We often hear that the poor state of health of much of our forest area is due to the exclusion of wildfire as a result of the aggressive fire control policy of forest managers in recent decades. Blame it on Smokey Bear?
There seems to be recognition of the fact that much of our forest area is overstocked — just plain too thick. This means too many trees and overpopulation, which is not healthy. In more technical terms (hey, especially our students young and not so young, let’s not be afraid of technology!), stocking, which essentially is total biomass of the forest stand, can be expressed in terms of the combination of basal area (tree trunk cross-section area in square feet per acre) and stand density (number of trees per acre). This provides a basis for stand modeling, in which growth can be related to stocking level. Both understocked and overstocked stands tend to grow slowly under similar site conditions (mainly soil quality). There is a happy medium, like Goldilocks – not too much, not too little.
Growth is healthy. It is slow in overstocked stands as trees under severe competition try to survive. Growth and vigor go together. Growth, especially in diameter, is an indication of health. As stocking increases toward a theoretical maximum level, growth decreases and net stand growth approaches zero — stagnation. The forest as a whole becomes more unhealthy and prone to insects and disease, which cause increased mortality, which, in turn, increases the dry fuel load, resulting in greater susceptibility to wildfire. The eventual outcome is the destruction of the stand by natural or human-caused fire. The term “destruction” is not really adequate in that in nature’s scheme of things, it’s only a temporary setback, a sort of “restart” button that triggers the healing process of ecological succession.
Overstocked forest stands are unhealthy due to excessive competition for site resources, mainly moisture as the limiting factor in our dry climate. How do forests get to be too thick? They grow! More trees are born (regeneration) and they grow thicker in diameter, which is reflected in basal area. If there is not enough natural thinning, at a certain point (a natural threshold), trees become weakened and susceptible to insect infestation, such as bark beetle and spruce beetle and disease.
Is this mainly due to the exclusion of fire? What about forest types like mixed conifers, mostly spruce-fir, which generally don’t live with fire (see article in the Oct. 27, 2016, edition)?
The exclusion or minimization of wildfire through fire suppression does affect forest health, but mainly in forest types like ponderosa pine, which have evolved with fire. Is the lack of proactive extractive forest management practices, such as timber harvesting and thinning, a factor, which is rarely mentioned for some reason? It seems that the “logging is bad” type of thinking prevails, a bias that impedes effective reasoning.
We’ve completed another year and 12 articles of ideas and reflections, hopefully toward achieving a better understanding of how forests work in nature and how they respond to treatment. Happy holidays. May 2017 bring happiness and satisfaction to all.
This is article 153 in the Taos News Natural Resources Notebook. Articles one to 99 are in “Forest Power: Adventures in Ecology and Forest Management.” Others are available online. Contact firstname.lastname@example.org for more information.