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FOREST
ROCKY MOUNTAINS
TYPES OF THE NORTHERN
CONTROLS1
AND THEIR CLIMATIC
J. A.
LARSEN
Iowa State College
Introduction
The purpose in this report is to describe the natural forest types of the
northernRocky Mountains in Montana and northernIdaho, to point out their
natural distributionand chief silvical characteristics,and to show in what degree they are controlled by differencesin topography and climate. Such information may be useful in laying the foundation for later, more intensive
silvical investigations and practices in a region rich in forest resources.
Information on the character and distributionof the forests has been obtained from the silvical maps and reports prepared in the various forest supervisors' offices;by conversation and correspondence with the forest supervisors
and members of the District I Office (Missoula, Mont.) of the Forest Service, and by the writer's own work in this region covering a period of 14 years.
Some difficultywas experienced in assembling the forest type map (Fig.
i),
because most of the existing maps for the individual forests show the
present " cover " types 2 rather than the climatic or climax types (associations). Also, two or more persons may differin type designations and interpretations. The author has, therefore,been forced to use a certain freedom
in correlating and adjusting his material. In some instances where the subalpine forests were not clearly shown, the boundaries have been drawn according to topography and knowledge of the forest conditions in the region.
In all cases the lines drawn around the types have followed natural divisions
of permanent tree associations.
Lists of the most common species of grasses, herbs and shrubs found in
each forest type, obtained from various published and unpublished sources,
are presented because this informationis of value in silviculture,grazing, and
ecological studies.
The climatic controls of the forest types are based entirely upon air temperature and precipitation records. Such indices of forest type requirements
as the relation of air temperatureto precipitation,or of the latter to evapora1 This paper includes the results' of work done for the Northern Rocky Mountain
Forest Experiment Station of the U. S. Forest Service.
The word " type" is virtuallythe equivalent of " association." Thus the western yellow pine type is the same as the Pinits ponderosa association.
2 The " cover " type is the growth at present on the ground, and may he a stage in
the successional series or may be the climax association.
63I
632
J. A. LARSEN
Ecology,Vol. XI, N1o.4
tion,have beenpurposelyavoidedfortwo reasons. In thefirstplace,evaporation recordsare as yetverylimited;and secondly,few botanistsagree on the
truesignificance
of theserelationships.
The data on climatehave been obtainedfromthe printedreportsof the
United States Weather Bureau, and from some records gatheredby the
Forest Service of summermeteorologicalconditionson mountains. Whenever possibleat least 5 weatherstationshave been chosenforeach foresttype
and an efforthas been made to have one at eitheraltitudinalextreme. Records fromthe higherelevationshave been very insufficient.
In the summationsof temperature
and precipitation
whichare given,the
monthlydata are stressed. These no doubt reflecta strongerlimitinginfluence in manycases thando annualtabulations. Deficitsin the springrainfall
restrictgrowthof conifersin the west. This is amplyshown by recordsof
climateand heightgrowthof trees at the Priest River ExperimentStation
(Brewster,'28) and otherplaces (Pearson, '28). The amountof summer
rainfall,on the other hand, particularlythat which falls during July and
August,will indicatethe relativedroughtresistanceof the species.
Dates of the last killingfrostin the springand the firstin the fall are
takenfromthe averages for the stationswithineach type. It is well to bear
in mindthatnoneof theconiferousforesttypesin Montanaor Idaho are free
fromkillingfrostat any time duringthe growingseason. For this reason
frostdata are of littlesignificance
as limitingfactorsor as indicatorsof the
lengthof the active growingseason. They reflect,nevertheless,important
climaticdifferences.The data on snowfallrepresentthe averages for the
typestations. These figuresalso, at best, reflectonly the amountof winter
precipitation
and air temperature;unfortunately,
the muchmorevaluable figures on durationof snow cover and dates of disappearanceof snow are yet
largelylacking.
Broad Topographic and Climatic Controls of Forest Types
Montana and northernIdaho centeraround two great mountainsystems,
the ContinentalDivide and the BitterrootRange. Betweenthesetwo lie the
Bitterroot
and Flatheadvalleys,whichdrainnorthwest
intoLake Pend Oreille.
From the crestof the BitterrootRange the forestedspursand sharp canyons
descendwestwardand southwestward
to the borderof the treelessColumbia
River Basalt Plateau. Centraland easternMontana slope graduallyfromthe
elevatedregionalong the ContinentalDivide to the Great Plains.
The area under discussionthereforeis divided into three distincttopographicdivisions: (a) Washingtonand Idaho to the west of the Bitterroot
Mountains; (b) Flatheadand Bitterroot
valleysbetweentheBitterrootMountainsand themain ContinentalDivide; and (c) CentralMontanalyingto the
east of the ContinentalDivide. These major divisionsare the foundations
uponwhichthedata and descriptions
rest,and theywill be adheredto throughout thisreport.
FOREST
October, I930
TYPES
OF ROCKY
633
h
QD
?J1
MOUNTAINS
'TWA
0 1-U
pI
v
td t
(L
e- ,Jy
0
2i, 0- . a-
V
0
IN
Qj
MIN R En
14-4
0
04
b.0
10
flu
J. A.
634
Ecology, Vol. XI, No. 4
LARSEN
In each of thesethreetopographicunitsthe forestsrange fromprairieat
the lowerpointsto subalpineor alpineconditionsnear the mountainsummits,
througha series of altitudinalzones characterizedby definiteassociationsof
trees,whichare called foresttypes. These foresttypesare outlinedin Table
I, and are mappedin Fig. i. Table II presentsthearea and volumecontained
in each type.
L
Z
rotnt
/#~~~~~~~~~~~
[
Oelltr
FIG. 2.
Ad,/'rF-IoRf
mf
/
,
Ica/w
Map showing National Forests in the northernRocky Mountains
Table III showsthatthewesternsectionscontaina muchgreatervarietyof
trees than centraland easternMontana. In Idaho, in particular,thereis a
wealth of species. Conspicuousamong these are mesophytictrees such as
westernred cedar, westernhemlock,westernwhitepine, and lowland white
fir,whichare no~tfoundeast of the ContinentalDivide. Even the western
larch,muchless exactingin waterrequirements,
does not appear in centralor
easternMontana.
Climate,as affectedby topography
and geographicalposition,plays a leading partinlaffecting
thevariationsin the forestcover. The essentialelements
of climateforthe threemajor sectionsare set forthin Tables IV to X. The
October, I930
0
Cd
r.
Cd
TYPES
FOREST
zt
OF ROCKY
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636
J.
TABLE
A.
Ecology, Vol. XI, No. 4
LARSEN
Areas occupied by forest types,Montana and north Idaho *
II.
(Areas in thousand acres; stand in million board feet)
Per cent by species
Section
Open
grassland t
W. y.
pine
5,247.3 10.0
I5.00
estimated stand
(b)
Wash.-
I d a ho
Area
-
_
_
Stand 26,594
_
Area
Western
8,540.3
Montana
Stand I9,724
_
_
3.4
_
Area
Central
8,592.9 15.7
Montana
Stand I6,826
Total
_
D. fir, D fi
Cedar;
. r, hemlodgeEng.
pole
W.c
lock,
spruce
larch W. w. P.
pine
I7.5 14.70 I9.2
_ _ _ _ _ _ _ _ _ _ _
28.I
7.IO
8.50 41.2
11.70
33.2
14.20
40.0 23.10
3.IO
_
0.04
23.90
4.1
4.I
4.5
_
9.0
4.4
13.3
54.8
0.50
3.1
83.5
0.02
5.1
U
canclassified
1.7
I7.4
_
_
Barrens
and
alpine
Subalpine
_
_
_
_
5.6
-
10.0
_
-
I I.3
Area 22,380.5
Stand 63,144.0
* Data from figurescompiled by the U. S. Forest Service, Missoula, Montana.
t Including non-reproducingburns.
TABLE
III.
Evergreen trees of Montana and northernIdaho
Arranged according to light requirement,the most tolerant of shade being placed last.
West of ContinentalDivide
Juniperus occidentalis Sarg.
Western juniper
East of ContinentalDivide
Juniperusscopulorum Sarg.
Rocky Mountain Juniper
Pinus albicaulis Engelm.
Whitebark pine
Pinus albicaulis
Pinus flexilis James
Limber pine
Pinus flexilis
Pinus ponderosa Laws.
Western yellow pine
Pinus ponderosa
Larix lYalli Parl.
Mountain larch
Larix occidentalis Nutt.
Western larch
Pinus contortavar. rnlrrayanaEngelm.
Lodgepole pine
Pinus contorta
Pseudotsuga taxifolia
(Poir) Britt.-Douglas fir
Pseudotsuga taxifolia
Pinu-smonticola D. Don
Western white pine
_
5.6
3.2
15.9
_
I 2.8
_
October, 1930
FOREST
TYPES
OF
TABLE
III-
ROCKY
637
MOUNTAINS
(Conitinued)
Divide
East of Continental
Picea engelmannii
Divide
West of Continental
Engelm.
Picca enqelmannii
spruce
Engelmann'
BabiesgrandisLindl.
Lowland white fir
Abies lasiocarpa
BabieslosiocarpaNutt.
Alpinefir
Sarg.
Tsuga heterophylla
Westernhemlock
Sarg.
Tsuga mertensiana
Mountainhemlock
Thuja plicataD. Don.
Westernredcedar
Taxus brevifoliaNutt.
Yew
TABLE
IV.
Sunshine, wind and relative humidity
Averagesof all recordsup to the timeof latestperiodicsummary,
fromU. S. WeatherBureau Bulletinand laterreports
Station,
region
and
typeof vegetation
Annual
Spokane
E. Washington
W. yellowpine
52
Lewiston
N. Idaho
N. w. Montana
Prairie
70
Aug.
Annual
May-
Aug.
Annual
76
5.7
5.8
5.0
50
31.2a
25
4.3
4.4
4.3
48C
33.6C
31C
(1Norecord)
Prairie
Kalispell
Aay-
Relative humidity
per cent 6:oo P.M.
Wind, miles
per hour
Sunshine,per cent of
possible
SMeapy Aug.
48
62
68
4.8
5.3
5.1
57
42.0
37
58
65
73
7.5
7.7
7.3
50
38.4
32
6.i
6.2
5.3
61
48.2
43
7.8
7.3
6.7
55
43.0
37
Helena
N. centralMontana
Prairie
Miles City
(No record)
S. e Montana
Prairie
Yellowstone
Nat. Park,Wyo.
S. centralMon-
56
64
7I
tana
Values forSpokane,5 P.M., local time.
Mean forthefivemonthperiod,May to Sept.,incl.
e Noon values,no availablevalues for6 P.M.
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Ecology, Vol. XI, No. 4
J. A. LARSEN
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October, I930
FOREST
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Ecology, Vol. XI, No. 4
J. A. LARSEN
640
foundin the westernand easternsections
outstandingclimaticcharacteristics
are: in the west,relativelymild winterswithheavysnowfall,and warm,dry
summers;in the east, colderwinterswithlightsnowfalland somewhatmore
summerrains. Thus some partsof Idaho show an annual summerprecipitationof only5 inches,althoughthetotalfortheyear is 25 and over; whilecen%.5A6.5/V4L
.3'
'.
.s.we
32
7704'
ayOF
oI257r.9/l
RI~6/Pre7/0V
.
^1017h
/oo7 fla
/6
qi
QJ
/e
8
82JSsfQj
ull
0
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ciii
FIG. 3.
Hul
-rIol
I~~~qJ
an a/
I.
Nt>2
a~9nn
.rts.
0
t
t
Distribution of annual precipitationby months in eastern WashingtonIdaho, western Montana, and central Montana
tral Montana receivesan average of above 7 inchesduringthe summer,the
totalannual therebeingabout i5 inchesfortheprairiesand 24 inchesforthe
subalpineforests.
Climate,as affectedby topographyand geographicalposition,plays a leadthe variationsin forestcover. There are two outing role in determining
betweenthe westernand easternsections
standingmeteorologicaldifferences
October, I930
FOREST
TYPES
OF ROCKY
Th'/EC/
0.1
4o
,
MOUNTAINS
64I
P/ T4 TI/ 0/
/eS
g/ncAe
J.
Jsd
94
-
5C.0f
Oct
/ov.
D
tI6I l*7
7. 1
yesee
2
2~~~~~~~oe
3
sS
Ll
+
|
|
?e~~$-5zer4
*/fio
feA
7'd' pae
/%o,7477n
-
Cedgar
-
/?r~~~e~~yf
v6sett &
J4d'f/0C4
efe.,
_
FIG. 4.
Seasonal distributionof precipitationfor the principal types of vegetation in
eastern Washington-Idaho,
western Montana,
and central Montana
Ecology,Vol. XI, No. 4
J. A. LARSEN
642
9/--
Ao
R Z
A/
'60~~~~.K
0
60
I&.
At
/
,~~~
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I~~
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I~~fv
I
~i
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20
G
. Cuve
shwn
th
meaaigrn tempratr
b
oth
ouhu
the ya
westernMontana,and
in easternWashingto-n-Idaho,
fortheprincipaltypesof vegetation
centralMontana.
October, I930
FOREST
TYPES
i/REc/R/
6
l
eT
l
a
l
/%
l
OF ROCKY
643
MOUNTAINS
7-,9 7-1 O /V
l
l
l
l
l
l
6
l~~~~~~~~~~~W
w ll
lyel
7?
6-P
5
<
Cerf~~~~~~~~~~~rev/
f=/ofhesci-H/e~~~~~erroo
Qs
-e/e,
f
Do
Wstr
lu
W,
aSvsti
ydlla/ysow'pin
N
3~~~~~~~
t-7
a~ ; j
FIG. 6.
4
Ze/o. , PA-/0
oW~~~~~~~~~~~~~~~c-
-
Zr/
//
|0
J
e
Curves showing precipitationby months throughoutthe year for eastern
Washington-Idaho, western Montana, and central Montana
644
J.
Ecology, Vol. XI, No. 4
A. LARSEN
of the NorthernRocky Mountainregion. In winter,Idaho has mildertemperaturesbut more snow thaneasternMontana; in summer,it has considerbeably less rain. The climateof the intermountain
valleys is intermediate
p1/-? 7-T6WP6,Re9 7-&eoF
{c~~~~o
-Pelee.
ee
W*e//ow&ire,
44CfA9
4eoe
Ceca,'-kem
/V r765,
j.
W68H/N1AI67-04'- /.O6llo
50O
0 Sono
/oc/r &/C.
o*.
6r a0o
6Z
FIG. 7. Air temperaturegradients for eastern Washington-Idaho, showing the relation of altitude to the number of days with a mean temperatureabove 430 F., and a
mean temperaturebelow 320 F.
are brought
tweenthatof the regionson eitherside. These characteristics
out graphicallyin Figs. 3, 4, 5, and 6. The relationof altitudeto the length
above 430 F., is shownin Fig. 7.
of thegrowingseason,based on temperature
Section Lying West of the BitterrootRange
PRAIRIES OF PASTERN WASHINGTO.N
The prairie lands overlyingthe Columbia Basalt Plateau, between the
Cascade Mountainsin Washingtonand the BitterrootMountainsin Idaho.
October, I930
FOREST
TYPES
OF ROCKY
MOUNTAINS
645
are for the most part flat. They are brokenhere and there by old water
courses which have exposed basaltic cliffs,and round boulders or "nigger
heads." Occasional depressionsof better,moistersoil are occupiedby alfalfa
ranchesand may containa few plantedpoplars. These brightgreen patches
standout in vivid contrastto the otherwiseparchedlandscape.
The arid nature of this region is reflectedby the dominantxerophytic
A. tripartite,
ncuseosus,C.
Chtrysotamnus
vegetationof Artemisiatridentata,
Sarcobatus verniculatus,Rhus toxiEriogonummicrothecuns,
vescidiflorus,
codendron,Erigeronconcinnus,Lupinus pusillus,Zygadenuspaniculatus,and
Rumnexvenosus (Weaver, 'I7, Gail, '24).
These prairiesare chieflyof interestin this studybecause of their hot
summerdays and the dryingwinds which.come fromthem,causing extreme
droughtand dangerousfireweatherin the forestedmountainsto the east.
These winds also carryparticlesof soil fromthe semi-aridregioncausing it
to be depositedoverthe Palouse Plains and to some extentover the forestsin
the Clearwaterdrainagebasin (Larsen, '23).
THE
PALOUSE
REGION
Betweenthesemi-aridColumbiaBasin and thewesternyellowpine forests
area in eastern
is a billowy,treelessregion. This is the richwheat-producing
Washingtonand adjacent Idaho, knownas the " Palouse country." The naand theclimaticconditionshave
of vegetation,
tureof thesoil,thedistribution
been well described by Weaver ('27).
Climaticconditions,as represented
by recordsfromMoscow, Rosalia, and
of 46.90 F., and a yearlyprePullman,show a mean annual air temperature
cipitation of 20.54 inches, of which 2.49 inches occur during July,August and
September.
as well as the amountof precipitationwhich falls
The air temperature,
here,appearsto be suitablefora forestof westernyellowpine. Probablythe
principalreasonwhythisarea is not coveredwithtimberis the extremelyadverseconditionprevailingin summer,due to extremedroughtand high winds.
It is not unlikelythatrecurringprairiefiresand shiftingsoil have also helped
to tip the scales to the disadvantageof the trees. Measurementsmade by
in dryingpowerof the air beGail ('24) show a reallyremarkabledifference
tweenexposed and protectedaspects. He founda wind movementi9. times
greateron the southwestthan on the northeastaspect, and a loss of water
fromevergreentwigs2.89 timesgreateron the exposed thanon the protected
slopes. Consequentlyit is not surprisingthat pine is actuallyfound on the
northside of SteptoeButteand along the Palouse River,and thatthe eastern
or northernaspectsof the smallerhummocksmay readilybe reforested.
THE
WESTERN
YELLOW
PINE
FORESTS
The lowerborderof the forestin the sectionwest of the Bitterrootrange
consistsof thewesternyellowpinetype. The treeline followsthe Clearwater
J. A.
646
LARSEN
Ecology, Vol. XI, No. 4
canyon fromGrangevilleto Orofinoand Lapway; then closelyparallels the
NorthernPacificbranchline to Moscow; thengoes northalong the eastern
hi
k!
W
^
FIG 8
4
,.,
,%
","
pine Prnus ponderosa LawsinF
Western yellow
easternWashingtonF
27
~~~~~~~~~~~~~~~~~~~~~~~~~~~~A;
FIG. 8. VWeS-tern
yellow pine, Pinutsponderosa Laws in eastern Washington
edge of the Palouse Plain, cuttingnorthwestabout 20 miles south from
Spokane, Washington. This type of forestis found generallybetweenan
elevationof 2,000 and 4,000 feet,but goes down to i,ooo feetin the Clear-
October,1930
FOREST
TYPES
OF ROCKY
MOUNTAINS
647
water canyon. In the Salmon River drainage on the Nezperce National
Forest it reachesan elevationof 6,ooo to 7,000 feet. The upper line is very
irregular,recedingalong streamsand protectedslopes and advancingupward
on warmand dryaspects.
Westernyellowpine is everywherethe climax species of this typeand it
usuallymaintainsitselfin pure stands,once the ideal forestcover of needles
and lightgrass has been established. It is mainlyafterfiresthatDouglas fir
and lodgepolepine seed in. On the bettersites,at lower elevations,as well
as along the upper edge of the type otherspecies are frequentlyassociated
withtheyellowpine.
yellowpine forestshows a ratheropen,park-likestand,
The characteristic
with lightvegetation(Fig. 7). This permitsof wind movementalong the
surface,and more sunlightand evaporationthan occurs in the other forest
belts. These conditions,combinedwiththe scant humusand litter,resultin
capacity. There is invariably
a soil poor in loam and of low water-holding
muchrockmaterialnearthesurfacewhichcauses it to heatgreatlyin summer,
than in the otherforest
fluctuations
and bringsabout wider soil temperature
types (Larsen, '23).
The more outstandingspecies of shrubsand othervegetationcommonly
associatedwithwesternyellowpine are listedbelow: (Much moreshrubbery
is encounteredon the mountainslopes than on the more level and even surfaces near the lowertypeborder).
Uva-ursi (L.) Spreng.......
........
Arctostaphylos
AgropyronspicatumPursh. .......W................
L . ...................
Apocynumandrosaemifolium
sagittataPursh. ......
..............
Balsamtorrhiza
BerberisaquefoliumGray. ........................
.................
BrornusmarginatusNees ........
Cala-magrostis
suksdorfiiVasey ....................
Clarkia pulchellaPursh.
CampanularotundifoliaL . ........................
.............
CeanothussanguineusPursh...........
DrymocallisglandulosaLinl. ......................
Pursh. ......
...........
Erythronium
grandiflorum
Heuchera avalifolic Nutt. ........................
...............
Hieraceum albiflorumHook. .......
................
Holodiscus dumosus Nutt. ........
Lupinus ornatusDoug. ...........................
Kinnickinnick
Wheatgrass
Dog bane
Balsam root
Oregon grape
Bromegrass
Reed grass
PhiladelphusLezmisiiPursh .......
PhysocarposmalveceusKuntze ......
Mock orange
Nine bark
Nacrea lanata A. Nels ............................
Pteridium aquilinum ........
................
..............
.....................
.................
Prunus demissa (Dietr.) ........
Pentstemonsp. ..................................
..................
Salix scouleriana(Barr.) ........
Senicio-var.species..............................
...................
Spiraea lucida Doug. ..........
Bluebell
Mountainbalm
Cinquefoil, five-finger
Dogtoothviolet
Alum root
Hawkweed
Oceanspray
Lupine
Everlasting
Brake fern
Chokecherry
Pentstemon
Willow
Groundsel
Spiraea
648
J.
A. LARSEN
SedurnDouglasii Hood. .......
Rosa nutkana..................
Zygadenus venenosus...............
..........
Ecology, Vol. XI, No. 4
Stone crop
Wild rose
Death camas
The weatherdata forthistypewereobtainedfromninestations: Spokane,
Coeur d'Alene, Potlatch,Port Hill, Bonners Ferry,Newport,Orofino,Culdesac, and Kooskia. Orofino,which lies in the ClearwaterCanyon at an
elevationof only 1,027 feet,has the highestmean annual air temperature,
49.80 F. Newport,on the plateau south of the Selkirksat an elevationof
2,300 feet, has a mean temperature of only 43.60 F.
From these figures it
appears that43 and 5o degrees representroughlythe limitingmean annual
of theyellowpine typein the regionwest of the Bitterroots. It
temperatures
mustbe stressed,however,thatthese figuresare mere approximations,
since
it is quite probablethatat otherlocalitieswherethereare no weatherstations
the yellowpine exceeds this range. As regardsprecipitation,
the lower limit
of thistypewould seem to fall betweenthe 17.47 inchesof annual rainfallof
Spokane,and the i6.34 inchesof rainfallat Reardon whichlies just outside
thistype. As fortheupperlimit,the 28.03 inchesof precipitation
at Orofino
was thehighestencountered.
It is not consideredthat maximumair temperaturesper se, or the extremesof air temperatureare sufficient
to impose limitingconditionsto the
downwardextensionof the westernyellowpine in this region,for Orofino,
withexcellentyellowpine forests,exhibitsextremescomparableto those observed over the open prairies. The limitationis found ratherin deficient
precipitation.
As to the upperaltitudinallimit,the line betweenthe yellowpine and the
whitepinetypeis drawnratherclearlyat 43 or 44 degreesF. as a meanannual
air temperature,
and at a growingseason of 200 days duringwhichthe mean
averages above 43 degrees. It should be observedalso that at the Dalles,
Oregon,elevation112 feet,underconditionsof higherrelativehumidityand
less of the drywinds than obtainin easternWashington,the westernyellow
pine thriveswith a mean air temperatureof 52.9 degrees F., and only 15.4
inches of precipitationannually. Evidentlyincreasedatmospherichumidity
in thiscase.
compensatesfordecreasedprecipitation
From the standpointof silvicultureit may be said that the bulk of this
foresttypeis characterized
by pure or nearlypure standsin groupsof different age classes. These range fromlarge and old trees,sometimes400 years
in age, to patchesof reproduction.
WESTERN WHITE
PINE TYPE
The commercialvalue and greatabundanceof the westernwhitepine has
led to the adoptionof the name " westernwhitepine type,"thoughin reality
thispine is not a climax species,sincethe moretoleranthemlock,westernred
cedar,and even whitefirultimately
replaceit.
October,1930
FOREST
TYPES
OF ROCKY
MOUNTAINS
649
The westernwhitepine typeextendsfromsouthernCanada to the Locksa
Divide betweenthe Selway and Locksa rivers. To theeast it extendsto some
of the bettersoils in the Purcell,Cabinet,and northernBitterrootmountains.
On the west it is terminatedby the upper edge of the yellowpine type. It
occurs also in scatteredpatches of littlecommercialimportanceoutside of
theseboundaries.
moistsoil, and is thereforefoundon
It thrivesbest on deep, well-drained,
wherethe extremesof climateare conprotectedslopes in brokentopography
and cloudiness,but also by prosiderablyreduced,not only by precipitation
tectionfromsun and wind. Thoughmuchof the forestarea is now occupied
principallyby even-aged white pine forests,canyon bottoms still contain
enormoustrees of live or dead-mostly dead-virgin cedar and hemlockin
uneven-agedforest.
T'he westernwhitepine typeis richerin plant associates than any other
speciesare givenbelow:
foresttypein the region. The mostcharacteristic
...................
Acer glabrum.Torr...
..................................
Actaea arguta.
AdenocaulonbicolorHook............
.............
AdiantumpedatumL ......
Alnus tenuifoliaNutt...................
Aralia nudicaulisL ...................
...................
Aspidium spW
......
Asarum caudatumLindl. .............
AtrageneoccidentalisHornem. ....................
Betula fontinalisSarg. ...........................
........
Circaea pacificaAsch, and Magn. ..........
Claytonia;perfoliataDonn ........................
ClematisoccidentalisHornem. Hort. ...............
Clintoniaunifolia (Schult.) Kunth ................
Coptis occidentalis(Nutt.) T. & G. ................
Cornus canadensisL. ............................
Cornus stoloniferaMichx. ........................
......
DryopterisFelix-nsas (L.) Schott. ...........
.....
Epilobiumadenocaulon .........
Fatsia horridaBent. & Hook.....................
Michx. and asperrin'zumt
Galilmetriflorum
Gray ......
GeraniumcarolinianumL . ........................
................
.............
Geum imacrophyllumn
Linnaea borealisL . ..............................
Banks .......................
Lonicera involucrata.
................
Lonicera ciliata Poir .............
Lyco podium an-notinumand clavatum ..............
Mertensiaciliata (Torr.) Don. ....................
L . ............................
Mentha cancadensis
Grahamand stauropetala............
Mitella trifida.
........
Montia spatulataacerifoliaand siberica .....
Osmsorihzasp. ..................................
Meis ......
..........
Polygonumspergularaeforme
................
PolysdictumlonchitisL. ..........
Rockymountainmaple
Bane berry
Silver green
Maidenhairfern
Alder
Sarsaparilla
Wood fern
Wild ginger
Clematis
Birch
Circaea
Springbeauty
Virginbower
Clintonia
Gold thread
Trailing dogwood
Dogwood
Shield fern
Willow herb
Devil's club
Northernbedstraw
Geranium
Large leaved aven
Twin flower
Honeysuckle
Honeysuckle
Clubmoss
Lungwort
Wild mint
Bishop's cap
Miner'slettuce
Sweet cicily
Knot weed
Holly fern
650
J.
A.
LARSEN
Ecology,Vol. XI, No. 4
Pyrola secunda and bracteata.....................
Ribes viscossimumPursh. ........................
Rubus melanolasiusFocke ........................
..................
Rubus parviflorusNutt. ........
Rubus sp. ......................................
.............
Sambucus melanocarpaA. Gray ......
Samxbucus
glauca Nutt. ...........................
...............
SmilacinasessilifaliaNutt..........
..................
Spiraea,densifloraNutt. ........
Spiraea lucida Dougl. ............................
..............
Stellaria longpipeslaeta Nutt. .......
Wintergreen
Gooseberry
Red raspberry
Thimbleberry
Blackcap raspberry
Elderberry
Elderberry
Solomon seal
Spiraea
Spiraea
Chickweed
................
Tiarella,unifoliataHook...........
.............
Thalictrumoccidental A. Gray ......
Trautvetteriagrandis Nutt.
...............
TrilliumpetiolatumPursh..........
Valerianasitchensis.............................
Vacciniumimembranaceum(Doug.) Hook. .........
............
VacciniumoccidentaleA. Gray ........
Vagnerica lilacea (Greene) Rydb. .................
Viola glabella Nutt. ..............................
Viola blanda Wild ...............................
Zylosteon sp .................................
Coolwort
Meadow rue
Streptopus amplexifolius .........................
Twisted stalk
Trillium
Valerian
Huckleberry
Huckleberry
False solomonseal
Violet
Violet (yellow)
Bush honeysuckle
Dense virginstandscontainno grass and scant underbrushbecause very
plants,
littlelightreachesthe ground. There do appear a few characteristic
often in distinctcolonies,includingTriarella unifoliata,Asarum caudatum,
Aralia nudicaulis,Cornus canadensis,Linnaea borealis, Coptis occidentalis,
several species of Lycopodiumand many mosses. Along the streamsis a
great profusionof herbaceousplantsamong whichare Adenocaulonbicolor,
Ribes and Fatsia hor0smiorihzanuda, Actaea argitta,Galiumtasperriiuinm,
rida. Some of thetypicalshrubsare Amelanchieralnifolia,Alnus alternifolia,
Ceanothusvelutinus,Acer glabrumand Cornus stolonifera.
After fires,however,a great manyherbaceousspecies take possessionof
the ground,includingthe majorityof the plants listed above (Larsen, '29).
angustiThese cover whole hillsideswithluxuriantgrowthof Chama-enerion
streptopus,etc. After five or six years these
folium,Ribes zviscossimum,
giveway to shrubsof Ceanothusvelutinus,C. sanguineus,Acer glabrum,AmeLonicerainvolucrataand
lanchieralnifolia,Symphoricarpos
recemosus,,Alnus,
L. utahensis,etc.3
of the westernwhitepine forestare
The weatherstationsrepresentative
Sandpoint,Lakeview, Priest River Experiment Station, Prichard, Avery,
Murray,Wallace, Musselshell,Elk City,and Burke. Of these,Sandpointis
the lowest and warmest, with a mean annual temperature of 44.90 F., andh
Burke the highestand coldestshowinga mean annual temperatureof 40.40.
The range in temperaturerequirementfor this type lies thereforebetween
3 Fires and forest succession in the Bitterroot Mountains is more fully treated in
author's report,Larsen, '29.
October,
1930
FOREST
TYPES
OF ROCKY
MOUNTAINS
651
about 400 and 45? F. The growingseason is from i65 to 200 days. The
mean annual rainfallvaries between27 and 45 inches,with not less than 2
inchesduringJulyand August. It maytrulybe said thatthe southwardand
moisture,and the
downwardextensionof this type is limitedby insufficient
upward or northwardextensionby low temperature. A minimumof 27
inchesper year is requiredin the formercase, and a mean annual temperature
of 40? F. in the latter.
of this type is the abundanceof
One outstandingclimaticcharacteristic
snowfall. The contrastis very distinctbetweenthis type and the western
yellowpine, wheresnow is shallow and intermittent.The deep snow cover
is naturallya great protectionto seed and seedlings,as well as a source of
moisturein springand earlysummer.
On the moistersoils, especiallyalong watercoursesand on northaspects,
westernred cedar, westernhemlock,and Engelmann spruce are abundant.
On thedriersouthand westaspects,and on theexposed,rockyslopes Douglas
fir,westernlarch,and lowlandwhitefirare muchin evidence,while western
found. Lodgepolepine is foundon the poorersites,
yellowpine is frequently
whilealpine firis commonat the upper edge of the type. The whitepine is
youngstands have such a
rarelyfound in pure stands,but not infrequently
large proportionof thisspeciesas to appear practicallypure at firstsight.
westernwhitepine standsare characteristically
of fires.
Due to theinfluence
happensthatthesefiresdo not completely
even aged. However,it frequently
destroythe originalforest,and in such case a two or more aged forestmay
result. The more tolerantcedar, hemlock,spruce,and whitefiroftenenter
the standconsiderablyafterthe dominantspecies.
White pine forests(Fig. 8) are among the most beautifulin existence.
The maturetreesare tall, straight,full bole and cylindrical,yieldinga high
amountof selectlumberand a muchheaviercut per acre thanany otherforest
in thisregion: certainsectionshavingaveraged50,ooo board feetper acre at
150 years,over and above the usual reservefor seed treesand fireinsurance.
Many westernwhitepine trees attaina heightof 200 feetand diametersup
to 50 inches. Westernred cedar also is a tree of no mean statureforit frequentlymeasures200 feetin heightand sometimes12 feetin diameter.
SUBALPINE
FORESTS
The subalpineforestsin the BitterrootMountains (Fig. IO) begin at an
elevationof 5,500 feet,wherethe whitepine typeceases. They continueupward to mountaintops at six and seven thousandfeetelevation. In general
this high countryis not precipitous,althoughthere are conspicuousexceptions. The soil, especiallyon the broad ridgetops,is ratherdeep and fertile,
fosteringexcellentstandsof mountainhemlockwhichis here the climax species. The Engelmannspruce and alpine firinhabitnorthslopes and moist
situations,while the lodgepolepine, Douglas firand whitebark pine prefer
exposed and driersites.
J. A. LARSEN
652
Ecology, Vol. XI, No. 4
-.Cd
t_
l
~~~~*
S
._..E0q
0
'44
0
o
October,1930
FOREST
TYPES
OF ROCKY
653
MOUNTAINS
Ai;
IIM7
Aw.
654
J.
A.
LARSEN
Ecology, Vol. XI, No. 4
Under matureclimax hemlockforeststhe vegetationis composedprincisedges,and broomgrasses. Under spruce
pally of Vacciniuntmicrophyllurn,
Sorbus
and alpinefirare foundMenzisia glabella,Vacciniummembranaceum,
scopulina,and Alnus tenuifolia. Aroundeach springand seep is muchlaurel,
alder,elder,and a wealthof succulentspecies,but these have no bearingon
forestdistribution.The completecorrelationof vegetationto foresttypes
has not yetbeen ascertained.
Recurringfiresoriginatingfromlightninghave greatlyreducedthe areas
and
properlybelongingto the climax species and have favoredreproduction
spread of lodgepolepine and to some extentDouglas fir,forthe latterspecies
withstanddroughtand exposurein the seedlingstage muchbetterthan hemas protectorsof
lock,spruceand fir;but theyare not as valuableor effective
thegroundand conserversof moisture.
Stands of lodgepolepine and Douglas firare abundanton the southand
west aspects. Lodgepole pine is inavirablymostabundanttowardthe upper
partof theslope whileDouglas firis moreplentifulas a generalslope species.
This forestmay be even aged over large areas, havingoriginatedaftera fire
of considerablesize, or even aged in small irregulargroups. In the latter
case it is the resultof groundfiresin youngstands. Sometimesveteransof
treesgrow in draws.and protectedsituamucholderage thanthesurrounding
tions. The matureDouglas firtreesmayvaryin heightfromi00 to i50 feet
accordingto thequalityof the site,whilelodgepolepine seldomexceeds 8o or
go feetin height. The treesin thiszone are rathertaperingand limby.
On the wholethereis littleunderbrushpresenton the upper part of such
southerlyslopes, but much grass, much of which is bear grass. One very
typicalplantassociationunderthe upperslope lodgepolepine is Xerophyllum
does not
naturalreproduction
tenaxand Vacciniummicrophyllum.Sufficient
take place and thereare very few seedlingsof any kind,or none,underthe
trees.
Whitebark pine is a treeoccurringmostlyin openingson southand west
aspects. It is therea shorttreeseldomover 6o feetin height,moreoften30
crownand taperingtrunk. Lyall larch
or 40 feetwitha low, wide-spreading
is foundon isolatedhigherpeaks above 7,500 feet. This speciesis not plentiful,but the stands foundare even-agedand pure. It merelymarksthe beginningof what would be a true alpine type had the mountainsbeen of
greaterelevation.
C. H. Shattuck('I5), in ascendingGraves Peak on the ClearwaterForest
in I9I7, listedthe followingspecies:
Trees
Babieslasiocarpa.(up to 8,ooo)
Larix Iyalli (7,500 to 7,800)
Picea Engelmanni(up to 8,ooo)
Pinus albicaulis (timberline)
October,1930
FOREST
TYPES
O;F ROCKY
655
MOUNTAINS
Shrubs
AInus sp.
campanulatus.....................
Cladothaimnus
Juniperusnana.....................
Kalmia gland'ulosa
.....................
Ledum glandulosum
.....................
Fowler, Flora of
the Northwest
Coulter and Nelson,
Coulter and Nelson,
Rocky Mt. Flora
Fowler
Piper
Coulter and Nelson
Sambucus mnelanocarpus
.....................
Spiraea arbuscula......
...............
Vacciniumoccidentale
.....................
Vaccinium microphyllum
...
.....................
Coulter and Nelson
Fowler
Coulter and Nelson
Fowler
Gaultheriahumtifusa
.....................
Gaultheriahumifusa
.....................
Phyllodoce impetriformis.........................
Ptcridofphytes
Cryptogammafragilis.....................
acrosticoides
.....................
Cryptogammna
.....................
Cystoperisoccidentale
Isoetes sp. (in the lake)
Herbaceous Plants
Antennariaparviflora
.....................
media.....................
Antennariaa
Arnica pedunculata
.....................
Aster palustris.....................
Boykiniamajor.....................
Campanula rotundifolia
.....................
.....................
Campanula uniflora
Cicuta purpureata
.....................
Clematis douglasii.....................
Crepis elegans.....................
..............
Epilobiumspicatum.......
Eryogonumjamesii.....................
....
.................
Erythroniumn
grandiflorum
Gentianacalycosa.....................
Hypericumformosumn
.........
............
Media citriodora
......
...............
Mimulus lezwisii.
.....................
.....................
Nartheciumamericanum
Pedicularis lunata.....
Phlox diffusa
.....
Potentilla uniflora
.....
Poligoniumviscosum.......
Rumex occidentalis
....
.
.
.
Valerianasitchensis..
Veronica scutilata
.....
Zerophyllumtenax.....
43
Coulter and Nelson
Fowler or Gray
Manual of Botany
Fowler or Gray
Fowler or Gray
Coulter and
Coulter and
Coulter and
Fowler
Fowler
Coulter and
Coulter and
Fowler
Coulter and
Coulter and
Coulter and
Coulter and
Coulter and
Coulter and
Coulter and
Fowler
Coulter and
Nelson
Nelson
Nelson
Nelson
Nelson
Nelson
Nelson
Nelson
Nelson
Nelson
Nelson
Nelson
Nelson
Coulter and Nelson
Coulter and Nelson
Coulter and Nelson
Fowler
Coulterand Nelson
Coulterand Nelson
Coulter and Nelson
Coulter and Nelson
656
Ecology, Vol. XI, No. 4
J. A. LARSEN
Unfortunately,year-longweather records at these high elevations are
limited. Roosevelt,Idaho, at 7,200 feet,south of the Salmon River in the
Thunder Mountain region,was the nearest station. This is, of course, a
good distancesouthof the westernwhitepine type,but muchhigher. Here
of
of 36.40 F. is recordedand a totalprecipitation
a meanannualtemperature
in summerde26.59 inches. The site may be too cold and the precipitation
and whitefirtype. No permanentsnow records
ficientforthecedar-hemlock
are available,but casual observationsshow thatsnowfallhere is muchgreater
thananywhereelse in thesectionwestof theBitterrootMountains. On Cook
Mountain,6,575 feet elevation,the snow usually covers the buildingscompletelyand does not disappearentirelybeforeJulyI.
Observationsof weatherconditionson lookoutpointsin thisregionduring
July,August and September,i919, show that the air is cooler by day and
warmerby nightat stationslower down, such as Oxford and Musselshell.
are about I o F.
The differences
The relativehumidityfluctuatesless on the mountainthanin the valleyin
summer,and wind movementon the mountainis from3 to 4 timesas great
and fairlyconstantbothnightand day, while at low stationsthe air is fairly
calm at night.
elevariationsat different
One verynoticeablefeatureof the temperature
whichappear in thespringand fall. In the spring
vationsis in thedifferences
altitudesthanin the fall. This is
a greatergradientis observedfordifferent
mostlikelybecausethe snow coverlingerslate in the mountainsin the spring,
at all
whileduringthe fall the snow cover comes morenearlysimultaneously
elevations.
Flathead and BitterrootValleys
basins of Flathead and BitterrootValleys another
In the intermontane
succession of forest types occurs, ranging from
altitudinal
fairlyregular
prairieson the bottomlands and rollingplains at about 3,000 feet elevation,
throughwesternyellowpine on the foothills,Douglas firand westernlarchon
slopes,to subalpineand alpine forestson higherslopes
lowerand intermediate
and summits. Since the westernlarch does not go southinto the Bitterroot
typeabove thewesternyellowpine southof
Valley generally,theintermediate
Missoula consistschieflyof Douglas fir-lodgepolepine. This is in mostrespectssimilarto that foundin centralMontana and centralIdaho.
PRAIRIES
OF THE
FLATHEAD
AND
BITTERROOT
VALLEYS
valley floorsare in most cases ratherflat,originating
The intermontane
from old lake bottoms. They are sometimesgentlyrolling,the result of
wind-blowndeposits.
The line betweenthe open grasslandand the westernyellowpine forests
is in most places regularand distinct. On the west side of the valleys the
thinlowerborderof yellowpine followscloselythe lowestpart of the slopes,
October, 1930
FOREST
Cd
TYPES
OF
4 4 c,;
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MOUNTAINS
ROCKY
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October, I930
FOREST
TYPES
MOUNTAINS
OF ROCKY
659
buton theeast side theoutlyingfoothillsare bare of forestup to a distanceof
500 and sometimesI,ooo feetabove the valleyfloor. At the mouthof lateral
canyonson the east side the demarcationis abruptand sharplydrawn,with
foreston northaspectsand prairieon thosefacingwest.
The weatherstationswhich were chosen to representthis type are St.
Ignatius,by far the most typical,Kalispell and Hamilton,somewhaton the
borderlinebetweentheprairieand thewesternyellowpine. Deerlodgeis also
a prairiestationbut muchhigherand colder than Kalispell. These stations
show a variationin mean air temperaturefrom42.8 to 46.o0 F., Deerlodge
being the coldestand Hamiltonthe warmest. Neitherof these recordsnor
to accountfor the absence of
the extremeslistedin Table VII are sufficient
treegrowth,sincethe temperature
conditionsare less extremethan those observed to the west of the BitterrootMountains. The general absence of
forestmustbe ascribedto deficientannual rainfallwhichaveragesonly I3.50
inches,and in some years drops as low as IO inches. Here and therethe
cause is evidentlylack of drainage,alkalinity,and recurringfires; but these
merelyexercisea local effect.
WESTERN
YELLOW
PINE
FORESTS
The forestsof westernyellowpine and the associated vegetationin the
Flathead and Bitterrootvalleys are, in most respects,similarto the IdahoWashingtonyellow pine forests. It is in effecta part of the same forest
type,joined to it by narrowstripswhich followthe south and west slopes,
often steep rockycliffs,along the Flathead and Kootenai rivers. Its best
development
is reachedin the southernportionsof the BitterrootValley from
Hamiltonto Como.
The upperlimitof the typeis near 4,000 feetin the northernportionsof
the Flathead National Forest, and near 6,ooo feet in southernparts of the
Bitterroot. However, this type does not reach its lowest possible elevation
herebutcontinuesdownwardalong theriverswhichdrainintonorthern
Idaho
rathergenerallyassociated
and Washington. The tree line is, nevertheless,
withthe base of the mountains,givingway to prairiesas statedabove.
The weatherstationsselectedto representthis typeare Libby,Thompson
Falls, Superior,and ColumbiaFalls. Of these,ThompsonFalls is the lowest
of 45.o0 F., whichColumbia
and warmestwitha meanannualair temperature
Falls, the coldest,has a mean of 42.80 F. The latteris apparentlyclose to
the minimumfor the yellow pine here, as shown both by comparisonwith
otherrecordsin Idaho and the sudden transitionat Columbia Falls froma
westernyellowpine to the larch-Douglasfirtype.
reach such high points
Nowherein these valleysdo the air temperatures
as in the Idaho yellowpine type. The maximaare lowerhere,and the absolute minimum is
-
400 instead of -
30?.
It should be noted that the aver-
age lengthof thegrowingseason in thistypehas here only I79 days,and that
it is over 200 days in the westernpart. The conclusionis reachedtherefore
66o
J. A. LARSEN
Ecology, Vol. XI, No. 4
that the yellow pine is not growing under optimum temperature conditions in
the Flathead or in the northernparts of the Bitterroot Valley.
The precipitation is about 20 inches, one station, Superior, within the type
This compares well with the minima recorded in eastregisteringonly I7.50.
ern Washington, Spokane, near the lower edge of the type, showing I7.47.
The station Fortine near the very edge of this type has a precipitationof i8.io,
and Kalispell, outside the type, I5.2I inches. But the summer months, April
to September inclusive, register about 9 inches rainfall in the intermontane
valleys and about 8 inches to the west. Most likely less severe drying conditions and more rainfall compensate somewhat for decreased air temperature.
The conclusion is reached in this case also that the lower or downward extension of the western yellow pine type is limited by insufficientmoisture rather
than by too high temperature.
DOUGLAS
FIR-WESTERN
LARCH
FOREST'S
Within the Kootenai and Flathead watersheds in northwestern Montana
the position between the upper margin of the western yellow pine type and the
subalpine forests is occupied by Douglas fir-westernlarch forests (Fig. 9).
These occur at elevations from 3,ooo to 5,500 feet on benchland, foothills,and
slopes and ridges generally. To be sure, there is also a great abundance of
Engelmann spruce and lodgepole pine, the former mostly on north slopes,
benches and along streams, the latter everywhere without reference to aspect.
The larch and lodgepole pine occupy extensive areas as temporary forests because they have been favored in their distribution and quantity by past fires.
The larch resists fire well on account of its thick bark; the lodgepole pine
seeds in on burns very readily, and is favored by its early seed production, and
the preservation of the seed within the tightlyshut cones. Both species show
prompt germination and establishment on the ashes.
Western larch, Douglas fir and lodgepole pine make up at least 90 per
cent of the species within the type. Englemann spruce appears mainly along
creeks and bordering swamps or low places. Certain pockets with more
favored soil and moisture are occupied by the cedar-hemlock and white fir
mixture representative of northern Idaho. The latter type has a scattering
of western white pine; but the form, growth, and health of these mesophytic
trees are far inferior to those growing in Idaho.
Even-aged stands are the rule everywhere within the type, the age classes
being well represented and having originated after more or less general fires.
Since larch is very fire-resistant,veterans of this species exist everywhere,
these having survived several very bad fires. Douglas fir, since it is more
tolerant of shade than the larch, reproduces prolificallyunderneath the larch.
The natural tendencyis therefore for Douglas firto supplant larch, and, were
it not for recurring fires which destroy the Douglas fir and cause profuse
larch restocking by exposure of fresh ashes as a seed bed, this type would
naturally revert to Douglas fir and Engelmann spruce.
October,I930
FOREST TYPES OF ROCKY MOUNTAINS
66I
Foes of wetr
ai
n
ac
ciesNt.
VleM
FI. II.
tana.
Udrtor
taio LinFaha
fDulsfrPeudtsg
M.)BrtEnlmn
nemn oeapnfiAbe
spuePcaeglan
lasicra(okr ut
662
J. A. LARSEN
Ecology,Vol. XI, No. 4
larch timThe vegetationwithinand underneaththe Douglas fir-Western
ber is not so variedin speciesnor so tall or luxuriantas thatobservedin the
firforestsof Idaho. In this it reflectsthe driercondicedar-hemlock-white
tions of Montana as comparedwith Idaho. Shrubs of Anielanchier,CeaLonicera,Kalmia, etc. are comnothus,Shepherdia,Sorbus,Symphoricarpos,
mon in minoropeningsor on double burns. Other typicalspecies are listed
of the vegetationsee Harshberger
below. For the characterand distribution
p. 550), and Whitford('05, pp. 99, 194, and 276).
('II,
................
AnielanchieralnifoliaNutt............
ArctostaphylosUza-ursi (L.) Spreng. ................
...........
Antennariarose (D. C. Eat.) Greene .....
Antennaria.racemtosaHook. .........................
BerberisrepensLindl. ..............................
Calypso borealisSalisb.
....................
Castilleja sniniataDougl. ........
.................
CeanothusvelutinusDougl..........
..............
Chimlaphilaumbellata(L.) Nutt. ......
glandulosa Lindl..
Drym1tochallis
Fragaria sp. ......................................W
Linnaea borealis L . ................................
Lonicera UtahensisWats............................
Raf..........
.................
Pachystimamyrsinites
Michx. ...................
rarcemosus
Symphoricarpos
...................
ShepherdiaargentiaNutt. ........
...................
Sorbus angustifoliaRydg. ........
Juneberry
Kinnickinnick
Everlasting
Everlasting
Oregon grape
Indian paintbrush
Mountainbalm
Princesspine
ild strawberry
Twin flower
Honeysuckle
Goat brush
Snowberry
Silver bush
Mountainash
larch foresttype are
Climaticconditionswithinthe Douglas fir-Western
taken fromFortine,Haugan, Belton and Upper Yaak. For these stations
varies between40.6? and 42.4' F. Belton
the mean annual air temperature
and Fortineare the colderand Haugan the warmer. The growingseason as
recordsgive contakenfromthe curvesgives I70 days. These temperature
ditionsnearerthe optimumthan the average for the type. It is impossible
fromtheserecordsto determinethe average or optimumas well as the minitoleratedby this type.
mumtemperature
Precipitationrecords indicatean average of 27.83 inches for the year.
This, however,is far above the minimum,Fortine on the lower borderline
showing i8.io inches. The exact requirementwill naturallyvary according
qualities.
to the local soil and its moisture-holding
The conclusionsare thatthe lack of moisturelimitsthe downwardextenwhichprevailhere are suitable
sion of thistype,and thattheair temperatures
is generallyinsuffifirtypebut thatprecipitation
forthe cedar-hemlock-white
cientforit.
SUBALPINE
FORESTS
Above 5,500 feet elevationin the northernFlathead Valley, and above
6,500 in the BitterrootValley, the forestsare distinctlysubalpine,composed
of alpine fir,Engelmannspruce (Fig. 12), and white bark pine.
October,I930
E
.
.
_
.....
....
;
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.
.......................
.
.
663
MOUNTAINS
OF ROCKY
TYPES
FOREST
...
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Engelm.,BlackfeetNational
FIG. I2. EngelmannsprucePicea engelfnanni
Montana
Forest,northwestern
664
J. A.
Ecology,Vol. XI, No. 4
LARSEN
For this type the same general characteristics
previouslydescribedfor the
subalpineforestswest of the BitterrootDivide hold true. Points of difference are: a muchgreateramountof Engelmannsprucein the northernFlathead watershed,sometimesformingextensivepure or nearly pure forests;
the absence of mountainhemlock; and the greaterabundanceof lodgepole
pine and Douglas fir,especiallyon southand west slopes. This typeis chiefly
of importancefor watershedprotection. It is moreovertoo inaccessiblefor
presentday exploitation.
The followingspeciesof truesubalpineplantsare foundabove 6,ooo feet
in the Selkirk Mountains (Harshberger,'ii):
simplexE. Hitchcock
Botrychiumn
PhegopterisalpestrisHoppe
LycopodiumSelago L.
Lycopodiuxm
sitchenseRupr.
Festuca brachyphylla
Schultes
TriseturnsubspicatumL.
Britton
Carex atratiformis
Carex pseudo scirpoideaRydg.
Carex rupestris
funcusMertensianusBorg.
JuncusParryi Engelm.
Luzula spicata,DC.
TofieldiaborealisWahlenb.
Oxyria digynaL.
Silene acaulis L.
Silene Lya.lliiWats.
Alsine laeta Rich.
ArenariacapillarisPoir. v. nordifolia
AnemoneDrummondiiWats.
Aneilmone
patensL. v. Nutt. G.
RanunculusnivalisL.
RanunculusalpeophilusA. Nelson
RanunculuspygonaeusWahl.
Viola cania L. v. adunca G.
Drayas octopetalaL.
Rubus arcticusL. v. grandiflorus
Sibbaldia procumbensL.
Oxytropis(Aragallus) alpicolaRydg.
Lam.
Epilobiumanagallidifolium
G.
Bryanthusglanduliflorus
GaultheriahumifusaGraham
AndrosacesubumbellataA. Nelson
Castelleja pallidcaKunth.
Veronicaalpina L.
MyosotesalpestrisSchmidt
AplopappusLyalli Gray
Aplopappus (Pyrrocomea)Brondegei
A. Gray
ErigeronsimplexGreene (~ E. uniflorusHook.)
Senecio triangularisHook.
TaraxacumrupestreGreene
TaraxacumscopulorumGray
For thesubalpineforestsno trueclimaticrecordsare available. Snowfall
in 1926 on Mt. Silcox (6,870 feet) northof Thompsonfalls,
measurements
showthe following:
Date
Depth,inches......................
Weight,lbs. of cu. ft.ofsnow
.
Jan. I5
Feb. 24
Mar. 3I
May 2
June2I
76.5
105.0
156.o
27.2
142.0
42.4
9........
195
36.2
43.7
21.7
The observersin climbingthe mountaintook measurementsat different
depthsas follows:
Elevations
3,723
Type
Yellow pine
Feb. 24
Mar. 31 ......
I 5.3,,t
21.0
4,924
Yellow pine
29.0
5,795
Larch-D.
52.0
79.0"
6,870
f.
Subalpine
105.0o*
156.o0
October, I930
FOREST
TYPES
OF ROCKY
665
MOUNTAINS
Central Montana
Throughoutmostof centralMontanathetransitionfromprairiesto forest
is to the Douglas Fir-LodgepolePine Zonation,thus skippingalmostentirely
the zone of westernyellowpine so commonin the two westernsections. A
poorlydevelopedforestof yellowpine occurson the Helena National Forest.
We occasionallyfindthejuniper-limber
pineborderassociationon steepslopes
overlyingcoarse sandstoneformations. From Douglas fir-lodgepole
pine the
forestchangesat higherelevationsto subalpinein character,with a greater
proportion
of alpinefirand Engelmannspruce. Eventually,towardtheupper
limitsof treegrowthtruealpine conditionsprevailwithlimberpine,alpine fir
and Engelmannspruce.
PRAIRIES
The Great Plains sectionin thisterritory
changes fromlevel plains at the
lowerpoints,to rollingundulatingplains and to steeperfoothills. It exhibits
wide variationsin floristiccompositionaccordingto differences
in soil and
situation. Ecologists and botanistswill recognize Sage-Brush Formation;
Grama-GrassFormation; Wheat-GrassFormation,CercocarpusFormation;
Wet Meadow Formation,etc. The studentis referredto the excellentworks
of Harshberger,Shantz,Rydbergand Kirkwood. The vegetativecomposition
is generally xerophytic,with Stipa, Conmata,Agropyron spicatumI,Astralagus
mollissimc, Tradescantia virginica, etc. as leading species.
Stationsrepresenting
the climateof thesetreelessstretchesare locatedon
the lowestand mostlevel parts of the plains withinthe agriculturalsections.
They are; Helena, Dillon, Renova, Deerlodge, Phillipsburg,and Virginia
City,varyingin elevationfrom4,000 to 6,ooo feet. For thesethe mean annual temperature is 43.40 F., with extremes of
1030
and
-
400;
187 days
durationabove 43 degrees,and precipitation
under I5 inchesper year. These
values, comparedwiththose prevailingin the Westernyellowpine zones to
the west, are dangerouslylow. Furthermore,thereare on record 3 years,
1917, i9i8 and i9i9, when the average annual precipitation,taking the 3 years
together,was below 12 inches. From I902 to I905, inclusive,the annual
precipitation
recordsforHelena, Havre and Miles Cityaveraged io.47 inches
per year per station. Under such criticalmoistureconditionsnot only the
naturalrestockingof the forest,but its maintenanceand persistencein the
face of fireand droughtis seriouslyjeopardized. Temperatureforthecentral
in Table
and easternMontanasectionis givenin Table IX, and precipitation
to altitudeis shownin Fig. 13.
X, and the relationof air temperature
666
Ecology, Vol. XI, No.4
J. A. LARSEN
ON,
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October, I930
FOREST
TYPES
OF ROCKY
667
MOUNTAINS
Cd
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/80
Ecology, Vol. XI, No. 4
A. LARSEN
-_
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Joo.
<busts ,*.Cenfro/
So
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FIG. 13. Air temperaturegradients for central Montana, showing the relation of
altitude to the number of days with a mean temperatureabove 43? F., and a mean temperaturebelow 32? F.
DOUGLAS FIR-LODGEPOLE
PINE
FORESTS
The outstandingand predominatingforesttypethroughoutcentralMontana is a mixtureof Douglas firand lodgepolepine. L~eiberg('-)
has well
describeda typicalarrangement
and occurrenceof the specieson the Gallatin
and AbsarokaNationalForestsas follows: from5,ooo to 6,ooo feetelevation
limberpineand a smallproportionof westernyellowpine may be seen, while
scatteredgroups of Douglas fir formthin fringesof forestwhich become
fairlywell stockedon northernslopes. From 6,ooo to 8,ooo feet lodgepole
pine is abundant,eitherin closelystockedpure standsor mixed withDouglas
fir and Engelmannspruce. The formeris more abundanton dry, rocky
slopes,whilethelatteroccursmostcommonlyalong canyonbottomsand places
withconsiderableseepage. Above 7,800 feetthe lodgepolethinsout and is
October,1930
FOREST
TYPES
OF ROCKY
MOUNTAINS
669
replaced by limberpine, alpine fir and Engelmannspruce, which together
constitutethe subalpineforest. Timberlineis foundat 9,300 feet on north
and east aspectsand at 9,800 feeton southand westexposures;in some places
on theeasternpartof BeartoothPlateau it occursat Io,ooo and I IOoo. Near
timberlinethe Engelmannspruce is found in greaterabundanceand vigor
thanany otherspecies,withlimberpine second. Both are mereshrubsat the
uppermostlimits.
These forestsare invariablyeven-agedin character. The Douglas firis
seen in greatestabundanceon southand west aspects,while pure stands of
lodgepolepineare morecommonon northand east slopes. It is herealso that
Engelmannspruceoccursespeciallyalongthecreeks. Alpinefiris also rather
prevalentin lodgepolepine stands on east and northaspects. It is a climax
speciesover mostpartsnow occupiedby the Douglas fir-lodgepole
pine type,
beingmuchmoretolerantof shade thaneitherof thosespecies.
The greatabundanceand wide distribution
of lodgepolepine is due to extensivefires,it beingwell knownthatthe fireopens the cones of this species
therebymakingthe seed available forpromptgermination
in the ashes. The
denseyoungstandsof lodgepolepine whichhave sprungup on burnedground
formwell-nighimpenetrable
thickets.
Typicaland commonplantassociatesoccurringwiththe Douglas fir-lodge-
pole pine forest are: Delphinium. cucullatum (tall larkspur) ; Geranium viscosissim-um(geranium) ; Sieversia ciliata (sieversia) ; Festuca ovinla (roll leaf
festuca) ; Agropyron tenerumt (wheat grass) ; Bromus pasteri (drooping
brome grass); Mertensia ciliata (bluebell); Thalictrum occidentale (meadow
rue) ; Dasiophora fructicosa (shrubby cinquefoil); Vaccinium scoparium
(small blueberry); Cercocarpasledifolius(mt. mahogany).
A crosssectionof the climaticconditionsof this foresttypeis obtainedby
recordsfor Red Lodge just below the forestborderat 5,548 feet,and for
Hebgen Dam at 6,700,well withintheupperhalf of thetype. At Red Lodge
the mean annual air temperature is 39.90 F., average maximum for July of
absolute minimum -400;
and the growing season is 138 days. This would be far too cold for westernyellowpine.
75.40 F., absolute maximum iio1,
Red Lodge receivesan annual precipitation
of 19.72 inches,whichis probably
near the minimumforDouglas fir,and Hebgen Dam shows 24.16 inches. It
is thewriter'sconclusionthatthisregionreceivesinsufficient
rainfallfor such
mesophytic
speciesas hemlock,whitefir,westernwhitepine,larchand cedar,
whichare foundwest of the ContinentalDivide. Westernlarchwould come
nearestto findingsuitablemoistureconditionshere,but the air temperature
appears far too low and the growingseason too short. Larch in western
Montanagrowsundera meanannualair temperature
of 42.4? and a growing
season of I70 days. The recordshere show a mean from34.5 to 40.00 and
a growingseason 20 to 30 days shorter.
670
J.
A. LARSEN
SUBALPINE
Ecology,Vol. XI, No. 4
FORESTS
In the subalpineforesttypeEngelmannspruce,alpine fir,and white-bark
pineincreasein proportion
to increasein elevationuntillodgepoleand Douglas
firdisappearentirelyfromthe stand. The onlyavailable weatherstationfor
this zone is Lake Yellowstoneat 7,733 feet. This shows a mean annual air
of 3I.40 F., a growingseason about I50 days, and precipitation
temperature
of 24.53 inchesper year. This appearsmuchtoo cold fortreessuch as western larch,and bothtoo dryand too cold forwesternhemlock,whitefir,western red cedar and westernwhitepine.
The alpinefloraof theYellowstonePark as listedby Tweedy (i886) is as
follows:
Antennaria,alpine Gaertn.
Draba crassifolia Graham
Dryas octopetacla
L.
L.
Gray
Epilobiu-nlatifoliurn
Arenariaverna L. var.hirtaWats.
EritrichiumaretioidesDC.
Arenia strictaMichx.
ErigeronuniflorusL.
ArtemisiascopulorumA. Gray
ErigeronursinusEaton
Astragalusalpinus L.
ErigeronradicatusHook.
Bryanthus (Phyllodoce) enmpetri-Festuca ovinaL. var.brezvifolia
Wats.
formiisSmith
Habenaria obtusataRichards
Castilleja pallida Kunth.var. septen- Hulsea nana A. Gray
trionalisGray ( C. acuminata Ivesia (Horkelia) Gordonii Hook.
Pursh)
JuncusDrummondiiE. Meyer
Carex atrataL.
JuncusParryi Engelm.
Care alpina Swartz
Lloydia,serotinaSweet.
Carex concinnaR. Br.
Luzula spicata Desv.
Carex seirpoideaMichx.
Mertensia.alpina Torr.
Carex rigida Good.
Oxyria digynaCamptd.
Douglasia,montanaA. Gray
PedicularisParryiA. Gray
Draba,alpina L.
Pedicularisscopulorumn
A. Gray
Draba area Vahl.
Pedicularis groenlandicaRetz.
Aplopappus (Pyrrocorna) Lyallii A.
Summary and Conclusion
A studyof the distribution
and requirements
of permanentforesttypesin
Montanaand northernIdaho has led to the followingconclusions:
i. The occurrenceof climax or permanentforesttypesis mainlyin altitudinalbeltsor zonationswhichare determinedchieflyby air temperature
and
precipitation. Minor variations or differencesin the forest composition
withinanyone of thesebeltsor zones are due to local variationsin soil,aspect,
gradient,etc.
2. Each of theseclimaxbeltsor permanent
foresttypesexhibitsa definite
requirementin temperatureand precipitationwhich differsmateriallyfrom
any othertype. The typesat loweraltitudesrequirerelativelylarge amounts
of heat and littlemoisture,and those of high elevationslittleheat and relativelylarge quantitiesof moisture.
October,
I930
FOREST
TYPES
OF ROCKY
MOUNTAINS
671
3. In everycase thedownwardextensionof thetypeis limitedby deficient
too low forthe
by a temperature
moisture,whiletheupperlimitis determined
species which occur withinthe given type. The grasslands exhibita wide
range of temperature requirement from
390
to
500
F.
These grasslands
for tree growth. For
is insufficient
occur whereverthe annual precipitation
most sections17 inchesa year or less resultin grassland,regardlessof air
temperature.
4. Each permanentforesttype exhibitsa fairlydefiniteassociationof
vegetationin the formof annuals,shrubs,and otherperennials;and these,as
well as densityand compositionof the forestitself,react upon the site and
tend to formfor each foresttypea fairlytypicalsoil and surfacecondition.
typesof forest. They
These conditionsvary considerablyfor the different
of trees,and therefore
influenceboththe naturaland artificialestablishment
thesilvicultural
management.
5. Since the annual precipitationis much less east of the Continental
Divide than in the westernsections,such mesophyticspecies as cedar, hemlock, lowland whitefirand whitepine are not presentthere. On the other
hand, on accountof the verydry summersin the western,comparedto the
easternsection,Douglas fir,lodgepolepine,and westernyellowpine, require
in Idaho thanin centralMontana.
a greaterannual precipitation
forthevarioustypes: The western
6. The followingare the requirements
rangingfrom440 to
yellowpine grows witha mean annual air temperature
50? F., precipitationfrom I7 to 22 inches per year. The cedar-hemlockwhitefirtypein Idaho grows undera mean annual temperaturefrom400 to
450,
and an annual precipitation ranging from 27 to 44 inches. The larch-
also from400 to
Douglas firtypein Montanarequiresa meanair temperature
firtype. For
450 F., but requiresless moisturethanthecedar-hemlock-white
the larch-Douglasfir the precipitationranges from about 20 to 30 inches
annually. The Douglas firand lodgepolepine typethriveswitha mean annual air temperature ranging from 350 to 400 F., and an annual precipitation
from20 to about25 inches. Subalpineforestsrequiremean air temperatures
from 300 to
350
F. and precipitation varying from 24 to 30 inches in central
Montana,and up to 36 inchesin Idaho.
In subalpineforeststhe lengthof the growingseason is usuallyless than
I50 days, i.e., the period duringwhich the mean air temperatureaverages
above 430 F. In westernyellow pine forestson the otherhand it is from
I80 to 24i days.
7. It followsalso that foresttypesof high elevationsshow muchgreater
snowfall,greaterdepthof snow and longerdurationof snow cover than the
lower types. Snowfall in the subalpinetypein Idaho is up to 207 inchesa
year,whilethatin westernyellowpine is usuallyless than50 inches. Furthermore,snow cover in subalpineregionsis continuousthroughoutthe winter,
whilein the westernyellowpine forestthe groundis oftenbare duringwarm
periodsin winter.
44
672
J. A. LARSEN
Ecology,Vol. XI, No. 4
The preparationof this paper was begun on the suggestionof Raphael
Zon of the U. S. Forest Service. It could not have progressedwithoutthe
kindcooperationof the membersof theU. S. WeatherBureau and the supervisorsof the different
NationalForests. Valuable suggestionsand criticisms
have beengivenbyJ. Kittredge,Jr.,G. A. Pearson,C. G. Bates, J. F. Preston,
J. WV.
Toumey,and RobertMarshall.
LITERATURE
CITED
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conditions. Jour. Forestry, 16: 861-870.
Gail, F. G. 1921. Factors controlling the distribution of Douglas fir in semi-arid
regions of the Northwest. Ecology, 2: 281-291.
Gaskill, Alfred. 1906. Why prairies are treeless. Proc. Soc. Am. Foresters, 1: 158178.
Harvey, Leroy H. 1908. Floral succession in the prairie grass formation of southeastern South Dakota. Bot. Gaz., 46: 81-108.
Harshberger, John W. 1911. Phytogeographic survey of North America, pp. 516550. Vegetation de; Erde. Vol. 13, New York, G. E. Stechert and Co.
Larsen, J. A. 1929. Fires and forest succession in the Bitterroot Mountains.
Ecology, 10: 67-76.
1922. Weather records at lookout stations in northern Idaho. U. S. Dept.
Agr. Mon. Weath. Rev., Vol. 50, No. 1.
. 1923. Physical factors of site. Ms. Report U. S. Forest Service, Missoula,
Mont.
1922. Soil shifting and deposits. Science, 55: 457.
Leiberg, John B. 1904. Forest conditions in the Absaroka Division of the Yellowstone Forest Reserve. Prof. Paper U. S. Geol. Surv. No. 29, p. 13.
Pearson, G. A. 1928. The relation between spring precipitation and height growth
of western yellow pine saplings in Arizona. Jour. Forestry, 16: 677-689.
Piper, Charles V. 1906. Flora of eastern Washington. National Herbarium, 11:
38-40.
Shattuck, C. H. 1915. Observations within the Clearwater National Forest. Ms.
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Tweedy, Frank. 1886. Flora of the Yellowstone National Park. Published by the
author.
U. S. Dept. of Agriculture, Weather Bureau. 1921-22. Climatological summaries
by sections.
Weaver, J. E. 1914. A study of the vegetation of southeastern Washington and
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