Forest community biomass is the best index of forest ecosystem productivity, the most direct expression of forest ecosystem structure and function, and the comprehensive embodiment of forest ecosystem environmental quality. The biomass of forest community refers to the total amount of organic matter accumulated by the community in a certain period, which is usually expressed by the average mass or energy accumulated per unit area or unit time. Existing biomass refers to the dry weight of organisms, and the main difference between them is whether it includes litters accumulated in forest land. At present, the commonly used concept of biomass is the latter meaning, that is, it does not include the dry weight of litter. Forest community biomass includes tree layer biomass and undergrowth vegetation biomass. The biomass of undergrowth vegetation was measured by quadrat harvesting method, that is, 5- 10 quadrats of 1-2m2 were mechanically arranged in the quadrat, all grasses and shrubs (above ground and underground) were harvested and weighed, and the dry weight rate was determined by drying. Calculate the undergrowth vegetation biomass of the whole forest with the average of quadrats. The determination of tree layer biomass is complicated and there are many methods. The commonly used method is equal cross-sectional area and diameter classification in logging method, that is, a group of standard trees are selected according to certain standards, and their biomass is measured after logging, and then a regression equation is constructed according to the measured data of sample group biomass, and the tree biomass is calculated from the regression equation.
Monitoring Project: (Land 62)
Biomass of tree layer organs: diameter-step equal ratio standard wood method, once every five years, which are stem, branch, leaf, flower and fruit, root respectively.
Tree layer biomass is the most important component of forest community biomass, and its accurate determination plays an important role in studying forest growth and forest ecosystem productivity. This standard specifies the diameter-step equal ratio standard wood determination method of forest layer biomass, which is applicable to the determination of forest layer biomass and other terrestrial ecosystems. Diameter-step equal ratio standard wood method is to select standard wood according to diameter-step equal ratio, measure the mass of each standard wood's organs respectively, and establish regression equation with diameter or DBH and height. Substitute independent variables (diameter, DBH and height, etc. ) into the equation, you can get the biomass of each tree. Add up the biomass of each plant to get the total biomass of the tree layer in the sample plot. This method has less labor intensity than the original logging method and higher accuracy than the general standard wood method.
Determination steps:
Establishment of standard plots.
According to the regulations in the standard of Investigation and Sampling in Biological Community Monitoring, several representative standard sample plots, the number of which is generally more than 6, are established. Each sample plot is square or rectangular, with an area of 0. 1 hectare, and it is circled with measuring ropes. Destructive investigation cannot be carried out on this fixed standard land.
Standard environmental records.
Record the hierarchical structure, canopy density, density, species and undergrowth plants of each tree species.
Investigate each tree in the quadrat.
In all kinds of sample plots, all the trees in the sample plots should be measured at breast height and tree height one by one, and recorded, and each tree should be numbered to avoid missing measurement. The DBH D is measured with the benchmark of 1.3m high, and the benchmark is set on the ground on the uphill side of the trunk, and the circumference of the trunk is measured with a tape measure at the upper end of the trunk, so as to find out the diameter (in cm), or directly measure the diameter with a measuring ruler. The height h of the tree is measured with a measuring rod or altimeter. When measuring the height of a tree, it must be based on the condition that the surveyor can see the top of the tree, so as to minimize the error and take m as the measurement unit.
Selection and cutting of timber with standard diameter.
Taking 2cm as a diameter class, the number of neutral trees in different diameter classes is determined according to the proportion of neutral trees in each diameter class, and the standard trees in the diameter classes are selected respectively. The diameter class with the least number of stumps is 1 standard wood, and the number of standard trees of other diameter classes is determined according to the requirements of diameter class ratio. When choosing a standard tree, you should choose a normal tree without dry folding and splitting, and don't choose a forest edge tree to avoid too many branches and leaves. After cutting the standard wood, saw a section every 1m or 2m (but the first section is 1.3m). If the trees are tall, the sectional area can be increased to 4m or 8m. The fresh mass of stems, branches, skins and leaves of each section were measured respectively, and some samples of each section were taken, put into bags, brought back to the laboratory, dried to constant weight at 80℃ and weighed. Calculate the water content of the sample, and calculate the dry weight according to the fresh weight of the stems, branches, skins and leaves in each district and the water content of the sample. For the mass of the trunk of a big tree that cannot be weighed by a scale, we can measure the cross-sectional area and length at both ends of each section, multiply the average of the two cross-sectional areas by k degrees, calculate the volume, and then convert it into mass. Determining the quality of root is a laborious and time-consuming task, and when the number of standard wood is large, it can be reduced appropriately. For standard wood whose root quality must be determined, all roots should be dug out. According to the size of the tree, estimate the root area and soil depth to be dug. After cutting standard trees, roots with an area of 1m2 and a depth of 0.5m are generally dug around the tree base (the digging depth depends on the distribution depth of the roots), and rhizomes, thick roots (more than 2cm), middle roots (1cm-2cm) and small roots (0.2cm-1cm) are cut respectively. Take each part of the sample back to the room, dry it, calculate the water content, and estimate the total root dry weight. When measuring fresh quality, we should try to remove the sediment attached to the roots. For fine roots, we can put them in a sieve and wash them with water, then use paper or cloth to absorb the attached water, dry them and then weigh them. It is of great significance to measure the biomass of fine roots (roots below 0.2 cm in diameter), mainly because of its fast turnover speed. The accurate determination of fine root biomass adopts endogenous soil core method. Firstly, the rootless soil column with a diameter of 5 cm ~ 10 cm and a depth of 0.5 m ~ lm was constructed by using the method of inner growing soil core. When making rootless soil columns, you can borrow a net bag with a certain aperture to facilitate the formation of soil columns. Put the soil column (net bag) into the pit prepared in advance and fill the surrounding gap with rootless soil. You can also dig a pit in advance, put it directly into the soil mold, then put it into a net bag, then fill it with screened rootless soil, and the surrounding area is also filled with rootless soil, and finally take out the mold. The rootless soil that constitutes the soil column can also be replaced by sand. The advantage is that it is easy to separate roots from sand, but it forms a completely different environment from the surrounding, which will affect the growth of roots to some extent. After the soil column is buried in the soil for one year, it should be taken out of the soil, and the connection between the soil column and the surrounding root system should be cut off before taking it out. Wash the soil column with water, take out the fine roots, and weigh the fresh mass and dry mass as the approximate annual output of the fine roots. Results Calculation: (1) regression equation was established. According to the biomass (part or whole plant) of standard trees with different diameter classes in each plot, the average values of corresponding indexes of different diameter classes of the mountain are obtained, and the regression equation with each diameter class is established by least square method. The form of the equation is shown in Equations (1) and (2):
W=a×Db……..( 1)
W=a×(D2×H)b……..(2)
Where: w-the mass of the whole standard wood (the mass of each part of the standard wood can also be used as a dependent variable), kg; D—— height at breast height, m; H—— standing height, m; A- coefficient, kg m-3); B- constant term. The regression equation should be tested for significance (generally using F test), and only if the significance test exceeds the requirements can it be used. (2) Calculation of tree layer biomass. The biomass of tree layer in each sample plot is calculated according to formula (3).
…………………………………………(3)
Where: Bi-the biomass of tree layer in the I-th sample plot, kg; Mi—— tree diameter grade of the I-th plot; Nij—— the number of plants in the j-th diameter class in the i-th plot; Wj—— the average biomass of the j-th diameter class calculated by formula (1) or (2), and the average tree layer biomass calculated by formula (4):
Where: b-average tree layer biomass, kg m-2; Double biomass of the I-th sample; kg。 N—— number of sample plots; A—— area of each plot, m2.
Biomass determination method of tropical and subtropical natural forests-important value method
Diameter-step equal ratio standard wood method is generally suitable for forests or artificial forests with single tree species in the north. For the tropical and subtropical natural forests in the south, it is impossible to apply this method to the biomass determination of each species because of its complex species. Therefore, diameter step is more difficult to be applied to biomass determination of tropical and subtropical natural forests with complex species composition than standard wood method. According to the international common method for measuring tropical forest biomass, this method establishes a biomass model of mixed tree species (Kira et al., 1967) by measuring all plants in a certain area and supplementing the forest biomass of plants, so as to estimate the biomass of the community. The specific method is as follows:
According to the data of the fixed sample plot of the community object studied, a basically homogeneous experimental sample plot is selected near the fixed sample plot, that is, the community characteristics of the experimental sample plot (including the composition of basic species, the distribution pattern of DBH and tree height, the distribution of population important values, etc.). ) should be similar to the fixed sample plot, the area of the test sample plot should be greater than 0. 1hm2, and all trees with DBH ≥2cm in the test sample plot should be removed. The aboveground biomass of each plant was measured according to the single plant biomass measurement method provided by the diameter standard wood method. If there is an important value ≥ 15% in the constituent population, a single population biomass estimation model should be established according to the measurement results of diameter standard wood method.
Shrub biomass: harvesting method, once every five years.
This standard specifies the determination method of forest shrub layer biomass, which is applicable to the determination of forest shrub layer and shrub layer biomass of shrub communities in humid areas.
Determination method 1- quadrat for single shrub species
According to the standard "Setting of Sample Plot, Sample Line and Sample Square in Biological Community Research", there are several representative shrub sample plots with an area of 0. 1 hectare, generally more than 6. On each sample plot, the number of branches and the diameter grade of main branches of shrubs were measured, and the average value was obtained to find the standard tree. According to the regulation of 5.4 in the standard "Determination of Forest Layer Biomass by Diameter Standard Wood Method", the aboveground part (trunk and N 10 should be separated) and underground part of standard plants in various plots were collected to determine their fresh weight and dry weight. The biomass of forest shrub layer is calculated according to the following formula:
In which: BS-biomass per unit area of forest shrub layer, kg m-2; N—— number of sample plots; A—— the area of each plot, m2; Bi—— dry weight of shrub standard wood in the I-th sample plot, kg; Mi-the number of shrubs in the I-th plot. Determination Method 2- For quadrats with multiple shrubs
Six 3m×3m quadrats were set up, and the species, quantity, height, ground diameter and crown width of the community were investigated in detail. Harvest all shrub species in the plot according to the aboveground part and underground part. The aboveground part should be divided into two parts: stem and leaf, and their fresh weights should be measured respectively. Take 300-500 g fresh samples according to the three components (stem, leaf and root), bring them back to the laboratory and dry them to constant weight, and then calculate the dry weight of each component of the shrub after calculating the dry-fresh ratio; Calculate the dry weight (horse) of shrubs in the j-th quadrat;
Where Wsi, Wli and Wri are the stem, leaf and root biomass of the first shrub, respectively; I = 1...s, which means S species. Calculate the dry mass (Bs) of shrub biomass per unit area;
Where: n- square number of small samples, n = 6；; A- small quadrat area. The allowable deviation is 15%.
Above-ground biomass of herb layer: harvesting method, once every five years.
This standard specifies the process of determining the biomass of forest herb layer by harvesting method, which is applicable to the determination of forest herb biomass and other herb communities. Determination steps: (1) According to the standard of Setting up Sample Plots, Sample Lines and quadrats in Biological Community Research, 30 small quadrats with an area of 1m2 are set up in the forest according to the method of mechanical sampling. (2) Dig out the medicinal materials in each quadrat one by one, wash away the soil with water, divide them into two parts, the aboveground part and the underground part, weigh them fresh respectively, and then dry them and weigh them dry. Results Calculation: The biomass of forest herbs is calculated according to the following formula. Herb biomass in a single quadrat bi in:
Where: the double dry weight of herbs in quadrat I, kg; Bgj-aboveground biomass of the j-th herb; Underground biomass of the j th herb; I = 1...n: the number of species in the quadrat. The average biomass of the herb layer in 30 quadrats is calculated according to the following formula:
Where: BH-biomass of forest herb layer, kg m-2; A—— quadrat area, m2; Double dry weight of herbs in quadrat I, kg. The allowable deviation is 15%.
Underground biomass: once every five years,
Litter quantity of forest land in that year: quadrat survey method, once every five years.
Litter layer is an important basis for the self-fertilization process of forest ecosystem and plays an important role in the material cycle. As a part of forest net primary productivity, it dies and falls off every year, and it is recycled after being decomposed by soil animals and soil microorganisms. The determination and decomposition process of litter volume are introduced as follows.
Determination of litter quantity: Litter collector is generally a wooden box with 1.0× 1.0× 0.2 or 0.5×0.5×0.2m, and several small holes are drilled at the bottom to drain water, and metal mesh or nylon gauze with the aperture below 3mm can also be used as the bottom of the box. In the sample plot, the number of collectors is not less than 10, and the sum of their areas is not less than l% of the area. Generally, it is put into the forest before the growing season, and collected and measured once a month, taking one year as a cycle, in order to obtain a complete seasonal dynamic process. During each measurement, all the litters in the collector are put back indoors in plastic bags, and the fresh weights of leaves, branches, peels, fruits, insect droppings and so on are measured. Weighing, drying at 80℃ to constant weight, and then weighing the dry weight to calculate the water content. Finally, it is converted into the amount of litter per plot or unit area.
Annual litter t/hm2 = annual litter g/m2× 10-2.
Where: K 1- water conversion coefficient; 10-2- the coefficient from g/m2 to t/hm2.
Decomposition cycle of forest litter: once every five years.
Litter decomposition rate: the decomposition process is expressed by the weight loss rate within a certain period of time. Put about 200 grams of garbage in a nylon gauze bag (18cm× 18cm) with a diameter of 2mm and number it. After drying at 40℃ to constant weight, weigh the dry weight. Each sample was repeated three times. The sampling time is autumn defoliation. Spread the simulated natural state in the litter layer of the sample plot, and the bottom should be in contact with soil layer A. Each sample can be all leaves or a mixture of leaves, branches and barks. It can be the same tree species, or it can be a mixture of all tree species in the study plot. The location can be the same habitat or different habitats. All of the above depends on the purpose of the study. Take back the sample bag every month, remove the impurities attached to the sample belt, weigh the dry weight by the original method, calculate the weight loss rate, and put the sample bag back in its original place. You can get the monthly decomposition process. The decomposition rate in the first year can also be measured only once in the early spring of the second year, and once again when the leaves fall in the second year. For several years, until the sample completely loses its original shape, a complete decomposition process can be obtained year by year with soil layer A.
Litter decomposition rate (%) =
Maximum net photosynthetic rate of main tree species: the amount of carbon dioxide absorbed by leaves per unit area per unit time, excluding the photosynthetic part after respiration. Once every five years.
Leaf area and leaf area index of standard wood
Cut down standard trees, measure the dry weight of all leaves, calculate the total leaf area of standard trees according to the measured specific leaf area, and then convert it into the leaf area index of the stand.
Instruments and appliances: chainsaw; Gram scale or balance (sensitivity:1100g); Photoelectric leaf area meter; Vernier caliper (accuracy: 0.0 1 cm); Oven.
Operating steps:
Measurement of leaf weight: select a standard wood in the stand. Not only the DBH and tree height of standard trees are higher than the average level of stands, but also their growth space and crown shape are representative. Cut down standard trees, divide the crown into three layers (parts) evenly from top to bottom, cut off all branches and pile them up in groups according to layers. Determine the base diameter and branch length of all branches in each layer, and calculate their arithmetic average. Based on the average soil amplitude of about 3%, three standard branches are selected for each layer. The leaf measuring tool on the standard branch is medium level. Separate the leaves on the branches and divide them into new leaves and old leaves (Jrt for 2-year-old leaves), and calculate the leaf (fresh) weight of the whole tree according to the following formula (the calculation method of new leaves and old leaves is the same):
Where: WF-fresh weight of all leaves, g; Number of branches in ni-I layer; Standard branch weight of layer I of Wij- j, g
Mix all new leaves and old leaves together, weigh them as Wtfo, and each fresh sample is about 100g(Wsfo), and put them in paper bags and bring them back indoors. Weigh the collected leaf sample (Wsfi) again, take110 (Wf 1 and Wf2), dry at 80℃, weigh the dry weight (Wd 1 and Wd2), and calculate the dry weight (Wd) of the whole leaf according to the following formula.
Where: WD-dry weight of all blades, g; WTFO-fresh weight of all old leaves and new leaves, g; Wsfo—— fresh weight of the above-mentioned old leaves and new leaves, g; WSFI-laboratory fresh weight of the above samples, g; Wf 1, wf2-the weight of the two samples before drying, g; Wd 1, wd2-weight of two samples after drying, g
Specific leaf area: randomly select 10 leaves (30 needles) from the remaining fresh leaves to measure their leaf area. The leaf area of broad-leaved trees is measured by photoelectric leaf area meter, and the needles are measured by 1% caliper, and the leaf area is calculated according to the corresponding surface area formula. The unit is square centimeter, accurate to 0.0 1 square centimeter. Dry all the leaves at 80℃ and calculate the specific leaf area according to the following formula:
SLA=LA/LW
Where: SLA specific leaf area, cm2g-1; LA- 10 leaf (30 needles) fresh leaf area, cm2；; LW- dry weight of the above-mentioned leaves (needles), g.
The leaf area index is calculated by the following formula:
In which: leaf area index; W—— weight of standard leaves, g; SLA specific leaf area, cm2g-1; A- projection area of standard wood, cm2.
Determination of net photosynthetic rate of tree layer
Instruments and meters: infrared carbon dioxide analyzer; Wet and dry thermometer; Illuminator; Label; Balance (sensitivity:1100g); Punching machine; Oven, etc.
Operating steps:
A) Selection of sampling points: select several healthy and normal stumps for each tree species in each sampling area of the forest community to be tested. Select at least 5 samples from each plant (i.e. different heights, different main stem directions and different development stages), and each sample point can be represented by a leaf (broadleaf tree) or a branch (such as conifer tree).
B) Description of plot: record the basic characteristics of plot in detail, including the name of forest, species composition, growth stage, etc.
C) Description of environmental factors during measurement: During each measurement, environmental factors, including light intensity, sunshine time, temperature, humidity, wind speed and direction, should be recorded in the pre-made table.
D) Put the branches or leaves of the selected sample points in the assimilation chamber (box), and measure the CO2 concentration (C2) at the outlet of each sample assimilation box with a portable or desktop, single-channel or multi-channel infrared CO2 analyzer. If it is a single-channel analyzer, each measurement needs to be circulated at each sampling point, and each measurement time does not exceed 2min (assuming that the ambient air concentration does not change within 2min). Before each measurement, the concentration of CO2 in the air (C 1) should be measured first. See 9. 1.3 and 9.2,3 for details.
E) Calculation of leaf area of arbor layer: The key to determine the photosynthesis and respiration rate of forest community is how to reasonably extrapolate the results measured at the leaf level of arbor layer to the community level. Leaf area index of tree layer is usually used to connect the two. The common method to determine the deciduous area index of forest group is to select sample branches, and determine the leaf area of sample branches through the correlation between leaf area and weight, so as to estimate the leaf area index of the whole plant and the whole tree layer (see 6.2.3). Plants of different tree species in the forest are usually identified separately.
F) The calculation formula of net photosynthetic rate of tree layer is as follows:
Where: PNT-net photosynthetic rate of tree layer, CO2 absorption per unit time and unit area, μ mol m-2s-1; Pnij—— the net photosynthetic rate of the first sample in one day, the amount of CO2 absorbed per unit area per unit time, μ mol m-2s-1; Lai-leaf area index of tree layer; N- number of samples; M- the number of time periods.