Wood density variation of different provenance for exotic loblolly pine in China
Abstract
Variation patterns and range of juvenile wood basic density (BD) of 30 loblolly pine provenance s in Zhejiang Province of China were reported in this paper. There were four radial variation patterns of BD within 310 10-year-old trees of 30 provenance s, but the main pattern was a steadily increasing trend from pith to bark. The early -late correlation coefficient of BD for loblolly p ine strengthens with trees age and t he value of BD in 5 years old trees can be used for predict that in 10 years old trees. The BD mean change of 30 provenances is similar to normal distribution and the BD varies from 0.343 to 0.412 g/cm3. The BD mean of t he contrast provenance is 0.369 g/cm3 and in medial level. There is an obvious difference in BD among 30 provenances. Further analyses show that the difference among trees within a provenance is greater than that among provenance s and the environment has s ignificant effects on its BD. The broad heritability of BD is 0.72. The individual tree selection within a provenance was much better than that among different provenance.
The BD mean of 30 provenance s is related positively to the provenance latitude , Long itude of provenance is related negatively to wood density in East Coast and positive to wood density in South Coast and Gulf. There is a tendency for BD of loblolly pine provenance to be lower from west to east and from north to south . This variation in pl antation in a common environment turned out contrary to that of natural at different environment. The BD of loblolly pine provenance s introduced from high latitude is greater than that from low latitude, but tree growth properties from low latitude were mu ch faster than those from high latitude.
The BD mean value of 310 trees at the same growth stage (the same age) was negatively related to the diameter at breast height and volume of these trees. Wood density was significant correlated negatively with trach eid width and tracheid diameter at different growth stage of loblolly pine. DBH was significant positively correlated with tracheid width, tracheid diameter and negatively distinct related to ratio of tracheid double wall thickness to tracheid diameter. That DBH was related positively to ratio of tracheid diameter to tracheid width and negatively to tracheid wall thickness showed that the tracheid wall thickness of fast trees or fast provenances did not increase in proportion as tracheid width and tracheid diameter increased. This would lead to the decrease in wood basic density. Better provenance selection for pulpwood and building lumber should be determined from both tree growth and wood properties.
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Introduction
Pinus taeda L originated from the southeastern of the U. S. A. is one of the most important exotic species for wooden industrial materials in subtropical area of the world. It was first introduced to plant in China in 1933 (Peng, 1992). Now it is extensively planted on hilly lands and low mountains in the Southern China for pulpwood and building lumber. It was estimated that the areas of its plantation is at least more than one million hectares in 1995. Most of these stands for loblolly pine are 20~25 years old and do not look good in both its stem shape and wood quality. It is necessary for them to be replaced with better provenances of loblolly pine within 10~15 years.
Although loblolly pine has been culturing in China for more than seventy years, its provenance tri al was not formally done until 1981 (Peng, 1992). According to the statistics in 1992 its seed orchard in China was about 809 hectares and its seed stand about 2720 hectares. Every year about 25000kg of seeds was imported from the American (Peng, 1992). Th e seed output is far from the demand of our forestry production and the genetic quality of seed is low. Because its natural growing range in the American is large and there are significant differences in its tree growth, resistance and wood quality among t he seed sources (Zobel 1958 and 1989), it is significant to for us to select better provenance for tree growth and wood improvement (Liu 2010; Kimura 2014; Sharma 2015; Takeuchi 2016) .
Page | 45 In the United States wood properties of loblolly pine usually follow a rather predictable pattern (Koch 1972 and Zobel 1989).
The inland and northern sources of loblolly pine have lower specific gravity and frequently shorter tracheid length than southern and coastal sources (Jackson and Strickland 1962, Mitchell 1964, Talb ert and Jett 1981, Zobel 1958 and 1989). But the studies carried out by Byram (1980), Tauer (1990), Jayawickrama, Mckeand and Jett (1997) showed that wood properties of loblolly pine did not follow the rather predictable patterns. These showed the environment had a significant effect on variation of wood basic density for loblolly pine (Zobel 1989). What is about variation of wood basic density for loblolly pine provenance in China? Is there a rather predictable pattern in its wood basic density in China? W e would like to know these answers. The provenance trial of loblolly pine organised by Chinese Academic of Forestry was carried out two times in 1981 and 1983 in China, respectively. The seeds for experiment in 1981 were collected from the natural stands and for experiment in 1983 were obtained from the improved seeds orchard of loblolly pine in United States (Peng 1992).
Wood density is an important index for both wood properties and wood improvement in tree breeding (Panshin 1980; Zobel 1984; Liu 2010; Ki mura 2014; Sharma 2015; Takeuchi 2016). Its variation will affect wood quality, pulp yield per hectare, quality of paper and pulp and wood products. The objectives of this paper will study the variation patterns of wood basic density for loblolly pine on t he bases of its provenance trial in 1983 in China. The results obtained will supply the theoretical bases in wood improvement of loblolly pine, its plantation culturing and reasonable and efficient utilizing of its wood resources.
Conclusion
Based on the present study, the following conclusions can be drawn: 1 There were four radial variation patterns of wood basic density (BD) within 310 trees of 30 loblolly pine provenances, but the main pattern was a steadily increasing trend from pith to bark. The early -late correlation coefficient of BD for loblolly pine strengthens with trees age. Th e BD value of 5 -year-old loblolly pine is able to predict that in 10 years old trees. 2 The BD mean change of 30 loblolly pine provenances is similar to normal distribution, the BD varies from 0.343 to 0.412 g/cm3. The BD mean of the contrast provenance is 0.369 g/cm3 and in medial level. Statistical difference in BD is found among 30 loblolly pine provenance. Further analyses show that the difference among trees within a provenance is greater than that among provenance and the environment has significant effects on the BD of loblolly pine. The broad heritability of BD for loblolly pine is 0.72. The individual tree selection within a provenance was much better than that among different provenance. 3 Wood basic density (BD) of 30 exotic loblolly pine provenances was related positively to the provenance latitude.
Longitude of provenance was related negatively to wood density in East Coast and positive to wood density in South Coast and Gulf. There was a tendency for BD of loblolly pine provenance to be lower from west to east and from north to south, this variation in plantation in a common environment turned out contrary to that of natural at different environment. The BD of loblolly pine provenance introduced from high latitude was greater than that from low latitude, but tree growth properties from low latitude were much faster than those from high latitude. 4 The BD mean of 310 trees at the stage of the same age was negatively related to the diameter at breast height and volume of these trees. Wood density was significant correlated negatively with tracheid width and tracheid diameter at different growth stage of loblolly pine. DBH was significant positively correlated with tracheid width, tracheid diameter and negatively distinct related to ratio of tracheid double wall thickness to tracheid diameter. That DBH was related positively to ratio of tracheid diameter to tracheid width and a little negatively to tracheid wall thickness showed that the tracheid wall thickness of fast trees or fast provenances did not incr ease in proportion as tracheid width and tracheid diameter increased. This would lead to the decrease in wood basic density. Better provenance selection for pulpwood and building lumber should be determined from both tree growth and wood properties.
