Visitors to the UW-Madison Arboretum this fall have been exclaiming about the brilliant red, orange, and yellow fall foliage colors in Curtis Prairie. The colors in the western part of Curtis (shown below) are especially vibrant this year.
This fall scene may be a visual delight to some, but to the prairie enthusiast, a shift in the species composition in Curtis Prairie from grasses and forbs to shrubs and trees may be a warning sign that an ecological tipping point has been reached.
The missing elements in these scenes are the equally striking reds, browns, and oranges of the prairie grasses such as big bluestem (Andropogon gerardii), and Indian grass (Sorgastrum nutans) and flowers such as blazing stars, sunflowers, and golden rods that typically dominate the tallgrass prairie landscape at this time of year.
The photo above (taken in late fall of 2007, from a nearby, vantage point similar to that used in the first two photos) shows how the prairie grasses used to appear and dominate the prairie.
Another “then and now” photo sequence will show how the species composition, frequency, and distribution of Curtis Prairie has changed in six growing seasons.
This ecosystem change should generate a set of questions for site managers. For example:
1. Is the shift to shrub dominance one that should generate a management response? In other words, will a shift to shrub dominance cause a restoration to stray from the project objectives?
2. How does one identify potentially undesirable changes in your restoration?
You can look to several sources of information to help you decide.
A. The community-ecosystem model that was used in establishing the goals and objectives for the site plan.
B. The original site inventory and analysis, especially with regard to site context and the type and magnitude of cross-boundary influences.
C. The degree of flexibility called for, or allowed, in the restoration goals and objectives.
D. The nature of the site use-policy, and the potential for, and nature of, continuing on site human impacts. Human use impacts are also restoration stressors that can exacerbate abiotic or biotic stressors.
E. What site managers know, and don’t know about how the system operates.
In short, it takes studied observation and monitoring, over time, to understand how impacts to a restoration site can cause changes in ecosystem structure and function.