ENVIRON 102 Lecture Notes - Lecture 7: Duke Forest, Secondary Succession, Nitrogen Fixation
4 May 2018
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2.10.15 Lecture Notes
Ecosystem disturbance, change, and management
Starting from scratch – Primary Succession
Since its mapping by George Vancouver (1798), glacier has retreated over 60 miles
Studying ecosystems along the path of glacier’s retreat permitted reconstruction of the process of
ecosystem establishment and development – succession
Glacier Bay – found that there is a predictable pattern
0-10 years: pioneer mosses and lichens – weather rock and accumulate organic matter
o Secretion of acid that break down rock
30 years: dryas (important herb becomes common); symbiotic bacteria fix nitrogen (i.e. convert
nitrogen to organic nitrogen)
o Dryas do not need nitrogen to grow
10-60 years: herb-low shrub diversity increases; soil develops
60-100 years: invasion by alder-nitrogen fixing tree
100-200 years: invasion by spruce and other conifers
200+ years: mature old-growth forest
Succession following glaciation
Increasing soil depth, carbon and nitrogen concentrations, and litter fall
Key Lessons
Succession follows a distinct and directional path
Early pioneers have high dispersal ability and tolerance to limited resources
Succeeding stages modify environment making it more favorable for other invaders
o By fixing nitrogen, improving soil, etc.
o Later stages make it harder for earlier stages to survive
▪ Shading out, etc
Ultimately leads to a climax community that is able to maintain itself indefinitely
Very few examples of primary succession, so still not sure if these patterns apply always
Secondary Succession – starting with a few ecological legacies
North Carolina Piedmont: Agricultural field abandonment
European settlement begun (~1750)
By 1850 – virtually all arable land in cultivation
Following Civil War through Great Depression, extensive land abandonment
Much of Duke Forest (est. 1931) was abandoned farm land when it was acquired by Mr. Duke in
1920s
Inaugurated 4 generations of research on forest change beginning with work by H. J. Oosting
(~7000 acres)
Secondary Succession on abandoned farmland
Secondary succession is accelerated by legacies
o e.g. patterns of change following forest cutting
Pattern influence by facilitation and competition
(A) Hardy wind-dispersed herbs and grasses dominate old fields in the first few years following
abandonment
(B) In the high light and poor soil conditions, pines are able to grow more rapidly than other trees
and form an even-aged stand in 10-15 years
(C) Pines are not able to reproduce in their own shade and are eventualy replaced by deciduous,
broad-leaved trees like oaks, maples, and hickories
NPP increases until it hits 15 years, then NPP drops
Primary/Secondary vs. Spectrum
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