29 Dec Botany for Bush Pilots
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.
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
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 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, 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.
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
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.
Hummocks are small, elevated mounds of two types: bog and rock.
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 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.
This transitional zone extends from timberline, the upper limit of continuous forest, to treeline, the upper limit of stunted trees.
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.
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.
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.
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.