Patterns of cone production in Sitka spruce (Picea sitchensis (Bong.) Carr.) and the prediction of cone crops
The location of cones in crowns of grafts and mature planted tress was studied in detail and relationships between cone type and shoot characteristics were investigated. The results enabled a regression model to be developed to relate cone counts in certain crown zones to overall cone bearing. It was demonstrated that there are patterns of cone production in the crowns of Picea sitchensis. Preferred zones for female bearing are high in the tree. Male cones tend to occur lower in the tree and more proximal to the stem than female cones. As total female cone production increases, cones are borne progressively further down the tree and towards the main stem. In all cases there were shoots that remained vegetative, regardless of total cone bearing. There were also interactions between the type of cone and the nature of the bearing shoot. On lower order shoots both male and female cones tended to be borne in the proximal lateral position. On progressively weaker shoots there is a tendency for cones to be borne in progressively more distal positions. The same progress of cone bearing - from proximal to distal positions - occurred on shoots of decreasing size. On forest trees the vast majority of cones are borne on trees of above average dimensions. Of the three measured variables (height, dbh and crown depth) height appeared to be the most important in influencing cone production. Prognostic tree and stand models were developed which were quite successful in predicting cone production in forest stands, particularly at low or zero levels of bearing. The presence of female cones on the bearing shoots affected both the development of more proximal buds on that shoot and the characteristics of offspring shoots. Offspring shoots on bearing parents were smaller and tended to bear fewer needles. The effect on the number of buds formed was not conclusive.