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in order of their EO rank. However, EO ranks have not recently been updated, so some <br /> additional editing and re- ordering of the tables will likely occur as more information becomes <br /> available. <br /> The attached maps are referenced to the element occurrences listed in these tables. <br /> Larger Scale Management Issues <br /> As the landscape of the Willamette Valley has shifted over the last 150 years from one <br /> dominated by native prairies to one dominated by agricultural lands, the abundance of most <br /> native prairie species has greatly declined. Much of this decline can probably be attributed <br /> simply to loss of habitat. However, a number of complicating factors, which are most <br /> readily apparent when viewed from a landscape scale, or from a long -term time frame, may <br /> also be invoked to explain species declines. Consideration of these issues provides a <br /> framework with which to consider the additional question of whether the declines will, with <br /> the protection of known existing habitats, be ending, or will continue into the future. <br /> Time scale - Many, if not most of the native grasses and forbs of the Willamette Valley <br /> prairies are long -lived perennial species. For example, at Willow Creek, 177 Lomatium <br /> bradshawii plants were individually tagged in 1983. In 1992, 34% of the tags that could still <br /> be found were marking live plants. Since the plants were already at least 3 years old when <br /> tagged, this suggests that L. bradshawii plants can live for at least 10 -12 years, and probably <br /> more. <br /> This longevity has several implications. First, individual plants in a population may have the <br /> ability to persist even if conditions are not suitable for recruitment of new individuals in the <br /> population. This may allow populations to continue to exist despite less than optimal habitat <br /> conditions, which can help to buy time until the opportunity exists to apply management <br /> treatments. However, the long lifespan makes it more difficult to assess trends over the <br /> short term because of the difficulty in extrapolating long term trends from small annual <br /> changes. The transition matrix models of demographic data used to predict longer term <br /> trends may miss pulses of recruitment that occur only once every few years, and thus not <br /> accurately predict demographic trends. Thus, it will take many years of data and many years <br /> of appropriate management to reverse negative population trends and document population <br /> increases in these long -lived perennial species. <br /> Habitat Fragmentation - While presettlement prairies typically occurred as large, continuous <br /> areas of habitat, but now most remnants are small areas of habitat isolated from other areas <br /> of habitat by developed or agricultural land. This isolation severely constrains the movement <br /> of organisms and genes between populations, and may be problematic for organisms that <br /> originally occurred as "meta - populations ", with individual patches scattered over broad areas <br /> of suitable habitat. As a result, isolated populations may be below levels needed to maintain <br /> viability over the long term. Loss of long term viability may be due to genetic factors, such <br /> as inbreeding and reduced within - population genetic variation (especially in naturally <br /> 16 <br />