Graduate Thesis Or Dissertation

 

Characteristics of spring foraging ecology among black bears in the central coast ranges of Oregon Public Deposited

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  • I studied spring food habits, focusing on cambium-feeding, of black bears (Ui-gus americanus) in the Central Coast Ranges of Oregon (1987-90) by comparing an area with high levels of timber damage caused by bears (north area) with an adjacent area of low levels of bear damage (south area). I also conducted a survey of forest stands in both areas to measure levels of bear damage, describe damage and forest stand characteristics, and determine if site characteristics were useful in predicting future bear damage. I compared the contents of black bear scats collected in spring (March - mid-July) from the north area ( = 61) with scats from the south area ( = 92). I also fed cambium to captive black bears to establish whether cainbium was readily identifiable in scats and determined it was about 50% digestible, dry matter basis. Scats from the north area had a higher percent frequency (51%) of forbs than did scats from the south area (29%) (G = 7.16, 1 df, = 0.007). Scats from the north area included small quantities (5% frequency) of many species of forbs: only clover (Trifolium repens) seemed important (12%). Cow parsnips (Heracleum lanatum) was the most common forb (10% frequency) in scats from the south area. Scats from the south area had a higher frequency (50%) of shrubs than did scats from the north area (20%) (G = 15.04, 1 df, P < 0.001), although the only shrubs occurring in scats from either study area were the leaves, stems, and fruits of Devils club (Oplopanax horridum) and Rubus spp. Cambium occurred at a higher frequency (12%) in scats from the north area than in scats from the south area (2%) (G = 5.71, 1 df, P = 0.017). Animal matter consisted primarily of black-tailed deer (Odocoileus hemionus Coluznbianus), a variety of small mammals, and ants (Formicidae). Forty randomly selected forested stands with dominant trees ranging from 10-50 cm dbh were surveyed in each of the 2 study areas. Overall site characteristics differed between stands classified by the presence or absence of bear damage ( for Wilk's = 2.62, 11,68 df, = 0.008). Forest stands with bear damage ( = 33) had lower densities of trees >40 cm dbh (F = 5.97, 1,78 df, P = 0.017), lower total basal area ( = 4.92, 1,78 df, = 0.030), occurred on less steep slopes ( = 3.80, 1,78 df, P = 0.055), and differed by aspect (cosine(aspect): F = 5.28, 1,78 df, P = 0.022) compared to forest stands without bear damage (n = 47). Forest stands had a random distribution of aspects when examined by total sample (n = 80), study area ( = 40 for each area), and all stands without bear damage. Only stands with bear damage had a non-random distribution of aspects (a = 31°; x2 = 10.5, j = 5, 4 df, P < 0.05). Average dbh of damaged trees (22 cm ± 0.98 SE) differed from the average dbh of undamaged trees (16 cm ± 0.95) within stands containing bear damage (ii = 4.23, 1 df, P = 0.0001). Bears fed on trees <10 cm dbh less than available (x2 = 65, 3 df, P < 0.005), trees 11-20 cm dbh in a ratio equal to their availability and bears selected for trees 21-30 cm dbh ( = 73, 3 df, < 0.005). Most damage (91%) occurred on trees 11-30 cm dbh. Bears damaged from 7-185 trees/ha ( = 39 ± 7.7) and 19% of trees damaged were completely girdled. Measured site characteristics were poor predictors (R2 = 0.14; correct classification rates = 70%) of a stand's potential vulnerability to damage by bears. Retaining or creating patches of known bear foods, including planting skid roads and log-landings to grasses and forbs and retaining coarse woody material as substrate for wood-nesting insects, could supplement animal damage control efforts by providing nutritious spring forage. The similarity of bear damage descriptions in the literature from regions across western North America suggest site characteristics may influence feeding behavior of bears. Identifying these characteristics, which may include parameters related to carbohydrate production, and combining them with characteristics discussed here, may allow prediction of future bear damage.
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