ECOSYSTEM PROCESSES
Ecosystem: an organized system made up of plants,
animals, and inorganic components which are linked
together by flows of energy and materials.
Harnessing solar radiation is the basis of ecosystem energy
flow.
Biomes: regional ecosystems with generally similar
climates, soil forming conditions & plant-animal
communities
tropical forests, temperate grasslands, deserts, etc...
-------------------------------------------------------------------------------PLANT-ENVIRONMENT INTERACTIONS, PRODUCTIVITY
which plants dominate?
competition and ecologic niche
sunlight, temp, H2O, nutrients
tolerance and the ecological optimum:
(draw the curve)
Limiting factor of production: physical or chemical abiotic
component that most inhibits biotic activity.
(sunlight, nutrients, water, temperature, physical habitat & more)
photosynthesis harnesses carbon dioxide, water, and solar
energy to form high energy carbohydrates:
6CO2 + 6H2O + solar energy → C6H12O6 + 6O2
respiration: the breakdown of carbohydrates for maintenance,
releasing the energy they contain:
C6H12O6 + 6O2 → 6CO2 + 6H2O + heat energy
primary producers: organisms that use light energy to convert
CO2 and water to carbohydrates through photosynthesis.
Gross Primary Productivity (GPP) = total amt. of energy fixed
by primary producers (photosynthesis)
Net Primary Productivity (NPP) = GPP - Respiration. NPP is
indirect measure of accumulation of biomass over time.
----------------------------------------------------------------------------------Typical NPP: fixed carbon per square meter per year (g/m2/yr):
Terrestrial:
tropical rainforest
2200
trop. deciduous forest
1300
temperate (mid latitude) forest
1200
temperate grassland
600
tundra & alpine
140
desert
50
Marine
open ocean
125
upwelling ocean zones
500
coastal algal beds, coral reefs 700-2500+
----------------------------------------------------------------------------------NPP geography in above table explained by limiting factor(s):
Function of water abundance in soils:
Rainfall and evaporation influence nutrient availability in an
ecosystem. The rainfall in wet environments leaches (removes)
nutrients from soils more than in drier environments. Therefore:
1) ecosystems in wet environments have a significant
proportion of total nutrients in biomass (forests), while
2) ecosystems in desert and semi-arid (grassland) environments
have a greater share of their nutrients in the soils
Efficient nutrient cycling in coral reefs and rainforests
overcomes otherwise limited nutrient availability.
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Oceans and Land as Habitat
Oceans cover 70% of Earth’s surface, but 99% of living volume
(land’s inhabited zone ~ 30m above surface to ~1m below, while
oceans are inhabited down to ultimate depths of 11,000m).
There are far more total land species (perhaps 20 million) than
marine species (perhaps 250,000).
Why?
-Diversification/speciation require the isolation of small
populations by geographic barriers to dispersal. The ocean
is continuous, relatively stable and uniform. The terrestrial
environment is not. (only 2% of marine species inhabit the
water mass itself; 98% are associated with the more
diverse and fragmented bottom sediments)
The terrestrially dominant photosynthetic organisms
(autotrophs) are much larger than the marine ones (most are
microscopic). Why?
1. Many land plants grow tall to compete for light. But
average depth of seas is 4000m. (not an option)
2. Living tissue is denser than sea water due to organic
molecules and salts. Marine autotrophs need to be in
photic zone, and smaller organisms sink more slowly than
larger ones. (weight is proportional to volume, frictional
resistance is proportional to surface area, and small
objects have a large surface area in relation to their
volume)
3. Rapid herbivory and need to be in photic zone favors a
more rapid reproduction than would be possible with larger
organisms. Small organisms can reproduce more rapidly.
4. Small organisms have a greater nutrient uptake to mass
ratio, and marine organisms can not afford to have the
larger mass required by the roots that most land plants
have.
5. Thus, being small helps.
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VEGETATION CHANGE THROUGH TIME
plant succession: where one type of plant is replaced by
another.
pioneer species: dominant invaders after a major disturbance,
often fast growing and aggressive, but generally short-lived.
seral species: those that dominate after the pioneers
W. forests – Douglas-fir, near coasts Sitka Spruce, in riparian
environments Red Alder
climax vegetation: the phase of vegetation succession where
the structure of the plant community sustains itself indefinitely,
without major changes. (in absence of disturbance) W.
forests: Western Redcedar, Western Hemlock
WHY DO THESE TREES BECOME DOMINANT, EVEN IF
THEY DON’T DOMINATE FIRST?
Some Kinds of Succession:
1. linear succession: when plants cause changes in their
environment which result in progressive patterns of vegetation
change that are generally not repeated. example: lake infilling
2. cyclical succession: when a pattern of vegetation leads to
a new pattern, only to be later succeeded by the original pattern.
ex: forestation of permafrost areas (draw)
3. allogenic succession: when an outside force induces
vegetation change that has long term persistence.
Example: planting of European Beach Grass on Nehalem Spit
(OR Coast) forestation now happens due to dune stabilization
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