FEATURED PROFESSIONAL: Dan Miller, Ph.D, Precision Forestry LLC
For many forest owners, their forests are an investment and a good return is desired. Many of these forests are regenerated naturally using the seedlings and saplings that remain after harvests. This regeneration may not be as free as it seems if these future crop trees are not growing rapidly from the start. The key to rapid growth is vigor. Leaving green trees with poor vigor can create the appearance of a well stocked and healthy forest but can significantly delay the development of the young forest. Low vigor trees that have been suppressed by the shade of overstory trees or by competition in overly dense stands have become adapted to growing under those conditions. Once tree growth slows and stabilizes at a reduced rate, it takes years, and sometimes decades, for them to recover. This delay adds years to the rotation length and reduces the financial returns. Green isn’t always good, and the key to managing a successful natural regeneration program lies in being able to recognize and evaluate tree vigor. The following indicators can be used to evaluate tree vigor.
The best indicator of tree vigor is the amount of foliage or live branches on the tree. This is best expressed as the percent of total tree height occupied by a full complement of live branches (the crown). Foresters call this percentage the live crown ratio (LCR). Trees with 40% or more of their total height with this full complement of live branches are currently growing well or have the potential to resume rapid growth relatively quickly. Trees with smaller crowns may require many years to resume rapid growth. Some species such as western redcedar may never recover from suppressed conditions.
Annual height growth (new top growth above the highest branches) of six to eight inches on trees over three feet tall is also a good indicator of tree vigor. Trees with poor vigor grow only a few inches every year.
Diameter growth is directly related to the amount of foliage on the tree and is a good indicator of vigor and growth potential. Diameter growth is difficult to assess visually but the width of the most recent growth rings should exceed 1/8 inch.
Trees damaged by logging with broken tops, large bark scrapes, or with many branches broken off are not good trees to leave for future crop trees. Breaks and scrapes allow decay to develop which will reduce the future value of the tree. These trees may be well suited for wildlife trees however.
Selecting and saving high vigor regeneration or replacing poor vigor trees by planting seedlings is the best way to insure that your future forest will be both productive and healthy.