ALL GROWTH PERIODS 



The magnitude of the growth response to release 

 differed among the four growth periods. The best 

 diameter growth occurred 5 to 10 years after a release 

 treatment and the poorest growth for the same trees 

 occurred between 1975 and 1979. 21 years after 

 release (fig. 3). Likewise the proportions of trees 

 growing faster than a predicted nonreleased tree 

 differed among the four growth periods. The propor- 

 tions for the 0-5, 5-10, 10-15, and 1975-79 periods were 

 51, 52, 39, and 26 percent, respectively (fig. 3). 



|H Maximum difference in DDS for released and predicted 

 nonreleased Western Redcedar 



] Percentage of released Western Redcedar growing faster 

 than predicted nonreleased Western Redcedar 



GROWTH PERIOD 

 (YR) 



L 



1975- 79 

 10 - 15 

 5- 10 

 0-5 



j I 



1.0 0. 5 



L0G e (DDS 11 released ")- 

 L0G e (DDS " predicted ") 



20 40 

 PERCENT 



60 



Figure 3.— Maximum difference in DDS 

 and percentage of released western 

 redcedar trees having a positive response. 



Discussion 



Diameter-growth response to release appeared to be 

 best on north-facing slopes. Certain characteristics of 

 growing sites on northerly exposures perhaps amelio- 

 rate changes in microclimate caused by a release 

 cutting, thus shade-adapted leaves respond favorably to 

 release as shown by increasing tree diameter growth. 

 On north-facing slopes the light sensitive stomata of 

 shade-grown leaves after a release cutting would be 

 open less than the stomata of shade-grown leaves after 

 a release cutting on other exposures. In addition, better 

 leaf turgidity could be maintained, thus reducing the 

 amount of photochemical damage to the shade leaves 

 while new sun-adapted leaves could form. If not 

 damaged excessively when exposed to the sun, shade 

 leaves are capable of increasing in thickness and in 

 weight-to-length ratios. This makes them more sun 

 tolerant (Tucker and Emmingham 1977) and enables 

 the tree to survive changes in microclimate. Other 

 shade-tolerant species also respond to release best on 

 cool, moist sites. These include grand fir (Abies grandis 

 [Dougl.j Lindl.) (Ferguson and Adams 1979), amabalis 

 fir (Abies amahilis [Dougl.j Forbes) (Herring and 

 Etheridge 1976), subalpine fir (Abies lasiocarpa [Hook.) 



Nutt.) (Herring 1977), and nutall oak (Quercus nuttallii 

 Palmer) Johnson 1975). 



Young western redcedar trees appear to respond to 

 release from surrounding and overhead competition 

 better than older trees. Several factors could be 

 involved in changing this relationship, including 

 natural senescence, crown depletion resulting from 

 suppression, and damage due to many kinds of agents. 

 When shade-tolerant trees are grown for long periods in 

 suppressed conditions, their crowns develop to be 

 shorter and thinner than their open-grown counter- 

 parts. Because trees with long, dense crowns are the 

 most vigorous they are more likely to respond to release 

 (Graham 1980b; Seidel 1977). Understory western red- 

 cedar are often subjected to heavy snow loads that 

 damage the crowns and boles, thus decreasing their 

 ability to respond to release. The capacity of a tree to 

 respond to release generally declines with age (Baker 

 1950; Ferguson and Adams 1979), but age does not 

 appear to affect the release of some species such as 

 subalpine fir and balsam fir (Abies balsamea [L.] Mill.) 

 (Herring 1977). 



The larger diameter western redcedar trees in a stand 

 had the better diameter growth responses to release. 

 The larger diameter trees in a stand are usually the 

 taller trees with larger crowns, have more crown that is 

 sun adapted, and have more extensive root systems. 

 Therefore, when a release cut occurs in a stand those 

 trees with larger diameters can respond to the more 

 favorable growing conditions more quickly than smaller 

 trees. The faster growing western redcedar in a stand 

 may have adequate growing space before a release 

 treatment, so any additional space from release cutting 

 would not be utilized. Therefore, prereleased diameter 

 growth rates do not always indicate, as well as d.b.h. 

 does, the growth performance after release. This has 

 also been demonstrated by Baker (1950), Cole and 

 Stage (1972), and Stage (1973). 



The diameter-growth response of western redcedar to 

 release was significantly (P<0.05) related to habitat 

 types. Western redcedar on the THPL/PAMY habitat 

 type had the best release response. This is the warmest 

 and driest habitat type where western redcedar grows 

 (Daubenmire and Daubenmire 1968). Western redcedar 

 is the climax species on this habitat type and can 

 dominate in eventual size and number over the other 

 species. On the TSHE/PAMY habitat type, western red- 

 cedar cannot compete with the other species as readily 

 when released. Any disturbance in stands growing on 

 the TSHE/PAMY habitat type usually results in a tre- 

 mendous western hemlock regeneration that can 

 compete with the released western redcedar trees. The 

 occurrence of western redcedar on the ABLA/PAMY 

 habitat type is very limited, making release operations 

 marginal. It appears that on this habitat type, western 

 redcedar is limited by cold temperatures. Any release 

 cutting will increase the probability of frost damage to 

 the released trees, making the release treatments less 

 effective. Likewise release treatments on the 

 THPL/ATFI habitat type could be less successful 

 because of cold temperatures and high ground-water 

 tables. Habitat types have also been found related to 



8 



