Genetic Resistance in Douglas.. fir to Damage by Snowshoe Hare and Black..tailed Deer

EDWARD J. DIMOCK II ROY R. SILEN VIRGIL E. ALLEN

Abstract. Genotype of Douglas-fir significantly affected feeding selection for foliage by both snowshoe hare and black-tailed deer in pen tests with captive animals. Nine clones were rated independently for each animal species. Genotypes preferred by deer and hare ranged up to 64 and 178 percent more attractive, respectively, than those least preferred. Order and magnitude of damage resistance in pen tests, as predicted for full-sib F, prog­ enies based on preference shown among clones, closely conformed to resistance traits .. indicated for parents. In one 4-family test, captive deer selected between resistant and susceptible families with feeding incidence levels of 41 and 78 percent, respectively, at the point of maximum difference between extremes. In another 4-family test, captive hare also showed comparable selection of 35 and 82 percent between extremes. Resis­ tance to wild hare, in a 4-family field test with seedlings, also conformed closely to that predicted from preferences established in clonal pen tests. Damage incidence levels ranged from 56 to 86 percent for most resistant and susceptible families, respectively, after one winter's exposure to severe hare clipping. A later 4-family trial with seedlings exposed to wild hare in the field established close agreement among related materials in clonal pen tests, family pen tests, and family field tests. Differences were highly signifi­ cant with the most resistant family damaged 37.5 percent and the most susceptible 62.5 percent after one winter. In this test, moreover, significant damage resistance was shown by 2 families during a second winter of exposure. Genetic analysis suggests that resis­ tance to animals based on nonpreference is strongly inherited and chiefly additive. forest Sci. 22:106-121.

Additional lcey words. Animal damage control, heritability, Lepus americanus, Odocoi­ leus hemionus columbianus, Pseudotsuga menziesii, seedling survival.

NATURAL RESISTANCE in trees to damage (Squillace and Silen 1962); and black-tailed by animals remains essentially unrecognized jackrabbits (Lepus californicus melanotis) and unexploited. Within-species variations in Nebraska (Read 1971). in such damage are not extensively docu­ Douglas-fir (Pseudotsuga menziesii) is mented and have usually been noted as in­ an obvious candidate for scrutiny. A spe­ cidental traits in tree provenance studies. cies of relatively high susceptibility to ani­ Among important western conifers, only mal damage (Moore 1940), Douglas-fir in ponderosa pine (Pinus ponderosa) has been clearly shown to elicit variable foraging re­ The authors are, respectively, principal silvicul­ sponses by herbivores. Documented obser­ turist, Pacific Northwest Forest and Range Ex­ vations concerning this species include: periment Station, USDA Forest Service, Cor­ mule deer (Odocoileus hemionus hemionus) vallis, Oreg.; principal plant geneticist, Pacific in South Dakota (Bates 1927; Leopold Northwest Forest and Range Experiment Station, USDA Forest Service, Corvallis, Oreg.; and 1933, p. 273); mule deer, snowshoe hare forestry technician, Olympic National Forest, (Lepus americanus), and porcupine (Erethi­ USDA Forest Service, Shelton, Wash. Manu­ zon dorsatum) in Oregon and Washington script received March 10, 1975.

106 I Forest Science young plantations frequently needs protec­ snowshoe hare was 0.4 hectare ( 1 acre) tion. Genetic resistance in the form of non­ in area and, at various times during the preference might prove a useful adjunct to course of our studies, held 7 to 12 ani­ traditional methods of damage control. De­ mals of both sexes. A 1-hectare (2.5-acre) termination of possible benefits, however, portion of a 4-hectare ( 10-acre) enclosure must await demonstration that resistance holding about 25 animals was used for test­ traits not only exist but also affect damage ing cuttings on deer. Mixed-sex groups of incidence by practical amounts. 5 to 8 animals were randomly chosen for Preliminary studies by Dimock (1971) individual tests, and numbers were held suggested that black-tailed deer (Odocoi­ constant during each trial. Hare and deer leus hemionus columbianus) would discrim­ moved freely within their respective enclo­ inate as much as 2 : 1 between local races sures and at all times had access to cover, of Douglas-fir, but almost entirely because a maintenance diet, and some natural for­ of differences in seedling size. With this age. Preference testing with captive ani­ lead, we began further trials aimed at two mals followed general procedures described animals considered serious obstacles to re­ by Cardinell and Hayne (194 7) and Hil­ _ .. forestation in the Pacific Northwest-snow­ dreth and Brown (1955), with specific shoe hare and black-tailed deer. methods of design and analysis outlined by The experimental approach was sequen­ Dodge and others (1967) and modified by tial. In a succession of interrelated studies, Dimock ( 1971 ) . we sought answers to the following ques­ Our selection of clones for parent pen tions regarding Douglas-fir: (1) Do geno­ tests was both limited and arbitrary, and typic differences in foliage affect feeding necessarily reflects only part of the varia­ selection by deer and hare; and, if so, how tion likely in a natural gene pool. The consistently and to what degree? (2) Are Olympic National Forest's Dennie Ahl resistance traits due to nonpreference for Seed Orchard near Shelton, Washington, foliage transmittable through tree breeding; provided a source of clones that had been and, if so, how predictably and to what grafted from superior phenotypes growing extent? (3) Can nonpreference be exploited at middle elevations wtihin one township to give practical and predictable amounts on the northwestern part of Washington's of animal resistance to seedlings in the Olympic Peninsula. Since clones were not field? Answers to the first question were equally represented in the seed orchard, the obtained in 1967 and 1968 with foliage sole criterion for selection was availabil­ materials from grafted clones tested on cap­ ity. We therefore concentrated on clones tive deer and hare. Insights from this ex­ with best representation and confined selec­ perimental series led to similar preference tion to larger ramets about 5 to 8 meters trials on captive animals in 1970 with fo­ (16-26 feet) tall. Cuttings were chosen for liage from selected progeny of the clonal morphological similarity both within and parents previously tested. Finally, we prop­ between clones, and about ten 30-centi­ agated seedlings from the same parents for meter cuttings were taken from the lower testing on free-ranging hare in the field. crown of each selected ramet. To mini­ Two separate trials were initiated-the first mize possible confounding due to genotype­ in 1970 and the second in 1972-and each microsite interactions, the same part of the was monitored for a 2-year period. orchard was used to sample all clones used in any particular test. Also, insofar as pos­ Parent Pen Tests sible, all cuttings were collected and subse­ Procedures. Preference tests with cuttings quently tested during cool, rainy winter from 9 Douglas-fir clones were conducted months to minimize reductions in palat­ on captive snowshoe hare and black-tailed ability through desiccation. Normally, time deer in large outdoor pens maintained by between collection and test installation dtd the U.S. Fish and Wildlife Service at Olym­ not exceed 24 hours. pia, Washington. The enclosure containing Heavy concentration of deer and hare in

volume 22, number 2, 1976 I 107 DAYS UNTIL BROWSED DAYS UNTIL CLIPPED 8

3 ~DEER 7 A ~HARE 6

2

.3

2

o--­

FIGURE 1. Mean time required for incidence of feeding by captive animals on Douglas-fir cuttings from 5 clones tested separately on deer and hare. (Browsing represents combined selection by 5 deer; clip­ ping represents combined selection by 8 hare. Each bar is the mean of 100 observations. Within each test, means not superposed by a common letter differ significantly at p < 0.05.) restricted areas provided extreme feeding blocks. Cuttings were individually random­ pressure and rapid testing. Cuttings were ized at a 0.9- by 0.9-meter (3- by 3-foot) offered to test animals simply by tamping spacing to assure that item-by-item discrim­ them into prepared spots so that each cut­ ination on the part of test animals would ting simulated a live seedling. As small be responsible for any observed differences dtfferences in seedling size have been pre­ among clones. Two measures were used viously shown to influence feeding selection to evaluate relative preference: ( 1 ) mean by deer (Dimock 1971 ), all cuttings were exposure in days required for all cuttings presented to both deer and hare at a con­ within a clone. to be clipped or browsed stant 25-centimeter (10-inch) height. Cut­ and (2) where applicable, mean residual tings were checked daily for evidence of height of cuttings within each clone after feeding, and the day of earliest hare clip­ 1 week's exposure. Analysis of variance, ping or deer browsing was noted for each. supplemented by the "Q" method, was Examinations in each test continued until used to compare individual clonal means, all cuttings had been fed upon--or for pe­ and linear correlation analysis to compare riods varying from 1 to 4 weeks. clonal means in duplicate tests (Snedecor A randomized block design was used in and Cochran 1967). Results were consid­ all pen tests. Each trial contained 5 clones ered significant at p < 0.05; highly signifi­ with 10 cuttings per clone replicated in 10 cant at p < 0.01.

108 I Forest Science DAYS UNTIL BROWSED DAYS UNTIL CLIPPED 8 5 w DEER_ 7 ll ~HARE 6 - 4

5

4

'L

2

FIGURE 2. Mean time required for incidence of feeding by captive animals on Douglas-fir cuttings from 5 clones tested separately on deer and hare. (Browsing represents combined selection by 6 deer; clip­ ping represents combined selection by 7 hare. Each bar is the mean of 100 observations. Within each test, means not superposed by a common letter differ significantly at p < 0.05.)

A series of 6 winter-season tests were tests (Fig. 1). Significant clonal preferences used to evaluate the 9 clones upon which were demonstrated by each species of test subsequent work was based. Initially, we animal (F = 5.59 and 3.33 for deer and conducted 2 simultaneous tests of the same hare, respectively, with 4 and 36 df). 5 clones (8, 10, 13, 15, and 17) on deer Clone 13 was consistently least preferred and hare in early 1967. Again including by each animal--differing significantly from clone 13 as a common standard, we added all other clones in the case of deer, and 4 different clones ( 1, 19, 22, and 23) in a from clones 10 and 15 in the case of hare. similar pair of simultaneous tests conducted A reasonably consistent order of prefer­ 1 month later. Finally, to confirm differ­ ence among all five clones was also shown ences observed in the latter 2 tests, we re­ by both deer and hare, with only clone 15 peated them both with the same 5 clones ranking noticeably out of line. In view of (1, 13, 19, 22, and 23), but with different the close experimental control maintained ramets and different groups of deer and in testing, genotypic variation seemed the hare, in the winter of 1968. most likely explanation for the differences observed. Results and Discussion. For comparative In the second pair of 5-clone tests in purposes, results for deer and hare are 1967 (Fig. 2), clonal preferences of obvi­ shown together for the first pair of 5-clone ously high significance were again shown

volume 22, number 2, 1976 I 109 196 7 1968 DAYS UNTIL BROWSED DAYS UNTIL BROWSED

~ 1967 A

6 -­ 3

4 - 2

2­ --1

1 3 22 23 19 CLONE

FIGURE 3. Mean time required for incidence of browsing by captive deer on Douglas-fir cuttings from 5 clones tested separately in each of two successive years. (The 1967 test represents combined selec­ tion by 6 deer; the 1968 test represents combined selection by 8 deer. Each bar is the mean of 100 observations. Within each test, means not superposed by a common letter differ significantly at p < 0.05.) by both test animals (F = 32.90 and 32.22 year earlier (Fig. 3). The correlation be­ for deer and hare, respectively, with 4 and tween both years' preference rankings for 36 df). Of the 10 possible paired compari­ all five clones was highly significant ( r = sons between clonal means in each case, 6 0.98 with 3 df). Though some sensitivity were significant for deer and 7 for hare. of the 1968 comparison was lost because However, though clone 13 was again least of heavy feeding pressure (F = 7.23 with preferred by deer, three others (1, 22, and 4 and 36 df), clone 13 significantly dif­ 23) were even less preferred by hare. Only fered from all other clones as it had in one clone in each trial differed significantly 1967. from all others-clone 13 with deer and Results of the 5-clone test repeated on clone 22 with hare. Barring the inconsis­ hare in 1968 were also completely consis­ tency of clone 13's preference ranking with tent with 1967 data. Because of difficulties each animal species, the remaining 4 clones in anticipating and subsequently regulating ranked identically for deer and hare. animal feeding pressure, much sensitivity of Though the 1968 test with deer pro­ comparison by the measure previously used ceeded more rapidly than its counterpart (mean days of exposure) was lost due to in 1967, due to the vagaries of animal feed­ an excessively rapid test. In fact, none of ing habits or to other variables affecting the clonal means compared in that way clone palatability, deer discriminated among differed significantly. An alternative mea­ clones in an order identical to that of a sure, residual height of each cutting after

11 0 I Forest Science HEIGHT AFTER ONE WEEK (em) 2or------. A ~ 1967

~ 1968 16 -

12 -

8 -

4 -

0 19

FIGURE 4. Mean residual heights of 25-centimeter Douglas-fir cuttings from 5 clones exposed for 1 week in separate tests to captive hare in each of two successive years. (The 1967 test represents com­ bined selection by 7 hare; the 1968 test represents combined selection by 12 hare. Each bar is the mean of 100 observations. Within each test, means not superposed by a common letter differ sig­ nificantly at p < 0.05.)

1 week's exposure to hare clipping, gave of Douglas-fir consistently influenced am­ more readily interpretable results (Fig. 4). mal feeding preference. Up to this point, It not only reflected a tendency for hare however, we had no evidence regarding ca­ to clip preferred clones repeatedly but also pacity of the underlying factors involved to provided a highly significant comparison combine through breeding and be passed (F = 51.62 and 45.06 for 1967 and 1968 on to succeeding generations. We there­ tests, respectively, with 4 and 36 df). Of fore proceeded to seek evidence of inher­ the 10 possible paired comparisons between ited resistance stemming from nonprefer­ clonal means in each year, 7 differed sig­ ence among F1 progeny. nificantly in 1967 and 8 in 1968. Of perhaps greater importance are the close Procedures. Trees in the Dennie Ahl Seed agreements between both years in order Orchard within families averaged about 5 and relative magnitude of preference (r = years old and 2 meters (7 ft) tall in 1970, 0.92; p < 0.05 with 3 df). The high pref­ and were thus able to provide limited erence expressed for clone 19 in both trials amounts of foliage as a source of cuttings is also clearly evident. for use in pen tests for comparing selected families. Six of the clones previously tested Progeny Pen Tests (1, 8, 10, 13, 19, and 22) were represented Data from the preceding tests both estab­ as both parents (female x male) in each of lish and confirm that variations in genotype seven families (8 X 1, 10 X 1, 10 X 8, 13

volume 22, number 2, 1976 I 111 X 22, 19 X 1, 19 X 8, and 22 X 1). Ac­ susceptibility. Hence, in the 4-family trial cordingly, we conducted pen tests in early conducted on penned deer in 1970, the 1970 with 4 families (8 X 1, 10 x 1, 13 following resistance levels were forecast for X 22, and 19 X 1 ) on deer and with 4 fam­ the progeny under test: ilies (10 x 8, 13 x 22, 19 X 8, and 22 x 1) on hare. Predicted Family Assuming that previously established Parental traits resistance preferences for different clones might be 13 X 22 Resistant X ranked to predict approximate damage re­ Resistant Resistant sistance in their progeny, we combined all 8 X 1 Intermediate X Susceptible Intermediate 9 clones used in preceding trials into a 10 X 1 Susceptible X composite preference array based on 1967 Susceptible Susceptible data (Figs. 1 and 2). Clone 13 served as 19 X 1 Susceptible X the common standard for combining data Susceptible Susceptible by direct proportion for each test animal separately. Then, again by direct propor­ Similarly, in the 4-family trial conducted tion, these data were converted to mean on penned hare during the same period, the exposure preference index (MEPI) values following resistance levels were forecast: by further adjusting so that the clones most Predicted resistant to each test animal ( 13 with deer; Family Parental traits resistance 22 with hare) equaled 100. Relative mag­ nitude of differences between clones, as 22 X 1 Resistant X demonstrated previously, thus remains un­ Resistant Resistant 13 X 22 Intermediate X changed. MEPI values were then divided Resistant Intermediate into three subjective levels of estimated re­ 19 X 8 Susceptible X sistance based on relative position in the Intermediate Susceptible array: 10 X 8 Susceptible X Intermediate Susceptible Deer Hare Estimated MEPI MEPI resistance Testing procedures were similar to those Clone value Clone value level used in parent pen tests and we employed 13 100 22 the same facilities. Study design with mixed­ 100 22 127 23 127 l Resistant sex groups of deer ( 6 animals) and hare 15 130 141 (10 animals) was the same in each test: 4 families with 10 cuttings per family repli­ 17 135 13 179! cated in 10 blocks. From 5 to 10 lower­ 8 135 17 204 . Intermediate 23 147 8 238 crown cuttings were taken per tree within each cross until 100 cuttings had been ac­ 1 149 19 250 cumulated per family. Randomized individ­ 10 152 15 256 l Susceptible ually at a 0.9- by 0.9-meter (3- by 3-foot) 19 164 10 278 spacing, cuttings were tamped into place as As ranked above for the 6 parents (under­ before at a constant 25-cm height and ex­ lined) represented in the 4-family tests de­ amined daily for first incidence of feeding scribed previously, common levels of resis­ on main stems. Observations were contin­ tance against both target animals appear ued until all cuttings had been browsed or associated with four clones (8, 10, 19, and clipped. Percent differences in feeding se­ 22) ; differing levels for deer and hare with lection among families were evaluated daily two (1 and 13 ) . by analysis of variance to bracket that Predictions for full-sib families were portion of the test period in which signifi­ based on the premise that male and female cant differences occurred. Percentages were parents were equally capable of transmit­ analyzed in raw form and as transformed ting traits leading to damage resistance or to angles by arc sine. Since transformed

112 I Forest Science BROWSING IN PERCENT 100 ..... -· -· -· :;;__-:,_-:....-._-.::::::_-=-;;:::::-..:.;;~ ~· /__ ... ,.r··-··- .. --./

// ~...../· ,.,.,. ;· 80 ~· / . II I ...... // I ./ /i I,1--.._/../ i 1: i -·-·-· 10 X 1 ...... I:1/ 60 -19X1 i ~· I I --- 8 X 1 i I: i ,.,.f - ..- 13 X 22 / __ ,. : / / .J .,.""·' // /' 40 / / __ _...... · I / / !! ,-- / , .. -/ _;,I I I ' 20 , ....·I ..--· ...·::.--' / ;:r I / ·: I I I I I / , ..- ...... J I II II 0._.__._._.._._.__._.~./' __._.__._._.__._.__._._.._._.__._.__._._. 0 5 10 15 20 25 DAYS OF EXPOSURE

FIGURE 5. Cumulative incidence of browsing by 6 captive deer on main stems of Douglas-fir cuttings from 4 full-sib families. (Each family comprises 100 cuttings. Differences exceeding bar lengths are significant at p < 0.05.) and untransformed percentages gave SIIDl­ (Fig. 6). In this case, discrimination among lar results, raw percentages are presented families was not apparent until the 5th day for clarity. when preference for two families suddenly became significant and remained so through Results and Discussion. The 4-family trial the 11th day. Highly significant differences on penned deer required 26 days for all were clearly evident during this portion of cuttings to be browsed (Fig. 5). Discrimi­ the trial and reached a maximum separa­ nation among families began immediately tion of 35 and 82 percent between family and differences were significant from the extremes at 1 week. Although agreement 5th through the 18th day, or for about one between test results and prediction was less half of the test period. Moreover, results than perfect, it was nevertheless quite close. agreed closely with our predictions. Family At midtest, those families predicted to be 13 X 22 was most resistant of the four; most susceptible (19 X 8 and 10 X 8) were 10 X 1 and 19 X 1 were most susceptible; highly preferred over those rated interme­ and 8 X 1 fell into an intermediate position. From test beginning, incidence of browsing diate (13 x 22) and resistant ( 22 x 1 ) . on the most susceptible family (lOx 1) was The above results appear notable for approximately twice that on the most resis­ several reasons. Tests with progeny re­ tant (13 X 22), and it remained so on a vealed differences in animal feeding prefer­ cumulative basis throughout the lOth day. ence that were sharply defined and similar Penned hare clipped all cuttings from in magnitude to those previously shown the 4 families exposed to them in 15 days with parents. The differences seemed un­

volume 22, number 2, 1976 I 113 CLIPPING IN PERCENT 100 .-· -· -· -·-_.-A--.._----­ ~·""""'·-· ~· ..... ""'· /"" ~· .... ~· . / I I / / / 80 i . .... / i .;."""" --19 X 8 i •I ,"' -·-·10X8 i :1 ---13 X 22 i ·I 60 · · .. 22 X 1 i :I i :I'I i ;I •I :I 'I 40 .i •I Y' -· ,(' /· /. / . 20 / : / . / .. :,...,-;.· I I I I I

5 10 15 DAYS OF EXPOSURE

FIGURE 6. Cumulative incidence of clipping by 10 captive hare on main stems of Douglas-fir cuttings from 4 full-sib families. (Each family comprises 100 cuttings. Differences exceeding bar lengths are significant at p < 0.05.) likely to be chance in view of both statisti­ Accordingly, we describe two different cal significance and consistent demonstra­ trials aimed at snowshoe hare as the target tion with two species of test animal. Most animal. Both studies included Douglas-fir importantly, the relative animal resistance seedlings rated for resistance to hare clip­ of first-generation progeny appears to be ping on the basis of their parentage. The duectly predictable from parental charac­ first of these, installed in November 1970, teristics with a fair degree of accuracy. was an attempt to discover if field perfor­ mance of full-sib families could be pre­ Progeny Field Tests dicted from parental attributes as rated by Both magnitude and consistency of animal clones in pen tests. In the second trial, preferences shown in pen tests suggested installed in November 1972, we attempted that resistance in the form of nonpreference to assess the reliability of clonal prediction might give effective protection in the field. plus the comparability of both pen and field However, we had only been able to specu­ tests with identical family groups. late that animals would discriminate under Procedures. Seedlings for the 1970 study field conditions in ways consistent with were grown in cold frames at the Dennie their behavior as captives. Moreover, ef­ Ahl Seed Orchard for 1 year, then were fective protection would require that con­ transplanted to cold frames at Olympia siderable numbers of seedlings be damaged in early 1970 for an additional season's lightly or not at all over at least the peak growth. The four families selected (1 X 22, damage period in a typical field situation. 22 X 1, 1 x 8, and 8 X 10) had been arti­

114 I Forest Science ficially bred from clones tested for hare already pen tested as cuttings in 1970, we preference in 1967. To minimize possible would also predict unchanged resistance confounding due to variations in nursery levels for them: 22 x 1 (Resistant), 13 bed environment, we systematically spaced x 22 (Intermediate), 19 x 8 (Susceptible), portions of each family throughout each and 10 X 8 (Susceptible). In addition, we cold frame; all families were subjected to a had opportunity in this case to compare di­ common regime of irrigation and nitrogen rectly the results from three distinct ex­ fertilization. perimental phases: pen tests with clones, We also prepared in early 1970 to propa­ pen tests with families, and field tests with gate seedlings for the 1972 study-a 4­ families. family field test designed to duplicate the Field testing procedures varied but little 1970 pen test on hare with cuttings. Using in the two studies, and chiefly due to dif­ ferences in numbers of available seedlings. : standard controlled breeding methods, we crossed selected ramets to reproduce the Both studies were installed as randomized families (22 X 1, 13 X 22, 19 X 8, and blocks. The 1970 trial contained 400 seed­ 10 X 8) ultimately needed for field testing. lings-four families with 20 seedlings per ·- Cones were gathered in late 1970 and family replicated in five blocks; the 1972 transported to Corvallis, Oregon, where trial contained 576 seedlings-four families seed was processed and seedlings started with 36 seedlings per family replicated in under greenhouse conditions in styrofoam four blocks. As in pen tests, all seedlings containers. Transferred to Olympia in mid­ were individually randomized, but at a 1971, seedlings continued growth under a spacing of 2.4 by 2.4 meters (8 by 8 feet) uniform greenhouse regime of irrigation to approximate commonly accepted stan­ and fertilization with nutrient solution. All dards of plantation density. Uniformity of families were transplanted to cold frames seedling height was sought in each trial­ near the end of the growing season, and 32 centimeters (12.6 inches) in the 1970 cultivated by procedures similar to those study; 40 centimeters (15.7 inches) in the described for the 1970 study through the 1972 study-and attained by deep planting 1972 growing season. of larger stock to a measured height ap­ Relative resistance for families used in proaching that of smallest seedlings. Vari­ the 1970 field study was predicted, as be­ ations among families in mean height at fore, from the array of preference charac­ planting were thus held to a minimum­ teristics derived from 1967 clonal tests. maximums of 3.5 centimeters (1.4 inches) Only one of these families ( 22 X 1 ) had in the 1970 study; 2.2 centimeters (0.9 been previously tested on captive hare. We inch) in the 1972 study-and in no case therefore predicted that this family and its were they significant (p < 0.05). Both reciprocal cross (1 X 22) would show about studies were located within 25 miles of the same level of resistance, and that both Olympia. Test areas were selected to pro­ would rank more resistant than either of vide maximum exposure to snowshoe hare the two families compared against them: on clearcuts logged 5 to 30 years previously and were sufficiently separated to insure Predicted Family Parental traits resistance that each replicate catered to a different hare population. 22 X 1 Resistant X Resistant Resistant In both 1970 and 1972 studies, seed­ 1 X 22 Resistant X lings were checked weekly during the first Resistant Resistant winter after planting, and damage by hare 1 X 8 Resistant X to terminal shoots was recorded as it oc­ Intermediate Intermediate curred throughout the season when clipping 8 X 10 Intermediate X of Douglas-fir seedlings is normally most Susceptible Susceptible prevalent. We continued observations in Similarly, since the families compared in each study until about a month past May the 1972 field study were identical to those bud burst to assure that all damage by hare

volume 22, number 2, 1976 I 115 CLIPPING IN PERCENT

100

80 IIIIII ,.,.,·''------­ ,·-·-·'' /,/·~·-·-•'' 60 ~··-"_"_,------­...... _,,_ -·/' ...... ,.,.~· -· -· -·-·-· ..______...... / // ?/ i 40 i i i i p/ -­ 8X10 /~-.--:-.:.:.=,;:=:.:...... f;;;;o I -·-·-· 1 X 8 20 III --- 22X1 Jvl - ..- 1 X22 /· I I

5 10 15 20 25 WEEKS OF EXPOSURE NOV DEC JAN FEB I MAR I APR MAY

FIGURE 7. Cumulative incidence of clipping (terminals only) by wild hare on Douglas-fir seedlings from 4 full-sib families, 1970-71 field test. (Each family comprises 100 seedlings. Differences exceeding bar lengths are significant at p < 0.05.) would be documented. Seedlings in both 1971, when virtually all hare clipping studies were again evaluated following their ceased. Only three seedlings were clipped second winter's exposure to hare clipping, thereafter prior to resumption of damage but not on a weekly basis. (Confounding during the following winter. Discrimination of results due to deer browsing was not by hare began almost immediately (Fig. 7). encountered, as damage by this animal oc­ Differences between families were signifi­ curred to less than 1 percent of the seed­ cant by the 3rd week, highly significant by lings in each study.) Cumulative levels of the 4th week, and significant from the 13th terminal shoot clipping in percent were week throughout the remainder of the first periodically analyzed during the first winter winter. Damage to terminal shoots at 25 by the same procedures used in family pen weeks ranged from 56 percent for the most tests. Analysis of variance was also used resistant family (1 X 22) to 86 percent for to compare seedling status in terms of sur­ the most susceptible (8 x 10). The 30­ percent difference suggests that resistant vival, total height, and damage to new ter­ families could give practical amounts of minal shoots after two winters of exposure protection over at least one winter season. to hare clipping. Terminal clipping of the susceptible family (8 X 10) accumulated to over twice that Results and Discussion. on each of two resistant families (1 x 22 Snowshoe hare (1970).-Seedlings were and 22 x 1) for about 2 months during the damaged severely from time of planting in period of most severe damage just after November 1970, to the end of February planting.

116 I Forest Science CLIPPING IN PERCENT

80

-- 19X8 I 60 -·-· 10X8 I ---13 X 22 • • • • 22 X 1

40 ...... • .. • 20 .. .. III I I

5 10 15 WEEKS OF EXPOSURE NOV DEC I JAN I FEB MAR

FIGURE 8. Cumulative incidence of clipping (terminals only) by wild hare on Douglas-fir seedlings from 4 full-sib families, 1972-73 field test. (Each family comprises 144 seedlings. Differences exceeding bar lengths are significant at p < 0.05.)

Of equal or possibly greater interest, planting, and there were some indications wild hare followed the predicted preference that first-year effects confounded any com­ order without exception. Nearly identical parisons that could be made thereafter. resistance was shown by families 1 X 22 Most notably, numbers of heavily damaged and 22 x 1 throughout the test, and there seedlings differed significantly among famt­ : was no evidence that either male or female lies after one winter's clipping. Though not characteristics predominated in contributing closely monitored, seedlings from suscepti­ to resistance. Furthermore, the susceptible ble families grew fewer and smaller shoots (8 X 10) and intermediate (1 X 8) families than those from resistant families as a con­ differentiated early and maintained their sequence of having sustained heavier dam­ relative rankings as predicted. age the previous winter. Such effects, we The capacity of resistance characteristics believe, influenced animal feeding selection to protect Douglas-fir seedlings against and thus biased subsequent comparison. snowshoe hare damage in the field for peri­ Reexamined the second winter, 49 weeks ods exceeding one season was not evident after planting, the 1970 field study did not in the 1970 study. Heavy animal pressure reveal any significant differences among resumed during the second winter after families in mean seedling survival, seedling

volume 22, number 2, 1976 I 117 height, or incidence of damage to new ter­ of 1974 at 68 weeks after planting. From minal shoots : their practical ramifications, results were Terminals distinctly more encouraging. Differences Survival Height clipped in mean seedling survival and seedling Family (percent) (em) (percent) height, as in the 1970 field study, were not significant. However, differences in hare 55 1 X 22 99 27 damage to new terminal shoots, though not 55 22 X 1 97 25 overwhelming, were clearly consistent with 1 X 8 93 27 48 results from previous pen tests and the 95 27 49 8 X 10 preceding year's damage patterns among Though resistance characteristics could well the same seedlings. (Family means not have continued to operate, their effects may followed by a common letter differ signifi­ have been nullified, as previously specu­ cantly at p < 0.05.): lated, by unequal availability of new foliage Terminals among families. In any event, the param­ Survival Height clipped eters measured in the above study failed to Family (percent) (em) (percent) mdicate second-year protection. 22 X 1 95 38 54 (a) Snowshoe hare (1972).-The 1972 field 13 X 22 96 36 56 (a) study was checked first at 6 weeks after 19 X 8 93 34 65 (ab) November installation, weekly thereafter 10 X 8 91 34 70 (b) until March 1973, then sporadically until June 1973. Severe hare damage to seed­ The two most resistant families (22 x 1 and lings occurred early and continued for 12 13 X 22) were damaged 16 and 14 percent weeks until late February. Terminal clip­ less, respectively, than the one most sus­ ping during the first winter ceased at 16 ceptible ( 1 0 x 8). Though family differ­ weeks. ences in terminal shoot clipping were only Field results (Fig. 8) corresponded well about half those of the previous year, they with those from pen trials among both were nevertheless significant (F = 6.46 with clones and families. Family differences 3 and 9 df). Resistance characteristics were were highly significant at 6 weeks and re­ evidently strong enough in this case to over­ mained so throughout duration of the test. ride any family biases due to previously Maximum separation between resistant (22 sustained damage. x 1) and susceptible (19 x 8) families oc­ curred at 8 weeks with 27- and 58-percent Genetic Analysis terminal clipping, respectively. The 31-per­ Procedures. Genetic analysis was performed cent difference decreased only slightly to by use of parent-offspring correlations ac­ 25 percent at the end of the winter. Dif­ cording to the method of Falconer (1960). ferences between the two susceptible fami­ Since different measures were used to eval­ lies ( 19 X 8 and 10 X 8) were not signifi­ uate results from pen and field trials, a cant, a result agreeing fully with predicted common statistic that could be applied to resistance as determined by clonal traits all tests was determined for pen tests with and with demonstrated family resistance as cuttings and for field tests with seedlings. rated by pen testing (Fig. 6). The inter­ We termed this measure mid-test selection mediate position of family 13 x 22 in the index (MTSI) and defined it as the pro­ field agrees closely with prediction but is portion of each clone or family clipped or somewhat inconsistent with the nearly iden­ browsed when half the materials in a par­ tical ranking of 13 X 22 and 22 X 1 in the ticular trial had been fed upon. pen. All elements considered, however, By methods of direct proportion previ­ concurrence among 3 independent evalua­ ously described, we combined results from tions-prediction, the 1970 pen test, and 1967 clonal tests by using clone 13 as a the 1972 field study-is generally high. common standard to generate MTSI values Seedlings were reexamined in early spring for all nine clones originally compared. As

118 I Forest Science TABLE 1. Mid-test selection index cant for deer and also for hare (r = 0.90 (MTSI) and mean exposure preference in­ and 0.97, respectively, with 7 df). There­ dex (MEPI) values for deer and hare among fore, we concluded that both MTSI and nine Douglas-fir clones. 1 MEPI should be similarly effective as pre­ dictors of progeny performance. Deer Hare We then correlated actual performance Clone MTSI MEPI MTSI MEPI of each family, as determined by its MTSI value, with its predicted performance as 1 53 149 42 141 estimated by mid-parent value (MPV). 8 44 135 67 238 10 53 152 69 278 This latter measure was calculated as the 13 37 100 47 179 mean index value--determined separately 15 48 130 67 256 by both MTSI and MEPI values-for any 17 55 135 47 204 two parents in a given cross and a statistic 19 60 164 59 250 expected to relate to the combined additive 22 47 127 23 100 genetic component of resistance expressed 23 53 147 29 127 in first-generation progeny. 1 Each statistic represents a mean of 100 ob­ Finally, we tested the actual correlation servations. between deer and hare preferences on the basis of demonstrated clonal traits as mea­ sured by both MEPI and MTSI. before, deer and hare were rated sepa­ rately. We then compared MTSI values to Results and Discussion. Although limited the corresponding mean exposure prefer­ by the small number of families (10) tested ence indices (MEPI's)-the values actually in pen and field on deer and hare, the cor­ used to rank predicted progeny resistance­ respondence between parent and offspring for the same clones (Table 1). Correlation gave ample evidence of strong additive ge­ between the two indices was highly signifi­ netic variation (Table 2). Correlations be-

TABLE 2. Relationship between mid-parent value (MPV) and mid-test selection index (MTSI) in jour trials with full-sib Douglas-fir families. 1

MPV Test Predicted Trial animal Family MEPI basis MTSI basis resistance MTSI 1970 Deer 13 X 22 113.5 42.0 Resistant 34 pen test 8 X 1 142.0 48.5 Intermediate 46 10 X 1 150.5 53.0 Susceptible 67 19 X 1 156.5 56.5 Susceptible 53 1970 Hare 22 X 1 120.5 32.5 Resistant 31 pen test 13 X 22 139.5 35.0 Intermediate 31 19 X 8 244.0 63.0 Susceptible 65 10 X 8 258.0 68.0 Susceptible 73 1970--71 Hare 22 X 1 120.5 32.5 Resistant 33 field test 1 X 22 120.5 32.5 Resistant 34 1 X 8 189.5 54.5 Intermediate 62 8 X 10 258.0 68.0 Susceptible 71 1972-73 Hare 22 X 1 120.5 32.5 Resistant 35 field test 13 X 22 139.5 35.0 Intermediate 45 19 X 8 244.0 63.0 Susceptible 62 10 X 8 258.0 68.0 Susceptible 58 1 In all three 1970 trials, each MPV and each MTSI represent means of 200 and 100 observations, respectively; in the 1972 trial, means of 288 and 144 observations, respectively.

volume 22, number 2, 1976 I 119 tween MPV and MTSI were constrained two animals is anything but close when ac­ by only two degrees of freedom in each of tual index values are compared (Table 1 ). the four 4-family trials. Therefore, signifi­ Correlations between deer and hare prefer­ cance could be demonstrated only by very ences among all nine clones were not sig­ high correlation coefficients (r values ex­ nificant for either index (r = 0.26 and 0.03 ceeding 0.95 at p < 0.05 = *, and 0.99 at for MEPI and MTSI, respectively, with 7 p<0.01=**): df). Therefore, although preferences shown by both animals agree in certain gross re­ MPV-MTSI spects, underlying factors that govern palat­ correlation coefficients ability of Douglas-fir foliage to each ani­ MEPJ MTSI mal species probably differ in more ways Trial basis basis than they agree. 1970 pen test on deer 0.818 0.790 1970 pen test on hare 0.992** 0.998** Conclusions 1970-71 field test on hare 0.969* 0.991 ** The preceding series of interrelated experi­ 1972-73 field test on hare 0.951 * 0.931 ments provides abundant evidence that ge~ netic factors in Douglas-fir can measurably Although MPV -MTSI correlations in the influence the palatability of its foliage to at 1970 pen test on deer were not significant, least two animal species that damage forest they were nonetheless similar and encour­ plantations by their feeding activities. Pref­ agingly high. In the case of hare, all three erences for morphologically similar but ge­ trials indicated that MPV's for clones could notypically different foliage approached a effectively predict relative levels of resis­ ratio of 5 : 3 for black-tailed deer and ex­ tance for progeny. Moreover, MPV's based ceeded 5 : 2 for snowshoe hare. Deer and on either MEPI or MTSI appeared equally hare showed both parallel and differing effective as predictors. preferences for genetically alike material. Heritability values can be estimated However, preference agreement was almost directly from the regression coefficients certainly more apparent that real. Both of parent-offspring relationships (Falconer animal species probably react to a complex 1960). If MTSI-based MPV's are pro­ of underlying factors that variously affect portionally adjusted to a scale equivalent to the palatability of Douglas-fir to each. that of MTSI values for offspring, resulting That factors affecting preference could regression coefficients for each of the pre­ be predictably transmitted to full-sib Doug­ ceding family trials are 1.74, 1.19, 1.03, las-fir progeny by crossing clonal parents and 0.62, respectively. Heritability esti­ was clearly demonstrated. Hence, we sug­ mates exceeding 1.00 may arise by chance gest that animal resistance through non­ with so few observations, but more prob­ preference for seedlings could become a ably stem from nonrandom choice of ex­ perimental materials. Thus, the above practical aim for tree improvement pro­ estimates are unusable for prediction of grams. Moreover, such animal resistance potential gain, but obviously express a high appears to be strongly inherited, and the component of additive genetic variation. genetic component of variation appears to Similarities between deer and hare in be chiefly additive. Differences between feeding preferences for identical Douglas­ susceptible and resistant progenies were on fir genotypes are not as close as indicated the order of 2: 1 in pen tests with captive by subjective levels of resistance estimated deer and hare and also in field tests. with from data in Figures 1 and 2. These levels, wild snowshoe hare over a full winter sea­ which depend upon ranking in an array son. These results imply that not only is rather than the magnitude of individual in­ practical animal protection in the field at­ dex values, lend an exaggerated impression tainable, but also that field performance of preference agreement. In fact, agree­ of progeny is predictable. Correlations be­ ment in feeding preference between the tween performance of parent and off­

120 I Forest Science spring were sufficiently high to suggest that Literature Cited full-sib progeny resistance could be accu­ BATES, C. G. 1927. Varietal differences. J For rately estimated from parental characteris­ 25:610. tics alone; that is, without the necessity of CARDINELL, H. A., and D. W. HAYNE. 1947. progeny tests. Pen tests of rabbit repellents. Mich Agric Exp As forest practices become more in­ Stn Q Bull 29:303-315. tensive, most commercial forests in the DIMOCK, E. J., II. 1971. Influence of Douglas­ fir seedling height on browsing by black-tailed Douglas-fir region are now beginning tree deer. Northwest Sci 45:80-86. improvement programs. The potential for DoooE, W. E., C. M. LoVELESS, and N. B. animal resistance as a forest protection tool KVERNO. 1967. Design and analysis of forest­ is high. Obviously, it must be compatible mammal repellent tests. For Sci 13:333-336. with more highly sought after traits affect­ FALCONER, D. S. 1960. Introduction to quanti­ ing quantity and quality of tree growth. tative genetics. Ronald Press Co, New York, 363 p. Our demonstration of damage resistance as HILDRETH, A. C., and G. B. BROWN. 1955. Re­ a function of varying animal preference pellents to protect trees and shrubs from dam­ among superior phenotypes within a local age by rabbits. US Dep Agric Tech Bull 1134, race of Douglas-fir is especially encourag­ 31 p. ing. Exploitation of local variation would LEOPOLD, A. 1933. Game management. Charles Scribner's Sons, New York. 481 p. seem a more promising approach toward MooRE, A. W. 1940. Wild animal damage to attaining practical resistance than one aimed seed and seedlings on cut-over Douglas fir at utilizing racial variation among widely lands of Oregon and Washington. US Dep differing provenances. Agric Tech Bull 706, 28 p. Our work merely shows that practical READ, R. A. 1971. Browsing preference by jackrabbits in a ponderosa pine provenance levels of animal resistance in Douglas-fir plantation. USDA For Serv Res Note RM­ exist and that their exploitation is possible. 186, 4 p. Rocky Mt For & Range Exp Stn, Success will hinge upon development of less Fort Collins, Colo. costly and more rapid methods for evalu­ SNEDECOR, G. W., and W. G. CocHRAN. 1967. ating parents and progeny. Considerably Statistical methods. 6th ed. Iowa State Umv Press, Ames, Iowa, 593 p. ~ore research will be needed to expand SQUILLACE, A. E., and R. R. SILEN. 1962. Ra­ upon our findings and translate them into cial variation in ponderosa pine. For Sci Mon­ useful future applications. ogr 2, 27 p.

volume 22, number 2, 1976 I 121