Study on the wood anatomy, annual wood increment and intra-annual growth dynamics of <em>Podocarpus oleifolius</em> var. <em>macrostachyus</em> from Costa Rica

Abstract

Tropical countries in the future will have an increasing demand for softwoods which favours mixed plantations possibly with minor portions of native conifer species. In this context numerous tropical species of the Podocarpaceae can be of ecological and economical interest. In Costa Rica the native species Podocarpus oleifolius var. macrostachyus (Parl.) Buchholz & Gray could be attractive for the establishment of manmade forests. However, profound knowledge on growth characteristics and wood properties is missing. In particular, information on the annual wood increment and intra-annual growth dynamics under natural site conditions at higher altitudes where P. oleifolius var. macrostachyus competes with hardwood species is not available and therefore the objective of this study. At the Cordillera de Talamanca (approx. 2,700 m a.s.l.), Costa Rica, an old-growth stand was chosen from which in total 5 trees (40 to 80 cm diameter at DBH) were sampled by taking stem sections and discs (2 trees)or increment cores (3 trees). During the period from October 1998 to December 2000, two trees of the site were pinned monthly for exact determination of the annual wood increment and the intra-annual growth dynamics in relationship to climate. The results of one of these pinned trees are demonstrated. It turned out that at high altitude the annual wood increment of old growth trees amounts to 1-2 mm (diameter) only. The tracheids show a rather constant cell wall thickness (2.5-4.5 μm) throughout the year, but a very variable radial cell diameter from 29 to 61 μm. The exact age of the tree cannot be determined anatomically, as there are no distinct tree-ring boundaries, but only very moderately developed terminal bands of flattened tracheids which do not circle the entire circumference of the stem. The monthly pin-labelling documents that during the dry season from about January until March in 1999 and 2000, virtually no cells were formed. However, with the beginning of the rainy season, about 59 % of the wood increment resulted from the months April to June. This increment rate already decreased from July to September to 32 %. Due to a distinct decrease in precipitation towards the end of the year, only 9 % of the wood increment were formed in the last quarter of the year, mainly consisting of the hardly visible terminal and flattened tracheids. The wood of this species is of very homogeneous structure and certainly attractive for highquality wood production.