Studies on Rubber ( Hevea brasiliensis ) Trees Exist Plant Type after Planting and Available Tapping Tree of Rubber Plantation in China

Existing plant types of rubber tree after planting and available tapping tree were investigated, and there were about 28 rubber plantations with different tapping years of 8 varieties “CATAS7-33-97”, “CATAS8-79”, “CATAS7-20-59”, “PR107”, “RRIM600”, “GT1”, “INA873”, “93-114” in South China. The results showed that there were six kinds of existing plant types of rubber tree after planting of rubber plantations, which were available tapping trees, wind damaged trees, cold damaged trees, tapping panel dryness trees, absent trees and weak trees, respectively. These data investigated also showed rubber trees under available tapping, stoppage due to tapping panel dryness, absence, wind damage, cold damage and weakness were counted and calculated and made up for 72.21%, 14.75%, 5.61%, 3.86%, 2.68% and 1.89%. Tapping panel dryness trees, wind damage and absent trees are major factors for the loss of tapping rubber trees in the rubber plantations. Of these investigated varieties, available tapping trees per 100 trees of rubber plantation of “PR107” at the 1st, 12th, 14th, 16th, 20th, 24th tapping year were 96, 67, 70, 75, 66, 46 trees in Hainan planting zone, respectively. Available tapping trees per 100 trees of rubber plantation of “RRIM600” at the 9th, 15th, 20th, 22nd tapping year were 88, 62, 55, 36 trees in Yunnan planting zone, respectively. Available tapping trees per 100 trees of rubber plantation of “93-114” at the 10th, 19th, tapping year were 94, 62 trees in Guangdong planting zone. These results showed that available tapping trees of rubber plantation decreased with increasing tapping age under different planting zones in China.


Introduction
It is a decisive yield factor to the available tapping trees in the specific rubber land on dry rubber production.Through grasping the situation of how many available tapping trees are in the rubber land, the enterprisers and growers can estimate the production capability.Then they can make the yield plan each year and the trees renewal in time.They also can establish tapping strategy and put investment reasonably for rubber plantation.There was a very significant positive correlation between dry rubber yield and the available tapping trees for rubber plantations of variety RRIM600 in the rubber tract of Xishuangbanna [1].Some studies showed that high dry rubber yield of rubber plantations was often attributed to higher available tapping trees [2] [3].The low available tapping trees or the low number of tapping trees of rubber plantation was one of the reasons for low yield in the rubber plantations of Hainan State Farms [4].In addition, the available tapping trees of rubber plantations also were one of the main factors affecting rubber production efficiency in Hainan State Farms [5].Some researchers analyzed that severe cold injury was the main reason for low number of mature trees, and that improving number of mature trees in rubber plantation helps to achieve sustainable development of the rubber plantations [6].Some factors such as plant density of rubber plantation [7], human behavior and its decisionmaking errors [8], strong typhoon [9] affected the growth of the rubber trees in South China.The rubber plantations yielded 1200 kilogram of dry rubber by average in China, which is quite low as compared to other natural rubber producing countries in the south-east Asia [10].There is still a lack of objective and comprehensive understanding of the problem of low dry rubber yield for rubber plantations in China.It will help solve the problem through analysis of existing plant types of rubber tree after planting and available tapping tree of rubber plantations.This paper preliminarily studied existing plant types of rubber tree after planting and available tapping tree for rubber plantations in Hainan, Yunnan and Guangdong rubber planting zone.

Material and Methods
Rubber tree varieties "CATAS7-33-97", "CATAS8-79", "CATAS7-20-59", "PR107", "RRIM600", "GT1", "INA873", "93-114", about 28 rubber plantations with different tapping years were investigated in the major three rubber planting zone in South China, Hainan, Yunnan and Guangdong provinces during the research survey in 2014.The survey was focused on exist plant types of rubber tree after planting and available tapping tree, and 100 trees would be selected from each rubber plantation investigated.Plant and row spacing ranged from 2.5 m to 3 m and from 6 m to 7 m, respectively in the rubber planting areas in Hainan and Guangdong provinces, and from 2.5 m to 3 m and 9 m to 7.5 m, respectively in the rubber planting area in Yunnan province.The rubber cultural practices and latex harvest technology for the rubber plantations selected followed "Technical Regulations for Cultivation of Rubber Tree" which was issued and implemented by the People's Republic of China [11].

Statistical Analyses
All statistical data were analyzed using Microsoft Excel and SAS statistical analysis software.Survey data were used for data analysis using the following method: Percent tapping tree (%) = (Number of tapping tree/Total number of rubber tree investigated) × 100; Percent wind damaged tree (%) = (Number of wind damaged tree/Total number of rubber tree investigated) × 100; Percent cold damaged tree (%) = (Number of cold damaged tree/Total number of rubber tree investigated) × 100; Percent tapping panel dryness tree (%) = (Number of tapping panel dryness tree/Total number of rubber tree investigated) × 100; Percent absent tree (%) = (Number of absent tree/Total number of rubber tree investigated) × 100; Percent weak tree (%) = (Number of weak tree/Total number of rubber tree investigated) × 100.

Results and Discussion
This investigation showed that there were six kinds of existing plant types of rubber tree after planting of rubber plantations (Table 1), which were available tapping trees, wind damaged trees, cold damaged trees, tapping panel dryness trees, absent trees and weak trees, respectively.From the point of view of all varieties survey, rubber trees under available tapping, stoppage due to tapping panel dryness, absence, wind and cold damage and weakness were counted and calculated and made up for 72.21%, 14.75%, 5.61%, 3.86%, 2.68% and 1.89% of the total number of trees of the planting density, respectively (Figure 1).The above findings showed tapping panel dryness, absence and wind damage are major factors for the loss of tapping rubber trees in the rubber plantations.This investigation showed that rubber available tapping trees of rubber plantations presented downward trend with increasing tapping age (Table 1).In Hainan planting zone, available tapping trees per 100 trees of rubber plantation of "PR107" at the 1st, 12th, 14th, 16th, 20th, 24th tapping year was 96, 67, 70, 75, 66, 46 trees respectively, and available tapping trees per 100 trees of CATAS 7-33-97 at the tapping year 1st, 5th and 10th was 96, 85 and 71 trees, respectively.In Yunnan planting zone, available tapping trees of rubber plantation per 100 trees of "RRIM600" at the 9th, 15th, 20th, 22nd tapping year was 88, 62, 55, 36 trees, respectively, and available tapping trees per 100 trees of rubber plantation of "GT1" at the 10th, 16th, 22nd tapping year was 88, 84, 22 trees.In Guangdong planting zone, available tapping trees per 100 trees of rubber plantation of "93-114" at the 10th, 19th tapping year was 94, 62 trees, respectively.These results also showed that available tapping trees of rubber plantation decreased with increasing tapping age under different planting zone of Hainan, Yunnan, Guangdong in China, and available tapping tree densities in rubber plantations of different varieties showed a similar decline trend with the increase of tapping years.
This result showed existing plant types of rubber tree after planting of rubber plantations were various.That is to say, there were numerous factors affecting the available tapping trees in rubber plantations: poor cultural practices for immature trees, damages due to cold, drought and wind, as well as root disease, etc.A clear understanding of these factors will help to take targeted measures for rubber cultivation and plantation management.
Available tapping trees and individual yield significantly declined with a rise in elevation in Vietnam, and as available tapping trees increased yield per tree declined whereas latex productivity rose [12].High-density planting has been proven to be effective in minimizing wind damage.Bole growth and yield were strongly influenced by planting density, and the optimum planting density was determined at 650 trees/ha in south western Côte d'Ivoire, but available tapping tree did not vary much with the density of planting [13].Bark thickness and number of latex vessel rings of rubber trees declined as the planting density increased from 400 to 920 trees per ha, and yield per tree per tapping decreased, but yield per ha per tapping and net present value increased with the increase in planting density [14].Smallholders generated the highest income and profits from their land only when their smallholdings maintained at 401 -500 effective tapping trees per ha at the tapping ages of 10 -15 years old, and the initial planting density of the smallholdings should be 600 -750 trees per ha to ensure this number of available tapping trees per ha since rubber trees had a mortality rate of 10% after planted, and in fact only about 75% of the plants were available tapping [15].The percentage of infected and stubble trees was getting rise with the increase of rubber tree tapping years, and available tapping trees after 7 years of tapping declined with the increase of rubber tree tapping years [16].
Rubber tree generally has an economic life cycle of over 30 years, and is cultivated and managed as a longterm crop once planted.Hence, good management of each rubber tree in rubber plantations at the early stage is an important factor for high available tapping trees when the rubber tree enters into the latex harvest period.Wind and cold damages are common factors reducing available tapping trees of rubber plantations.The wind and cold often threaten the rubber production in the main rubber producing areas in China: Hainan, Yunnan and Guangdong.Rubber producing areas are zoned based on the pathways of cold current and typhoon.Varieties of rubber trees with wind or cold tolerance are planted based on the environments and protected in different ways whenever cold current and typhoon attack the rubber plantations.It is important for rubber growers to be conscious of the importance of environmental approach to plant rubber trees in the non-traditional area.
The tapping intensity is also an important factor affecting the available tapping trees of rubber plantations.Tapping system taken should be based on the performance of rubber plantations and clones, and tapping skill has a very important impact on yield and TPD.Latex yield harvested from rubber plantations should be reasonably based on the growth of rubber trees.Annual check on TPD index should also be done continuously when a tapping system is introduced.

Conclusion
The results of this study indicated that there were six kinds of existing plant types of rubber tree after planting of rubber plantations in South China, which were available tapping trees, wind damaged trees, cold damaged trees, tapping panel dryness trees, absent trees and weak trees, respectively.These data investigated showed rubber trees under available tapping, stoppage due to tapping panel dryness, absence, wind damage, cold damage and weakness were counted and calculated and made up for 72.21%, 14.75%, 5.61%, 3.86%, 2.68% and 1.89%.Tapping panel dryness trees, wind damage and absent trees are major factors for the loss of tapping rubber trees in the rubber plantations.These results also showed that available tapping trees of rubber plantation decreased with increasing tapping age under different planting zones in China.

Figure 1 .
Figure 1.Type and ratio of rubber plant standing under different growing environments in China.

Table 1 .
Analysis of available tapping trees under different growing environments in China.