An Ecological Assessment of the Louisiana Tensas River Basin Chapter 3 
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Forest and Crop Land Along Streams 
Figure 3.14 
Net percentage of change in the NDVI for the Tensas River Basin from 1972 
to 1991/92 by subwatershed. All changes represent net losses. 
The strip of vegetation along streams is known as the 
riparian vegetation zone. It is commonly described by the 
types of vegetation it contains. In an ideal situation, many 
pollutants and fertilizers will be intercepted or absorbed by 
the riparian vegetation, and this process helps to keep the 
streams clean. Bank erosion is also mitigated by intact 
riparian vegetation. The Tensas River Basin is unique in 
the natural levees along with the riparian vegetation lie on 
the highest ground in the Basin. This causes drainage 
water to run parallel to streams for many miles before 
actually entering the streams and river water channels. 
Wetlands and backswamps then become the vegetation 
filtering areas for pollutants and nutrients. 
Forested riparian zones are a natural part of the healthiest 
stream ecosystems in the southern United States. They 
provide an effective barrier to runoff of water, pollutants, 
and excess fertilizer and support a variety of valuable plant 
and wildlife species. Conversely, when riparian forests 
are replace by agriculture, the riparian zone not only loses 
its natural buffering capacity but now becomes a potential 
source of pollution and excess fertilizer. Agricultural 
practices usually employ fertilizers, pesticides, and other 
chemicals that are essential to crop growth and yield. 
These chemicals can more readily be moved into 
streams which flow through agricultural fields, in compari¬ 
son to streams which flow through forests. The maps on 
these pages illustrate differences among watersheds in 
the length of stream that has either forest or crop cover in 
the riparian zone. 
Figure 3.15 shows the relative amount of forests and 
human use land cover within a 360-meter buffer riparian 
zone along the Tensas River and its major tributaries. 
Figure 3.16 shows the amount of forests and human use 
land cover within a 120-meter buffer zone on either side of 
all the stream reaches of the Tensas River Basin. 
Subwatersheds 2 and 3 have the least percentage of 
forest in riparian zones. Subwatersheds to the south have 
the greatest amount of forested riparian cover. All of the 
sub-watersheds have stream length with some cropland 
cover. The watersheds with the highest potential for 
negative impacts are in subwatersheds 2, 3, and 4. 
Whereas the distribution of riparian forests is an indica¬ 
tor of natural buffering capacity, the distribution of crop 
land cover in riparian zones is an indicator of potential 
problems. Figure 3.17 zooms in on stream length 
between subwatersheds 5 and 8 and shows cropland 
cover (human use) and forested areas in the riparian 
zone. All of the areas shown in red were historically 
forested and are now cropland cover. 
