How to Count Trees, Estimate Carbon Stocks
To address the promise of the Trillion Trees Initiative, https://www.trilliontrees.org, IGC has two related goals: First, to assess how many trees IGC projects are contributing to this international effort, and second, to calculate the contribution of the projects to global carbon storage. Each team is requested to conduct these assessments using the guidelines below or an effective equivalent.
This is not intended to be a precise exercise but a thoughtful estimate. We want our projects to improve global conditions, but are our designs of big-enough size, or sufficiently bold in conception to make a difference if widely adopted in our regions, nations, or globally?
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Is my solution the most effective or can I learn from others who have achieved more?
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Are the policies and practices of my locality restricting what our projects can do to assist with fighting climate change?
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Can we reverse carbon accumulation or only slow it?
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What can we do to alleviate migration pressures in the short-term while our trees grow?
How many trees are there?
Green streets: which city has the most trees?
Oliver Balch in The Guardian, November 2019
The world's 3 trillion trees, mapped
Chris Mooney in the Washington Post, September 2015
Crowther et al. (2015) Estimated total global trees and trees per hectare for forested biomes. Based on extensively ground-validated remotely-sensed data they have created robust estimates for tree numbers per hectare for each of the 13 biomes. At regional, national and global scales, tree numbers for ex-urban forests are estimated by assigning biome values for tree stems per hectare to planted map polygons. Pre-design and post-design numbers are generated by comparing the tree canopy areas at each stage of the geodesign scenario.
Tree-counting for planted and managed forests is less amenable to an estimation method. For example, Nguyen et al. (2016) observed tree densities from 0 to 6621 in diverse species forest plots in the Phillipines. Nevertheless, forest managers will have target densities for their forests to maximize their commercial benefits. There are, however, numerous sources of guidance, for example:
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Wales, A Basic Guide to Tree Planting, http://coed.cymru/images/user/Tree_Planting__Coed_Cymru_2017.pdf
In urban situations, tree counts may be more precise counts or estimates based on pre-determind spacings. While simple counting is feasible at the level of small neighborhoods, for larger areas estimates will be based on scaling-up based on sampling at smaller sizes.
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Street-tree planting is highly variable and place-specific
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Tree numbers derived from spacing x length of planted area in design
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Carbon storage based on trees/species/size x storage capacity
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For IGC, counts will be based on estimates based on typical street and neighborhood conditions as samples
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Many cities have comprehensive urban tree inventories
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Existing conditions can be sampled on the ground or via Street View and totals estimated using satellite imagery
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See sample references below. Where possible, identify local equivalents.
How much carbon do trees and forest store?
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Trees and forests are carbon sinks
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A temperate forest tree absorbs up to 20 kg CO2 per year = about 1 tonne of carbon by age 40.
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Add another 33% for below-ground and a component for carbon stored in forest soils.
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Bigger trees are usually older and have captured more carbon dioxide from the atmosphere and therefore contain more carbon.
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About 50% of the dry weight of a tree is carbon.
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Carbon calculation is tree and forest-specific. See sample references below and substitute equivalent local material.
Different trees and different forests store
different amounts of carbon.
Rob Wreglesworth for Innovate Eco, 2020
Mat McDemott for Treehugger, 2018
Estimating carbon for regions with forest, woodland and interspersed trees
IGC recommends using IPCC classifications and IPCC naming conventions for land use/land cover for assessing land use transitions resulting from geodesign scenarios. The transition table below indicates the range of possible LULC geodesign changes and the associated naming conventions.
Keith, Mackey and Lindenmayer (2009) estimated average biomass carbon by forest type based on a wide range of global biome site data. They provide average carbon per hectare measures for a range of tropical through boreal forest types. At regional, national and global scales, carbon storage for ex-urban forests is estimated by assigning biome values for metric tons of carbon per hectare to planted map polygons. Pre-design and post-design estimates are generated from tree canopy areas.
The IPCC--Intergovernmental Panel on Climate Change publishes comprehensive methodological guidance for Agriculture, Forestry, and Other Land Use and tables of carbon storage for different land use/land cover categories in tropical through boreal biomes (see links below)
Click on image above to access full library of IPCC guidance and worksheets
Estimating carbon for urban and suburban regions
Carbon storage of individual trees is a function of trees/species/size x storage capacity.
Guides and calculators are available from various sources--the links are a few examples:
Tree carbon tools, US Forest Service
Tropical tree carbon sequestration
Berkeley Carbon Calculator for forests
Wales, Carbon storage calculator
Continuous mature urban forest stores carbon proportionate to tree cover area
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e.g in UK, 0.67kg CO2/m2
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University College London has shown that urban forests can store 178 tons of carbon per hectare, slightly short of tropical rainforests at 190 tons.
At smaller regional, community and neighborhood level the US Forest Service has the iTree suite of tools. iTree Planting and iTree Design are tools for estimating individual tree and property-level ecosystem services, but are only available for the United States. However, two have been successfully adapted for international use and calibration data is already available for several locations:
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i-Tree Eco is adapted for use in Canada, Australia, the United Kingdom, Mexico, South Korea, Colombia and most of Europe. Some global city locations are also available: Viable Locations
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i-Tree Canopy is an online tool available for international users and has been used successfully by users outside the United States
Click on iTree Eco and iTree Canopy images for video presentations
i-Tree Canopy is an online tool that has been used internationally for estimating canopy cover. Canopy does not require software installation. Users define project areas using a Google Map interface or by uploading an ESRI shapefile. Ecosystem service estimates for pollution and carbon are limited by U.S. models. Change analysis can be conducted using Google Earth and available historical imagery. See https://www.itreetools.org/resources/videos.php or visit the online application https://canopy.itreetools.org/index.php. See https://canopy.itreetools.org/index.php/how-to-use for guidancee on conducting change analysis.
i-Tree Eco v6 can be used internationally depending on country. Eco v6 has been adapted for Australia, Canada, the United Kingdom, many cities in Mexico and most European Union countries, based on local cooperator pollution and other data. The Eco model limitations when applied internationally are detailed in the Eco v6 International Guide. https://www.itreetools.org/resources/ma ... ojects.pdf. Application: https://www.itreetools.org/tools/i-tree-eco/i-tree-eco-international
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Support and documentation: 简体中文, 繁體中文, Español, Français, Deutsche, Italiano, 日本語, 한국어, Português. https://www.itreetools.org/support/resources-overview/i-tree-international/support-language
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International reports: https://www.itreetools.org/support/resources-overview/i-tree-international/reports-nation
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iTree workshops: https://www.itreetools.org/support/resources-overview/i-tree-workshops
The Climate Positive Design group in the United States offers extensive resources for detailed examination of carbon storage and climate implications to the level of evaluating material choices and maintenance regimes. The Pathfinder online calculator, https://climatepositivedesign.com/pathfinder/, guides the choice of materials at the site design level. See the Landscape Carbon Calculator Report linked here:
Maximizing the urban contribution
The urban contribution to carbon storage is small, so needs to be as effective as possible.
https://www.globalchange.gov/browse/indicators/terrestrial-carbon-storage. Structural and species richness increases ecosystem carbon storage (Liu et al. 2018).
There is little available guidance on the contribution of urban and suburban landscapes to carbon storage.
Non-forest contributions to stored carbon
Up to 50% of the carbon stored by trees is below ground as roots, and then there is the soil.
Carbon is held in soil as organic material and absorbed carbon dioxide. Two soil amendments can add significantly to the carbon storage capacity:
Biochar
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Pyrolysis, partial combustion, converts biomass to energy producing biochar as a by-product. Biochar can transfer 50% of carbon to inactive soil carbon pool.
Crushed rock
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A University of Sheffield study found that adding crushed silicate rock like basalt can act as a carbon sink. When fine rock grains dissolve chemically in the soil, carbon dioxide is absorbed and essential nutrients are released for plants.
