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XIV WORLD FORESTRY CONGRESS, Durban, South Africa, 7-11 September 2015

ENRICHING POOR DIPTEROCARP FORESTS WITH TEAK

(Tectona grandis L.f.) IN THE CENTRAL HIGHLANDS OF

VIETNAM

Bao Huy1

1Assoc.Prof.Dr., Tay Nguyen University, Vietnam; Email: baohuy.frem@gmail.com

Abstract

Dipterocarp forest in Vietnam is distributed mainly in the Central Highlands. After years of logging, forest

becomes poor, no longer contribute to the economy and thereby converted to industrial crops such as

rubber. This leads to the risk of destroying dipterocarp forest ecosystem. This research studied to enrich

dipterocarp forest with Teak trees to meet economic requirements and also prevent destruction of

environment values of this forest type. In reality variation of ecological factors, terrain, physical and

chemical properties of soil in dipterocarp forests are large, so research to find appropriate sites, forest

conditions and techniques to enrich the forest by using Teak species is crucial. 64 experiment plots with

an area of 4900 m2 each plot for enriching the forest with Teak were done in different forest site conditions

in 3 – 4 years. Based on database of teak growth under the combination of factors, weighted nonlinear

multivariate regression models were used to detect key factors influencing adaptability of teak; using

remote sensing to build map layers of key factors and intersect in GIS to design a map for enrichment of

dipterocarp forest with teak. As a result, teak used to enrich the dipterocarp forest is potential, based on

dominant average height (Hdom) determined 4 adaptation levels of teak (very good, good, average and

poor), at the age of 4 years the Hdom reached to 8.1 – 9.9 m for very good, 6.4 – 8.1 m for good, 4.6 – 6.4

m for average and under 4.6 m for poor adaptation level; six key factors affecting the adaptation of teak

is waterlogging, altitude, forest stand volume, soil type, % sand and P2O5 in soil; dipterocarp forest area

to be enriched with teak is 42,292 ha in the Central Highlands of Vietnam.

Keywords: Dipterocarp Forest, Forest Enrichment, Teak, Tectona grandis, Vietnam

Introduction and main objectives

In Vietnam, Dipterocarp forest distribution is concentrated in the Central Highlands. After years of

exploitation, the forest have become impoverished in wood production, but still maintaining ecological

functions. Due to poor dipterocarp forest on the economic value of the timber, so the forest area has been

converted to crops like cashew, rubber and acacia. The dipterocarp forest clearing for cultivation will

bring the risk of long-term environment. So there is a need to find valuable timber species, consistent with

ecological sites to enrich dipterocarp forest (Simmathiri et al. 1998, Peter and Huy 2003). Meanwhile teak

(Tectona grandis Linn.F.) is a species of timber with high economic value, grow rapidly, can provide

wood for a short period; and its requirement of ecological site has many similarities with dipterocarp

forest.

Teak is a species of large trees, deciduous, over 30-40 m height in favorable conditions. Growth of teak

is large variation depending on the site, from 2 - 30m3 / ha / year and the business cycle is from 4 years to

80 years (Kollert and Cherubini 2012). According to ICRAF, teak growth in normal conditions at the age

of 5 is 13 m in height and 10 cm in diameter. White (1991) showed that the distribution of natural teak in

India, Myanmar, Thailand and Laos. Also teak grows naturally not pure, it grows in deciduous forests at

a rate of 4-35 % of density (Kollert and Cherubini 2012). Natural teak grows mixed with some species

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present in dipterocarp forest (Kollert and Cherubini 2012). Teak distributed widely from the dry areas

with rainfall of 500 mm/year to the humidity of up to 5,000 mm/year. However, the optimal growth of

teak in the range 1200-2500 mm rainfall with 3-5 month dry season (Apichart 1998, Seth and Khan 1958

refer to Kaosa-ard 1988). The optimal temperature for growth and development of this species is 27-360C

(Gyi 1972, Kanchanaburangura 1976 refer to Kaosa-ard 1998). Teak trees has need of light completely,

regenerated shoots under small canopy opening go well (Qumruzzaman et al. 2008). Teak can grow on a

variety of soils from different rocks like sandstone, shale. However requires deep soil, drainage, pH from

6.5 to 7.5, less growth than on dry sandy soils, thin soil layer or wetland (Apichart 1998, Kulkani 1951,

Kiatpraneet 1974, Bunyavejchewin 1987, Srisuksai 1991 refer to Kaosa-ard 1998,). Soil is suitable for

teak is relatively fertile with high levels of calcium (Ca), phosphorus (P), potassium (K), nitrogen (N) and

organic matter (OM) (Bhatia 1954, Seth and Yadav 1958, Samapuddhi 1963, Kiatpraneet 1974, Sahunalu,

1970, Kaosa - ard, 1981, Bunyavejchewin 1987, Srisuksai 1991 refer to Apichart 1998).

The objective of this study is to find out the adaptability of teak in dry dipterocarp forest and what

ecological factors, site, state of forests, soil physical and chemical properties influence the adaptation of

teak in the Central Highlands of Vietnam.

Methodology

Characteristics of the study area and materials:

Research area of dipterocarp forest is 91,088 ha, mainly the poor forest state after harvesting, density 50

– 500 trees/ha, standing volume 50 – 150 m3/ha; major species of Dipterocarpaceae family including

key species are Shorea siamensis , Shorea obtusa , Xylia xylocarpa , Terminalia alata , Terminalia

chebula , Dipterocarpus tuberculatus , Dipterocarpus obtusifolius. Figure 1 shows the distribution of

this forest type.

Fig. 1: Distribution of Deciduous Forest (Dipterocarp Forest) in the Central Highlands of Vietnam

Study site is located at altitude of 100 - 500 m; the terrain is relatively flat; the average annual rainfall of

1,600 - 1,900 mm/year; the average annual temperature of 23.0 - 25.5oC; there are 4-5 months of

drought and forest fires; some area is wet/flood in rainy season; soils formed on 4 types of rock are

shale, bazalt, acid magma and sandstone; soil thick layer is varied from < 30 cm to > 50 cm, the soil

surface has many rocks and stones; soil nutrient composition is changed.

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Studied tree species to enrich dipterocarp forest is Teak, scientific name: Tectona grandis L.f. belongs to

Verbenaceae family. Teak was planted by stump that was one year old with diameter from 1.0-1.5 cm,

length 15-20 cm.

Teak planted in dipterocarp forest in 2 times in June 2010 and 2011, the period of data collection was in

November 2013 and 2014.

Methods:

- Set of 64 experiment plots, each plot area of 4900 m2 (70*70m) on various combinations of the 3

groups of factors: ecological sites, forest and soil conditions.

- Density of planted teak in the forest: Mixed teak in the forest canopy gaps; distance of teak to

natural trees (DBH>10cm) and other planted teak trees at least 3m. Fig. 2 shows teak planted in

the forest. An average 263, at least 88 and the highest is 482 teak trees were planted per one plot.

100m

70 m

15m wide fire breaks

> 3m

> 3m

North

100m70 m

> 3m

> 3m> 3m

Cây ng

Forest

tree

> 3m

> 3m> 3m

> 3m> 3m

Teak

> 3m

TeakTeak

Teak

Teak Teak

Teak

Forest

tree

Forest

treeForest

tree

Forest

tree

Forest

tree

Fig. 2: Experiment plot for teak planting in Dipterocarp Forests

- Data collection in experiment plot and analysis:

Data of teak: Height (H, m), diameter at root (Droot, mm), diameter at breast height (DBH, mm)

and number of dead trees.

Ecological sites including nine factors: altitude with GPS, topography, slope; rocks and soil type

according to the GIS map (FAO 2008), soil depth by drilling and define waterlogging in rainy

season, determine the rate of stone (%) on the diagonal line in cell 10*10 m.

Forest conditions, directive plant with seven factors: Appearance of species of Dillenia hookeri

Pierre or Holarrhena curtisii King et. Gamble which indicate waterlogging; Eupatorium odoratum

Linn indicates good growth potential of teak; canopy cover (%) on the diagonal line of 10*10 m; 5.5

trees plot establishment to determine basal area (BA, m2/ha), dominant tree species, tree density (N,

trees/ha), standing volume (M, m3/ha), an area of canopies per hectare (St, m2/ha).

Collect and analyse soil: sample soil is 0.5 kg of 0-30 cm soil layer at 3-position represents; 4 soil

physical indicators analysed: % clay, % rich soil, % sand and % gravel in soil; 8 analysed soil

chemical data: pHKCl; N (mg/100g soil); P2O5 (mg/100g soil); K2O (mg/100g soil); Ca2+ (meq/100g

soil) and Mg2+ (meq/100g soil; H+ (meq/100g soil) and Al3+ (meq/100g soil).

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- Identify the adaptation level of teak for each experiment plot: Use the adatability classification

equations of teak plantation in Central Highlands with indicator is average height of dominant

trees (Hdom, m) by age (A, year) of Huy et al. (1998, 2015) in Table 1.

Table 1: Equations Hdom = f(A) for different adaptation levels of teak in the Central Highlands, Vietnam (Huy et al. 1998, 2015)

Hdom = a*exp(-b*A-0.796)

Adaptation

Levels a b

Upper 32.028 3.535

1: Very good 30.439 3.665

Upper 28.859 3.816

2: Good 27.289 3.994

Upper 25.732 4.207

3:Average 24.195 4.466

Under 22.685 4.789

- Method of determining the combination of factors that affect the adaptation of teak:

Encoding the qualitative and class factors is 1, 2, 3, 4, etc in the same direction with average height

increment of teak dominant trees.

Modelling the adaptation of teak under the influence factors as a function of Power:

Y = b0 * X1 b1X2b2…….Xn

bn (1)

Where Y is the adaptation level of teak is coded 1: Very good, 2: Good, 3: Average, 4: Poor. Xi is data

or code of ecological factors, site, and forest state, soil physical and chemical properties.

Use indicator of Mallow’s Cp (1973) to select the number of Xi factors involved in model with Cp as

close to the number of variables p, the more appropriate model.

Applying weighted nonlinear multivariate regression, the criteria to select the best model were

(Picard, Saint Andre et al. 2012):

- R2adj.%: Generally, the highest R2 value with statistical significance level exhibits the optimal

model.

- MAE: Mean absolute error. Smaller values are preferred:

MAE = 1

n∑ Yipre − Yi

n

i=1

(2)

- MAPE%: Mean absolute percent error. Smaller value is preferred (Mayer et al., 1993):

MAPE% = 100

n∑

Yipre − Yi

Yi

n

i=1

(3)

where, Yipre: the predicted value, Yi: the observed value, n = number of plots

Weight = 1/Xia, where Xi is the key independent variables and a variable from -20 to +20; changes to

obtain statistical indicators of the optimal model.

- Mapping teak adaptation in dipterocarp forest: Set map layers according to the ecological factors,

terrain and dipterocarp forest status based on Landsat image 2014, DEM of Jarvis et al. (2008),

soil map of FAO (2008). Map overlay of the key factors and combined with the model to

determine the level of adaptation to each area.

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Results

The adaptation of teak in dipterocarp forest:

Using the average height of dominant trees to evaluate the adaptation of teak. Dominant trees are

defined as 20% of the tallest trees in the experiment plot. From the models in Table 1, Hdom for age (A)

calculated for 4 adaptation levels of teak in Table 2. Since it determines the adaptation of 64 experiment

tested by using Hdom.

Table 2: Adaptation levels of teak based on Hdom and Age (Huy et al. 1998, 2015)

Adaptation levels and code

Hdom (m) / A (year)

2 3 4 5

Upper 4.2 7.3 9.9 12.0

1: Very good 3.7 6.6 9.0 11.0

Upper 3.2 5.9 8.1 10.0

2: Good 2.7 5.2 7.3 9.0

Upper 2.3 4.5 6.4 8.0

3: Average 1.8 3.8 5.5 7.0

Upper 1.4 3.1 4.6 6.0

4: Poor Under average adaptation level

As a result in 64 experiment plots, adaptability of teak has 4 levels: Very good (4/64 plots, 6.3%), good

(5/64 plots, 7.8%), average (18/64 plots, 28.1%) and poor (37/64 plots, 57.8%). Fig. 3 shows images of

dominant teak at 4 adaptation levels.

Very good adaption = 1

Age = 2.3 years

Hdom = 4.74 m

Good adaptation = 2

Age = 2.3 years

Hdom = 3.59 m

Average adaptation = 3

Age = 2.3 years

Hdom = 2.69 m

Poor adaptation = 4

Age = 2.3 years

Hdom = 1.26 m

Fig. 3: Dominant trees of teak at 4 adaptation levels

The study also showed the average growth and survival rate values of teak at the age of 4 years for 4

adaptation levels in Table 3.

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Table 3: Average growth and survival rate of teak at 4 adaptation levels at 4 years old

Adaptation

levels

Hdom, m H, m Droot, cm Survival rates,

%

Very good 9.0 8.0 8.5 98

Good 7.3 4.9 6.5 92

Average 5.5 3.0 5.2 89

Poor 3.8 1.9 4.2 74

The factors affecting the adaptation of teak:

Three models performed that predict the adaptation of teak under three groups of factors are: Eco-site,

forests state and soil physicochemical properties in Table 4. The results show that the model with key

factor in soil physical and chemical properties has R2adj highest, MAE and MAPE% smallest, followed

by the factors under forest state.

Table 4: Model to estimate teak adaptation levels under three groups of factors

Id Factor

groups Models

n

plot

R2 adj.

%

Weight

variable MAE

MAPE

%

1 Ecological

sites

Adaptation Level/Waterlogging =

5.91431*Altitude^-

0.351225*(Soil Type^3*Soil

Depth*Small Stone)^-0.137971

64 64.44 1/Soil

Type^-3

0.58 34.69

2 Dipterocarp

forest status

and

directive

plants

Adaptation Level =

6.37316*((Dominant Tree*Forest

Stand Volume)^ Eupatorium

odoratum species)^-0.309562

64 72.81 1/

Dominan

t Tree ^-

10

0.51 25.45

3 Soil

physical

and

chemical

properties

Adaptation Level =

0.362604*(Sand/Gravel in

Soil)^0.58802*(P2O5*Ca)^-

0.0770309

64 81.85 1/Sand^6 0.35 19.56

From the three models above shows that there are 12 factors that affect the level of teak adaptation. A

further analysis has performed to determine the key factors affecting the adaptation of teak. Six key

factors were detected: Waterlogging, altitude, forest stand volume, soil type,% sand, P2O5 in soil in a

model shown in Table 5.

This model has R2adj. highest and MAE, MAPE% smallest when compared to models under factor

groups; so if this is the only model fullest factors affecting the growth and adaptation of teak.

Table 5: Model to estimate teak adaptation levels under 6 key factors

Model n plot R2 adj. % Weight

variable

MAE MAPE %

Adaptation Level/Waterlogging =

0.105505*(Altutude*Forest Stand

Volume)^-0.0950788*Soil Type^-

0,274821*Sand^0.937015*P2O5^-

0.199017

64 82.18 1/Sand^7 0.22 12.98

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In model of table 5, variables have code and value: i) Adaptation Level: Different adaptation levels of

teak: 1: Very good adaptation, 2: Good adaptation, 3: Average adaptation and 4: Poor adaptation; ii)

Waterlogging: 1: No, 2: yes in rain season; iii) Altitude: 1: 300-400m, 2: 100-200 m and 3: 200-300 m;

iv) Forest Stand Volume: 1: 100-150 m3/ha, 2: <50 and > 150 m3/ha and 3: 50-100 m3/ha; v) Soil type:

1: Stagni-Arenic Fluvisols, Hyperskeletic Leptosol, 2: Dystri-Plinthic Planosols, Endoleptic Luvisols,

Geri-Acric Ferralsols, Geri-Acric Ferralsols, Hapli - Arenic Lixisols, Arenic Acrisols, 3: Endoskeleti-

Arenic Luvisols, Eutri-Anthraquic Planosols, 4: Endoleptic Acrisols, Epileptic Acrisols, 5: Episkeletic

Acrisols, 6: Endoleptic Lixisols; vi) Sand: % sand in soil, no code, value from 34 – 85%; vii) P2O5: in

soil, no code, value from 1.6 – 10.6 mg/100g soil. This model used to set up an adaptation matric of teak

under six key factors.

Mapping adaptation of teak in dipterocarp forest:

The study has established a model to determine teak adaptation based on the factors of map layers, as a

result 4 map factors affecting the teak are soil type, slope, soil depth and forest canopy area in the model

in Table 6.

Table 6: Relationship between teak adaptation levels and key map factors

Model n

plot R2 adj. % Weight variable MAE MAPE %

Adaptation Level = 8.21654*(Soil

Type^4*Slope*Soil Depth*Canopy

Area)^-0.17781

64 57.43 1/Soil Type^-4 0.56 36.89

Map layers of soil type, soil depth, slope, forest canopy were intersected and combined with the model

in Table 5 to produce a map of teak adaptation in dipterocarp forests in Figure 4.

Fig. 4: Map of teak adaptation in dipterocarp forests

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From the adaptation map, identify dipterocarp forests adapted to be enriched by teak in 4 different

levels in Table 7.

Table 7: Dipterocarp forest area to be enriched by teak at 4 adaptation levels in the Central Highlands of Vietnam

Adaptation Level of Teak / Code Area (ha) Rate %

Very good adaptation – 1 190.0 0.2

Good adaptation - 2 18,260.4 20.0

Average adaptation - 3 23,842.2 26.2

Poor adaptation - 4 18,973.0 20.8

Another 29,822.1 32.7

Total (ha) 91,087.7 100.0

Discussion

While there has been difficulty to find trees that have the ability to adapt to the extreme conditions of

dipterocarp forest as forest fires, drought in dry season, flooding, waterlogging in rain season and gravel

in soil; enriching dipterocarp forest with teak has shown the ability to adapt in 4 different levels compared

with teak plantations, in that 3 high adapted levels can be applicability.

As a result, the growth of teak are very volatile due to the large variation of many factors. Surveying the

model of six key factors affect the adaptation of teak in Table 5 indicated: Soil types for a highly

adaptive teak are Endoleptic Acrisols, Epileptic Acrisols, Episkeletic Acrisols, Endoleptic Lixisols;

altitude of 200 - 300 m is good, the worst is 300-400 m; where not waterlogging, teak adaptation at all

four levels, while slightly waterlogging the adaptation within the average to poor; teak was well adapted

at forest stand volume is 50-100 m3/ha, poor adaptation at volume of 100-150 m3/ha; the % sand in the

soil significantly influence the adaptation of teak, % sand increases, the adaptation decreases; P2O5 also

help increase growth teak and reach better adapted.

Conclusions

Teak used to enrich the dipterocarp forest is potential with four different adaptation level. At the age of 4

years the Hdom reached to 8.1 – 9.9 m for very good, 6.4 – 8.1 m for good, 4.6 – 6.4 m for average and

under 4.6 m for poor adaptation level. Survival rate of 74-98 % in four levels to adapt.

Six key factors affecting the adaptation of teak is waterlogging, altitude, forest stand volume, soil type, %

sand and P2O5 in soil.

Dipterocarp forest area to be enriched with teak is 42,292 ha in the Central Highlands of Vietnam,

accounting for 46 % of this forest area at three high adaptation levels are very good, good and average.

Acknowledgements

The author would like to thank colleagues in consultative group "Forest Resources and Environment

Management - FREM" have actively participated in this study include: Dr. Vo Hung, Nguyen Cong Tai

Anh, Nguyen The Hien, Pham Cong Tri, Nguyen Duc Dinh, Dr. Cao Thi Ly, Pham Phu Quoc Doan, Do

Van Nhuan, Trieu Thi Lang, Hoang Trong Khanh, Ho Dinh Bao and forestry students of Tay Nguyen

University, Vietnam.

The views expressed in this information product are those of the author(s) and do not necessarily reflect

the views or policies of FAO.

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