It had a large fire scar on its upslope side and may have had other diseases like heart rot. Many smaller stems also died during the monitoring. Since yellowwood is at the very edge of its range in Illinois, climate stress is a logical suspect. The one tree that died was on a drier west-facing slope indicating moisture stress may be a factor. No increase in disease mortality following the severe cold of 1989 indicates that cold stress may not be the culprit although we did not monitor into 1991 when increased disease could have been more apparent.
Stress related to physical injury is also probably a factor.
It seems unlikely that shade stress would be a factor in a subcanopy species adapted to filtered light. Healthy populations in deep shade in other states like Indiana argue against shade as a problem. These healthy Indiana trees, farther north than Illinois' populations, argue for moisture stress as opposed to temperature as the stress factor. Air pollution may also play a role in stress. A few holes were observed in canopy leaves, indicating insect grazing or a leaf disease.