Riparian Restoration
CHAPTER 3: HOW RECREATION IMPACTS AFFECT KEY CHARACTERISTICS OF RIPARIAN ECOSYSTEMS (CONTINUED)
Soil and Vegetation Diversity (Continued)
Loss of vegetative cover, duff cover, and the subsequent loss of the organic horizon or topsoil by flooding and/or by continued human disturbance, such as trampling, exposes mineral soils. Furthermore, trampling frequently increases light intensities and temperatures, both above and below the soil surface (Cole as quoted in Alexander and Fairbridge 1999). Increased light intensity and temperature disturb the physical, biological, and chemical characteristics of the soil, resulting in lower productivity and lower water infiltration rates. See figures 38, 39, 40, 41, and 42.
Figure 38—Use at this dispersed site has isolated young trees.
The stump
of one is
visible.
Figure 39—An ever-expanding dispersed site.
Figure 40—This Alaskan trail is in a rain forest, so it is always
wet.
Hikers
walk on the edges of the trail, trampling
plants,
ever widening the trail, and
exacerbating the
problems.
The trail is also compacted,
muddy, and rutted.
Figure 41—This dispersed parking lot is growing because there
are
no boundaries.
The vegetation is becoming more and more
trampled. Angler access to the river
has caused a large chunk
to erode. High flows eventually will cause further
erosion
at this
vulnerable spot.
Figure 42—Windfall Lake Trailhead. There is no defined boundary
and therefore
no edge to this parking area. Parking areas with no
boundaries expand when
they become
crowded or as drivers
seek to park under
shade.
Pore spaces in the soil aerate roots and hold water. Compaction packs the soil particles closer together and eliminates pore spaces (Cole as quoted in Alexander and Fairbridge 1999). Compaction allows less infiltration, which leads to lower soil moisture content, fewer seeds germinating, and lower rates of seedling survival. “Young and Gilmore (1976) found that even when relatively high levels of organic matter and soil nutrients were present, they may be unavailable, perhaps due to high soil compaction and low soil moisture and oxygen content” (Manning 1979). Reduced or eliminated pore space also weakens plant vigor and reduces root penetration. Compaction also decreases soil-building plant litter and the number of arthropods, earthworms, and beneficial bacteria and fungi present (Ferren and St. John 2000).
The following diagram illustrates the cumulative effects caused by trampling and treading as vegetation is weakened and soil is compacted. See figure 43.
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