Effects of late-season drought

For the most part, 2013 has been a very good year for tree growth in Frederick County with abundant rainfall until the end of August. Since the beginning of September rainfall has been scarce and spotty at best. This late season dry spell, though not as severe as a prolonged drought, can impact tree health and development.

A tree under water stress initiates a number of physical and chemical changes to conserve water. The tree may close the stomatal openings to conserve water, limit the production of chemicals, nutrients, and food reserves, drop its leaves early or curtail its growth altogether. Will these changes have any effect on trees? According to experts, the answer may be “yes.” One of the immediate changes is that leaf drop may occur early and fall colors may not be as brilliant. Another change that might occur is that the height and diameter growth may be reduced along with root development and possible flowering and seed production.

Young and newly planted trees are more sensitive to water stress than well-established plants. Drought damage may also impact a plant’s ability to ward off attacks by insects and disease, since drought-stressed plants are unable to produce defensive chemicals or simply outgrow the attack.

Desiccated leaves and cracked bark are more easily compromised by pathogens than healthy tissue. Therefore less drought- hardy plants or plants that already harbor infections are less likely to keep these pathogens at bay during dry periods. Indeed, the incidence of bacterial leaf scorch and oak and ash decline has increased during our late summer drought. Some pathogens that more easily impact drought-stressed trees include pine bark beetle, pine nematode, armillaria root rot, Dutch elm disease, bark cankers and verticillium wilt.

This late season dry spell may also be setting the region up for a more severe forest fire season because the lush herbaceous vegetation that grew when water was abundant is now drying up, adding to existing light, flashy fuel material.

Fall Mast Crop for 2013

Our wildlife is very dependent on native fruits and nuts to tide them over during the lean months of winter. Many animals gorge themselves now to store layers of fat.

They also store the fruit and nuts somewhere where they can be accessed later in the season. The fall of 2013 looks like a good year for soft mast (fruits, berries, samaras) and a fair to poor year for hard mast (acorns, hickory, beech, walnuts). Some of the more prolific soft mast producers this season include crabapple, dogwood, spicebush, hawthorn, sumac, ash, and grapevine. There are very few acorns out there this year, but hickory nuts seem to be fairly plentiful.

Walnuts are off a bit, but some trees seem to be producing, especially in the eastern portion of the county. Since acorns are one of the most important sources of food for many over-wintering wildlife, the poor fall mast production is bad news for animals like turkey and deer that are dependent on acorns as a winter food source.

Nature Notes for 8/4/23