beaver pond (willow) habitat and the adjacent non- 

 willow riparian habitat. Nearly half of the plot en- 

 compassing the beaver pond habitat was made up of 

 willow/mesic herbaceous communities. The census 

 plots, 600 by 150 m, were oriented lengthwise along 

 Summit Creek and included both sides of the creek. 

 Plots were surveyed and gridded with points flagged 

 and marked with numbered stakes at 25-m intervals. 



Eleven census visits were made to each plot from 

 May 17 to June 29, 1989. Most of the bird registra- 

 tions were recorded from sunrise to early afternoon 

 when birds were most active. To ensure complete 

 coverage, the plot was censused by walking within 

 25 m of all points on the grid. Census routes were 

 varied. Recorded bird observations extended a mini- 

 mum of 50 m beyond plot boundaries. 



At the end of the sampling period, clusters of 

 observations on species maps were circled to define 

 breeding bird territories. Fractional parts of bound- 

 ary territories were included in the results. The recip- 

 rocal of Simpson's index (D = 1/Ep,^, where p. is the 

 proportion of the sample belonging to the ith species) 

 was used to calculate species diversity (Hill 1973). 



Vegetation and other features of the census plots 

 were measured from July 17 to August 30, 1989. A 

 50- by 50-cm (0.25-m2) quadrat was located at each of 

 20 systematically positioned sample locations in each 

 major vegetation community type on the study plots. 

 Canopy cover (Daubenmire 1959) was ocularly esti- 

 mated for the total of each plant life form (graminoid, 



forb, shrub) and recorded as the midpoint of one of 

 eight percentage cover classes (0-1, 1-5, 5-10, 10-25, 

 25-50, 50-75, 75-95, 95-100 percent). Percentages 

 of litter, rock, bare ground, and lichen-moss were 

 similarly estimated. The vegetative height (excluding 

 flower and seed-head heights) of each graminoid, forb, 

 and shrub nearest the center of each quadrat was 

 recorded. 



Biomass of graminoids, forbs, and small shrubs was 

 determined by clipping vegetation from ground level 

 upward within a vertical projection from the 0.25-m2 

 quadrats. Clipped materials were bagged, ovendried, 

 and weighed. A 3- by 3-m.(9-m^) plot, concentric to 

 each 0.25-m^ quadrat, was used to sample biomass 

 of large shrubs. Basal diameter, maximum height, 

 and species were recorded for each shrub stem rooted 

 within the plot. For willow clumps, average stem 

 diameter and average stem height were recorded 

 instead of individual stems. Equations provided by 

 Brown (1976) were used to estimate biomass of the 

 large shrubs. 



Plant names follow Hitchcock and Cronquist (1973). 

 Bird nomenclature is from the 1983 AOU checklist 

 (American Ornithologists' Union 1983). 



RESULTS AND DISCUSSION 



Major structural (physiognomic) differences in the 

 vegetation occurred between the beaver pond complex 

 and the adjacent riparian habitat (table 1). The most 



Table 1 — Vegetation and other features of a beaver pond complex (willow) and adjacent 

 (nonwillow) riparian habitat, Summit Creek, ID, 1989 



Beaver pond Adjacent 

 (willow) (nonwillow) 



Item 



Mean^ 



SD 



Mean^ 



SD 





Graminoid 













Biomass (g/m^) 



342 



220 



268 



254 



0.07 



Canopy cover (pet) 



60.8 



22.9 



61.6 



30.5 



.86 



Height (m) 



.29 



.15 



.18 



.09 



<.01 



Forb 













Biomass (g/m^) 



23.7 



29.3 



24.9 



29.8 



.82 



Canopy cover (pet) 



12.0 



13.1 



12.0 



13.2 



.99 



Height (m) 



.08 



.06 



.07 



.05 



.58 



Shrub 













Biomass (g/m^) 



183 



295 



71.1 



164 



<.01 



Canopy cover (pet) 



12.3 



20.7 



7.4 



14.5 



.10 



Height (m) 



.64 



.57 



.34 



.21 



<.01 



Other 













Bare ground (pet) 



15.7 



14.3 



20.3 



25.0 



.21 



Litter (pet) 



13.0 



12.3 



10.4 



11.5 



.22 



Rock (pet) 



.46 



1.42 



.64 



1.52 



.48 



Lichen-moss (pet) 



.24 



1.05 



.30 



1.15 



.76 



'/? = 80 except for shrub height mean where n = 79. 



=n = 60 except for forb and shrub height means where n = 5& and 52, respectively. 



^ Probability associated with unpaired f-tests. P of 0.10 or less was considered significant. 



2 



