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Instead, the growth curve is steady. However, because the growth rates are not high this would <br />indicate that the linkage to groundwater may be fairly deep, that is, the groundwater may be several <br />feet below the surface in most areas. This has both good and bad aspects. On the one hand, a deep <br />groundwater that is reached by tree roots is a reliable source that is fairly independent of <br />precipitation effects except in very dry years when the water table would decline. On the other hand, <br />a permanent decline in groundwater could kill the trees. The stability of the nearby large wetland <br />indicates that groundwater in this area is currently very stable. <br />Thus, the dramatic decline in the trend lines in the first and second graphs is due to the <br />inclusion of an abundance of smaller willows in the samples than were found on the transects. But <br />cottonwood data for the exclosure as a whole and the transects are reasonably consistent. Therefore, <br />because the height frequency distribution shows close to a normal distribution curve it is clear that <br />the trend line changes are anomalous. <br />The photographs also support this conclusion. That is, the trend line changes are certainly not <br />reflected in the photographs. In fact, the photographs show that essentially all is well in Exclosure 2. <br />What this shows more than anything else is that changing sampling methods can sometimes produce <br />undesirable results that need to be more closely interpreted rather than taken at face value. It also <br />shows that when monitoring the development of vegetation, the selection of a representative transect <br />can result in actually measuring non - representative transects. It is not possible to know beforehand <br />whether a transect will in fact be representative of the larger unit being sampled. Of greater <br />importance than the trend lines are the frequency distributions. Trend lines are only most valid if the <br />sample is very large or if the same individuals are measured at different times as was done with the <br />transects. But frequency distributions actually show a great deal more useful information about the <br />structure and dynamics of the vegetation than trends. <br />When the frequency distributions of cottonwood and willow in Exclosure 2 are examined it is <br />clear that the cottonwood population exhibits diverse dimensions with a good abundance of smaller <br />plants, most of which are first or second year plants. Compared to Exclosure 1, the curves are quite <br />similar and even show a distinct break at about 7 feet. In both exclosures, most of the cottonwood <br />plants are between 4 and 7 feet tall. Because the habitat in both exclosures are quite different with <br />respect to moisture, it can be reasonable to assume that moisture is not the determining, primary <br />factor in the growth - essentially the same results in different moisture regimes. Therefore, a simple <br />factor is probably not controlling the structure of the vegetation, but rather a complex of factors. <br />Willow is far more abundant in Exclosure 1 than Exclosure 2 and because most of the <br />willows are Salix exigua, an obligate wetland species, it is possible that dense willow growth is <br />limiting cottonwood growth by limiting not the total moisture but the available moisture. Thus <br />cottonwoods are somewhat smaller in Exclosure 1 because the willows are "robbing" the water while <br />in Exclosure 2 an actual lack of available moisture is limiting growth and thus producing the same <br />results in both habitats - same effect from different causes. <br />2011 Annual Report Coal Creek Wetland Mitigation Permit DA 198811488 Page 11 <br />