Silvicutural Growth Performances of Thirteen Endemic Broadleaf Trees of Taiwan

We investigated the growth potential of some endemic broadleaf species in restorative reforestation. In March 1993, mix-plots planting of the test species was carried out in a tract of land situated at 800 m elevation with south-west facing slope at the Tamalee Research Center of the Taiwan Forestry Research Institute, Taitung, Taiwan. Each species was planted with 3~5 plot repetitions, and in each plot 50 trees of the same species was planted with a 2 x 2 m spacing. A total of 13 species were tested. Survey of the sapling growths were carried out yearly from May of 1996 on, and the frequency changed to 2-year since February of 2003. Tree height and diameter at breast height (DBH) growths were compared from year-to-year, and tree forms were also investigated at the later years. The common elaeocarpus (Elaeocarpus sylvistris) and incense machilus (Machilus zuihoensis var, zuihoensis) saplings grown at the experimental plots, showed good growth and survival rates. After out-planting for 108 mos, the average height growths reached 750 and 730 cm, respectively. And their survival rates in the plantation were about 60%. Other indigenous broadleaf trees, with the exception of Pasania kawakamii which had not reached 5 m in average height, all other endemic broadleaf trees native to the mid-elevation forests of Taiwan, including Pasania kawakamii, Schima superba, Schefflera octophylla, Lithocarpus castanopusisifolius, and Cinnamomum micranthum, although not as fast growing as some traditional plantation species such as Fraxinus formosana, reached average height growth > 5 m, and their average DBH growth all reached 7 cm, nevertheless. The net height growth of the various species in the first 3 yrs, with the exception of Zelkova serrata which reached 80 cm yr-1, all other species had rates of 30~50 cm yr-1. In the 3rd to 5th years, however, all species had net height growths over 80 cm yr-1, with E. sylvistris reached 140 cm yr-1. These were the fast-growing period of the saplings and the rates maintained until the 88th month of out-planting. These results suggest that the endemic broadleaf species have tremendous afforestation potential in the mid- and low-elevation plantation forests of Taiwan. When coupled with good tending and management of the forests, even greater potential can be realized.
Even in the early-stage of growth, the saplings often had forking tendencies with crown cover of 2 m or more, which may cause problems for subsequent growth performances and the form and quality of the timber utilization. In particular, as the average forking rate reached 40%, we deem that advancing the schedule for pruning and thinning of the small-diameter-log shall be practice to promote healthy growth of the stand. Regression analysis using tree height growth and tree age as variables generated regression equations having R2 of 0.90 or better, indicating that the 2-variable polynomial regression equations can be used to predict the early growth of forest trees. The information may be also useful in estimating the year-to-year carbon dioxide sequestration amounts in man-made broadleaf forests.