2010-12-29_REPORT - M1988044 - Laserfiche WebLink

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Results of graphic analysis: The effects of the different moisture patterns in each year is clearly evident in the two graphs on page 8. In both average and tallest plant height lines, the decline in 2008 is evident. In contrast, the line for these two aspects show a distinct upward trend between 2006 and 2007 and between 2008 and 2010. It is important to note, however, that different precipitation patterns occurred in these two periods that showed an upward trend. The wet 2006- 2007 year was a result of a very wet (snowy) winter followed by a summer with only occasional rain while the 2008-2009 year had an opposite pattern - fairly dry winter and quite wet summer. The 2010 year had a fairly dry summer until the end of the season. The stable minimum plant height at this exclosure is due to the continued appearance of new arrivals. This is normal for a site that is toward the wet end of the moisture spectrum and will likely continue for years to come. Unfortunately, this does tend to pull down the average height to a value that is below what would be the case if the new arrivals (and older young plants that do not put on much growth) were eliminated from the analysis. Various techniques have been tried to eliminate this factor in the numerical structure, but the results lack confidence as to whether what is being removed actually should be removed. The problem is some earlier new arrivals gain in height and thus enter a data zone of taller plants while other new arrivals die or fail to thrive or gain much height. Without knowing exactly which plants are current year new arrivals, which are stunted former new arrivals, and which former new arrivals died and were replaced there is no way to confidently eliminate these plants from the determination of the average height of all cottonwoods. Thus, all that can be said is that probably the real average height of long term survivors is higher than the calculated average height which includes all the smaller plants included in the sampling. How much greater cannot be determined though. In the second graph the percent change in height from the previous year is charted for the average height and the maximum and minimum heights. With four years of data it can be seen that drier years reduce the percent change while wet years increase the percent change. This is sensible in that more water resources provides greater growth. The important point in this though is that the percent change is remaining on an overall positive side of zero change. That is, even though drier years reduce the amount of growth there are still growth gains. The negative change in the minimum is simply due to scatter in the heights of small plants (new arrivals and failure to thrive new arrivals in previous years). Because this involves only seedlings for the most part, a negative change in this category is of no concern and is actually an indication that new generations of plants are continuing to be established on an annual basis. Cover: Cover values for 2010, although not shown, increased very little because it was already at nearly a maximum value for the local microenvironment. Any increase in woody plant cover occurred primarily in the willows as they continued to spread their branches widely. In many places, willow cover is 100%. Cottonwood cover increased some as well, but not nearly as much because at this stage in the cottonwood development they are still putting most growth effort into 2010 Annual Report Coal Creek Wetland Mitigation Permit DA 198811488 Page 9