We have a dilemma and would appreciate your advice.
We have a 60 foot Ponderosa pine that died from bark beetles. We want to eliminate the fire and tree falling hazards but the tree has served as a pole for my ham radio antenna. I would like to keep 50 feet of the tree trunk standing in place for the antenna and have the limbs and some of the top removed to reduce the fire and falling hazards. A tree service suggested that the trunk would “last” about 15 years.
What are your thoughts on leaving the shortened trunk in place?
I am generally in favor or taking down dead trees on home grounds unless they are valued for habitat (or in your case, an unusual service the tree provides) and the likelihood of impacting a target is improbable.
In terms of formal Risk Assessment, moderate, high or extreme risks should be mitigated to “low,” but the decision is up to the owner, not the arborist.
1. The likelihood of tree failure in a given time frame;
2. The likelihood of impact on a “target;”
3. The potential consequences of the impact.
Using the current Tree Risk Assessment system, we use a matrix presented in two tables in our guidebook. Here is an abbreviated look at the process:
— Likelihood of failure in a given time frame: Is it imminent? Probable? Possible? Improbable? Choose one.
— If it is improbable, the risk rating is low, regardless of target and consequences of failure.
— If it is possible, the risk rating will be low or moderate, depending on the severity of the possible consequences.
— If it is probable, the risk ranges from low (if there is no target or the impact on a target would be negligible), to high risk if there is a target and the impact would have severe consequences.
— If it is imminent, the risk rating ranges from low to extreme, depending on the consequences of impact on the target.
See? It is largely about the target: what or who is at risk, and the severity of the consequences.
As you explained your plan, I think the likelihood of failure in the time frame of one year would be improbable, therefore low-risk no matter what or who is within falling distance.
But it is iffy to assess the stability of a dead (or living!) trunk and buttress roots. Decay may be present on the undersides of the trunk butt and buttress roots.
Decay may be actively progressing and will certainly progress over time, but nobody can say with certainty how long it will take.
Decay in conifers, typically brown rot, turns the inner wood into crumbly bits. The trunk or roots might fail unexpectedly.
If the remaining section of trunk were to be guyed like radio antennae generally are, it would probably buy some time but the tree could fail unexpectedly, creating an awkward situation where removal would be very dangerous.
That estimate of 15 years is possible. Based on that, the risk would be moderate or low, depending on the severity of consequences.
But I do not recommend a time frame of 15 years. I usually make it one year or maybe up to five years.
I suggest you:
1. Assess the structural stability of the dead tree as best you can.
2. Have a plan for removing the remaining trunk when it is no longer reliable for a tree worker to climb and take down in sections. (Fell the whole thing with the antenna still on it? Take down with a crane?)
3. If it shows no evidence of decay, and potential targets do not include structures, people or vehicles frequently present go ahead and top it and remove the branches, and keep the antenna on it.
4. Do not guy cable it.
5. Assess condition for evidence of decay every year. That is a job best left to a qualified arborist.
6. Be prepared to call it before it is ready to fall over. That cut-off point is going to be as much a hunch as a factual analysis.
Strength loss evaluation in trees is fraught with uncertainties.
I would be far more comfortable with just taking it down now and finding another tree.