ARTHUR W. SAMPSON, Professor of Forestry, Emeritus, and ARNOLD M. SCHULTZ, Associate Specialist, School of Forestry, University of (California
This article is the fourth and last section of a paper which was prepared at the request of FAO. Earlier sections appeared in Unasylva, Vol. 10, Nos. 1, 3 and 4. Following the publication of this sections the whole series is being made available under a separate cover.
Conservation in Land Clearing
THE intimate relations of soil and climate, and the effects of land treatment on stream flow, have been recognized for decades. Since we live in an environment composed of many facets, the best pattern of land use is not always or immediately discernible. Too often the operator goes in for short-term gains, overlooking the long-term advantages of more conservative use.
Before an operator can be assured that his plan for removing vegetation from his land is sound, it is well that he first considers a few basic principles of wild land management.
In order to put a given parcel of land to its best permanent uses, be it brushland, savanna, or swamp, the owner or administrator - whether federal or private-must consider the effect of his operational plan on the land in the long run. This precaution applies as well to legislative policies pertaining to disposal of lands under government ownership or control as it does to the private operator. However, avoidance of faulty practices is not always possible in a young country where experience in land use is limited.
The intensive and often irrational use of both farm and publicly-owned wild lands of all countries has in many localities resulted in serious soil 1088 and in less usable water (Figure 70). Too commonly old stumps and snags show that many inches of soil have been carried by sheet erosion into drainage channels during flash storms and periods of strong winds. As a result, farmers and graziers over much of the world must now till pasture, and conserve the remaining relatively unproductive B-horizon, since most or all of the fertile A-horizon - the virgin top soil-has been lost (37).
(U.S. Forest Service)
(After Sampson [33])
It is well to keep in mind that the primary objectives of soil conservation and watershed management are to stabilize and maintain the natural resources to the greatest extent economically feasible. On wild lands this can best be done by maintaining an abundant and vigorous plant cover (Figure 71).
By maintaining a desirable porosity and permeability the soil absorbs rainfall readily, hence erosion is greatly minimized. The roots also function to maintain permeability. The litter furnishes food for microorganisms which help maintain soil permeability, and the organic matter gives the soil properties to resist compaction. Another important function is the sheltering effect of the soil from direct insolation and desiccating winds, and from the full force of rainstorms (32, 33). On well-vegetated lands a goodly portion of the rainfall is intercepted and released gently to the soil. On the other hand, faulty logging, excessive grazing and wild fires are among the most common causes of upsetting plant-soil relations.
Another effect of vegetation on watershed management is its capacity to withdraw water from the soil and thus, in a measure, reduce water yield. Kittredge (22) has estimated annual evapo-transpiration loss from southeastern pine forests at 30 inches (75 cm.) and oak-hickory forests at 20 to 30 inches (50 to 75 cm.). Hoover (20) found that a hardwood forest removed from 17 to 22 inches (43 to 66 cm.) of water annually. Since the anatomy of leaves of the various species composing the plant mantles are different, transpiration 1088 would also be different. To offset this seeming loss by transpiration is the fact that the soil mass is again receptive to water absorption as more rain falls, thus minimizing run-off and erosion.
Closely related to water loss is the character, volume and distribution of the root systems. Grasses have numerous fibrous roots which are localized in the upper few inches of the soil; trees have deep woody roots with few surface rootless; shrubs also have woody roots but they are less coarse than tree roots and are anchored at depths intermediate to those of grasses and trees. One plant community, therefore, may withdraw moisture from the soil over a much longer period than another composed of different species. On inferior steep slopes brush species, in contrast to grasses and trees, will send down "stringer" roots in rock crevices which will maintain these frugal plants indefinitely. Bleak watershed units should be left undisturbed as no vegetation will serve better than the well-adapted natural cover which they already support. It is, therefore, necessary for the land manager to learn as much as possible about rates of water 1088 and root system characteristics of the dominant trees and shrubs of his land.
Protection of watersheds against uncontrolled fires is of utmost importance because of the danger of serious damage to the soil. The remaining plants may be deprived of needed water, and the run-off carries with it plant nutrients, ashes, and surface soil, thus lowering the quality of the site. Further soil depletion accrues during dry weather from sheet erosion (31).
The time required for a watershed to recover from a severe burn varies according to climate, type of soil, steepness of slope, length of time the soil remains bare, and several other such considerations. Recovery may take several decades or even centuries where much soil has been lost. If left to nature, recovery will pass through the entire sequel of successions and reach the tree stage or climax when the soil is again productive. Seeding and planting, though costly, will greatly speed up the time of recovery.
Whether the amount of usable water is increased or diminished by burning and thinning of the stand remains a moot point. More snow or rain will reach the soil on burns, but surface run off is correspondingly greater.
Nearly all operators and administrators have encountered from time to time unexpected if not baffling problems in maintaining the desired returns from their lands. Some of the areas may be in need of reforestation, other parts may have a thinned out forage cover, still others may have become brushy-. The suggestions which follow may be helpful in meeting some of the problems involved.
Seeding and planting
Reforestation. There is urgent need to re-establish trees on forest lands where the timber has been logged or burned off. After fire or logging watershed values are lowered, and a new tree stand should be started to stabilize the soil and to put the land back into commercial use. This is expensive and requires skill (30).
Reforestation by natural means is relied on where adequate trees of desirable species remain. On heavily burned or improperly logged areas, on the other hand, seeding or planting of trees is the only means available for restocking the land.
Range seeding. Prompt re-establishment of a forage cover on cleared grazing land is important for three reasons:
a
) to protect the soil from excessive erosion;
b) to curtail establishment of brush seedlings;
c) to provide feed for livestock.
In order to protect the soil, the land should be revegetated the first year after clearing. By careful selection of site and species, and by proper planting and management, earlier and more palatable forage may be obtained than the lands produced when in their virgin state (10).
Outstanding features of range management
Attempts seeding of cleared brush or forest lands are doomed to failure if grazing is allowed before the resulting seedlings have developed a strong root system. The fact must not be overlooked that these woody species are hardy and vigorous, thus indicating how well adapted they are. The species that are to be introduced, therefore, must be given all cultural advantages possible over the potential reinvasion of the hardy woody plants.
In the western United States, areas seeded to perennial grasses should have at least one full year, and in many instances two years, of total protection before grazing is allowed. Rodents should be poisoned where numerous, and, if possible, heavy invasions of weeds should be mowed in early summer or sprayed with a selective herbicide.
Satisfactory distribution of livestock over the range is of great importance in order to avoid spotty overgrazing and undergrazing. On cattle range this can be dope by salting away from the water, development of watering places remote from meadows and other favorite units, and by fencing to prevent drifting and better control of the animals. On open sheep range the herder should so direct the flock that the grazing pressure is properly distributed.
One of the cardinal principles of range management is that of determining and applying the proper season of use. The opening date for grazing should be delayed until growth is far enough along to afford a "good bite," and until the soil has become firm. Generally the grass leaves should be 3 to 5 inches (8 to 13 cm.) in length and all the free gravitational water should be drained away. A close relation exists between seasons of use and numbers of livestock grazed, for grazing cape capacity is determined in terms of total animal months use. Range that extends into different life zones should be grazed on a seasonal zonal basis. The earliest units should be grazed first, followed by the next higher elevational zone.
Harvesting of the forage crop should be conservative. Too close grazing ultimately leads to reduced forage yield and loss of soil fertility. Appraisal of range utilization, once a proper standard of use has been established for a given area, can be made by estimation, by measurement, or by a combination of these.
Most perennial ranges are properly stocked when about 60 percent of the year's growth is left on the ground at the end of the grazing season. This would be roughly equivalent to a stubble height of 4 to 6 inches (10 to 13 cm.) for the tall grass type composed of plants like the wheatgrasses, fescues, and bromes, and 1 ½ to 2 inches (4 to 6 cm.) for the short grass type, as for blue grama and buffalo grass.
Generally range utilization is uneven because of differences in preference of livestock for the various species. For practical reasons, the degree of utilization is based on so-called "key" species, or some two or three kinds of plants that provide most of the forage. When the key plants are properly utilized-as at the end of the grazing season-the range as a whole is also assumed to be properly grazed (39).
One complication in blooper stocking is that forage production may fluctuate widely from year to year because of differences in precipitation and temperature. Accordingly, stocking rate should be based on production between the average and the poorest years. The question of stocking must be settled for each individual ranch or administrative unit as local conditions and experience would indicate.
The recognized importance of brush control over large areas of the western and southern United States has been instrumental in initiating extensive research and practical control trials during the past 16 years. The studies have engaged the talents of mechanical engineers, chemists, ecologists and physiologists, agronomists, animal husbandmen, range and wildlife managers, foresters and economists.
There is much to be learned from the work which has been done in the United States and elsewhere, much of which can be applied to other regions of the world. On the other hand, it is well to recognize that each region of the world has its peculiarities and some specific research will need to be carried on within each region. Much of this will need to be done by governments or well-financed institutions with the co-operation of industry. Future research will no doubt best be continued in this cooperative manner.
Appendix-Comparative effectiveness, cost and other attributes of brush control methods in five distinct vegetation types
TABLE: 1. - ERADICATION OF BIG SAGEBRUSH IN WESTERN UNITED STATES (27)
|
Operation |
Percentage kill |
Other effects |
Adaptability to terrain |
Ease of after treatment |
Availability of equipment |
Cost of control¹ |
|
Discing |
70-90 % of old; slightly less of young |
Kills all other vegetation except sprouting shrubs; mulches stems and prepares seedbed. |
Limited to little or no rock except with brush-land plow |
Suitable for drilling; seedbed may be loose |
Most plows & discs commercially available, the brushland plow must be custom made |
$3 to $5 per acre |
|
Railing |
30-80 % of old; 15-30 % of young, flexible |
Damage slight except for pedestaled bunchgrasses and non-sprouting shrubs |
Limited to level or uniform slopes with no protruding boulders |
Not easily drilled unless piles of brush are burned. Hails cover broadcast seeding poorly |
Not commercially available; can easily be built in farm shop |
$0.50 to $1 per acre one-way on large tracts |
|
Harrowing |
30-70 % of old, brittle; 10-30 % of young, flexible |
Does not affect sprouting shrubs or annual vegetation; 10-20 % bunch-grasses |
Primarily suited to rocky ground and rough terrain |
Drilling difficult Seeding ahead of harrowing covers well |
Not commercially available; can easily tee built in farm shop |
$3 to $6 per acre |
|
Beating |
50-90 % of old; 30-60 % of young, flexible |
Little damage to herbs, grasses, or non-sprouting shrubs |
Limited to rock-free or slightly rocky sites |
Can be drilled unless brush is heavy; broad casting before beating has been successful |
Commercially available |
$3 to $8 per acre |
|
Grubbing |
90-99 % for all age classes |
Kills most other shrubs; bunch-grasses killed except when cut deep but then shrubs are not killed either. Rhizomatous grasses undamaged |
Limited to level and rock-free areas |
Some clearing is necessary before drilling is possible. Broadcast seeding not advised with out packing soil |
Commercially available |
Approximately $6 per acre |
|
Controlled burning |
96-100 % of all ages |
Kills non - sprouting shrubs and less than 30 % of grass; sprouting shrubs not affected much |
No limit except as imposed by fire danger and erosion hazard |
Can be drilled or broad-cast easily. Seedbed is firm. Ashes are beneficial to seedling growth |
Technical assistance or experience needed, equipment is generally available |
$0.50 to $2.00 per acre on tracts over 1,000 acres |
|
Spraying |
70-96 % of large, old; less of young |
Kills weeds as well as many palatable fortes. Grasses unharmed. Other brush plants not seriously affected |
Unlimited by air or ground |
Dead brush remains standing and must be removed before drilling, air broadcasting feasible |
Equipment and chemicals commercially available |
$3 to $6 per acre |
¹ 1 acre = 0.4047 hectare. The cost per hectare in, therefore, approximately two-and-a-half times greater.
TABLE: 2. - CONTROL CHAPARRAL IN CALIFORNIA (6)
|
Operation |
Percentage kill |
Other effects |
Adaptability to terrain |
Ease of seeding after treatment |
Availability of equipment |
Cost of control¹ |
|
Bulldozing (windrowing) |
95-100 % top kill is possible where terrain permits |
Does not prevent sprouting; windrows hinder subsequent management unless burned |
Limited to level or moderate slopes where erosion hazard is low |
Broadcast seeding only. Windrows are obstacles |
Commercially available |
$10 to $20 per acre |
|
Bulldozing (mashing) |
95-100 % top kill |
Does not prevent sprouting; mashed brush is easily burned or it may be left as mulch if not too thick |
Less restricted to gradual slopes than wind rowing method |
Broadcast seeding only; much litter on ground |
Commercially available |
$10 per acre |
|
Discing |
|
Breaks up woody stems and uproots many shallowly rooted sprouts. Infiltration enhanced |
Limited to gently sloping land or very short steep slopes. Excellent for ridgetops |
Broadcast seeding only; too many stems and stumps remain intact |
Commercially available |
$5 to $7 per acre |
|
Double-discing |
|
Besides above, good seed - bed prepared |
Same as above. Both should be done on contour |
Drilling may be possible in certain places |
Commercially available |
$10 to $12 per acre |
|
Controlled burning(conventional) |
0-95 % top kill. Variable due to weather conditions |
Seldom kills much more than 50 percent of sprouting species. Difficult to keep out steep slopes that should remain in brush. Most seeds remain viable |
No limit. Hazardous areas should be excluded if possible |
Broadcast seeding by air or on horseback. Seed coverage impossible |
Permit required. Co - operation of landowners and state agencies necessary |
$0.40 to $3.65 per acre (see Fig. 50) |
|
Controlled burning(area ignition) |
Up to 100 % top kills. Many more plants are completely killed than with conventional method |
Heat intense enough to kill all plants. Some sprouting will take place. Higher proportion of seeds scorched |
Limited to terrain where bulldozer can operate |
Burn is clean enough to make uniform seed distribution possible from ground. Seed can be covered with drag |
Bulldozers available. Technical assistance is most important item |
$2.50 to $10 per acre for mashing (see Table 1) |
|
Aircraft spraying with 2-4, D |
Variable, depending on species |
No effect on grasses; one application does not prevent sprouting; seed - lings very susceptible |
No limit, except canyons where drafts make it too dangerous to fly. Spray drift is biggest problem |
Seedbed not suitable after chemical treatment |
Chemicals are available; planes may be scarce during crop dusting period. Helicopters less generally available |
$3 to $6 per acre (fixed wing plane) $6.50 to $8.50 per acre (helicopter) |
¹ 1 acre = 0.4047 hectare. The cost per hectare is, therefore, approximately two-and-a-half times greater.
TABLE 3. - ERADICATION OF MESQUITE IN TEXAS AND SOUTHWESTERN UNITED STATES (2)
|
Operation |
Percentage kill |
Other effects |
Adaptability to terrain |
Ease of seeding after treatment |
Availability of equipment |
Cost of control¹ |
|
Hand grubbing |
85% |
Eradication can be confined entirely to mesquite bushes |
No limits |
Inadequate seedbed preparation |
All tools are available |
$20 to $32 per acre |
|
Kerosene basin |
92% |
Kills all herbaceous vegetation a foot or more from base |
No limits |
No seedbed prepared; brush still standing after treatment |
Kerosen and cans cheap and available |
$13 to $18 per acre |
|
Kerosene pour |
76% |
Small circle immediately around base has no herbaceous cover |
No limits |
No seedbed; brush still standing |
All materials available |
$4 to $14 per acre |
|
Aerial spray of 2, 4,5-T |
|
Aids in control of herbaceous weeds; does not affect grass |
No limit. Mesquite ranges are ideally suited for aerial treatment |
Standing brush is greatest obstacle |
Commercially available |
$3 to $4 per acre |
|
Chaining |
|
Takes out most of old, brittle brush; no effect on grasses |
Limited to fairly level wide expanses |
No special seedbed preparation; chains are good for covering seed |
Commercially available |
$2.50 to $3.00 per acre |
|
Machine grubbing |
|
Many young plants remain |
No limit, except on steep slopes |
Loose seedbed prepared |
Commercially available |
$10 to $15 per acre |
|
Rootcutter |
63 % |
Digs up soil and other plants. No erosion hazard on most mesquite ranges |
Limited to level or slightly sloping land |
Seedbed is loose and covered with uprooted plants |
Commercially available |
$3.50 to $6.00 per acre |
¹ 1 acre = 0.4047 hectare. The cost per hectare, is therefore, two-and half limes greater.
TABLE 4. - ELIMINATING HARDWOOD CULL TREES FROM WOODLAND IN CENTRAL UNITED STATES (2)
|
Operation |
Percentage kill |
Adaptability to terrain |
Suitability for seeding |
Availability of equipment |
Cost of control (U.S.$) |
|
Basal spray ¹ |
100% |
No limit |
Not seeded |
No special equipment needed. Hand sprayer, oilcan or paint brush can be used |
Labor: 0.0010D² + 0.0042 |
|
Frill method |
100 % |
No limit |
Not seeded |
Axe and oilcan needed |
Labor: 0.0015D + 0.0049 |
|
Cornell tool |
61-72 % |
No limit |
Not seeded |
Cornell tool available or can be made in shop |
Labor 0.0028D - 0.0007 |
¹ Chemical used was kerosene solution of 2, 4, 5-T containing 16 lb. (7 k.) acid equivalent per 100 gallons (455 liters) of solution
² D stands for diameter breast high. Thus for a 10-inch (25 cm.) tree, labor cost for basal spray is $0.01 + $0.004 and total cost is 14 ½ or 15 cents.
TABLE 5. - LAND CLEARING OF HAMMOCKS ¹ AND FLATLANDS IN FLORIDA (5, 16)
|
Operation |
Percentage kill |
Other effects |
Detailed description of vegetation |
Hours per acre |
Cost of control¹ |
|
Tree cutter ³ |
Cleared adequately for pasture establishment |
Underground stumps and root systems left in ground |
105 trees per acre: oaks, magnolia, gums, maple, also palmetto. Trees varied from 6-24 in. (15-61 cm.) d.b.h. |
Tree cutter: 0.95 |
$41.67 per acre.4 |
|
Detachable stumper |
Cleared thoroughly enough for cultivated crops |
Holes 10 feet (3 m.) in diameter and several feet deep were left by removal of large trees |
108 trees and stumps per acre: oaks, magnolia, gums, maple, and chest-high palmetto. Stumps and trees varied from 6-24 in. (15-61 cm.) d.b.h. |
Detachable stumper: 1.06 |
$52.32 per acre |
|
Bock rake |
Debris chopped and land leveled for cultivated crops |
Good layer of much on soil |
116 stems per acre, including 7 very large trees and 17 stumps. Species vere live oak, water oak, cherry, dogwood, vines, and palmetto |
Rock rake: 3.55 |
$60.56 per acre |
|
Bock rake |
Completely cleared |
None |
Heavy hammock with oaks, magnolia, dogwood, large vines and palmetto. Average of 88 trees per acre cleared and piled with rake and 7 with stumper |
Rock rake: 4.17 |
$76.47 per acre |
|
Detachable stumper |
Cleared adequately for pasture establishment |
Soil loosened bay plow |
Palmetto flatwoods: heavy growth of palmetto 5-6 feet (1.5-1.8 m.) tall; green pine trees and stumps with heavy tap roots. About 60 stems per acre |
Detachable stumper: 0.82 |
$31.03 per acre |
¹ In the southern United States, a piece of rich land with hardwood trees growing on it.
² 1 acre = 0.4047 hectare. The cost per hectare is, therefore, approximately two-and-a-half times greater.
³ All equipment attached to 155 hp. tractor.
4 Based on tractor rental or $15.00 per hour.
