Bald cypress trees (Taxodium distichum) are stately, pyramidal trees native to the wetlands of the eastern United States. Although tolerant of occasional dry conditions, newly planted trees or those in less than optimal soils can become stressed when summer is hot and rains scarce. Changes in the foliage and youngest twigs are the first signs of stress and, if heat continues and water remains scarce, extreme responses by the tree include dropping all leaves and entering dormancy.
Lack of water teamed with high summer temperatures causes the leaves to droop or wilt. This is most evident from midday to sunset; leaves usually become plump in the coolness and humidity overnight. In the coolness and dew of morning, the foliage will look healthy and be held upright to horizontally with straight, feathery form. When the day's heat calls for moisture that cannot be supplied by the roots in the dry soil, the leafs soften and droop slightly, with tips curving downward or leaves folding.
The feathery leaves of bald cypress are usually an even green. Repeated exposure to heat and dry soil will cause individual leaves to begin to yellow and then turn rusty orange. Leaf tips are first to discolor and, as stress intensifies, the yellow and orange color reaches across over one-half the leaf blades. An abundance of orange occurs before the entire leaf is shed.
Extreme drought or prolonged exposure to excessive summer heat will cause foliage to fully drop away when moisture is lacking. In fact, the tree may look as though it was turning color and dropping leaves as if it were autumn. The ground under the tree will be covered in rusty brown foliage that is crusted. Shedding is an emergency response to diminish water lost to evaporation and transpiration in the leaves. With no foliage to make food and soil moisture scarce, the plant enters dormancy to survive until more favorable growing conditions return later in the year or the next growing season.
Prolonged stress from heat or lack of soil moisture on bald cypresses will manifest in stunted growth or irregular distribution of new spring growth on the tree canopy. Often lower and side branches will have little or no new spring growth while the tree top is the primary location of lengthening stems and densest foliage.
Increase of Bare Twigs
Closely related to stunted new growth of foliage is an increase of bare, dead young twigs if there is long-term stress from heat and, particularly, water. Lower branches often will have the greatest number of dead twigs, as the tree redistributes resources for new growth and maintaining branches in the upper half of the canopy. However, irregular broad sweeps of bare twigs can occur anywhere on a stressed bald cypress.