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Interestingly, in the dry 2007-2008 year the smaller trees had huge gains with some decline in the <br />2008-2009 year. In 2010 the percent change curve continued to level out at around 25% to 30% gain. <br />This is indicative of a stabilization in the growth rates and reflects the steady change in height shown <br />in the first graph. Although these gains are far less spectacular than is evident in the other exclosures <br />the steadiness of the change in promising. In other exclosures the competition tends to be high due to <br />a contagious (clustered) distribution, but that distribution also results in the development of plateau <br />formation in the growth patterns. That is, once competition reaches a maximum the growth rate of <br />individual plants slows until environmental selection results in a thinning of the density by <br />elimination of weaker individuals. At that point the development surges up to the next plateau where <br />competition again limits the growth. <br />In this exclosure, the generally open, non-contagious distribution results in reduced <br />competition and steadier gains are seen in the data from year to year. Of course, factors other than <br />competition can act to limit growth and in Exclosure 2 that is probably due to available moisture. <br />Because this exclosure is drier the impact of dry seasons is greater, but wet seasons would induce an <br />increase in growth rate. Without knowing exactly what the sub-surface moisture structure is it is hard <br />to determine whether the moisture factor is linked closely to the stream corridor groundwater or is <br />more linked to precipitation. One indicator that there is a link to groundwater is the fact that the <br />growth curves do not show humps and valleys that would be associated with decreased moisture in <br />dry years and increased moisture in wet years. Instead, the growth curve is steady. However, because <br />the growth rates are not high this would indicate that the linkage to groundwater may be fairly deep, <br />that is, the groundwater may be several feet below the surface in most areas. This has both good and <br />bad aspects. On the one hand, a deep groundwater that is reached by tree roots is a reliable source <br />that is fairly independent of precipitation effects except in very dry years when the water table would <br />decline. On the other hand, a permanent decline in groundwater could kill the trees. The stability of <br />the nearby large wetland indicates that groundwater in this area is currently very stable. <br />Graph 1 also indicates that new arrivals are not occurring to any extent and that is probably <br />limited by the density of the herbaceous growth and dry upper soil zones. It is likely that new arrivals <br />are still coming, but are not showing up in the data collection. In fact, walking around the exclosure <br />shows there are new young plants but they do tend to be most often found a ways into the drier soils <br />from the encroaching edge of the large wetland where new arrivals are definitely limited by <br />herbaceous vegetation growth. Further from the edge of the wetland, new arrivals are rare and <br />limited to small low spots where moisture collects a little more abundantly. <br />2010 Annual Report Coal Creek Wetland Mitigation Permit DA 198811488 Page 13