Ecology of the Mississippi River Delta Region
PLANT SUCCESSION ON SPOIL BANKS
As discussed earlier, spoil banks are piles of soil that result from the creation of a canal, deepened channel, barrow pit, or some similar structure. They are unnatural and always have an effect on the area where they are situated. Hydrology (previously discussed) aside, they allow some plant species to invade broad habitats where they are normally absent.
Some years ago, a study (unpublished by Monte, as cited by Bahr and Hebrard, 1976: 73) attempted to quantify how plant succession would differ on spoil banks created in four different wetland habitats. The following shows the chronology of invasion by various plant species.
Swamp
- 1 yr - ragweed, goldenrod, Eupatorium, tree seedlings, peppervine, deer pea.
- 4 yr - 20 ft trees: willow, cottonwood, swamp red maple.
- 10 yr - oaks, etc.
Freshwater Marsh
- 1 yr - very diverse: groundsel, willow, bulltongue, goldenrod, aster, etc.
- 3 yr - 12 ft willows, 6 ft groundsel
- 5 yr - herbs shaded out
- 15 yr - 20 ft willows and swamp red maple; understory elderberry, Eupatorium, groundsel
- 30 yr - hackberry, willow, toothache tree, Chinese tallow
Brackish Marsh
- 1 yr - wiregrass, groundsel, and open ground
- 3-5 yr - wiregrass, groundsel, salt grass
- 10 yr - groundsel dominant, grasses gone, a few toothache trees
- 20 yr - groundsel, wax myrtle, toothache tree, elm, goldenrod
- 30 yr - hackberry, toothache tree, willow
Salt Marsh
- 1 yr - 50% oyster grass, rest open soil
- 5 yr - wiregrass dominated, spotted with groundsel
- 10 yr - groundsel and marshelder 7 ft tall, grasses gone
- 30 yr - hackberry, toothache tree, elderberry understory
When transects of bottomland hardwoods were compared to vegetation on spoil banks after 30 years of growth, there was a 34% similarity.