 1904 to 1956, dropping back about 1.08°C by 1980, followed by a rise of almost 1.10°C.
Between 1980 and 2008, all nine divisions showed precipitation climate indices increasing between 5.13cm and 13.14cm. There was a decrease in precipitation during the winter months and increases the rest of the year, mostly in May and June. Oklahoma has not had a severe drought in 60 years. Oklahoma’s climate has already changed.
Data on eastern red-cedar coverage was collected by the Soil Conservation Service in 1950 and 1985 and updated in 1994. In 1950 there were stands of cedar in three main regions in the northwest, southwest and northeast parts of the state. By 1985 these were fully developed and by 1994 had mostly coalesced.
From 1950 to 1994, cedar coverage increased at rates directly proportional to annual rainfall, averaging 3.3% per year with peaks of 8% in 1993.
Over twenty species of plants are invading Oklahoma. From 1950 to 1994 cedar ground cover has increased in direct proportion to rainfall. Cedar growth appears to be linked to precipitation and precipitation to climate.
The Oklahoma Invasive Plant Council lists 13 on its website and publishes a poster of the Dirty Dozen. Once these become established (some already are) we will have new plant communities, as predicted by global warming theory. We can observe climate change as it happens.