Succession describes a habitat’s growth from emergence to great age. Primary succession happens after catastrophic disturbance—glaciation, volcanic-island-creation, etc.—essentially removes all living material. Here’s a series for post-glacial succession in Áak’w Táak, inland from little lake, (Mendenhall Valley), inferred from a chronosequence on mesic surfaces (that is: not too wet, not too dry). Succession on poorly- or excessively-drained surfaces is quite different.

A Postglacial barrens with lichens, moss & dwarf fireweed. ● B Alder/willow thicket with small spruce saplings. ● C1 Thickets still productive but overtopped by cottonwood & spruce. ● C2 Cottonwood & spruce close canopy over senescing thickets. ● D Spruces overtop senescing cottonwoods. Small shade-tolerant hemlocks in subcanopy. Depauperate, mossy understory. Only after ~200 years does blueberry fill in. ● E After many centuries without stand-replacing disturbance, hemlock-dominated old growth develops, distinguished from D by gappy canopy, rich, patchwork of shrub & subcanopy layers, plentiful deer forbs & abundant standing & down dead wood.

Check out the Succession illustration below for comparison of secondary succession after logging and streamside flooding.

Successional stages  Community development takes many alternative pathways, but in Southeast Alaska we can at least make some rough generalization about structural stages. Here’s 5 stages span a series on well-drained lowland soils from earliest herbaceous colonizers to old-growth forest types.

1) Herbaceous communities Only the most violent of disturbances can knock a forest community all the way back to herbaceous successional stages. More typically, as with logging or blowdown, the initial response to disturbance is led by shrubs and tree saplings. Meadows on well-drained surfaces are fairly uncommon and usually ephemeral, because forest will be the concluding habitat here. One such community is uplift meadow on surfaces raised from tidal elevations by glacial rebound. Another is maintained in early successional status by repeated disturbance on the slopes of very active avalanche chutes. These sites are swept so frequently that even the flexible Sitka alder is incapable of gaining a foothold. Instead, productive communities of grasses, sedges, ferns,
and tall herbs such as fireweed and cow parsnip may develop, growing most luxuriantly on bombarded colluvial toe slopes.

2) Shrub thickets  Early shrub stages of post-logging (secondary) succession on upland sites are dominated by species that already existed in the understory of the logged forest: blueberry, salmonberry, and ferns. These species, plus trailing black currant, account for 90% of plant production in young Southeast clearcuts. This production increases with time, until the new forest closes canopy after 20–30 years. In post-glacial (primary) succession, no remnant shrubs from previous communities are poised to inherit the newly uncovered landscape. The first shrub to dominate the landscape is usually Sitka alder.

3) Mixed conifer-deciduous  Thicket species are short-lived, as indicated in the transition from stages C1 to C2 in the cartoon above. Because alder and willow are shade-intolerant, young plants rarely survive under the foliage of their parents. Aging willow and Sitka alder bushes begin to die back when overtopped by red alder, black cottonwood, Sitka spruce, lodgepole pine, or western hemlock. Only in perennially disturbed sites such as slide chutes can alder/willow thickets persist indefinitely. Large expanses of the mixed conifer-deciduous forest are limited mostly to post-glacial and active alluvial surfaces of the mainland.

4) Young, even-aged conifer  After logging or high-intensity blowdown on upland slopes, maturing forests often enter a stage in which young, densely stocked conifers close canopy, shading out the understory. From a forester’s perspective, this first-come-first-served second-growth has been called the “stem-exclusion stage.” Less vigorous overstory trees (“stems” in forester lingo) gradually die off and little colonization of tree seedlings can occur until canopy opens up again. From a community ecologist’s perspective, the young, closed canopy forest has been called the “depauperate understory stage.” Cover of shrubs and herbs drops to almost nil, typically for a century or more. In primary succession, forest takes longer to reach this closed-canopy stage (D in cartoon above).

5) Old growth  Stage E in the cartoon. Uneven-aged, with much more complex diverse structure than stage D. For resources on old-growth forest, see Nature>Habitats>Terrestrial>Forest.

In this section

False Island journal 20080806

Four years into the Ground-truthing Project, Bob Christensen and I helped explore northern Shee Ká, above Shee (Peril Strait). This…

2008 | Richard Carstensen | 70 pages

Hammered gems & unproductive leftovers.

In 2008, Bob Christensen and I were 3 years into the Ground-truthing Project. During those 3 years, the Forest Service…

2008 | Carstensen & Christensen | 30 pages

Ground-truthing Project final report, 2005

The Ground-truthing Project, sponsored by Sitka Conservation Society, ran from 2005 to 2010. Kenyon Fields at SCS administered the program,…

2005 | Carstensen & Christensen | 63 pages

2008 flight over Sitka use area

In September, 2008, I ferried to Sitka to help Sitka Conservation Society host funders and biologists. In a Beaver, we…

2008 | Richard Carstensen | 29 pages

Suitability for logging

In 2009, after several years of cruising the Tongass timberlands under the auspices of Sitka Conservation Society, I wrote them…

2009 | Richard Carstensen | 19 pages

Fickle fashions: stereoscopy

I wrote this as an appendix to my report with Kathy Hocker on repeat photography. It reviews trends in a…

2013 | Richard Carstensen | 6 pages

Discovery’s education and research at The Glacier

Discovery Southeast celebrates 4 decades of research and education at Áak’w Táak, inland from little lake (Mendenhall Valley) glacierdiscovery from…

2017 | Richard Carstensen | 27 minutes

Raven’s-eye views of postglacial succession

Aerial views of post-glacial succession. Combines UAV perspectives with high-res orthophotography plus forest profile views in the LiDAR point cloud.…

2017 | Richard Carstensen | 20 minutes

Cemetery stem mapping: then and now

Remapping with Montessori For a teacher at any of the downtown schools (Harborview, Montessori, JD High) with only an hour’s…

2017 | Richard Carstensen | 13 minutes

Sesquicentennial slideshow

For the sesquicentennial year of the 1867 Alaska Purchase, Juneau-Douglas City Museum asked me to create 3 banners showing 150…

2017 | Richard Carstensen | 28 minutes

1867-2017: 150 years of change

Background paper for 3 banners commissioned by the Juneau Douglas City Museum, showing changes to iconic landscapes of Áak’w Aaní…

2017 | Richard Carstensen | 41 Pages

Succession illustration

This info sheet explains how a forest changes as it matures from emerging forest to old growth. Download info sheet…

2015 | 1 Page

Northern Baranof Island: Past, present, and future

Reflections from our 2007 field surveys of northern Shee, volcano woman (Baranof Island). Covers history of logging in the province,…

2007 | Bob Christensen|Richard Carstensen | 12 pages

Documenting change through repeat photography in Southeast Alaska

Carefully framed retakes of historical photographs documenting vegetation and landform change in response to natural or human disturbance. . Due…

2005/2013 | Richard Carstensen, Kathy Hocker | 39 pages

Beavers by the Mendenhall Glacier in Juneau, Alaska

Introduction to a keystone species in recently deglaciated upper Áak’w Táak, inland from little lake (Mendenhall Valley). Can’t picture beavers…

2009 | Bob Armstrong|Mary Wilson | 62 pages

Lichens around Mendenhall Glacier

Another great example of Bob Armstrong’s many collaborations with experts, in this case Chiska Derr.  Beautifully illustrated guide to lichens…

2010 | Bob Armstrong & Chiska Derr | 50 pages

2011 spring newsletter, Geology and life: Connections between the living and non-living world

Feature article on response of flora and fauna to geologic landforms and bedrock types. †Includes article by Scott Burton on…

Spring 2011 | Richard Carstensen | 12 pages

Glacial rebound in the Mendenhall Wetlands

Vegetation types, tidal elevations, property boundaries, and their relation to glacial rebound and the conservation of accreted land on  Mendenhall…

2004 | Richard Carstensen & Terry Schwartz | 18 pages