EFFECTS OF FOREST CLEARING ON BROWSE PRODUCTION AND USE IN THE SAND RIVER AREA, ALBERTA

Transcription

1 EFFECTS OF FOREST CLEARING ON BROWSE PRODUCTION AND USE IN THE SAND RIVER AREA, ALBERTA ROBYN USHER, Dep.c;rtment of Biology, University of Calgary, Calgary, Alberta Abatnaet: Sampling of areas cleared of mature forest was begun in the spring of 1976, a year after clearing. A total of 343 ha was cleared. Cleared fields ranged in size from 1 to 20 ha, with an average size of ha. Eighteen of the 79 fields cleared were sampled to determine species composition, density of browse species, annual production and utilization of browse by moose, and the relative density of moose in the area. Microplots placed at 10 m intervals on 50 m transects were used to determine frequency and cover of the species present. The point-centred quarter method was employed to determine the density of browse species, while browse production and use were determined by twig count. Fecal pellet counts in conjunction with aerial surveys were carried out to estimate the relative density of moose. Early results suggest that clearing has appreciably affected browse production. Ivhile browse use is small, 2.5 percent of what has been produced, it is anticipated that use, lill increase. A 2nd season of sampling is planned for the summer of It is \'1e11 known that moose prefer young forests of early successional gro\vth. In the boreal forest where fire in combination with scattered logging has removed the older forest, increases in moose ~umbers occur, as has been observed across North America and Eurasia. Disturbed areas providing a variety of stand types which offer both open areas for food and mature conifers for cover are highly preferred (Prescott 1968, Krefting 1974, Le Resche et al. 1974, Peek et al. 1976). Logging operations which have produced extensive clear-cuts act like fire in creating young stands often similar in character to the early stages of successional growth. The value of clear-cuts has been examined by Peek (1971, Peek et al. 1976) and Telfer (1974a). Peek recommends small cuts approximately 80 ha in size. Telfer suggests that clear-cuts larger than 1.3 km 2 are not heavily utilized until stand growth is sufficient to provide shelter (10 to 15 years after clearing). 1

2 The value of intentionally clearing many small forest units as a tool in managing moose has yet to be investigated. A study begun in the Sand River area of Alberta has attempted to create favorable habitat by clearing a number of small forest blocks. The Sand River valley and surrounding area where the study \qas carried out is found 250 km north and east of Edmonton in the mixed wood section of the boreal forest. The general area is characterized by broadly rolling terrain of trembling aspen (Populu6 ~~~muloid~6), balsam poplar (P. bal6ami6~~a), and white spruce (Pieea glauea). This is broken by low wet areas of muskeg marked by willow (Salix sp.), black spruce (P. ma~iaha), and tamarack (La~ix la~ieilla). Moose (Alee6 ale~6) have used the Sand River area in the vicinity of Wolf and Sibert Lakes as a wintering area since the late 1960's (Fig. 1). During the winter a seasonal movement of moose into the area occurs south from the air-weapons range with a definite movement into the Sand River valley in mid winter. Densities have been roughly estimated at 0.25/km 2 (0.66/mi 2 ) in December, increasing to 0.81/km 2 (2.1/ mi 2 ) in March. STUDY AREA In the spring of 1975, portions of the forest on the west and east sides of the Sand River were cleared of mature aspen and balsam poplar in an attempt to encourage sucker growth in browse species. A total of 343 ha was cleared. Cleared areas or fields ranged in size from 1 to 20 ha, with an average size of 4 ha. Seventy-nine fields were cleared by bulldozer and the trees piled into windrows. Eighteen fields on the east side of the Sand River were sampled. They fell largely into 2 areas arbitrarily designated as Area 1 and Area 2 (Fig. 2). The fields in Area 1 lay on top of a well-drained ridge while those in Area 2 were found at a lower elevation and close to an area of extensive muskeg. Drainage in this area was impeded because of nearness of the water table to the soil surface. In contrast the fields in Area 1 were drier and better drained. These differences were

3 Square Lok. D.N.D. AIR WEAPONS RANGE w rj) a. z rj) z 0:: o >-165 SCt..Lt:,; o 1 4 miles P=' ' Ironwood Ll1ke RANGES 8 7 Figure 1 - Map of the Sand River area, townships 65 and 66. Hatched areas are cleared sites.

4 Hange 8 AREA Seismic Linos --- Township ond Rang~ Lines IC Sampl~d Block o M:::Jture s1ands o 0.5 Ws;::::::2: sampled 1 kilomelojr J WOLF LAI(E Twp 65 Figure 2 - Distribution of fields ill Area 1 and Area 2. Field numbers are given. 4

5 partly reflected in the species composition of the 2 areas such that those species which required moist conditions were more frequent in Area 2. Four sections of mature forest, 2 in each area, were sampled to provide information on the conditions which existed before clearing. The forest sections in both areas were largely comparable differing chiefly in their ages and moisture conditions. The forest in Area 1 was estimated at 80 years and in Area 2 at 65 years. This work was supported by a provincial grant from the Fish and Wildlife Division, Alberta. METHODS In the spring of 1976, a year after clearing, sampling was begun to monitor the project and was designed to determine species composition, density of browse, annual production and utilization of browse by moose, and the relative density of moose in the area. Seven transects 50 m in length were located parallel to the windrows in each field. Microplots placed at 10 m intervals along each transect were used to determine frequency and cover of the species present. The point-centred quarter method was employed to determine the density of browse species. Five circular plots were randomly located in each field, and within each plot, measurements for densities were taken. In addition, within each plot diameter, measurements at the point of browse (dpb's) and at the base of the previous year's growth (dcg's) were taken on selected sterns between 61 cm and 2.4 m (2 to 8 feet). Regression curves described by Telfer (1974b) w~re prepared, and based on the values obtained, browse productivity and use were calculated. Counts for pellet groups were made using 7 belt transects, 2 m by 50 m, for a sampling intensity of 1.75 percent. Counting for pellet groups proved to be useless as the sampling intensity was too low and sampling was undertaken too late in the season. Estimates of population size were taken from aerial surveys flown bimonthly from November to April through the winters of and

6 RESULTS Aspen, balsam poplar, and willow produced the greatest number of browse sterns in the 2 cleared areas (Table ll. Low bush cranberry (Vlbu~num edutel and hazel (Co~ytu~ co~nu~al in Area 1 and saskatoon (Ametanchle~ atn160tlal and birch IBe~uta papy~~6e~al in Area 2 ranked next in importance. The total density of browse species was greatest in Area 1 and least in the mature stands where low bush cranberry, aspen, and willow produced the greatest number of browse sterns. Browse yield of the 10 species studied in the cleared areas varied from 0.06 to kg/ha. In the mature forest values ranged from 0.19 to 9.09 kg/ha (Table 2l. Aspen produced the greatest amount of browse by weight in all 3 areas. In Area 1 balsam poplar produced the next largest amount (71.65 kg/hal followed by willow (57.22 kg/hal and birch (2.49 kg/hal. In Area 2, kg/ha of aspen was produced, while willow (18.83 kg/hal, balsam poplar (17.16 kg/hal, and birch (1.18 kg/hal produced lesser amounts. The mature forest stands produced aspen (9.09 kg/hal, willow (6.78 kg/hal, and low bush cranberry (2.40 kg/hal in decreasing amounts. Browse production was the greatest in Area 1 where a total of 378 kg/ha was produced. Approximately a 3rd of the amount was produced in Area 2 (139 kg/hal and much less in the mature stands (20.99 kg/hal. Browse use of the 10 species examined in the cleared areas varied from 0.00 to 4.2 kg/ha and from 0.00 to 0.73 kg/ha in the mature stands (Table 3l. Area 1 showed the greatest total browse use (10.21 kg/hal. The amount removed in Area 2 (0.73 kg/hal approximated that removed in the 4 mature stands (0.88 kg/hal. Aspen made up the greatest total amount of browse removed by weight. However, only 1.7 percent of the available total was used. While a smaller amount of birch was removed, 35 percent of the available total was used. Birch was the most heavily-used species followed by willow, dogwood, low bush cranberry, and aspen. In the mature stands, low bush cranberry made up the greatest amount of browse removed and was the most heavily-used species; 30 percent of the available 6

7 Table 1. Density of browse stems (between 0.61 and 2.4 m) in the sampled areas. Mature Browse Spec i es Area 1 Area 2 stands Popul us tremuloides P. balsamifera Salix sp Betula pap9iifera Viburnum edule 489 a Coryl us cornut:a Amelanchier alnifolia Prunus pensylvanica 56 P. virginiana 219 Cornus stolonifera aslashes indicate that the species in question was not present. 7

8 Table 2. Kilogram weight of browse produced/ha (between 0.61 and 2.~ m) in the sampled areas. Browse Spec i es Area 1 Area 2 Ma tu re stands Populus tremuloides 2~ P. balsamifera Salix sp Berula papyrifera Viburnum edule 2. ~9 1. ~ a ~O Corylus cornuta 0.31 o. ~O Amelanchier alnifolia Prunus pensylvanica P. virgini ana 0.96 Cornus stolonifera 0.~ aslashes indicate that the species in question was not present. blndicates that production figures were unobtainable. 8

9 Table 3. Ki logram weight of browse used/ha (between 0.61 and 2.4 m) in the samp I ed areas. Mature BrO\'Jse Spec i es Area 1 Area 2 stands Populus trernuloides P. balsamifera Salix sp Betula papyrifera viburnum edule Corylus cornuta Amelanchier alnifolia Prunus pensylvanica 0.00 P. virginiana 0.12 Corn us stolonifera aslashes indicate that the species in question was not present. blndicates that use values were unobtainable. 9

10 total was used. The percentage of browse removed in Area 1 was 2.7 percent of the available total for both the cleared fields and mature stands. Much less was used in the cleared fields in Area 2 (0.5 percent), while 1.5 percent was removed in the mature stands of this area. DISCUSSION The differences between the density of sterns and the amount of browse produced in the 2 cleared areas were large. Reasons for the differences were attributed to the more favorable site conditions of Area 1 (better drainage). The differences in production between the mature stands and cleared areas reflected the optimal growth conditions of the latter associated with increased light and temperature. Densities and browse yield are expected to increase to the time when browsing pressure and natural thinning begin to limit production. This is expected to occur 10 to 15 years after clearing. The greater use of browse in the 1st area was attributed to the traditional use of the area and to the greater number of sterns available for browse. Browse preference appeared to be closely tied to abundance in the mature stands. Low bush cranberry produced the greatest number of stems and was browsed the most heavily. This was not the case in the cleared areas where 35 percent of the birch was removed, yet only 54 stems/ ha were produced compared with 9,000 of aspen and 1.7 percent removed. Perhaps with the abundance of browse an animal can afford to be more selective in the cleared areas. While sufficient quantities of winter browse were produced, the amount used was small, 2.5 percent of the available total. Other factors may have been limiting. was snow, its depth, density, and hardness. An important climatic factor Snow conditions were not felt to have been limiting due to the mild winter prior to sampling. The age of the clearings may have been important; only a year old, colonization by dispersing juveniles may not have had a substantial impact on the area as yet. Possibly the lack of a large conifer component in the immediate W

11 vicinity might be significant with regard to cover. Finally, and perhaps most importantly, were the windrows. Long and commonly broken in only 2 places, they appeared to prevent random movement through the fields. Browse was used the most heavily through breaks in the windrows. Little use of browse was observed along the length of the fields. This may have been because of the restrictive nature of the windrows. With regard to future clearing it is recommended that windrows be shorter and more staggered or removed completely. Use is expected to increase as the moose population and familiarity with the area increase. It is probable that use will double over this winter and that Area 2 will be utilized more heavily. A brief trip into the area this winter has shown browse use to have increased considerably in both areas and, encouragingly, more browse to have been used along the length of the fields. Briefly then, clearing has been successful in increasing browse production markedly over mature stands. While use does not appear to have been influenced appreciably by clearing, this is expected to change for the reasons given above. A 2nd season of sampling planned for this summer will further help to determine the success of the project. LITERATURE CITED Krefting, L.W Moose distribution and habitat selection in North Central America. Naturaliste Can. 101: Le Resche, R.E., R.H. Bishop, and J.W. Coady Distribution and habits of moose in Alaska. Naturaliste Can. 101: Peek, J.M Moose habitat selection and relationship to forest management in northeastern Minnesota. Ph.D. Thesis. Univ. Minnesota. 250pp., D.L. Urich, and R.J. Mackie Moose habitat selection and relationships to forest management in northeastern Minnesota. Wildl. Monogr pp. 11

12 Prescott, W.H A study of winter concentration areas and food habits of moose in Nova Scotia. M.S. Thesis. Acadia Univ., Wolfville, Nova Scotia. 194pp. Telfer, E.S. 1974a. Logging as a factor in wildlife ecology in the boreal forest. For. Chron. 50: b. A trend survey for browse ranges using the Shaffer twig count technique. Paper Pres. loth N. Am. Moose Conf. and Workshop, Duluth, Minnesota, March u