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Peters Hills

29 Dec Botany for Bush Pilots

Posted at 11:57h in Exploration, General Interest, Technique by
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My first landing on a rocky hummock field in Alaska caused severe jackhammering of the landing gear – more than expected. It was a relief to find no damage, but I was still concerned about the takeoff. Sometimes that can be more worrisome than the landing.

I traversed the boulder-strewn humps back and forth, looking for the safest path to taxi and take off. Ultimately, I flew away unscathed. This was a great field experience, and it encouraged me to learn more about how ground cover correlates to surface conditions. Some of my roughest, wilderness-inspired landings surprised me because I misjudged the tundra’s surface.

Getting to know Alaska’s alpine plants, and the types of terrain they are commonly found can help pilots identify sites with the best landing potential. This post will briefly consider tundra plant communities in the alpine and subalpine zones – two areas above timberline where bush planes can land.

The Alpine

Hummocks (dark green bumpy areas) can be the safest sites to land in wet alpine regions. Alaska Range, mid-August, elevation 2800’.

Tundra is a treeless zone. Alpine tundra at upper elevations merges with arctic tundra in northern latitudes where the harsh climate restricts tree growth. A mosaic of low plants dominates this zone including delicate wildflowers, mosses, lichens, grasses, cushion plants, creeping mats, and dwarf shrubs. 

Alpine Tundra Close-Ups

Alaska mountain heather, alpine clubmoss, mountain spiraea, western oak fern.

Dwarf dogwood, bog blueberry, crowberry, Alaska mountain heather, western oak fern, mountain spiraea.
Early autumn color phase: dwarf dogwood, dwarf birch, alpine bearberry, bog blueberry, bog cranberry, bog rosemary, reindeer lichen, alpine grasses.

Tundra LZs are typically open and less constrained by hazards. Pilots can vary touchdown and rollout locations to minimize plant damage and avoid leaving obvious wheel tracks.

For quick interpretation by bush pilots, alpine tundra is divided here into three categories: rocky, firm, and soft.

Rocky Tundra

Rocky Tundra
The surface of this rocky tundra plateau is a mix of gravel and alpine grasses. Some of the gravel areas here were saturated, draining meltwater from a nearby mountain. Alaska Range, late July, elevation 5800’.

Rocky alpine tundra is sparsely vegetated with firm to hard substrate. Sharp, frost-shattered rocks, embedded rocks, and abrasive conglomerates are common. Light braking will minimize tire damage and tail-high wheel landings will help to protect the empennage.

In areas with permafrost, saturated gravels may be softer than the surrounding vegetated surfaces. 

Firm Tundra

Firm Tundra
Firm alpine tundra heathlands (Alaska mountain heather, clubmoss, true mosses, alpine grasses, and lichens). Look carefully to find a safe line – embedded rocks can be camouflaged by vegetation. Alaska Range, early July (during drought conditions), elevation 3900’.

Firm tundra, found at elevated, well-drained sites, is characterized by a thin layer of low vegetation. Surfaces provide more cushioning than rocky tundra.

In alpine zones such as the Tordrillo Mountains, volcanic deposits create widespread areas of smooth, firm tundra with excellent landing potential and fewer rock hazards.

Alpine Bearberry
Alpine bearberry (green in summer, phasing red to burgundy in autumn) and creamy reindeer lichens imply well-drained, firm, rocky soils.

Soft Tundra

Soft Tundra
This soft tundra, bog hummock site is a mix of fireweed, dwarf willow, dwarf birch, bog blueberry, crowberry, alpine rosemary, mosses, lichens, and grasses. Tordrillo Mountains, early July, elevation 1900’.

Common at lower elevations, soft tundra supports a diversity of plant species – typically a moss understory with an overstory of lichens, club mosses, cushion plants, grasses, sedges, heather, and dwarf shrubs. This gives soft tundra a thick, sponginess and the ability to absorb considerable amounts of water. 

Tussocks and Hummocks

Esker
An esker covered by rock hummocks. Alaska Range, mid-August, elevation 3100’.

The terms tussocks and hummocks are often confused, so let’s sort it out here.

Tussocks are raised clumps of grasses or sedges common in northern and western Alaska. 

Tussocks, BLM Alaska, CC BY 2.0 https://creativecommons.org/licenses/by/2.0, via Wikimedia Commons

Hummocks are small, elevated mounds of two types: bog and rock.

Bog Hummocks
Alpine bog hummocks are often closely spaced, uniform, and cored with soil. Alaska Range, mid-August, elevation 2700’.

Bog hummocks form in elevated bogs of moss cushions with a dwarf shrub overstory. Bog hummocks are generally landable. Look for hazardous holes and rocks. Use caution braking and taxing. 

Rock Hummocks
Rock hummocks are rocky debris covered by vegetation. Exposed rocks may be visible, particularly along boundary areas. Alaska Range, early July, elevation 3000’.

Rock hummocks are formed by alpine rock deposits or rocky avalanche debris blanketed by matt-forming vegetation. 

Use caution when landing on rock hummocks! Many areas are landable, but they are typically firmer and less forgiving than bog hummocks. Beware of lichen-camouflaged embedded boulders. 

The Subalpine

This transitional zone extends from timberline, the upper limit of continuous forest, to treeline, the upper limit of stunted trees.

Subalpine Tundra
Subalpine bench in early autumn color phase. Shrub tundra ranges from green to yellow (alder, willow, dwarf birch). Low tundra plants are cream and red (reindeer lichen, alpine bearberry, crowberry, bog blueberry, and others). Mid-August, Alaska Range, elevation 1800’.

In the subalpine zone, tree cover may be clumped, stunted, and sparse at upper elevations. As latitude and elevation increase, trees are replaced by alpine grasslands and shrublands dominated by alder, willow, and dwarf birch. Elevated areas are typically covered by low tundra plants.

Grasslands

Grasslands
Shrub tundra and grasslands in their early autumn color phase. Dwarf birch (foreground) has turned yellow – and will soon change to burgundy. Other dominant shrubs pictured are willow (slightly taller yellow clumps) and alder (dark green). The distinct transition to alpine tundra is visible near the top of the photo. South Peters Hills, late August, elevation 2400’.

Subalpine grasslands are common in discontinuous forest and alder shrublands. Potential landing sites in this zone are difficult to assess. Avoid rocks, wet areas, holes, woody debris, and ditching. Tall or thickly matted grass may conceal hazards. Without regular use or mowing, many established landing sites become overgrown and unusable by early summer. 

Shrub Tundra

Shrub Tundra
This subalpine area supports stunted cottonwood and spruce, and a variety of tundra types. South Peters Hills, late August, elevation 2400’.

Subalpine shrub tundra (stunted alder, willow, and dwarf birch) extends to alpine tundra. Elevated alpine areas with low vegetation offer good landing sites.  

This is meant to be an introductory overview of ground cover types for aviators. To learn more about identifying individual plants check out the references below.

References

Gabriel, H. W., & Talbot, S. S. (2001, October). Glossary of Landscape and Vegetation Ecology for Alaska. Anchorage; U.S. Dept of the Interior Bureau of Land Management. 

Pojar, J., & MacKinnon, A. (2013). Alpine Plants of the Northwest, Wyoming to Alaska. Lone Pine Publishing. 

Johnson, D., Kershaw, L., MacKinnon, A. (1995). Plants of the Western Boreal Forest and Aspen Parkland. Lone Pine Publishing.

NPS DenaliFlora App

Walker, M., Walker, D., Auerbach, N. ‘Plant communities of a tussock tundra landscape in the Brooks Range Foothills, Alaska‘ , 5 ( 6 ): Journal of Vegetation Science 1994; 843 – 866

Thank you to Anja Kade, UAA Department of Biological Sciences for helping in this research.