Cover 



The second component of safe sites is the influence of 

 vegetation and debris. The occurrence of different seedling 

 species varied according to the amount of shrub canopy 

 cover (shade) over the seedling plot (table 3). However, the 

 trends for most species were similar between habitat 

 types. Most seedling species occurred in moderate (33 to 

 66 percent shrub canopy cover) and heavy (67 to 100 per- 

 cent) shade. This included even the shade-intolerant 

 species ponderosa pine and lodgepole pine (as defined by 

 Daniel and others 1979; Minore 1979), which were found 

 predominately in moderate shade in all three habitat 

 types. Douglas-fir was found most often under heavy 

 shade. Engelmann spruce, which is rated as less shade 

 tolerant than Douglas-fir (Minore 1979), was found most 

 often under heavy shade in grand fir/mountain maple h.t. 

 and under light (0 to 33 percent) shade in the grand 

 fir/blue huckleberry h.t. 



Table 3— Occurrence of tree seedlings (percentage) by shrub 

 canopy cover for Douglas-fir/white spirea, grand 

 fir/mountain maple, and grand fir/blue huckleberry 

 habitat types 



Shrub canopy cover 



Occurrence by 



Light 



Moderate 



Heavy 



species 



(0-33%) 



(33-66%) 



(66-100%) 



Douglas-fir/White Spirea Habitat Type 





Percentage of 









microplots 



42 



36 



22 



Lodgepole pine 



16 



44 



40 



Ponderosa pine 



17 



42 



41 



Douglas-fir 



31 



32 



37 



Grand Fir/Mountain Maple Habitat Type 





Number of microplots 



34 



26 



40 



Lodgepole pine 



20 



80 





Western larch 



34 



58 



8 



Ponderosa pine 



27 



49 



24 



Douglas-fir 



23 



14 



63 



Engelmann spruce 



15 



20 



65 



Grand fir 



32 



38 



30 



Grand Fir/Blue Huckleberry Habitat Type 





Number of microplots 



28 



35 



37 



Lodgepole pine 



12 



60 



28 



Ponderosa pine 



28 



45 



27 



Douglas-fir 



35 



22 



43 



Engelmann spruce 



46 



17 



37 



Grand fir 



26 



25 



49 



While the large occurrence of shade-tolerant species on 

 moderately or heavily shaded plots would be expected, the 

 high occurrence of shade-intolerant species on such plots 

 appears incongruent. McConkie and Mowat (1936) found 

 that germination of ponderosa pine in central Idaho was 

 higher under heavy shade, though the death rate of the 

 first-year germinants was also higher under heavy shade 

 than under more intermediate shade or no shade. The net 

 effect at the end of the year was an increase in seedling 

 occurrence with increasing shade. This relationship may 

 hold for many years. The presence of a shade-intolerant 

 species under heavy shade may indicate a safe site— that 

 is, a favorable microenvironment for germination and 

 establishment. However, other safe sites such as a safe 

 site with light shade may provide for faster seedling 

 growth. 



Several safe site covers were encountered for the vari- 

 ous seedlings throughout the three habitat types (table 4). 

 While the cover RE values often varied considerably be- 

 tween habitat types for the same conifer seedling species, 

 in some cases the RE values for cover species were con- 

 sistently high or low across habitat types. Notably, 

 thimbleberry (Rubus iparviflorus) was very efficient for 

 lodgepole pine, ponderosa pine, Douglas-fir, Engelmann 

 spruce, and grand fir in the grand fir/blue huckleberry h.t. 

 and for ponderosa pine and Engelmann spruce in the 

 grand fir/mountain maple h.t. Cover of forbs and grasses 

 and sedges was consistently either very inefficient or in- 

 efficient for all species in all three habitat types. The use 

 of a "cover species" and the associated RE value does not 

 intend to imply that a particular cover precludes or is re- 

 quired to obtain a particular seedling. In many cases, the 

 relationship between the cover species and the seedling 

 species may be coincidental; the seedling and the cover 

 species may merely have established in the same location 

 at the same time. On the other hand, a very high or very 

 low RE value may indicate a relationship. The particular 

 cover species may be established in a microenvironment 

 that is favorable or unfavorable to a particular conifer 

 species, and therefore can be used as an indicator of a 

 suitable or unsuitable microenvironment. An example of 

 such a species is Sitka alder (Alnus sinuata), which is a 

 very efficient cover species for Engelmann spruce in the 

 grand fir/mountain maple h.t. Sitka alder often occurs in 

 wetter portions of the grand fir/mountain maple h.t., in- 

 dicating areas that are well suited to Engelmann spruce 

 (Steele and Geiqr-Hayes 1985). Other cover species may by 

 their characteristics affect the safe site. On one hand, an 

 allelopathic species may preclude the formation of a safe 

 site. On the other hand, a species that supports nitrogen- 

 fixing organisms may create a safe site by providing a 

 favorable rooting environment. 



4 



