10-20-30 Rule for Diversity
While we don’t currently offer tree planting, we do often come across various issues correlating to tree decline, such as pests, fungi, poor soil conditions, etc - that could, at the very least, be lessened by following the guidelines laid out in the 10-20-30 rule. The 10-20-30 rule is a ‘rule of thumb’ suggested by Dr. Santamour, for planting trees. Stating that urban & municipal forests should comprise no more than:
10% of any particular species
20% of any one genus
30% of any single family
For example, from the Wisconsin DNR webpage:
30% Family: Sapindaceae (soapberry) - Includes maples, horse chestnuts, buckeyes, etc.
The total of all horse chestnuts, buckeye and maple should not make up more than 30% of the community’s tree canopy.
20% Genus: Acer (maple) - Includes sugar maple, silver maple, red maple, box elder, Norway maple,mayabi maple, Japanese maple etc.
The total of all maples together should not exceed 20% of a community’s tree canopy.
10% Species: platanoides (Norway maple) Includes - Deborah, Schwedler, Crimson king, Emerald queen, columnar, etc. these are all Norway maples. Generally speaking, if something has a proper name like Deborah or a flashy name like Autumn Blaze or Exclamation you are looking at a specific cultivar of a species.
Some commonly known instances of widespread tree loss that could have been reduced if more diversity had been present are:
Dutch Elm Disease, first recorded in Minnesota in 1961 and became a widespread issue in the region throughout the 70s and 80s. The disease was so prevalent that some companies focused most of their work following the progression and spread of the disease and necessary removals
Emerald Ash Bore, first recorded in Minnesota in 2009 has been making its way further and further out. Now affecting 48 counties in Minnesota and causing substantial loss of ash trees.
A few key reasons to follow diversity guidelines are:
- Cultivars & varieties within a genus are often susceptible to the same pests
- Some species are more vulnerable and prone to abiotic features such as storm climate damage. Planting a variety of species can reduce the risk that all trees will be severely damaged by harsh weather or other conditions
- Diverse vegetation adds interest to urban settings
- We can help diversify habitats and enrich our surroundings with a greater variety of wildlife
“A greater focus on diversification of a community’s trees should be a goal of every tree board and urban forestry department.”
- Tree City USA Bulletin No. 94 Arbor Day Foundation
https://www.arborday.org/trees/bulletins/coordinators/resources/pdfs/094.pdf
