Saltwater Inundation of Oak Trees
Oak trees are symbols of strength and endurance in the landscape. The deciduous oak grows in forests or is planted as a shade or ornamental tree in the home garden. The lobed leaves are a unique and classic feature of the tree as are the capped nuts called acorns. Oaks of one variety or another are found in almost all areas of the United Sates. Some oak trees possess salt spray tolerance and can even withstand a little salt soil, but full immersion of the roots and trunk area in salt water can be dangerous.
The majestic oaks of Galveston, Texas, were inundated by salt water from Hurricane Ike in 2009, and the majority could not be saved. The excessive salt left behind in the soil slowly poisoned the trees, and salt spray from inland flooding damaged foliage and woody growth.
Excessive salt limits the ability of the oak tree to take up fresh water and stunts and reduce growth and vigor. Instead, the root system of the oak uptakes salt that does not hydrate and nourish.
Effects on Reproduction
Heavy flooding and the subsequent receding flood waters carry away the seeds of plants before they can germinate. Those that have germinated are in such a tender condition that salt of flood waters will burn the foliage and the baby plant will suffocated. Oak acorns, the fruit and the seed of the oak tree, are no exception. Most acorns will be carried into the sea with flood water recession or will find the soil inhospitable for germination both from water saturation and salinity aspects.
Components of Salt Toxicity
Salt is made up of sodium and chloride. Both elements are toxic to plants. The two elements separate in water and the sodium absorbs water that could go to the plant. The sodium also reduces levels of other important nutrients like magnesium. Tree roots absorb the chloride that goes into the tree's vascular system and interferes with photosynthesis and chlorophyll production. The overall effect is a gradual reduction in the oak tree's health.
Hydric hammocks are habitually flooded areas with swamp-like forest characteristics. There are two types: the prairie hydric hammock and the coastal hydric hammock, and both experience the effects of total immersion in water on trees. Coastal hammocks are borders between the sea and the alluvial forest. They are flooded frequently and the resultant rises in sea level will mean even more saline exposure. Swamp laurel oak do better in highly saline soils and excessively wet ground but live oaks need drier soil and are adversely affected by salt exposure.
The degree of exposure and length of inundation to an oak tree will affect its saline tolerance. Red oak show some degree of acceptance salt soil exposure as do white and pin oaks. Willow and English oaks can tolerate only salt spray. More hardy types of oaks can survive the effects of soil salinity and salt sprays. These include the Bur oak. Even though some oaks can handle limited exposure, any tree that is not strictly a coastal specimen will have cumulative effects from saltwater overexposure and toxicity.
- Virginia Cooperative Extension: Trees and Shrubs That Tolerate Saline Soils and Salt Spray Drift
- Iowa State University: Understanding the Effects of Flooding on Trees
- FNAI: Hydric Hammock
- Houston Chronicle: Thousands of Dead Trees to be Removed Soon
- Purdue University: Salt Damage in Plants
- Blackwell Science: Plant Stress