ENVIRONMENT .AND WHITE PINE BLISTER RUST INFECTION 



483 



In the meso climatic scale, the hill-valley structures are super- 

 imposed on the macro climatic scale and modify the large-scale distribution. 

 Rust is more prevalent at high elevations and scarce in broad river valleys 

 (Van Arsdel, Parmeter, and Riker, 1957). 



In the microclimatic scale, the stand structure and small topo- 

 graphic features are superimposed on the mesoclimatic scale and further 

 modify the climatic distribution. The bases of slopes, small narrow 

 valleys, and small openings in the crown cover of the forest have abun- 

 dant rust. Zone 1 in the map in Fig. 2 shows where rust is found only in 

 these cool wet sites. Shoulders of hills and large openings in the 

 forest have less rust on the pines (Van Arsdel &t at. , 1961) . The 

 meteorological forces that cause locally cool wet places are illustrated 

 in Fig. 5. 



\ : : •• e 

 r E : _ e: 



LIMITED TO SITES V. 

 COOL AND KfET BY 

 - z DRAINAGE AND 

 RAC ANT HEAT .CSS. 



IN ZONE 2 (Fl G. 2 ) 



infe :~e: ~ = ETES 



ARE MORE COMMON 



ON T -ESE S ":":. 



■I - -- -. - = 



s - ■ ; ■ : f a : - 9 . - s - •: - - : . 

 ::- : I - •- = -- •: e . - e ■. : e : 



Figure 3. Drainage of cold air at night and radiant heat loss 

 make locally cool wet spots. 



The patterns of climate-controlled rust distribution are determined 

 by temperature and moisture effects on the production of spores, the 

 duration of spore viability, the germination of spores, the penetration 

 into the host, and the establishment in the host. The patterns of spore 

 dispersal are controlled by night air circulation. 



