last update March 27, 2001
Local records suggest that large accretion dunes, which formed around mesquite (prosopis glandulosa var. torreyana) trees, covered sizable areas of the Imperial Valley before it was developed for agricultural purposes. Today, these “mesquite mounds: are abundant only near the southwest corner of the Salton Sea, around the lower San Felipe Creek. There, they provide habitat for several species of birds, mammals and lizards, and serve as a model of a rare pre-settlement ecosystem.
We recently received mitigation and research funding from the California Department of Transportation to reconstruct mesquite mounds form by a gradual accumulation of fine-grained sand around mesquite already growing in the soil, we decided to plant mesquite seedlings on low mounds of imported, coarse sand. We felt that this accelerated process would create a favorable soil environment for mesquite and make dune habitat available for more immediate use by animals.
After an exceptionally windy spring in 1995, our initial observations suggest that crimped straw and coir netting are the most effective sand stabilizers. However, the cost of crimped straw was one-tenth the cost of coir netting ($3.50 versus $35.00 per mound) , although installation costs were the same. Xantham gum showed promise, but the gum crusts shattered during the installation of the irrigation system, and we could not reapply them in time to obtain any definitive results. Bark mulch was not an effective sand mound stabilizer, and barrier fencing appear to be of intermediate effectiveness.
In general, the mesquite mounds are developing as we hoped that would. Water-retaining gypsum soil moisture blocks, which we placed within and beneath the sand mounds, show that the mounds hold water very effectively. The mesquite has responded well to outplanting, with some individuals more than doubling in height (from 25 to 55 cm [10 to 22 in] ) in six weeks. The plants appear to grow equally well within and outside treeshelters, although initially the tallest plants grew in tall ( 60 cm [24 in] ) shelters and the more highly-branched plants were found either in short ( 30 cm [12 in] ) shelters or in the open. While no seedlings have died, we have had to replant several whose roots had become exposed. Finally, increasing numbers of burrowing lizards and rodents are beginning to occupy the mounds even at this early stage of plant development.