2.1 Scale: From Thailand to Global
Thailand is located in Southeast Asia, at the center of the Indochinese Peninsula, with a total area of 513,120 km² (Fig. 2). Most of the country's climate is classified as Köppen's tropical savanna, with some regions having a tropical monsoon or tropical rainforest climate. (Beck et al. 2018) The annual average temperature is 27.1°C with an average total annual rainfall of 1,587.7 mm (1981–2010) (Thai Meteorological Department, Ministry of Digital Economy and Society [TMD] 2021). Bamboo is one of Thailand's most socio-economically important species, generally found in natural forests and developed for cultivation (Ramyarangsi 1985).
Historically, bamboo was harvested as food, household handicrafts, source materials for construction (which remained in the vernacular architecture), especially in the northern provinces (Correia et al. 2013). The research selected Thailand as the testbed to trial the experiment due to its potential for bamboo production, the country´s scale, and its cultural compatibility aspect. Further research could be scaled up or down, mosaicking the source data as a detailed area on the municipal level, or globally analyzed on a planetary scale. The proposed methodology can be implemented to visualize entire material flows and identify development opportunities along the VCA on any preferable scale.
2.2 From Bamboo to Other Crops
The research analyzed the potential for bamboo growth and harvesting based on critical natural factors influencing agriculture – precipitation, soil, and topography based on the specific bamboo species requirement, in this case, Dendrocalamus Asper due to the high yielding rate and its endemic nature over the study area. Each parameter defines the possible area layer for individual growth aspects and is then aggregated with the others to define the areas containing valid data for all criteria. This methodology can be replicated to another bamboo genus, depending on the geographical condition, or expanded further to other economically valuable crops such as cereals, oil-yielding crops, or lumber trees by defining different parameter ranges (filters) on the geospatial data, as shown in Fig. 3.
To explore the initial steps in new material VC and identify their potential in extensive heterogeneous landscapes, however, it further requires specific criteria for different vegetation types.
2.3 Datasets
Data Source Description. The geospatial data for this research was gathered from two primary sources: (1) geo-referenced raster images generated from the public data catalog for digital elevation model (DEM) and bioclimatic map in the global scale dataset, combined with (2) local vectorized data provided by the Land Development Department (LDD) and Royal Forest Department (RFD) under the Government of Thailand, who generated it using a combination of remote sensing and physical surveyed on-site validation.
The soil properties data contained the description in Thai soil categorization with 62 types which were aggregated with the texture and acidity (pH level) data according to LDD soil literature supplements (Udomsri & Hoontrakul 1997). Some areas are missing LLD soil properties data, such as gullied lands or areas with a slope over 35% (19.29°), as the area was difficult to manage or maintain for agriculture, which aligns with this research's objective. Land use and land cover (LULC) with level-2 classification are divided into 32 types. To achieve a country-wide dataset, 76 tiles with every region in Thailand were combined using QGIS 3.18 and its native vector merging algorithm. The same method was used on the existing oil palm dataset to aggregate five region files. Lastly, the forest cover map contains 17 types, including existing bamboo forests. The polygon shapefiles were organized in QGIS and exported as shapefiles to upload into the GEE system. The vector files were rasterized and exported as raster assets for web-based optimization with a resolution of 100 m per pixel. The entire list of input data included in the workflow is presented in Table 2.
Table 2
Input data for the interpretation of potential bamboo agroforestry land.
Input data
|
Name of dataset
|
Year
|
Data type
|
Resolution (m)
|
Provider
|
DEM
|
NASA SRTM Digital Elevation 30m
|
2000
|
Raster
|
30
|
NASA / USGS /
JPL-Caltech
|
Bioclimatic map
|
WorldClim BIO Variables V1
|
1991
|
Raster
|
927.67
|
University of California,
Berkeley
|
Soil properties map
|
Soil Series
|
2019
|
Vector
|
50
|
LDD
|
LULC
|
Landuse Thailand – Level 2
|
2018
|
Vector
|
12.5
|
LDD
|
Forest map
|
Thailand forest type database
|
2018
|
Vector
|
25
|
RFD
|
Oil palm map
|
Zoning by Agri-Map, Zoning Palm
|
2019
|
Vector
|
12.5
|
LDD
|
Driving Parameters Selection. Agricultural production is affected by various social and ecological factors, which are often challenging to integrate into the analytical framework. This research implements the capacity of online geospatial data analysis processed on a cloud-based system that could potentially manage petabytes of information to aggregate and weight geo-climatic conditions that generate a comparable score and identify the potential hotspots for bamboo farming. The crucial geo-climatic factors for agriculture include (1) terrain slope, (2) terrain elevation, (3) soil acidity, (4) soil texture, (5) average annual rainfall, (6) temperature. However, the research team decided not to include this variable due to Thailand´s geographic location, close to the Equator, with a stable average temperature (22–28°C) all year round. For the existing land cover factor, LULC and forest locations were used to consider the national economy's land resources and land use types aside from bio-physical systems. The land distribution information provides the specific scope that could be exploited for the potential bamboo agroforestry area. Interested stakeholders can use this information in decision-making to eliminate incompatible land uses, such as high-density urban clusters, humid evergreen forest, or sensitive wetlands. Lastly, the research incorporated the oil palm cover, resulted as one of the fastest-growing agricultural land uses. Its expansion significantly impacts the environment in a negative way; deforestation lessens the habitat area of endangered species and degrades land quality (Meijaard et al. 2020). The oil palm parameter underlines the potential benefits of significantly substituting mixed bamboo agroforestry to achieve higher ecosystem biodiversity, better soil quality, more resilient agricultural land, and a more sustainable cultivated development (Yiping et al. 2010).
Acceptable Thresholds. The data input was initially classified into viable and non-viable values (binary). To define the viable values, the developed workflow focuses on framing the ideal growth conditions based on the agricultural requirements of various high-yield bamboo species (Phyllostachys edulis, Dendrocalamus Asper, Guadua Angustifolia), thus filtering the suitable land surface for agroforestry according to:
a. Terrain slope – several studies show a wide-range optimal slope for bamboo; however, the highest productivity is found around the 25-degree slope (Cheng et al. 2015). Another indicator is the Thailand forest type database, which shows a similar result with bamboo forests situated on a range from flat land to hillsides with over 35-degree slopes. However, areas with more than 20% slope have a high erosion risk and difficult accessibility for farming (Jarasiunas 2016), reason for which this becomes the maximum admissible slope value for this research.
b. Terrain elevation – the studies on bamboo productivity based on elevation show bamboo could be found at altitudes as high as 7,000 m in rare cases (Shi et al. 2020). However, the elevation with the highest density of existing forests falls between 0–2,400 m above sea level (Schröder 2021). Over this altitude, lower air temperatures start to play a limiting factor.
c. Soil acidity – the suitable pH condition falls in slightly acidic soil to neutral, the range from several pieces of research are shifting within pH values of 4.5-7 (Fu 2001; Da Silva Sobrinho Junior et al. 2009).
d. Soil texture – bamboo can grow in different soil classifications. However, the smaller-size particles of soil, such as heavy clays, are less suitable for bamboo cultivation due to the high density that restricts the rhizome and root growth. While the too-light texture, such as sand, has an inadequate water-holding capacity (Kleinhenz & Midmore 2001). The acceptable threshold in this research is limited to combining loamy soils with other textures, as defined in the USDA Textural Soil Classification: sandy loam, loam, clay loam, and silty loam (United States Department of Agriculture [USDA] 1987).
e. Average annual rainfall –in Thailand, the minimum water requirement for bamboo growth was reported to be 1,000 mm/year without the maximum indicated, yet several studies demonstrated the yearly maximum admissible rainfall within 4,000–5,000 mm, which has been defined as the threshold limit of average annual precipitation for this research (Kleinhenz & Midmore 2001).
f. LULC – LDD classifies the LULC level-2 data into five main categories: (1) urban and built-up land, (2) agricultural land, (3) forest land, (4) waterbody, (5) miscellaneous land, with 32 sub-types. The data were analyzed according to the possibility of developing the area for future bamboo cultivation land. The acceptable threshold is shown in detail in Table 4.
g. Forest cover – the entirety of existing forest areas, wetlands, and natural land cover is considered as non-viable values to preserve fragile ecosystems and their biodiversity and mitigate climate change.
h. Oil palm – as previously mentioned regarding the climate impact of oil palm production, this intensive agricultural area represents an additional viable layer to promote as the prioritized land cover shifts towards bamboo production after its productive lifespan is over (circa 20 years).
2.4 Calculations
Scoring System. Multi-variable analysis plays a crucial role in land development policy. After gathering geospatial data related to bamboo farming factors and literature reviews, the previously binary filter was created; furthermore, this study proposes a scoring system to benchmark the potential for bamboo cultivation development, corresponding to the VCA. The system classifies numeric or non-numeric data in a range from 0–3 (normalization) with the criteria as shown in Table 3. However, due to limitations on the available data inputs, the research could only apply this scope of the method to ecological factor parameters (a-e). The scoring approach offers an intelligible area comparison for complex data; therefore, decision-makers, investors, or general audiences could effortlessly interpret the analyzed result and use this information through corresponding actions. The score value was added to the geospatial data by filtering and overwriting selected pixels' data properties.
Table 3
Scoring system on ecological factor parameters.
Layer name
|
Score
|
Reference
|
|
0
|
1
|
2
|
3
|
|
Terrain slope (degree)
|
> 35
|
0–5,
25–35
|
5–15,
20–25
|
15–20
|
Cheng et al. (2015),
Jarasiunas (2016)
|
Terrain elevation (m)
|
> 2,400
|
1,800-2,400
|
1,200-1,800
|
0–1,200
|
Shi et al. (2020),
Schröder (2021)
|
Soil acidity (pH)
|
0-4.5, >7
|
4.5-5,
7-7.25
|
5-5.25,
6.5-7
|
5.5–6.5
|
Fu (2001),
Da et al. (2009),
Government of Western Australia (2014)
|
Soil texture
|
sand,
clay,
silt
|
silty clay loam, sandy clay loam
|
-
|
sandy loam, loam,
clay loam, silty loam
|
Kleinhenz & Midmore (2001),
Nath et al. (2015)
|
Average annual rainfall (mm)
|
0-1000,
> 5000
|
1000–1500,
4000–5000
|
1500–2000,
2500–4000
|
2000–2500
|
Kleinhenz & Midmore (2001),
Schröder (2021)
|
This research did not create a specific weighting coefficient for each factor to generate the formula for the final data score due to the lack of consensus on the matter from multiple literature sources; for example, two pieces of research indicate the contradiction in the slope parameter importance. One suggests slope as the most crucial variable for enhancing bamboo productivity (Cheng et al. 2015), while another clearly states slope aspect had no significant effect (Chen et al. 2017).
Masking. The masking step was included to differentiate viable values (1–3) from non-viable ones (0), as the output from the scoring system step still contains scores with unsuitable areas. The masking process generates an output image that retains the metadata and footprint of the input image. Pixels will be excluded where the mask changes from zero to another value. The filter input variable is a mask image containing only the viable value area pixels. It is noteworthy to mention that the input for this step must be raster and not vector data. In vector data such as the soil texture properties, the workflow requires an additional rasterization process, which was achieved through GEE JavaScript API, as shown in Fig. 4.
Map Superposition. Overlaying is the last step to generate the final map to identify the potential bamboo agriculture hotspots through the geographical intersection of previously mentioned databases. The overlaying map composites all the images containing the same data attribute (score) to a single image representation, using the mean value as the data reducer for each pixel. After generating this mean map, it must be masked to exclude the pixels with a non-viable value. The map superposition shows area data as every pixel shown on this map can grow bamboo according to all geo-climatic parameters and contains a comparable score system (Fig. 5).
Qualitative Layers. Non-numerical layers (strings) that are by definition not compatible with the scoring system will be used as binary filters (true or false). In this case, this method applies to social structure factor data: (1) LULC; (2) forest map; (3) oil palm map. These layers are used in two ways, excluding the non-viable area or additionally promoting specific areas, as shown in Table 4. The meaning of qualitative layers differs from the scoring layers; the data would not be included in the score calculation but instead, operate as extra information layers for decision-making.
Table 4
Binary filter system on LULC parameters.
Layer name
|
Binary filters
|
|
false (non-viable)
|
true (viable)
|
LULC
|
A8 Aquatic plant
A9 Aquacultural land
F1 Evergreen Forest
F2 Deciduous Forest
F3 Mangrove Forest
F4 Swamp Forest
F5 Forest plantation
F6 Agroforestry
F7 Beach Forest
U1 Urban and Commercial
area
U2 Residential area
U3Governmental and
Institutional land
U4 Transportation
Communication and
Utilities
U5 Industrial land
U6 Other Built-up areas
U7 Golf Course
W1 Natural water body
W2 Artificial water body
M3 Mine and Pit
M4 Other Miscellaneous
lands
M5 Salt flat
M6 Beach
|
A0 Integrated farm
A1 Paddy field (Rice field)
A2 Field crop
A3 Perennial
A4 Orchard
A5 Horticulture
A6 Swidden cultivation/
Shifting cultivation
A7 Pasture and Farmhouse
M1 Rangeland
M2 Mash and Swamp
|
Forest map
|
All Area
|
-
|
Oil palm map
|
-
|
All Area
|
In further research, the qualitative layers could be included in the scoring system to enrich the benchmarking output with adequate literature support; for instance, the LULC or forest class could be classified according to local land development guidelines.
2.5 Validation
This research compares predicted data to the existing current RS imagery from official authorities to validate the prediction outcome. The most up-to-date information on the current bamboo area in Thailand was found in LULC level-3 data conducted between 2018–2021 at a scale of 1:25,000 provided by LLD from the LANDSAT 8 OLI satellite. According to the data description, the classification accuracy ranges between 85 and 98%, depending on the city. The datasets are separated into 232 subclasses, with bamboo falling under subclasses A315 (bamboo) and M103 (giant thorny bamboo).
The employed procedure filters the existing bamboo area (LULC l-3 vector data) using the predicted potential bamboo agroforestry layer (the research result as raster data, vectorized at a scale of 1km/pixel) as a clipping mask. The area of the filtered land surface is calculated with the “.geometry().area()” command and printed out with “ee.Number().divide(1e6)” to convert the result into km² using the GEE interface. Finally, the result of this operation is divided by the total existing bamboo area from LULC l-3, to determine the percentage of the masked area that corresponds to the actual data (i.e., where the prediction matches RS observations).
Due to availability limitations, several cities lacked data, particularly in the country’s central region. The complete sets of data are available only for the northeast and south regions. As a result, the described validation method could only be performed on these two specific regions, which contain 34 from 77 different cities and cover 242,702 km² (47% of the nation's surface).