small mammals and regeneration of white spruce forests in western alberta

Small Mammals and Regeneration of White Spruce Forests in Western AlbertaAuthor(s): Andrew RadvanyiSource: Ecology, Vol. 51, No. 6 (Nov., 1970), pp. 1102-1105Published by: Ecological Society of AmericaStable URL: http://www.jstor.org/stable/1933641 .

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SMALL MAMMALS AND REGENERATION OF WHITE SPRUCE FORESTS IN WESTERN ALBERTA1

ANDREW RA1YVANYI

Canadian Wildlife Service, Edmonton, Alberta, Canada

Abstract. The fate of 7,800 pesticide-treated and radiotagged white spruce seeds (Picea glauca (Moench) Voss var. albertiana (S. Brown) Sarg.) was studied under field conditions near Hinton, Alberta, Canada, from 1962 to 1967. Approximately 50% of spring-placed seeds were destroyed by small mammals within 4 months, whereas only 19% or less of winter- placed seeds were lost within a year. From five to six times more seeds germinated following the winter seeding operations than after the first spring seeding test. Calculated ground seed- eating small-mammal populations varied from 2.0 to 7.4 (average 4.5) animals per acre in spring and from 4.9 to 12.2 (average 8.1) in the fall. Percentages of seeds destroyed were more directly related to time of seeding than to the number of animals present.

INTRODUCTION

Since the turn of the century, foresters have been interested in the effects of small mammals on regeneration of logged or burned-over forest lands. In many instances seed-eating small mammals are largely responsible for inadequate regeneration of these areas (Hooven 1958, Radvanyi 1966a). Most of the pertinent data, however, are based either on feeding experiments with captive animals, or short-term field studies in which seed losses are recorded but mammal species are un- determined. Fate of seeds has been determined by use of enclosures (Roy and Schubert 1953), by marking individual seeds (Farrar and Fraser 1952), or by examination of seed spots dug up by small mammals (Garman and Orr-Ewing 1949). A need remained for a method of relo- cating seeds without disturbing the soil surface and thereby attracting small seed-eating mammals to the location. This need was met largely with the development of the radiotracer technique (Lawrence and Rediske 1959).

This study sought to determine the degree to which small-mammal populations impede the regeneration of white spruce on cutover lands. Data are included from 5 years of research on the fate of 7,800 radiotagged white spruce seeds set out in two spring and two winter seeding operations. The study was conducted on areas leased to North Western Pulp and Power Limited at Hinton, 180 miles west of Edmonton, Alberta.

MATERIALS AND METHODS

The fate of white spruce seeds which were obtained from the Alberta Forest Service and which originated from stock collected in the Hin- ton area was determined with a modified radiotracer technique (Radvanyi 1963, 1966a, 1966b). Germination tests indicated that the seeds ex-

1 Received November 11, 1969; accepted April 29, 1970.

ceeded 90% viability. Radioisotopes used in tagging the seeds were obtained from Atomic Energy of Canada at Chalk River, Ontario.

On June 1 and 2, 1962, 2,000 white spruce seeds, each tagged with approximately 3 Vc of the radioisotope scandium-46 and subsequently coated with endrin, arasan, aluminum flake, and latex, were placed on 20 randomly selected 36- by 36-ft plots on two cutover areas for recovery the following September. The 100 seeds per plot were individually placed on the surface and spaced at 4-ft intervals. The habitat surface varied from exposed mineral soil to spruce needles, brush, wood chips, rock, moss, or dense grass. A model 118B PRI (Precision Radiation Instruments) portable scintillometer, equipped with a 3'/2-inch thallium-activated sodium iodide crystal and ca- pable of a counting rate of 1 million gamma ray emissions per minute in a 1-MR field of radiation, was used to check the locations of the seeds. Re- covered radiotagged seeds and fragments were examined under magnification and assigned to the following seed-fate categories (Radvanyi 1966a): (1) unchanged, (2) germinated, (3) slight change to complete dessication, or (4) destroyed (a) by mice, (b) by chipmunks, (c) by shrews, (d) by insects, or (e) by others.

To relate seed losses to possible destructive agents, small-mammal populations were studied. Live traps were placed at 50-ft intervals on the two rectangular grids, each encompassing 12.6 acres. The traps were checked twice daily for 10 consecutive days in early spring and again in late summer. Calculations of the small seed-eating mammal densities were based upon mark-and- release trapping techniques as outlined by Hayne (1949). Similar grids and trapping procedures were used in subsequent years.

Seed-trap data from earlier studies (Radvanyi 1962) indicated that the peak seed fall of white



Autumn 1970 ANDREW RADVANYI 1103

spruce occurred in late September. The largest portion of the seeding operations by the pulp mill was, however, being carried out in late spring. To determine the fate of seeds placed on the cutover environment during late fall or early winter, the radiotagging experiment was repeated during 1962-63. Two thousand seeds tagged with zinc- 65 radioisotope were placed on 20 plots just before a heavy snowstorm in mid-October 1962. The seeds from odd-numbered plots were recovered during early June 1963 to provide information on winter losses; the seeds from even-numbered plots remained in the field until September 1963.

Recovery of the winter-placed seeds proved difficult due to considerable leaching of the zinc-65 radiotag into the soil. The overwinter studies were repeated during 1963-64 with the placement of another 1,800 white spruce seeds on two new study areas during November 1963 and February 1964. The seeds were tagged in three equal por- tions with radioisotopes scandium-46, zinc-65, and cobalt-60. Treated seeds were recovered in early spring, midsummer, and late summer 1964.

No field studies were conducted during 1965. During spring 1966 a second spring placement of 2,000 cobalt-60 radiotagged spruce seeds was made to test whether broadcast seeding would be suc- cessful during years when small-mammal populations were at low levels. One-half of the seeds were sought during September 1966. The second 1,000 were allowed to remain in the field for 1 year until early June 1967.

RESULTS

Movement of radiotagged seeds

A preliminary search of the seed plots revealed that many of the tagged seeds were no longer at the points of placement. Seeds or hulls were relocated in small-mammal runways, beneath logs or stumps, inside crevices, under the bark of logs, in saw kerfs, stuck to twigs, inside curled leaves,

and even between bracts of open pine cones. Seed movements were undoubtedly related to topog- raphy, agents of destruction, and climatic factors such as wind or rain, or both. Although most of the radiotagged seeds or fragments were located at or near the surface, several were recovered at soil depths as great as 15 inches. Lateral movements ranged up to 28 ft from the nearest point of placement. Of 1,819 seeds recovered in Sep- tember 1962, 28% had moved an average lateral distance of 15.1 inches. Residual radioactivity on the soil surface was not adequate to permit tracing the travel route of the seeds.

Fate of radiotagged seeds The radiotracer method enabled the recovery

and subsequent fate determination of 87.7% (6,838/7,800) of the radiotagged white spruce seeds, many of which had remained in the natural environment for 1 year (Table 1). On the basis of 88.5% (4,954/5,600) recovery of radiotagged seeds set out in two spring and two winter seeding operations and considering only recoveries made during September, several important considerations appear: (1) small mammals can destroy within 3-4 months approximately 50% of the seeds placed in the field during spring months, whereas (2) only one-third as many are destroyed if seeding is carried out during winter. On the other hand, twice as many seeds germinated from winter- placed seeds as from those placed in June. Five to six times more winter-placed seeds germinated than spring-placed seeds if data from only the first three seeding operations are considered. Mice destroyed 35% of spring-placed seeds within 4 months and just under 43% within 1 year. Only 1 1 % of winter-placed seeds were destroyed by mice in 10-12 months.

Small-mammal studies A total of 1,926 small mammals was handled

in 4,506 captures on the eight cutover areas studied

TABLE 1. Fate of radiotagged white spruce seeds in field studies at Hinton, Alberta, Canada-1962-67

Item 1962 1962-63 1963-64 1966&67

Date of seed placement .June 1962 Oct. 1962 Nov. 1963 Feb. 1964 June 19(6 Numberofseedplaced . . 2,000 1,000 + 1,000 600 + 600 600 1,000 + 1,000 Date of seed recovery . .Sept. 1962 June 1963 Sept. 1963 May 1964 July 1964 Sept. 1964 Sept. 1966 June 1967 I'1umber of seeds recovered .1,819 713 703 595 576 549 930 953 Percentage of seeds recovered . 91.0 71.3 70.3 99.2 96.0 91.5 93.0 95.3 Fate of recovered seeds

Percentage unchanged.. 20.6 16.6 7.8 80.6 68.8 48.0 16.5 11.1 Percentage germinated........................... 5.8 39.0 36.1 12.8 13.2 28.2 24.1 28.5 Percentage with slight change or dessicated. 24.3 30.3 37.0 - 2.4 7.6 9.0 4.8 Percentage destroyed .49.3 14.1 19.1 6.6 15.6 16.2 50.4 55.6

by mice. 35.2 10.5 12.7 3.9 9.2 9.7 35.8 42.6 by chipmunks ................................ 9.5 1.4 2.7 2.4 3.1 1.8 6.0 1.9 by shrews .2.9 1.5 2.6 0.3 3.3 4.7 8.0 10.5 by insects .1.7 0.7 1.1 - - - 0.5 0.4

by others .- - - - - - 0.1 0.2



1104 REGENERATION OF SPRUCE FORESTS ]'Ecology, Volume 51, No. 6

during 1962, 1963, 1964, 1966, and 1967. Two new cutover areas were studied during the first 3 years and one during each of the last two (total eight study areas). The two study areas used during each of the first 3 years were 12.6 acres in size and 18.4 acres during 1966 and 1967. The num- bers of small mammals tagged on the areas were: white-footed mice (Peromyscus maniculatus), 492; meadow voles (Microtus pennsylvanicus), 443; cinereus shrews (Sorer cinereus), 362; red-backed voles (Clethrionomys gapperi), 222; red squirrels (Tamiasciurus hudsonicus), 206; chipmunks (Eu- tamias amoenus), 167; short-tailed weasels (Mus- tela arminea), 17; flying squirrels (Glaucomys sabrinus), 8; marten (Martes americana), 6; jumping mice (Zapus princess, 2; wood rat (Neotoma cinerea), 1. The calculated number of ground seed-eating small mammals varied during the 5 years of study from 2.0 to 7.4 (average 4.5) animals per acre in the spring and from 4.9 to 12.2 (average 8.1) in the fall (Fig. 1). Of the above species only Peromyscus, Microtus, Clethri-

? Is_ W

4 F 14_

12 , FALL F

z n

4 ill S

Z1 SPRIN

0-

19 9 63 1964 8965 1966 196?

FIG. 1. Population densities of seed-eating small mammals on eight field study areas, Hinton, Alberta, 1962-67. Vertical rectangles above and below the mean (horizon- tal bars) indicate fiducial limits (P = 0.95).

onomys, Eutamias, and Sorex are considered as feeders on individual seeds lying on the ground, and thus only these species are included in the calculations. Although coniferous seeds play a prominent role in the food habits of Tamiasciurus and Glaucomys (Brink and Dean 1966), this would occur in the natural environment through the taking of cones and not scattered seeds.

DISCUSSION

Various current forestry practices have not suc- ceeded in eliminating or controlling seed-eating small-mammal populations. The destructive ca- pacity of these animals is further accentuated by increased populations following logging. Tevis (1956a) noted that mouse populations erupted and became three to four times more numer-

ous on cutover areas than in the surrounding forest. Slash burning has not proven to be a suc- cessful method of eliminating small mammals from cutover areas (Horn 1938, Stickel 1946, Tevis 1965b). Ahlgren (1966) maintains that burning creates habitat favorable to increased populations of seed-eating mice, which are very detrimental to forest seed supply and must therefore be considered in post-fire reforestation practices.

The widely accepted procedure of coating coniferous seeds with endrin, arasan, aluminum flake, and latex has yielded only qualified success. As both this study and that by Lawrence and Rediske (1962) show, small mammals and insects continue to destroy coniferous seeds even though they are treated with the highly lethal insecticide endrin. Lawrence and Rediske found 197 of Douglas-fir seeds destroyed within 22 weeks. Losses were substantially greater in spring-placed white spruce seeds in the current study. Regen- eration practices of North Western Pulp and Power Ltd. called for the greater portion of broadcast seeding to be carried out during May and June in earlier years. In many years the regeneration was largely inadequate. Seeding in August and September gave equally poor results. Radio- tagging studies suggest that more favorable results can be achieved through mid-winter seeding of white spruce. Cayford (1961) noted similar better germination following early spring seeding of jack pine in Manitoba.

The following hypothesis is suggested to ex- plain in part the reduced destruction of winter- placed coniferous seeds. Several species of seed- eating small mammals remain active under the snow. Their activities must be appreciably con- fined to pathways, and seeds placed into 10-12 inches of snow may be largely unavailable to them. Freezing, thawing, and moisture from melting snow covers many of the seeds with soil. Of great importance is the natural stratification and presence of abundant moisture during the time of rapid germination. On the other hand, seeds placed out in June may encounter prolonged dry periods and take on "secondary dormancy." Such a situation could lead to sporadic germination throughout the first or even second growing sea- son. Prolongation of the germination period would increase the possibilities of depredation on the seeds by small mammals. In the light of the fate of the radiotagged spruce seeds, a reconsideration of the time of seeding is recommended.

LITERATURE CITED

AhIgren, C. E. 1966. Small mammals and reforestation following prescribed burning. J. Forest. 64: 614-618.



Autumn 1970 ANDREW RADVANYI 1105 Brink, C. H., and F. C. Dean. 1966. Spruce seed as a

food of red squirrels and flying squirrels in interior Alaska. J. Wildly. Manage. 30: 503-512.

Cayford, J. H. 1961. Broadcast seeding jack pine at weekly intervals in Manitoba. Canada Dep. Forest., Forest Res. Br. Tech. Note 106. 12 p.

Farrar, J. L., and J. W. Fraser. 1952. A method of marking seeds used in experiments. Canada Forest. Branch Res. Dev. Silv. Leafl. 71. 1 p.

Garman, E. H., and A. L. Orr-Ewing. 1949. Direct- seeding experiments in the southern coastal region of British Columbia 1923-1949. Brit. Col. Forest. Serv., Tech. Publ. T. 31. 45 p.

Hayne, D. W. 1949. Two methods for estimating population from trapping records. J. Mammal. 30: 399-411.

Hooven, E. F. 1958. Deer mouse and reforestation in the Tallamock Burn. Ore. Forest Land Research Center, Res. Note 37. 31 p.

Horn, E. E. 1938. Some wildlife-forest relationships. N. Amer. Wildly. Conf. Trans. 3: 376-380.

Lawrence, W. H., and J. H. Rediske. 1959. Radio- tracer technique for determining the fate of broadcast Douglas-fir seed. Soc. Amer. Forest. Proc. 1959: 99-101.

. 1962. Fate of sown Douglas-fir seed. Forest Sci. 8: 210-218.

Radvanyi, A. 1962. Effects of small mammals on forest regeneration in Alberta. Canadian Wildl. Serv., Edmonton, Alberta. Prog. Rept. II. 68 p. - . 1963. Effects of small mammals on forest regeneration in western Alberta. Canadian Wildl. Serv., Edmonton, Alberta. Prog. Rept. III. 64 p. ---. 1966a. Destruction of radiotagged seeds of white spruce by small mammals during summer months. For- est Sci. 12: 307-315.

. 1966b. Small mammals and forest regeneration in western Alberta. Canadian Wildl. Serv., Edmonton, Alberta. Prog. Rept. IV. 33 p.

Roy, D. F., and G. H. Schubert. 1953. K-screen seed spots. U. S. Forest Serv. Calif. Forest Range Sta. (Berkeley), Forest Res. Note 88. 2 p.

Stickel, L. F. 1946. The source of animals moving into a depopulated area. J. Mammal. 27: 301-307.

Tevis, L., Jr. 1956a. Response of small mammal populations to logging of Douglas-fir. J. Mammal. 37: 189-196.

. 1956b. Effects of a slash burn on forest mice. J. Wildly. Manage. 20: 405-409.



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