1. Can it handle the summer droughts down here.
2. How fast does it grow.
3. Can it be coppiced.
4. Does it spread and how does it grow in general in the lowlands.
I just wanted to update a few of my own observations over the last year.
My property, and particularly the mountain that extends North beyond my property, has sitka alder growing naturally on it. It tends to grow most often on open semi disturbed steeper slopes, but is not at all confined to slopes or open ground. I have seen it growing amongst 100-year-old trees on flatter land, but generally, this is rare, and most often, when it does occur, the spacing of the larger trees is wide enough to allow space for sunlight. But it should be noted in relation to this that I am at 53 N latitude and The Pacific Northwest (Washington) has a considerably longer growing season, sun cycle, climate. We do have intense long summer days that try to make up for the shorter season. My climate though interior based has a strong west-coastal influence because of the Rocky Mountains that begin in the back yard, but is definitetly much more of a prime location for Sitka Alder than the Pacific North West.
a specific population of Sitka Alder they found growing at ~200ft elevation in the Columbia River Gorge.
Sitka Alder also grows in disturbed ground on the North Coast of B.C (I grew up in the Skeena watershed of the Coast Mountains)., but is generally confined to slide zones; all other disturbed locals are dominated by Red Alder rather than Sitka Alder. This far in the interior, where I presently live, there are no red alder.
This last summer, the local road crew finally brushed my ditch down, after about 7 years of growth. The ditch species list was mainly comprised of various species of willows, with some birch, red dogwood, and sitka alders. All of these managed to regrow from brutally smashed stumps in the previous brushing. This creates a dense shrubby ditch 'hedge' that actually bows out over into the roadway and is about 20 feet tall. I will try to update in this thread as I watch the regrowth, although they are harder to identify when they are small and the bush comes in dense, I can do so from leaf shape if I take the time.
I am building a trail up the mountain from my place. The growth pattern of various shrubs as the lower to middle elevation is probably the most difficult aspect of the project. Sitka Alder, and false azalea (menziesia feruginea) are the most common, but Douglas maples are also common. All of these grow in an explosion of stems, spilling outward like a fountain (which makes me think that coppicing will not be a problem for any of them **). The azalea is a many-stemmed (like maybe50 to 100) beast that is tricky to plan a trail through or near. They, particularly, grow also in dense colonies, making them further challenging to deal with. The alders and the maples however are generally confined to less than 10 stems, and often only 6 or 7. The stems of the alders tend to bow down with snow loads, whereas the maples tend to stand tall in spite of the snow. They are stronger in this regard. What I have been doing is building the trail on the high side of alder clusters (which also happens to be the North side) with the idea that if I do have to cut them to enable walking space on the trail, that the shrub will be allowed to spring it's growth up on all other sides where the stems still exist. Although I suspect they will also be sprouting up some new fresh first year growth near the stem base that was cut, I think that (hope that) it channels the vast majority of it's energy into the existing larger stems which are bowed away from the trail; I think that this may be aided by the fact that the exisitng stems will be facing South, SW or SE.
My thinking (from my observations), is that S Alder will take well to coppicing, but that the plants need a chance to get established first. As I mentioned earlier in this thread, the alders get smashed down and sometimes buried in avalanches and debris flows/rock slides and recover prolifically. These alders are small trees, with the longest stems maybe reaching 25 feet. Red Alders on the coast are a much larger tree and tend to have vertical, rather than sprawling growth.
Apparently it also has moderate shade tolerance unlike Alnus rubra.
When I lived on Haida Gwaii (previously known as the Queen Charlotte Islands), I did see red alder growing in heavily shaded old growth cedar/hemlock/spruce forests. In this case, I think it is likely that the seeds germinated after one of the larger specimines tipped over, which not only exposed bare soil at the root mass but also opened up sunlight temporarily. Over a relatively short time the over arching canopy from the dominant species closes the main sun out again, but not before the alder gets going. In the end, the alder tends to be a shrub with an apple tree-like shape, not the 50-foot tall tree that it can become in the open. It is indeed true that Sitka Alder is more likely to grow in the shade than red alder, but it is probably truer to indicate that all alders tend to enjoy/prefer growing in open-ground, and that shade tolerance exists more so with the Sitka variety. Just trying to clarify what's rattling around in my head from observations over the years.
As for maples: they tend to have the same sprawling nature, but as I mentioned, tend to be more vertical. I think that once established they would take well to being coppiced down for regrowth. I have heard, but I have not seen the practice that local people around who have selectively left one large most vertical stem out of the cluster growth of Douglas Maples that are otherwise heavily prunned of shoots every year in order to have one much larger stem to tap for maple syrup production. The roots might compete with your fruit trees for space and thus I would limit there proximity to crop trees. I would consider, in the minimum, that if maples are to be used, that Alders be placed between them and the fruit trees, and that all of these support species be considered potentially (but not necessarily) as temporary support that will eventually be chopped out. Maple are harder wood than alders and might lend themselves well or better to rocket fuel.
**From my understanding: Coppicing is done at specific times of the year. Generally it is done either in really early spring, or mid-to-late fall. This is so that winter moisture can be put to advantage in the regrowth/recovery strategy. Some climates would place the ideal time as just before the rainy season. Coppicing at the wrong time of the year can have a detrimental effect on the plant's ability to recover from the damage, and thus limit the potential of the coppicing being worth while.
I have several infrastructure projects on the go this year, but if I can allow the time (plan), I will go to the logging roads on the other side of mythe Upper Fraser) valley on the Caribou Mountains side, and gather young Sitka Alder for transplanting in my orchard and future planting zones. These may require a few waterings to get properly transplant established, but it would be very worth the effort. Once established I can not see a reason why they would not flourish and be very useful for biochar, biomass, rocket fuel and other purposes.