Thomas Rosburg Interview Part 2

You include information about champion trees—the tallest trees and trees with the largest diameter—in your new guide. Tell us about the Big Tree program.

The Big Tree program was conceived and is sponsored by American Forests, the oldest nonprofit conservation organization in the United States. It was established about 70 years ago to find, protect, and appreciate the largest individuals of tree species in all 50 states. American Forests maintains the National Register of Big Trees, which lists the biggest trees in America. Big trees are determined by combining together three measurements – the circumference (or diameter), the height, and the diameter of the crown. More than 870 species of trees are eligible for the register. Each state has its own register to recognize the largest individuals in the state. Big trees epitomize an important natural resource value – one that is embedded in the quality of old-growth forest. For most species, big trees exist because they have lived a long time, at least relative to the typical life span for the species. That suggests to me that they deserve our respect and admiration. They are not replaceable.

Do you have favorite tree families? Favorite species?

It would probably have to be the oaks because of their predominance and ecological importance in much of the country. Also most oaks are capable of very long lives, so they provide a bridge to the past. A big 300-year-old oak was beginning its life before America fought for its independence. If they could talk, they could tell us many interesting (and ecologically valuable) stories.

Of the oaks, the bur oak is my favorite. The big old trees often display a lot of character in their gnarled, twisted, and worn-out appearance.

You’re wrapping up another project for UI Press: all-new photographs for a second edition of Wildflowers and Other Plants of Iowa Wetlands. How has this summer’s extreme drought affected Iowa’s wildflowers and plants in general?

In ways that most of us have never seen before, but mainly because of the very early phenology initiated by the extremely early spring. Many plant species bloomed up to 4 weeks early. This combined with wetlands that are or have dried up has made the task of finding wetland plants in photographic form (in flower) very difficult. The extreme drought has certainly decreased plant growth and productivity and in some cases flowering. This has generally resulted in lower vigor and photogenic quality.

Some species, however, have bloomed at their normal time, which indicates that those species are responding to photoperiod for phenology. It would have been a good growing season to study phenology and determine which species are keyed into temperature (growing degree days) or photoperiod. 

Thomas Rosburg, author of Trees in Your Pocket: A Guide to Trees of the Upper Midwest