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Monday, February 23, 2009

A Slightly Salty Shade Tree

A Slightly Salty Shade Tree

Naomi Black

In the coolness beneath a giant salt cedar tree, I look up at the towering tree and think what a great shade this is! However, not everyone would agree. The salt cedar, an evergreen with gray-green foliage, which may grow to 18 meters in height, is in the family of tamarisk that includes over 50 species. However, many scientists, environmentalists and researchers view this family of tamarisk as a despised enemy!

The salt cedar thrives in alkaline and saline soils and can tolerate high levels of salt and is often found in the lowland shores of Sonora and Baja California. The salt cedar is a fast-growing tree which may grow four meters in a single growing season! The adult salt cedar is remarkably tolerant to stress, including heat, cold, drought and flood.

The salt cedar doesn’t exclude salt intake by roots, as do other plants. It actually transports salt from the groundwater up into its leaves. The leaves are dotted with salt-excreting glands which cause them to become encrusted with salty secretions. Year after year, the salt-drenched leaves drop beneath the tree and the salinity beneath the tree increases tremendously. In areas where there is little rainfall or flooding, the soil will not get flushed of this overabundance of salt. In time, the soil around the tree is not conducive to other plant growth. These trees are extremely invasive, competing successfully and aggressively overwhelming all other native plants.

Salt cedars are popular shade trees and used as windbreaks in the southern United States and Northern Mexico; yet many environmental groups consider the species as a whole to be an unwanted guest. In the United States, people known as “tammywackers” spend their day trying to eradicate stands of tamarisk, pulling the plants up by the roots or cutting them down and painting a solution on the stumps to prevent regrowth. Other scientists believe that introducing the Diorhabda beetle, a beetle which basically kills off tamarisks, might be a viable solution. These beetles have already been introduced in areas such as Texas, and recent studies are underway to research a similar release of these beetles in Northern Mexico.

So the next time you sit under a giant, shady (and perhaps to some, unwanted) salt cedar, just look at the leaves . . . that salty residue may just be tears.