MINISTRY OF EDUCATION MINISTRY OF AGRICULTURE AND TRAINING AND RURAL DEVELOPMEN VIETNAM NATIONAL UNIVERSITY OF FORESTRY SING SOUPANYA SOME SCIENTIFIC BASES FOR REHABILITATION OF POST FOREST FIRE IN NA[.]
MINISTRY OF EDUCATION MINISTRY OF AGRICULTURE AND TRAINING AND RURAL DEVELOPMEN VIETNAM NATIONAL UNIVERSITY OF FORESTRY SING SOUPANYA SOME SCIENTIFIC BASES FOR REHABILITATION OF POST FOREST FIRE IN NAMNGUM PROTECTION AREA, LAO’S PEOPLE DEMOCRATIC REPUBLIC MAJOR: FOREST RESOURCE MANAGEMENT CODE No: 62 02 11 SUMMARY OF PhD DISSERTATION HANOI, 2022 This scientific work has been accomplished at Vietnam National University of Forestry Supervisor: Prof.Dr Bui Xuan Dung Reviewer 1: ………………………………………… Reviewer 2: ………………………………………… Reviewer 3: ………………………………………… This Doctoral dissertation will be defended in front of the University Doctoral Committee at Vietnam National University of Forestry, Hanoi, Vietnam at …… This dissertation can be found at: - National Library of Viet Nam - Library of Vietnam National University of Forestry PREFACE The Urgency of dissertation topic Nam Ngum forest protection s had established Year 2005, this area located at the importance point to project forest, trees, water resource, for Nam Ngum and Nam Ngum Hydro Power Plants The protection forest area had 289.635 The kind of trees mixed witbeen laCiObe leafs and slimply leafs there are natural seperating on the geography and classification diferance class The Protection Forests areas at Nam Ngum there are many domestic and foreign scientists to the reseach and evaluated this area is a center of many biologies of Loas and this area there is many kinds of wildlifes and Organisms are Red book of Laos and Red list of Threatened Species (IUCN, 2021) Moreever, the last many years the wildlifes and Organisms are destroyed from many reasons, out of this, these reasons is forest was fired is mainly drive, cover 80% for forest areas had been destroyed and attached The forest areas had gone 2.000 by fired, Especaly forest areas was fired in year 2016 to be effected 230ha gone so there effective to many natural resource, properties, environmental, biologies eco system, Bio-Eco Tourisms The forest had been fired many hectares mention above, the management, post fire rehabilitation at Nan Ngum Protection Forest Areas This area are many offical and organizes and scientists and poeple who living in that area only This mention just listing areas had been fired, economic effective, and to figthing the forest to be fired No one eld and other research should be mention on this problem as technical rehabilitation methode ans eco system delivers after forest had fired in Nam Ngum area is dificult for theory methodes and practicing to protect forest from fired Theory should be resolve problem as (i) How to repit delives eco system and rehabilitation and fit for weather and land condition, (ii) Technical methods and effective to forest areas be fired The practicing method should be (i) Can not specific of forest characters and to be able delivers of forest ans ecology (ii) Can not seperate the forest kinds (iii) Can not update the information of forest and bio-eco delivers after forest fired Stemming from the above reasons, I carried out the dissertation "Some scientific bases for rehabilitation of post forest fire in namngum protection area, Lao’s People Democratic Republic” The dissertation aims to provide a scientific and practical basis to rehabilitation forest areas after fire in the most effective and appropriate way in Nam Ngum forest protection as well as other forests of Lao PDR with natural conditions naturally similar Objectives 2.1 General objective: To identify some characteristics of post fire fluctuation in forest flora and forest land over time as a scientific basis for assessing post fire forest rehabilitation in Nam Ngung protection forest, Lao PDR 2.2 Specific objectives - To identify basic characteristics and fluctuation in structural indicators of forests and forest land on mixed broadleaf and coniferous forests post fire in Nam Ngum forest protection - To identify and propose some solutions to improve the efficiency of post fire forest rehabilitation, applied to mixed broadleaf and coniferous forests in Nam Ngum forest protection, Lao PDR Research object The object of the study is a mixed forest flora of broadleaf and coniferous trees and some forest soil properties after a major fire in 2016 in the Nam Ngum forest protection area, Lao PDR New contributions of the dissertation - Assessing abilities post forest fire rehabilitation of the mixed forest flora of broadleaf and coniferous trees and forest soil in Nam Ngum forest protection , Lao PDR - Identify and propose a solution to post forest fire rehabilitation of the flora of mixed broadleaf and coniferous forests and forest land in Nam Ngum forest protection , Lao PDR Scientific and practical significance of the dissertation 5.1 Scientific significance of the dissertation Assessing and supplementing the current situation of fluctuation by burn severity and time after fire of mixed broadleaf and coniferous forests in Nam Ngum forest protection , Lao PDR, as a basis for proposed solutions for post forest fire rehabilitation 5.2 Practical significance of the dissertation Identify and build specific plans and technical solutions for post forest fire rehabilitation on each burn severity for mixed broadleaf and coniferous forests in Nam Ngum forest protection , Lao PDR Limits of the dissertation 6.1 Limitation of research content - The dissertation only studies some features of the structure of tall trees, layers of regenerated trees, shrubs and fresh carpets, physicochemical characteristics of forest soil after fire on non-impact areas and areas with technical measures silviculture 6.2 Research area limitation The research site of the dissertation is: - Area of forest plant communities after fire in Nam Ngum forest protection , Lao PDR; 6.3 Research time limit About time: The dissertation is carried out during the period from January 2017 to 2021 Dissertation structure In addition to the introduction and conclusions, references, appendices, the dissertation is structured into chapters A total of 138 pages of dissertation, of which: Introduction - pages; Chapter 1: Literature review – 19 pages; Chapter 2: Contents, research methodologies and Natural conditions of the Research area – 28 pages; Chapter 3: Results and discussion - 73 pages; Conclusion, limitation, suggestion pages; References 10 pages In this dissertation, there are 18 tables, 32 figures Chapter LITERATURE REVIEW The dissertation has consulted and summarized about mains related issues in the world, in Vietnam and in Laos: (1) Forest fire concept and level; (2) Overview of research on natural post forest fire regeneration; (3) Overview of research on post forest fire rehabilitation by silvicultural techniques and the existence of research on post forest fire rehabilitation so that to determining the research problem for the dissertation topic About the concept and level of forest fire An overview of the research problem has helped to have a correct and comprehensive understanding of forest fires and forest fire classification Overview of research on natural post forest fire regeneration An overview of the research problem has helped to have a correct and comprehensive awareness of natural post forest fire regeneration Accordingly, regeneration and rehabilitation of natural forests after a fire is not only the rehabilitation of burned forest plots and forests to become forests, but also the transformation of a certain forest block or burned forest into a better fores, has higher stand stock, with the best possible quality, and serves both hedge and trading purposes Overview of research on post forest fire rehabilitation by technical measures The overview of the research problem has helped to identify the impact engineering solutions and some achievements on forest regeneration and rehabilitation after grandchildren Notable achievements in: - Achievements in the study of classification of impacts on forest rehabilitation after fire; - Achievements in research and application of technical solutions for forest rehabilitation after fire About the existence of research on post forest fire rehabilitation Although many achievements have been achieved, the research on forest rehabilitation after fire still has some shortcomings, which can be summarized as a few main problems: - The structure, regeneration as well as the ability to recover after fire have not been determined for specific objects, including post-fire forest in Nam Ngum forest protection - Affected objects have not been classified yet, so it is not possible to propose appropriate solutions to shorten the time for forest rehabilitation for each specific object, including post-fire forest in Nam Ngum forest protection Determining the research problem for the dissertation topic The research forest object of the dissertation is the post forest fire plant community, so the dissertation chooses the direction to rehabilitation the forest from the forest after the fire by means of impact measures to become a better post forest fire Because from the post forest fire to forest with better rehabilitation, the scientific basis for post forest fire rehabilitation in the dissertation is the characteristics of the existing forest; variation of these characteristics over space (OTC) and over time (by survey year) The application of improved methods of dividing the affected objects as a basis for proposing technical solutions is very necessary to study Chapter CONTENTS, RESEARCH METHODOLOGIES AND NATURAL CONDITIONS OF THE RESEARCH AREA 2.1 Research contents 2.1.1 Research on forest status and forest fires in the study area - Area, classification of forest types and some typical criteria on the main forest types - Number of forest fires, serious fires and forest fire severity (burn severity) of serious forest fired in 2016 2.1.2 Research on fluctuation in indicators reflecting forest structure and forest land over time after fire - Fluctuation a number of indicators of forest soil in the unburnt forest area (control) and burned forest area according to burned levels - Fluctuation some structural indicators of unburnt areas and burned forest areas according to burned levels 2.1.3 Evaluation of results treatment of technical measures by post forest fire rehabilitation - Evaluation of fluctuation in some forest soil loss on technical measures to post forest fires rehabilitation by Nurtural and promoting regeneration; Salvage logging, nurturing and Native trees sowing seeds: - Evaluation of fluctuation in some criteria reflecting forest structure on technical measures to post forest fires rehabilitation by Nurtural and promoting regeneration; Salvage logging, nurturing and native trees sowing seeds: 2.1.4 Research and propose some management measures and silvicultural techniques to post forest fires rehabilitation - Technical silvicultural measures: Select group of species for the purpose of post forest fires rehabilitation; Classification of forest burn severityapplying silvicultural techniques to post forest fires rehabilitation - Measures for management and protection 2.2 Research Methods 2.2.1 Methodology In order to have a scientific basis for the study of structural fluctuations, regeneration and some properties of forest soil after fire, it is necessary to establish the study area as: Non burned area (control area), burned area no application measures and the burned area has silvicultural application Next, the plots (OTC) will be established for each established area to evaluate the characteristics of post forest fire fluctuation Based on the characteristics of fluctuation after the fire as a basis to propose silvicultural measures affecting post forest fire rehabilitation In order to ensure the division of forest objects after fire into groups that are homogenous in terms of the above criteria to apply technical solutions, the dissertation will: - Paying attention to spatial factors: Research OTCs have different characteristics of investigation and based on these factors to establish investigation OTC - Paying attention to the time factor, specifically, the dissertation has measured and counted data times, years apart Data on the status of the forest and its fluctuations are used to classify the affected objects Applying the methodology of the dissertation, a diagram of the research approach of the dissertation is shown below (Figure 2.1) Step Step Step Step Assess the Evaluation of Classification of Proposing current status structural fluctuation, objects according to measures to apply of forests, regeneration and restoration post forest fire forest fires, some properties of characteristics rehabilitation causes of forest soil after fire (structure of tree according to the forest fires in according to layer, regeneration, characteristics of the study area identified objects forest land) the divided objects Figure 2.1 Logical framework of research process 2.2.2 Research Methods 2.2.2.1 Methods of investigation and assessment of forest status and forest fires in the study area (i) Determine the type of forest / forest status distributed in the area: Classification of forest status/ forest type is determined according to the classification system prescribed in the Lao Forestry Law 2019 (Laos National Assembly, 2018) (ii) Methods of characterization of forest status In order to fully collect the characteristics of the forest structure and status, the dissertation sets up survey routes The survey route is a typical route (typically according to the type of forest), representative of the forest types, the length of the route is unknown (according to the length of the forest type) (iii) Methods of investigating the number of forest fires, the causes of forest burn - Information on the situation of forest fires in the study area is collected through annual statistics of the Xieng Khoang Forest Protection Department, the Forest Protection Department, the Protection Forest Management Board, from 2010 to present (iv) Method of assessing forest fire severity (burn severity) of serious forest fired in 2016 - Investigate and evaluate the composite fire index (CBI) Evaluation of the forest fire severity at the fire scene was carried out according to the method of Key and Benson proposed in 2003 (Key and Benson, 2003) According to Key and Benson, the fores fire severty is divided into levels, including: (1) Low burn: CBI ≤ 20%; (2) Moderate burn: 20% < CBI ≤ 80%; (3) High burn: CBI > 80% The method is described in Table 2.1 Table 2.1 Evaluation and description of the forest fire severity of Key and Benson CBI fire index by fire class (%) No Strata rates factors Low Moderate Hight Substrate A Dry carpet, fallen leaves (sample plot, area 1m2) Dry carpet, fallen leaves 0,1< CBI ≤ 20 20< CBI ≤ 80 80< CBI ≤ 100 Substrate B Shrubs, fresh carpets and regenerated trees ≤ 1m (ODB, 25m2) tree, TT, TS 0,1< CBI ≤ 20 20< CBI ≤ 80 80< CBI ≤ 100 Substrate C Shrubs, trees, vines, etc with a height of 1< H ≤ 5m (ODB, 25m2) CB, CG, DL 0,1< CBI ≤ 20 20< CBI ≤ 80 80< CBI ≤ 100 Substrate D The trees in the middle canopy layer (OTC, 2000m2) Wood tree 0,1< CBI ≤ 20 20< CBI ≤ 80 80< CBI ≤ 100 Substrate E Trees beyond the canopy Trees over the canopy 0,1< CBI ≤ 20 20< CBI ≤ 80 80< CBI ≤ 100 Low floor = 1+2+3 = A + B + C High floor = 4+5 = D +E Fire Index CBI = +2 +3 +4 +5 = A + B + C + D + E (Source: Key and Benson, 2003) 2.2.2.2 The method of studying fluctuation in indicators reflecting forest structure and forest land above the level of fire has no impact and has an impact on experimental measures to post fire rehabilitation (i) Set up plots sites, measure land in the field and measure research criterial The dissertation conducted Nurtural areas, arranged 21 typical plots, semi-permanent (typically according to burn severity and semi-permanent in years), including: (1) Area 1: above burn severity, no application on silvicultural restoration techniques; (2) Area 2: over burn severitywith silvicultural application and (3) Area 3: on the control area to measure, take samples and evaluate fluctuation in research indicators in years The subdivision diagram and arrangement of 21 plots, soil profiles for the collection and measurement of field research indicators are shown in Figure 2.3 Figure 2.3 Geographic location, plots and land profile distribution by burn severity (ii) Soil Sampling and Collection of Research Indicators on plots a Soil sample collections To analyze some characteristics and fluctuation in physical and chemical properties of soil on non-impact and active burn severity, in the control area over time, soil samples were taken on profiles arranged in different areas OTC research b Collect data to calculate fluctuation in some structural indicators - Attach the tree number Plot (OTC) to measure the study criteria of trees layerin the control area and on different levels of fire ODB was established to measure the study data on the layers of regenerated trees, shrubs, and fresh carpets corresponding to the control and post-fire zones on the respective burn severity Attach the number of trees layerin OTC, regeneration trees in ODB for measurement The trees layerin the OTC and the regenerated tree in the ODB are divided into prizes in the direction from North - South (1 prize is equal to ¼ of the area of OCT, ODB), running along the OTC length Tree numbers are assigned according to natural numbers, from to n -1 for each OTC, ODB The first number is attached at the tree with the first distribution in the East - West angle, the tree number is consecutively attached in the same direction to a direct projection in the main South direction By attaching such tree numbers, the re-investigation process in the following years: 2018, 2019, 2020 and 2021 is facilitated, with no deviation in tree data and OTC and OBD locations next measurement year - Collect research data (1) Tree layer Year 2017: (i) In the OTC, all trees that have been labeled are identified with species names according to common names in Laos, Vietnam and scientific names.(ii) Measure and count all numbered trees: (1) High-rise trees were measured with the number of trees with diameter at breat height (D1.3) ≥ 6cm Measurements include: Diameter at breat height (D1.3); canopy diameter (Dt); Tall height (Hvn); Height under branches (Hdc) Measuring instrument with laser altimeter (Nikon forestry Pro) and glass caliper - Evaluation of plant quality through morphological criteria at levels: (1) Quality tree (AB); (2) The tree is not qualified (C) The survey results are recorded according to the trees layerfloor survey form for each survey year (2) Regeneration layer (sapling and seedling) Year 2017: (i) In the ODB, all trees that have been attached and numbered are identified with the tree species name according to the common name of Laos, Vietnam and the scientific name.(ii) Regenerating plants include seedlings and seedlings with a diameter of D1.3 < cm Measurements: peak height measured by laser altimeter (Nikon forestry Pro) for seedlings and bymeter gauge for seedling 2018; 2019; 2020 and 2021 will re-measure all trees with the same brand, method and location as in 2017 - Assess the quality of regenerated plants through morphological criteria at levels: (1) Quality tree (AB); (2) The tree is not qualified (C) The survey results are recorded according to the form of the regeneration tree class survey form (3) Investigate shrubs and fresh carpets Shrubs and fresh carpets were surveyed on a 25m2 plot along with a survey of regenerated trees The number of times to survey and the time to survey the same class of regenerative trees On the ODBs, surveys on shrubs and fresh carpets were carried out according to the following criteria: Name of tree species, height, canopy diameter, species coverage and growth situation of shrubs on ODB The survey results are recorded in the survey form for shrubs and fresh carpets 2.2.2.3 Experimental arrangement for post forest fire rehabilitation by silvicultural techniques a Measures to post forest fire rehabilitation by nurtural and promoting natural regeneration on low burn area Contents of measures: In the low burn area, the dissertation established hectares to experiment with measures to post forest fire rehabilitation by Nurtural and promoting regeneration according to the Ministry of Agriculture's process of Nurtural and promoting regeneration Agriculture and Forestry promulgated in 2013 b Technical measures to post fire rehabilitation by salvage logging and nurturing on moderate burn Content: On the fire area with Moderate level, the dissertation established hectares to experiment with measures to post fire rehabilitationby cutting and nurturing All the dead trees, whole body burned, poor quality trees, trees not able to recover, branches, branches, fallen objects, shrubs were cut down (Nurture salvage logging) Exploiting method: conducting manual mining, cutting down each burned, dry tree, branch, etc Harvesting techniques were carried out according to the Manual Harvesting Process of the Ministry of Agriculture and Forestry in order to minimize adverse impacts on the remaining trees and the number of seeds accumulated in the topsoil All trees and branches cut down were transported out of the study area to create space and prevent the source of disease and damage to naturally regenerated trees after cutting and nurturing c Technical measures to post forest fire rehabilitation by direct native tree species sowing seeds on high burn area Content: In the area of high burn area, the dissertation established hectares for experiment with methods of direct sowing of native seeds including: 2-leaf pine (Pinus merkusii Jungh) and Schima wallichii (Schima wallichii) (DC.) Korth,) Method of sowing: Sowing evenly on the surface with an area of The process of sowing seeds is carried out according to the following step by step: 2.2.2.4 Research data processing The soil physical and chemical parameters of the samples were analyzed in the laboratory, the indicators reflecting the forest structure were processed and calculated using R, SPSS, Excel, ArcGis 10.1 and other specialized softwares other uses The order of analysis and processing is performed according to the steps below a Soil sample analysis method - Analysis of soil samples: The methods applied for analysis include: (i) Soil chemical properties include: (1) The pH H20 was determined according to TCLs 0932: 2013 standard (the Lao standard is similar to the Vietnamese standard (TCVN 7377: 2004); (2) humus content according to Triurin method; (3) Easy phosphorus content pepper (mg/100g soil) according to Triurin - Kononov method; (6) Easily digestible nitrogen content (mg/100g soil) according to TCLs 2231: 2011 standard (similar to Vietnam's 5255: 2009 standard (TCVN 5255): 2009)); (7) Easily digestible Potassium (mg/100g of soil) by flame photometric method; (8) Total phosphorus content by TCLs 4554:2015 test method (similar to standard TCVN 8940: 2011) and (9) Total nitrogen content by Kjeldahl method (ii) Physical properties: (1).Soil mechanical composition determined by Robinson suction method; (2) Porosity is determined through density and density of soil, according to the formula: X = (1-D/d)100 Where: D is the weight; d: is the weight of the land b Calculation of characteristics of forest structure - Calculate the cross-section G (m2/ha): 𝑖 𝜋 (𝑚2 ⁄ℎ𝑎) 𝐺 = ∑ 𝐷1.3 - Reserves M (m3/ha) (2.1) M = GHf (2.2) Where: D: Diameter at chest height M: reserve (m3/ha) G: Total cross-section of the stand (m2/ha) H: Average Lorey height of the stand (m) f: Figure (f = 0.5) (according to the convention of the number of trees in Laos) - Calculate important index (IV %) The important index of species (IV: Important Value) is calculated according to the method of Daniel Marmillod through criteria: percentage of density (N%) and percentage of cross section (G%) of a species according to the following formula: 𝑁 (%)+𝐺𝑖 (%) IVi % = 𝑖 (2.3) In there:N% is the ratio% the number of trees of the species compared to the total number of trees/ha G % is the ratio % cross-section of the species compared to the total crosssection/ha IV % is an important indicator of species/ha If IV % > %, species that are ecologically significant are included in the compositional formula If IV % < %, that species is not included in the nesting formula According to Thai Van Trung, the total IV% of 10 species ≥ 40% are the dominant species in the biome and this species is often used to name the biome - Determination of species richness Species richness is quantified through the formula s R = n (2.4) Where: - n: is the number of individuals of all species - s: is the number of species in the biome - Compare the occurrence of tree species between the trees layerlayer, the regenerative tree layer To compare the occurrence of tree species in the high tree layer and the regenerated tree layer, the dissertation uses the method of determining the similarity index SI (Index of Similarity or Sorensen's Index): The SI similarity coefficient is determined by the formula: SI = (2C/(A+B))*100 (2.5) Where: C: Number of species appearing in both groups A (high tree layer) and B (regenerative tree layer); A: Number of species of group A tall trees B: Number of species of group B regenerated trees B: Number of species of group B regenerated trees c Variation of growth quantities and high tree density 11 Chapter RESEARCH RESULTS AND DISCUSSION 3.1 Characteristics of the current status of forest and forest fires in the study area 3.1.1 Area, classification of forest types and some characteristics of stands in the main status of forest (i) Area and classification of forests in protection forests The ratio of the area of land resources and some types of forests distributed in the protection area is shown in Figure 3.1 LRTX TN- LRTX 15% 10% Grasslands; rocks, soil: 15% HGCLK - LR 60% Grasslands; rocks, soil: HGCLK - LR LRTX TN- LRTX Figure 3.1 Rate of forest status in Nam Ngum forest protection Acronyms in the figure: HGELST - LR: Area of mixed coniferous and broadleaf forests; LRTX: Area of eveCiObreen broad-leaved forest; TN -LRTX: Area of bamboo forest with eveCiObreen broadleaf trees and TC, rocks, soil: Area of grassland, rocky mountains and fallow bare land Protection forest with 217,195 of natural land, mixed forest of conifers and broadleaf trees with an area of 130,317 ha, accounting for 60%, eveCiObreen broadleaf forest with an area of 32,579.3 ha, accounting for 15%, forest mixed with bamboo and broadleaf trees with an area of 21,718 ha, accounting for 10% The remaining area consists of unused bare land, rocky mountains and grasslands (ii) Some structural characteristics on forest types in protection forests The survey results on a number of forest survey factors are summarized in Table 3.1 Table 3.1 Average indicators of some forest survey factors on forest types Quality (%) Hvn D1.3 Dt G Mbq No Forest type (m) (cm) (m) (m /ha) (m /ha) TB -T Bad Forest 12,83 18,71 6,35 27,925 179,522 85,76 14,24 HGLKLR (±2,88 (±2,89) (±1,74) (±5,20) (±12,89) (±12,42) (±4,45) 11,11 16,38 5,96 14,609 159,833 93,64 6,36 Forest LRTX (±1,67 (±2,25) (±1,84) (±5,55) (±12,57) (±11,77) (±3,56) HG bamboo 10,59 12,59 5,27 9,58 30,99 88,60 11,40 forest (only (±2,21 (±2,45) (±1,23) (±5,16) (±13,54) (±11,41) (±3,77) counting trees) Average (±SD)p 11,98 17,46 21,61 128,79 87,86 12,15 (±2,67) (±5,33) 6,06 (±1,04) (±5,23) (±12,11) (±11,62) (±3,49) 0,000 0,000 0,000 0,002 0,001 0,000 0,001 12 Acronyms in table 3.1: (HGLKLR: Mixed coniferous with broadleaf; LRTX: Broadleaf eveCiObreen: HG: mixed; G: Mean basal area ha-1 (m2/ha-1); M: Mean stand volume -1( m3/ha1 ) D1 3: Mean of diameter at breat height per year (cm/year -1); Hvn: Mean of height per year (m/year -1);∆G: Mean variation of basal area per year (m2/year -1ha) (± SD = standard error) The results in Table 3.1 above show that: (i) HGLKLR forest: the average volume of standing trees is 179.522 m3/ha-1 The taCiObet height is soaring (Hvn), reaching 12.83 m The average diameter at breat height of the stand (D1.3), reached 18.71 cm The total cross-sectional area is 27,925 m2/ha-1 The percentage of trees with Moderate to good quality was 85.76%, and the rate of trees with bad quality was 14.24% (ii) Greenwood forest: the volume of standing trees is 159.833 m3/ha-1 The indicator of soaring height (Hvn), reached 11.11 m The mean diameter at breat height (D1.3), reached 16.38 cm The total cross-sectional area is 14.60 m2/ha-1 Average reserve is 79.83 m3/ha-1 The percentage of trees with Moderate to good quality was 93.64%, and the rate of trees with bad quality was 6.36% (iii) HG bamboo forest The indicator of soaring height (Hvn), reached 10.59 m The mean diameter at breat height (D1.3), reached 12.59 cm The total cross-sectional area is 9.58 m2/ha-1 Average reserve is 30.99 m3/ha-1 (reservoir is only for trees) The rate of trees with Moderate to good quality reached 88.60%, trees with bad quality was 11.40% 3.1.2 Number of fires, fire severity, and fire severity index (burn severity) of fire severity a Number of fires and extent of damage caused by forest fires According to the statistics of the Xieng Khoang FPD, the situation of forest fires in the protection forest in recent years is listed in Table 3.2 Table 3.2 Area of forest burned in Nam Ngum forest protection (2010 - 2021) (Damage unit: ha) No Years Location/area Damaged area Phu Cut District 2,5 2011 Pak District 5,5 Kham District 13,5 2015 Pak District 3,5 Phu Cut District 5,5 Phu Cut District 5,0 2016 Pak District 230 Kham District 11,53 2019 Phu Cut District 6,0 Kham District 9,0 2020 Pak District 15,0 Phu Cut District 8,0 total 315,03 (Source: Xieng Khoang Forest Protection Department, 2010 - 2021) The statistics in Table 3.2 show that: During the period from 2010 to 2021, forest fires in protection forests in the districts have caused 315.03 of forest damage Forest fires occurred mainly in the state of mixed broadleaf and coniferous forest types (79.51%), followed by grasslands and shrubs (14.16%), eveCiObreen broadleaf forest types (6.15) %) and mixed bamboo forest types (0.18%) In particular, the laCiObest area of forest fires occurred on a laCiObe scale in 2016, with 230 hectares (accounting for over 75% of the forest fire area in 10 years) b Serious forest burn in 2016 13 - Area affected by burn severity The results of extracting the standardized fire index - NBI on the severe fire area, based on the strong correlation between the NBI index and the established CBI, the area by fire severity level is summarized in Table 3.4 and diagram of burning area (see Appendix 3.2) Table 3.4 Statistics of area by level of serious fire 2016 No Burn severity Area (ha) Fire Index (%) High burn 67,85 CBI > 80 Moderate burn 45,70 20 < CBI ≤ 80 Low burn 116,45 CBI ≤ 20 Total area burned and damaged 230,00 Where: CBI: The composite combustion index at the scene of a forest fire, calculated by the Key and Benson method, (2003) Calculation results and determination in actual fire, burned area 230ha Where, the low burn area is 116.45 hectares, accounting for 50.63%; the moderate burning area is 45.70ha, accounting for 19.87% and the high burning area is 67.85, accounting for 29.50% 3.1.3 Causes of forest fires According to statistics and interviews with people, the number of fires is mainly caused by burning for cultivation, accounting for 60%, the rate of common opinion is 50/70 respondents The remaining causes are fire spreading from other fields, careless use of fire and other causes The main causes of forest fires are listed in Table 3.5 Table 3.5 Statistics on the causes of forest fires Number of Ratio Number of cases No Reason Form handling forest fires % to find the culprit Burning fields for To administrative 16 farming sanctions Careless use of fire in To solve the the forest, on the edge problem of the forest Undefined reason 19 76 0 Total 25 100 (Source: Xieng Khouang Forest Protection Department, and trainees' calculation results, 2021) The above results show that the causes of forest fires are ouDaCuated agro-forestry practices, affecting forests and fire prevention and fighting; The conversion of land use purposes of Nam Ngum hydroelectric projects has reduced a part of the agricultural production area of the people, significantly reducing food production, putting great pressure on forests and forestry land in the protection forest Besides, most of the villages are located near the forest and along the forest edge, in the highlands, people's lives are still facing many difficulties, their lives mainly depend on forests; Due to frequent shifting cultivation and expansion of new areas, shifting cultivation is the direct cause of forest loss; The unmanaged swidden cultivation and burning of vegetation are the main causes of forest fires According to statistics and interviews with people, the number of fires is mainly caused by burning for cultivation, accounting for 60%, the rate of common opinion is 50/70 respondents The remaining causes are fire spreading from other fields, careless use of fire and other causes 3.2 Fluctuation in indicators reflecting fores structure and forest soil over time by post forest fire 3.2.1 Fluctuation in some indicators of post forest fire soil properties 3.2.1.1 Fluctuation in some chemical properties in forest soil after fire 14 (i) OCiObanic humus (OM) layer: The results of calculating the total humus content (OM) under the influence of levels of fire and control over time after fire are shown in Figure 3.3 Figure 3.3 Fluctuation of humus content by post fire years The results shown in Figure 3.2 show that: Forest fires affect the oCiObanic humus layer, and different levels of fire have different effects Forest fire has reduced the oCiObanic humus layer of the soil immediately after the fire and the humus content tends to increase gradually after the fire year, in 2021, compared to 2017, the humus content on burn severityhas increased significantly However, in the control area (without burning) the humus content was almost unfluctuation during the years of follow-up and research 3.2.1.2 Fluctuation in some post forest fire soil physical properties (i) Mechanical components: The results of analysis of the effects of forest fire on the change in the mechanical composition of forest soil after fire on different levels of fire are analyzed and summarized in Table 3.6 Table 3.6 Mechanical composition of soil under the action of forest fire Year 2017 Year 2021 Burn Grain Grade Ingredients (%) Grain Grade Ingredients (%) No severity 0,02 0,02 2,0 - 0,02 < 0,002 0,002 2,0 - 0,02 < 0,002 0,002 mm Control 14,23 46,23 39,54 14,55 46,23 39,22 Low 14,84 47,77 37,39 13,44 46,36 40,2 Moderate 16,56 45,93 37,51 14,75 44,54 40,71 High 12,34 48,65 39,01 11,89 47,68 40,43 The results of analysis of the mechanical composition of the soil under the impact of forest fire on different burn severity over time show that forest fire has an impact on the physical properties of the soil Under the impact of forest fire, in years, the percentage of sand grains (2.0 - 0.02 mm) has decreased significantly Forest fire significantly increased the percentage of limon (0.02 - 0.002 mm) on Low burn and High burn with 47.77 respectively; 48.65 compared to the unburnt limon ratio of 46.23% (ii) Soil porosity: The analysis results of soil porosity under the influence of burn severity and the fluctuation of forest soil porosity over time after fire are shown in Figure 3.8 Figure 3.8 Fluctuation of soil porosity by year across burn severity 15 The results shown in the figure show that: Forest fires have had a great influence on soil porosity, different levels of fire have different effects The impact of forest fires has reduced the porosity of the soil General assessment of fluctuation in some chemical and physical properties of forest soil after fire Research results show that: Forest fires have a very significant effect on the physicochemical properties of the soil The degree of influence is proportional to the level of fire - The pH indicator decreased, N% decreased sharply, after years of recovery, the increase was not equal to the control area Indicators of total phosphorus and total potassium increased sharply right after the fire This result partly has a positive effect on the recovery of trees layerand regeneration after fire because phosphorus and potassium have the effect of stimulating the root system to develop, increasing resistance to strong impacts such as after fire Forest fire affects and reduces porosity, after years of post-fire fluctuations, porosity is still lower than the control (lower than the pre-burn severity) This result partly has a negative effect on the recovery of the trees layerlayer and the regenerated tree layer after the fire because the porosity indicates the ability to absorb water, hold water, facilitate stimulation of the root system to develop, increase the resistance of the tree to water resistant to strong impact 3.2.2 Post fire fluctuation of some forest structure indicators 3.2.2.1 Tree layer by burn severity (i) Density The results of the investigation and calculation of the average density of trees layer/ha over time corresponding to each burn severity are shown in Figure 3.9 Figure 3.9 Change in average density/ha by post fire years The results in Figure 3.9 show that the average density/ha in the control area in 2021 reached 774 trees/ha-1 On burn severity, the density of burn severity is low, in 2017 it reached 692 trees/ha-1, by 2021 it will reach 706 trees/ha-1 At Moderate and high burn severity, the average density in 2021 will reach 442; 251 plants/summer iii) Fluctuation in the number and richness of species composition - Number of species: The fluctuation of the corresponding number of species over time on each burn severity is shown in Figure 3.11 Figure 3.11 Fluctuation in number of species by post fire years 16 The results in Figure 3.11 above show that, with different levels of fire, the number of species of trees layer fluctuation differently In the control area, in years, the number of trees layer species did not change and the laCiObest number of species was recorded, 44 species were recorded On different burn severity, the number of species decreases gradually as the burn severity increases, the number of trees layer species is recorded at least at high burn severity - The level of species richness The level of species richness on each burn severity and the variation of species richness over time after the fire are shown in Figure 3.12 Figure 3.12 Fluctuation in species richness over time across burn severity Similar to the number of species, the richness of species at different burn severity, the richness of species composition is different, the level of species richness decreases corresponding to each burn severity and is proportional to the number of species The number of species decreased gradually according to the burn severity, the species richness (R) also fluctuated accordingly: In the control area, R = 2.33, at low, moderate and high burn severity, species richness, respectively R= 2.01; 1.97; 1.65 (iv) Predominant species composition on burn severity + Control area Of the total 44 species of trees layerrecorded belonging to 24 plant families, including tree species: the family Fabaceae, there are species The family Pinaceae has species Bamboo pine family (Podocarpaceae), has species, etc Based on the species importance index (see Appendix 1), the tree species composition formula is established as follows: Composition formula (CTTT): 16,90PiMe + 9,55CiIn + 8,11DaEl +7,37ElSt + 58,06OTSP (3.4) Where: Where: PiMe: Pinus merkusii; CiIn: Cinnamomum iners; DaEl: Dacrydium elatum; ElSt: Elaeocarpus stipularis (E siamensis); and OTSP: Other species + Low burn severity Out of 39 species, species have important index IV ≥ 5% Thus, the forest burned with low burn severity has co-dominant species: the tree species composition formula is set up as follows:: CTTT: 15,40PiMe + 8,05ScWa + 6,61DaEl +5,89ElSt + 70,06OTSP (3.5) Where: PiMe: Pinus merkusii; ScWa: Schima wallichii Choisy; DaEl: Dacrydium elatum; ElSt: Elaeocarpus stipularis (E siamensis) and OTSP: Other species + Moderate burn severity: Among 21 species of trees layerrecorded in 19 plant families, there are co-dominant species The formula for the composition of trees layerafter fire in 2021 is established as follows: CTTT: 16,40PiMe + 9,05CiIn + 7,11PiKe + 6,62ShHy +5,33ScWa + 55,51OTSP (3.6) Where: PiMe: Pinus merkusii; CiIn: Cinnamomum iners; PiKe: Pinus kesiya; ShHy: Shorea hypochra; ScWa: Schima wallichii Choisy and OTSP: Other species + High burn severity Out of the total of 17 plant species recorded, there are species with important index IV ≥ 5% Thus, the forest burned with high burn severity has co- 17 dominant species The formula for the composition of the burning rubber tree species in 2021 is established as follows: CTTT: 17,4PiMe + 10,0CiIn + 8,61ScWa+ 7,89ElSt +5,28ScWa + 5,02DaEl + 45,8OTSP (3.7) Where: PiMe: Pinus merkusii; CiIn: Cinnamomum iners; ScWa: Schima wallichii Choisy; ; DaEl: Dacrydium elatum and OTSP: Other species 3.2.2.2 Regeneration layer (i) Density The average density/ha of the burn severity and density fluctuation over time after fire are shown in Figure 3.13 Figure 3.13 Fluctuation in regeneration density over time by burn severity The results in Figure 3.11 show that the average density of regenerated trees on different burn severityis very different At high burn severity, the average density of regenerated trees was the lowest, in 2018, (ii) Number and abundance of species - Number of species: The number of species corresponding to each burn severity and time after fire is shown in Figure 3.14 Figure 3.14 Fluctuation in number of species over time on burn severity The results in Figure 3.14 show that the number of regenerated tree species fluctuates greatly between different burn severity In the control area, the number of species regenerated in 2017 reached 45 species At a high level of fire, right after the fire, in 2017 (4 months after the fire), no regenerative tree species were recorded, which proves that the high level of fire, at the time immediately after the fire, caused death completely burn the number of regenerated tree species iii) Subspecies and dominant species: a Control area: The total number of regenerative tree species recorded was 45 species, belonging to 26 main species families including: Cinnamomum obtusifolium (Cinnamomum obtusifolium), Vang Tam (Manglietia fordiana (Hemsl.)), Trac dao, etc CTTT: 6,63CiOb + 5,47ScWa + 5,41DaCu + 5,2DaEl + 5,02PiMe + 72,18 OTSP (3.8) Where: CiOb: Cinnamomum obtusifolium; ScWa: Schima wallichii Choisy; DaCu: Dalbergia cultrata; PiKe: Pinus kesiya and OTSP: Other species b Low burn: The total number of regenerative tree species recorded is 33 species, belonging to 24 main species families, including: Pinus kesiya (Pinus kesiya); Schima wallichii Choisy, etc CTTT: 10,44PiMe + 8,28ScWa + 8,16LiFo + 7,92DaCu + 7,44DaEl + 6,60PiKe +5,40CaCe + 45,74OTSP (3.9) 18 Where: PiMe: Pinus merkusii; PiKe: Pinus kesiya; DaCu: Dalbergia cultrata; ScWa: Schima wallichii Choisy; DaEl: Dacrydium elatum; LiFo: Liquidambar formosana Hance; CaCe: Castanopsis ceracantha and OTSP : Other species c Moderate burn: The total number of regenerative tree species recorded in 2021 is 26 species, belonging to 22 families, The main species include: Medicinal plant, falsified eucalyptus, sauerkraut, cranberry, dicotyledonous pine, etc CTTT: 11,01ScWa + 9,54DaEl + 8,39LiFo + 8,18ShHy +7,764PiMe + 7,02PiKe 5,56CaCe + 42,56OTSP (3.10) Where: ScWa: Schima wallichii Choisy; DaCu: Dalbergia cultrata; ; DaEl: Dacrydium elatum; LiFo: Liquidambar formosana Hance; PiMe: Pinus merkusii; PiKe: Pinus kesiya; CaCe: Castanopsis ceracantha and OTSP : Other species d High burn: The total number of regenerative tree species recorded in 2021 There are 26 species, belonging to 22 main species families, including: Medicinal vine, Pseudocephalus, sauerkraut, fenugreek, Pinus merkusii, etc CTTT:10,55PiMe + 9,28PiKe + 6,28LiFo +6,04ShHy + 5,62ScWa + 62,13OTSP (3.11) Where: PiMe: Pinus merkusii; PiKe: Pinus kesiya; ScWa: Schima wallichii Choisy; LiFo: Liquidambar formosana Hance and OTSP: Other species 3.2.2.3 Fresh carpet, shrubs layer The results of the study and calculation of the characteristics of average height, coverage ratio and their fluctuations over time after fire are shown in Figure 3.15 Figure 3.15 Fluctuation in average high of shrubs over time by burn severity The results in Figure 3.13 show that: The average high of shrubs in the control area reached 0.79m, at the time of the survey in 2021, the average height of shrubs increased insignificantly, reaching 0.8m 3.3 Results of appling silvicultural techniques to post fire rehabilitation 3.3.1 Fluctuation of some soil criteria on silvicultural techniques for post fire rehabilitation 3.3.1.1 Fluctuation of some chemical properties in forest soil on silvicultural techniques for post fire rehabilitation (i) Humus matter (OM): The results of calculating the total humus content (OM) under the influence of silvicultural techniques for post fire rehabilitation over time are shown in Figure 3.17 Figure 3.17 Fluctuation of humus content by year on post fire rehabilitaiton measure ... Doctoral Committee at Vietnam National University of Forestry, Hanoi, Vietnam at …… This dissertation can be found at: - National Library of Viet Nam - Library of Vietnam National University of... OTC, all trees that have been labeled are identified with species names according to common names in Laos, Vietnam and scientific names.(ii) Measure and count all numbered trees: (1) High-rise trees... been attached and numbered are identified with the tree species name according to the common name of Laos, Vietnam and the scientific name.(ii) Regenerating plants include seedlings and seedlings