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<br />Ditch Maintenance Guidance <br /> <br />6 <br /> <br />. <br /> <br />. <br /> <br />Maximum Allowable Disturbance Area: This category describes the maximum area that can <br />be disturbed or lost and stilI be considered "not likely to adversely affect" (ie, insignificant <br />or discountable effects), This is further defined by the two folIowing habitat types, based <br />upon the life-history needs of the Preble's meadow jumping mouse: <br />1. Shrub habitat: As described above, a conservative estimate for the minimum <br />amount of shrub habitat required for a Preble's meadow jumping mouse is 0.25 acre <br />(ae), The Service feels that it is prudent to define a discountable and insignificant <br />level of temporary habitat disturbance along a ditch to be no more than 5% of the <br />average minimum home range for this species. Given a shrub habitat requirement of <br />0.25 ac, 5% is represented by an approximately..2.lioot by 23 foot area (see Science <br />Team White Paper, Attached). Therefore, regarding shrub habitat, no more than 5% <br />of any 0,25 ac area can be disturbed, except as detailed above. However, this area <br />must be further defined by wheth~r the shrub habitat is relatively continuous for the <br />-110 foot length of ditch being examined, or whether it is patchy in distribution. To <br />this end, the Service recommends that the folIowing measurements apply: <br />a. For relatively homogenous or uniformly continuous shrub vegetation, no more <br />than 23 feet, measured linearly along the ditch, can be disturbed for any non- <br />overlapping 110 foot length of ditch if the width of the shrub vegetation <br />(measured perpendicular to the ditch) is 23 feet or less (Figure 2): If the width <br />of the disturbance to shrub vegetation is greater than 23 feet, the linear length . <br />must be decreased accordingly, such that not more than 530 square feet is <br />disturbed (Figure 3). <br />b. For a patchy or discontinuous distribution of shrub vegetation, no more than 5% <br />of the total shrub habitat within a 110 foot linear measurement along a ditch can <br />be disturbed or lost (See Figure 4). <br />2. Foraging Habitat: Based upon the best available scientific data the Service has at <br />this time, Preble's meadow jumping mice use upland locations adjacent to shrub <br />vegetation extensively for foraging. Therefore, mowing, cutting, and spraying of <br />herbicides for weed control along ditches has the potential to impact these foraging <br />areas, Again, the Service believes that it is prudent to allow a maximum 5% loss or <br />disturbance of foraging habitat within any area required to support the mouse (see <br />Science Team White Paper, Attached). In this case, this would be measured as no <br />more than 5% of any upland area on both sides of the ditch, measured 300 feet <br />perpendicularly from the centerline of a ditch or the exterior boundary of any <br />contiguous shrub habitat along a ditch, for any 110 foot linear distance of a ditch <br />(See Figure 5). Given that foraging habitat is defined as occurring on both sides of <br />the ditch, the maximum allowable disturbance area for this habitat type can occur all <br />on one side of the ditch or be split between both sides of the ditch, as long as the <br />cumulative disturbance for any non-overlapping 110 foot linear distance of ditch <br />does not exceed 5%. <br /> <br />. <br />