Silvicultural Growth Performances of Thirteen Endemic Broadleaf Trees of Taiwan

Abstract

We investigated the growth potential of some endemic broadleaf species used in restorative reforestation. In March 1993, mix-plot planting of the 13 test species native to mid-elevation forests of Taiwan was carried out in a tract situated at 800 m elevation with a southwest facing slope at the Taimali Research Center Taiwan Forestry Research Institute, Taitung, southeastern Taiwan. Each species was planted with 3~5 plot repetitions, and in each plot, 50 trees of the same species were planted with a 2×2-m spacing. A survey of sapling growth was carried out periodically, and tree forms were also investigated in later years. Results showed that common elaeocarpus (Elaeocarpus sylvestris) and incense machilus (Machilus zuihoensis var. zuihoensis) saplings had better growth performances and survival rates, and the respective mean height growth had reached 750 and 730 cm 9 yr after out-planting. Their survival rates all reached 60%. With the exception of Pasania kawakamii and Tricalysia dubia which did not reach 5 m in height, the mean height growth of the other indigenous broadleaf trees including Pasania ternaticupula, Schima superba, Schefflera octophylla, Lithocarpus castanopsisifolius, and Cinnamomum micranthum, all exceeded 5 m, although their growth was not as fast as some general plantation species such as Fraxinus formosana, and their mean diameter at breast height (dbh) growth all reached 7 cm. The net height growth of the studied species in the first 3 yr, was 30~50 cm yr^(-1), with the exception of Zelkova serrata which reached 80 cm yr^(-1). However, all species had net height growth exceeding 80 cm yr^(-1) during 3~5 yr, with E. sylvistris reaching 140 cm yr^(-1). The fast-growing period of the saplings among tree species lasted to 88 mo after out-planting. These results suggest that endemic broadleaf species have tremendous afforestation potential in mid- and low-elevation plantation forests of Taiwan. When coupled with good tending and management of the forests, even greater silvics potential can be realized. Even in the early stage of growth, saplings often had forking tendencies with 2 m or more of crown width of planted trees, which may cause retardation of subsequent growth performance and may also influence the tree quality for timber utilization. In particular, as the average forking rate reached 40%, we deem that pruning and thinning of small-diameter logs should be scheduled to promote tree form quality. A correlated regression analysis of tree height growth and tree age indicated that 2-degree polynomial regression equations (R^2≥0.90) by tree age of tree species can be used to predict the early growth performance of planted trees at the site.