sp,k,(x,y),t sp,k,(x,y),t sp,k, x,y ,tk
CGMM introduces heterogeneity within the element through local interactions including:
- Separate d0.3 classes in a group : cumulative diameter growth is updated for each year. When the mean cumulative diameter and the observed diameter exceed the class size interval, a new size class is defined, the tree
transferred to this new class.
- Competition within multiple plants : competition between plants is represented by the FA factor:
X thr = f(dist)
= f(R k,t )
R j k,t
is the average value of the influence area of the jth class d0.3 different from k
k is the affected layer d0.3
X thr is the threshold of R j k,t , depending on the average distance between trees
dist is a function of the total number of trees in the element and the element area
( dist 0, 5. )
is the value that determines the slope of the FA curve k,t , depending on the influence area Rk ,t of the kth layer d0.3.
Elements in the model interact through subtree dispersal. The number of trees Ns (x,y),t added to element (x,y) at time t is the total number of subtrees from element (x,y) and from other elements multiplied by probability P(x, y).
Inheriting the CGMM model structure, the author proposes a model structure for the study area with some changes (adding temperature factors to environmental factors - however, due to conditions that do not allow, in This project only calculates one elevation factor ( submergence ).
Figure 2. 4: Conceptual structural design diagram of the model in the study area
RESEARCH RESULTS AND DISCUSSION
3.1. Current status of mangrove forests in the study area
3.1.1. Species composition in the study area
In the study area, most of the mangrove forest area is planted forests with the main, initial goal of the forest planting and development programs here being coastal protection. With that goal, species composition and afforestation techniques should be designed in a positive direction for that set goal. To achieve the goal of forest protection as soon as possible, K. candel has been chosen as the main species, accounting for a large proportion of the tree species composition. And also to ensure the fastest coastal protection, the planting density is relatively high (70cm x 70cm). With a fast natural regeneration rate (after 3 years of age, most of the trees here are capable of flowering, bearing fruit and performing the task of maintaining the species). For those reasons, the tree density in the study area is very high.
Table 3. 1: Statistics on the number of species at OTCs
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It can be seen that in the current species composition, the ornamental tree is absolutely dominant. At the investigated bands, Band 3 had absolutely no Sour Sora trees, Band 2 had only 1/108 trees and Band 1 had 13/398 trees.
With the current state of species composition, mangrove forests in the study area are still relatively poor, and in the future there should be a plan to intercrop some more species.
new growth and development conditions suitable for the Xuan Thuy National Park area.
3.1.2. Growth characteristics of main species in the study area
In the research area, the trees were measured according to the following criteria: number of species, diameter at breast height (for the bamboo tree is the diameter at a height of 0.3m; the bamboo tree is the diameter at a height of 1.3m). m), crown height, canopy diameter, canopy height, results are shown in the table below.
a. Body diameter
5, 3 8
5, 5 1
At Xuan Thuy National Park, forests are planted at high density, so the impact of competition between trees is very high, causing the growth process of CNM to slow down. Here the trees are grouped by age from 1 year onwards:
Figure 3.1: Tree diameter values by age groups
Trees in the 3 - 7 year old group have relatively uniform trunk diameters, the average trunk diameter ranges from 5.38 cm to 7.34 cm. Groups of trees with ages outside the above range have much larger or smaller diameter ranges (the average trunk diameter of tree groups 1, 8, and 9 years old is 0.67 cm; 14.5 cm and 14.5 cm, respectively). cm) (Figure 3.1).
b. Body height
In the study, stem height was measured in the field, shown in Figure 3.2.
45 , 70
Figure 3.2: Tree height in OTCs
From the chart, it shows that among the age groups, there is not much difference in height value, the 1-year-old tree group has the lowest average value (45.70 cm), the 7-year-old tree group has the average height value. The tallest average (180.77 cm), among the age groups of trees can be divided into 3 bands, one band includes a group of 1 year old trees with a height of less than 50 cm, a band includes a group of trees from 3 to 6 years old with a height of The average height is from 110 to 150 cm, the remaining group with trees older than 6 years old has an average height greater than 50 cm. Thus, groups of trees of the same age have quite small differences in trunk height and trunk diameter (for example, groups of 8- and 9-year-old trees have a lower average height than groups of 4 and 7 years old, but the trunk diameter is much higher. other groups).
c. Tree density
The standard plots also measure the number of trees by age group:
18. 9 38 18. 3 50
12. 1 67 12. 1 00
3.7 0 0
Figure 3.3: Tree height in OTCs
Among the age groups, the 1-year-old tree group has the lowest density in the plots at about 3,700 trees/ha. Among tree age groups, the density of trees at 3, 4, 8, and 9 years old is much higher than other groups (density ranges from 15,000 - 20,000 trees/ha). The group of 5- and 6-year-old trees is the first group of seedlings born (about 3 years after the mother tree was planted), and currently has a much lower density than the group of newly born seedlings and parent trees (Figure 3.3). This is due to the effect of natural thinning in the plots.
d. Tree biomass
According to the results of calculating the biomass of trees for the research species, currently the number of Solanthus Sora trees is not much but the biomass is relatively large. In the research area, Sora Sora is the species with the largest biomass in the same age class. tree. Measurement results showed that the biomass of Sour Soap at the time of the investigation (2012) was about 300 tons/ha, 1.5 times that of the Trang tree. In Xuan Thuy National Park, the Solanum species grown intercropped with Trang (the main crop to block waves and protect the coast) has grown relatively strongly and has given birth to the next generations. Although it has grown into a mature tree, under the influence of temperature factors, from 2008 until now, many mature Soap areas have died or degraded.
3.2. Results of modeling the influence of changes in inundation due to climate change on mangrove dynamics in Xuan Thuy National Park
3.2.1. Results of running the model
In this project, we build an ecological model to simulate the evolution of mangrove forest distribution. This model is established through the integration of many steps: from applying spatial point statistics to determining the correlation equation between plant growth and the values of specific environmental conditions. specifically, apply hierarchy theory to design the operating order of subprograms in the model, and then build a model.
The simulations run for 110 years (1990-2100) over the entire area of mangrove forests and coastal mudflats from the Central dyke to 0 m sea water depth in the current period. The time we choose to start implementing the simulation model is when there is only a small area of mangrove vegetation left in the area, not concentrated. The simulation process was strong after 1996-1998 when a significant, concentrated area of mangrove trees was planted in the region. The simulation is based on the interaction of two factors: changes in sea level and competition for space between individual mangrove trees.
In addition to the main environmental factor of interest in the study, which is the inundation factor, the evolution of vegetation in the region is also analyzed in terms of relationships between individuals as well as compliance with the life process: biology. grow, develop and die. (Figure 3.4)
Disperse young plants
Figure 3. 4: Simulation model of each individual's interaction with each other and their development process