Study on planting technique and management of dendrocalamus membranaceus forest for establishment of large-scale plantations

July 4, 2006 by

Study of planting technique and management of Dendrocalamus membranaceus forest for establishment of large-scale plantations

Tran Nguyen Giang, Luu Pham Hoanh

Hoang Vinh Tuong,Doan Chuong &

staff of Thanh Hoa Dendrocalamus Station

INTRODUCTION

Dendrocalamus membranaceus is a valuable bamboo species found mainly in Thanh Hoa province. Local people have had experience in growing this species on old burnt-over land. To meet the requirement to establish large-scale plantations, there are many problems to be overcome, such as:

– Supplying sufficient planting stock for the planting plan,

– Increasing planting seasons,

– Finding out planting techniques for poor soils and for slopes in planned areas,

– Applying techniques which can maintain soil fertility,

– Applying an exploitation mode which can maintain the productivity of the forest in both quality and quantity,

– Controlling pests and diseases.

To this end, a State-level research project was begun in 1975. The Forest Research Institute in cooperation with Thanh Hoa Forest Service has carried out experiments in Ngoc Lac district, the centre of the area planned for Dendrocalamus planting.

RESEARCH CONTENTS AND REMARKS

Experiments in soil, physiology, and pest and disease control were carried out in the laboratory and in the field, at permanent research points.

I- PLANTING MATERIALS

Due to a great demand for planting stock, as well as rhizomes and stems with roots and branches, which are commonly used in practice, research must be extended to the use of other parts of Dendrocalamus trees such as branches and stems with dormant buds for use as planting materials.

In general, for planting stock used in plantation establishment, the normal process is for leaves to appear first, then roots. However, in some cases when roots develop slowly or do not develop, leaves will be yellowish and die. In the propagation stage, there was sometimes high mortality in the nursery (30-50% or sometimes up to 60-70%).

1- Branches

a- In order to use branches as planting materials, they must be stimulated to develop roots, therefore, the effect of some growth stimulators on the propagation of Dendrocalamus branches was investigated. After the research process, the following conclusions were drawn:

* The growth stimulators having the best effect are:

– 2,4,5-T with concentration of 10-20 mg/l water

– 2,4-D with concentration of 20-30 mg/l water.

* Twelve-fourteen month old branches gave a high rooting percentage and did not show yellow leaves.

* Air temperature during the rooting period of branches affected the rooting percentage. The best time for cutting propagation is during those months which have an air temperature higher than 22.6oC (April to October).

* After being treated with growth stimulators, branches were inoculated at 20 days until roots emerged, then they were kept in a nursery so that a high survival rate could be obtained.

b- Study on the standard of planting stock by using rooted branches has shown that:

* Rooted branches having one stem with leaves, but still having no young shoots at the base, may have a low survival rate (45-50%) after planting.

* Rooted branches developed into a clump with one generation of shoots (shoots having branches and leaves), may have a survival rate of more than 90% after planting.

* Rooted branches with 2-3 generations of shoots with branches and leaves, could be divided into two sets and planted, and may also have a high survival rate of more than 90%.

Therefore, planting materials prepared in April and May will be suitable for planting in July, August and September, while planting materials prepared in July and August can only be planted in the following spring.

c- In order to solve the problems of transporting planting stock long distances, experiments were done using PE bags for rooting of branches. Branches were treated, inoculated and grew small roots. They were then put into PE bags of 15 cm in length and 10 cm in diameter. Bags were put in beds having a hard base or in normal beds covered by soil. This method could reduce labour and irrigation, however fertilizer, especially N, must often be used. Rooted branches must be kept in bags until they meet all conditions for planting such as one generation of shoots (having branches and leaves as mentioned above).

2- Stems with dormant buds

Propagation experiments were carried out on stems with dormant buds. Results showed that these gave strong shoots and fast growth in comparison with other material types. Nevertheless production of planting stock by this method still depends on the weather: success could be 70-90% in July and August, but was very variable in other months.

2,4,5-T with a concentration of 10-60 mg/l water was used but did not show any effect.

II- Planting techniques and modes

Studies relating to planting time and planting mode were carried out in order to complement the technical standards available.

1- Planting time

According to local custom, the most suitable planting times are July and August.

Due to the requirement to extend the planting season, continuous experiments were done in the two years 1976 and 1977. Experimental sites were barren land after burning-over for cultivation, the lowest site class for planting Dendrocalamus. Planting stock was developed from stems without bags. Experiments were carried out from February to September and 50 trees were planted on the 21st of each month. The following results were obtained:

– Survival was highest (80-100%) in February/March and July/August.

– Survival was 60-70% in June and September

– Survival was only 40% in April and May.

Considering soil and climatic conditions on experimental sites, the most suitable time for planting Dendrocalamus was not only July and August, but also February and March (spring).

In order to plant Dendrocalamus in spring, soil preparation (hole digging) must be done from November, December and January.

2- planting mode

In order to overcome the bad effects of mono-species Dendrocalamus forest on soil, an experiment was carried out to plant Dendrocalamus with timber tree species. The mixed plantation was only 2 years old, so that the effect between trees and trees and between trees and the environment could not be evaluated. However, the following observations were made:

* Dendrocalamus trees were planted in strips where big broad-leaved trees were cut, but vegetation was maintained (shrubs, regenerated trees). This mode proved to be much more promising in comparison with planting after clear felling. The most suitable spacing between strips was 10m.

* Broad-leaved species such as Erythrophloeum fordii, Peltophorum ferrugineum, and Cassia siamea used for planting in Dendrocalamus mono-species forest were shown to be very promising.

III- Exploitation technique

An experiment was carried out with 3 intensities of cutting on the basis of trees to be maintained .

* Maintain 1 year old trees to ensure that each young shoot has one tree.

* Maintain 1 and 2 year old trees to ensure that each shoot has two trees.

* Maintain 1, 2 and 3 year old trees to ensure that each shoot has three trees.

After 3 years of monitoring, it was apparent that cutting with high intensity gave the most shoots – twice as many shoots as cutting with low intensity. However, shoots were small and up to 45% were very small. In addition, the height of of the shoots was also clearly reduced.

Cutting with low intensity produced a low number of shoots but there were no small or very small shoots and shoots were not found in high density. Cutting with medium intensity resulted in only 80% of shoots compared with the high intensity cutting treatment. However, there were only a few small shoots (15%) and in 2 years, these could achieve a similar size to shoots of similar age in the low intensity cutting treatment.

From the above remarks and to follow silviculture requirements, it can be seen that medium intensity cutting should be applied to Dendrocalamus forest (maintaining 2 trees for each shoot) and rotation should be 3 years (2 yearly interval).

IV- Control of Cyrtotrachelus longimarus

Cyrtotrachelus longimarusFabr. is a serious threat to Dendrocalamus forest. Each year up to 40-60% of new shoots may be destroyed by this insect.

1- Characteristics of Cyrtotrachelus longimarus

The life cycle of this insect in one year has been determined: stages, length of each stage, habit of egg production, activity mode of mature insects after leaving the ground, number of eggs produced by one insect, eating mode of juvenile insects and damage to new shoots.

2- Control measures

Based on the characteristics of the insect, it was realised that killing mature insects on the ground can be very difficult and less effective, therefore control was carried out in two ways:

a- Kill pupa and mature insects in the ground by turning up the earth to 1m in width and 20cm in depth around the Dendrocalamus clump. In this way the ecological habitat of the insects in the stage when they lived in the ground could be destroyed, creating an adverse environment for their normal growth and development and at the same time tending Dendrocalamus clumps.

b- Kill juvenile insects in the shoots by injecting Bi58 poisonous compound into shoots carrying insect eggs. This method gave good results because the insects were killed while shoots still developed normally.

Results

After 3 years investigation, some preliminary results had been achieved.

1- Propagation by branch was successfully established and can be applied in large-scale production because there are many branches, they are easy to find and easy to root.

2- Standards of planting stock were determined in order to achieve a high survival rate after planting.

3- It was found that spring is also a suitable planting time for Dendrocalamus.

4- It was realised that the decision to plant Dendrocalamus in a mixture with broad-leaved trees was correct and can achieve the desired objective.

5- The number of trees to be cut (or maintained) and suitable rotation were determined to meet the requirements in economic terms and silviculture of Dendrocalamus forest.

6- A method was determined to control/kill juvenile insects of Cyrtotrachelus longimarus by using chemical.

Conclusion

The Scientific and Technical Council of the Forest Research Institute has approved the preliminary results mentioned above. Many opinions emphasized two areas which must be investigated: planting broad-leaved trees with Dendrocalamus and planting agriculture crops with Dendrocalamus. The Council made the following suggestions:

1. To approve the following technical methods in 1978:

+ Propagation technique of Dendrocalamus by branch

+ Technique to maintain rooted branches in PE bags

+ Planting time

+ Cutting intensity and rotation for Dendrocalamus exploitation

+ Technique to control Cyrtotrachelus longimarus insects.

2. To continue research on:

+ Techniques for planting Dendrocalamus on poor soil and slopes

+ Techniques to plant crops with Dendrocalamus.

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