Grenier and Nelson 



Chapter 19 



Inland Habitat Associations in Oregon 



However, data concerning tree damage or abnormalities were 

 collected and may indicate presence of nesting platforms. 

 Sixty-three percent (45 of 72) of the occupied sites had tree 

 damage or abnormalities, 33 percent (15 of 45) of which 

 included mistletoe infestations. Damage or abnormalities 

 observed in random sites was similar (59 percent; 128 of 216 

 trees), however mistletoe infestation was less common in 

 random sites (12 percent; 15 of 128 trees). 



National Forest Land Databases 



Vegetation Resources and Structure Examination 

 Databases Douglas-fir was the most common dominant tree 

 in occupied and random sites. However, western red cedar 

 (RC_DBH3, Thuja plicata), which occurred in approximately 

 33 percent of occupied sites, had the largest mean diameter 

 ( x= 114.3 cm, s.e. = 6.65, n = 10). Occupied sites had an 

 average of 1 3.4 remnant trees/ha (REM, trees >100 cm d.b.h.), 

 and 63.7 percent canopy closure (table 2, appendix 2). 



Ecology Databases Occupied sites were mid-serai 

 stage stands with large tall conifer trees (table 3, appendix 

 3). Most (75 percent) occupied sites were located in western 

 hemlock climax forest types. The most common (17 percent; 

 13 of 75) plant association in occupied sites was western 

 hemlock/Oregon oxalis (Oxalis oregona). This plant 

 association only occurred in 5 percent (11 of 225) of 

 random sites, and the frequency of occurrence was 

 significantly less than in occupied sites (x 2 = 30.2, df= 9, 

 P = 0.0004). The most frequently occurring plant association 

 in random sites was western hemlock/vine maple (Acer 

 circinatum)/'weslem swordfern (Polystichum munitum) (12 

 percent; 27 of 225). The western hemlock/Oregon oxalis 

 sites occur on moist, shaded upper slopes and benches or 

 alluvial terraces and have high conifer basal area (79.7 m 2 / 

 ha, s.e. = 4.6, n = 9 compared to 71.0 m 2 /ha average for 22 

 plant associations, s.e. = 2.0, n = 178; Hemstrom and 

 Logan 1986). 



Research Database 



Ten occupied sites from this study were located in the 

 western hemlock (n = 6) and Sitka spruce (n = 4) Zones 

 (Franklin and Dyrness 1973), and included one or more of 

 the following plant associations: vine maple (n = 4), salal 

 (Gaultheria shallon) (n = 3), sword fern (n = 5), salmonberry 

 (Rubus spectabilis) (n = 2), Pacific rhododendron (Rhodo- 

 dendron macrophyllum) (n = 1 ), and Oregon grape (Berberis 

 aquifolium) (n = 2). All sites had two or more canopy layers 

 ( x= 2.2, s.e. = 0.1), were located between middle of the 

 slope and the ridgetop, had > 25 percent moss ( x index = 

 3.8, s.e. = 0.2), contained some mistletoe or witches brooms 

 ( x index = 2.2, s.e. = 0.3), and had platforms for nesting ( x 

 = 1.3 per plot, s.e. = 0.3) (table 4). The number of suitable 

 platforms was correlated with the number of canopy layers 

 (r = 0.39, P = 0.02, n = 34) and with mistletoe abundance (r 

 = 0.43, P = 0.01, n = 34). 



Habitat Associations 



State Lands 



Twenty-one of 34 habitat variables were significantly 

 different between occupied (n = 72) and random (n = 216) 

 sites (P < 0.05) (table 1). In general, occupied sites were 

 older (AGE1993), contained larger diameter conifers (DBH1- 

 4, CDBH, CBA) and hardwoods (HDBH), had more large 

 remnant trees/ha (TPH66), and had fewer small/medium- 

 sized trees (TPH 15-36) and hardwoods/ha (HTPH) than 

 random sites (table 1, appendix 1). 



Stepwise logistic regression suggested a model with 

 only large remnant tree density (TPH66) as a significant 

 predictor of murrelet habitat (P = 0.0164; n = 46 occupied 

 and 80 random sites). It was estimated that the odds of use 

 were 4.9 percent higher for each unit increase in large remnant 

 tree density (95 percent Confidence Interval [CI] = 0.8 percent 

 to 9.1 percent; s.e. = 0.02). 



National Forest Land Databases 



Vegetation Resources and Structure Examinations 

 Seven variables differed (P < 0.05) between occupied (n = 

 30) and random (n = 90) sites. Occupied sites had less slope, 

 less canopy closure (CC), more large Douglas-fir/ha 

 (DF_TPH3), larger midstory western hemlocks (WH_DBH 1 ) 

 and western redcedars (RC_DBH1, RC_DBH2), and fewer 

 shade tolerant trees/ha >41 cm (STH_40) than random sites 

 (table 2, appendix 2). 



Stepwise logistic regression suggested a model with 

 larger diameters of midstory western redcedar (RC_DBH1) 

 and less canopy closure (CC) as significant predictors of 

 murrelet habitat. It was estimated that the odds of use were 

 48.3 percent higher for each unit increase in diameter of 

 midstory western red cedar (95 percent CI = 9. 1 percent to 

 100 percent; s.e. = 0.1565, n = 12 occupied and 28 random 

 sites). Also, it was estimated that the odds of use were 16.5 

 percent higher for each unit decrease in canopy closure 

 when comparing occupied to random sites (95 percent CI = 

 2.8 percent to 32.1 percent; s.e. = 0.064). 



Ecology Four habitat variables were significantly 

 different (P < 0.05) between occupied (n = 75) and random 

 sites (n = 225). Occupied sites were in later serai stage 

 classes (SERAL), and had taller (HT), older (AGE), and 

 larger diameter trees (DIA) than random sites (table 3, 

 appendix 3). 



Stepwise logistic regression suggested a model with 

 tree height (HT) and percent cover of understory trees 

 (TREER) as significant predictors of murrelet habitat. It 

 estimated that the odds of use were 2.3 percent higher for 

 every unit increase in tree height (95 percent CI = 0.8 

 percent to 3.7 percent; s.e. = 0.0022; n = 34 occupied and 86 

 random). Also the odds of use were 4.3 percent higher for 

 every unit increase in percent cover of understory trees (95 

 percent CI = 0.3 percent to 8.5 percent; s.e. = 0.0202). 



USDA Forest Service Gen. Tech. Rep. PSW-152. 1995. 



195 



