What was done
Using aerial photographs taken over a 46-year time period, the authors analyzed the dynamics and spatial extent of gallery forest on the Konza Prairie Research Natural Area (KPRNA) in Kansas, USA, between 1939 and 1985.

What was learned
Over the 46-year period of study, total gallery forest area increased from 157 hectares in 1939 to 241 hectares in 1985.  Going back further in time, additional historical information obtained from examining the Original Land Office Surveys of KPRNA revealed that total forest area in this region increased 97% between 1859 and 1939, leading the authors to conclude that there is "no question that the absolute amount of forested areas has increased."

What it means
Referring to the Great Plains of America, Coronado in 1541 stated "there is not any kind of wood in all these plains, away from the gullies and rivers, which are very few."  A dramatic increase in forest growth has certainly occurred in this region since that time, and in particular over the last century and a half.  One of the reasons for this increase is most certainly the rise in earth's atmospheric CO2 concentration.  Rising from a concentration of 265 ppm at the time of Coronado, to a value of 370 ppm today, the increased CO2 has had a pronounced effect on the photosynthesis and growth of woody species on every continent of the globe where trees are found (Idso, 1995).

Reference
Idso, S.B.  1995.  CO2 and the Biosphere: The Incredible Legacy of the Industrial Revolution.  Department of Soil, Water and Climate, University of Minnesota, St. Paul, MN.