Safety of trees

Just thought I would query the collective knowledge of the community about the safety of tree skiing in regards to avalanches. There is a scenario I’d like to present where I can stand to learn more, so feel free to help me out. In higher avalanche danger, I often seek ski terrain in the "safety" of trees....

I understand about the danger of skiing trees located below runout zones. This is not what I am after. I understand about skiing trees with mixed glades, or trees near the edge of timberline or that are sparse or spread out. This is not what I’m asking about either. I understand in those scenarios, avalanches in tress do occur.

What I am asking about is forested terrain well below timberline, and not exposed to the mentioned above, where the entire run is enclosed under the canopy of forest. I’ve been told that any trees or other vegetation that provides enough anchors to prevent avalanches is "too tight to ski". With regards to that I have many places in my bucket list that I ski easily, yet in my mind think there is enough trees to prevent avalanches. Is this incorrect?

Let me help define what I mean, since I’ve never gone out and measured the distance between trees let me share a few pics.

I consider these “tight” but skiable… This is primarily what I am talking about: 1) http://v6.cache1.c.bigcache.googleapis.com/static.panoramio.com/photos/original/65137079.jpg?redirect_counter=2

then, I consider these a bit more open… 2)

And then what about burn areas… where understory vegetation while growing back is thinner? 3)

3 different stashes where I find no flagging or other evidence of avalanches.

Do you know the slope angle of the slopes in the photographs? Hard to tell sometimes.  Looks under 30 degrees, which if so in this case you are probably fine.

Your question is very subjective and there can be quite a few variables, however for me I avoid all terrain over 30 degrees in 'High' to 'Extreme' conditions.

Do you know the slope angle of the slopes in the photographs? Hard to tell sometimes.  Looks under 30 degrees....

  I just got an inclinometer late last season so only one of those pics I've actually measured. The last one #3 in the burn is under 30°... 25 to 28°.

the first one #1 is steeper by my judgement, probably closer to 35°. #2 ~30°

Your question is very subjective and there can be quite a few variables, however for me I avoid all terrain over 30 degrees in 'High' to 'Extreme' conditions.

this is true, I should say I'm not looking for a definite answer or rule like yes or no... to clarify I'll never say on any given day these places are always 100% safe. I'm looking more for observations from others, maybe someone has triggered a slide under a thick forest canopy, or maybe learn more about a relation between [tree] spacing and successful anchoring. maybe there is a relation between slope angle and spacing.... ie: for #2 i would not ski that on a 'high to extreme' condition if it was steeper. I've seen small surface slabs propagate and release in similar tree environments but steeper.... there is enough open space in photo #2 for a large slab.

From limited experience, snow tends to be less unstable in the trees. Lots of factors, including decreased wind action, snow-filtering by the branches, tree drip crusts, etc. may help. The improved anchoring probably doesn't hurt either. Skiing inbounds yesterday, the snow was cracking as much in very tight trees (~2' between trees, at times) as on open slopes. It all depends.

I suspect that your picture #1 will slide occasionally with the right loading and layering. I'll ski things that look like that on some days and not others (Probably wouldn't touch it today, for example. The underlying icy crust is present everywhere, including the trees.).

I think the key is whether or not the "treed" slope is canopied or not. Canopied means you can see little sky. #2 photo is not canopied and hence surface hoar can form. Open treed areas are "great" for surface hoar formation and maintenance.

For a canopied forest, I have only a few times released a slab. This was on steeper areas of forest above 35-40 degrees. The slides were soft slabs (with snow falling heavily at the time) and because of the forest released over a limited area. Forested areas are more often than not bumpy which makes a slope less planar for slab formation.

Canopied forests: 1) act as a reservoir for falling snow and then subsequently drop that snow as a stabilizing influence, 2) anchor the snowpack in localized areas, 3) restrict windflow, meaning windslab is unlikely.

I think the key is whether or not the "treed" slope is canopied or not. Canopied means you can see little sky. #2 photo is not canopied and hence surface hoar can form. Open treed areas are "great" for surface hoar formation and maintenance.

For a canopied forest, I have only a few times released a slab. This was on steeper areas of forest above 35-40 degrees. The slides were soft slabs (with snow falling heavily at the time) and because of the forest released over a limited area. Forested areas are more often than not bumpy which makes a slope less planar for slab formation.

Canopied forests: 1) act as a reservoir for falling snow and then subsequently drop that snow as a stabilizing influence, 2) anchor the snowpack in localized areas, 3) restrict windflow, meaning windslab is unlikely.

excellent input on how a canopy affects surface hoar. The tree environment I am primarily interested in is a canopied forest. #1 photo is such a condition, those trees are tight and under a heavy canopy. I'd like to hear more input on this environment because much of the terrain in my home court is heavily forested canopy.

But not withstanding photos 2 and 3..... in regards to the #3 "burn" photo, I think the heavily treed (albeit burnt dead trees) should not distract from the danger of a complete lack of canopy. Thanks for sharing how the canopy affects stability, when I was focusing on other elements of the study like spacing.... hence my comment on the burn photo.