100KTrees — Selecting Trees
Many trees live 50 to 100 years, therefore, your urban tree planting program needs to be mindful of biodiversity and replanting native species, along with trends in the local climate which will become more pronounced in the coming decades. In How to Start, we described starting a Tree Board, then recommended pulling adding to the initial Tree Board an Arborist, Forester, Scientist and a Master Gardener.
Each of these experts is likely to have favorite trees to recommend, and the discussions between them are likely to be engaging and fruitful. The goal is to select several species which will be able to tolerate changes in temperature and rainfall throughout their lives.
At 100KTrees for Humanity, our goal is to plant one additional tree per person in the community. We have found the best mix is typically predominantly native species, with about 25% to 30% tree species identified as heartier, faster growing, climate-ready and suitable for common planting locations.
Your area’s local and regional experts can compile a list, but your city is likely to already have recommendation or approved species list. Diversity, tree size, and ongoing care are critical components for planning — you want to plant trees that will survive.
Much has been written on tree selection, but Biomass, Carbon Sequestration, and Avoided Emissions: Assessing the Role of Urban Trees in California is a place to start. This report was prepared for CalFire’s Urban and Community Forestry Program, and compares many places in California and was provided by researchers at University of California at Davis.
Another resource, from The Nature Conservatory, is Climate Ready Trees: Tree Species Selection Guidelines for the Albuquerque Metro Area, which details a process of species selection, in New Mexico.
We recommend reviewing your list of tree species from multiple perspectives:
Combating climate change by sequestering carbon (CO2),
Tree canopy to reducing energy use with shade.
Rainfall interception, reducing flood risk, water pollution and extreme weather events,
Air pollution and air-borne particulates,
Debris, leaf litter, and fruit,
The impact on property values, with curb appeal and neighborhood charm,
City maintenance and required pruning, and
Water needs. (Most trees require more water while becoming established, and less when mature.)
Tree survival, if the climate changes faster than expected,
Noise reduction, and reduction in stress leading to improved quality of life.
Needless to say, it is impossible to write an article from one location and offer specific advice to readers around the world. Your tree board needs to develop a local selection list with a rationale for the species mix. From the Biomass and Carbon Sequestration article above, a flowchart to assist thinking through the issues.
In arid areas, which historically haven’t supported a large number of trees, consider combining shrubs and succulents, with a small number of trees. This can be combined with solar panels for shade, which farmers call agrivoltaics. Farmers are using these tools to moderate the impact of increased heat. Many parking lots also use solar panels to reduce heat. Urban planners should think of solar panels as a source of shade, which can help young urban trees and other plants.
For areas which are experiencing desertification and would like to fight this trend, there are insights to be gained from the efforts by China. (China is 27% desert and has been working with regenerative agriculture for decades.)
Of course, the earlier Great Wall of Trees, with over 200 million trees planted in one decade, was an depression era project in the American Midwest:
FDR’s Great Wall of Trees and the Inflation Reduction Act of 2022
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One of the keys to the success of keeping trees alive is the biodiversity of the soil microbes. Trees, more than most other types of plants, need a diverse community of fungi. Some of these fungi have been shown to break down petrochemicals and other pollutants.
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Why does SymSoil care? We focus on solutions to environmental issues, with a focus on soil biology. Trees and plants feed, and are fed by, the soil microbiome. Healthy soil influences water, carbon sequestration and human health. SymSoil holds a patent on the first scalable approach to manufacturing Soil Food Web products as an alternative to agrochemicals.
SymSoil is a supporter of 100KTrees4Humanity, an urban tree planting project focused on action that moves us towards solutions to climate change with equity and inclusion.