Abstract:
The inter-relationship of salmonberry and Douglas-fir on cutover areas was investigated in the Coast Range of western Oregon. Animal influences affecting the survival of Douglas-fir in a salmonberry
habitat were also investigated. The autecology of salmonberry was considered first by formulating a mathematical model to characterize the lateral encroachment of the shrub on an opening containing a Douglas-fir seedling or sapling. The height response of Douglas-fir along with its general physiological condition were examined under
different degrees of competition imposed by salmonberry. The response of salmonberry s growth to the development of Douglas-fir
was also generally described. Data were obtained in cutover and burned areas containing several age-classes of salmonberry that had Douglas-fir seedlings
or saplings interspersed within the shrubs. For the purpose of characterizing the lateral encroachment of salmonberry by a model, origins of the shrub stems and the shrubs' area of occupancy around an opening were mapped. A ratio of the area of an initial opening before brush encroachment and the area after brush encroachment was used to give a relative size of opening value This ratio served as the dependent variable in the model. Average maximum heights of the shrubs, the initial size of the opening, time or age of salmonberry,
and the number of stem origins or clumps of salmonberry were used as the independent variables, The data were analyzed with
the aid of a multiple regression program. Height increments that had accrued in 1968 on Douglas-fir seedlings were examined under
conditions ranging from total suppression by salmonberry to no suppression. Data were obtained from 1, 950 two-year-old nursery
seedlings (Douglas-fir) that gave an index of animal damage with respect to succession.
The findings indicate that the mathematical model formulated is deficient in its prediction ability although it is useful in that it gives a first approximation to the growth characteristics of salmonberry. The growth in height of the shrubs and the initial size of the opening are especially important variables in determination of encroachment. Suppression by salmonberry substantially reduces the growth of Douglas-fir. Moreover, seedlings dominated by salmonberry or even in close proximity to the shrub are frequently damaged by rabbits. Results reveal that the succession of salmonberry on cutover areas causes an increased frequency of damage to Douglas-fir
seedlings. Seedlings that are planted early will have a much better chance of avoiding suppression by the brush and will be less
likely to be severely damaged by rabbits, at least during the first year. The interrelationship of salmonberry and biotic influences are formidable to the establishment of Douglas-fir, both because of
salmonberry' s fast growth and the increasing rabbit damage to seedlings
with increasing age of the shrub.
