The main difficulty in the study of the variation in flowering and fruiting and the search for factors regulating their periodicity and intensity is the gathering of quantitative data over a long period of time. In this Section the annual variation in sycamore flowering is investigated. At each site three branches per tree were collected and brought back to the laboratory in 1986. The estimates of flowering intensity were made using the method described in Section 2.6.2. Flowering intensity in any one year is expressed as the average percentage of buds flowering.
Population flowering intensity is the average percentage flowering of all the trees.
Due to time and physical constraints only one branch from each of five trees was sampled in summer 1988. Because the trees were free standing it is believed that inter-branch variation in flowering intensity is limited, though the small number of trees investigated may not be truly representative of the population. In Ireland all trees flowered every year between 1980 and 1986, but large variations were observed between years and between trees. 9.6 79.0 8.8 88.3 6.4 Table 2. At Le Mollard four of the five trees were found not to flower during at least one year and the variation in flowering intensity between trees appeared to be greater than in Ireland.