Ch. 9 Communities

Community Characteristics• Many!

• Mechanism: Opening occurs– Trees die: damage by ice (winter), drying (summer)

• Wave moves 1-3 m/yr (cycle 60 yr)

Disturbances

• Elements cycle• Communities differ in

rates, where nutrients located

Nutrient Cycles

• Ex: • Tropical rain forest

– C in

– Litter decay weeks

Nutrient Cycles

?

• Ex: • Tropical rain forest

– C in

– Litter decay weeks

• Subalpine forest– C in

– Decay 1/2 life 10 yr

Nutrient Cycles

• Standing biomass: aboveground dry – desert 100 kg/ha– rain forest 500,000 kg/ha

Productivity

• Net primary productivity: energy to biomass/ Productivity

• Desert: • Mangrove forest, marsh, swamp:

Net primary productivity (Pn)

B=standingbiomass (tons/ha)

Pn=net primary productivity(metric tonsper ha/yr)

• Energy conversion efficiency: % incoming • Note small values

– Rain forest _____ efficiency desert!

Energy Conversion

Community Characteristics• Change through time......

Community Characteristics• Change through time......• Succession: will discuss later• Stability: response community to

disturbance/stress• Several components:

– Resistance: ability remain unchanged during stress

– Resilience: rate return to normal

– Persistence: extent community unchanged over time

Only resistance not worth effort to quantify. WHY??

Community Characteristics• Change through time......

Community Characteristics• Change through time......• Succession: will discuss later

Community Characteristics• Change through time......• Succession: will discuss later• Stability: response community to

disturbance/stress• Several components:

– Resistance: ability remain unchanged during stress

– Resilience: rate return to normal

– Persistence: extent community unchanged over time

Only resistance not worth effort to quantify. WHY??

Community Characteristics• Resistance is futile.....

Classification of communities

And now, for something completely different....

Classification of communities• Data collection (sampling) covered in lab lectures

Classification of communities• Data collection (sampling) covered: lab lectures• Recall…….• Association: more formal and precise unit

– basic unit plant community classification

– composed of stands (stand: particular member association)

– taxonomic analogy: association = species, stands = individuals

• How decide which stands belong to same association?

Classification of communities

• 4 major approaches:• 1) Tabular methods• 2) Cluster analysis• 3) Association analysis• 4) Ordination methods

Tabular methods

Tables…….

Tabular methods• American approach: based on “dominance”

(physiognomic)– Rel. cover, density, basal area, biomass

– Importance

Plant Ecology

Tabular methods• Association based on (layers)

– Ex, Pinus ponderosa/Agropyron spicatum woodland

• Samples: some

Tabular methods• European approach: based • Braun-Blanquet technique (relevé technique)

Sounds French

Tabular methods• Braun-Blanquet technique (relevé technique)• Sample called relevé

– 1) Get

– 2) Choose

– 3) Compile

– 4) Do sp.-area

– 5) Place 1 (relevé) subjectively

– 6) Data: sp.

Tabular methods• Classification: table method. • Sort species: discard widespread & rare,

Cover, sociability (dispersion)

Tabular methods• Differentiated table has differential species: characteristic

of – Have hi fidelity: few stands

– Have hi constancy: most stands

Tabular methods• Note: • 1) • 2) differential sp.

– Ex, moss sp. on trees

Olympic National Park,Washington

Cluster analysis• Expresses ____________ of stands graphically (2 D)• Similarity? Coefficient of Community (CC)• CC: how

Cluster analysis• 2 major indices:

– Jaccard’s Index – Sorensen’s Index

• Presence or cover (“weighted by cover”)• Values: from 100 (same) to 0 (no sp. in common)

Cluster analysis• Generate dendrogram (tree diagram ________________)• Y axis = “resolving power”: 40 great power, 0 no power,

to distinguish diffs.

Cluster analysis• Decide level similarity:

– CC = 10 (threshold III): 2 associations– CC = 20 (threshold II): 7 associations– CC = 30 (threshold I): 15 associations

• Result: associations based