BY MARINUS WESTVELD
Spreading the seed. The plane flew at about 80 miles per hour, 50 to 75 feet above level.
This paper was presented at the national meeting of the Society of American Foresters, Boston, Massachusetts, 16-18 December 1948. A number of members of the Northeastern Forest Experiment Station of the U. S. Forest Service assisted in this project. Among them were: A. G. Hart, V. S. Jensen, W. J. Kidd, Jr., T. W. McConkey, J. R. McGuire, T. F. McLintock, W. E. McQuilkin, S. F. Ricker, P. M. Rushmore, E. J. Schreiner, R. F. Taylor, and M. J. Williamson. The writer gratefully acknowledges their assistance.
DEVASTATING forest fires such as those that swept through Maine in October 1947 present difficult and challenging problems in re habilitation. How can such areas be brought back promptly into tree production? Forest fires frequently burn with such intensity that they destroy not only all reproduction but the timber as well. This is the condition in which thousands of acres of white pine forest were left following the Maine conflagration last fall. If the Massabesic Experimental Forest (which lies in the center of the York County burn) is a fair sample, about 40 percent of the burned forest area is in such a condition. If such areas are to be rehabilitated in the near future, artificial reforestation will be necessary.
This can be accomplished in two ways: (1) by planting nursery grown stock, and (2) by direct seeding. On the Massabesic Experimental Forest direct seeding by airplane was chosen for several reasons. The area in need of reforestation was extensive and afforded an opportunity to test direct seeding on a reasonably large scale. The method possessed possibilities for rapid ground cover and for speedy reforestation at greatly reduced costs. Ground conditions were favorable for germination of seed because most of the underbrush and other competing vegetation had been detroyed by the fire. The danger of serious seed losses from rodents had been minimized by the hot fires which had reduced rodent population to a considerable degree. And lastly, the method provided the opportunity for developing much needed information on the potentialities of airplane seeding as a means of successfully regenerating recently burned forest land. The venture would also yield valuable by-products such as the cost of airplane seeding compared with other direct seeding methods and planting operations, as well as procedures to be followed to obtain the best results from this method of reforestation.
The Massabesic aircraft seeding project was not the first of its kind attempted in the United States. In 1946 the State of Oregon seeded a 500-acre burn (200 ha.) to Douglas fir, Pseudotsuga taxifolia, and Port Orford cedar, Chamaecyparis lawsoniana, in equal proportions at the rate of ½ pound per acre (0.6 kg. per hectare) and 100 acres (40 ha.) of grass and brushland to western hemlock, Tsuga heterophylla, Sitka spruce, Picea sitchensis, and Port Orford cedar at rates of 1/8 and ¼ pound per acre (0.14 and 0.28 kg. per hectare). The State Forester reports that 21.7 percent stocking resulted.
The Crown-Zellerbach Corporation in 1947 undertook airplane seeding of 1,100 acres (450 ha.) in Oregon. The success of this seeding remains to be determined. The company schedule called for the seeding of 2,600 additional acres (1,100 ha.) by helicopter in 1948.
Airplane seeding of burns has also been undertaken in Canada. The Ontario Department of Lands and Forests has sown spruce, Picea sp., as well as red pine, Pinus resinosa, and white pine, Pinus strobus, by aircraft. Sowing densities ranged from 5 to 10 thousand seeds per acre (12 to 24 thousand seeds per hectare). The Department has pronounced these seedings moderately successful.
The New Brunswick-Department of Lands and Forests has also been active in this field. In 1947 it undertook to reseed burned-over Crown lands from the air. Germination as high as 6,000 seedlings per acre (15,000 per hectare) was obtained on 1947 burns. Results on 1944 burns, however, have been disappointing. This poor showing is attributed to excessive competition from the vegetation with which the older burns are clothed.
A survey of the Massabesic Experimental Forest after the forest fires indicated the need of artificial reforestation on some 2,200 acres (890 ha.). The original plan of the Northeastern Station was to sow both red and white pine seed. However, no red pine seed could be obtained, and white pine seed proved to be both scarce and costly - only 800 pounds available at a cost of $6 per pound (360 kg. at $13 per kg.). Thus, relatively light sowing densities were essential to assure seeding of the 2,200 acres.
Densities of 4,000 and 8,000 seeds per acre (10,000 and 20,000 seeds per hectare) were decided upon for most of the area. For small test tracts, plans called for densities of 20,000, 40,000, and 56,000 seeds per acre (50,000, 100,000, and 140,000 seeds per hectare).
Before the seeding could be undertaken, it was necessary to conduct test flights to determine the best methods for attaining these dispersal rates. The problem was to dilute the seed with some other substance. Tests were made early in February 1948 at the U. S. Department of Agriculture's Beltsville Research Center airfield, in co-operation with the Bureau of Entomology and Plant Quarantine. The airplane used was a Navy trainer biplane. The same plane was used later in the Massabesic seeding operations.
This plane carried the seed mixture in a 17-bushel* hopper installed in front of the pilot's cockpit. The seed mixture was fed by gravity to the bottom of the hopper where agitators (powered by wind-driven propellers mounted on the plane wing) kicked it through the slot gate (regulated by a lever in the cockpit) into a simple fishtail spreader attached to the under side of the fuselage. From the spreader, the slip stream blew the seed mixture out through Venturi vents designed to spread the mixture.
* 1 U.S. bushel = 35.24 liters.
Two diluents, wheat and sawdust, were tested. In the first tests wheat was used. It was soon evident that a very high ratio of diluent to seed would be required for sowing densities as low as 4,000 and 8,000 seeds per acre. With wheat priced at an all-time high, there was strong inducement to experiment with a cheaper diluent. After a number of runs with wheat, sawdust was used as a substitute. Using varying proportions of diluent, test flights were run at different elevations under varying hopper apertures, wind velocities, and wind directions.
To get a measure of these factors on width of swath and density and uniformity of seed distribution, seed counts were made on a series of seed traps. Two types of seed traps were used. The first type, a paperboard box 3 feet by 3 feet with 12-inch sides (90 cm. x 90 cm. x 30 cm.), proved unsatisfactory. It was observed that occasional seeds bounded out of these containers. A more secure trap was finally devised. It consisted of a 3-foot-square flat surface of thin wallboard over which strips of cotton batting were glued. Seeds striking the surface of this batting were held firmly in place.
A total of 48 seed traps in three parallel rows spaced 100 feet (30 m.) apart comprised the series. Each row contained 16 seed traps spaced 3 feet (90 cm.) apart, so that the length of each row was 93 feet (28 m.). This pattern permitted evaluating the density of seed distribution both parallel and at right angles to the line of the plane's flight.
The early test runs were made with all Venturi vents open. The resulting seed distribution pattern is indicated in Figure 1. It shows a high concentration of seed along a relatively narrow band straddling the near center of the swath. To reduce the heavy seed density deposition along the center and to attain a more uniform spread over a wider swath, a number of flights were made with the center Venturi vent covered with a tin cap. The greatly improved distribution which resulted is indicated by Figure 1.
Approximately 80 flights provided an adequate basis for determining effective swath width and the ratio of diluent required to attain a specified seed dispersal rate. By trial and error, proportions of 12 sawdust to 1 seed, 6 to 1 and 3 to 1 by volume were found to give density rates of approximately 4,000, 8,000, and 16,000 seeds per acre (10,000, 20,000, and 40,000 seeds per hectare) with the hopper aperture set at ¼ inch (6 mm.). Effective swath width was calculated to be approximately 50 feet (15 m.). From Fig. 1 it can be seen that the actual spread of the seed was greater than this by some 25 feet (7.6 m.). This overlap assured a fairly uniform density sowing.
The seeding operation on the Massabesic burn was begun late in February 1948. The conditions at the time were considered ideal. The ground was covered with 2 feet (60 cm.) of snow. The snow surface was frozen and dotted with countless small pits that acted as small traps to catch and hold the seed.
In preparation for the seeding flights, a ground crew marked the boundary lines and corners of the area and erected windsocks.* Since the Massabesic Forest consists of two areas, a north unit and a south unit, both extremely irregular in shape, 64 markers were needed to define the boundaries of the areas to be seeded. The ground crew spent a total of 156 man-hours in erecting and dismantling the windsocks.
* The crew members were John W. Regan and Walter R. May, on loan from the Bureau of Entomology and Plant Quarantine and one assistant. The first two men were experienced in organizing and setting up ground installations for aircraft spraying.
The white pine seed was mixed with the sawdust in a small motor-driven cement mixer. Fresh white pine sawdust, which had previously been screened through a ¼-inch (6 mm.) mesh, was stockpiled under cover. A crew of from two to three men was used to operate the mixer and sack the material. Two men can handle the job with little difficulty. The usual charge was one bushel of sawdust plus the required amount of white pine seed. The machine was run until the charge was thoroughly mixed, then the seed mixture was poured into a basket and sacked in 2-bushel lots.
Mixing output ran about 16 bushels of mixture per hour. It was noted that the bottom of the charge tended to be poorly mixed. This was overcome by loading half the quantity of sawdust then half the required amount of seed followed by the remainder of sawdust and seed. The mixer had to be operated at least 3 minutes to assure a good mix. Different lots of sawdust may require longer mixing time. This can be determined by inspecting the charge and increasing the time if necessary.
A light truck was used to transport the bagged seed mixture to the airplane base 7 miles (11 km.) away.
On the seeding flights, the airplane flew at about 80 miles (130 km.) per hour, 50 to 75 feet (15 to 23 m.) above tree-top level. The interval between flight lines was about 50 feet (15 m.). The pilot was provided with a map of the forest showing the areas to be seeded, the acreage in each, and the density of sowing desired. Prior to the actual seeding, the pilot made "dry runs" over each of the two units of the forest to gain familiarity with the areas to be sown. In addition to the windsock markers, he used roads and fields as flight guides.
To assure uniform seed distribution the two units were subdivided into flight blocks. These ranged in size from 140 to 265 acres (57 to 107 ha.). The quantity of sawdust-seed mix required to cover each block was calculated in advance. The hopper of the plane was filled with an amount of mix sufficient to cover the block at the desired sowing density. Thus each block was assured its calculated quota of seed. In several instances the pilot flew the same block more than once, broadcasting the seed several times in different directions.
Approximately 1,000 acres were sown at a density of 4,000 seeds per acre. Another 1,100-odd acres were sown at a density of 8,000 seeds per acre. To provide a wider range of sowing densities, three small tracts aggregating approximately 120 acres were sown to densities of 20,000, 40,000, and 56,000 seeds per acre. Distribution of sowing densities is shown in Table 1.
Such ground cheeks as could be made showed very satisfactory distribution. Since 11 flight blocks were established, 11 separate flights were required to seed the 2,200 acres of severely burned area to sowing densities of 4,000 and 8,000 seeds per acre. A total of 154 bushels of seed mix was used in the process. The air base from which the plane operated was approximately 6 miles (10 km.) from the seeding operations. Total elapsed time per flight, including loading of plane, map checking, lunching, and other incidentals, averaged one hour.
TABLE 1. - QUANTITIES OF WHITE PINE SEED MIX SOWN BY AIRPLANE ON BURNED AREAS OF THE MASSABESIC EXPERIMENTAL FOREST TO GET SEED DISTRIBUTION OF VARIOUS DENSITIES
|
Location |
4,000 seeds per acre1 |
8,000 seeds per acre1 |
||
|
Area sown2 |
Seed mix sown |
Area sown2 |
Seed mix sown |
|
|
acres |
bushels |
acres |
bushels |
|
|
North unit |
220 |
15.4 |
235 |
16.5 |
|
North unit |
140 |
9.8 |
170 |
11.9 |
|
South unit |
265 |
18.5 |
160 |
11.2 |
|
South unit |
202 |
14.1 |
229 |
16.0 |
|
South unit |
203 |
14.1 |
220 |
15.4 |
|
South unit |
- |
- |
160 |
11.2 |
|
Total |
1,030 |
71.9 |
1,174 |
82.2 |
1 acre =.4047 hectare.
1 bushel = 35.24 liters.
4,000 seeds per acre = 10,000 seeds per hectare.
8,000 seeds per acre = 20,000 seeds per hectare.
1 Sowing densities of 20,000, 40,000, and 66,000 seeds per acre (50,000, 100,000, and 140 000 seeds per hectare) were undertaken on blocks of 57, 28, and 32 acres (23, 11, and 13 hectares) respectively using mixtures of 3 volumes of sawdust to 1 volume of white pine seed.
2 Three cheek areas of 24, 34, and 38 acres (10, 14, and 15 hectares), the first two in the south unit and the last in the north unit, were established on which no airplane seeding was undertaken.
Almost as soon as the sowing was completed, snow began to fall, and covered the area to a depth of 5 to 8 inches (13 to 20 cm.). This undoubtedly helped to reduce depredations by birds and rodents to a minimum.
Close view of the hopper, from above, showing the slot gate and agitators.
In addition, under a co-operative arrangement with the St. Regis Paper Company, the Station seeded by airplane 400 acres (160 ha.) on company holdings, near Whitneyville, Maine, which had also burned in 1947. Seeding was at a rate of 5,000 seeds per acre (12,000 seeds per hectare). Ground installations on the St. Regis operation were simple. The tract was a rectangle, and required only six windsocks.
Cost records maintained for the airplane sowing operations indicate an approximate cost of $3 per acre ($7.25 per hectare) for a sowing density of 8,000 seeds per acre (20,000 seeds per hectare). This cost was made up as follows:
|
|
Cost per acre |
Cost per hectare |
|
Seed |
$2.40 |
$5.90 |
|
Ground installations |
.20 |
.50 |
|
Flying costs |
.30 |
.75 |
|
Seed-mixing costs |
.04 |
.10 |
|
Total |
$2.94 |
$7.25 |
The flying cost item of 30 cents per acre (75 cents per hectare) does not include rental or depreciation charges for the airplane. However, a highly reputable airplane service corporation offered to undertake the seeding of the area for 50 cents per acre ($1.10 per hectare).
The major cost item was seed. The sowings of 4,000 and 8,000 seeds per acre called for 1/5 and 2/5 pound of seed per acre (1/5 and 2/5 kg. per hectare for sowings of 10,000 and 20,000 seeds per hectare). With white pine seed selling for $6 per pound ($13 per kilogram), the cost of seed alone amounted to $1.20 and $2.40 per acre ($2.95 and $5.90 per hectare). The total cost of the Oregon airplane seeding project - including rodent control and snag felling was $5.13 per acre ($12.70 per hectare). With the present high cost of planting stock and prevailing high wages it is doubtful that planting operations can be conducted for much less than $35 per acre ($86 per hectare), more than ten times the aerial seeding costs. Cost of sowing seed by hand varies considerably, depending upon sowing densities and techniques used. Experience indicates that for comparable sowing densities, hand-sowing costs are approximately double those calculated for airplane sowing. Thus airplane sowing costs are substantially lower than other orthodox methods of artificial reforestation. In the final analysis, however, airplane seeding costs mean little until more evidence is available on the degree of success to be expected.
It is still too early to judge the success of the airplane seeding venture. However, seedling counts made last summer and fall show reasonably satisfactory results. Counts made on the Massabesic burn late in August showed from 25 to as high as 2,475 seedlings per acre (60 to 6,120 seedlings per hectare). Success varied with the character of the seedbed as influenced by degree of burn. For example, Table 2 shows that germination on the severely burned areas ranged between only 2.5 and 11.9 percent in contrast to more than 25 percent on the moderately burned areas. Although further research is needed to account fully for these striking differences it is believed that high soil surface temperatures and deficient moisture were major factors. Few seedlings were found in heavy charcoal soils.
From Table 2 it will be seen that most satisfactory results were obtained on the moderately burned areas, with 725 stocked quadrats per acre out of a possible 1,000 and an average of 2,475 seedlings per acre for the 8,000 sowing density. For the 4,000 sowing density the corresponding figures are 525 and 1,325. On the heavily burned areas the 8,000 and 4,000 sowing densities yielded only 150 and 25 stocked quadrats per acre with 175 and 25 seedlings per acre respectively.
TABLE 2. - SUMMARY OF SEED GERMINATION AND SEED COUNTS IN THE MASSABESIC EXPERIMENTAL FOREST AIRPLANE SEEDING EXPERIMENT AT THE END OF THE FIRST SEASON
|
Method and density of sowing |
Germination |
Seedlings |
Stocked quadrats |
|
|
percent |
number |
number |
||
|
MODERATELY BURNED AREAS |
||||
|
Airplane: |
|
|
|
|
|
|
4,000 seeds per acre |
28.4 |
1,325 |
525 |
|
|
8,000 seeds per acre |
28.4 |
2,475 |
725 |
|
Natural |
- |
298 |
134 |
|
|
SEVERELY BURNED AREAS |
||||
|
Airplane: |
|
|
|
|
|
|
4,000 seeds per acre |
2.5 |
25 |
25 |
|
|
8,000 seeds per acre |
11.9 |
175 |
150 |
|
Natural |
- |
0 |
0 |
|
|
By hand: |
|
|
|
|
|
|
4,000 seeds per acre |
8.2 |
250 |
200 |
|
|
8,000 seeds per acre |
8.2 |
400 |
175 |
1 acre = 4047 hectare.
1,000 seedlings per acre = 2,500 seedlings per hectare.
Part of the good stocking on the moderately burned areas must be attributed to germination of natural-borne seed that survived the fire. On the basis of counts made on check areas, naturally shed seed accounts for approximately 300 seedlings per acre. It is interesting to note that on severely burned check areas where no aerial seeding was done not a single white pine seedling was found. In general, newly germinated seedlings on the burned areas are large, vigorous, and thrifty. Some mortality is expected in the course of the winter, but these losses may be compensated by delayed germination next spring. Counts on the St. Regis tract show an over-all average of approximately 175 seedlings per acre.
In conclusion it may be stated that aerial seeding of burned-over timber lands, if undertaken under proper conditions, is economically feasible. Rapidity of seed distribution and favorable cost factor are its chief attractions. There is much still to be done in improving methods and techniques. It is clear, however, that airplane seeding did partially stock the burned areas with white pine.
All photos courtesy U. S. Forest Service
