Provenance studies in the phytotron

Provenance studies in the phytotron

For the experiment in the phytotron, where at first space was limited, five provenances from extremes of the natural range were sampled: two areas in Mindanao, Philippines, one in New Britain, PNG, one from mainland PNG lowland and one from mainland PNG highland.24The seed from Mindanao was collected by the Larsen-Cameron field trip and had recently become available from the Forestry and Timber Bureau Tree Seed Centre in Canberra.

In a preliminary experiment, eight seedlings from each of the five provenances were grown in a C-type cabinet for 108 days at 27/22 °C and 12 hour daylength. Measurements were made in each of the final five weeks and at harvesting. The results were investigated using PCA and FA to determine the main components of variation among the provenances when grown at a specific temperature - daylength regime.

Provenance ranking in descending order based on average whole seedling dry biomass harvested above the surface of the growing medium was New Britain (Keravat), Mindanao (Caliwan River), Mindanao (Milbuk), Mainland PNG lowland (Raba Raba) and Mainland PNG highland (Kundiawa).

PCA and FA were carried out on the correlation matrix of all the variables listed above (Nos 28 – 42). The cumulative percentage of eigen values indicated that 82% of the total variation across the 15 variables measured on the seedlings could be described by four components (45.7, 21.5, 8.1 and 6.7% respectively). The two density values, weight of stem and branches, rate of diameter growth of the node from where one of the density samples was taken and seedling size (basal diameter and total height) were correlated with the first component. Leaf length, width and area were very highly correlated with the second component. Number of nodes produced and their rate of elongation featured in the third component. Rate of height and basal diameter growth were prominent in the fourth component.25 These results mean that while whole stem density is strongly associated with seedling height and basal diameter at any fixed point in time, whole stem density varies relatively independently of the rate of growth of the seedling over time. Put another way, one could simultaneously set both a size and a particular density goal and separately select the individual(s) that grow to that goal at the fastest rate (that is under the shortest rotation, if the analogy is extended to full size plantation trees).

24 See Chapter 9, pages 175 – 189 In Davidson J 1972 loc. cit. 25 See Table 9.5, page 185 In Davidson J 1972 loc. cit.