Data from 753 sample trees, representative of conditions commonly encountered in forests of southeastern Iowa indicate that:

1. Volume loss from all types of defects averaged 8.5 percent of the total volume of trees in the merchantable size class, 5.2 percent of the total volume of large poles and 6.2 percent of the total volume of saplings.

2. In white oak, the most important species represented, the percentage of defective volume decreased with increasing diameter.

3. Slightly over 60 percent of the trees were partially defective from one or more causes.

4. In three out of every four defective trees the defects were evident only after felling and splitting.

5. Over 90 percent of all trees had branch stubs larger than 0.5 inch in diameter, but only 11 percent of these were defective, probably due to the fact that the majority of the sample trees were of the younger age classes.

6. Eight percent of all trees bore fire scars, and 50 percent of the scarred trees were defective. Most of the scars were found in trees of merchantable size.

7. The oldest fire scar found in one of the larger trees dissected, originated in 1847-48. Fires have occurred at irregular intervals from that date until the present time.

8. Butt rot, transmitted from the parent stump, was found to be present in the young sprout growth and less prevalent in the older sprout stands.

9. Stereum gausapatum was isolated more than five times as often as any other fungus. It was responsible for almost all of the basal rots of which the causal agent was identified.

10. Sixty percent of all trees bore insect injuries, although the defects caused by insects averaged less than 2 percent of the total volume for all diameter classes.