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Criteria for selection of superior bamboo varieties, propagation and plantation establishment - Fu Maoyi

Research Institute of Subtropical Forestry CAF, Fuyang, Zhejiang 311400 China.

Background

Bamboo is one of the fastest growing, most versatile, 'woody' plants with highest productivity in the world, and is annually renewable and harvestable if managed appropriately. Bamboo, is not only of economic importance to rural communities in most Asian countries but also of ecological importance in preventing soil erosion by its strongly developed rhizomes and roots. Selective harvesting has been practised for a long time in many countries to obtain multiuse timber, edible shoots and for paper-making. Another major advantage is that it takes a relatively short time to establish a matured commercial plantation - about 3 years for sympodial (clumping) bamboo and 6 years for monopodial (running) bamboo.

China is rich in bamboo resources, with 39 genera and about 500 species covering more than 5 million ha. About 9 million tons of culms and 1.6 million tons of shoots were harvested in 1996. China's total bamboo production output value amounted to 1.5 billion US dollars in 19961. The cultivation and utilization of bamboo in China not only plays an important part in rural economy but also helps conserve natural forests and protect environment.

1 1US$ = 8.16 Yuan
However, the combination of the large population increase, excessive harvesting and unsuitable cultivation techniques led to large areas with low-yielding bamboo forests in the past 30 years. For example, there are more than 2 million ha of low-yielding moso bamboo (Phyllostachys heterocycla var. pubescens) forests with a yearly output of only 1.5 tons of culms and 0.5 tons of fresh shoots per ha until recently. But the output of shoots and culms in some high-yielding forests amount to over 15 tons and 1.5 tons respectively. The shortage of bamboo shoots and culms in 2005 is estimated at 1.6 million and 4 million tons respectively. To increase productivity to meet the demand, Chinese authorities and farmers have been requested to improve the productivity of the low-yielding or degraded bamboo forests for increasing the income of poor people in mountainous areas and an alternative raw material for the wood production industry in China where it will help to preserve the native hardwood forests and protect the natural environment.

Some distinct biological characteristics of bamboo have led to some specific difficulties in furthering research on genetic enhancement and in establishing intensive cultivation technique models of bamboo forests. For instance, there is the uncertain development period of flowering, due to long flowering cycles with or without seed production. Moreover, erratic growth of bamboo rhizome, sprouting of new bamboo culms randomly out of soil, and strong physiological integration of culm-rhizome in a clonal community, have impeded further research on development of cultivation models. The mineral requirements and soil management have also hindered the development of intensive cultivation techniques.

There are extensive sparse moso bamboo forests throughout southern China with about 1800 standing culms per ha, which is much lower than the productive forests with 3000 culms per ha (Chinese Ministry of Forestry 1992). Low productivity and excessive cutting mostly resulting from inappropriate silvicultural practices in hilly and mountainous bamboo areas not only have caused decline of productivity but also led to degradation of soil and water conservation of bamboo forests. In China, there is considerable concern about excessive harvesting and human disturbances on bamboo forest ecosystems. Chinese forest scientists are particularly concerned about the needs for improving the productivity of vast degraded and low-yielding bamboo forests, the identification, preservation and utilization of bamboo genetic resources, and balanced ecological function of managed bamboo forests. The methods outlined below will be followed to improve production and quality of bamboos.

Selection of superior varieties, provenances and clones

Population survey for priority species

a) Selection of study areas

The natural distribution of several species and varieties is being investigated. The limits of population will be determined within the defined areas and relationship of mountain and river systems. The vegetative propagation methods of the species, and the limitations of reproduction will be determined.

b) Establishment of sample plot and field investigation

For each population, 3-5 stands will be selected to set up plots (400-600 m2). The determination of the stand is important to ensure the similarities of site class, management history and to compare with naturally established stands with little or no management of the plot. Such plots could be similar in stand composition, stand density class, on or off-year pattern of stand and so on.

The characteristics to be determined will include productivity of stand, utilization of bamboo culm, taxonomy, interspecific variation, and some quantitative traits that are convenient to measure and analyze. Circumference at eye-height (1.6 m) or DBH, culm height, internode length, internode number below branching, branching pattern, thickness of culm section and its ratio with cavity diameter, leaf area and ratio of length and width, culm basic density, fibre length and width, culm sheath, blade length and others will also be studied.

The ecological and geographical factors recorded include climate, latitude and longitude of the stand, topography, soil of the plot, stand condition index such as community composition, culm age constitution, stand density and stand volume. The adaptation of degraded soils and soil/moisture conservation will also be recorded.

Except for the stand condition index and culm diameter which need overall measuring, other traits will be investigated with standard culms. The selected 5 year or 6 year old culms will be cut down to measure their height, internode, branch, and leaf traits and to obtain wood samples. The measuring and sampling position of these will be identical between culms and different plots. The sampling culms would be collected at random in the plot to reflect the differences in stand.

c) Laboratory analysis and data processing

The culm density and fibre morphology will be determined in the laboratory. The tender organs of standard culms (leaf, shoot) will be sampled. The sample tissues will be ground and then mixed with extraction buffer, extracted DNA (50 mg/ml) will be used as PCR template. About 500 primers will be screened for polymorphism. After amplification reactions, the products will be separated by electrophoresis on agarose gels and staining with ethidium bromide and then photographed. The intensity and molecular weight of amplified belt of DNA map will be quantified using computer software. The polymorphism percent and the genetic distance among samples will be calculated.

The phenotypic trait and the genetic difference at every level, between population, stands, sampling culms, will be analyzed, and the differentiation between populations will be recognized using multivariate methods (principal components analysis, clustering analysis).

Based on results of population survey, evaluation of traits with proper statistical design will be carried out to identify superior genotypes for specific end uses.

Criteria for selection

Selection criteria will include 4 categories of targeted uses as listed below:

i. Structural uses, construction, furniture frames and plywood bamboo

Species with the relevant properties are well known but the following should rate highest priority: Bambusa bambos, B. balcooa, B. blumeana, B. vulgaris, Dendrocalamus giganteus, D. strictus and Phyllostachys pubescens.

Harvestable culms from clumps or plants in case of Phyllostachys will be extracted, their height and diameter at the 8th internode be measured along with a count of the number of nodes. Wall thickness will be recorded at the top and bottom ends as well as the middle of each culm.

ii. Thatching, walling and handicrafts

Highest priority should be accorded to Bambusa blumeana, B. textilis, Cephalostachyum pergracile, Gigantochloa apus, G. levis, Ochlandra stridula and Phyllostachys pubescens.

Harvestable culms/clump or plant should be determined, extracted, and their height and diameter at 8th internode be measured along with a count of the number of nodes.

iii. Pulp, paper and rayon

Highest priority should be accorded to Bambusa textilis, Dendrocalamus strictus, and Phyllostachys pubescens.

Harvestable culm per clump/plant should be counted and further analyzed in the laboratory for content of silica, lignin and fibre quality.

iv. Edible shoots

Highest priority should be given to Dendrocalamus asper and others including Bambusa blumeana, D. latiflorus and Phyllostachys pubescens.

Harvested weight of shoots should be recorded with suitable sampling and weight of the edible portion should be determined. Additionally due attention should be paid to environmental stabilization. In this case the selection criteria are broad guidelines which have to be modified as needed for each species.

Propagation

i. Vegetative propagation of monopodial bamboos

Vegetative reproduction for raising plantations generally include three methods: planting rhizome, planting culm, and cuttings. If there are enough seedling sources, we can use these also.

Planting rhizome: In monopodial bamboo, rhizome buds can grow into rhizomes and shoots, and this can be used to raise plantings, especially when mother offset sources are not enough. The best season for planting rhizome for raising plants is in spring (February-March). Soil preparation, methods of building seedbed and planting stage management are the same as that of raising seedlings. Select robust rhizome with plump buds and sound roots (for big and middle size bamboo using 2-4 year old rhizomes, for small size bamboo using 1-3 year old rhizomes). Pay attention to protect rhizomes, rhizome buds, and roots, and keep enough soil to cover the rhizomes. After the rhizome is dug out, cut the rhizome into units of 30-50 cm long by a pair of pruning scissors or a sharp knife. Plant them in seedbed 15-20 cm deep and spacing of 30-50 cm. Place the rhizomes horizontally and cover them with 4-6 cm soil and press the soil firmly, then cover them with another layer of loose soil and finally cover them with straw to keep the seedbed moist. The rhizome buds gradually sprout and grow up into plants in April and May i.e. after 8-10 weeks. Select 2-3 plantings from one rhizome. Provide shade and irrigate the plantings frequently.

Planting culms: Planting culms for raising plants is more complicated. The whole culm including stump and tiny roots is planted horizontally in the soil to facilitate the culm nodes striking roots and growing plants.

This method is used in the middle of March. Select 1 to 3 year old, well-developed bamboo with 2 cm culm base and low branching. First dig a circle around the mother bamboo stump with diameter of 15 cm, separate the mother bamboo culm carefully from its rhizome at the “crew point”. Keep the culm upward with side branches, 2-3 internodes long and cut off the other branches. Transport it with host soil to nursery. Prepare trenches as wide as pruned bamboo crowns and about 10 cm deep, spacing 40 cm. Dig a hole of 30 X 30 cm for planting bamboo stump. Fertilize with suitable amount of decomposed barnyard manure. When planting culm, first put the stump into the hole, and the culm slanting at 150°. Keep the main branches spreading and lateral branches upward. Fill the hole with earth gradually, spray enough water, keep the side branch straight and with 1-2 branches out of the soil. Finally cover seedbed with straw, water again and cover it with a plastic film. According to results obtained each culm can produce 8-23 plants (offsets) within a year.

Cuttings: Select 1 to 3 year old healthy bamboos with about 2 cm culm base diameter. Cut the culm into sections with two-internode lengths starting from the first internode along with main branches. Insert cuttings at an oblique angle in the seedbed with the spacing of 15 X 30 cm and remaining 1-2 branch buds out of the soil. Cover them with straw and spray enough water, finally cover them with plastic film.

Tillering: In spring, dig out the seedling clumps and separate them. Pay attention to protecting tillering buds and roots along with enough host soil and cutting off 1/3 to 1/2 branches and leaves. Plant the offsets in the nursery bed at a spacing of 30-40 cm. Finally water them and cover the land with soil. The offset survival rates of this method is over 90%. A clump of seedlings can tiller about 10 offsets of 1 m height, and grow 1-8 rhizomes in a year. It can grow for 4-5 years, keeping good tillering ability and doubling the offset rate.

Layering: Select young offset around the clump of seedlings. Press it down, burying the culm into soil except the top of seedling. After layering for about one month, the nodes in the soil grow roots and sprout buds. Layering time can be April to September, but the best months are May and June in which layers grow roots quickly.

Remaining rhizome after digging seedling: After seedlings are dug out, parts of seedlings and a great quantity of rhizomes are left in nursery beds, which can be used to establish a permanent base for raising plantings. The holes left after digging out seedlings should be fertilized and filled with soil and hoed shallowly, then there will be many growing shoots in spring.

ii. Vegetative propagation of sympodial bamboo

Culm planting (with or without its stump): It has a few advantages such as simple, high survival and growth rate. Besides the difference of culm with or without its stump, the whole culm or part of it can be used. The latter with stump is the best way, because the section can promote the node buds to sprout. This method overcomes the disadvantage that most buds on the culm do not sprout in raising plantings. Internodes of the culm and stump are not cut off completely, and the stump can still be transported for planting during its early growth period.

The method is as follows: Dig out the selected mother bamboo together with its stumps. Keep perfect buds on the stump. Maintain 1-2 main branches and buds at each node and cut off other branches around the culm. Dig a long trench 12-15 cm deep, with planting space of 20-25 cm. The planting hole should be a little deeper. Place the whole culm horizontally in the trench and bury the same. Finally, cover it with a layer of 5-10 cm soil, press the covered soil tightly, cover it with straw and water it frequently.

Layering: This is suitable in the sparse bamboo stands located on smooth terrain. Starting from the base of selected mother bamboos dig a straight trench, 15-20 cm deep and wide and long. First, fill a layer of soil in the bottom of the trench, fertilize with manure, and mix the manure and soil thoroughly. Cut a section at culm base at the backside against the trench. Keep about 20 nodes and cut off the top of the culm. Keep the branches and leaves of the first node in the upper part of culm, for other internodes only keep the main branch with 2-3 internodes and buds on each node and cut off the other branches around the culm. Push the mother bamboo slowly into trench, and cover it with a layer of 5 cm soil and press the covered soil tightly, only revealing the branches and leaves of the end node. Finally, cover it with straw and water it. The nodes sprout roots and shoots around 100 days. In the next year saw off each internode into an independent planting. Dig out these plantings and use them for planting again or remove them into nursery land for raising plantings again.

Planting nodes: This method includes planting one or two noded culm. The steps are as follows: Cut off the top of culm, saw the culm into 1-node or 2-node units, then plant them in the soil horizontally or vertically slanted. Generally 2-node culm is planted horizontally, 1-node culm slightly slanted or vertical. When sawing the culm into 1-node, leave about 10 cm above the node and 20-25 cm below the node; the length of 2-node culm can be shorter than that of 1-node culm. The sections can be sawed horizontally. When sawing the culm, do the best to avoid culm damage. Plant 1-node culm horizontally, let the nodal buds face upwards; 2-node culms horizontally, let the node buds face upwards. The other steps are the same as raising plantings of culm cutting. According to the research results in different areas, the cuttings can be treated with NAA (1-Naphthalene acetic acid) which improves rooting and increase their survival rate.

Planting stump: The stump can be dug out together with conducting the tending of the bamboo clumps or independently. The robust stump is the best one for reproduction. When we dig out the stump, roots and buds should be protected from damage. The thick and strong culm can be cut into halves for propagation, and each half will have roots and buds. Trench and bury the stump horizontally or vertically at a spacing of 15 X 25 cm, cover it with a layer of 3 cm soil and press the soil tightly. Finally cover it with straw and water it. Generally the stump can shoot and grow roots in 30-50 days, which can be dug out and planted in the next spring.

Branch cuttings: Both main branch and sub-branch cuttings of sympodial bamboo can be used for propagation, for they have adventitious buds that sprout and grow roots. This method causes no injury to the mother bamboo. Branches are easy to transport. Survival rate is high. Branch cutting has two types: the main branch and the sub-branch. The operation is as follows: Cut branches from a 2 to 3-year old healthy and strong culm, pay attention to selecting the branches and sub-branches which are thick and strong, with short internodes, and plump buds on the first to third nodes and big branch bases with roots sprouting point. Cut the branch where it is attached to the culm. Soak the cut branches in water and store them in a shady and cool place. Pack them in wet straw bags for transportation. Insert them slanting into a trench at a spacing of 15 X 25 cm and the depth of 6 cm in seedbed, while the internode remains above the ground. Pack them tightly and water them. Watering should be done in the morning or evening. In about 40 days roots emerge. Three months later they will grow into young plants and 4-5 months later they can be planted out. Raising plantings by branch cutting can be done in spring, winter and autumn, but the best time is from March to April. In recent years, raising plantings by branch cutting has been developed rapidly.

Plantation establishment

Land selection, preparation and selection of species

There are many bamboo species and varieties, and the main cultivated ones are more than 100. Different species have different growth rates, development patterns, and different requirement of environmental conditions. Their economic potentials vary. Bamboo growth and development depend on the genetic character of the species and the environmental conditions. Plantation establishment is longer than that of agriculture, more than ten or 12 years needed. Although bamboos mature within a few years after planting, they should be managed continuously. In order to achieve the expected objectives i.e. fast growth, high quality and high yield, certain species should be selected that have adaptability and bring economic benefits and are suitable for particular environmental conditions, soil and topography. In order to reach the targets, it is necessary to know the requirements of species with reference to climate, topography, soil and others. For example, different species need different suitable climatic conditions such as temperature, precipitation, relative humidity and so on. Most sympodial bamboos have lower cold-resistance, only very few such as Bambusa glaucescens can grow in the natural condition of the central subtropical area. Most of the monopodial bamboos are cold-resistant and they can be planted even in warm temperature zones. Some high mountain bamboo species, such as Yushania and Fargesia, have high cold-resistance, but those species must grow in middle or high mountainous areas in the south of Yangzi River with relative high humidity.

After selecting the land, soil preparation is an important part for planting. This influences the planting quality and the time taken for closing of the stands. Clearing and weeding, improving soil quality for better growth and new bamboo sprouting are important. Soil preparation must be done in autumn or winter before planting. There are usually three kinds of land preparation i.e. overall, strip and lump ones.

Overall land preparation: The overall land preparation can change land environment and be favourable to monopodial bamboo's survival and growth. It includes three steps: Clearing, loosening soil, and digging planting holes. First, clearing away shrubs and weeds in the forest floor. Then overall loosening soil to 39 cm deep and clearing away rocks, tree roots and stumps. Finally, digging planting holes according to spacing adopted. For big or middle size bamboos, 3X4 m or 3X3 m is adopted. When digging a planting hole, the underearth and surface soil should be separated and put at the two sides of the hole. The planting hole sizes are also determined according to the bamboo species. If offset is used as planting material, for big and middle size bamboo, it should be 1 m long, 0,6 m wide, and about 0.5 m deep, but for small size bamboo, it can be 0.8-1.0 m long, 0.5-0.6 m wide and 0.3-0.4 m deep. If seedlings are used as planting material, the hole sizes vary depending on seedling sizes.

Strip land preparation: To prevent soil and water loss, strip land preparation can be made parallel with the contours. The strip width and distance between strips is about 3 m for big or medium size bamboo, 2 m for small size bamboo, and depth of loosening soil is about 0.4 m. The steps for strips and preparation are the same as those of overall land preparation.

Lump land preparation: In steep sloping fields, there is loss of soil and water, so lump land preparation can be used. First, determine the spot according to the spacing, then clear away weeds and shrubs within 2 m2 land around the planting spot, finally dig planting holes.

Establishments of monopodial bamboo plantation: Monopodial bamboos prefer sites with warm, moist climates and annual precipitation over 1200 mm. The central distribution area is located between south of Yangzi River and the north of Nanling mountains. The northern part of distribution area and introduction is between the north of Yangzi River and Yellow River basin. The main climatic factors that affect monopodial bamboo growth are drought in the growing season and severe cold in winter. Select the lee side and sunny places with high rainfall in spring and summer that are easily irrigated. Scorching sun and typhoon in summer affect growth. Monopodial bamboos grow fast and have strong underground rhizome-root systems which vary from 20-30 cm deep, but not deeper than 50 cm. So they require fertile, moist, good draining, acidic to acidic neutral sandy loams (suitable pH 4.5-7.0), and the groundwater level should be under 1 m. If the water level is too high, it is harmful to rhizome growth. It is not suitable to plant monopodial bamboos in sticky, barren or saline-alkali soil.

Topographic conditions have direct and indirect influence on growth of monopodial bamboos. The direct influence is on the rhizome growth which is prevented by snow pressure and windfall in steep slopes. The differences in topography result in changes of microclimate such as air temperature, moisture content, soil conditions and others. It is better to select the valleys, the foot of mountain and half way up the mountain under the elevation of 800 m as planting areas. In high mountains, dry and windy ridges, hillside and level ground are suitable. The water logged areas are unsuitable for growth. In northern distribution area, it is better to select lee and southern mountain valleys, foot of mountains under the elevation of 500 m as planting land in order to survive in winter and protect bamboos from freezing. In the southern area, it is better to select lee and northern mountain valleys and foot of mountain under the elevation of 100 m as planting area.

Planting season: Monopodial bamboos can be planted every month as long as some attention is paid to key techniques. Table 1 shows results of shoot stand establishment, such as Ph. praecox etc., planted in three different seasons in Anji county, Zhejiang province. The planting survival rates in three seasons were well over 90%, and the highest rate was in spring. Large scale planting is better in winter and early spring when bamboo rhizomes and buds grow slowly. At that time removing bamboo for planting causes little injury to rhizomes and roots, also has little influence on bamboo growth, and nutrient loss of mother bamboo in transportation. These are favourable conditions for bamboo survival and growth (Table 1).

Table 1. Survival rates in different seasons

Planting seasons

Winter

Spring

Rainy season

Number of units planted

420

392

240

Average survival rate (%)

96.4

99.5

91.3


Establishment of sympodial bamboo plantation

Planting land selection: Sympodial bamboos grow with high humidity and temperature, and are mainly distributed in the south of Nanling mountains and Sichuan basin. Dendrocalamus latiflorus and Bambusa oldhami require annual average temperature 18-20°C and in January, the average temperature is about 6-8°C, annual precipitation more than 1400 mm. Neosinocalamus affinis and Bambusa multiplex in the northern part require lower moisture and temperature conditions with the annual average temperature of 16-18°C, in January, the average temperature is 2-4°C, and the annual precipitation more than 1200 mm. Sympodial bamboos grow fast, and the planting land should be on foothills, 200-300 m above sea level. Gentle terrain site should have deep, loose and fertile sandy loams. Dry, barren sites are suitable, rocky or too sticky soils are not suitable for planting.

Planting time: Sympodial bamboos can be planted throughout the year, but the best time is from January to March or in the rainy season. Planting in high temperatures and dry seasons requires intensive management techniques, watering and more labour.

Planting methods: Select 1 to 2-year old healthy mother bamboos for planting, which should have many shoot buds on the stump, and be free from diseases and insect pests. The diameter of culms should be 3-5 cm for big size bamboos, and 2-3 cm for smaller bamboos. Dig out the soil to 30 cm outside the mother bamboo, dig deep gradually and pay attention to protecting bud eyes, find out the connecting point between the culm handle and stump of old bamboos. Use a sharp knife and avoid damage to the rhizome. Remove the stump together with soil, and roots. Cut off the top of branches, seal the section with mud to prevent the culm from losing water. Culms can be dug out and planted in clumps with 3-5 culms. The planting spacing can be determined by the size of mother bamboos. The spacing of 3 X 4 m, 4 X 4 m, 5 X 4 m is suggested. The size of planting hole can be determined by the size of the stump, generally 50 X 70 X 30 cm. Fill surface soil into the hole, then place mother bamboo in the hole vertically or slanted (better to put it slanted), then fill the hole with soil and press the layers, water, and cover the surface with a layer of loose soil again.

Planting of young bamboos: First, cut off most part of a culm except 2-3 nodes above the stump. Divide each clump into small units with 2-3 culms. Pack the seedling stump, and transport it for planting. The method of digging holes and planting is the same as that of planting by removing mother bamboos. The planting depth can be 3-4 cm deeper than the original one.

Planting culm with its stump: Dig out mother bamboo and cut its culm into about 1 m long pieces. Pack the stump and transport to planting land. Dig planting hole and put it into the hole horizontally; other details are same as above.

iii. Amphipodial bamboo planting

The mixed type of bamboo not only has a spreading rhizome system but also the adventitious buds in its stump. The growth characteristics are intermediate between monopodial and sympodial bamboo, but closer to those of monopodial bamboo. Therefore, the methods suitable for monopodial bamboo can be followed.


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