trees shading calculation

The LEED BD+C v4 Reference Guide Table 3. Nonroof strategies states: "Assume 10-year canopy width at noon (i.e., in plan view, plant canopy width has no extending shadows, regardless of time of year)." Hope this helps.

How does one calculate a tree's total spread when species all grow at different rates - and reach maturity at different ages? Most resources (USDA, nurseries, land grant university extension offices) provide spread at maturity, growth rate per year, or a broad growth rate classification.

I suppose the logic behind using a 10-year canopy size is understandable given the lengthy lifespan of most trees - but taking a shot at interpolating tree growth seems like an inaccurate, arbitrary calculation.

Has anyone uncovered a particularly useful resource for this non-roof measure?

I have been advised by GBCI on past projects that determination of 10-year canopy size based on soil conditions, climate, and species by a landscape professional would be a sufficient resource. Assume 10-year canopy width at noon (i.e., in plan view, plant canopy width has no extending shadows, regardless of time of year) for v4 projects.

I've ranted about this on another post.  LEED 2009 used to require an average shading area based on 10am, 12 noon, and 3pm on summer solstice. I would suggest that Equinox is a more appropriate condition to analyze (since it represents the annual average solar elevation), but I am confused and frustrated by the fact that they have removed site-specific analysis (and basic science) from this credit.  Instead, v4 assumes that all projects are in the tropics and actually have overhead sun.  To make matters worse, they label this condition "noon," which is an insult to our intelligence on several accounts.  If anyone has any idea why the solar study component was removed from this credit, I'd like to hear it.  Otherwise, I will continue to grieve for the loss of natural, site-based design and scientific literacy.
 

Lyle: here's a live link (says "proposal" but it's broader than that):

Call for Proposal | U.S. Green Building Council (usgbc.org)

"Proposals must meet the following criteria in order to be evaluated by USGBC and LEED Committees:

• Proposals shall be expressed in terms of actual edits to existing LEED language using tools provided by USGBC.
• Proposals for change must be specific.
• The rationale and technical justification for each proposal for change must be provided and must be technical in nature.

Multiple proposals for change from the same person/organization for each LEED credit are permitted."