_Adaptability to climate_ is the first requisite in the species to be
planted.
It is best to choose from the native growth of the region which is
known to be adapted to it. With regard to species not native, the
reliance must be placed upon the experience of neighboring planters
and upon experiment (at first on a small scale), after study of the
requirements of the kinds proposed for trial.
Adaptation must be studied, not only with reference to temperature
ranges and rainfall, but especially with reference to atmospheric
humidity and requirements of transpiration.
Many species have a wide range of natural distribution, and hence
of climatic adaptation. If such are to be used, it is important to
secure seeds from that part of the range of natural distribution where
the plants must be hardiest, i. e., the coldest and driest region in
which it occurs, which insures hardy qualities in the offspring. For
instance, the Douglas spruce from the humid and evenly tempered Pacific
Slope will not be as hardy as that grown from seed collected on the dry
and frigid slopes of the Rockies. Lack of attention to this requisite
accounts for many failures. It must also be kept in mind that, while
a species may be able to grow in another than its native climate, its
wood may not there have the same valuable qualities which it develops
in its native habitat.
_Adaptability to soil_ must be studied less with reference to mineral
constituents than to physical condition. Depth and moisture conditions,
and the structure of the soil, which influences the movement of water
in it, are the most important elements. While all trees thrive best
in a moist to "fresh" soil of moderate depth (from 2 to 4 feet) and
granular structure, some can adapt themselves to drier or wetter,
shallow, and compact soils. Fissures in rocks into which the roots can
penetrate often stand for depth of soil, and usually aid in maintaining
favorable moisture conditions. In soils of great depth (i. e., from the
surface to the impenetrable subsoil) and of coarse structure water may
drain away so fast as not to be available to the roots.
Soil moisture must always be studied in conjunction with atmospheric
moisture; for, while a species may thrive in an arid soil, when the
demands of transpiration are not great, it may not do so when aridity
of atmosphere is added. Trees of the swamp are apt to be indifferent to
soil moisture and to thrive quite well, if not better, in drier soils.
_Adaptability to site._--While a species may be well adapted to the
general climatic conditions of a region, and in general to the soil,
there still remains to be considered its adaptability to the particular
"site," under which term we may comprise the total effect of general
climate, local climate, and soil. The general climatic conditions are
locally influenced, especially by the slope, exposure, or aspect, and
the surroundings. Thus we know that eastern exposures are more liable
to frost, western exposures more liable to damage from winds, southern
more apt to be hot and to dry out, and northern to be cooler and
damper, having in consequence a shorter period of vegetation. Hollows
and lowlands are more exposed to frosts and more subject to variations
in soil moisture, etc.
Hence for these various situations it is advisable to select species
which can best withstand such local dangers.
_The use value, or utility_, of the species is next to be considered.
This must be done with reference to the commercial and domestic demand,
and the length of time it takes the species to attain its value. The
greater variety of purposes a wood may serve--i. e., the greater its
general utility--and the sooner it attains its use value the better.
White pine for the northeastern States as a wood is like the apple
among fruits, making an all-round useful material in large quantities
per acre in short time. Tulip poplar, applicable to a wider climatic
range, is almost as valuable, while oak, ash, and hickory are standard
woods in the market. Other woods are of limited application. Thus the
black locust, which grows most quickly into useful posts, has only a
limited market, much more limited than it should have; hickory soon
furnishes valuable hoop poles from the thinnings, and later the best
wagon material, not, however, large quantities in a short time; while
black walnut of good quality is very high in price, the market is also
limited, and the dark color of the heartwood, for which it is prized,
is attained only by old trees. The black cherry, used for similar
purposes, attains its value much sooner.
By planting various species together, variety of usefulness may be
secured and the certainty of a market increased.
_The forest value_ of the species is only in part expressed by its use
value. As has been shown in another place, the composition of the crop
must be such as to insure maintenance of favorable soil conditions,
as well as satisfactory development of the crop itself. Some species,
although of high use value, like ash, oak, etc, are poor preservers of
soil conditions, allowing grass and weeds to enter the plantation and
to deteriorate the soil under their thin foliage. Others, like beech,
sugar maple, box elder, etc., although of less use value, being dense
foliaged and preserving a shady crown for a long time, are of great
forest value as soil improvers.
Again, as the value of logs depends largely on their freedom from
knots, straightness, and length, it is of importance to secure these
qualities. Some valuable species, if grown by themselves, make crooked
trunks, do not clean their shafts of branches, and are apt to spread
rather than lengthen. If planted in close companionship with others,
they are forced by these "nurses or forwarders" to make better growths
and clean their shafts of branches.
Furthermore, from financial considerations, it is well to know that
some species develop more rapidly and produce larger quantities of
useful material per acre than others; thus the white pine is a "big
cropper," and, combining with this a tolerably good shading quality,
and being in addition capable of easy reproduction, it is of highest
"forest value."
Hence, as the object of forestry is to make money from continued wood
crops, use value and forest value must both be considered in The
selection of materials for forest planting.
_Mutual relationship of different species_, with reference especially
to their relative height growth and their relative light requirements,
must be considered in starting a mixed plantation.
Mixed forest plantations (made of several kinds) have so many
advantages over pure plantations (made of one kind) that they should
be preferred, except for very particular reasons. Mixed plantations
are capable of producing larger quantities of better and more varied
material, preserve soil conditions hotter, are less liable to damage
from winds, fires, and insects, and can be more readily reproduced.
The following general rules should guide in making up the composition
of a mixed plantation:
_a._ Shade-enduring kinds should form the bulk (five-eighths to
seven-eighths) of the plantation, except on specially favored
soils where no deterioration is to be feared from planting only
light-needing kinds, and in which case those may even be planted by
themselves.
_b._ The light-needing trees should be surrounded by shade-enduring
of slower growth, so that the former may not be overtopped, but have
the necessary light and be forced by side shade to straight growth.
_c._ Shade-enduring species may be grown in admixture with each
other when their rate of height growth is about equal, or when the
slower-growing kind can be protected against the quicker-growing (for
instance, by planting a larger proportion of the former in groups or
by cutting back the latter).
_d._ The more valuable timber trees which are to form the main crop
should be so disposed individually, and planted in such numbers among
the secondary crop or nurse crop, that the latter can be thinned out
first without disturbing the former.
Where a plantation of light-foliaged trees has been made (black walnut,
for instance), it can be greatly improved by "under-planting" densely
with a shade-enduring kind, which will choke out weed growth, improve
the soil, and thereby advance the growth of the plantation.
The selection and proper combination of species with reference to
this mutual relationship to each other and to the soil are the most
important elements of success.
_Availability_ of the species also still needs consideration in
this country; for, although a species may be very well adapted to
the purpose in hand, it may be too difficult to obtain material
for planting in quantity or at reasonable prices. While the beech
is one of the best species for shade endurance, and hence for soil
cover, seedlings can not be had as yet in quantity. Western conifers,
although promising good material for forest planting, are at present
too high priced for general use. Some eastern trees can be secured
readily--either their seed or seedlings--from the native woods; others
must be grown in nurseries before they can be placed in the field.
_Whether to procure seeds or plants_, and if the latter, what kind,
depends upon a number of considerations. The main crop, that which is
to furnish the better timber, had best be planted with nursery-grown
plants, if of slow-growing kinds, perhaps once transplanted, with
well-developed root systems, the plants in no case to be more than 2 to
3 years old. The secondary or nurse crop may then be sown or planted
with younger and less costly material taken from the woods or grown in
seed beds, or else cuttings may be used.
In some localities--for instance, the Western plains--the germinating
of seeds in the open field is so uncertain, and the life of the young
seedlings for the first year or two so precarious, that the use of
seeds in the field can not be recommended. In such locations careful
selection and treatment of the planting material according to the
hardships which it must encounter can alone insure success.
Seedlings from 6 to 12 inches high furnish the best material. The
planting of large-sized trees is not excluded, but is expensive and
hence often impracticable, besides being less sure of success, since
the larger-sized tree is apt to lose a greater proportion of its roots
in transplanting.