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• Abiotic

e.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

Severity

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 dynamics1. 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 a

TIFF (Uncompressed) decompressorare 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

Light

leve

l

Sun

Deepshade

Organic matter depthThin Thick

climax forest trees

pioneer treesw

eeds

time-trajectory

regeneration niche

Forest succession patterns

slowe

r, le

ss c

ompl

ex

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 gapsSTEP 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 analysisSTEP 4: represent as a Markov chain,

showing transitional probabilities

Alder Fir Hemlock

0.7

0.81.00.1

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