Larch dwarf mistletoe not found on alpine larch

6 Pages·1995·0.57 MB·English

by  Mathiasen, R.L

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Rocky Great
Mountains Southwest Plains
Research Note
RM-RN-533
April 1995
USDA
Forest Service
Rocky Mountain Forest and
Range Experiment Station
Larch Dwarf Mistletoe Not Found on Alpine Larch
Robert L. Mathiasen1 Brian W. Geils1
, ,
Clinton E. Carlson2 and Frank G. Hawksworth1
,
Reports of larch dwarf mistletoe parasitizing alpine larch are
based on two collections of this host/parasite combination made
by J.R. Weir in Montana during the early 1900s. Examination of
host material from these collections indicates that the host is
western larch, not alpine larch as previously reported. Attemptsto
locate larch dwarf mistletoe on alpine larch were unsuccessful,
leaving no valid reports of larch dwarf mistletoe on alpine larch.
Keywords: Arceuthobium laricis, Larix lyallii, Larix occidentalis,
hosts
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Larchdwarfmistletoe (Arceuthobium laricis (Piper) Alpine larch (Larix lyallii Pari.) occurs at upper
St.John) isa commonparasite ofwesternlarch(Larix timberline inthe NorthCascades ofWashingtonand
occidentalis Nutt.) throughout the range of this com- extreme southern British Columbia, in the Northern
mercially valuable conifer (Hawksworth and Wiens Rocky Mountains ofwestern Montana and northern
1972).Severelyinfectedtreesexhibitreducedgrowth Idaho, and in the southern Canadian Rocky Moun-
and are eventually killed by the parasite (Weir 1916, tains of southeastern British Columbia and south-
Pierce 1960, Baranyay and Smith 1972). Surveys con- westernAlberta (Arno and Habeck 1972). According
ducted during the late 1950s found that over 60% of to Arno and Habeck (1972), the species ranges from
m m
western larch stands in eastern Washington, north- approximately 1500 (5,000 ft) to 3000 (9900 ft).
ern Idaho and western Montana were infested with Alpine larch generally inhabits cold, rocky sites and
larchdwarfmistletoe(Graham1960). Althoughlarch is seldom sympatric with western larch. Although
dwarfmistletoeparasitizesseveralotherconiferspe- the two larch species frequently occur in the same
cies, parasitism of these secondary hosts is usually mountain ranges, they are usually separated by 150-
m
neither severe nor damaging (Hawksworth and 300 (500-1000 ft) of elevation. The different larch
Wiens 1972). species, however, are only rarely found together, for
example inareas where alpine larch descendsbelow
' Robert L. Mathiasen, volunteer; Brian W. Geils, Research its normal range by colonizing avalanche chutes,
Plant Pathologist; Clinton E. Carlson, Project Leader; Frank G. talus slopes, or burned areas. Carlson and Blake
Hawksworth, Research Plant Pathologist (deceased). Rocky
Mountain Forestand Range ExperimentStation. Headquarters (1969) and Carlson et al. (1990) identified several
is in Fort Collins, in cooperation with Colorado State University. natural hybrid populations in the Bitterroot Moun-
2 Forestry Sciences Laboratory, Intermountain Forest and tains of Montana where these species are sympatric.
Range Experiment Station, Missoula, in cooperation with the
University ofMontana.
1
Alpinelarchhasbeenreportedasa secondaryhost (somatic mutation) or other (unknown) causes as
oflarchdwarfmistletoe (Gill 1935, Hawksworthand described by Buckland and Kuijt (1957) for alpine
Wiens 1972). These reports were based on only two larch and other conifers.
We
collections from Montana. These collections were furtherexaminedseveralsitesonCarltonRidge
made by J.R. Weir in the early 1900s (Hawksworth where western and alpine larch are sympatric and
and Wiens 1972), and the associated label informa- hybridize (Carlson et al. 1990). No infectionofeither
tion is very brief. Weir only described the collection hostbylarchdwarfmistletoeoccurredatanyofthese
from the Bitterroot Mountains as "near Lolo, Mon- sites. Lodgepole pine dwarfmistletoe (Arceuthobium
tana" and the collectionfromthe CabinetMountains americanum Nutt.) was present on lodgepole pine
as "region Scotchmans Peak." Because he provided (Pinus contorta Dougl. ex Loud.) at one site, but no
no data on the abundance of infection at the collec- crossover infection to alpine larch was observed.
tion sites, the susceptibility of alpine larch to larch Because western larch is thought to be immune to
dwarf mistletoe could only be tentatively assigned lodgepole pine dwarf mistletoe (Hawksworth and
by Hawksworth and Wiens (1972). Wiens 1972), it is unlikely that lodgepole pine dwarf
To assess the natural susceptibility of alpine larch mistletoe would parasitize alpine larch.
to larchdwarfmistletoe, we surveyed larchstands in Inadditionto these field surveys, we re-examined
the general locations where Weir reported making Weir'scollectionstoconfirmhostidentification.These
his collections: a large population of alpine larch on specimens Weir 8366, Lolo, MT, 1914 and Weir3250,
(
km
Carlton Ridge in the Bitterroot Mountains (7 Scotchman Peak, n.d.) are deposited at the Univer-
southwest of Lolo, MT), and a small population on sity of Illinois Herbarium, Urbana, Illinois (ILL) and
the north-facing slopes ofSavageMountainand East at the USDA Forest Service Forest Pathology Her-
Fork Peak in the Cabinet Range (3 km north of barium,FortCollins,Colorado(FPF).Specimensfrom
Scotchman Peak and 13 km northeast of Clark Fork, these two collections were examined by the first
ID). Our extensive surveys of the Carlton Ridge and threeauthorsandStevenArno,USDAForestService,
Savage Mountain locations during 1992 and 1993 Missoula, MT.
failed, however, to locate any dwarfmistletoe infect- Host material from Weir's specimens was com-
ing alpine larch. Larch dwarf mistletoe populations pared with herbarium specimens of both western
infecting western larch were located at 1720 m (5500 andalpinelarchdepositedattheUSDAForestService
m MT
ft) near Carlton Ridge and at 1590 (5200 ft) near Herbarium, Missoula, (MRC). Larch characters
SavageMountain. Noalpinelarcheswerefoundnear examined included pubescence and bark color of
dwarf mistletoe-infected western larches on Carlton young twigs, and pubescence and color of short
Ridge or at the Savage Mountain location. shoots (Hitchcock et al. 1973). The collections con-
Although we found no alpine larches that were tainedonlya few1-or2-year-oldtwigs; thosepresent
infectedbydwarfmistletoe, theCarltonRidgepopu- were glabrous to lightly pubescent rather than to-
lation did include a few isolated alpine larch trees mentose. The several short shoots present were not
with one or two large witches' brooms in the middle tomentose but rather resembled those of western
or top of the crown. These brooms were, however, larch.Barkcoloralsomatchedthatofwesternlarchof
not caused by dwarf mistletoe. The general appear- similar age. No ovulate cones were available with
ance of mistletoe-caused brooms is usually deter- Weir's specimens. Because of the lack of tomentose
mined by the parasite rather than the host pubescence on this host material and other similari-
(Hawksworth and Wiens 1972); these brooms did ties of the material to western larch (short shoot
not resemble typical mistletoe brooms on western pubescence and bark color), we concluded thatboth
larch. Because dwarf mistletoe spreads primarily by specimens collected by Weir were western larch.
anexplosivefruit,infections(andeventuallybrooms) Thus, these specimens donotrepresentcollectionsof
tend to occur in clusters and more often in the lower larch dwarf mistletoe on alpine larch.
crown; these brooms were isolated and high in the Even though this identification leaves no valid
crown. Finally, most dwarf mistletoe infections pro- report of larch dwarf mistletoe parasitizing alpine
duce distinctive, aerial shoots; no mistletoe shoots larch, the species is probably susceptible to larch
We
were associated with these brooms. therefore dwarf mistletoe. Closely related conifer species are
concluded these brooms were induced by genetic frequently parasitized by the same dwarf mistletoe
2
(Hawksworth and Wiens 1972). Based on artificial toe where alpine and western larch are sympatric
inoculations of seedlings, Weir (1918) demonstrated and to proceed with artificial inoculations of larch
that European larch (Larix decidua Mill.) and Japa- dwarf mistletoe on alpine larch seedlings and ma-
nese larch {Larix kaempferi (Lamb.) Carr.) are suscep- ture trees.
tible to larch dwarf mistletoe. Because alpine and
western larch are closely related (Carlson and Blake
1969; Carlson et al. 1990, 1991; Carlson and Theroux Distinguishing Alpine Larch
1993), alpine larch is also likely susceptible to larch
dwarfmistletoe. Furthermore, larch dwarfmistletoe Alpine larch is easily distinguished from
has a relatively wide host range. As summarized by
western larchbased on several morphologi-
HawksworthandWiens(1972),itcommonlyparasit-
cal characteristics (Hitchcock et al. 1973,
izes lodgepole pine, subalpine fir (Abies lasiocarpa
(Hook.), Nutt.) and mountain hemlock (Tsuga Carlson et al. 1990, Carlson and Theroux
mertensiana (Bong.) Carr.). These species are even 1993). The most notable characteristics are
lesscloselyrelated towesternlarchthanalpinelarch. that young twigs and short shoots of alpine
Artificial inoculation experiments should be at- larcharedistinctlytomentose,whereasthose
tempted under field conditions to test the suscepti- of western larch are glabrous to slightly pu-
bility of alpine larch to larch dwarf mistletoe. Field
bescent. The leaves of alpine larch are four-
inoculations on alpine larch would not only provide
angled in cross section, about as thick as
informationonitssusceptibilitytolarchdwarfmistle-
toebutcouldalsoprovideinformationonwhetheror broad, and possess two relatively large resin
notlarchdwarfmistletoecansuccessfullyreproduce ducts visible inleafcross sections magnified
at elevations above its known altitudinal limits. 25x.
Larchdwarfmistletoe specimensdepositedatFPF In contrast, leaves of western larch are
have seldom been collected above 1520 m. The only triangular incross section, the upper surface
specimens of larch dwarf mistletoe collected above
m almostflatwithonlyaslightridge, the lower
1520 are from the Blue Mountains of eastern Or-
m surface ridged in the middle; and they pos-
egon at 1980 (Hawksworth 981). The specimens of
larchdwarfmistletoe fromotherstates (Washington, sess small resinducts visible incross section
Montana, and Idaho) were collected below 1550 m. (Carlson and Blake 1969). Alpine larch foli-
During our field surveys, however, we found larch age is blue-green and not shiny; western
m
dwarfmistletoeashighas 1720 nearCarltonRidge larch foliage is olive-green and shiny Bark
m
and 1590 near Savage Mountain. texture and color of3-year-old branches dif-
Most dwarf mistletoes have elevational limits be-
fers between the species as well: alpine larch
low that of their principal hosts (Hawksworth 1956,
Hawksworth and Wiens 1972, Acciavatti and Weiss bark on 3-year-old branches is gray and
1974, Mathiasen and Hawksworth 1980). rough-textured and bark ofwestern larch is
Hawksworth (1969) suggested that dwarf mistletoe brown and smooth (Carlson et al. 1990).
fruits may notmature atelevations above theirnatu- Other characters that distinguish these
ral limits because of short growing seasons. This species are themorphologyofovulate cones
situationcouldcertainlyinfluencethedistributionof and seed shape (Carlsonand Theroux 1993).
larch dwarf mistletoe. Even if alpine larch were Alpinelarchhas ovulatecones from3.5to4.5
susceptible to larch dwarf mistletoe, prevailing cli-
cm long; shorter western larch cones are
matic conditions inalpine larch stands athigheleva-
tions could still prevent larch dwarf mistletoe from from 2.5 to 3 cm long. Seeds ofwestern larch
reproducing. Nonetheless, if alpine larch were sus- are narrower, shallower, and have thinner
ceptible to larch dwarf mistletoe, then cross-over seedcoats than those ofalpine larch. Chemi-
infections from western larch should occur where cal differences (foliar terpenes) also occur
both species grow in close proximity (within 10 m). betweenthetwospecies(Carlsonetal. 1991).
We
plantocontinuesearchingforlarchdwarfmistle-
3
Acknowledgments Carlson, C.E.; Theroux, L.J. 1993. Cone and seed
morphology of western larch (Larix occidentalis),
We
gratefullyacknowledgetheassistanceofSteven alpine larch {Larix lyallii), and theirhybrids. Cana-
Arno and PeterStickney withthe species determina-
dian Journal Forest Research. 23: 1264-1269.
tion of host material for the larch dwarf mistletoe Gill, L.S. 1935. Arceuthobium in the United States.
specimens collected by J.R. Weir. The late Frank G. Connecticut Academy of Arts and Science Trans-
Hawksworth assisted with most of the initial work actions. 32: 111-245.
involved with this study, so we acknowledge his Graham, D.P. 1960. Surveysexpose dwarfmistletoes
contributions by including him as an author. Frank problem in Inland Empire. Western Conservation
initiated thisworkand wasa constantsourceofideas
Journal. 17: 56-58.
and encouragement until his death in January 1993. Hawksworth, F.G. 1956. Upper altitudinal limits of
dwarf mistletoe on lodgepole pine in the central
Rocky Mountains. Phytopathology. 46: 561-562.
Literature Cited Hawksworth, F.G. 1969. Ecological aspects of dwarf
mistletoe distribution.In: Proceedings, 16thWest-
Acciavatti,R.E.;Weiss,M.J.1974.Evaluationofdwarf ern International Forest Disease Work Confer-
mistletoe on Engelmann spruce. Fort Apache In- ence. 1968October28-November l;Coeurd'Alene,
dianReservation,Arizona.PlantDiseaseReporter. ID: 74-82.
58: 418-419. Hawksworth, F.G.; Wiens, D. 1972. Biology and clas-
Arno, S.F.; Habeck,J.R. 1972. Ecology ofalpine larch sification of dwarf mistletoes (Arceuthobium). Ag-
(Larix lyallii Pari.) in the Pacific Northwest. Eco- riculture Handbook 401. Washington, DC: U.S.
logical Monographs. 42: 417-450. Department of Agriculture, Forest Service. 234 p.
Baranyay,J.A.; Smith, R.B. 1972. Dwarfmistletoes in Hitchcock, C.L.; Cronquist, A.; Ownbey, M. 1973.
British Columbia and recommendations for their Flora of the Pacific Northwest. Part 1: Vascular
control. InformationReportBC-X-72.Victoria,BC: cryptograms,gymnosperms,andmonocotyledons.
CanadianForestryService,PacificForestResearch Seattle,WA:UniversityofWashingtonPress.914p.
Centre. 18 p. Mathiasen, R.L.; Hawksworth, F.G. 1980. Taxonomy
Buckland,D.C.;Kuijt, 1957.Unexplainedbrooming and effects of dwarf mistletoe on bristlecone pine
J.
ofDouglas-firandotherconifersinBritishColum- on the San Francisco Peaks, Arizona. Research
bia and Alberta. Forest Science. 3(3): 236-242. Paper RM-224. Fort Collins, CO: U.S. Department
Carlson, C.E.; Arno, S.F.; Menakis, 1990. Hybrid of Agriculture, Forest Service, Rocky Mountain
J.
larch of Carlton Ridge Research Natural Area in Forest and Range Experiment Station. 10 p.
westernMontana. NaturalAreasJournal. 10:134-139. Pierce, W.R. 1960. Dwarf mistletoe and its effect
Carlson, C.E.; Blake, G.M. 1969. Hybridization of upon the larch and Douglas-fir of western Mon-
western and alpine larch. Montana Forest and tana. Bulletin 10. Missoula, MT: Montana State
Conservation Experiment Station Bulletin 37. University, School of Forestry. 38 p.
Missoula, MT: University of Montana, School of Weir,J.R. 1916. Larchmistletoe: Someeconomic con-
Forestry. siderationsofitsinjuriouseffects. AgricultureBul-
Carlson, C.E.; Cates, R.G.; Spencer, S.C. 1991. Foliar letin 317. Washington, DC: U.S. Department of
terpenes of a putative hybrid swarm {Larix Agriculture. 25 p.
occidentalis x Larix lyallii) in western Montana. Weir, J.R. 1918. Experimental investigations on the
Canadian Journal Forest Research. 21: 876-881. genus Razoumofskya. Botanical Gazette. 56: 1-31.
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