2011 lecture 4b ecosystem dynamics ii

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Ecosystem Dynamics II

NR216 Introductory Ecology

February 1, 2011

E&FB Ch 20, 21, 22 & 23

Kimmins Balancing Act Chapter 5 pp. 17 - 20



Focus is on

Community Dynamics

Ecosystems and their communities change -

over distance &

over time

which leads to :

Patterns of Zonation & Succession



Patterns of Zonation & Succession

FOUR PRINCIPLES

1. The fundamental niche of a species is the

most important factor :

where does it grow (distribution) &how much is there (abundance)

2. Species vary in their fundamental niches because

they have different sets of environmental tolerances

3. environmental conditions change in both time &space

4. Species interactions affect the fundamental niche

(realized niche)



Community Dynamics:

Patterns of Zonation

Zonation : change over distance in response to

environmental gradient ie.

Temperature Moisture

Elevation & altitude

LatitudePatterns of zonation in a salt marsh E&FB p. 405

Distribution of tree species along an elevational transect E&FB p.399



Community Dynamics:


Ecocline :

the sequence of biotic communities & associated physical environment

along a major environmental gradient, like

elevation or latitude



Community Dynamics:


Clinal Variation (in species) :

Variation in physiological characteristics such

as time of bud flush of plants/trees orseasonal coat colour change of some animals

Genetic basis

Seasonal fluctuation Diurnal variation



Community Dynamics:


Ecotone :

The interface or zone of transition between

two plant communities that differ in life formor in species composition, or both.

A zone of tension between two different

communities characterized by higher

environmental, species & structural diversity

than the adjacent communities



Community Dynamics:


Site:

Any physical or chemical condition or factor that sets thepotential for vegetation development, net PP andaccompanying animal & microbial communities.

ie.

soil & geology

topography (aspect/slope, slope position, elevation)

slope stability

hydrology

cold air drainage & frost pockets

fire risk

wind exposure



Community Dynamics:


Classify Site :

Site Index tree growth potential

Ecological Land Classification vegetationcommunity potential

Wildlife habitat potential

Some other objective or goal forforest/watershed/land management



Change over time :

Ecological Succession

Process of change in an ecosystem, over time

Complex interactions among plants, animals &

microbes (ie. pioneering species may make iteasier for other species to grow or may make

it difficult for other species to grow;

sometimes both)

Sere or seral stage = product of succession



Change over time :


A sere is the sequence of ecosystems that

successively replace each other on a given

area of land, over time.



Change over time :


Each stage in that sere :

Different plant associations (species

composition & community structure) Different age structure of dominant

vegetation (ie. even-aged, un-even aged trees)

Different microclimate, soil, forest conditions Different animal communities



Change over time :


Pioneering stage Mid-seral stages Late seral stages

Pioneering Transitional Sub-climax Climax

relatively stable self-replicating

reproduce in own

shade

uneven-aged same species mix &

balance



Change over time :


Primary succession from bare rock or water(E&FB pp.408ff.) more

Secondary succession reestablishment aftershort-term disturbance more



Change over time :


Strongly influence by what was there before

(root sprouts, seed banks)

Xerarch = dry/xeric

Edaphic = soil (dry or wet and/or acidic)

Mesarch = mesic

Pyric = fire (cyclical climax) Hydrarch =wet/hydric



Change over time :


Autogenic succession : E&FB pp.434-437

Change caused by modification of

environmental by plants growing there

ie. bog forest



Change over time :


Biogenic succession :

animals/insects affect which plants survive

ie. spruce budworm

Tent caterpillar

grazing herbivores elephants



Change over time :


Allogenic succession : E&FB pp.441-443

Change caused by changes to the environment

independent of living organisms Climate change

Glaciation

Sedimentation in freshwater lakes moredeep lake shallow lake



Disturbances at the Landscape LevelE&FB Ch. 23

Typical landscape is

a mosaic of communities

at different successional stages and

occupying different habitats.

Rich, dynamic tapestry of vegetation,

providing an array of habitats for animals & microbes

(Perry, Forest Ecosystems, p.169)



Dynamics at the Landscape LevelE&FB Ch. 23

Landscapes are composed of numerous

community types

Corresponding to changes in elevation, aspect

& soils

Zonation



Dynamics at the Landscape LevelE&FB Ch. 23

Patterns of disturbance and change over time

overlay this with another pattern; succession sequence and timing

is not always predictable.

Succession



Disturbances at the Landscape Level

fire (can be cyclical)

water, wind, (flooding, erosion)

volcanic eruption, landslides/avalanches

frost damage, insect/disease, harvesting

pollution (ie. acid rain)




Mosaics of patches (E&FB p.450)

more

Practices across landscapes - Canada's ForestsEcosystem-based management - Canada's Forests

Edges (E&FB pp. 451-455) moresalt marshes




Disturbance major factor in ecosystems,

especially in forests

Originate from ± outside the ecosystem (ie. fire) or from

± within the ecosystem (ie. native insect outbreaks);

± often disturbances interact (ie. weather affects

susceptibility to in populations of insects, insect

damage increases incidence of fire)




Fire most common disturbance in wide variety

of forest types :

Coniferous forests of N, W & SNorth America more

Eucalyptus forests of Australia more more

Dry tropical forests in South Africa& North America



Fire Ecology

Factors affecting natural fires :

Time of year

Quantity, condition & distribution of fuel

Prevailing climatic conditions (rain, wind,temperature)

Slope, aspect & elevation

Type of vegetation (species, species habit,age)

Type of soil

Sever ity & int ensity of fi re



Fire Ecology

3 major Types of Fi res;

can occur in any combination

Ground fires

Surface fires

Crown fires



Fire Ecology

Ground fires

Largely flameless

Burns in OG matter/duff Can be most destructive because kills &

consumes roots, preventing root sprouts

Kills dormant seeds banked in site



Fire Ecology

Surface Fires

Move quickly, burn litter & above-ground

portions of herbs & shrubs Often sprouting from roots after

Often doesnt kill trees, esp. those with thicker

bark



Fire Ecology

Crown fires

Burns crowns of woody vegetation

Often leaves most of woody stems & forestfloor untouched



Fire Ecology

Technical Terms :

Intensity rate of energy released

Severity impact on organic matter Rate of spread speed leading edge travels

downwind

eg. High intensity/low severityFrom Ashes to Forest by Tony Ianzelo - NFB

2011 lecture 4b ecosystem dynamics ii

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