1.

Mean root lengths were significantly different between groups based on mature size (K), growth rate (r) and sprouting ability (Table 1 and Table 2). Differences between cutting beds were also significant within each group, which suggests that between-species variance was also large within the groups. Species groups with the smallest mature size (K<20 cm), the fastest growth rate (r>0.02 per year), and the most vigorous sprouting ability showed significantly longer mean root lengths compared to the other groups, between which there were no significant differences (Fig. 1 and Fig. 2).

The results suggest that the majority of species in a mixed dipterocarp forest have the potential for vegetative propagation from cuttings. We cannot conclude whether the observed proportion of rooting species (66%) is high or low compared to other tropical forests, because no comparable studies have been conducted. However, the observed rooting abilities are likely underestimates for most of the study species, because the cuttings were collected from suppressed forest saplings, and successful rooting from cuttings is affected by the age and the nutrient status of donor trees (Kantarli, 1993). Generally, rooting decreases with the age of donor trees ( Smits et al., 1990). Cuttings collected from donors in vigorous growing conditions root more successfully than cuttings from those growing in poor conditions (e.g., under low light), which generally have lower C:N ratios ( Kantarli and Veierskov). Most of the donor saplings in this study had been growing in shaded conditions for at least 10 years (A. Itoh, personal observation). The study results, therefore, should be considered to be a conservative estimate of the rooting ability of these species. It is likely that more species would have rooted successfully if we had taken cuttings from more vigorous donors. For example, cuttings from Dryobalanops aromatica, Shorea parvifolia, and Shorea macroptera did not root in our experiment, but were reported to produce roots when collected from young healthy seedlings grown under nursery conditions (e.g., Aminah; Smits; Dick and Aminah). In addition, rooting percentage could be improved in the species that successfully rooted during this experiment by choosing more suitable donors. Therefore, vegetative propagation by cuttings seems highly viable for many mixed dipterocarp forest species, especially for those that have small mature sizes.
 

This study showed that the majority of species in a mixed dipterocarp forest in Sarawak have significant potential for vegetative propagation by cuttings. Small and fast growing species showed especially good rooting ability. Planting stock for these species can easily be produced from cuttings for restoration programs, even if seeds are unavailable. However, many upper canopy and emergent species, including dipterocarps, showed poor rooting ability, suggesting that seedling production from cuttings of these species may be difficult. Variations in rooting ability were related to both phylogenetic and ecological factors. Thus, knowledge of the ecological characteristics of species, especially sprouting ability, is useful for the preliminary selection of species for cutting propagation.

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