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 p
Trang 1THAI NGUYEN UNIVERSITY
ABSTRACT OF PH.D DISSERTATION IN BIOLOGY
Thai Nguyen – 2014
Trang 2Thai Nguyen University
Scientific supervisors:
1 Assoc Prof Dr Le Ngoc Cong
2 Prof Dr Sci Tran Dinh Ly
Opponent 1: Opponent 2: Opponent 3:
The dissertation can be found at:
- The national library
- Leaning Resource Center of Thai Nguyen University
- The Library at University of Education of Thai Nguyen University
Trang 3FOREWORDS
1 Reason for choosing the study
In the 21st 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 17thAugust 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 proposals of forest rehabilitation measures
3 The research scope
- In term of plants and soil environment, broad-leaved vegetation
cover types on soil hills, higher vascular flora and soil environment under the vegetation cover types are studied
- In term of causes of forest degradation, it focuses on study activities
caused forest degradation
- The studied selected site has similar characteristics such as topography, climate, exposed direction, parent rock, impacts of human, etc
- The dissertation is only to study the vegetation cover types that trends of upward succession of natural forest recovery
- Contains no climate research plant populations due to time and
- The dissertation does not study the climate of plant populations due to time and limitations of equipments
Trang 44 The scientific meaning and practice of the dissertation
4.1 In term of theory,
With the scientific data, the regenerated law and upward succession of
natural forest recovery in Vi Xuyen district have shed light on
It contributes to clarify the relationship between vegetation cover with soil environmental factors in the recovery process of natural forests
5 Novel ccontribution of the dissertation
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
Trang 5* The studies related to regeneration, succession and forest regeneration
There are many research papers about the recovery process of natural forest or the regeneration promoted process and succession process of forest vegetations Authors study process on regeneration, forest regeneration with multiple objects of different vegetations (secondary forest, shrub vegetation, grass vegetation) with methods abundant and suitable to each subject
* The studies the interaction between vegetation and soil
In the world and in Vietnam, there are many scientific studies works on the relationship between vegetation and soil environment Authors’ results of studies have confirmed that effects of the land reclamation vegetation are very significant
Chapter 2 SUBJECTS, CONTENTS AND METHODS OF STUDY 2.1 Subjects of the study
The vegetation cover types of natural recovery in Vi Xuyen district, Ha Giang province include: grass, low shrubs, high shrubs and secondary forests
3 It is to evaluate possibility and propose some solutions to restore
of natural forests in Vi Xuyen district, Ha Giang province
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
Trang 6In 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
physical and chemical properties and microorganisms and sampling of soil animals
2.4.2.3 Methods of analysis and data processing
* Analysis of plant samples: Determination scientific names, local names
of the plant species
* Analysis of soil samples
Description of soil profile under the method Le Van Khoa et al, 1998 The analysis of physical and chemical properties and microorganisms and soil animals at Institute of Chemistry, Institute of Biotechnology, Institute of Ecology and Biological Resources (Vietnam Academy of Science and Technology)
The analytical results are processed by biostatistical methods of Microsoft Excel software of computer
Chapter 3 NATURAL AND SCIO-ECONOMIC CONDITIONS
IN THE STUDY SITE 3.1 Natural conditions
Vi Xuyen district is the low mountainous district of Ha Giang
province with a forcefully divided and complex terrain Its height above
mean sea level is 500 meters Therefore, system of rivers and streams in the district is rather dense However, they are mostly small streams with large slopes There is only Lo River that is the largest river
Vi Xuyen district’s climate is affected by climate of the Northeast region It is due to be located deeply inland; entire district is less affected by rainstorms in summer and Northeast monsoon than the Northern Delta area
Trang 73.2 Scio-economic conditions
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 km2 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
Protective forests (ha)
Special use forest (ha) Total (ha)
1 Land with forests 51,869.96 25,268.40 24,933.70 102,072.06
- Natural forest 39,255.26 23,066.50 22,701.10 85,022.86
- Planted forests 12,614.70 2,196.70 2,201.90 17,043.70
2 Land without forests 13,838.60 2,419.80 360.90 16,619.30
(Source: Results of planning review of forest types in Vi Xuyen district, 2012)
The area of forest land of Vi Xuyen district is about 118,691.36 ha and accounts for 79.2% of natural land area Of which, forest land is 102.072,06 ha and accounts for about 86% of forest land area and accounts for 68% of total natural land area; area without forest land proportion is less than that of total area of forest land (about 14%) A large forest area is
a potential for developing forest economics (Table 4.1)
4.1.2 Current status of vegetation covers in Vi Xuyen district, Ha Giang province
4.1.2.1 Vegetation cover types in Vi Xuyen district, Ha Giang province
According to the International Classification of Vegetation (UNESCO 1973), in Vi Xuyen district there are following vegetation cover types: closed forests, open forests, shrubs and grass vegetation covers
Trang 84.1.2.2 Characteristics the flora in Vi Xuyen district, Ha Giang province
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, 30o 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, 30o slope and 70-80% of general coverage The height of grass types is below 0.8m
4.2.2 The change of the plant composition in types of vegetation covers
Table 4.10 Quantity of species, genera and families in vegetation
Trang 9vegetation and the lowest abundant grass vegetation (209 species belonging to166genera and 65families)
4.2.3 The change of quantity of tree species in vegetation cover types
Table 4.11: The change on quantity of tree species/standard plot
in vegetation cover types
Statistical criteria Grass
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
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
The table 4.13 shows that the density of regenerated plants increases rapidly in the stage of high shrub vegetation cover and secondary forests
Trang 10(the higest density in secondary forest is 5612 tree per ha) The reason is that in these two vegetation types, there is plentiful plant composition, a plenty of plants providing varieties, soil in high moisture, seeds easy to germinate and grow So, quantity of regenerated plants is more numerous
Table 4.13: Density, quality and origin of regenerated plants
in vegetation cover types
4.2.4.2 Quality of regenerated plants
Table 4.13 shows that rates of regenerated plants with good quality, average quality and bad quality are from 63.2% to 70.3%, from 18.2% to 28.4% and from 11.5% to 19.6%, respectively This is
necessary and convenient condition for faster recovered vegetation
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
4.2.5.1 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
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
Trang 11Figure 4.4: Distribution of timber trees under the high level in the
vegetation cover types
The data of Table 4.14 and Figure 4.4 shows that plant composition of grass vegetation cover is mostly herbal plants, small shrub and timber trees in few However, at the low shrub vegetation, it appears some light demanding pioneer species that grows rapidly Then the light demanding species are prevails and rapid development at high shrub vegetation Finally, at secondary forest, light demanding pioneer trees are replaced
by a combination of woody trees those are high, tall, slow-growing and perennial
Figure 4.4: The distribution of high level of timber trees of secondary forest has one peak form with a distributed line shifting to the right side
4.2.5.2 The rule growing diameter
Table 4.15: The distribution of diameter level (D 1,3 ) of timber trees of
vegetation cover types (%)
Vegetation cover types Diameter level (cm)
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
Trang 12Figure 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 shifting to the right side
4.2.6 The change in the growth rate of the main timber tree species
4.2.6.1 The change in height of the main timber tree species
Table 4.16: Growth rate of height of some main tree species
Duration of fieldwork (month/year) Ord Names of tree species
April 2010 Apr 2011 Apr 2012
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
Trang 13The data in Table 4.16 shows that the growth of the average height annually is 0.4 - 0.6m Of which, the fastest growth is Styrax tonkinensis (0.6m average annual growth), then Peltophorum tonkinense (0.5m per year), Canarium album and Trevesia palmata (0.45m per year) and the lowest growth such as Castanopsis armata and Actinodaphne cochinchinensis (0.4 m per year)
4.2.6.2 The change in diameter of the main timber tree species
Table 4.17: Growth rate in diameter of the main timber tree species
Duration of fieldwork (month/year)
Notes D: Diameter in average (cm); d: the growth rate of diameter (m per year)
Total number trees per species measured diameter is n = 30 trees
The results in Table 4.17 shows that at the secondary forest, some major timber tree species have from 9.1 cm to 20 cm in diameter and the growth rate is low diameters (ranging 0.3 cm - 0.6 cm per year ) Of them, Styrax tonkinensis is the fastest growing tree species Therefore, their diameters are usually larger than these other plants (20 cm) and Canarium album that is the slowest growing tree species (0.3 cm per year in average)
4.2.7 The change of characteristics of soil profiles in the vegetation cover types
- Of all four types of vegetation covers studied, soil profiles consist of 3 layers A, B and C In the forest restoration process, the thickness of the soil layers (A + B) has increased over the successional stages: the thicknesses
of soil layer in the grass vegetation cover, the low shrub vegetation, the high shrub vegetation and the secondary forest are 60 cm, 68 cm, 72 cm and 75 cm respectively The secondary forest has the thickest soil layer