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