As you might expect, our highest-scoring Landmark Tree stands are on the central and southern Tongass. But we’ve measured 10 sites within Áak’w & T’aakú Aaní, land of Auk & Taku people: ie, the CBJ. One, on Ch’eet’ Taayí, murrelet fat (Cowee Creek), ranks 31st of 71 Tongass stands; others rank 52 through 71, in the bottom quarter of the pool. Northeast of the blue line on the map on right, most alluvial Landmark Tree (LT) forests have tall but relatively young trees. Stands are almost pure spruce, with dominants roughly the same age. Where the Little Ice Age was most pronounced, increased flood frequency and severity apparently removed the all-aged alluvial stands with stronger hemlock/blueberry component that we find more commonly to the south.
Although I can speculate about this glacio-alluvial disturbance and its relationship to the northern large-tree forest, nobody has studied it quantitatively. It would be challenging, in spite of new technologies such as LiDAR that accelerate our cartographic capabilities into unimaginable new realms. For example, it still takes a long time to core a tree to determine age. And we can’t reach center of the very large trees on alluvium with even the longest increment borers.
In March, 2011, five of us hiked into the Héen Latinee Experimental Forest to revisit our highest-scoring LT acre in Áak’w & T’aakú Aaní—that largest yellow circle in CBJ portion of the map on right. I brought both of my increment borers. One is a standard-length 18 incher, and the other is the ‘big gun,’ a 24 incher, rarely used because it’s much harder to turn.
This forest feels even-aged to me. There are no hemlocks and not even many small spruces—essentially no subcanopy. So on the assumption that all biggest trees germinated within a few decades of each other after some megaflood, we searched for the most practical candidate. To maximize our odds of getting close to pith, we selected a codominant 5-footer that lacked strong root flare. Because the long borer is so hard to turn, we went in first with my 18-incher, drilling from the ‘upside’ of the slight lean, for even less distance to pith. After extracting the 18 inch sample, we went back in with the 24-incher.
In the mounted core below, ring width decreases smoothly throughout the tree’s life, as expected in a crown codominant that was never suppressed beneath taller trees. Because center rings were large, our error in estimating date of germination is probably small.
As John Caouette concluded from his coring here in 1997, it looks as though this magnificent forest is just a “teenager,” in tree years. A germination date of about 1830 is consistent with my assumption that the more active parts of the confluence fan were “set back to zero” at the peak of the Little Ice Age (~mid-1700s). By the early 1800s, things had stabilized enough for spruces to colonize. Slightly higher elevationally on the fan, trees are probably older. But I’d be surprised if even the biggest are much more than 300 years old.
Rick Edwards, lead scientist at the Héen Latinee Experimental Forest, tells me there are plans (late 2018) to map an alluvial forest on Ch’eet’ Taayí, murrelet fat (Cowee Creek). Thanks to LiDAR, this will be a much larger plot than is traditionally done from ground-based stem mapping. Combined with hands-on measurements (diameters still can’t be determined remotely), and some strategic tree-coring, perhaps this will shed some light on the evolution of glacially-influenced northern alluvial large-tree forests.
My Landmark Trees page has examples of the use of LiDAR in search of the giant-tree forest. There’s also a lot of examples in vimeo slideshows I’ve archived on subjects ranging from wetland delineation to restoration assessment to post-glacial succession. I won’t repeat that tech-talk here. As for what we’ve learned, my big light bulb moment was realizing that—at least in Áak’w & T’aakú Aaní—much taller and older trees are on steep, lee-side colluvial fans than on the riverbottom alluvium that was my search-image for the 10 years of the Landmark Trees Project.