Riparian Restoration
CHAPTER 3: HOW RECREATION IMPACTS AFFECT KEY CHARACTERISTICS OF RIPARIAN ECOSYSTEMS
The following paragraphs discuss recreation impacts to soil, plant species diversity, aquatic life, and wildlife.
Soil Moisture
Runoff and percolation patterns of natural areas within a developed site are often changed by recreation development. Abnormally low levels of soil moisture in certain areas and higher-than-normal levels in others, cause plant stress. Roads that are elevated above the natural grade can cut off water bodies from flood plains. Roads adjacent to streams or meadows act as levees, preventing natural flooding or redirecting surface flow movement. Improperly constructed roads may block or reduce water that normally seeps or flows from the upslope to the stream, thus reducing flow to the stream, drying out the soil, and reducing vegetation; that is, negatively affects the riparian ecosystem. Roads constructed across streams or meadows can dam water and drown vegetation on one side, and dry out vegetation on the other side. See figures 35a and 35b.
Figure 35a—Upstream. After this dirt road was built, trees on
both
sides died.
Trees on the upstream side died from too much water
and those on the downstream
side from
too little water.
Pavement, structures, vehicle use, and barren soils that result from overuse introduce more heat into the riparian ecosystem. Added heat dries the ground, weakens plants, and warms the water, which can have a negative effect on aquatic species. Heat can lead to less and less ground water availability for plants and for recharging streams and lakes during dry seasons and, ultimately, to aquatic and riparian habitat loss.
Soil and Vegetation Diversity
Human foot traffic in concentrated areas can be as destructive as cattle traffic. Horseback riding and vehicle use, including cars, trucks, OHVs, trailers, and mountain bicycles, also contribute to soil compaction. See figure 36. The potential for damage increases from human to pack stock to motorized vehicles. “A controlled experiment on a sloping mountain grassland (Poa pratensis and Festuca idahoensis) in Montana found that 200 motorcycle passes removed twice as much vegetation as the same number of passes by a horse and nine times as much vegetation as 200 hiker passes” (Weaver and Dale 1978). Motorized recreation causes “extreme and deeper soil compaction… [and] are (sic) significant agents of erosion” (Cole as quoted in Alexander and Fairbridge 1999).
Figure 36—Damage caused by OHV use on the Ocala National Forest.
Soil compaction begins with trampling and treading, which includes crushing, bruising, breaking, and uprooting vegetation. See figure 37. Manning (1979) lists a seven-step soil impact cycle that includes “the scuffing away of leaf litter and other organic material on the soil surface. Soil litter cover is pulverized when exposed to trampling and is then easily blown or washed away. ... Ordinarily, this surface material serves to cushion layers of soil from trampling and absorbs large amounts of rainfall. Washing [surface runoff] of this surface exacerbates the problems of compaction and runoff, and the cycle continues in this manner” (Manning 1979).
Figure 37—This user-made ATV trail detours around a locked gate.
It crosses
one of the few salmon-spawning streams in the area
and creates edges in the
riparian forest.
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