THE MINISTRY OF EDUCATION AND TRAINING

THAI NGUYEN UNIVERSITY

DO KHAC HUNG

STUDYING ON THE ACTUAL STATUS OF THE VEGETATION
COVER AND THE PROCESS OF NATURAL FOREST RECOVERY

IN VI XUYEN DISTRICT, HA GIANG PROVINCE
Speciality: ECOLOGY

Code: 62 42 01 20
ABSTRACT OF PH.D. DISSERTATION IN BIOLOGY


1

FOREWORDS

1. Reason for choosing the study
In the 21
st
century, human beings have witnessed the terrible
consequences caused by climate changes such warming phenomenon of
the earth, the rise and unusual appearance of storms, floods, land
degradation, epidemics, declining biodiversity, etc. They affect lives of
hundreds of millions of people on earth.
Being aware of serious harms caused by climate change, on the 17
th

August 2004, the Prime Minister has approved "Strategic Orientation for
Sustainable Development in Vietnam". It is until 2020, forest coverage
of our country will reach 45%.
Vi Xuyen district has a total large forest area. However, shifting
cultivation, nomadic life, deforestation for cultivation and exploitation of
forest resources make forest quality of serious deterioration.
Due to the above reasons, I choose the research thesis "Studying on the actual
status of the vegetation cover and the process of natural forest recovery
in Vi Xuyen district, Ha Giang province ".
2. The objectives of the study
It determines and analyzes several characteristics of the vegetation
cover types in Vi Xuyen district.
It clarifies the differences in physical, chemical and microbiological
properties and land animals of different vegetation types as a basis for

It studies systematically on the vegetation cover and flora in Vi
Xuyen district, Ha Giang province.
It provides the scientific material on the recovery process of
natural forests in Vi Xuyen district, Ha Giang province.
6. Structure of the dissertation
The dissertation consists of 127 pages. Apart from the foreword
part with 3 pages and two pages of conclusions and recommendations.
The main contents of the dissertation are presented in four chapters:
Chapter 1. Literature review includes 34 pages; Chapter 2. Objects of
contents and research methods consist of 8 pages; Chapter 3. Conditions
on nature, economic – society at studies area with 15 pages; Chapter 4
research results and discussion include 65 pages. There are 27 tables, 18
figures, annexes on component of regenerated plants composition of
regenerated plants and photos.

Chapter 1
LITERATURE REVIEW
To achieve the purpose of study and successful implementation of
research contents set forth, the dissertation refers to some concepts
related topics: vegetation, forest regeneration, forest secondary, etc.
There are 116 research literatures referred in the dissertation (103 Vietnamese
papers, 13 English papers) regarding the following major issues:
* The studies on vegetation classification
In the world and in Vietnam, the scientific research works on vegetation
are very abundant, including quantity of research papers as well as the
principles and methods of vegetation classification. Each classification system
also has advantages and disadvantages. In the dissertation, we select the
classified frame of UNESCO (1973) as a basis for classifying vegetation in
Vi Xuyen district, Ha Giang province.


2.4.1. Methodology
2.4.2. Specific research methods
2.4.2.1. Survey Method
During the research process of data collection, we use the method
of survey routes and standard plots of Hoang Chung (2008) and Nguyen
Nghia Thin (2004).
* The method of survey routes (SR)
The first survey route is perpendicular to the fundamental contour
line. The following survey routes are parallel to the first survey route.
Total survey routes are 15.
* The method of standard plots (SP)
On each survey route, standard plots are created and distributed
evenly in each vegetation cover type. Total standard plots are 60

4

In each standard plot (SP) in the secondary forest, there are five slab
cells (SC) established and arranged at corners those are intersections of
two diagonals of standard plots.
Samples are collected in standard plots and slab cells. Method for
collection of samples is similar to that of survey routes. In addition, it
measures total tree height (TTH), diameter at breast height (DBH),
counts regenerating trees and evaluate the original source and quality of
regenerating trees.
* The method of positioned cells (PC)
In each vegetation cover type, some specific standard plots chosen to
use as positioned cells (PC). Total positioned cells chosen are 9.
2.4.2.2. Sampling Method
* Plant sampling: Data collection in survey routes and in standard plots (SP)
* Soil sampling: Digging soil profile, taken land for the analysis of

Vi Xuyen district has a population of 100,800, accounting for
13.5% of the provincial population with average population density of
66.7 persons per km
2
. The structure is quite diverse nation, with more
than 20 ethnic groups living together: Tay, Kinh, Dao, Mong, Nung,
Giay, Pa Then, Hoa, Lo Lo, etc., of which, Tay ethnic group accounts for
the most proportion (36.1%). The ethnic groups have a unique cultural
identity, disparities on development level, education proficiency and
living standard.

Chapter 4
RESULTS AND DISCUSSION

4.1. Current status of vegetation covers in Vi Xuyen district, Ha
Giang province
4.1.1.
Current situation of use of forest land in Vi Xuyen district, Ha
Giang province

Table 4.1: Current status of forest land under 3 forest types of Vi Xuyen district
Soil type,
forest type
Production
forest (ha)

Protective
forests (ha)
Special use
forest (ha)

In the study area, the list of statistics is 557 species belonging to
393 genera, 114 families of five branches of vascular plants. Of 557
species in the study area, there are 33 rare and valuable plant species in
the Red Book of Vietnam and 7 species in ND 32/2006 ND-CP.
4.1.3. Causes of forest degradation in Vi Xuyen district, Ha Giang province

Forest area in Vi Xuyen district has been and exhaustedly exploited,
leading to serious forest degradation. The major causes of forest degradation
are logging activity, exploitation of non-timber forest products, forest fires, etc.
4.2. Changes of major factors in upward succession from grass
vegetation, low shrub vegetation, high shrub vegetation and
secondary forest in Vi Xuyen district, Ha Giang province
4.2.1. Characteristics of studied vegetation cover types
- Secondary forest (SF): It belongs to the closed forest formation
that is often green at the rainy season in low terrain and low mountains.
This vegetation type located in Trung Thanh commune had originated
after cultivating milpa with the recovery period of 25 years. The area of
forest is about 3 ha, 30
o
slope and 95-100% of land cover.
- The shrub vegetation cover (SV): it is shrub sub-formation
available timber trees distributed scattered. This vegetation type formed
on fallow and from 3 to 8 years in Dao Duc commune. Based on the
height of shrubs, we have chosen two states: high shrub vegetation (HSV)
and low shrub vegetation LSV).
- Grass vegetation cover (GV): the drought-tolerant grass formation
belongs to rice form in average of 0.5 -1 m with scattered timber trees
formed after cultivating milpa in Viet Lam commune. It has the recovery
time of from 2 to 3 years, with an area of 1.5 ha, 30
o


is

the most abundant

(
375
species belonging to

258

genera and 98

families)
.
Then
, secondary forests and
low

shrub

7

vegetation and the lowest abundant grass vegetation

(
209
species
belonging to


5  1 6  1 8  2 10  2
Under the results at table 4.11, in the process of succession from
grass vegetation to secondary forest, the average total number of tree
species in each standard plot has increased gradually. Of that, in a
standard plot there are 45 species in grass vegetation, 50 species in low
shrub vegetation and 58 species in high shrub vegetation and 79 species
in secondary forest the most species.
According to the data at Table 4.12, we find that in the process of
succession there are 206 tree species weeded. Eliminated process takes
place the most strongly in secondary forests (133 species). In contrast
with the process of elimination, there are 340 added species, of which in
the stage of high shrub vegetation, there is the highest number of
additional tree species (151 species).
Table 4.12: Fluctuations in the number of species in vegetation cover types
Vegetation
types
Quantity of exis.
tree species
Quantity of tree
species weeded
Quantity of tree
species added
GV 209 - -
LSV 285 12 88
HSV 375 61 151
SF 343 133 101
Total 206 340
4.2.4. The change on density, quality and origin of regenerated plants
in vegetation cover types
4.2.4.1. The density of regenerated plants

4.2.4.3. The origin regenerated plants
Regenerating trees originating from seeds in secondary forests and
shrub vegetation account for very high rates with a rate 65.3% and 58.8%
respectively. In contrast, those in grass vegetation cover and low shrub
vegetation account for high percentages with 56.5 % and 63.4% respectively.
4.2.5. The change of structure of formation in
vegetation cover types

4.2.5.1. The rule growing height
Table 4.14: The distribution of height H (m) of timber trees of
vegetation cover types (%)
Vegetation cover types
High levels
(m)
GV LSV HSV SF
Level I (<0.5) 42.87 14.34 8.95 2.61
Level II (0.5 -1.0) 28.57 16.09 10.44 6.80
Level III (1.0-1.5) 20.78 19.95 12.47 7.81
Level IV (1.5-2.0) 5.42 23.87 17.59 10.06
Level V (2.0-3.0) 2.36 15.06 25.11 17.22
Level VI (3.0-5.0) - 10.69 20.09 35.20
Level VII (>5.0) - - 5.35 20.3

9

(%)
0
10
20
30

Level I (< 1.0) 44.37 16.43 7.98 4.59
Level II (1.0 – 1.5) 27.59 17.08 13.34 5.93
Level III (1.5 – 2.0) 19.74 27.01 17.47 10.81
Level IV (2.0 - 3.0) 5.82 19.15 30.87 18.06
Level V (3.0 – 4.0) 2.48 14.05 20.25 34.75
Level VI (> 4.0) 0 6.28 10.09 25.86
Total 100.00 100.00 100.00 100.00

10

(%)
0
10
20
30
40
50
I II III IV V VI
diameter level (cm)
Grass vegetation
Low shrub vegetation
High shrub vegetation
Secondary forest

Figure 4. 5: The distribution of diameter level of timber trees of
vegetation cover types (%)
The data of Table 4.15 and Figure 4.4 shows that at grass vegetation
cover, it is mostly herbal plants, small shrub stems and timber trees with
small diameters. Therefore, the distribution of diameter is not significant.
However, there is a significant distribution of diameter with the peak

3 Trevesia palmata

h (m/ year)
- 0,4 ± 0,04 0,5 ± 0,04
H (m)
10,9 ± 0,5 11,5 ± 0,5 12,1 ± 0,6
4
Styrax
tonkinensis
h (m/ year)
- 0,6 ± 0,05 0,6 ± 0,06
H (m)
9,2 ± 0,5 9,7 ± 0,5 10,2 ± 0,5
5
Pelthophorum
tonkinense
h (m/year)
- 0,5 ± 0,05 0,5 ± 0,05
H (m)
7,2 ± 0,4 7,6 ± 0,4 8,0 ± 0,5
6
Castanopsis
armata
h (m/year)
- 0,4 ± 0,03 0,4 ± 0,04
Notes. H: Height in average (m); h: the growth rate of height (m per year)
Total number trees per species measured height is n = 30 trees

11


Actinodaphne
cochinchinensis

d (cm/ year)

- 0,4 ± 0,02 0,4 ± 0,03
D (cm)
16,5 ± 0,4 17,0 ± 0,4 17,5 ± 0,5
3
Trevesia
palmata
d (cm/ year)

- 0,5 ± 0,03 0,5 ± 0,04
D (cm)
18,8 ± 0,5 19,4 ± 0,5 20,0 ± 0,5
4
Styrax
tonkinensis
d (cm/ year)

- 0,6 ± 0,05 0,6 ± 0,05
D (cm)
9,6 ± 0,3 10,0 ± 0,3 10,3 ± 0,3
5
Pelthophorum
tonkinense
d (cm/ year)

- 0,4 ± 0,02 0,3 ± 0,02

colors of soil layers, it can confirm that the topsoil layer A in secondary
forest and high shrub vegetation cover has higher fertility than other
formations because it has a thicker litter layer (4.0 cm and 1.5 cm), with
grayish-brown soil, soil moisture, porosity, grain structure, etc.
4.2.8. Soil erosion level
Table 4.18: Soil erosion levels of vegetation cover types
Vegetation
types
Scattering
lam.
structure
(layer)
Thickness
of a litter
layer (cm)

Coverage

leve (%)
Soil erosion levels
GV 1 1.0 70 – 80
Light topsoil erosion

LSV 2 1.0 80 – 85
Light topsoil erosion

HSV 2 1.5 90 – 95
Not topso
il erosion
SF 3 4.0 95 – 100

02
(Sand)

0.02 -0.002

(Limon)
<0.002
(Clay)

0 – 10 29.3

51.2 37.0 29.6 33.4
10-20 27.6

49.8 38.1 27.0 34.9
GV 70 - 80

20 – 30 27.0

46.5 35.9 26.1 38.0
0 – 10 35.4

54.6 29.0 34.9 36.1
10 – 20 31.7

52.4 29.9 34.4 35.7
LSV 80 - 85

20 – 30 30.1


content of soil in secondary forest are 29.3% and 65.5% respectively.
In each vegetation cover type, the soil moisture content also
reduces over depth of soil profile, but this decrease is not significant.
4.2.9.2. The porosity
From 4.19 table shows the porosity of the soil in the vegetation
cover types increases gradually when coverage of the vegetation cover
increases. The lowest porosity of soil is grass vegetation (51.2%), that
increases in low shrub vegetation cover (54.6%) and high shrub
vegetation cover (58.5%) and the highest porosity is the secondary forest
soil (65.4%).
In each vegetation type, soil porosity is fluctuation under the rule
of decrease over depth of the soil profile.
4.2.9.3. Soil mechanical composition
The results of Table 4.19 shows that in the soil profile of the
vegetation type covers, contents of clay (<0.002 mm), limon (0.02 –
0.002 mm) and sand account from 33.4 to 46.1%, from 26.1 to 35.7%
and from 23.3 to 38.1% respectively. This demonstrates that all four
types of vegetation covers are a kind of light clay.
4.2.10.
The change on basic chemitry properties of soil in vegetation
cover types

4.2.10.1. Level pH
KCl

Soil in the studied vegetation cover types has relatively low value
of pH
KCl
ranging from 3.63 to 4.13. This demonstrates that soil in this
area is quite sour.

substances
(mg/100g)
Cation of
exchanges
(mg/100g)
Veg.
cover
types

Depth
(cm)
pH
KClTotal
pro.
content

(%)
Humus
(%)
P
2
O
5

K
2
O

5.18 9.14 3.49
HSV
20-30 4.06 0.15 2.78 5.01

4.63 10.02 2.67
0-10 4.13 0.42 4.86 8.58

11.20 11.36 4.42
10-20 4.11 0.30 4.02 6.50

6.02 9.04 4.36 SF
20-30 4.09 0.23 3.60 6.27

5.71 8.75 4.30
4.2.10.3. Total humus content (%)
Table 4.20 shows that the total humus content in the topsoil (0-10
cm) of vegetation cover types increase gradually through the stages of
the succession process of forest restoration. Humus contents in the grass
vegetation cover, the low shrub vegetation cover and high shrub
vegetation cover and secondary forest are 3.65%, 3.80%, 4.13% and
4.86% respectively. In the same vegetation cover type, the humus
content change under the rule of gradual decrease with depth of soil
profile.
4.2.10.4. Content of easily digestive phosphorus and potassium
* Content of easily digestive phosphorus
Table 4.20 shows that content of easily digestive phosphorus in
vegetation cover types studied is relatively high and tends to increase
gradually through the stages of the succession process. That in the
topsoil layer of the grass vegetation cover contains the most content of
easily digestive phosphorus (4.20mg/100g) and then that of the low and

2+
exchange of soil under vegetation cover types in
the studied area tends to reduce according to the depth of the soil layers
and increase when the level of vegetation cover increases. In soil of grass
vegetation cover, there is a low content of Ca
2+
exchange (5.61 mg/
100g) and the highest content of Ca
2+
exchange in soil of secondary
forests (11.36 mg/100g).
* Content of Mg
2+
exchange
The content of Mg
2+
exchange in soil of vegetation cover types has
similar rules to that of the content of Ca
2+
exchange. It is the lowest content
of Mg
2+
exchange in the grass vegetation (3.27 mg / 100g) and the highest
content of Mg
2+
exchange in the secondary forest (4.42 mg / 100g).
4.2.11. The change of soil microorganisms in the vegetation cover types
4.2.11.1. The change in the density of soil microorganisms in the
vegetation cover types
To see the change in density of the soil microorganism groups

3
1.7 x 10
3
2.7 x 10
7

2.7 x 10
5
1.2 x 10
4

1 GV
Hill base 2.2 x 10
6
2.9 x 10
3
2.3 x 10
4
3.8 x 10
7

3.1 x 10
5
2.2 x 10
5

Hillside 5.9 x 10
5
2.8 x 10
3

4
3.8 x 10
8

2.4 x 10
6
3.1 x 10
5

3 HSV
Hill base 5.4 x 10
7
5.2 x 10
4
4.7 x 10
4
5.1 x 10
8

3.4 x 10
6
4.2 x 10
5

Hillside 7.3 x 10
7
5.3 x 10
4
4.6 x 10
5

Location

1 2 3 4 1 2 3 4
Hillside 1.7 x 10
3

1.6 x 10
4

1.4 x 10
3

1.8 x 10
3

1.6 x 10
4

1.4 x 10
5

1.8 x 10
4

1.7 x 10
4

1 GV
Hill base 2.1 x 10
3

1.9 x 10
3

2.1 x 10
5

2.3 x 10
6

1.7 x 10
4
2.1 x 10
4

2 LSV
Hill base 3.3 x 10
4

2.4 x 10
5

2.3 x 10
3
2.5 x 10
4

2.8 x 10
5

4.6 x 10


3 HSV
Hill base 5.6 x 10
4

2.7 x 10
6

2.8 x 10
3

3.1 x 10
4

3.6 x 10
5

5.8 x 10
8

4.7 x 10
4
4.1 x 10
5

Hillside 4.8 x 10
5

4.4 x 10
7

4
4.2 x 10
6

7.4 x 10
8

6.8 x 10
4

6.3 x 10
5

Note: 1. Microor. of phosphate resolution; 2. Microor. of cellulose resolution; 3. Microor.of nitrogen fixation; 4. Microor.
creating mucous membranes

17

From the results in Table 4.21, it can take the following
observations:
There are 3 important groups of microorganisms in soil under 4
vegetation cover types. They are soil bacteria, actinomycetes and fungi.
The density of the soil microbial groups increases with the recovery
process of vegetation covers. It is the lowest density of soil microorganisms in
the grass vegetation cover. The density of soil microorganisms in the low
and high shrub vegetation covers increases. It is the highest density of
soil microorganisms in the secondary forest. At the same time, the
density of soil microorganisms in hillsides are always lower than that in
foothills. This can be explained reason of the topsoil layer carrying
microorganisms washouted. On the other hand, moisture and organic

After 2 years of research, density of soil microorganisms in
locations of hillside and foothills of vegetation cover types. We see that
there is an increase in the density of the soil microorganism groups. The
increase is in accordance with the laws of nature. This is a typical
example. The density of microorganism in the hillsides and foothills
(April 2011) ranged from 1.6x10
5
to 9x10
8
, depending on the sampling
location. However, after 2 years (April 2013), the density of
microorganism has increased from 2.7x10
7
to 9.6 x10
9
, the density of
other microorganism groups also increases similarly.
4.2.11.2. Composition of groups of soil microorgarnism in forest soil in
Vi Xuyen district, Ha Giang province.
The results of analysis of soil samples in vegetation cover types in
Table 4.23 shows that the composition of soil microorganism groups
includes namely:

18

+ The group of bacteria includes 5 varieties such as Pseudomonas,
Agrobacterium, Bacillus, Azotobacter, Nitrobacter.
+ The group of antinobacteria has only Streptomyces.
+ The group of microfungus includes 4 varieties of filamentous
fungus such as Aspergillus, Mucor, Penicillium, Rhizopus and two

Microorganisms of
phosphate resolution
Bacillus ++ +++ ++++ ++++
Bacillus ++ +++ ++++ ++++
Aspergillus +++ +++ ++++ ++++
Mucor - + ++ +++
Microorganisms of
cellulose resolution
Penicillium +++ +++ ++++ ++++
Berjerinckia + + ++ +++
Microor.of nitrogen
fixation
Azotobacter ++ ++ +++ +++
Microor. creating
mucous membranes
Lipomyces - ++ ++ ++

Notes: ++++: Very plenty; +++: plenty; ++: medium; +: few; -: None 19

4.2.12
. Changes on components, quantity and distribution of soil animals

in the vegetation cover types.
4.2.12.1. Changes on components, quantity and distribution of species
earthworms
Table 4.24: Components of species and abundance of earthworms
in the vegetation cover types

12.50

13.20Fam. MEGASCOLECIDAE
(part Rosa, 1891) 2 Pheretima adexilis Thai, 1984 14.29

3.17

3 Ph. digna Chen, 1946 9.52

3.17

8.69


1.94

6 Ph. exilisaria exlisaria Thai, 1984 19.52

2.53

25.47

5.97
7 Ph. hiepcatana Do et Tran, 1994 3.22

1.21 8 Ph. infantiloides Chen, 1938 14.29

1.585.64

20.38

6.25

17.25

12
Ph. manicata manicata
Chen, 1946 4.76

47.53
4.35

1.76

9.38

7.76

13 Ph. Neoexilis Thai et Samphon, 1988 4.76



16 Ph. socsonensis Thai, 1984
3.13

0.6

17 Ph. vuongmontis Thai, 1984 3.34

7.12 18 Ph. wui Chen, 1935 4.76

2.35



128Total biomass (g)

12.6212.6248.6761.9

Density in average (con/m
2
)
16.8016.8023.6025.60


of soil in secondary forest, high shrub vegetation, low shrub vegetation
and grass vegetation are 25.60 earthworms per m
2
and 12.38g/m
2
; 23.60
earthworms per m
2
and 9.73g/m
2
, 18.40 earthworms per m
2
and 4.92
g/m
2
, 16.80 earthworms per m
2
and 2.52g/m
2
respectively.
Thus, we can see that the humus content in the topsoil layer (0-10
cm) affects the distribution of earthworms. Secondary forests have high
coverage, the combination of large species composition. An amount of
deciduous branches and leaves falling back to soil is higher. Therefore,
there is the highest humus content (4.86%), from which, it is the most
species composition and earthworm quantity.
4.2.12.2. Changes on components, quantity of other Mesofauna groups
under vegetation cover types
Table 4.25: Abundance of other Mesofauna groups


3.02 19.05

4.40
5 Gryllidae 20.03

2.99 10.95

3.44 5.00 0.15
6 Homoptera 24.93

1.76
7 Isoptera 23.81

7.09
8 Isopoda 13.39

10.73

14.29

11.49

20.01

5.34
9 Polydesmida

4.76 5.06
10 Hirudinidae 9.52 5.07


17.00

28.00

40.00Biomass in aver.
(g/m
2
)

0.27

0.51

0.795.47

Note: n%: abundance on quantity; p%: Abundance on biomass

Table 4.25 shows that:
- In term of species component, it found 12 other Mesofauna groups
in the study area. The highest number of Mesofauna group in high shrub

21


secondary forests are the most abundant either the average quantity of
mesofauna per m
2
or average biomass per m
2
(g) and the lowest in the
grass vegetation.
4.3. Evaluation of ability and proposal of some solutions to recover
natural forests in Vi Xuyen district, Ha Giang province
4.3.1.
Assessment of ability and proposal of some solutions to recover
natural forests in Vi Xuyen district, Ha Giang province
- The forestry industry of Vi Xuyen district always receives the
attention and close guidance of leaders of Ha Giang province.
- In Vi Xuyen district, there are many programs and projects supported
by the central government to protect and develop forest resources.
- Natural conditions are suitable for many kinds of tropical,
subtropical and temperate plants.
- Density of regenerated trees ranges from 3,054 trees per ha to
5612 trees per ha. The quality of regenerated trees is assurance of
requirements for forest restoration. The rate of good regenerated trees
gains from 63.2% to 70.3%. The rate of regenerated trees from seeds
reaches from 36.6% to 65.3%.
- The study area is located close to Tay Con Linh Natural Reserve,
which is an important sowing source.
- Ethnic minority people in Vi Xuyen district are hardworking
people and have practices and experiences of agricultural and forestry
production on sloping land.
From the above foundations, it may allow to assess that ability of
natural forest to recover in Vi Xuyen district is to promise.

- The open forest formation, trees are usually evergreen and
broadleaves in lowland and low mountains. It is deciduous broad-leaved
in lowland and low mountains.
- Sub-formation of shrub trees has scattered timber trees belonging
to shrub vegetation and usually green on dry soil.
- Some drought-tolerant grass formation belong to the group of the high
and medium high rice and 10-40% of it area is covered by timber trees.
* Criteria of afforestation zoning to recover natural forest
- Regenerated trees have to reach the goal with 300 trees per ha
and 50 cm in high.
- Foots of maternal trees must be capable of regeneration of shoots,
there are at least 150 roots of tree per ha and distributed relatively uniform.
- There are maternal trees sowing in place over 25 trees per ha,
distributed relatively uniform or to have nearby sources sowing.
* Some mainly technical measures applied to forest enough regenerated
trees (≥ 500 target trees per ha)
- Cutting vines, shrubs, fresh vegetation.
- The places with high-density of regenerated trees is conducted to
prune and intercrop in less trees.
- Modifying foots of sprouts: it depends on each tree species to
spare foots of sprouts with appropriate height.
- Trimming sprouts: Bad sprouts trimmed and let 2-3 buds of good
develop.

23

CONCLUSIONS AND RECOMMENDATIONS

Conclusion
1. According to UNESCO classification (1973), the vegetation covers in

mainly (bacteria, antinomycetes and fungi), as well as microorganisms
with resolution of compounds of insoluble phosphates, microorganisms of
cellulose resolution, nitrogen-fixing bacteria, microorganism
creating mucus membranches are also to increase in proportional
to the rehabilitation period.