Switzer watershed

Three short nature trails at DZ

Shaded relief map outlines Switzer Creek Watershed in the context of the greater, glaciated Lemon Creek Watershed.

Dzantik’i Héeni Middle School (DZ) has perhaps the best quick access to nature trails of any school in Southeast Alaska. Within minutes on foot, students can reach: 1) the Dick Marriott Trail to the east; 2) a short interpretive loop around “restored” Kingfisher Pond near the Juneau Police Department, and; 3) the trails network constructed in 2005 directly behind DZ.

Discovery Southeast has been closely involved with natural history education at DZ since the school’s construction in 1995. All of the drawings on this sign were created by students in Discovery programs. Here we present an overview of the geology and natural communities of Switzer Creek Watershed.

Heinztleman Ridge

Bedrock and surficial geology

The series of parallel metamorphic rock types is increasingly altered as you travel NE across them toward the intrusive batholith underlying the Juneau Icefield. A typical metamorphic sequence is shale>slate/phyllite>schist>gneiss.

The steep, mountain goat cliffs of the Heinztleman Ridge sky-line are made of resistant schist bedrock (dark green on map, left). To the west, the mellower “nose” of the ridge is composed of slate and phyllite (lilac on map) that breaks down more readily. Soils weathered from slatey parent material support productive large-tree forest.

Surficial geologic maps lump all of the above but give detail for the loose, surface deposits that cover the bedrock–the work of gravity, glaciers, streams and fluctuating sea level.

Near sea level, bedrock is deeply covered with surficial sediments (lower map) left by glaciers, streams and the ocean when it stood at higher sea level. Transect A-B shows the juxtaposition of these deposits. DZ sits on a 100-acre alluvial fan (tan on lower map), the nutrient-rich deposits of East and West Spruce Tribs. Trees here were exceptionally vigorous. Some of the tallest spruces in Lemon Creek Valley grew on the fan where Switzer Village now lies. (1962 photo on opposite panel.)

Forest

Forest types vary according to soil moisture and time since last disturbance. Youngest trees in the uplift meadow and 1968 clearcut are now taller 
than indicated in this 1996 profile.

Majestic hemlock-dominated upland old growth covers much of Switzer watershed (italicized forest types are illustrated below). The tall flood-plain Sitka spruce forest on East and West Marriott Tribs was handlogged in the early 1900s; believe it or not, these are once-runty trees passed over by loggers, “released” by the removal of their overtopping neighbors.

In the forest fringing the Davis Meadows Trail, permanently damp soils result in slow-growing but ancient trees. DZ itself was constructed on such forested wetland; in mitigation, the CBJ building contract dedicated funds to environmental education.

Three clearcuts (1943, ~1945 and 1968 on center-panel air photo) allow comparative study of post-logging succession. Little but moss and ferns grows in the understory. The DZ Loop also features two very young red alder forests growing in recently drained reservoirs on Cookie and West Spruce Tribs. At the left end of the profile below are isolated uplift spruces growing on raised former tideland.

Emergent tidelands

Emergent tidelands: Profile of zonation on uplifting tideland. Color codes in lower, active tidal zone correspond to those on the salt marsh migration series. Meadow and ultimately forest colonize  former tidal marsh.

Land here is rising relative to sea level at about 0.5 inches per year. Active tideland (hatching on surficial geology map, left panel) is now restricted mostly to the flats south of Egan Drive. But tides once flooded all the way up to Sunset Street. The series on right shows changes to tidal communities with glacial rebound.

Wetlands fresh and salty

Auke Lake Area Map

Salt marsh occupies the vegetated high intertidal, divided into grass (red) and sedge (orange) subzones. With glacial rebound, these zones migrate seaward into the bare mudflats (blue). Overall, high-marsh grasses (Deschampsia caespitosum, Elymus mollis) are expanding at the expense of low-marsh Lyngbye sedge (Carex lyngbyei), the most important forage plant on the Mendenhall Refuge. Above the highest tides, uplift meadow colonizes, but this becomes prime real estate for homes and industry. Only Davis Meadows remain undeveloped today. With DZ students, we’ve mapped the migration of these zones by overlay of historical air photos.

Above about 30 feet–the highest reach of Little Ice Age tides–the most poorly drained surfaces have ancient wetlands with deep peat that took millennia to accumulate. A good example is the sedgey peatland at the north edge of Davis Meadows, on the Marriott Loop Trail. Here, you can plunge a hiking staff at least 5 feet into the saturated moss-sedge peat.

Streams

DZ students have monitored healthy (e.g. Robin Tributary) to impaired streams (e.g. Wimpy Trib) since 1996. Robin Trib has clear water and log-created pools. Winter temperatures are relatively warm due to upwelling groundwater, important for resident fish. At the other extreme is “Wimpy Trib,” ditched around developments at such low gradient that flow is impeded and iron flocculent accumulates. Invertebrate diversity is low.

Salt marsh migration

Colors on these map panels correspond to those on the zonation profile.

1910 The Louie Lund homestead (today’s Sunset trailhead) was accessible by skiff from the sea on an average high tide. Everything on this early geology map above the red ryegrass zone (superimposed) was old growth.

1948 The contact between sedge (orange) and grass (red) zones is typically at the 16 to 17-foot tidal elevation. Sedges probably grew right up to the often-flooded road in 1948. The lowermost sedges contacted bare mudflat (blue) at the 12 to 13 foot level. Dark patches in the extreme lower left were outlying clones of sedge or arrowgrass (Triglochin).

1962 The bare mudflat was being squeezed out by invasion of sedges that reached their maximum cover at this time. This was probably true also for the Mendenhall Wetlands as a whole. Prior to that, mudflat dominated; afterward, sedge-dominated low marsh declined steadily from 1350 to 700 acres on the Refuge, and will drop to only 400 acres by 2025.

1979 With uplift, bare mudflat migrated off the map. Construction of Egan Drive probably hastened decline of sedges by restricting tidal flow above (NE of) Egan, encouraging less salt-tolerant grasses.

2006 Sedges have disappeared above Egan Drive, except as a band along low tidal sloughs. Outboard, however, they still come closer to the expressway than anywhere else on the refuge. That’s why grazing Canada geese are more often seen here than elsewhere along Egan. On the northeast side, succession has proceeded to the grass-dominated high-marsh phase. Geese that used to graze there routinely are now infrequent.

Switzer watershed Area Map (Aerial photography, June 2006, City and Borough of Juneau)

Trail Access

DZ Loop
Distance (to and from the school): 0.8 miles
Total trail complex: 1.4 miles
Elevation gain: 90 feet
Difficulty: easy
Ownership: CBJ
Notes: includes large-tree and small-tree old growth, coniferous and deciduous second growth

Marriott Loop
Distance (from either Sunset or Lund trailheads): 1.3 miles
Elevation gain: 160 feet
Difficulty: moderate
Round trip from DZ: 2.0 miles
Ownership: CBJ
Notes: widest range of forest types; see profile on left panel

Kingfisher Pond Loop
Distance: 0.3 miles
Elevation gain: <10 feet
Difficulty: easy, ADA-accessible
Round trip from DZ: 1.7 miles Ownership: CBJ
Notes: pond and wetland restoration demo project.

Tread Lightly!
• Please do not pick or
dig up wild flowers.
• Do not feed wildlife.
Pack it out
• Carry out all trash.
• Please pick up after your pet.