A New FBRI Enterprise Service:

Estimation of Site Index Using Repeat Lidar Data

Just imagine if you could estimate the site index of a tree without extracting an increment core to determine its age or using a rangefinder/relascope to measure its height.  Well, if you have repeat lidar measurements from two flights spaced 6 to 10 years apart (or more!), then it’s possible to calculate the site index of a tree using a new and innovative procedure developed by FBRI.  The key is that the lidar data from both flights must be good enough to accurately determine the height of individual dominant and codominant trees at both points in time.  Using repeat lidar data of that quality, we developed a program that calculates site index from two height measurements on the same tree spaced 6 to 10 (or more) years apart.  Potentially, site index can be computed for millions of trees for a forest ownership if suitable repeat lidar data are available.  Additionally, the program estimates physiological breast height age for every tree at both points in time.

To utilize FBRI’s procedure an organization must:

  1. Possess repeat lidar data at least six years apart, and
  2. Estimate the required heights of dominant trees for both flights.

These are not trivial tasks, but we know several FBRI member organizations that have repeat lidar data and are developing analysis procedures to estimate the tree heights of individual trees at both points in time.  Once an organization has estimated the heights, these data are uploaded to a secure FBRI ShareFile folder in a CSV file containing up to 1 million tree records.

How does the FBRI program work?  Conceptually it simply finds the site index curve that intersects the two heights of a tree in the same number of years that separate the lidar flights.  (See Figures A, B, and C below.)  The site index equation to be used depends on the species.  To date we have tested King’s site index for Coast Douglas-fir, Monserud’s site index for Inland Douglas-fir, and Cochran’s site index for white fir or grand fir east of the Cascades.  The FBRI program can be applied to any species in the world for which there is a suitable site index equation such as King’s, Monserud’s, or Cochran’s.

Not only does the procedure result in an accurate estimate of site index for the tree, but it also provides estimates of the tree’s breast height age at the time of each flight.  The estimated ages can be thought of as physiological ages that are based on the height and height growth of a tree rather than counting rings at breast height.  It is likely to be a much better indicator of site productivity than traditional site index estimates based on data obtained from a timber cruise.

Figure A.  To estimate the site index of a tree using repeat lidar data, data are needed from two flights spaced 6 to 10 years apart (or more!).  In this example, the first estimated height of a grand fir tree is based on data from the 1st flight.  The second estimated height for the same tree is based on data from a 2nd flight which occurred six years later. 


Figure B.  The FBRI program determines the site index curve that touches the tip of the tree (defined by the tree’s height measurements) at both points in time.  Not only does the program provide an excellent estimate of the site index for the tree, but it also provides an estimate of the     physiological breast height age of the tree at the time of each lidar flight.  Cochran’s site index equation was used because the subject tree in this example is a grand fir. 


Figure C.  The repeat lidar data in Figure B displayed in relation to the fitted site index curve for the tree.  


The potential of this technology is huge, and the quality is unprecedented.  It is now possible to develop site productivity maps for an ownership at a fraction of the traditional cost based on measuring site trees in the field.  Site productivity for a forest ownership will be based on millions of trees rather than thousands.  Most importantly, growth & yield metrics from models will be vastly improved given the resolution and accuracy of these lidar-based site index estimates.

If you are interested in this new Enterprise Service offered by FBRI, please contact Dan Opalach using the form below or (971) 940-2409 for more information on program details, turnaround time, and costs.  An organization does not have to be an FBRI member to take advantage of this technology.