The Effects of Reforestation on Temperature in the Southeast United States

The Southeast United States has experienced suppressed warming compared with the rest of the country since the early part of the 20th century. This region has also undergone drastic land use/land cover changes – from depleted farmland in the 1920s to a flourishing forest landscape in the 1960s. This study investigates reforestation in the Southeast U.S. as a possible influence on the Southeast “warming hole.” The study region encompasses the naturally forested areas of the southeastern U.S.; the states or parts of states used are: Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, and East Texas. Historical forestland cover and temperature data for summer and winter seasons for the decades of the 1930s, 1960s, and 1990s were used. The seasonal decadal mean minimum and maximum temperature departures from normal are calculated for long-term stations with nearly-complete records. Temperature changes within counties are compared to changes in agricultural land cover (an opposite-signed proxy for forest cover in the region) in those same counties. The 1930s-1960s was a period of cooling, and counties in the region experienced more cooling with more reforestation. The 1960s-1990s was a time of warming with less apparent reforestation effect. Minimum temperatures showed a stronger effect than maximum temperatures. At the state level, counties within a majority of the states experienced more cooling (less warming) with more reforestation and less cooling (more warming) with less reforestation. The net effect of reforestation on regional temperature trends is a combination of the observed county-scale differences and aggregate region-scale impacts.