Foresters have traditionally used total tree height at a fixed index age to classify the forest productivity at any given location (soil, topography and climate). While useful in the 1930 – 1980 years, researchers such as Boris Zeide (1978) recognized that all trees of a species do not follow a single growth form (by site class) throughout their development.
The 10-meter site index methodology breaks tree growth down into three phases – micro-site effects, macro-site effects and local limiting factors (soil, climate, length of growing season).
The label “10mSite Index” is the name of this approach. It may be universally applied and is unique to the Forest Biometrics Research Institute. 10mSite Index classifies “rates of growth”, not “achieved height” as its basis for productivity measurement.
Phase I – The primary factor in early tree height growth is micro-site influence. Macro-site is secondary until trees achieve at least 20 feet (6 meters) in height with a full crown and root system.
Phase II – Macro-site (soils, climate, growing season days) becomes the primary factor above 10 meters in height (33-feet). Noticeable declines in the rate of height growth are not measureable until the tree has achieved heights above 20 meters (67-feet).
Phase III – Height growth rates between 20 to 30 meters in height begin to respond to the most limiting macro-site factor at that geographic location.
To observe 10mSite, count the number of annual rings at the bottom and top of the second 32-foot commercial log in a tree. Take the difference in ring counts to obtain the number of years to grow 10 meters in height. Divide 100 by this difference to calculate meters per decade as in the previous table.
This determination of site capacity may be exercised by anyone at anytime without tables, equations or lookup charts. It is universal.
Zeide, Boris. 1978. Standardization of Growth Curves. Journal of Forestry 76(5):289-292.