|
United
States
Department
of Agriculture
Natural
Resources
Conservation
Service
The
Natural Resources Conservation Service (NRCS) completed a resource
inventory of undeveloped lands within portions of Storey County during the
late fall and winter of 1999. The
area inventoried (Study Area) encompasses all of the western part of
Storey County (west of the 102 Ranch boundary), with the exception of the
Truckee River floodplain. A
small portion of Washoe County that abuts to the northwest border of
Storey County is also included. Total
area included within the inventory is 85,130 acres.
l (or native) plant communities within the study area were identified and
the present vegetation of these ecological sites was recorded.
Forty-two different ecological sites were recognized and more than
150 vegetation transects were completed during the course of the resource
inventory. Native plant
communities (or ecological sites) were then grouped into Range
Units. Each Range Unit is a landscape-scale subdivision of the Study
Area that encompasses a number of ecological sites that have similar
potential (or limitations) to use and management such as forage production
or topography. These Range
Units are relatively large tracts of land that can be used as a basis for
resource management planning and future monitoring.
All inventory data is referenced to these Range Units.
The
amount of forage available to grazing animals was also documented.
Total available forage was determined for each ecological site
included within each Range Unit. Available forage is the amount of forage present on a given
area that is suitable for consumption by a particular type of grazing
animal (i.e., horses). Utilization (harvest) levels were then
A primary objective of this
inventory was to gather sufficient information to make an estimate of the
grazing capacity for horses that graze year-around within the Study Area.
Grazing capacity is the total number of animals that can be sustained on a
given area based on total usable forages resources within the area.
Natural prescribed for the
available forage accounted for during the inventory. Forage utilization levels are provided as reference points in
evaluating the harvest of forages by grazing animals. Specific forage utilization levels are assigned to ensure
that forage plants remain healthy and vigorous and to provide opportunity
for forage plant reproduction.
Usable
forage is the amount of forage available for harvest when grazed at the
prescribed forage utilization levels.
Table I lists both the Usable Forage within each Range Unit
identified within the Study Area as well as the total Usable Forage for
all Range Units. Two listings
of usable forage
are given: Usable Forage with a cheatgrass
harvest allowance of 20%; and, Usable Forage with
no allowance for cheatgrass use.
Cheatgrass is an annual grass that provides nutritious feed to
grazing animals, however the year-to-year productivity of cheatgrass is
dependent on climate and is thus quite variable.
The productivity of perennial grasses is also influenced by annual
variations in climate but to a much lesser degree than annual plants and
therefore perennial grasses offer a more dependable source of forage to
grazing animals. Grazing capacity estimates for domestic livestock grazing on
northern Nevada rangelands typically do not include a harvest allowance
for annual forage plants.
The
number of months that a horse can be supported by the amount of usable
forage produced within each
Range Unit is also listed in Table I under the column headings of AUMs
(with cheatgrass @ 20%
utilization and with no use
allocated for cheatgrass). The
total number of Animal Unit Months (AUMs) with 20% cheatgrass use allowed
for is 6601 and the total number of AUMs with no allowance for cheatgrass
use is 3338. An estimate of
the total number of horses that can be supported within the Study Area
year-around is arrived at by dividing the total number of AUMs by 12
(months). The shaded areas at the bottom of Table I list the number of
horses that can be supported within the Study Area year-around when a 20%
forage allocation for cheatgrass is included in Usable Forage estimates
(550 horses) and with cheatgrass not included in the Usable Forage
estimates (278 horses).
Field
observations of present forage utilization by horses within the Study Area
indicate that forage harvest levels are generally in excess of levels
compatible with long-term resource sustainability.
Continued heavy and severe grazing use of perennial forage plants
will eventually result in loss of these forage plants.
Reproduction of the major perennial forage plants within the Study
Area is entirely by seed and, with heavy and severe grazing use,
reproduction of these plants is greatly restricted.
Additionally, the existing perennial forage plants within the Study
Area show signs of stress from excessive grazing use.
As perennial herbaceous vegetation is lost, woody plants (shrubs
and trees), cheatgrass, and other invasive plants replace perennial
grasses and herbs and the overall productivity of dependable forage
resources is significantly reduced.
(a)pounds (air-dry)/acre b
Animal Unit Month (AUM) = 800 pounds of usable forage (air-dry) c
Animal Unit (AU) = AUMs÷grazing period (in months) to be
accounted for
|
range unit number
|
total acres in range unit
|
forage-producing acres in range unit
|
usable
foragea
(cheatgrass
@
20% utilization)
|
usable
foragea
(no
use allocated
for cheatgrass)
|
AUMsb
(cheatgrass
@
20% utilization)
|
AUMsb
(no
use allocated
for cheatgrass)
|
|
|
|
|
|
|
|
|
|
1
|
4357
|
4357
|
344669.0
|
241265.0
|
430.84
|
301.58
|
|
2
|
8944
|
8496
|
520878.02
|
274656.0
|
651.10
|
343.32
|
|
3
|
191
|
182
|
30502.7
|
27408.5
|
38.13
|
34.26
|
|
4
|
4385
|
4028
|
293278.7
|
211303.7
|
366.60
|
264.13
|
|
5
|
5061
|
4919
|
419275.2
|
276485.7
|
524.09
|
345.61
|
|
6
|
874
|
874
|
57618.0
|
19031.4
|
72.02
|
23.79
|
|
7
|
947
|
900
|
85552.0
|
67606.3
|
106.94
|
84.51
|
|
8
|
3565
|
3387
|
197941.3
|
113664.7
|
247.43
|
142.08
|
|
9
|
4935
|
4702
|
253193.1
|
94447.5
|
316.49
|
118.06
|
|
10
|
219
|
217
|
11021.2
|
7911.4
|
13.78
|
9.89
|
|
11
|
1905
|
1811
|
103257.3
|
68744.0
|
129.07
|
85.93
|
|
12
|
10167
|
9895
|
614134.1
|
152677.7
|
767.67
|
190.85
|
|
13
|
3390
|
3236
|
186791.2
|
40246.2
|
233.49
|
50.31
|
|
14
|
2907
|
2373
|
136552.3
|
32351.6
|
170.69
|
40.44
|
|
15
|
3327
|
3173
|
175791.1
|
66824.2
|
219.74
|
390.03
|
|
16
|
3008
|
3008
|
169209.6
|
105197.0
|
211.51
|
131.50
|
|
17
|
2310
|
2195
|
152259.2
|
124771.2
|
190.32
|
155.96
|
|
18
|
1020
|
969
|
44533.2
|
16483.2
|
55.67
|
20.60
|
|
19
|
8389
|
7871
|
413029.3
|
97440.8
|
516.29
|
121.8
|
|
20
|
7639
|
6445
|
529671.1
|
305041.6
|
662.09
|
381.30
|
|
21
|
757
|
742
|
77032.3
|
58522.1
|
96.29
|
60.65
|
|
22
|
1198
|
1138
|
162844.1
|
125023.3
|
203.56
|
156.28
|
|
23
|
2415
|
2284
|
148853.9
|
88869.9
|
186.07
|
111.09
|
|
24
|
352
|
352
|
22700.5
|
14146.9
|
28.38
|
17.68
|
|
25
|
776
|
582
|
57745.3
|
36715.7
|
72.18
|
45.89
|
|
26
|
1945
|
1870
|
64711.2
|
9561.7
|
80.89
|
11.95
|
|
27
|
82
|
82
|
8532.1
|
3776.1
|
10.67
|
4.72
|
|
Riparian
|
65
|
65
|
11998.0
|
15846.0
|
22.6
|
19.89
|
|
|
|
|
|
|
|
|
|
|
85,130
acres
|
80,088
acres
|
5281577.00
|
2670173.44
|
6601.98
|
3337.72
|
|
|
|
|
|
|
550
AUsc/Year
|
278
AUsc/Year
|
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