An Ecological Assessment of the Louisiana Tensas River Basin Chapter 3 
ED 
The NALC images (Figure 3.9a and 3.9b) were classi¬ 
fied to show landuse (Figures 3.9c and 3.9d). The 
classifications were forest, human use (urban and 
agriculture), and water. The 1972 image was compared 
to the 1991/92 image and changes in forest areas and 
human use areas were calculated. The forest cover 
changes are shown in Figure 3.9e. As the figure shows, 
there was significant forest loss during that time period. 
Subwatersheds, 4, 5, 8, and 9 have had substantial 
forested loss. The northern subwatershed, 2 and 3, have 
had little forest loss because they had been converted to 
agriculture long before 1970. Where forests have been 
removed over the last 20 years, agriculture land cover has 
become more dominant, as can be seen by comparing 
Figures 3.9c with 3.9d. 
Forest Fragmentation 
As in other regions of the United States, forest fragmen¬ 
tation is an important issue in the Tensas River Basin. 
Although the word has several meanings, the general 
concept is that what was once a large continuous forest 
has been broken up into smaller pieces. In the eastern 
United States, forest loss is generally associated with 
agriculture and urban uses which remove some forest 
and leave the remaining stands in smaller, isolated 
blocks. The pattern of forest loss can be important as the 
amount lost. For example, a checkerboard pattern 
exhibits more fragmentation than a clumped pattern of 
the same amount of forest. 
Forest fragmentation was assessed by using the forest 
and non-forest data classification shown in Figures 3.9c 
and 3.9d. The fragmentation statistic measures the 
probability that a randomly selected forested spot is 
adjacent to another forested spot. High values indicate 
low fragmentation. This statistic was calculated for 1972 
as 88% and 1991/92 as 84%. These are relatively high 
values which indicate that much of the forest area in the 
Tensas River Basin is interconnected. Forest fragmenta¬ 
tion will be discussed in more detail later in this chapter. 
Percent of the Watershed in the Largest Forest 
Patch 
About 30 years ago, A.W. Kuchler made maps of poten¬ 
tial natural vegetation, that is, the vegetation that would 
occur if vegetation was only influenced by natural pro¬ 
cesses such as weather and fire. In the Tensas River 
Basin, Kuchler’s maps show that the potential natural 
vegetation is almost exclusively forest. 
Previous discussion introduced the concepts of forest 
loss (Figure 3.9) and forest fragmentation. Consider a 
watershed with some given amount of forest cover. If the 
forest is in one continuous stand, then the largest forest 
stand equals the total forest cover. If the largest stand is 
smaller than this expected value, then fragmentation has 
occurred and the remaining forest cover is discontinuous. 
The largest forest patch in the Tensas River Basin in 1972 
was 54,939.2 hectares compared to the largest forest 
patch in 1991/92 of 37,997.3 hectares. This is a loss of 
16,941.9 hectares from the largest patch. The average 
forest patch in 1972 was 38.9 hectares and in 1991/92 
was 23.1 This is a loss in average forest patch size of 
15.8 hectares throughout the Tensas River Basin. 
These forest patch size statistics may be used to deter¬ 
mine where local reforestation would best improve forest 
connectivity regionally. A significant increase in the size 
of the largest forest patch could be made by joining the 
two largest patches. More information on Wetland Forest 
restoration is given later in this chapter. 
