Grand River Ranger District – Allotments 1- 5 Vegetative Management Environmental Assessment 61 3.2.3 Cumulative Effects (Riparian) Other events within the cumulative-effects area may also influence riparian conditions on the project area’s National Forest System lands. The location of those events would largely determine their impact, with actions happening immediately upstream having the greatest influence, while actions happening downstream, far away, or in different watersheds having less influence. The impact of those events would also be determined by pre-existing stream condition, as streams that are in Proper functioning condition are better able to handle increased impacts than are streams in poor condition. For example, a particularly violent thunderstorm might cause only minor changes to a stream in Proper functioning condition, but severely degrade an already impaired stream. The past and present factors that have had the most influence on project area riparian areas are: upstream reservoir creation (which has changed downstream hydroperiod, sediment transport, ion balance, etc.), livestock grazing (which has a variety of effects as already discussed), and land conversion. The reasonably foreseeable events with the greatest potential to degrade project area stream habitat quality would be the additional conversion of surrounding private lands from native prairie to cropland; or from Conservation Reserve Program fields to cropland. As already noted (p. xx), the likely extent of additional land conversion within the cumulative-effects area is unknown, so only qualitative conclusions can be made regarding its likely impacts to local streams. Any additional loss of perennial grass cover would result in increased soil erosion and decreased soil moisture in the uplands and riparian areas; and decreased hydroperiod, increased turbidity, and increased average water temperatures in the streams themselves. These impacts would be particularly evident under Alternative A, as that alternative proposes no remedial actions to reduce the similar impacts currently occurring on National Forest System lands from livestock grazing. Conversely, the impacts from additional land conversion would be less evident under Alternatives B and C, and least evident under Alternative D, as those alternatives propose extensive remedial actions (ranging from creating riparian exclosures to ceasing livestock grazing; see p. xx to xx) for the intermingled National Forest System lands. Figure 42. Beaver dam. Beaver dams have increased the hydroperiod, enhanced infiltration of streamflow into the banks, and improved growing conditions for riparian plants. Humphrey Draw Wildlife Area, Grand River National Grassland, Perkins Co., SD. May 2008. Photo by Mark Gonzalez.
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Grand River Ranger District – Allotments 1- 5 Vegetative Management Environmental Assessment
61
3.2.3 Cumulative Effects (Riparian)
Other events within the cumulative-effects area may also influence riparian conditions on the project
area’s National Forest System lands. The location of those events would largely determine their
impact, with actions happening immediately upstream having the greatest influence, while actions
happening downstream, far away, or in different watersheds having less influence. The impact of
those events would also be determined by pre-existing stream condition, as streams that are in Proper
functioning condition are better able to handle increased impacts than are streams in poor condition.
For example, a particularly violent thunderstorm might cause only minor changes to a stream in
Proper functioning condition, but severely degrade an already impaired stream.
The past and present factors that have had the most influence on project area riparian areas are:
upstream reservoir creation (which has changed downstream hydroperiod, sediment transport, ion
balance, etc.), livestock grazing
(which has a variety of effects as
already discussed), and land
conversion.
The reasonably foreseeable events
with the greatest potential to
degrade project area stream
habitat quality would be the
additional conversion of
surrounding private lands from
native prairie to cropland; or from
Conservation Reserve Program
fields to cropland. As already
noted (p. xx), the likely extent of
additional land conversion within
the cumulative-effects area is
unknown, so only qualitative
conclusions can be made
regarding its likely impacts to
local streams. Any additional loss
of perennial grass cover would
result in increased soil erosion and
decreased soil moisture in the uplands and riparian areas; and decreased hydroperiod, increased
turbidity, and increased average water temperatures in the streams themselves. These impacts
would be particularly evident under Alternative A, as that alternative proposes no remedial actions to
reduce the similar impacts currently occurring on National Forest System lands from livestock
grazing. Conversely, the impacts from additional land conversion would be less evident under
Alternatives B and C, and least evident under Alternative D, as those alternatives propose extensive
remedial actions (ranging from creating riparian exclosures to ceasing livestock grazing; see p. xx to
xx) for the intermingled National Forest System lands.
Figure 42. Beaver dam. Beaver dams have increased the hydroperiod, enhanced
infiltration of streamflow into the banks, and improved growing conditions for
riparian plants. Humphrey Draw Wildlife Area, Grand River National Grassland,
Perkins Co., SD. May 2008. Photo by Mark Gonzalez.
Grand River Ranger District – Allotments 1- 5 Vegetative Management Environmental Assessment
62
Another particularly important reasonably foreseeable event regards the role of beaver (Figure 42).
Beaver have an overall beneficial effect on streams by stabilizing banks, raising water tables,
increasing above- and below-ground water storage, extending the hydroperiod, decreasing stream
power, and slowing sediment transport. Beaver populations are likely to continue to increase in the
project area under all alternatives, due to relatively low trapping levels (Doug Backlund, South
Dakota Game, Fish, and Parks Department, pers. comm.). However, beaver are not now, and will
not be, evenly distributed throughout the Allotments 1-5 project area. Beaver are most likely to
impact the largest and most-watered streams and stream segments in the project area. For example:
beaver colonization in Allotment 2A is more likely to occur along mainstem Horse Creek than it is
along either of the unnamed tributaries in Section 18 (Figure xx).
Just as beaver affect the quality of riparian habitat available for other land uses, other land uses
affect the quality of riparian habitat available to beaver. For example, beaver occupancy of streams
containing few riparian shrubs, high sediment loads, and widely fluctuating hydroperiods, will be
shorter than their occupancy of streams containing extensive riparian shrubs, low sediment loads,
and stable hydroperiods. Because of this, the interaction between beaver and Alternative A is
expected to result in lower riparian habitat quality on the project area’s National Forest System lands
than would the interaction between beaver and Alternatives B, C, and, especially, Alternative D.
This is due to the beneficial direct and indirect impacts to riparian habitat quality that are anticipated
under Alternatives B, C, and D (see discussion, p. xx to xx).
It is considered very likely that present livestock grazing would continue on neighboring land
ownerships under all alternatives. In general, that grazing is not focused on maintaining or
improving Proper functioning condition along project-area streams. Nevertheless, a cursory
examination of such streams from public roadways indicates many likely are in Proper functioning
condition. We have no indication that significant changes in that management would occur within
the reasonably foreseeable future under any alternative. Therefore, private land grazing is expected
to continue to make a relatively minor cumulative impact to project area stream habitat quality under
all alternatives.
It is likely that severe weather events would occur in the cumulative-effects area during the next 15
years. These events, while natural and considered part of the baseline conditions, would nonetheless
exacerbate any existing degradation occurring as a result of proposed activities. Furthermore, any
expected improvements in riparian conditions as a result of the remedial actions proposed under
Alternatives B, C, and D could be retarded by drought or accelerated by above-average precipitation.
As discussed above, the effects of severe weather events would be most apparent under Alternative
A (because it would result in the lowest extent of Proper functioning condition streams), and least
apparent under Alternative D (because Alternative D would result in the greatest extent of Proper
functioning condition streams at the fastest pace, and thus provide the greatest ―buffering‖ possible).
Grand River Ranger District – Allotments 1- 5 Vegetative Management Environmental Assessment
DESIRED* 5%-15% 10%-15% 20%-25% 15%-20% 25%-40% *(Source: Ecological Reference Worksheets, prepared and reviewed by J. Printz, NRCS State (ND) Range Specialist, 4-
20-05 drafts)
Basal Cover - Vegetative Composition Basal cover data also provides a basis to describe vegetative composition, recognizing, however, that
bunch grasses are more likely to be recorded than rhizomatous grasses (Dr. Kevin Sedivec, NDSU
Range Extension pers. comm.). For example in Allotment 1A, western wheatgrass, a late mid-seral
and late seral species, which is the desired dominant graminoid on at least 50%* of the loamy
ecological sites, is the dominant species on none (Table 16). In fact, it is only the fifth or sixth most
common native species (Table 16). Conversely, blue grama was the first or second most widespread
species (Table 16). Similar patterns can be noted in data from most of the other grazing allotments
in the project area. These data indicate that desired levels of late seral graminoid vegetation are not
currently present in the project area.
*Based on the Grasslands Plan objective for desired seral stages being: Early: 10-15%; Mid: 65-
75%; Late: 15-20%, where western wheatgrass is the dominant species on one-half of the mid-sere
(i.e. the ―late mid-seral‖) as well as on all of the late-sere plant communities [(70%/2) + 18% = 53%].