Assessing carbon stocks using the Invest Model - Guidelines and templates

1 CARBON-POOL-GUIDE MANUAL 1 INTRODUCTION TO THE GUIDE This manual is a guide to estimate the carbon storage in different land cover/land use (LCLU) types of a temperate wetland ecosystem by using the Microsoft Excel workbook “Carbon_pools_guide”. The purpose of the workbook is to calculate the carbon storage in four different carbon pools (above-ground, below-ground, soil, and dead organic matter) of a LCLU type and to utilize this information as input values for the InVEST® Carbon Storage and Sequestration model. The focus lies on wetland and floodplain ecosystems in the temperate region. The main LCLU types are forests, grasslands, croplands, and inland wetlands. The LCLU types of urban areas and water bodies are excluded from the calculations. Even though studies on carbon storage in urban areas, especially urban trees, exist, this information would go beyond the scope of wetland ecosystems. The reason why carbon storage of water bodies is neglected in the carbon stock calculations is that the carbon fluxes in streams are briskly changing at a spatial and temporal scale. The carbon stock values for each LCLU classification were gained from literature. The user has the option to add own values to the calculations, if necessary. In the following chapters, the different worksheets on the variety of the carbon pools are explained in further detail, and step-by-step instructions are given to perform the calculations and to prepare the data for the InVEST model. 2 CARBON POOL WORKSHEETS The workbook “Carbon_pools_guide” has one overview worksheet and 4 to 5 color-coded worksheets for each main LCLU type: • 1 overview worksheet • 5 worksheets for the LCLU type “forest” in green • 5 worksheets for the LCLU type “grassland” in light-green • 4 worksheets for the LCLU type “cropland” in orange • 4 worksheets for the LCLU type “inland wetland” in purple For each main LCLU type there is one worksheet for the above-ground carbon pool (_above), one for the below-ground carbon pool (_below), one for the soil carbo pool (_soil), and one for the dead organic matter carbon pool (_dead). In case there are 5 worksheets, the fifth sheet contains information on how to calculate carbon fractions from own biomass values (_carbon_fraction). 2 The carbon pool worksheets are divided into two sections: “Overview” and “Data selection”. The table in the overview section is identical to the table in the “Overview” worksheet. This means that if changes are made in the “Data selection” section, the mean carbon storage values are automatically calculated in the overview table which is automatically updated in the “Overview” worksheet. The carbon fraction worksheet can be used as a guide to calculate own carbon stock values for the LCLU types “forest” and “grassland”. For the above-ground carbon pool, carbon fractions are available to convert the mass of dry matter into carbon values. For the belowground carbon pool, ratios between belowand above-ground biomass (root to shoot ratios) are available. For the LCLU type “forest”, carbon fractions are also available to convert the mass of dry matter into carbon values for the dead organic matter carbon pool. 2.1.1 OVERVIEW The worksheet “Overview” is an overview for the calculated/estimated carbon storages of the main LCLU types forest, grassland, cropland, and inland wetland. The main LCLU types are visually separated by their color-code, and in each section the four carbon pools are represented with more detailed LCLU classes and their calculated mean carbon storage values (Figure 1). FIGURE 1. OVERVIEW WORKSHEET WITH THE MAIN LCLU TYPES, THEIR CARBON POOLS AND THE CALCULATED MEAN CARBON STORAGE VALUES. 3 The carbon storage values are calculated in metric tons per hectare (tC/ha). For each carbon pool, the mean carbon storage of each LCLU class is represented, the same as the overall average value for that carbon pool within the main LCLU type. An example on how to read the tables for a carbon pool of a given main LCLU type is shown in Figure 2. FIGURE 2. EXAMPLE OF HOW TO READ THE TABLE OF THE ABOVE-GROUNG FOREST CARBON POOL. Attention: The overview worksheet is only a visualization of the calculated carbon storage values. The calculations for each carbon pool need to be done in the corresponding worksheet. There are two options to get to the worksheet of a carbon pool of a main LCLU type which can be edited. Either one clicks on the title of the carbon pool one wants to work on (e.g., “Above-ground carbon storage” of the LCLU type “Forest”), or one skips through the worksheets at the bottom of the workbook until one finds the wanted worksheet. 2.1.2 FOREST There are 5 worksheets for the LCLU type “forest”: • Above-ground carbon storage (Forest_above) • Below-ground carbon storage (Forest_below) • Soil carbon storage (Forest_soil) • Dead organic matter carbon storage (Forest_dead) • Carbon fractions (Forest_carbon_fraction) For the above-ground, soil, and dead organic matter carbon pools, a variety of literature was available for the LCLU classifications general forest, hardwood forest, cottonwood forest, softwood forest, reforestation areas, and shrubs. The term “general forest” was used to describe merely terrestrial ecosystems and to make a distinction between floodplain or wetland forested areas, and terrestrial forests or woodland. Section of the main LCLU type “forest” Carbon pool “above-ground” with a link to the corresponding worksheet LCLU classes within the main LCLU type Mean carbon storage values in tC/ha of the LCLU classes Mean carbon storage value in tC/ha of the above-ground carbon pool 4 Literature is scarce for the below-ground carbon pool; only a few studies were performed to measure the below-ground biomass and carbon stocks in tree roots. Therefore, the LCLU classifications only cover deciduous and coniferous trees. Nevertheless, one can apply the conversion factors to estimate the below-ground carbon stock. In the worksheet on soil carbon storage, the carbon stocks are always linked to the soil types of the research sites and the depth of the analyzed soil samples. Furthermore, either the mean carbon stock values are represented, and/or the minimum and maximum values that were stated in the studies found in literature. 2.1.3 GRASSLAND There are 5 worksheets for the LCLU type “grassland”: • Above-ground carbon storage (Grassland_above) • Below-ground carbon storage (Grassland_below) • Soil carbon storage (Grassland_soil) • Dead organic matter carbon storage (Grassland_dead) • Carbon fractions (Grassland_carbon_fraction) Literature on grasslands in wetlands is scarce, especially for the above-ground and belowground carbon pools. Carbon stock values are available for general grassland, managed grassland, and natural and semi-natural grassland. These three LCLU classifications are mainly of terrestrial origin, but it was assumed that management practices are similar for terrestrial grasslands and floodplain or wetland grasslands. Dead organic matter is neglected for grasslands as the decomposition of the biomass is assumed to be fast, and is therefore considered in the soil carbon pool. Additionally, it is assumed that there is no woody vegetation in grasslands. Some literature was available for the soil carbon pool. In addition to the above-mentioned LCLU classifications, there is also the classification of floodplain grassland. The carbon stock values are always linked to the soil types of the research sites and the depth of the analyzed soil samples. Carbon stock values in grasslands are highly dependent on management practices, especially agricultural grasslands. This means that fertilized grasslands can be more productive and can have a higher biomass than grasslands which are managed extensively. Attention: The combination of the low number of available literature and the variability in management practices decrease the level of accuracy for carbon storage calculations in grasslands. Therefore, one must be careful in handling the available carbon stock values as they might not be adequate enough to represent the system one wants to investigate. 5 2.1.4 CROPLAND There are 4 worksheets for the LCLU type “cropland”: • Above-ground carbon storage (Cropland_above) • Below-ground carbon storage (Cropland_below) • Soil carbon storage (Cropland_soil) • Dead organic matter carbon storage (Cropland_dead) The carbon storage in cropland is difficult to quantify. Carbon stock values in the above-ground and below-ground carbon pools are highly dependent on management practices, the type of the cultivated crop, soil properties, and climate. In case of annual crops, there is no long-term carbon storage in the biomass as the biomass is removed from the system during harvest. Furthermore, post-harvest management practices can change the carbon stock in the above-ground and below-ground carbon pools. Therefore, the carbon stock values of these two carbon pools are set to zero. Additionally, the soil carbon pool can vary significantly and is also dependent on the soil properties, the type of the cultivated crop, rotation practices, tillage and residue management, and nutrient and water management. Thus, it is recommended to assess the soil carbon content of cropland, in order to apply more accurate and system related carbon stock values in the InVEST tool. The carbon stock in the dead organic matter carbon pool is also complex due to the same reasons mentioned above. 2.1.5 INLAND WETLAND There are 4 worksheets for the LCLU type “inland wetland”: • Above-ground carbon storage (Inland_wetland_above) • Below-ground carbon storage (Inland_wetland_below) • Soil carbon storage (Inland_wetland_soil) • Dead organic matter carbon storage (Inland_wetland_dead) Literature on carbon storage in inland marshes is scarce for wetlands in the temperate region. No literature was found for the above-ground, below-ground, and dead organic matter carbon pools. It is assumed, that below-ground carbon and dead organic matter are included in the soil carbon pool, since it might be challenging to distinguish between the origin of the biomass in these systems. More literature was available for the soil carbon pool, especially for peatlands and marshes. In the worksheet on soil carbon storage, the inland wetland types are listed, and the carbon stocks are related to the soil type, the depth of peat or the organic horizon (if applicable), and the sampling depth. 6 Attention: The gathered information on the carbon stock values might not represent the system one wants to investigate. The values can be used as guideline, but it is recommended to include own measurements to estimate the four carbon pools in order to perform the InVEST model. 3 HOW TO USE THE WORKBOOK? In this chapter, step-by-step instructions are given on how to use the Excel workbook “Carbon_pools_guide”. First, one has to define which LCLU classifications are present in the investigation site. Second, one must go through the Excel workbook and select the information one wants to include in the carbon stock calculations. Third, one has to prepare the carbon stock values in the correct format in order to use them as input for the InVEST model. For the purpose of this guide, a simplified example will be given on a hypothetical floodplain forest in the temperate region. 3.1.1 DEFINE LCLU IN THE INVESTIGATION SITE Before one can begin with selecting carbon stock values of the different LCLU classes, one has to define which LCLU classes are present in the investigation site. For that, one must extract that information from LCLU maps in a GIS mapping software, either GQIS or ArcGIS. Attention: This guide does not explain how to extract the LCLU classes from a GIS mapping software. It is a prerequisite for the user to have this knowledge. Once, one has obtained the information on which LCLU classes are present in the investigation site, one can start with the data selection in the Excel workbook “Carbon_pools_guide”. Example: In the hypothetical investigation site, two main LCLU types are present, “forest” and “water” (Figure 3). The detailed LCLU classifications show that the forested area is “broadleaved deciduous woodland”. There are three classifications for water; however, the LCLU type “water” is neglected for the carbon storage calculations. This means that one is left with the LCLU type “forest” and more specifically “broadleaved deciduous woodland”. FIGURE 3. LCLU TYPES IN THE HYPOTHETICAL INVESTIGATION SITE. 7 3.1.2 DATA SELECTION The data selection is the most crucial part and requires expert’s knowledge and opinion. The more detailed knowledge one has on the investigation site, the easier it is to select carbon stock values that could match the site. However, it might be challenging to choose from the list of carbon stock values that were found in literature, as they might not represent the site in question. Nevertheless, if one has done field measurements, one can add these values to the lists. For each carbon pools of each main LCLU type, the worksheet first shows an overview table and further down there is the section for data selection. The LCLU classifications listed in the overview indicate for which LCLU classes one can chose carbon stock values (Figure 4). FIGURE 4. WORKSHEET FOR THE ABOVE-GROUND CARBON STORAGE IN FORESTED AREAS. Once the LCLU classes are known, one can start filling out the worksheets for the four carbon pools of the main LCLU types. Figure 5 shows how to read the section on data selection. Attention: Only grey cells should be filled out by the user. 8 FIGURE 5. EXAMPLE ON HOW TO READ THE SECTION ON DATA SELECTION. Example: Since it is known what LCLU classes are present in the hypothetical investigation site, the next step is to select the carbon stock values for all four carbon pools for the LCLU type “forest”. As an expert of the area, I know that the broadleaved deciduous forest is a mixed floodplain forest of hardwood and cottonwood. I further know that the age of the trees is around 50 years old. Additionally, I happen to have done research on carbon stocks in the hardwood forest. Figure 6 shows how the section on data selection could be filled out for the above-ground carbon pool, considering all the knowledge of the site that I have. FIGURE 6. DATA SELECTION FOR THE HYPOTHETICAL INVESTIGATION SITE. LCLU class Carbon stock values from literature Write “yes” in the cell that matches the carbon stock of the site Space for own values Reference for more details on data origins 9 In the overview section of the above-ground carbon pool, one can then see the mean carbon storage values for each LCLU class, the same as the overall average of the carbon storage for the above-ground carbon storage in the hypothetical floodplain forest (Figure 7). FIGURE 7. CARBON STORAGE OVERVIEW OF THE ABOVE-GROUND CARBON STORAGE IN THE HYPOTHETICAL FLOODPLAIN FOREST. Once all the carbon stock values of all the applicable carbon pools are selected, one can continue with the “Overview” worksheet. 3.1.3 OVERVIEW After selecting all the carbon stock values for all four carbon pools of each main LCLU type which are present in the investigation site, all average carbon storage values can be seen in the worksheet “Overview” at a glance. The represented data cannot be edited in the list but must be corrected in the corresponding worksheet. Example: In the hypothetical investigation site, all four carbon pools are filled out for the main LCLU type “forest” (Figure 8). FIGURE 8. OVERVIEW OF CARBON STORAGE VALUES OF THE LCLU TYPE "FOREST" IN THE HYPOTHETICAL INVESTIGATION SITE.