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5-1955
A Study of the Winter Foraging Habits of Mule Deer in Enclosures in Northern Utah With a Test of the Half-And-Half Sampling Technique
Donald R. Flook Utah State University
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Recommended Citation Flook, Donald R., "A Study of the Winter Foraging Habits of Mule Deer in Enclosures in Northern Utah With a Test of the Half-And-Half Sampling Technique" (1955). All Graduate Theses and Dissertations. 3721. https://digitalcommons.usu.edu/etd/3721
This Thesis is brought to you for free and open access by the Graduate Studies at DigitalCommons@USU. It has been accepted for inclusion in All Graduate Theses and Dissertations by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. A STUDY OF THE WINTER FORA~IN~ HABITS OF MULE DEER IN ENCLOSURES IN
NOR'l'HEHN UTAH \iiTH A TEST OF THE HALF- AND-HALF SAMPLIN~ TECHNI~
by
Donald R. Flook
'
A thesis submitted in partial fulfillment of the requirements for the degree of
MASTER OF SCIENCE
in
Range Mana&emen t
UTAH STATE AGRICULTURAL COLLEGE logan, Utah 1955 ACKNOWLEDGMENT
I wish to express sincrer appreciation to Professor A. u. Smith,
Professor G. A. ~arris, and Mr. H. s. Raskell for their guidance dur
ing this study; to Dr. l. A. Stoddart for his advice in preparation of the manuscript; and to Professor Bliss Crandall and Dr. c. w. Cook for their suggestions in analyzing the data.
Donald R. Flook l TABLE OF COirrENTS
Page
Introduction • • • • • • 1
Review of 11 terature • • J
Location and description of study areas • • • • 11
Procedure • • • • • 19
Experiment of 1950 • • • • • • • 19 Experiment of 1951 • • • • • • 21 Experiment of 1952 • • • • • 22 Test of half-and-half technique • • • 25
Results and discussion • • • • • • • • 28
Sample size • • • • • • • 28 Test of the half-and-half technique • • • 35 Sampling results ' )8 • • • • • Comparison of sampling methods used "• • • 44 Utilization-class estimates • • • • 45 Feeding minutes observations • • • 49 Snow conditions • • .. 49 carrying capacity of study areas • • 52
Swmnary • • • • • • • 56
Literature cited • • • • • • • • • 58
Appendices • . . • • • • • • • 61 LIST OF TABLES
Table Page
1. Summary of previous findings concerning the winter diet of mule deer in Utah • • • • • • • • 10
2. Vegetn tion types, aerial dens! ty, and species compos ition of enclosed stady area, Card Canyon, Utah • • 1) ). Vegetation types, aerial density, and species compos ition of enclosed study area, Green Canyon, Utah • • 14
4. Vege~tion types, aerial density, and species compos ition of enclosed study area. foothill east of Mill- ville, Utah • • • • • • 15 5. Method of calculating forage production, consumption, and utilization of a browse species on one transect by the Wbefore-and-after" aampling technique, example-- Prunus virginiana • • • • • • • • 20 6. Method of calculating forage utilization, production, and consumption of a browse species by the "half-and half" sampling technique, example--Artemisia tridentate subsp. trpica • • • • 2) 7. Method of calculating estimated and actual values of forage utilization, production, and consumption, in simulated browsing experiments for evaluatl%18 "half-and- half" technique, example--Cercoearuus ledifolius 27
8. Coefficients of variation, sizes of samples ~en, and sizes of samples required for desired precision, Card Canyon enclosure, 1950 • • • • • • 29 Coefficients of variation, sizes of samples taken, and sizes of samples required for desired precision, Card Canyon enclosure, 1951 • • • • • • • • • )0 10. Coefficients of variation, sizes of samples taken, and sizes of samples required for desired precision, Green Canyon enclosure, 1951 • • • • • • • )1 11. Coefficients of variation, sizes of samples taken, and sizes of samples required for desired precision, Mill- ville enclosure. 1952 • • • • • • • )2 LIST OF TABLES (cont.)
Table Page
12. Comparison of estimated and actual values of forage utili~tion, production, and consumption, simulated browsing experiment for testing ~lf-and-half• technique • • • • • • • • • • • 36 Percent utilized, weight available, weight consumed, and percent of total consumption of browse species, from sampling data, Card Canyon, 1950 • • • • 39 14. Percent utilized, weight available, weight consumed, and percent of total consumption of browse species, from sampling data, Card Canyon, 1951 • • • • • • 40 15. Percent utilization, forage available, forage consumed, and percent of total consumption of browse species, from sampling data, Green Canyon enclosure, 1951 • • 41 16. Percent utilization, forage available, forage consumed, and percent of total consumption of browse species, from sampling data, Millville enclosure, 1952 • • • • 42
1?. Estimated weight of browse consumed per deer ~ from sampling data • • • • 4J
18. Periodic average utilization-class estimates, Card Canyon enclosure, period January 6 to January 2?, 1951 • 46 19. Periodic average utilization-class estimates, Green Canyon enclosure, period February 10 to March J, 1951 • 47 20. Periodic average utilization-class estimates, Hillville enclosure, period February J to March 9, 1952 • • • 48 INTRODUCTION
Mule deer provide recreational bunting to a large number of sportB
men in Utah, and also have a high aesthetic value.
Prior to settlement, deer are believed to have wintered in the
valleys and lower foothill areas. However, in northern Utah agri
cultural development bas removed many valleys and lower foothill areas ' from the available winter range. The winter deer range in this area has therefore been restricted to a relatively small area of foothill
country, and low elevation mountain slopes and benches.
The deer herds have increased great~ during the past 25 years, possibly as a result of protection afforded them by the buck law, and
reduction in the predator population. (The wintering of increased
numbers of deer on limited areas has resulted in very undesirable con
ditions.)(Heavy browsing has caused decrease in vigor and death of
valuable browse plants. 1Higb winter mortality of deer also has result
ed from malnutrition and secondary causes in foothill areas of high
concentration, especially in winters of heavy snowfall and low temper-
atures.) A deer management plan should be directed to maintain the produc
tivity of the valuable forage species. Two phases in which information
is needed are the relative palatability of the winter browse spbcies to
deer, and the carrying capacity of different winter range types. There
is also a need for an objective method of measuring browse utilization.
Purpose of axoeriment
This experiment was designed to obtain information as to the 2 utilization of the various forage species in three small. enclosed areas
of winter deer range typical of that found in northern Utah under con
ditione 9f known stocking of deer. and to determine the quantity of each
forage species consumed by the deer.
A second phase of the experiment vas to study the accuracy of the
half-and-half sampling technique as a means of measuring winter browse use. 3
REVIEW OF LITERA'l'URE
Several methods have been employed to study the food habits of deer and other browsing mammals. The botanical ana~sis of paunch contents has been used widely to determine the relative quantities of different forage species in the diet of ruminants in general, and deer in par ticular (DeNio 1938, Deen 1938, Carhart 194o, Nemanic 1942, and Rill and
Harris ~948).
In order to study the accuracy of this technique norris (1943) fed sheep measured quantities of various domestic and native forages, killed the sheep, and analysed the rumen contents both botanically and chemically.
He found major differences between the known relative proportions of species in the forage consumed and the proportions obtained by stomach analysis. Norris accounted for this discrepancy on the basis of residues from previous feedings remaining in the rumen, and different forages de composing in the rumen at different rates. He concluded that the analysis of rumen contents was of limited value in a quantitative study of the diet of sheep,.- and similar conditions might be expected in the case of other ruminants.
Cowan (1945) used stomach analysis in studying the food habits of the Columbian blacktail deer on Vancouver Island. Deer specimens taken for stomach analysis were shot towards the end of the morning browsing period before remastication had taken place. Succulent material of the spring and summer diet was effectively separated by flooding and decant ing in shallow trays. Fall and winter samples were washed, screened, and 4 separated by species. The quantities of each species vere measured by vater displacement. Covan reported that the difficulty of certain foods being more finely comminuted than others and passing through the screens vas not encountered in his vork.
Observations of the feeding activity of grazing and browsing animals has been used to advanta&e by a number of workers vho have re
corded the length of time spent by the animals feeding upon each species
in order to evaluate its importance (Cory 1935. Dixon 1934, Snyder 19)6,
Deen 19)8, and Nemanic 1942).
Hubbard (1952) studied the relationship between the time spent by
deer eating browse species and the weight of forage consumed. He found
that although the two methods showed similar rankinge for the preferences
of the species tested, it was not possible to estimate the weight of
forage consumed of different species on the basis of the time spent by
the deer feeding upon them.
Forage preferences and food requirements of deer have been studied
by controlled feeding in several regions. Maynard. et !!·• (1935) and Stegeman (1937) carried out feeding experiments with vhitetailed deer
in New York and North Carolina, respectively. Nickol (1938) studied
the forage requiramen te of mule deer and vhi tetail deer in Arizona
through feeding experiments. He rated the palatability of 168 native
forage species fed to the deer. Smith (1950) carried out a series of
feeding experiments using captive deer in corrals near Logan, Utah.
All of the winter browse species common to the Logan area were fed and
consumption of forage was calculated from the loss of weight of forage
bundles.
Deer have been trailed in the snow and evidence of t heir browsing 5 activity noted as a means of studying winter food habit~. This method has been used mostly in conjunction with other techniques such as stomach analysis, feeding time ob~ervations, and browse plot studies (Hosley and
Ziebarth 19J5 , Dean 19)8, DeNio 1938, Carhart L94o, and ~orten 1950).
Utilization is defined by Stoddart and Smith (1943) as • ••• the degree
to which animals have consumed the total herbage of a range area; it ie expressed in percentage by weight."
Writers who have extensively reviewed the techni~ues of determining utilization of range forage and discussed their merits are Stoddart and
Smith (194J, p. 1A6-197), Feady (1949). and Sampson {1952, p. 385-395).
Dasmann (1948) made a critical review ef range survey methode with par
ticular consideration to their application in deer range management.
Clark (1944) recommended that forage utilization be estimated as to
one of five "use clas ses." He found estimates made in this manner more
rapid and more accurate than direct estimates of the percent utilization.
Grimm (19J9) employed a weight sampling method to estimate intensity
of winter browsing of sagebrush by pronghorne in Yell owstone Park. One hundred-square-foot plots were established on heavily used and lightly
used range, and the crown of each sagebrush plant in each plot was divided
in half by a string drawn taut over the center of the plant. The foliage
and green twigs were clipped from one-r~lf of each plant in October and
the similar material remaining on the other half was clipued after the
animal~ had l eft the range in April. All samples were air-dried and
weighed, and the percent utilization of forage was determined from the
difference in weight between the samples collected before and after brows
ing. In order to determine the difference in forage production between
the heavily used and lightly used range, all forage was clioped from plots 6 in the two areas, air dried, and weighed.
Cassady ( 1941) developed a ''before-and-after" sampling technique to determine utilization of range forage by sheep. ThiE method entailed the collection from representative points on the grazing area of a pre determined number of plant units of each forage species concerned, a plant unit being a whole plant, stem, twig, leaf, or any other plant part which could be readily recognized. This sampling procedure was conducted immediately prior to and immediately following the grazing of the area. The samples were weighed green and average plant unit weights calculated. The difference in average weights of the before grazing and after grazing eam~les was attributed to utilization and was calculated as a percent of the average plant unit weight before grazing.
Everson (1949) tested the before-and-after sampling technique as a means of measuring forage utilization by sheep and deer in enclosures on northern Utah summer range. Plant units were collected on square-foot plots before and after grazing. Difficulty was encountered in defining a plant unit for some species, and under the conditions of the study, the number of samples required to measure utilization within an accuracy of 5 percent of the mean, vas eo great as to render the technique im practical.
Th~ intensity of utilization of forage species has been estimated by various methods on big game range as a means of studying the palat ability of the browse plants concerned.
Stegeman (19)7) made ocular estimates of the percent utilization of each plant species on representative plot~ on whitetail deer range.
Deen (19J8) estimated forage availability and percent utilization by a
twig tally method on representative milacre browse plotF. Cowan (1945 ) ? studied deer browse utilization on milacre quadrats by estimating for each species the percentage of plants browsed, and intensity of browsing.
Carhart (1940) determined annual growth and percent utilization of browse
twigs on milacre plots in conjunction with a study of changes in plant
cover resulting from deer use. Julander (19J?) suggested the use of
permanent deer browse plots on which utilization could be measured
annually by the twig-length method.
Julander (193?) made use of take-down enclosure which could be
opened as required in order to secure different intensities of browse
utilization by deer on the Kaibab National Forest. Garrison (1953)
used quarter-acre, game-proof enclosure in order to study the annual
fluctuation of shrubs in relation to climatic and biotic factor~. In
order to determine the carrying capacity of whitetail deer range, Daven-
port (19J9) noted the effect on the browse cover of different intensities
of use by captive deer in one-acre enclosures. Smith and Gaufin (1950)
confined deer and sheep in small, temnorary enclosures on northern Utah
summer range in order to study their forage preferences. Measurements• of the major forage species were made by clipping and weighing material
from each before grazing. The progressive utilization of the forage
species was noted through the grazing period in order to judge preference,
as well as to determine when utilization was complete.
In order to determine the relative quantities of browse in the diet
of deer, Aldous (1944) determined the percent utilization of each enecies
on plots by ocular estimate and also estimated the aerial density of each
species. The product of the average utilization and average density was
considered an index to the relative quantity of the species in the deer
diet. Smith (1952), in s tudying the diet of mule deer in Utah, a lso 8 determined relative consumption on the basis of forage utilization and production. Re determined forage utilization by species on plots of 48 or 96 square feet, depending on vegetation density, and determined pro duction by the weight-estimate method supplemented by a modified volume by-weight method.
It was noted by Cook and Stoddart (1953) that low-palatability forage species may form a large part of the diet of a grazing animal as a result of their greater abundance on the range as compared to the highly palatable plants. They recommended that palatability of forage species be based on relative percent utilization under normal range conditions where the plants studied are present in nearly equal amounts, and that species be rated in four categories of palatabili~y rather than having an exact numerical value attached to each.
Cowan (1945) pointed out that when big game popula tions are low, only the most desirable forage plants are utilized, but as the population increases toward overstocking, progressively less palatable specie~ will exhibit utilization approaching 100 percent. Cowan considered palat ability ratings applicable only under the precise local conditions exist ing when they were determined. He recommended the us e of four categories of palatability, as did Cook and Stoddart, broad aoplica tion of these being pos ~ ible.
Cook, et al., (1953) found that as the intensity of utilization of desert shrubs by sheep was increased, the animals were forced to consume the less nutritious portions of the plants. The same relationship was found by Aldous (1945) to apply to the browsing of mule deer. He noted that deer under light stocking use only leaves and bud ends of browse plants which chemical ana~vsis showed to be the most nutritious.
The results obtained in five studies of the winter diet of mule deer 9 in Utah are summarized in Table 1. The values listed for the studies by
Hubbard (1952) and Smith (1950) represent the order of preference of the browse species involved, as each species was made available to the deer in sufficient quantity that the amount consumed would not be limited by
the amount available.
The results of the studies by Smith (1952), Nemanic (1942), and
Snyder (19J7) represent the percentage of each species in the deer diet under the conditions of floral composition and forage availability on
the winter ranges where the studies were conducted. •
Table 1. Summary of previous findings concerning the winter diet of mule deer in Utah•
Hubbard Hubbard Smith Smith Nemanic Nemanic Snyder Snyder (1952) (1952) (1950) (1952) (1942) (1942) (1937) (1937) Bank by Bank by Rank by Rank by ~by tf, by tf,by %by time1 wei,ght2 weight3 %weig}lt 4 time5 weig}lt6 time? weightS Cercocarpua 1edifoliue X 1 1 2 Cercoearpus montanus Ceroocarpus ledifolius 2 2 1 6.2 0.3 1.7 8.9 Purahia tridentata 4 5 3 21 17.9 2.1 1.0 Prunus melanocarpa 6 14 8 o.6 Cereocarpue montanus 8 9 6 3 18.9 10.2 12.8 Chrysothamnus nauseosus 9 7 17 trace o.6 1.1 Juniperus scopulorum 10 8 10 ~elanehier alnifolia 11 10 9 1.4 Juniperus utahensis 13 15 12 8 Juniperus epp. 25.6 6.0 13.7 42.8 Acer Grandidentatum 14 12 14 1.7 Acer spp. 2.0 7.5 Artemisia t. typica 15 13 11 37 Artemisia t. nova 16 Artemisia t. subspp. 28.1 15.6 18.7 14.2 ~In part from Hubbard (1952) Table 1, p. 6. 1, 2 and 3. Controlled feeding trials, species available in similar amounts. 4. Plot estimates on the winter range. 5 and 7. Observation of wild deer. 6 and 8. Stomach analysis.
1--J 0 11
LOCATION AND DESCRIPTION OF STUDY AREAS
The experiment was conducted in the late winters of 1950, 1951, and 1952, using captive deer in study enclosures near Logan, Utah. In 1950 an enclosure in Card Canyon was used. In 1951 the experiment was carried on in the Card Canyon enclosure and a second enclosure in Green
Canyon was also used. In 1952 an enclosure on the west-facing foothill west of Millville was used.
Card Canyon opens into Logan Canyon 6.4 miles b,y highway from the mouth of the latter. This enclosure (a permanent one) 300 feet square was built in the autumn of 1949 on a bench on the east side of the canyon, 0.7 miles from its mouth. The lower row of wire was hung on
November 10, at ~ich time protection of the area from use b,y wild deer and livestock can be considered to have begun. The northeast corner of the enclosed area slopes slightly to the north, but the remainder has an approximate 13 percent slope to the southwest. The average elevation of the area is 5,500 feet. Green Canyon opPne into Cache Valley about 2.5 miles northeast of the Utah State Agricultural College campus. The enclosure in this canyon, which was a temporary structure, vas completed December 23, 1950. It was located on the north side of the canyon, 2.0 miles from its mouth. The study area--roughly triangular in Shape--included 4.6 acres, con sisting of 2.4 acres of fairly level ground, and 2.2 acres of preci pitous southwest-facing slope with an aTerage slope of 62 percent, topped b.Y a rock cliff. The cliff served to hold in the deer on the northeast 12 side, and the west and south sides were fenced with nine-foot poultry netting hung on a one-quarter inch cable, as described by Smith and Gaufin (1950}. The elevation of the area varied from 5,44o feet to
5,685 feet above sea level. The Millville enclosure which was of the temporary type was built
1n the winter of 1951-52. It was located 1n an alluvial fan at the base of the Bear River mountains three-fourths of a mile south of Providence
Canyon. This paddock, \fhich was 1.82 acres in area, was located adjacent to, and on the west side of the Cache big game drift fence, which had been completed the previous winter. The enclosed area had thus had approximate~ one year of protection from big game use.
Livee toek grazing 1n the Card Canyon area has been confined to reportedly moderate use by sheep in early years, and recently, light use as a spring and fall horse pasture. Green Canyon was used very heavily as a spring-fall cattle range
1n earlier years, but since 1946 livestock use has been confined to light summer use b,y cattle.
The Millville foothills area has been used rather heavily as a spring range for cattle.
All three areas 1n wieh the experimental enclosures were located had been subjected to ove~use by deer as winter range. Green Canyon, howeTer, has been particularly overstocked with deer. In order to provide a description of the browse types of the study area, they were type mapped and aerial density and species composition of the woody species were estimated. This informa tion is presented in
Tables 2, J, and 4. The three stu~- areas are illustra ted in Figures 1, 2, and J. lJ
Table 2. Vegetation types, aerial density, and species composition of enclosed study area, Card Canyon, Utah
T.ype Juniper sagebrush Douglas fir % % Percent of area 86 14 Aerial vegetation density J4 54
Species Juniperus scopulorum J2 Pseudotsuga taxifolia 28 Compo s1 t 1 on Artemisia t. typica 18 Prunus virginiana 28 Prunue virginiana 15 Syn:phori carpos va.ocinoidee 1? Symphoricarpos va.ccinoidee 12 Artemisia t. typica ? Cercocarpus ledifoliue 6 Trace species totaling 6 includings Trace species totaling 1? including: Populus tremuloides Acer grandidentatum Juniperus utahensie Sambucus coerulea Rosa voodsii Rosa woodsii ., ;) Purshia tridentata Purshia tridentata ... Chrysothamnus Cercoearpue ledifoliue -1 viscidiflorus Eriogonum heracleoidee ~ I Eriogonum heracleoides Mahonia repens Cercocarpus montanus Hahonla repens Table J. Vegetation t,ypes, aerial densit.y, and species composition of enclosed study area. Green Canyon, Utah
Tn>e Juniper Rock and tallus Mapl~L ~ ~ ~ _ ~ebrush ~ --- ~ Percent of area JJ 2? 23 17 Aerial vegetation denai ty 16 5 65 8 ~ ~ Species Juniperus Juniperus Acer Artemesia utaheneis )0 utaheneis 2? grand1dentatum 90 t. t.ypiea 78 Compo s1 tion Cercoearpue Cercooarpus Trace species Cercooarpus led1fol1us 28 ledifolius 2.5 totaling 10 led1fo11us 10 1ncluding2 Acer grand1- Artemisia t. typ1ca 20 Cercoca.rpus den tatum 17 Cercooarpue montanua ? Chryeo thamnus montanus Artemisia t. nauseosus 7 Artemisia t. nova J typioa 11 Pbysoearpus Mahon1a repens 6 malvaceus Chrysothamnus Cercocarpus nauseoeus 1 montanue 5 Holodisus dumoaa 5 Mahonia rapens Sambucus coerulea 1 Trace species Physocarpus Artemisia totaling 9 malvaceus .5 t. ty:pioa including: Ceroocarpus montanus 5 Prunua virg1n1ana Mahonia repens .Amelanchier alnifolla Rolodiseus dumosa
jJ ~ 15
Table 4. Vegetation types, aerial density, and species composition of enclosed study area, foothill east of ~~llvil l e, Utah
T.ype Sagebrush-Bitterbrush
Percent of area 100 Aerial vegetation density 60
Species Artemisia t. typica 63 Purshia tridentata 25 Composition Cercocarpus ledifolius 8 Trace species totaling 4 including:
Amelanchier alnifolia Juniperus utahensie Juniperus scopulorum Chrysothamnue nauseosus Cercocarpus montanus Cercocarpus montanue X Oercoearpue ledifolius
The three enclosed areas studied represent browse types which are fairly typical of northern Utah winter deer range.
In the Card Canyon enclosure browse cover was of moderate density, the dominant species over most of the area being Rocky Mountain red cedar (Juniperus scopulorum), with big sagebrush (Artemisia tridentata subsp. tyYica), the species second in importance.
The area contained in the Green Canyon enclosure was classed in four different browse types: a juniper type in which Utah juniper
(Juniperus utahends) wa.s the dominant species. with curlleaf mountain mahogany (Cercocarpus ledifolius) subdomi~t; an area of rock and
tallus with ver,y little soil, supporting an extremely sparse browse
cover of similar species composition to the juniper type; a maple type in which bigtooth maple (Acer grandidentatum) occurred in an almost pure 16 standi and a type in which big sagebrush vas dominant. Considering the
Green Canyon enclosure as a w.hole, it contained a very sparse browse cover.
The enclosure on the foothill area east of Millville supported a dense shrub cover in vhieh big sagebrush and bitterbrush (Pursh1a tr1- dentata) were the dominant species.
Figure 1. Enclosure in Card Canyon. 1?
Figure 2. South-facing slope of Green Canyon showing location of enclosure. 18
• t I
I
Figure J. Foothill east of Millvill e showing location of enclosure. I 19
PROCEDURE
Experiment of .1.2jQ In the phase of the experiment conducted in 1950 two captive deer
were used. These lf8re a short three-year-old doe and a short tvo-year-
old buck, bot.'l of which ha.d been captured as fawns in northern Utah.
They were held in the Card Canyon enclosure for a 20-d.q period from
January Jl until February 20. at which time the more abundant forage
species were arbitrarily judged to be properly used.
It was attempted to determine the production of each browse species
available in the area. and its degree of utilization and consumption b,y
the deer during the 20-day period. In order to do this. the before-and
after sampling technique described by Cassady (1941) was applied.
Prior to introducing the deer to the area. a large number of plant
units of each browse species in the enclosure was collected. These con
sisted of twigs of current year's growth. They were collected from
several randomly located observations of each species on six north
south belt transects. six inches wide. which crossed the enclosed area
at 50-foot interTB.ls. A similar number of plant units of each species
was collected in the same manner following the removal of the deer from
the area. Utilization of the browse species waa determined from the
aTera.ge difference in air dry weight between the "before" unite and the
"after" units.
In order to determine the volume of forage produced in the area
and the amounts consumed by the deer, it was necessary to relate forage
weight to area. The normal ground cover of each species was estimated
on each belt transect before browsing, using a square foot frame divided 20 into three-inch squares. Only the forage considered available to deer at the time of sampling was measured. This was the vegetation which was not covered by snow and w.hich vas belov a height of five feet measured from the ground or from the snow crust, if that was belieTed strong enough to support the deer. By measuring the normal ground coTer of each "before~ observation sampled and counting the number of plant units per square foot of normal cover, the weight of forage produced on each transect and on the entire area vas determined. The calculations made to determine util- ization, production, and consumption of a browse species on a transect are demonstrated in Table 5.
Table 5. Method of calculating forage production, consumption, and utilization of a browse species on one transect by the •before-and-after• sampling technique, example--Prunus virginian&
a b c d e f Density Plant Average Fora&e Forage Utilization Time per units per plant available consumed e/d x 100 150 sq.:tt. sq.f't._, unit wt. ax b x c dl- d2 1 sq. ft. no. gms. gms. gms. % Before .54 8.14 J/8 4o 1.42 23.57 After .42 6.22
Four browse species which occurred sparsely within the enclosure, but of which no available forage occurred on the transects, were: bitter- brush, Utah juniper, curlleaf mountain mahogany, and birch lea! mountain mahogany (Cercoearpus montanus). In order to obtain data on utilization of these species, collections of plant units of each were made throughout the area, and the total normal cover of each was measured over the entire area. 21
As curlleaf mountain maho~ is believed to be a ver,y important winter deer browse, and the amount of forage of this species available in the area was Tery small, the large trees being high-lined, a fev branches were cut from trees outside the area and stuck upright in the
snow. The forage on these was sampled along with the curlleaf mountain mahogany whiCh was available naturally in the area. Experiments of 1221 As the results of the work done in 1950 indicated that adequate
sampling of the winter browse could not be obtained by the "before-and- after" sampling technique in an area as small and heterogenious in browse cover as that studied without removal of excessiTe amounts of forage, it was decided to use a somewhat different method in 1951. This was the "half-and-half" method deTeloped by A. D. Smith in experiments on the forage preferences of deer and sheep on summer range in northern
Utah (Smith and Gaufin, 1950), Thirty-three circular, 100-sq. ft.-plots were selected by restricted randomization in the enclosure in Green
Canyon, and J2 plots in that in Card Canyon; and these vera sampled prior to introducing the deer to each. On each plot a branch of each browse species occurring was t9€ged, and on&-half of its available forage was rsmoTed. This was done by clipping entire twigs of current year's
growth, matching each twig removed vi th a similar one which was left. The tagged branches were termed observations. When the deer were re-
moved from the enclosures the current year's growth remaining on each observation was clipped, The percent utilization was determined from the difference in air-dry weight between the "before" and "after" samples.
As a few browse species which were reported highly preferred by . deer occurred sparsely in the study areas and were present in few or 22 none of the plots, supplementary observa tions of these species ~ere tagged where they occurred near to the plots, and these ~ere sampled to determine utilization.
Production and consumption values were obtained as tallows: When
the "before" samples were taken, it was estimated what traction each
tagged observation was of the available current year's growth of the
species in the plot. Production of the specie~ on the ~lot was then calculated by multiplying the air-dry weight of the "before" sample b.Y
two, and multiplying this product by the reciprocal of the estimated
fraction. Apparent consumption of the forage by the deer was then cal culated on the basis of percent utilization and volume of forage avail able. The computations involved are demonstrated in Table 6.
In 1951 two deer--a short three-year-old doe and a short four-year
old buck~vere held in the Card Canyon enclosure for 21 days, January 6
to 2?. After the initial sampling of the Green Canyon area had been
completed, a section of the fence around this area was ~uehed over b,y
drifted snow, and wild deer entered about February 1. Before this vas
detected and the fence repaired, they occupied the area for an estimated
four deer days, based on tracks and forage use. February 10, the two
deer which had been used in the Card Canyon enclosure ~ere placed in
the Green Canyon enclosure, along with another short three-year-old
doe. The buck used in this experiment had badly overgrown hoofs, and
in its foraging activity moved about with difficulty. It became very
emaciated and finally was found dead in the Green Canyon enclosure on
March J, on which date the two does were removed. Eroe ri men t of .!.2.£
The 1952 trial in the Mil l ville enclosure was carried out by
W. E. Clayeomb. In this trial two mature does were held in the paddock Table 6. Method of calculating forage utilization, production, and consumption of a browse species by the 11half-and-ha.lf" sampling technique, example--.AEtemieia tridentata subsp. Wica
a b c d e f g
"Before" "After" Estimate Forage Percent Plot Plot sample sample of browsed utilization production consumption weight weight fraction1 from d X 100 a x 2 E: obs. (a - b) a c c
"21. gms. gma. gnlB. ;c gma. gma. 3.52 2.39 1/13 1.13 32.10 45.?6 14.69
1. Estimate of tagged observation as fraction of forage of species on entire plot.
N \..) 24 for 35 days, February 3 to ~8rch 9. The "half-and-half" sampling technique of measuring utilization was employed. Twenty-four plots five feet square were selected by a system of restricted randomization.
Observations of big sagebrush and bitterbrush, the two major browse species in the area, were sampled at random to determine utilization.
Utilization observations of every plant in the area of the other six lees abundant browse species were sampled. In order to determine the volume of forage of each species, re maining in the area after the deer were removed, all available current year's growth of big sagebrush and bitterbrush was clipped from the
plots and all available current year's growth of the other less abundant
species was clipped from the entire enclosure. All samples were re
duced to air-dry weight. The amount of forage available before brows
ing vas determined b,y dividing the weight of forage available after
grazing by the difference between 1 and the utilization expressed as a
decimal.
As each utilization estimate vas not associated with a plot pro
duction value, individual plot consumption estimates could not be
determined. Rather, consumption estimates for the whole area were
determined by species from the mean utilization and the mean production
values.
In each year of the study frequent visits were made to the en
closures While the deer were present, and observations on their feeding
activity were made, recording the number of minutes they spent in feed
ing on different browse plants, as was done by Dixon (1943).
In 1951 periodic utilization-class estimates of each browse species
in the paddocks were made by reconnaissance in order to study relative 25 species preference and to judge when utilization had ~rogressed to the point where the animale should be removed. In 1952 similar estimates were made based on periodic plot examination.
Test of half-and-half technique In order to evaluate the "half-and-half" sampling technique more fully than was possible by the actual browsing experiments. a sampling experiment was conducted in March 1951, near the Green Canyon enclosure.
Tvo samplers vorked together, meChanically selecting circular. 100-equare
foot-plots. At each plot each sampler selected and tagged as an obser
vation one branch of each browse species available in the plot. He in
dependently estimated what fraction the available forage on hie tagged
obserTation was of the total forage of that species on the plot. Re
then removed an estimated one-half of the available current year's
grovth from his observation, retaining this material. Each sampler then
proceeded to the observation sampled D.r the other and clipped an amount
of forage from it to simulate browsing. The forage remoTed i.n this
manner from each obserTation vas also retained. Each sampler then re
turned to hl s own observation and removed the current year's growth
remaining on the tagged branch. Following this, all available current
year's growth of each species on the plot was clipped. Plots were
sampled until 10 observations of each of Utah juniper. -eurlleaf mountain
mahogany, big sagebrush, and bigtooth maple had been sampled. All
samples were air-dried in pa~er sacks and weighed. The validity of the
11 half-and-half" technique was then tested by comparing the utilization,
production, and consumption estimates obtained by the sampling technique
with the actual values known from the weight of forage clipped. In
order to obtain an actual consumption value for each plot it was necessary 26 to assume that the browsing intensity over the plot would have been the same as it was on the t agged observation. The calculations used to determine the actual and estimated values are shown in Table ?. Table 7. ~lethod of calculating estimated and actual values of forage utilization, production, and con- sumption, in simulated brmising experiments for evaluating "half-and-half" technique, example-- Cercoc~ ledifoliue
a b c d e f g h Remainder Apparent Es t11!8. ted "Before" "After" Weight of of forage Estimate wt. loss percent Observer sample "Browsed" sample half left left on of by utilization 1 weight weight veight to browse plot fraction browsing ~100 a- c a gms. gms. gms. gms. gms. gms. % 1 16.12 7.06 8.18 15.24 87.00 1/4 7.94 49.3 2 9.30 5.68 2.74 8.42 87.00 2/11 6.56 70.5
i j k 1 m Actual Estimated Actual EstUla.ted Actual percent plot plot plot plot utilization production production consumption consumption b X 100 a x 2 a1 t d1 t e h..U i X k d f 100 100 t a2 t d2 1 . ------gms. gma. gms. f!)nl.-
46.3 129.0 136.08 63.60 63.00 67.5 102.3 136.08 72.12 91.85
1. Estimate of tagged Qbservation as fraction of forage of species on entire plot.
1\) --.] 28
RESULTS AND DISCUSSION
Sample~ Tables 8 to 11 show the coefficients of variation, number of tran- sects, plots, or observations sampled; and numbers required for adequate sampling of forage utilization, production, and consumption by the methods used.
As the number of plots or transects sampled for forage consumption is the same in each instance as the number sampled to estimate fol'a€e available, no columns for the former are included in the tables.
The number of transects in Table 8 and of observations in Tables 9, 10, and 11 are shown which would be required to estimate the mean percent utilization within 5 percent precision at the 95 percent proba- bility level. By 5 percent precision it is meant, for example, that if the estimated utilization were 20 percent, the actual utilization ex- pected would be between 15 percent and 25 percent.
The number of transects in Table 8 and of observations in Tables 9 and 10 are sho'*'ll which would be required to estimate the mean weight of forage of each species available per plot within a precision of 5 percent of the average total weight of available forage per plot of all species except juniper, at the 95 percent probability level. 1
In 1950 plant units were collected from all the plants of curl- leaf mountain mahogany, birch-leaf mountain mahogany, bitterbrueh, and aspen in the enclosure, these species being present in very limited
1. Juniper was excluded from these calculations because estimates of the species were not considered reliable {see Sampling results, page )8). Table 8. Coefficients of variation, sizes of samples taken, and sizes of samples required tor desired precieion,l Card Canyon enclosure, 1950
U ti~ization For~ !Vailable For!i!:e conewned Species c.v. No. trans. No. trans. c. v. No. trans. No. trans. c. v. No. trans. ( ~ ) sampled required ({ ) eamuled required <1) required Artemisia t. typica 129 6 164 119 6 113 200 2, 080 Prunus virginiana 144 6 78 113 6 260 305 2,JJ6 Symphoricarpos vao- cinoides (large twigs) 581 6 630 71 6 5 582 60 Symphoricarpoe vae- oinoides (small twigs) 489 6 582 62 6 1 1,269 30 Rosa woodeU 230 4 155 154 6 316 36.996 1, 717 Juniperus soopulorum 44 6 74 55 6 - 83 1. For desired precision in estimating utilization, an error of 5 percent was allowed; for production an error of 5 percent of total forage production per plot of all species except juniper was allowed; and for eonaumption an error of 5 percent of total consumption per plot of all epecies except juniper was allowed.
~ Table 9. Coefficients of variation, sizes of samples taken, and sizes of samples required for desired pre cision, I Card Canyon enclosure, 1951
UtiUzati~ For!6e available Fora.r:e consumed Species c. v. No. obs. No. obs. c.v. No. plots No.ploh c.v. No.plots {~) sampled reaulred <%> sampled required <%> required Prunus virginiana 56 17 96 148 32 204 192 5.894 Eriogonum hera- cleoidee 141 6 423 274 32 284 415 2,632 Symphoricarpoe vaccinoidee 120 14 136 139 32 82 158 62 Artemisia t. typica 278 14 457 207 32 6,8?0 62,848 1,916 Rosa woodsH 1?8 6 282 307 32 8 263 2 Juniperus ecopulorum 201 12 1.58 802 32 - 331 2 Purshia tridentata 16 11 25 2 Cercocarpus montanus lJ 5 13
Cerco~us ledi- follue 1 Acer grand1dentatnm2 1
1. For desired precision in estimating utilization, an error of 5 percent was allowed; for production an error of 5 percent of total forage production per plot of all species except juniper was allowed; and for consumption an error of 5 percent of total consumption par plot for all species except juniper was allowed. 2. As these species were ver.y scarce, ~very plant in the area was sampled. \.N 0 Table 10. Coefficients of variation, sizes of samples taken, and sizes of samples required f or desired preciaion,1 Green Csnron enclosure, 1951
Utilization For~e available For~ consumed Species c. v. No, obs, No, obs. c. v. No.plote No. plots c.v. No, olots ($) sampled required C%> sampled required ( ~ ) required Acer grandidentatum 133.7 11 57 181.6 33 371 421.5 4,192 Cercocarpus montanus 157.0 6 291 374.1 33 276 427.2 4,336 Artemisia t. t.ypica 552.5 9 98 309,0 33 1,554 444,0 1,387 Ch.ryaothamnus nauseo sus 711.1 4 32 522.7 33 1,485 789.4 1,212
Holodiaeus dumoaa 196.7 3 102 393.4 33 266 744.6 375 Artemhia t. nova 230.7 5 198 430.7 33 2 1,208.3 19 Juniperus utahensis 2o4,8 9 110 288.3 33 - 449.7 Prunus virginiana 84.2 3 34 Amelanchier alnifolla 58.4 J 68 Cercocarpua ledifolius )0.9 7 76
1. For desired precision in eatimating utilization, an error of 5 percent vas allowed; for production an error of 5 percent of total fora.ge production per plot of all species except j'W'liper waa allowed; and for consumption an error of 5 percent of total consumption per plot for all species except Juniper was allowed.
\,J..... Table 11. Coefficients of variation, sizes of samples taken, and sizes of samples required for desired pre cieion,l Millville enclosure, 1952
Percent ut111zAU2n . For!&e availablt Fo~e consumed Species c. v. No. obe. No. obs. c. v. No.plote No.plots & c.v. No. obs. &. plots {~l sampled reguired (~l sam:eled obs 1 reg. {~2 reguired 2 2 Artemisia t. typica 69.0 12 81 487.4 24 939.29.5 1,072.5 1,682,087,101 2 2 Purahia tridentata 30.6 12 20 306.2 24 7.564 .53.5.3 26,726 2 Cercocarpus ledifolius 23.1 15 86 325.7 • 16,.59-? 356.7 62,851 Cercooarpus ledi!olius 3 3 (broken tops) 2.5 2 176 318.4 • 1,)61 319.4 132
Cercooarpus ledifolius X 3 3 Cerooearpus montanus 9.0 7 6 191.6 • 369 211.0 277 3 Ceroocarpus montanus 20.2 10 17 206.4 • 8.[J 289.3 142 Juniperus u\anensis 319.4 8 167 Juniperus scopulorum 304.9 .5 7 . Amelanchier alnifolia 822.7 6 3.5 1. For desired precieion in estimating utilization, an error of .5 percent was allowed: for production an error of .5 percent of total forage production per plot of all species except juniper was allowed; and for consumption an error of 5 percent of total consumption per plot for all species except juniper was allowed. 2. Number of utilization observations and of 5-foot-square plots required when these are equal in number. 3. Number of utilization observations required when available forage is clipped from entire enclosure instead of plots only.
\..) • All available forage of these species ~rae clipped fro:n enclosed area. N JJ amounts. As utilization of the total of all plants of each of these species was estimated, no coefficients of Tariation or sample si~es were calculated, and these species are excluded from Table a. In subsequent experiments, when the half-and-half technique was used, aeparate ob-
serTations ~ere sampled on different plants of these species, and it was therefore possible to determine coefficients of variation and number of observations required to estimate utilization.
In 1950, in order to reduee variation, the plant units of snow-
berry were stratified in tvo size l'Blll;es, one of large twigs a!ld one of short, slender twigs of Tery light weight. These are shovn separ- ately in Table a. In order to calculate the sample size required to estimate the
mean utilization per plot for each year of the study, and also to cal- eulate sample size required to estimate production and consumption per plot for the sampling procedures followed in 1950 and 1951, the formula
applied was: n• where tis deriTed from Student's •t~ table, s2 is the variance, and (i-m) is the prescribed limit of error as indicated abOTe in each instance. In the 1952 experiment i:t1 the Millville enclosure, a large propor- tion of the utilization obaervations vere not associated with parti-
cular plots. Therefore, an estimate of the mean weight of fo~ avail-
able per plot before browsing was calculated by dividing the mean weight of forage available per plot after browsing by the difference between
one and the mean utilization expressed as a decimal. In order to de-
termine the variance of the mean production value, it vas necessary to consolidate the variance of the mean utilization and the variance of the )4 mean weights of forage availo.ble after brawling. This was done by the formula: • 82 • 2 c c where o. = 1- (mean forage utilization expressed as a decimal),
b- = mean forage available per plot after browsing. c = b/a = forage available per plot before browsing. A consolidated •t• value for mean forage available before browsing was calculated b.Y the formula:
s2 62 t - tl f - t2 = a b 82 f 8~ a b where t 1 = "t" value for mean utilization. and t 2 = •t• value for mean forage available after browsing. The mean weight of forage consumed per plot was estimated ey multi- p~ing the mean utilization expressed as a decimal by the mean forage production. The variance of the mean forage consumption and its •t• value were consolidated from those of the mean utilization and mean forage pro- duction in the same manner as was done for the variance of the mean fora&e production and its •t• value. The variances of mean production Md mean consumption obtained ey this method of anal.7als are much higher than would have been obtained had each utilization estimate been associated with a plot, so that separate production and consumption estimates could have been calculated for each plot.
In determining required sample size for desired precision in the
Millville enclosure, the number of observations and of plots for Table 12, Comparison of estimated and actual values of forage utilization, ~roduet1on, and consumption, simulated browsing experiment for testing "half-and-half" technique
Percent utilization For~e available For~e consum~tion r ~ t - % r Species n t % 1 r t - J 1 error error1 error
.¥' Cercooarpua ,. led1fol1us 10 .977*• .447 -0,72 .988•• 2,657* -21,04 .921•• 2,542• -20,21 Acer grandi- den~tum 10 .906.. .)61 -).58 .620 J,26 -).)2 .09) ,1)4 -1), ?1
Juniperus ut.ah- ensis 10 .86o•• .754 -21,99 ,752• ;.oo6• -25.72 .426 1.387 -71,12 Artemisia tri- dentata t. 10 ,672** 1,130 -8,21 ,877** 3,072• -27,65 .64Q• 1,481 -34,49
Total 40 _,_9_Q5_!•~--- - •9l0 __ ___ -5.1J ,865•• 3.558• -24.10 .631 .. 2,114* -41,16 r = correlation coefficient. t c Student's •t• value. 1, Percent error • 100 (estimate-actual value) actual value • Significant at the 5 percent probabilit.y level. •• Significant at the 1 percent probabi11~ level.
\....) ~ J? utilization estimates is shown to be satisfactory for the species tested except juniper. The correlation 1s highly significant for curllea.i' mountain mahogany, bigtooth maple, Utah juniper, and for the total of all species, big sagebrueh showing a significant correlation. The difference between actual and estimated values is not significant for any species or for the total of all species. The mean percent utili zation of Utah juniper was, however, underestimated b.r 21.99 percent.
This could be due to experimental error, in which case it would probably disappear w1 th an increase in sample size. !!owenr, 1 t ~ indicate an inherent error in the technique of sampling juniper.
The estimates of weight of forage available ahow a highly signi ficant correlation with the actual values for curlleaf mahogany, big sagebrush, and for the total of all species, a significant correlation
for Utah juniper, and a correlation approaching significance for bi~ tooth maple. Rowever, significant •t• values and large negative errore for curlleaf mountain mahogany, Utah juniper, big sa&ebrush, and for
the total of all species ind1.cate a consistent tendency to underestimate the fora&e production except in the case of maple. It would appear that there is a greater tendeney to underestimate forage available on plots where the production is high.
AnY errors in individual forage utilization and production eet~tes
are reflected in the consumption estimates since they are calculated from utilization and production estimates. Curlleaf mountain mahogany was the onl7 species showing a highly significant correlation between estimated and actual forage consumption. A highly significant •t• value and a negative error of 20.21 percent shoved that the consumption of
this species was underestimated consistently. Of the remaining three
species, only big aagebrueh showed a significant correlation. None J8 shoved significant differences, but in each the averago consumption was underestimated by a large amount. The relationship between esti mated and actual values of the consumption of these species was there
fore rather inconsistent. ~or the estimated total consumption of all species a highly significant correlation, significant "tN value, and large negative error indicated a negative bias in estimating con
sumption. Sampling results The mean percent utilization, weight of forage available, and
veight of for~ consumed of each browse species are shown w1 th con fidence limits, for each experiment in Tables lJ, 14, 15, and 16. The mean weights of available forage and forage consumed are the estimates for the entire enclosure& calculated from the means of plot estimates vi th confidence 11m1 ts. The apparent percent of each species in the total consumption of all species was caleulated from the mean consumption estimates. The junipers vere excluded from this calculation in each expericent, as due to the nature of the foliage, great difficulty vas experienced in con
sistently estimating the available forage, and this is believed to have caused excessive errors in the utilization estimates.
The confidence intervals of mean estimates obtained by either method used are, in almost every instance, so broad as to make it im possible to reach definite conclusions regarding the percent utilization, production, or consumption of forage of the species studied. '1here utilization vas uniformly heavy, reasonable precision was
obtained. However, for species the use of vhieh vas light and variable,
confidence interTale tended to be very wide. Table 1). Percent utilized, weight available, weight consumed, and percent of total consumption of browse species, from sampling data, Card Canyon, 19501
Forage Forage Forage Percent of Species utilized available consumption total coneumption2 if ~ ----~ ---~~-- gtl1s=- -- gms. f.
Oercocarpus ledifolius {broken tops) 99.8 6,280 6,264 49.2 Artemisia t. typica 24.8!;;.6 8,5)6!10,7)4 J ,426!7' 170 26.9 Prunus virginians.J 15.)!27.4 1),720!:16,254 2. :376!7. 620 18.7 Purshia tridentata 65.1 )54 2)1 1.8 Symphoricarpos vaccinoides (large twigs) -10.S:77.9 ),0)6:!: 2,256 19~1.224 1.6 Symphorlcarpos vaccinoides -12 • .3!74.9 1,884! 1,224 66!: 864 o.5
A Cercocarpus montanuaJ 61.2 124 76 o.6 4 PseudotsU8a taxifo1ia 49 • .3 106 53 o.4 Rosa woodsU -42.8!:156.4 11,118:27,174 18!9.894 0,1 4 Populus tremuloides 61.1 )6 18 0.1
Juniperus scopulorum 49.3!22.5 16),)62!94,814 88,104:!:76,896 1. Confidence 1nt~rva1s at 95 percent probab111t,y. 2. Juniperus eoopulorum excluded from thia calculation. ;. All shrubs o! these species vere sampled as they did not occur on transects. 4. Species occurred on one traneect on~. \...) \,() Table 14. Percent utilized, weight available, weight consumed, and percent of total consumption of browse species, from sampling data, Card Canyon, 19511
Percent Forage Forage Percent of Spec_ie_s______l1t_il_1.zeti ~va11ll}).._e______(3onsumption __ total eon11unmt~ % gJDS• gJnS~-----u·------J
Prunus virginiana 43.4!12.6 9.09?: 4,789 3,8oo±: 2,591 4o.7 Eriogonum herac1eo1des )6.6!54.0 5, 79'7! 5. 739 3,35Z: 5,026 35.9 s.rmPhoricarpoa vacc1noides 24.2!16.8 6,172± 3,088 1,358± 774 14.5
Purshia tr1dentata3 79.7 825 621 6.6 Rosa woodsH 23.5!44.1 882± 978 141! 134 1.5 Cercocarpus montanus3 71.2!11.3 . 62 49 .5 Artemisia t. typica 19.2!30.9 15,516!11,580 19! 4,287 .2 Cercocarpus ledifoliue 66.5 4 J .OJ Acer grandidentatumJ 58.6 4 J .OJ Juniperus ecopulorum -15.'t-2o.o 12,032±34, 294 -9.569:11,275
1. Confidence intervale at 95 percent probabi11~. 2. Juniperus scopulorum excluded from this calculation. 3. Species occurred on one plot only.
g Table 1.5. Percent utilization, forage available, forage consumed, and percent of total consumption of browse species, from sampling data, Green Canyon enclosure, 19.511
Percent Forage Forage Percent of 2 Species utilized:£------available------consumption total consumption(£- , gma • gms. ,
Cercocarpus montanus 27.~44.8 3.56"n 4.739 1,54J: 2,344 23.3 Acer grandidentatum 14.2!12. 7 8,496! 5,486 1,.539!: 2,306 23.3 Cercocarpus ledifolius3 70.6:20.1 1,242 1,120 16.9
Artemisia t. typica 4 • .5!19 .0 10' 219!11' 231 839:!: 1,326 12.7 Chrysothamnus nauseosus 2.0:!22 .4 5.911!10,983 761! 1,563 11 • .5 s,ymphoricarpoa vaccinoides3 3.5.3!51.1 552 261 3.9 Holodiacus dumosa 12. 9!62.9 3 ,326! 4, 6.52 260!: 689 3.9 Artemisia t. nova 1.5.2!43. 7 30 • .537!87 .484 240! 368 3.6 Prunus virginiana3 17. :?.!)6.1 lj.(jl 53 o.a Juniperus utahensis 12.a!20.2 4,91.5! .5.038 70,713±102,492
1. Confidence intervale at 9.5 percent probab111 ty. 2. Juniperus utahensia excluded from this calculation. 3. Species occurred on one plot on~. Additional shrubs sampled for utilization.
~ Table 16. Per~ent utilization, forage available, forage consumed, and percent of total consumption of browse species from sampling data, Millville enclosure, 19521
Percent Forage Forage Percent __ ·ecies utilized available consum}!tion total consumption2 Cl ~a. €Jill. % Artemisia t. typica 32.-r-14.3 61,971±130.552 20,226±94,005 58.9 Cercocarpus ledifolius 58.5! 7.5 8,;8o! 15,118 4,902!11,124 20.1 Cercocarpus ledifo11us (broken tops) 92."r-2l.O 411! 11,791 381!10,965 1.1 Purshia tridentata 36.4:t 7.1 12,076! 15.985 4,38.5± 9 .925 14.8 Cercocarpus ledifoliua X Cercocarpus montanus 68.o± 5.7 1,856! 3.296 1,262! 2,479 .J. 7 Cercocarpus montanus .so.&t 7.3 907! 1,344 459! 950 1.3 Juniperus utahensis 10. ~26.9 Juniperus scopulorum 2.2! 8.3 Amelanchier alnifolia -1.8±15.6
1. Confidence intervals at 95 percent probability. 2. Juniperus spp. and .Amelancbier alnif'olia excluded from this calculation.
~ l\) 43
The estimated weight of each browse species consumed per deer ~ was calculated from the sampling data from each experiment, and this information is shown in Table 17. For reasons explained elsewhere, it was not possible to account for forba, grasses, the junipers, and certain trace browse plants in these consumption estimates.
Table 17. Estimated weiP.ht of browse consumed per deer day from sampling datar
Card Card Green Speciee C&nyon Canyon Canyon J.tillrtlle 12~0 12~1 1221 1222 lbs. 1bs. lbs. lbs •
Cercocarpus 1edifo1iue • )4 tr • .04 .21 Artemisia t. typica • 18 tr. .OJ .59 Prunus virginiann .13 .21 tr.
Purshia tridentata .01 .OJ .15 Symphoricarpoe vacc1no1des .01 .07 .01 Cercocarpus montanus tr. tr. .os .01 Pseudotsuga tax1fol1a tr.
Rosa woods11 tr. .01 Populus tremulo1des tr.
Er1ogonum herac1eo1des .18 Acer grandidentatum tr. .os Chrysothamnus nauseosus .OJ Holodiscus dumosa .01
Artemisia t. nova tr.
Cercocarpus led1fo1ius X Cercocaruus montanus .04
Total ~zo -~ .22 1.00 1. Exclusive of Jun1J2;!!rus spp. grasses and torbs. 44
Comparison of sampling methods ~ Although these experiments were not designed to compare the before- , and-after and half-and-half sampling techniques, a few observations can be made regarding the relative merits of the two methods as found in this study.
At the intensities of sampling used by the two techniques, more forage was removed by the before-and-after technique, and the precision obtained was somewhat less than that obtained by the half-and-half method.
It might be that increased efficiene.y could be obtained from the before- and-after technique by altering the number of unite per ~ransect.
Similarly, if observations were grouped by the half-and-half technique, increased precision might result. As no records were kept of the time spent in sampling, it is not possible to compare the precisions obtain· able by the two techniques in relation to the labor expended.
Two methods were used in estimating forage production in the half- and-half' technique: (a) that used in 1951 of estimating forage weight on the plot relative to the weight of the observation: and (b) that used in 1952 when the forage available before browsing was estimated on the basis of percent utilization, and the forage remaining in the plot after browsing determined by clipping. A comparison of the accuracy of the two methods was precluded by the fact that in the 1952 experiment each utilization estimate was not associated with a plot, and as was pointed out earlier, this resulted in a much larger variance of the mean weight of forage available than would have been the case had it been possible to calculate forage production estimates for each plot, Also, only 24 plots five feet square were used in this season as compared to 32 and
33 circular plots of one hundred square feet used in the Card Canyon and
Green Canyon enclosures in 1951. As compared to the method of estimating 45 forage production on the basis of the before sample weight the method of
clipping all forage from the plots after browsing 1e much more time
consuming, and due to its detrimental effect on the browse plants, it
would be unsuitable for permanent enclosures.
In order to increase the precision of utilization estimates de
termined by the half-and-half technique. and also to increase the pre cision of forage production determinations, it would be neceaaar,r to increase the number of plots sampled. Those browse species found to be
low in preference might be eliminated from future experiments so that
more effort could be concentrated on adequately sampling the important
species. The aeeuraey of estimating utilization and production might be improved with practice in the field, checking estimates by weighing
clipped samples in the green condition. Utilization-class estimates The average utilization-class estimates made periodicallY in the
course of the experiments in 1951 and 1952 are shown in Tables 18, 19,
and 20. Under the system proposed b,y Clark (1944) forage use vas esti
mated to fall within one of five classes, each of which includes an in
terval of 20 percent utilization. In the present study, in order to allow for the greater dif!icult,y involved in estimating utilization accuratelY at the intermediate intensities, wider interTals were set for the utilization classes at the intermediate levels than at the low
or high intensities of use. These intervals are shown as a footnote
to each of the tables.
It is evident that bitterbrush, curlleaf mountain mahogany, birch leaf mountain mahogany, and hybrid mountain mahogany (Cercoearpus Table 18. Periodic average utilization-class eetimates. Card Canyon enclosure, period January 6 to January 27, 19.51
January January January January January January January January January Species 81 10 12 1~ lZ 12 22 24 26 Purshia tridentata 4 4 4 5 s s s 5 s Cercocarpua montanua 0 4 4 4 4 s 5 s s Cercooarpus 1edifolius 2 4 s s s 5 s 5 s
Acer grandidentatum 0 1 1 l 1 1 1 1 2
Prunus virginiana 1 1 2 2 2 3 3 3 3
Symphoricarpos vaccinoides 0 0 0 1 1 1 1 2 2
Rosa woodeU 0 0 1 1 1 1 1 2 2
Artemisia t. typica 1 1 1 1 2 2 2 2 2
Juniperus scopulorum 0 0 0 1 1 1 1 1 1
1. Utilization c1nssee: 0 = 0 percent. 1 => 0 percent to 10 percent. 2 => 10 percent to 30 percent. 3 : > 30 percent to 70 percent. 4 = > 70 percent to 90 percent • .5 => 90 percent to 100 percent. 8: Table 19. Perio~ic average uti1ization-c1aes estimates, Green Canyon enclosure, period February 10 to March J. 1951
February February February February February February J.larch Species . 101 14 17- ~. - u - -- - 21_ 24 28 J
Cercocarpus 1e~lfolius 2 J 4 5 5 5 5 Cercocarpus montanus 1 1 J 4 4 4 4 Artemisia t. typiea 1 1 1 1 1 1 1
Artemisia t. nova 0 1 1 1 1 1 1
Chr,ysothamnus naueeoeus 1 2 2 2 2 2 2
Acer grandidentatum 0 1 1 1 2 2 2
Juniperus utahensie 0 0 0 1 1 1 1
Holodiecua ~umosa 0 0 0 0 0 0 0
Prunus virginiana 0 1 1 2 2 J J Amelanchier alnifolla 0 0 0 2 2 2 2
1. Utilization claeeew: - 0 = 0 percent. 1 = ) 0 percent to 10 percent. 2 => 10 percent to JO percent. J => JO percent to 70 percent. • 4 => 70 pereent to 90 percent. 5 =) 90 percent to 100 percent. +:- """ Table 20. Periodic average utilization-class estimates, Millville enclosure, period February 3 to March 9, 1952
Febr1lal'y February February February February 7-farch Species .51 7 9 12 16 6
Cercocarpus ledifolius 1 1 1 1 1 2 Cercoca.rpue ledifolius X Cercocarpue montanus 1 1 2 2 3 3
Cercocarpus montanus 0 1 1 1 1 2
Purshia tridentata 1 1 1 1 1 2
Artemisia t. typica 0 0 1 1 1 2
Juniperus utahenais 0 0 0 0 1 1
Juniperus scopu1orum 0 0 0 0 0 0
Ame1anchier a1nifolia 0 0 1 1 1 1
1. Utilization classes: 0 = 0 percent. 1 =) 0 percent to 10 percent. 2 : ) 10 percent to 30 percent. 3 = ) JO percent to 70 percent. 4 => 70 percent to 90 percent. 5 = > 90 percent to 100 percent.
~ CD ledifolius X Cercoearpue montanus were the species which were browsed most heavily, and of which intense utilization became evident earliest in the browsing period. It can be concluded, therefore, that of the browse species present 1n the enclosures, these were most highly preferred by the deer.
Feeding minutes obserTations
The feeding minutes observa tions made in each year of the study are
summarized in Appendices 1 1 2, 3, and 4. The forage species are listed in descending order of total time the deer were observed feeding on them.
The total duration of observations 1n each experiment i s so limited that these data are of little value as an indication of relatiTe quantities of species consumed. However, considered with the sampling data and periodic utilization-class estimates they contribute to the total picture of deer browsing. Of note i s the important place of forbs and grasses in terms of the feeding time observed. As the grasses and forbs avail able during most of the winter were dead, dry material, difficult to define, readily destroyed by wind, and frequently covered by snow. and as the green grass available late in the season grew rapidly, it was not practical to estimate utilization of these forms by the methods employed.
The feeding observations, therefore, provided the only method by which their use could be noted.
Snow conditions
DeNio (1938), on the basis of data collected 1n Montana, Idaho,
Washington, and South Dakota, reported that deer and elk vill readily paw through 30 inches of snow to reach feed, but at greater depths they move to different range or else subsist on taller browse plants.
Sevy (1937) observed that deer in northern Utah were able to trail 50 through soft anov )0 inches deep on steep slopes, but on level ground, snow 18 inches deep caused them difficulty, and a light crust was especially troublesome.
The depth and condition of the snow accumulation was observed to have an important effect on the feeding activities of the deer during
this 8 tu.dy.
Snow accumulation measurements taken on the Spring Hollow snow
course at 7,000 feet elevation by the Soil Conservation Service provide
some guide for judging how nearly nonnal were the snow depths in the years of the study.
In 1950 the average depth on the snow course on February 1 was
10 inches greater than the average of the preceding 26 years for that date, and on March 1 1 t was two and one-half inches greater than
aver8l;e. At the beginning of the 1950 experiment on January )1, the
snow in the Card Canyon enclosure was about 20 inches deep, and had a
strong crust about fiTe inches below the surface. The crust supported
the deer and permitted them to move about without difficulty. However, it prevented them !rom using grass and forbs, except where the ground
became exposed due to thawing which began February 5.
In 1951 the monthly snow depth meaauremente on the Spring Hollow
course were about normal during the period of the browsing experiments
in Card Canyon and Green Canyon. There were fiTS inches less than
average on January 1, two inches greater than average on February 1,
and aTerage on March 1. The average snow depth in the Card Canyon en
closure at the beginning of the experiment on January 6 was about two
inches, and was increased to seven inches by a snowfall on January 8,
and to 10 inches by another snowfall on January 17. Up until that time, .51 the deer often were seen to take eriogonum under the snow which was still soft. They appeared to identify the flowering stalks b,y sight or touch and then probe down with their muzzles and paw away the snow with their forefeet to reaeh the leafy rosette• which th«r took with relish. Dry gra.ssee and forbs shoving above the snow often were ob served to be grazed and sometimes the deer pawed craters in the snow to reaeh these. After a heavy snowfall on January 19, which increased the snow depth to 18 inches, the use of eriogonum, graeses, and !orbs was greatly reduced, and after another fall of wet snow on January 22 increased the total depth to 27 lnchee, the deer confined their feeding to certain trails and areas adjacent to juniper trees where there was lees snow. After a thaw on January 2.5, a crust formed which vas not strong enoU&h to support the deer. They were then observed to have great difficult,y in moving about whenever th~ left the broken trails.
The snow depth in the Green Canyon enclosure during the period of the experiment varied between six and 10 inches on the level, and the steep southwest-facing slope remained free of snow through most of the period. Snow did not appear to inhibit movement or restrict the feed ing of the deer in this enclosure, as warm weather caused it to settle so that 1 t 1rm.s packed sufficiently to support a deer's weight. Through out this period, low-growing forms of vegetation were available on the slope and around the bases of junipers and maples, where the snow vas frequently melted off.
In 19.52 late 'Winter snowfall was considerably heavier than U8U81. furing the period in lfbich deer were held in the Millnlle enclosure the depth and nature of the snow accumulation entirely prevented them from utilizing lo~growing plants, although apparently it did not in hibit their movement greatly. The snow was abnormally deep and bore a 52 crust which would support the deer when they were put in the enclosure on February J. and on February 19 this was covered by another heavy snow fall. The snow remained unusually deep for that area until the deer were removed on March 9.
Carrying capacitl ~ study ~reas Doman and Rasmussen (1944) reported that good foothill browse range in the Intermo'Ul'ltain region in an avera&e growing season has a winter eapacit.y of one deer month per acre. As each of the three enclosures studied represented a somewhat different type of plant cover, the rate at which they were stocked and the effects of the rates of stocking on the deer and on the important browse plants are of significance. The time at which to remove the deer from each enclosure was arbi trarily decided on the basis of the apparent lntenel ty of uae of the brovse plants. In both 1950 and 1951 the deer were removed from the Card Canyon enclosure when the chokecherry was judged to be utilized about .50 percent. In deciding when to remove the deer from the Green Canyon and Millville enclosures, the intensity of use of all of the more abundant browse species vas considered.
The use of the Card Canyon enclosure in 19.50 vas 40 deer-days, or 19.3 deer-days per acre. In 1951 this area was used for 42 deer-days, or 20.3 deer-days per acre. No data on deer weight losses were obtained
in 19~0. Of the deer used 1n 19.51, the doe put in the Card Canyon enclosure was in fair cond1 tion and the buck was quite thin. They were weighed a.t the beginning and end of the 1951 experiment in the Card
Canyon enclosure and they were found to have lost nine and eight and one-half pounds, respectively, which is a. rate of approximately o.4 53 pounds per day during the 21-d.a,y period.
The Green Canyon study a rea was browsed for an estimated 66 deer days in 1951. This was 14.3 dee~s per acre. Ac~ual figures are not available because of use by wild deer and uncertainty as to the date of the death of the buck. The doe which had been. held in the Card
Canyon enclosure prior to placing it in the Green Canyon enclosure lost five pounds, or 0.24 pounds per day. A second doe taken from the feed ing corral 1n fair cond.i tion and put in the Green Canyon enclosure lost
5. 75 pounds, or 0.27 pounds per clay. The buck which was used 1n both enclosures and which died before the end of the Green Canyon experlmen t had continued to lose weight until it died.
In Card Canyon in both 1950 and 1951, and in Green Canyon in 1951, the intensi~ of use by wild deer of the browse plants in the area surrounding the enclosure were judged to be very similar, and at the time the deer left the winter range, to the intend ty of use in the enclosure.
In both the Card Canyon and Green Canyon enclosures, the three highly preferred browse species--curlleat mountain mahogany, birch- leaf mountain mahogany, and bit terbrush-were severely overbrowaed at the rates of stocld.ng of the experiment. This beeame most apparent in the spring of 1951 when ·branches of several plants of these apecies in the Card Canyon enclosure were in a dying condi Uon. .All of the bitter brush plant9 were severely hedi;ed, reducing their !ora&e produetivi~y.
In both enclosures most of the curlleaf mountain r:18hogany was severely hed€ed and in a poor state of vigor. It is apparent that if these species were to be maintained in a productive condition, the utilization intensity would have to be greatly reduced. 54
Rorm~ (19)4b) and Mcllulty" j l947) reported that the annual utili
zation of bi tterbrush should not exceed 60 percent of th~ ~th of the current---- year's twig growth if-- the plants are to retain v!gor and produce -seed. In terms of percent by weight this would be less than 60 percent as the terminal portions of the tvigs are lighter per un1 t length than
the basal portions. Table 18 Shows that after f our deer-day's use of
the Card Canyon enclosure, the utilization by weight of bitterbrush vae
estimated to be in the 70 to 90 percent class. Similarly, in the Green
~on enclosure after 16 deer-~•s use, the utilization of curlleaf
mountain mahogany was estimated to be between 35 and 70 percent; and after 25 deer days the utilization of birch-lea! mountain mahogany vas estimated to have reached the same utilization-class (see Table 19).
It is evident, therefore, that if bro~e use w.as to be regulated to
maintain these highly preferred species in a vigorous cond1 t1on, the
rates of stocking would have to be much lighter than those perm! tted
in the experiments.
The use of the Millville enclosure in 1953 was 70 deer-days, or
38.5 deer-~a per acre. The two does held in this enclosure were tn poor condition at the beginning of the experiment and lost 11.5 and
17.0 pounds, or o.; pounds per dey and 0.5 pounds per ~. respectively,
during the 3~ period. The greater abundance of browse and the
greater percentage of bitterbrush and eurlleaf mountain mahogany in the
species composition made this a much more favorable type of winter deer
range than either of the other enclosures. As this area had been pro-
tected from deer use by the big-game fence during the winter of 1950-
1951, the browse plante were in a more productive condition than those
in the other enclosures. The utilization determ1nat1ons made at the
end of this experiment 1nd1eate that the utilization of bi tterbrueh 55 was moderate, but that the use of curllea.f and hybrid mountain mahogany was heavy and probably excessive (see Table 16). To maintain the latter three species 1n a vigorous condition would probably require a lighter rate of stoeldng than that which was permitted, although the reduction necessary would be much less than that required in the two other enclosures where the preferred browse was present 1n only trace amounts.
If further studies are carried out on the relationship of the stocking of deer to the utilization of browse on the winter range, lt is suggested that consideration be given to carrying out same of the experiments on the open range, sampling the vegetation on plots in order to estimate forage utilization, and esttmBting the etocking of deer by pellet group counts on the same or larger plots. In encloeure experiments where deer used have been fed in captivity for long periods it would seem possible that they might exhibit someWhat different feed ing behavior and food preferences than normal for wild deer. This factor could be excluded by carrying out the studies on the open range, and the expense of erecting enclosures could be eliminated. SUMMARY
1. A study was conducted in 1950, 1951, and 1952 to obtain infor mation concerning relative palatability of winter browse species to mule deer in northern Utah, and carrying capacity of different types of winter range. A test of the accuracy of the half-and-half sampling teclmique as a means of estimating browse utilization, production, and consumption was also conducted. 2. Captive deer were held for short winter browsing periods in
three Blllall enclosures which represented different tnes of deer winter
range, located near Logan, Utah. J. The utilization, production, and consumption of forage of each browse species in the enclosures were estimated by vegetation sampling.
The before-and-after technique was employed 1n 1950 to sample an en
closure 1n Card Canyon. The half-and-half technique was used to sample
the enclosures in Card Canyon and Green Canyon in 1951, and one near
Millville in 1952. 4. The intensity ot sampling in each enclosure was found inadequate for estimating utilization. production, and consumption of the browse species with the precision desired. The sample size required to estimate utilization varied greatly, but was largest tor species of light and variable intensities _of utilization, and smallest for species which were
uniformly heavily browsed. The sample sizes required to estimate pro duction and consumption with the precision desired varied greatly, and
in many eases were so large as to be prohibitive. 57 5. A simula ted browsing experiment was conducted to determine how accura tely utilization, production, and consumption of four browse species could be estimated by the half-and-half technique. Accurate estimates of utilization were obtained for species tested except juniper, but the plot production estimates were consietently low. The consumption estimatetl, since they are calculated from utilization and production values , were likewise underestimated.
6. At the intensities of sampling used it was found that equal or greater precision in estimating utiliza tion could be obtained with less removal of forage in sampling by the half-and-half technique as compared to the before-and-after method.
7. The depth and condition of the snow accumulation was found to have an important effect on the feeding activities of the deer.
8. The species which were browsed mo!t heavily and of which in tense utilization became evident earliest in the browsing periods were: bitterbrush. curlleaf mountain mahogany, birch-leaf mountnin mahogany, and hybrid mountain mahogany. 9. The rates of stocking permitted in the enclosures varied be tween 14.3 and 38.5 deer-days per acre. These were believed too heavy to maintain the more preferred browse species in a vigorous condition.
10. It is suggested that in future studies of the relationship of the rate of stocking of deer to the intensity of browse utilization, fewer species be studied so that they can be sampled more intensively.
It is also suggested that in studies of this kind, utilization might be estimated on ' plots on the open range, and the r a te of stocking of deer determined by pellet group counts on the same or larger plots. 58
LITERATURE CITED
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Stoddart, Lawrence A., and Arthur D. Smith. 194). Range Managements. New York: McGraw-Hill Book Co,, Inc. 547 pp. Appendix 1. Feeding minutes observations, Card Canyon enc1o~re, period January 3 to February 20. 1950
February February February February February Species 1 2 11 16 18 Total Forbs and grass 46 75 44.5 45 210 Cercoearpus ledifoliua 29 47 2 12 90 Juniperus acopulorum 16 1.5 7 25 Prunus vi rginia.na J 10 2 2 18
Paeudotsuga taxi!olia 7 2 2 11 Artemisia t. typica J 2 J 8 Eriogonum herac1o1des 6 6
Acer grandidentatum 2 1 2 5 Cercocarpus monta.nus 5 5 Mahonia repens J J
Rosa woodsH 1 1 .5 2 Symphoricarpos vaccinoides 1 .5 .5 2 Purahia tridentata 1 1
'l...... "' Appepdix 2. Feeding minutes observations, Card Canyon enclosure, period January 6 to Jan~ry 27, 1951
January January January January January January January Species 8 10 12 15 17 22 24 Total
Forbs and grasses 20 12 9 54 7 6 109 Eriogonum heraeleoides J 1 23 39 8 74 Artemisia t. typiea 2 4 12 6 5 15 44 Prunus vlrginlana 2 2 4 10 10 28
Juniperus scopulorum 1 4 2) 28
~phoriearpos vaeoinoidee 5 7 3 15 Cercocarpus 1edifo11us 1 14 15
Purshia tridentata 8 4 12
Aeer grandidentatum 8 1 9 Rosa woods11 1 2 4 7 Mahonia repens 1 1
0\ N .,A .· Appendix J. Feeding minutes observations, Green Canyon enclosure, period February 10 to March J, 1951
February February February February Species 14 17 21 24 Total
Acer grandidentatum 8 2J 37 12 80
Cereocarpus 1ed1fo1ius 48 2 5 5 60 Mahonia repens 2 11 12 25
Forbs and grasses 5 7 7 19
Cercocarpue montanus 1 2 J
Petrophytum caespitoeum J 3 Juniperus utahensis 1 1
Artemisia t. typica 1 1
Chrysothamnus nauseosus 1 1
Artemisia t. nova 1 1
0'> w Appendix 4, Feeding minutes observations, Millville enclosure, period February J to March 9. 1952
Februa.a 2J March 2 Species Deer No, 1 llo, 2 llo, 1 No, 2 Total
Purshia tridentata 166 1)8 108 97 511 Cercocarpue ledifoliue 6J 120 20 28 2)1
Artemisia t, t,ypica J 21 9 28 62 Cercoearpus montanue 4 0 10 10 25 Cercocarpue 1edifol1us X Cercocarpus montanue 14 J 17 Juniperus utahensis 4 5 10
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