Exposing codominant Doug Firs. Advice?

[davepell]

Howdy all,

I'm looking for advice on actions needed when construction will expose several large codominant douglas firs to wind.

I've heard the term idiot strips applied to narrow strips of codominant trees being left by planners. That's essentially what I'll be looking at in the near future.

Thanks,
Dave

 

[southsoundtree]

Seems like either remove and replace being one option.

Or

Cable and brace.

How large are they? If large, then co-dominant remnant trees sound like extra hazards that should be basal pruned.

Will there be tree protection measures to protect the critical root zones?

Geographically speaking, where are they located?

What is the general health?

Will they be ripping out the adjacent trees' stumps?

Grade changes?

Sudden high intensity sun to the ground and thinner bark (sunscald possibility)?

Is this a case of the trees have to stay, or is removal and replacement an option?

 

[Gord]

Do you mean the trees have multiple tops or that there are several large trees of similar size? In either case, you'll have to assess each tree individually.
In some cases tall firs with short crowns are more or less a lost cause in terms of preservation after the removal of neighbor trees.
For the trees that have a substantial healthy crown thinning (concentrating the pruning on the top third or so of the canopy) may be an option, as well as lightly heading back some of the lower heavier limbs. You must be careful not to overprune and induce the remaining limbs to bush out, increasing the likelihood they'll break.
In many 'idiot strips' the best option is to remove all the tallest trees, leaving as many short/medium and healthy trees as possible which will come to provide whatever the landowner is seeking (privacy, green space, shade etc.) Also if the nearby construction is going to affect the drainage/available water etc. enough to seriously stress the health of these trees, is it a gamble to spend money on windfirming?
Douglas-firs show a tremendous amount of variability, and obviously you'll have to look at the trees in question in context of the site: prevailing winds, soil types and levels of saturation, root disease locally etc.

 

[John_Paul_Sanborn]

Also use Matthecks failure ratio, he has statistically shown that a diameter above flair:height of 1:50 is a critical threshold; 1:30 seems to be nominal. This is a mixed species assessment, he had numbers for European species several years ago.

I think it is Gary Johnson who did a lot of storm failure stat's here in the US and showed the lost cause Gord talks of. Large spruce/fir that predate construction have a very high tendency for wind throw years after the stand was disturbed. He saw several main causal variables, such as insufficient anchoring root system and rootplates compromised by construction.

I have heard that spiral pruning and "wind-firming" are supposed to reduce this risk, but we need to make a hazard assessment in these situations when we say "it might work". ill the spiral pruning reduce the pressure-of-height enough to take away the leverage on the rootplate when there is a supersaturated soil condition?

Can we say that there is a very low probability of catastrophic property damage or injury/death if the trees remain?

Is this a situation where topping in manner that that simulates storm related stem failure would be more desirable then complete removal? Will the owners stick to a maintenance plant that will mange the risk that our profession is concerned with vis. topping? (I've actually heard of companies pricing it into cost of the topping, a ten year management plan for future maint. paid up front.)

As professionals we need to let our clients know all the variables so they can make the discussions.

 

[davepell]

Howdy again,

Thanks for the response.

These are several large doug firs of similar size on site.
The location is Portland, Oregon. This is on a fairly steep slope. No work yet on if the stumps will be ripped out or left. Their will be a Tree Protection Zone for the roots.
I'm recommending removal and replacement. This is a government property. Their is a good chance of property or people being injured if they remain.

Dave