Steep places Archives | JuneauNature

Goaty places: The unviewed viewshed of Lingít Aaní

In winter 2020-21, I became interested in the geology and ecology of steep slopes—neither lowland nor highcountry—that dominate viewsheds of most Southeast Alaskan residents. Oddly, I hadn’t much focused on these precipitous habitats—and I’m not sure anyone else has either, except for a few grouse hunters and avalanche researchers. Partly, it’s rational avoidance. Here’s how Doug Chadwick describes the habitat in Beast the color of winter, 1983:

“Take a staircase in your home (30 to 35 degrees), tilt it to match Egypt’s Great Pyramids (52 degrees), remove some of the steps, and shovel ice and snow over the whole affair. . . Then move the whole concocted cliff atop an apartment building so the next step below bottom is at least a couple stories down.”

My definition of Goatlandia has expanded a bit since beginning Jánwu studies in October, 2020. Safe to say, though, that not much of it is flat!

As for my annoying subtitle, the ‘unviewed viewshed, ‘ sorry, :) That’s a rebuke not to you but to me. As a wannabe natural history jack-of-all-trades—what Matt Goff humbly calls “aspiring,”—I’d like to think I notice stuff that drops through cracks in scientific specialties. With steep places though? . . . Not so much.

One of the blades in ArcMap’s swiss-army-knife for analyzing/visualizing terrain is called the viewshed tool. Clicking your observation point on a DEM (digital elevation model), the tool creates a polygon highlighting everything a viewer there can see. It’s used primarily in landscape architecture, the discipline of (cynically speaking) making our residential-and-recreational world seem less damaged than it really is. Until stumbling into goatography, I hadn’t used it much.

Pink tints are nearby conifer-tops and distant cliffs-&-alderjungles viewable from my observer point on Behrends Avenue.

Until recently, viewsheds have built upon relatively crude ~30-meter terrain models. But it occurred to me that thanks to LiDAR, by clicking on Δobserverpoint—my standard tripod station at Behrends Avenue—I could generate a more detailed viewshed, showing literally every goatcliff, and even the sprucetops blocking them in our Highlands neighborhood foreground.

Picture yourself in lowlands, but close to that ’tilted staircase’ in Doug Chadwick’s quote above. The viewshed tool will illuminate its ‘risers’, but the ‘treads’ are mostly hidden. In mostly mountainous Lingít Aaní, 99% of human activity transpires in this bowlbottom. But who among us really sees its walls? Yeah, if transported to Kansas, we’d miss it. Yet I can’t think of a single scientific study addressing the ecology of Goatlandia, or even defining it as a legitimate habitat. We’re pretty good on flat-&-gentle places, and passable on the alpine-subalpine convexities (well, maybe mostly flunking . . . ) But in between. . . that’s the unviewed viewshed. Maybe it takes a neighborhood evacuation to get us measuring things?

When we’re not there To learn what wintering mountain goats are up to in places we can’t scan with spotscopes, Discovery naturalist Steve Merli and I have deployed motion cams in steep forested habitats. Climbing to and from these cameras we’re almost constantly in sight of super-tall Sitka spruce. This was first of many unexpected discoveries about steep places. During the Landmark Trees project, 1996 to 2005, I’d never have suspected that colluvial (gravity-deposited) landforms might support higher-scoring mega-stands than our finest forests on alluvial (water-deposited) fans and floodplains. Not until receipt of LiDAR in 2014 have we been able to easily identify tallest trees in local watersheds.

Danny Stahle, Erich Pietzch (USGS, Montana) and Eran Hood (UAS) coring on margins of Nettleslide. Impact scars in the tree-ring sequence give dates of past avalanches.

In early June, 2021, I joined UAS researcher Eran Hood, and tree-ring dating experts from Montana on slopes above our Highlands neighborhood. Snow avalanches and rockfall bombard Goatlandia conifers and alders, leaving evidence in tree rings. These clues are assembled into a story of disturbances from minor and localized to catastrophic, of interest to skiers, avalanche forecasters and especially residents downslope. Studies will fine-tune maps of recurrence intervals. Eran and Erich’s Fireside in Feb 2021 summarized year-one of their project.

Nettleslide (Behrends Avenue chute) is one of the most dangerous urban avalanche paths in North America. Disturbance regime also creates some of the finest winter goat range in Lingít Aaní.

Ribs and gullies On mainland cliffs facing Séet ka (Gastineau Channel), giant-tree forest closely alternates with tangled slide alder. This combination gives Jánwu, mountain goat, the ideal combination of deep-snow refugia and ultra-rich foraging terrain. Intermediate between these extremes is tall-spruce-red-alder woodland. Because this habitat has only just come to my attention, I can’t say how widespread it is. On very steep slopes above J-town—around the orange eye for example—this open woodland offers better forage than closed conifer forest, along with snow interception giving access to grazer-browsers when slide paths are deeply buried. I suspect some of the majestic red alders could reach 200 years, unheard of in rainforests to the south.