On a day-to-day basis, it can be hard to notice gradual changes in the plants and landscapes around us. But comparing landscapes across extended time periods can illustrate striking changes.
As part of my dissertation research, I’ve been using aerial photographs to examine how tree cover in Ozark glade landscapes has changed between 1939 and 2014.
Tree and shrub cover has greatly expanded in Ozark dolomite glades (rocky, dry calcareous grasslands) since 1939, when most glades had relatively few trees. Today, some–but not all–glades that have been managed with prescribed fire and mechanical thinning remain nearly as open as they were in 1939. But most glades, and nearly all unmanaged glades that never burn, have become partly–or completely–covered in trees and shrubs.
Here some examples of changes in glade landscapes in the Ava District of Mark Twain National Forest.
Below: McClurg glade. On the left side of the photo is unmanaged glade that has become filled with cedars. On the right side, an area that has been mechanically thinned and frequently burned remains open. Local ecologists consider this one of the highest quality remnant glades in the Ozarks.
These images sequence through (1) a 1939 image, (2) a 2014 image, (3) a 2014 false color image, and (4) overlay of fire unit for areas that are burned (in pink). The false color image shows cedars in dark green, broadleaf trees and shrubs in light green, and open grassland in orange.
Below: a glade in the Hercules Glades Wilderness that has not been burned for many decades:
Below: A glade that has been regularly burned over recent decades but still has noticeably higher woody vegetation cover than it did in 1939.
Below: A glade complex that has been unburned for decades: