Tides, toads & topography: Natural & cultural history of big valley In 2003 I had the privilege of directing a…2003 | Alder House students | 27 pages
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.
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
Cybertracking the ‘power outlet’ On July 29th, 2022, 14 Discovery naturalists and their 3 visiting instructors gathered on tidal sand…2022 | Richard Carstensen | 23 page journal excerpt & pageflippers
Exhuming an early slideshow Back in 2011, preparing for a Charter School/Goldbelt Heritage overnight expedition to Methodist Camp,’out-the-road,’ I created…2010: uploaded 2022 | Richard Carstensen | 16 minute slideshow
Traversing the 2014 wetlands conservation parcel On July 16th, about 25 bushwackers assembled in the parking area at end of…2022 | Richard Carstensen | 11 minute slideshow
Four days at the delta and Eaglecrest From June 9 to 12, 2022, Discovery gave the 4th in our series…2022 | Richard Carstensen | 46 page journal
Environmental analysis of lower Jordan Creek From March through July, 1987, I assisted Dan Bishop and Bob Armstrong with an…1987 | Bishop, Armstrong & Carstensen | 40 pages
Focus group tour On Thursday, August 26th, about 30 masked aficionados of dynamic Fish Creek delta assembled on invitation from…2021 | Richard Carstensen, Bob Armstrong | RC-59 pages: BA vid-links
Fifty friends on backloop moraines On a sunny July 17th, 2021, Discovery Southeast and the Southeast Alaska Land Trust hosted…2021 | Richard Carstensen | 8 minute slideshow
Touring lands on Back Loop Road Discovery Southeast and the Southeast Alaska Land Trust (SEALT) have similar missions. Discovery works…
Retakes field journals, 2005 season Summarizing the Repeat Photography Project for 2005, Kathy Hocker and I divided our field reports…2005, 2nd ed 2013 | Richard Carstensen & Kathy Hocker | 40 pages
Retakes field journals, 2005 season Summarizing the Repeat Photography Project, Kathy Hocker and I divided our reports into 2 parts:…2005; 2nd ed, 2013 | Richard Carstensen & Kathy Hocker | 39 pages
Materials from the Eisenhower Math and Science series In March, 1991, with Discovery director Cinda Stanek and naturalist Cathy Pohl,…1991 | Richard Carstensen | 22 pages
History from the air Georeferencing old and recent vertical air photos in ArcMap makes it easy to export exactly scaled-&-aligned…2021 | Richard Carstensen | 8 pages
Effects of age and succession type on forest overstory and understory In 1991 I assisted highschool students Joey Bosworth and…1991 | Joey Bosworth & Erika O'Sullivan | 1 page poster
Journal for my favorite glacial valley A scoping document and collection of journals from 40 years of visits to what…2020 | Richard Carstensen | 62 pages
Powerpoint & script for Discovery Nature Studies One of my educational mentors, a charismatic high school teacher, when hearing of…1990 | Richard Carstensen | powerpoint & script
Materials from the Eisenhower Math and Science series In February, 1991, with Gustavus master-naturalist Greg Streveler, Discovery director Cinda Stanek…1991 | Carstensen, Streveler, Stanek & Merli | workshop materials
New angles on Tʼóokʼ dleit ḵaadí, nettle snowslide (Behrends Slide) Late September, 2020 It’s probably time we stopped calling this…2020 | Richard Carstensen | 90 second slideshow
Rebound, succession, fish&wildlife, and aviation on our frontyard wetlands In 2011, Jeff Sauer at Juneau Audubon asked for a presentation…2011 | Richard Carstensen | 36-minute slideshow
The Wayback app JuneauNature relies heavily on historical series from precisely registered aerial photographs, presented either in slideshows, with long…2020 | Richard Carstensen |