Agriculture Reference
In-Depth Information
Table 4.1
Summary of Ecological Succession from Early Developmental Stages to a
Mature Community
Ecosystem attributes
Developmental stages
Mature stages
Community energetics
Gross production/community respiration
(P/R ratio)
Greater or less than 1
Approaches 1
Gross production/standing crop biomass
(P/B ratio)
High
Low
Biomass supported/unit energy low (B/E ratio)
Low
High
Net community production
High
Low
Food chains
Linear, predominantly
grazing
Weblike, predominantly
detritus
Community structure
Total organic matter
Small
Large
Inorganic nutrients
Extrabiotic
Intrabiotic
Species diversity: richness
Low
High
Species diversity: evenness
Low
High
Biochemical diversity
Low
High
Stratification and spatial diversity (pattern
diversity)
Poorly organized
Well organized
Life history
Niche specialization
Broad
Narrow
Size of organisms
Small
Large
Life cycles
Short, simple
Long, complex
Nutrient cycling
Mineral cycles
Open
Closed
Nutrient exchange rate, between organisms
and environment
Rapid
Slow
Role of detritus in nutrient regeneration
Unimportant
Important
Selective pressure
Growth form
For rapid growth
(“
r
-selection”)
For feedback control
(“
K
-selection”)
Production
Quantity
Quality
Overall homeostasis
Internal symbiosis
Undeveloped
Developed
Nutrient conservation
Poor
Good
Stability (resistance to external perturbations)
Poor
Good
Entropy
High
Low
Information
Low
High
Source:
From Odum, E.T. 1969. The strategy of ecosystem development.
Science
164:262-270. With permission.
Conventional tillage practices alter the distribution of organic material within the soil pro-
file and disrupt soil aggregates, releasing and exposing sequestered organic material to
microbes and invertebrates, thereby accelerating the mineralization of carbon and nitro-
gen. Minimum tillage and no-tillage practices disrupt soils to a lesser extent but often
rely on herbicides to control weeds with nontarget effects on humans and other biota.
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