FIRES AND FOREST SUCCESSION IN THE BITTERROOT MOUNTAINS OF NORTHERN IDAHO J. A. LARSEN Iowa State College Foresters have recently begun to seek a more intimate knowledge of the natural, successional stages by which forests regain terrain lost by extensive fires or other pronounced denuding agencies. Studies in this field lead to a closer understanding of the factors which control the distribution, compo- sition and density of the present forest, the silvical requirements of the various species which compose the existing forest and of the soil building or soil deteriorating influences which are operative after large fires. It is the author's privilege in this paper to record certain observations on forest succession in the Bitterroot Mountains in northern Idaho, gathered in the course of several years of forest research in that region. This is the terri- tory lying north of the Salmon river between the crest of the Bitterroot divide and the Columbia river plateau. Perhaps no other region in the United States is visited by forest con- flagrations of similar magnitude, frequency or degree of destruction. The contributing causes are mainly as follows: the moist winter and spring which give rise to a profuse and luxuriant forest vegetation of a highly in- flammable nature; an invariably dry summer with afternoon temperatures often ranging between 95 and ioo degrees F. (350 to 380 C.); the low atmospheric humidity which frequently falls to I5 per cent and lower. These critical conditions are combined with strong, desiccating winds sweeping in from the arid region to the southwest. The fires, therefore, when once under way, travel with great speed and rapidly assume uncontrollable pro- portions. Not infrequently an entire township (approximately 95 sq. km.) of timber is wiped out in the course of one or two days. These large forest fires kill all of the trees and the seedlings. In from ten to twenty years most of this dead timber lies prone, and it then presents a fire hazard of greater magnitude than existed in the green, virgin forest. The second fire, on this account, is even less controllable and more destructive than the first. The return of the forest to the climax composition subsequent to these devastating fires proceeds along certain well defined steps or stages which may be considered parts of the entire cycle of succession, or the natural process of regeneration. The first steps in this succession begin with the appearance of species intolerant of shade, and capable of withstanding con- siderable drought and exposure, and concludes with the establishment of 67 This file was created by scanning the printed publication. Errors identified by the software have been corrected; however, some errors may remain.
Fires and forest succession in the Bitterroot Mountains of northern
IdahoFIRES AND FOREST SUCCESSION IN THE BITTERROOT MOUNTAINS OF
NORTHERN IDAHO
J. A. LARSEN
Iowa State College
Foresters have recently begun to seek a more intimate knowledge of
the natural, successional stages by which forests regain terrain
lost by extensive fires or other pronounced denuding agencies.
Studies in this field lead to a closer understanding of the factors
which control the distribution, compo- sition and density of the
present forest, the silvical requirements of the various species
which compose the existing forest and of the soil building or soil
deteriorating influences which are operative after large fires. It
is the author's privilege in this paper to record certain
observations on forest succession in the Bitterroot Mountains in
northern Idaho, gathered in the course of several years of forest
research in that region. This is the terri- tory lying north of the
Salmon river between the crest of the Bitterroot divide and the
Columbia river plateau.
Perhaps no other region in the United States is visited by forest
con- flagrations of similar magnitude, frequency or degree of
destruction. The contributing causes are mainly as follows: the
moist winter and spring which give rise to a profuse and luxuriant
forest vegetation of a highly in- flammable nature; an invariably
dry summer with afternoon temperatures often ranging between 95 and
ioo degrees F. (350 to 380 C.); the low atmospheric humidity which
frequently falls to I5 per cent and lower. These critical
conditions are combined with strong, desiccating winds sweeping in
from the arid region to the southwest. The fires, therefore, when
once under way, travel with great speed and rapidly assume
uncontrollable pro- portions. Not infrequently an entire township
(approximately 95 sq. km.) of timber is wiped out in the course of
one or two days.
These large forest fires kill all of the trees and the seedlings.
In from ten to twenty years most of this dead timber lies prone,
and it then presents a fire hazard of greater magnitude than
existed in the green, virgin forest. The second fire, on this
account, is even less controllable and more destructive than the
first.
The return of the forest to the climax composition subsequent to
these devastating fires proceeds along certain well defined steps
or stages which may be considered parts of the entire cycle of
succession, or the natural process of regeneration. The first steps
in this succession begin with the appearance of species intolerant
of shade, and capable of withstanding con- siderable drought and
exposure, and concludes with the establishment of
67
This file was created by scanning the printed publication. Errors
identified by the software have been corrected;
however, some errors may remain.
68 J. A. LARSEN Ecology, Vol. X, No. i
shade-tolerant trees or species which are both tolerant and
moisture loving. The exact number of the steps in the succession,
depends, however, in a great measure upon the factors of
topography, soil, degree of exposure, the intensity of the fire and
the amount of destruction wrought.
It is of considerable interest to note that the subordinate forest
vegeta- tion also develops after these fires in regular
successional stages in its pro- gression toward the climax
subordinate vegetation, and that the final, climax association, or
ultimate type, is attained and developed underneath the climax type
or association of the forest trees. Those subordinate species of
tem- porary occupancy become established immediately after the
forest fire and generally simultaneously with the appearance of the
temporary arborescent species, while those of permanent occupation
follow directly upon the heels of the climax arborescent
species.
In composition the subordinate vegetation which follows the fires
is also governed by the condition of the habitat, the degree of
destruction and the requirements of the individual species, so that
in the subordinate flora there is also distinct grouping in
accordance with these characters or qualities. However, since the
seedlings of the aborescent species develop very slowly during the
first three or four years, and much slower than the annuals of the
subordinate flora, the latter are in much greater evidence in the
beginning. A superficial examination would ordinarily give the
impression that there existed nothing but these rapidly growing and
very dense annuals during the first few years following the
fire.
FOREST ZONES AND SILVICAL REQUIREMENTS OF THE TREES
In this region, in which the elevations of the mountains vary from
6,ooo to 8,ooo feet (I,800 to 2,400 meters) above sea level, and
the valleys from 2,000 to 3,ooo feet (6oo to goo meters), the
western yellow pine forests, which are composed mainly of Pinus
ponderosa, occupy the lowest zone of tree growth; the western white
pine (Pinus monticola), with its associated species of western red
cedar (Thuja plicata), western hemlock (Tsuga heterophylla), grand
fir (Abies grandis), Douglas fir (Pseudotsuga taxi- folia), and
western larch (Larix occidentalis), occupy the slopes of inter-
mediate elevation ranging from 2,500 feet to 5,500 feet. Above this
middle zone the forest is composed of subalpine species represented
by Engelmann spruce (Picea engelmannii), mountain hemlock (Tsuga
mertensiana), white bark pine (Pinus albicaulis), alpine fir (Abies
lasiocarpa), and lodgepole pine (Pinus murrayana var. contorta).
These subalpine species are fre- quently individually present also
within the intermediate forest zone. The discussion in this article
deals exclusively with the conditions surrounding the succession
within the intermediate forest zone.
This middle forest zone is designated by foresters in the region as
the western white pine type, chiefly because of the abundance and
economic im- portance of the white pine. This tree is not a climax
species, however, for
January, i929 FIRES AND FOREST SUCCESSION IN IDAHO 69
hemlock, western red cedar and grand fir are the only true climax
repre- sentatives among the trees.
The western white pine and its associated species thrive best on
well drained and fertile soil such as is found on the protected
easterly or north- erly gradients and on lower slopes, bottoms and
benches. In these locations the soil remains moist throughout the
entire summer, being sheltered by a broken topography, a very dense
crown canopy of the trees, and covered by deep layers of " duff "
and humus.
The forests composed chiefly of western white pine are usually
even- aged and rather dense. Over large areas the pine is the
predominant spe- cies. It maintains a rather rapid and remarkably
uniform rate of height growth by which, in most cases and
situations, it overtops its competitors. Although both the
lodgepole pine and the western larch grow as fast as the pine in
most locations, these two are more intolerant of shade and
therefore not in a position to arrest its growth seriously or to
crowd it out. Mixed with the western white pine there is generally
an understory of hemlock, cedar or grand fir wherever the soil is
rather moist or the site well pro- tected, especially at the low
elevations, while toward the upper margin of the zone and more
particularly on the exposed south of west aspects we find more of
the Douglas fir and lodgepole pine.
Another characteristic of the western white pine, and one which
gives it a considerable advantage over the associated species, is
the ability of its seed to lie over in the duff on the forest floor
for a period of two or three years and then germinate upon the
removal of the overhead canopy. Some of this seed is ordinarily
deeply buried by rodents and may escape injury in the course of a
forest fire. On account of this prolonged or delayed germi- nation
and preservation of the seed there is usually a greater quantity of
seed of this species available for germination subsequent to a fire
than of any of the other trees in the forest.
All of the forest trees which are found in mixture with the white
pine are listed below. The arrangement is such as to show the
relative require- ments of the trees for light, moisture and soil
fertility, and to bring out their
Tolerance Moisture Soil Permanency
W. yellow pine W. yellow pine Lodgepole pine Lodgepole pine Western
larch Lodgepole pine W. yellow pine West. larch Lodgepole pine
Douglas fir Douglas fir
Douglas fir West. larch West. larch Douglas fir W. white pine W.
white pine Grand fir W. white pine Grand fir Grand fir W. white
pine Grand fir
Alpine fir West. hemlock Alpine fir Alpine fir Eng. spruce Alpine
fir Eng. spruce W. hemlock W. red cedar W. red cedar W. red cedar
Eng. spruce W. hemlock Eng. spruce W. hemlock W. red cedar
70 J. A. LARSEN Ecology, Vol. X, No. I
permanency or lack of permanency in the forest as this develops
toward the climax association for a particular site. The least
shade-tolerant, the least moisture demanding, and the least
fastidious as to soil quality, are placed first on the list.
The effect of these differences in requirements of light, moisture
and soil is observed in adjustments of the species in distribution
and composition according to local variations in the habitat.
Whenever there occur a great variety of the species of trees in the
unburned virgin forest there is a dis- tinct grouping in harmony
with the above factors and requirements.
FIRST STAGE IN SUCCESSION
It would simplify our position greatly if we could consider first
all fires occurring in the climax forest, for from this viewpoint
we could more easily trace the influences of the fires and the
various steps in the succession. Unfortunately fires do not wait
for the completion of the cycle. They are of frequent occurrence,
and relatively few stands are permitted to reach the true climax
complexion before being overtaken by conflagrations. Nevertheless,
whatever the condition of the forest at the time of its destruc-
tion, lodgepole pine and western larch become established first on
the most severely burned and denuded areas. After small fires the
forest ordinarily comes back directly to cedar and hemlock, but
after the larger fires the other species may come first, though
sometimes with the climax trees in the mix- ture. One of the most
noticeable effects of extensive and repeated burns is the
appearance of considerable bodies of lodgepole pine and western
larch.
These two species usually appear groupwise according to local
conditions. The lodgepole pine grows nearly pure on the dry knolls
and exposed ridges or otherwise denuded and deteriorated sites,
especially toward the upper part of the western white pine zone.
Pure stands of lodgepole pine may also be seen on gravelly slopes
and benches of relatively low elevation. On north and east
exposures, however, where the soil possesses greater mois- ture
holding capacity than on south aspects, western larch generally
appears in extensive bodies of pure forest in the first stage of
the succession. Al- though both of these trees are intolerant of
shade, the lodgepole pine seed- lings survive and the larch
seedlings succumb on dry warm and exposed sites. On the cool and
moist aspects, however, the situation is reversed.
Both of these species possess characteristics which enable them to
re- claim burned ground speedily. The lodgepole pine produces seed
at an as- tonishingly early age, and the seed is withheld and
preserved within the unopened cone until the fires have prepared a
suitable germinating bed. It is well known that some of the cones
open and shed the seeds shortly after the fire, while numerous
others remain firmly closed for an indefinite period. Unopened
cones with enclosed seed have been found entirely over- grown with
wood. The western larch, on the other hand, is favored by a
January, i929 FIRES AND FOREST SUCCESSION IN IDAHO 7I
remarkably long life and a very high degree of resistance to injury
from fire, in that it possesses an unusually thick bark and a
foliage of less inflammable nature than the lodgepole pine. On this
account very good trees of larch will survive and bridge several
critical fires, thereby retaining, after the fire, large seed-trees
which become important factors in a speedy restocking with
larch-provided only that the soil is not too warm and dry for the
rather tender larch seedlings.
On sites suitable for the western white pine, and especially where
the pine existed in large numbers before the occurrence on the
fire, the white pine usually comes in strongly after the burn and
becomes a part of the first stage in the succession.
Much depends also upon the size of the area burned. If the fire
which takes place in the climax forest is small, the climax
arborescent species will succeed themselves directly without going
through the temporary and inter- mediate stages. The same is true
of any climax forest anywhere. It may be observed to good advantage
in the Beech-Birch-Hard maple forest of the northeast United
States.
SECOND STAGE OF SUCCESSION
In the absence of fires in the temporary stands of lodgepole pine
and western larch the western white pine and Douglas fir will
establish them- selves under and among the former and eventually
crowd them out. These intermediate species, when in possession of
the ground, represent the second stage in the forest succession.
Stands properly belonging to this intermedi- ate step in the
succession are on the whole rather abundant. The reason is that the
forest of this composition is an excellent soil builder, and
because white pine and Douglas fir reproduce unusually well after
single fires. Stands of these two species are considered the second
stage in forest suc- cession whether they come in under lodgepole
pine and larch, or directly after a single fire which has destroyed
a climax cedar-hemlock forest or a white pine or Douglas fir
forest. In fact the larger percentage of the western white pine
stands in Idaho at present have succeeded directly after burns
which have destroyed white pine and Douglas fir stands, that is,
single fires. It is mainly after double fires that lodgepole pine
and larch seed is in abun- dance.
THIRD AND FINAL STAGE IN SUCCESSION
As soon as the western white pine and its associates of
intermediate light and moisture requirements reach maturity, begin
to decay and thereby pro- duce a broken forest canopy, the western
hemlock, western red cedar and grand fir begin underseeding. The
forest is then in the early stages of the climax association. These
last species of greater shade-tolerance than the former effectually
prevent the natural reproduction of the white pine and the Douglas
fir. It should be made clear that the grand fir, which is
less
72 J. A. LARSEN Ecology, Vol. X, No. i
tolerant than the hemlock and cedar, is often found growing with
white pine and Douglas fir in the intermediate stage. The fir is
then present only as scattered individuals on northerly aspects,
but may be in greater abundance on south slopes, particularly the
lower parts of such slopes where the soil is deep and moist.
These climax species respond readily to local differences in the
habitat. The western red cedar requires distinctly wet soils but
not stagnant condi- tions of water; the hemlock needs a rather
moist soil without free water, and the grand fir thrives with much
less moisture than either cedar or hem- lock. The result of these
different demands is a grouping of the species according to
variations in the soil moisture. The cedar occurs in greatest
abundance near the streams and on well watered soil. The hemlock is
found much oftener on moist flats and on lower north aspects, while
the grand fir prefers the rolling lowland and favorable south
aspects.
Within the western white pine forest zone one may find considerable
Engelmann spruce and alpine fir, but these trees do not properly
belong in the intermediate zone. They are at home in the higher
zone above the white pine. When found in mixture with the white
pine, etc., it is only along the cool streams and in deep sheltered
canyons where the soil is moist but cold and where there is
comparatively little sunlight.
Of the three climax species mentioned above, the cedar is king. It
is by far the largest and the longest lived tree in this region. It
attains diameters from six to ten feet and an age up to 6oo years.
It is furthermore much less afflicted with fungous and insect
attacks than the other trees. The hem- lock and grand fir are in
the great majority of cases defective. For these reasons many
large, old cedars exist as the only remnants of a former climax
forest. These large trees remain chiefly along the stream flats and
in deep canyons, where they have escaped destruction by the fires
which ravaged the slopes.
The natural tendency, therefore, of repeated forest fires in this
forest zone is to limit more and more the numbers and distribution
of the tolerant forest trees and relegate them to flats and canyons
or lower slopes, while at the same time extending the ranges and
increasing the numbers of the in- tolerant species, particularly
western larch and lodgepole pine, and, to some extent also, the
western white pine.
SUCCESSIONAL STAGES IN THE SUBORDINATE VEGETATION
In the first stage of the succession the subordinate species are
mostly those of herbaceous character and of relatively rapid
growth, as well as those whose seed is carried to great distances
by the wind. The principal mem- bers of this association are:
Antennaria densiflora Nutt. Pearly everlasting Antennaria racemosa
Hook. Everlasting
Chaemenarion angustifolium Scop. Fire weed Epilobium palmer Rydb.
Willow herb Geranium carolinianum L. Wild geranium Salix
scouleriana Barr. Willow Spiraea lucida Dougl. Spiraea Solidago sp.
Golden rod Monarda menthaf olia Graham Horsemint Sidalcea
neomexecana A Gray Hollyhock Xerophyllum tenax (Pursh) Nutt Pine
grass
Among the above species the everlasting, hollyhock, pine grass,
golden rod, horsemint and spiraea occupy southerly aspects, and the
geranium, fireweed and others prefer the northerly slopes.
Practically all of these temporary and shallow-rooted species are
beneficial to the site and to the establish- ment of the
arborescent species which follow, for, although they do not pre-
vent erosion or appreciably increase the quality of the soil and
site they throw considerable shade the result of which is a
reduction of surface tem- peratures and decreased transpiration of
the tender evergreen seedlings underneath. This protection is, of
course, most needed on the south and west aspects. On moist and
fertile soil the temporary herbaceous vegeta- tion is sometimes
altogether too dense for the survival of evergreen seedlings,
especially those of larch, lodgepole pine and Douglas fir.
SECOND STAGE IN THE SUCCESSION OF THE SUBORDINATE SPECIES
The subordinate species listed above give way after two or three
years to a second stage of plants composed mainly of perennials,
the majority of which possess berry fruits so that the seedling is
effected by birds. This seedling evidently begins during the first
season after the burning of the forest. In the case of the various
species of Ribes information is far from complete. The
investigations on the seedling of Ribes carried on in connec- tion
with the blister rust control will undoubtedly yield some very
interesting and valuable information in this respect. The principal
species composing the second set of plants are:
Alnus tenuifolia Nutt. Alder Acer glabrum Torr. Rocky Mountain
maple Betula fontinalis Sarg. Mountain birch Ceanothus velutinus
Dougl. Mountain balm Cornus canadensis L. Trailing dogwood Cornus
stolonifera Michx. Willow dogwood Fragaria sp. Strawberry
Holodiscus dumosus Nutt. Ocean spray Lonicera utahensis Wats.
Honeysuckle Lonicera involucrata Banks Honeysuckle
Prunus demissa Nutt. Choke cherry Ribes reniforme Rydb., Nutt.
Currant Ribes viscossimum Dougl. Currant Rubus parviflorus Nutt.
Thimble berry Rubus strigosus Michx. Raspberry Sambucus glauca
Nutt. Elderberry Sambucus melanocarpa Gray. Elderberry
Symphoricarpos racemosa Michx. Snowberry Sorbus angustifolia Rydb.
Mountain maple Vaccinium nembranaceum Dougl. Huckleberry Vaccinium
occidentale A. Gray. Huckleberry
Among the above species the Acer, Holodiscus, Ceanothus and Betula
may be either wind disseminated or arise by sprouts from earlier
specimens.
Lonicera, Ceanothus, Prunus, Holodiscus and Vaccinium are
distinctly dry site species, while Betula, Alnus, Sambucus, Rubus
parviflorus, Rubus strigosus and Cornus are moisture loving. The
remaining species are some- what intermediate in their moisture
requirements. After a second burn dry south slopes may support
nothing but a scattered growth of Ceanothus velu- tinus or C.
sanguineus. Along the water courses where the forest canopy is
broken and small patches of fertile soil occurs, one may find
impenetrable thickets of Cornus stolonifera, Spiraea tomentosa and
Ribes reniforme.
The influence of this group of shrubs is distinctly beneficial, for
the rapidly accumulating leaf mold expedites the rehabilitation of
the impover- ished soil, the foliage shades and shelters seedlings
of the mesophytic forest trees of fir, spruce and white pine, and
the roots provide an effective check on soil erosion. This stage of
the subordinate vegetation, therefore, becomes an important nurse
crop for the white pine and its associated species. After eight or
ten years the young white pines emerge from underneath the shrubs,
overtop them, and crowd them out entirely. The maple, only, may
persist within and underneath the new evergreen forest for a period
of fifty to sixty years.
With the elimination of this second set of subordinate species the
forest builds its own layers of litter and humus, paving the way
for a third set of subordinate vegetation of somewhat uninfluential
and unassuming propor- tions composed of the following
species:
Adenocaulon bicolor Hook. Silver green Actea rubra Ait Baneberry
Adiantum pedatum L. Maiden hair fern Boykinea heucheriforme Rydb.
Boykinea Aralia nudicaulis L. Wild sarsaparilla Circea pacifica
Asch. and Magn. Circea Claytonia chrysantha Greene Spring
beauty
Celernatis occidentalis Homen. Virgins bower Clintonia uniftora
(Schult) Kunth Clintonia Felix mas Wood fern Galium triflorum Michx
Three-flowered bed straw Galium boreale L. Northern bed straw
Limnia spathulata (Dougl.) Heller Miner's lettuce Mertensia
spathulata (Dougl.) Howell Mentha canadensis L. Wild mint Mertensia
ciliata (Torr) Don. Bluebell Osmorrhiza sp. Sweet cicily Seraphis
gigantea Dougl. Hellebore Streptopus amplexifolius L. Trilium
petulatum Purch. Trillium Valeriana septemtrionalis Rydb. Valerian
Vagneria liliacea (Greene) Rydb. False Solomon seal Valeriana
sitchensis Bong. Veronica scutellata L. Veronica Veratrurn
Eschscholtzianum (R. & S.) Rydb. Skunk cabbage
Of the above, Boykinea, Seraphis, Streptopus, Montia, Mentha and
Veratrum grow only along the streams or on the very wet ground
under the broken forest canopy. The remaining species may be found
anywhere on moist soil wherever the forest canopy is not dense. The
influence of the above species on soil building or in preventing
erosion is almost negligible. It is much less important than in any
of the preceding associations.
Almost simultaneously with the invasion of this climax formation
will appear the climax species in the subordinate forest
vegetation. The out- standing species in the subordinate climax
associations are the following:
Arctostaphyllos uva-ursi L. Kinnikinnick Asarum caudatum Lindl.
Wild ginger Berberis sp. Oregon grape Chimalphila umbellata Nutt.
Pipsissiwa or Princess pine Coptis occidentalis Nutt. T. and G.
Gold thread Fatsia horrida Benth. and Hook. Devils club Heuchera
ovalifolia Nutt. Alumroot Linnea borealis L. Twin flower Lycopodium
selago L. Clubmoss Lycopodium sitchensis Rydb. Clubmoss Pachystima
myrsinites Raf. Goat brush Pyrola uliginosa Torr. Round shinleaf
Claytonia chrysantha Greene Spring beauty Tiarella unifoliata Hook.
False miterwort Viola glabella Nutt. Violet
76 J. A. LARSEN Ecology, Vol. X, No. i
In this association, Fatsia and numerous ferns line the water
courses; Coptis, Asarum, Pyrola, and Lycopodium are of the most
tolerant, for they persist underneath the densest forest. In the
intermediate class as to mois- ture and light requirements are
Linnaea, Pachystima, Berberis, and among these one finds many
species of the foregoing group, especially Tiarella, Claytonia,
Galium, Montia and Circea.
The influence of this series upon erosion, soil building or
protection to the seedlings is nil.
SUMMARY
When the cedar-hemlock-grand fir forest in the Bitterroot Mountains
has been destroyed by fire the forest eventually returns to the
climax composi- tion through a series of associations which follow
each other in regular suc- cession, beginning in most cases with
two intolerant or drought resistant species, western larch and
lodgepole pine. This first stage, together with the distinct first
stage of the subordinate vegetation improve the site and pave the
way for a second forest association composed chiefly of Douglas fir
and western white pine with its own peculiar subordinate type of
vegetation. This second stage eventually gives way to the climax
forest association of cedar, hemlock and grand fir and its own
distinct and permanent subordinate vegetation of perennial
evergreen species.
Front Matter
Studies in Animal Aggregations: Natural Aggregations of the Isopod,
Asellus Communis [pp. 14-36]
Atometric Rates Read Instantaneously and an Automatic Continuous
Recorder for Rate Fluctuation [pp. 37-46]
Comparison of the Physical Factors of Habitats [pp. 47-66]
Fires and Forest Succession in the Bitterroot Mountains of Northern
Idaho [pp. 67-76]
Influence of Certain Water Conditions, Especially Dissolved Gasses,
on Trout [pp. 77-96]
Fresh Water Studies. I. The Relative Temperature, Oxygen Content,
Alkali Reserve, the Carbon Dioxide Tension and pH of the Waters of
Certain Mountain Streams at Different Altitudes in the Smoky
Mountain National Park [pp. 97-111]
Factors Controlling Forest Types on the Cloquet Forest, Minnesota
[pp. 112-125]
Animal Communities of an Illinois Prairie [pp. 126-154]
Reviews
Review: untitled [pp. 157-158]
Review: An Ecological Study of Vegetation on Mt. Desert Island,
Maine [pp. 158-160]
Notes and Comment
The Determination of Dissolved Oxygen with the Micro-Winkler
Apparatus of Thompson and Miller [pp. 163-164]
Combined Edition of Clements' Plant Succession and Plant Indicators
[pp. 164-165]
Back Matter