Life of a Snag 

A snag is a dead tree that is still standing. Snags come in all sizes and occur in all species. The Douglas Fir snag is of particular interest as it is the tree that occupies the majority of the timbered regions in western Oregon.  

BY Melvin Thornton | Communities For Healthy Forests | 9/16/2022

The changes of a snag vary depending on the size of the tree. The larger the tree, the slower the process. No matter the size, every dead tree is in the process of breaking down and eventually falling – or burning in future fires. Whether standing or on the ground, snags become part of the fuel regime that carries fires throughout the forest if not removed in some manner.  

The following descriptions roughly describe the phases – or lifespan of a large old growth snag in western Oregon.   

Year 1: Death occurs – Fire or disease kills the tree. This may happen quickly or occur over a few years depending on the root cause and health of the tree. Unless burned in a crown fire, generally it is most notable that the needles turn red. A crown fire will burn all the needles and leave the tree with few if any needles. 

(Surrounding Fuel) – Light – Generally, if a forest fire occurs, ground fuel is reduced to minimal loading and is generally not a fire hazard of significance. 

Year 1-5: The snag continues to deteriorate. Remaining needles fall to the ground. Small limbs (less than .5 inches in diameter) also begin to fall off. But overall, assuming the tree had solid wood and little rot, it is still a solid tree. If the tree was dying from old age and contained rotten spots in the snag, it could fall at any time. This is why snags are extremely dangerous to visitors to the forest, or firefighters during a fire. A tree that was decaying prior to the event that caused it to die – such as fire – could vary considerably from this timeline and fall at any time. In addition to the danger it presents to people on the ground, after a snag falls, it becomes part of the fuel-load buildup starting on the forest floor.  

(Surrounding Fuel) – Light – Sometimes following fires, the landowner or manager of the land may opt to seed grasses on the fire area to help minimize soil erosion. This grass will then be present for the next several years – or until new trees/brush crowd out the grass. This grass burns quickly when it is dry and cured, and becomes part of the surrounding fuel load if a fire should occur. However, because most of the snags are still standing and have not yet decayed, fires are generally easier to control in this fuel type. 

Year 6-10: Snags continue to decay, larger limbs continue to fall to the ground from wind and snow, adding to the fuel buildup on the forest floor. Weaker trees start falling during weather events. In a fire, the snags would be very dangerous to firefighters.  

(Surrounding Fuel) – Medium – Brush and other trees become more entrenched on the forest floor. Depending on seed availability after a fire, this may include conifer trees and other brushes. Limbs falling from the snag continue to add to fuels on the forest floor. Snags are good lightning rods, and because of the dry fuel in the snag, they are frequently where lightning fires start. A large number of snags inhibit fire control. Depending on the terrain, snag patches make it impossible for firefighters to safely make an initial attack, or to take fire control actions. Because snags are a major cause of fatalities and injuries to firefighters, crews must mitigate the risk of being struck by a dead, dry, flammable snag. 

Year 11-20: Many snags become very unstable. Their root systems have rotted. They can fall without notice in a fire or windstorm. Depending on the terrain, when 100-foot plus tall snags fall, they can travel considerable distances downhill endangering firefighters, hikers, and even roads. At this time, the snags are simply ready to fall with any disturbance.   

(Surrounding Fuel) – Heavy – By this time the surrounding vegetation has grown considerably. Brush reaching 15-20 feet high in some cases. Some snags have already fallen due to decay and the forest floor now has a heavy loading of dead, burnable fuel that ignites easily during the summer months. This is the period where many large fires in western Oregon have occurred. Each one hotter and larger than the one before it.  

The history of wildfire in the state of Oregon is filled with examples of forests that have burned multiple times in a short period of time. One of the hardest hit areas of reburn is in the Kalmiopsis Wilderness area in southern Oregon which has hosted numerous fires that have reburned larger and hotter in each successive fire: 

  1. Silver Fire in 1987 – 110,000 acres 
  1. Biscuit Fire in 2002 – 490,960 acres 
  1. Chetco Bar Fire 2017 – 190,000 acres 

Salvage operations would remove dead standing timber and replace it with seedlings that would outcompete brush and return the area to beneficial habitat that would be more resistant to low-intensity fire. 

Communities for Healthy Forests advocates for change in forestry management practices in our public forests to protect the resources of habitat, timber, and recreation opportunities they were meant to provide. 

Melvin Thornton is the former district manager of the Douglas Forest Protective Association (2000- 

2017). He is an active member of Communities for Healthy Forests.