Dry Sites in Your Yard

This week we are going to talk about trees in dry areas.  Not only dry to due to climate but for other reasons also.  This is called a dry site.

A dry site is one in which a tree's water deficits are likely to be more frequent, severe, or longer than is normal, for the local climate.

Sites become dry due to:

1. Insufficient rain (drought), or irrigation
Drought, quite obviously, can be caused by less than normal rainfall, but it can also be caused by hot or cold temperature extremes where the top several inches (cm) of soil may freeze, and roots may be unable to take up water. Reduced water uptake in the winter can make trees, in particular evergreens, more vulnerable to drying out. Be sure to water in the winter if the ground is dry, including soil in containers and raised planters.

2. Not enough soil volume in the planting area
Most trees, and especially urban trees, and trees in containers, become stressed when they have a disproportionately small volume of soil for their roots. Reduced soil volume leads to soil that dries out rapidly as the root system absorbs moisture, often causing a chronic water deficit for the trees.

General signs of water stress include:
Reduced growth
Poor flower or fruit production
Limp, slightly curled or scorched leaves
Abnormal changes in leaf color

3. Various soil texture characteristics
Sandy soils tend to drain rapidly making the soil drier than silt loamsoils. Clayeysoils tend to have dry to very wet moisture extremes depending on rainfall amounts. Depending upon your climate and soil type, you can have very dry soil conditions.

How Trees Adapt to Lack of Water:
To survive prolonged water stress, trees must be able to prevent or reduce water loss from certain tissues.

Common leaf adaptations include
1. Thickened waxy layers on leaf surfaces, increases in leaf thickness, and coverings of
    short hairs (pubescence).

2. Some trees reduce moisture loss by closing their leaf pores (stomates) or decreasing leaf
    surface or size of new leaves, both of which decrease the amount of water loss.

3. Narrow or spiky leaves of conifers enable them to survive not only the droughts of hot
    summers but also the cold induced droughts of winter.

4. An extreme form of dealing with water deficits is leaf drop.
5. Some trees adapt to dry conditions by developing massive, spreading roots, or deep roots,
    either of which can enable the tree to absorb larger volumes of water.