Bumping the table!
Time: past future
global
localSPACE
Why are the pieces laid out as they are, and how are their distributions changing?
Evolving and mobile pieces(life-forms)
Changing table-top(environment)
Disturbance and succession
•Forms of disturbance•Spatio-temporal-severity variation in disturbance regimes•Primary & secondary succession•Documenting successional change•Autogenic and allogenic processes•Forest dynamics•Change as a stochastic processes•Climax?
Forms of disturbance
• Abiotice.g. fire wind landslides avalanches volcanic eruptions flooding glaciation bolide impacts
• Biotice.g. tree-fall herbivore damage pathogens
• Anthropogenice.g. logging urbanization pollution fire
Spatio-temporal-severity variation in
disturbance regimes
Size
Inte
rval
Severit
y
How often is the communityimpacted (=can populations reproduce?)How severe is the damage (=do populations recover?)How big are the disturbed patches (=how long to recolonize)?
Disturbances: spatio- temporal variation
Cox CB, Moore PD. 2000. Biogeography: an ecological and evolutionary approach. Blackwell Science, 298 pp.
images: http://www.thomasbdunklin.com/albums/HumboldtRedwoods;
http://sofia.usgs.gov/publications/fs/2004-3016
Small-scale disturbances:right: treefall in redwoods (CA);below: lightning kill in mangroves (FLA)
Wind
• e.g. Coastal forest, BC, December 2006.
• In Stanley Park some 10% of the trees were blown down or severely damaged by winds gusting >100 km/hr.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Avalanche
Subalpine forest
restricted to slopes that are stable and not prone to snow
slides or avalanches
(Cascade Highway, WA)
• severe fires remove forest canopy> increase light level on forest floor
• many tree species fire tolerant
• fires mineralize organic layers on forest floor
> increase nutrient availability
Fire
Adaptations to fire: forest trees
thick bark (e.g. ponderosa pine) regrowth from epicormic shoots (e.g. eucalypts; new leaves 2 weeks after fire) stimulation of seed dispersal in serotinous species (e.g. jack pine)
Fire intervals
• Fire scars indicate thermal damage to the cambial layer; rings indicate age of event
Images: http:// www.ltrr.arizona.edu/ sngc/studies/pftrd.htm
After the disturbance: succession
• “Species - by - species replacement process in an ecological community through time”.
• Focus: short-term temporal change in a community as it develops or recovers from disturbance.
• Modern ideas about succession derive from Gleason’s (1920’s) individualistic species behaviour concept and Horn’s (1970’s) notions of replacement as a stochastic process.
Primary and secondary succession
• Primary - development from an initial condition or after a disturbance that sterilized the local landscape (i.e. colonization of a barren substrate).
• Secondary - recovery from a disturbance that did not extinguish all life forms in the local area.
Primary successions on
“sterile” coastal
substratesmudflat
beach gravel
dune sand
Primary succession on “sterile” rocky
substrates
debris flowlava flow
Primary succession:where do the
colonizers come from?
What controls their success?
Mt. St Helens, 1981
Secondary succession: disturbance
does not clean the
slatecomplete burn
partial clearancepartial burn
Documenting succession
• DIRECT OBSERVATION:useful for situations where species turnover is rapid
• SPATIAL ANALOGUE:most-commonly employed - requires mosaic of communities of different ages
• TEMPORAL RECONSTRUCTION:possible only in depositional environments
Ways of studying
succession: the example of the River
Fal (UK) estuarine-floodplain core site
marshwoodland
Spatial analogue: a transect from marsh
through woodland
communities
replacement series?
Temporal re-
construction: a core
from floodplain of
River Fal(core site on
previous slide)
Successional processDegenerative: e.g. scavengers on carrion
(Gail Anderson); bacteria, fungi, etc. skeletonizing a leaf, …..
Allogenic: community changes driven by external forces (=exogenous) such as sedimentation on a floodplain.
Autogenic: community changes driven by internal forces (=endogenous) such as shading of forest floor by tree canopy
Allogenic succession: e.g. progradation and
aggradation of a river delta
(~AD 1850-80)
10 ka
5 ka
now
Allogenic succession: e.g. Fraser River delta
Primary driving factor - sedimentation, which is linked to channel position and tidal currents. The channel banks are better-drained than the areas between the distributaries.
Relay dynamics
1. Mature, even-aged stand of pioneer trees with understorey of shade-tolerant species;
2. Pioneers die, replaced gradually by shade-tolerant trees;
3. Mixed canopy with replacement by shade-tolerant trees
graphic: www.na.fs.fed.us/spfo/ pubs/misc/ecoforest/dyn.htm
Canopy-gap dynamics
graphic: www.na.fs.fed.us/spfo/ pubs/misc/ecoforest/dyn.htm
1. Mature, mixed-age stand with canopy and understorey of shade-tolerant trees;
2. Canopy trees die (by senility or windthrow), competition in gaps
3. Replacement by trees that grow most quickly in gap environment
Autogenic succession
on deglaciated
terrain, Glacier Bay foreland,
AK.
Glacier Bay successiona
l stages
Glacier Bay community dynamics
Sadava, D. et al. (2004) Life: The Science of Biology, Sinauer Associates and W. H. Freeman.
Seed sources and succession
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Deglaciated in 1968, this surface supported a continuous carpet of Dryas plus scattered willow and cottonwood saplings in 2005. Alder and spruce seed sources are too distant to allow rapid colonization of this site,
but in areas closer to seed sources colonization by these species can be rapid.
Source: Milner et al., 2007, Bioscience, 57, 237-247
Concomitant environmental changes [acidification, paludification]
http://arnica.csustan.edu/boty1050/Ecology/glacier_bay.htm
Autogenic succession:
natural reforestation
of abandoned fields in the southeaster
n U.S.A.
(Georgia, Carolinas)
RELAY GAP
Abandoned field succession - birds
Forest succession: regeneration niches
Lig
ht
level
Sun
Deepshade
Organic matter depthThin Thick
climax forest trees
pioneer treesw
eed
s
time-trajectory
regeneration niche
Forest succession patterns
slow
er,
less
com
ple
x
Succession: a stochastic process
Basic concept: forest succession is a lottery that can be modelled by a Markov chain process (which assigns probabilities to competing outcomes in a sequence).
Ideas primarily developed by Henry Horn in 1970’s based on his observations in the Princeton Research Forest (a mixed hardwood forest) in northeastern U.S.A.
Markov chain analysis of forest succession: a lottery to replace
canopy dominants in gaps
STEP 1: map forest structure focussing on species of canopy dominants (X) and saplings (x):
AF
H
a
h
f
a
hh
h h
hh h
h
h
If this alder dies, what will replace it?
transect in plot
Markov chain analysis
# saplings (replacements)Canopy # alder firhemlocksum
Alder 13 2 4 14 20Fir 5 1 1 8 10Hemlock 2 0 0 14 14
STEP 2: Tabulate replacement matrix for all transects
(based on hypothetical example from SFU woods)
Markov chain analysisSTEP 3: Calculate transitional probabilities:
e.g. for a dying alder 2/20 potential replacements are alders = 0.1 probaility of an alder x alder replacement.
saplings (replacements)Canopy alder fir hemlock
Alder 0.1 0.2 0.7Fir 0.1 0.1 0.8
Hemlock 0.0 0.0 1.0
Markov chain analysis
STEP 4: represent as a Markov chain, showing transitional probabilities
Alder Fir Hemlock
0.7
0.81.0
0.1
0.2
0.1
0.1
Predicting future forest structure from Markov model
STEP 5: Multiply canopy structure by transition matrix
For alder: each of the 13 canopy alders will likely be replaced by 0.1 alder saplings = 1.3 alders; each of the 5 fir canopy trees will likely be replaced by 0.1 alder saplings = 0.5 alders; and each of the 2 hemlock canopy trees will likely be replaced by (2 x 0.0 alder saplings) = 0.0 alders. Alder abundance in the plot in the next generation is therefore = 1.3 + 0.5 + 0 = 1.8 alders
Multi-generation forecasting
STEP 6: Repeat step 5 ad nauseam
GenerationCanopy 1 2 3 4
Alder 13 1.8 0.5 etc.Fir 5 3.1 0.7 etc.
Hemlock 2 15.1 18.8 etc.
Comparing successional pathways and outcomes
Horn suggested that successional transition matrices can be grouped into three types illustrating:
A BA. Chronic, patchy disturbance:
C D
B. Obligatory succession: A B C D
C. Competitive hierarchy: A B C D
Is there a predictable endpoint? Is there a singular “climax” forest? Horn’s “quasi-reality” from the Princeton forest
plot
blackgum
beech
redmaple
graybirch
Quasi-stable monoclimax:forest of beech + others
Are polyclimaxes possible? Jerry Olson’s study of the Lake
Michigan dunes
Lake Michigan dunes: polyclimax succession?
Landscape-scale analysis of the successional mosaic
Date of wildfire
50 km
http://www.gsfc.nasa.gov/topstory/2003/0311firecarbon.html http://earthobservatory.nasa.gov/
Boreal forest, Canada Simpson Desert, Australia
~5km
Disturbance and invasive species
The tallow tree (Sapium sebiferum L.), a native of China introduced into the US by Benjamin Franklin in 1776, is rapidly invading the disturbed areas. Its seeds, which can remain viable in the soil for >100 years, are spread by birds, and it grows rapidly to 10 m tall.
13.6 M m3 of timber (mainly in Louisiana) damaged by Hurricane Katrina in September, 2005
Chinese tallow tree