Ecosystem processes and
heterogeneity
Landscape Ecology
Today
Global NPP
 Lake position
 Moose impacts

Questions/Comments
Ecosystem processes

What do we mean?
◦ Energy
◦ Matter
 Carbon
 Nutrients
Spatial Heterogeneity in ecosystem
process

What can cause ecosystem processes to
vary spatially?
◦ Temperature
◦ Moisture
◦ Topography

What factors affect NPP?
◦ Climate
 Temperature
 Light
 Precipitation
◦ Nutrients

Where is global marine NPP highest?

Why?

Where is global terrestrial NPP highest?

Why?
Paradox…
How do the factors that drive NPP differ
between marine and terrestrial ecosystems?
 the basic processes of plant photosynthesis
are the same for terrestrial and
marine/aquatic plants
 the key factors must be the physical and
chemical properties of the environments in
which plant growth occurs,
 or the carbon allocation and life history
dynamics of the plants themselves.

Marine NPP
“Marine NPP was a major driver of the
preindustrial cultures and economies of
civilizations in the higher latitudes, and is
still a major driver of the global fishing
industry”
 Driven by:

◦ Nutrients – upwelling
◦ Geology
Terrestrial NPP
“The most remarkable feature of the
terrestrial NPP distribution is that it is
the opposite of the pattern of marine
NPP”
 Driven by:

◦ Climate?
◦ Why not nutrients?
Nutrients in Tropics
Are the tropics a good place for
agriculture?
 The basic processes of soil weathering have
several inevitable consequences that result
in a decline in soil fertility, and thus in the
resources available to support plant growth
and NPP over time as soils age.
 All of these processes occur most rapidly
in the tropics.

Global
Nutrient
Content

“Why should marine productivity be
positively correlated with the availability
of mineral nutrients in the oceans and the
adjacent continents, while the productivity
of the plants growing in the soil on those
continents is inversely correlated with
nutrient availability?”
Conclusions
In fact, the highest short-term rates of NPP
(eNPP) apparently occur in temperate and
boreal forests.
 These patterns of forest productivity are
consistent with the global distribution of soil
fertility
 as well as the productivity of certain types of
crops
 and the standardized economic value of
agricultural production

Why is might our current paradigm
about NPP wrong?
Hard to measure NPP
 Satellites measure green leaves, not
necessarily carbon that goes into wood.

Landscape Position and Lakes

What factors influence the ecosystem functions
of a lake?
◦
◦
◦
◦

Geology
Size/Depth
Climate
Terrestrial inputs
What about the spatial arrangement of lakes can
influence functions?
◦ Geology
◦ Climate
◦ Hydrologic connectivity
What type of ecosystem properties
could be influenced?
How to test?

Observational study..
Conclusion

Many factors change with position
◦
◦
◦
◦
Ionic composition
Biota
Size
Primary Production
Species and ecosystem function

How do species influence ecosystem
function?
Effects of Moose Browsing on Vegetation and Litter of the Boreal
Forest, Isle Royale,Michigan – McInnis et al.
Spatial patterns in the moose-forest-soil ecosystem on Isle Royale,
Michigan USA – J. Pastor et al.
Background
Landscape heterogeneity affects
population dynamics and movement.
 Animals can alter ecosystem function due
to their behavior.

◦ Ecosystem engineer?

Large herbivores could have large
impacts:
◦ Large home ranges.
◦ Eat a lot.
 But only what is tasty.
Background cont.

With selective feeding, herbivores can
affect species composition, nutrient
cycling, etc.
◦ Obvious on a local scale.

Can herbivores alter ecosystem function
at the scale of their home range, or of a
valley?
Effects of Moose Browsing on Vegetation and
Litter of the Boreal Forest, Isle Royale,Michigan

Observations:
◦ Herbivores change the structure, biomass,
production, and species composition of
vegetation in heavily browsed or grazed areas

Questions:

Results:
Effects of Moose Browsing on Vegetation and
Litter of the Boreal Forest, Isle Royale,Michigan


Observations:
Questions:
◦ What are the effects of browsing upon the
biomass and production of trees, shrubs, and
herbs?
◦ Does browsing alter species composition of the
vegetation?
◦ Do changes in species composition affect the
quality and quantity of litterfall in browsed areas?

Results:

What are the effects
of browsing upon the
biomass and
production of trees,
shrubs, and herbs?

Does browsing alter species composition of the
vegetation?
Effects of Moose Browsing on Vegetation and
Litter of the Boreal Forest, Isle Royale,Michigan
Observations:
 Questions:

◦ What are the effects of browsing upon the biomass
and production of trees, shrubs, and herbs?
◦ Does browsing alter species composition of the
vegetation?
◦ Do changes in species composition affect the quality
and quantity of litterfall in browsed areas?

Results:
◦ Higher biomass, alters species composition, …
Spatial patterns in the moose-forest-soil ecosystem
on Isle Royale, Michigan USA – J. Pastor et al.

Observations:

Hypotheses:

Results:
Spatial patterns in the moose-forest-soil ecosystem
on Isle Royale, Michigan USA – J. Pastor et al.

Observations:
◦ Moose preferentially forage on aspen and
avoid conifers.

Hypotheses:
◦ If moose browsing causes a shift in dominance
from hardwoods to conifers across adjacent
areas, we should expect corresponding
changes in soil nutrient availability over the
landscape.

Results:
What was the study about?

Examine the large-scale landscape
distribution of moose browsing intensity
in relation to plant community
composition and size structure, as well as
soil nitrogen availability.
◦ Do moose control plant community
composition and soil nitrogen at large scales?
What did they measure?
Available browse.
 Annual consumption by moose.
 Soil nitrogen availability.

They tested three models
Random
 Short-range autocorrelation
 Higher order of regularly arranged
patterns

What would these models look like?

Random
◦ No autocorrelation – constant variance

Short-range autocorrelation
◦ Low-variance at short distances

Higher order of regularly arranged
patterns
◦ Low-variance at short distance and lowvariances at large distances as well.
Spatial patterns in the moose-forest-soil ecosystem
on Isle Royale, Michigan USA – J. Pastor et al.

Observations:
◦ Moose preferentially forage on aspen and
avoid conifers.

Hypotheses:
◦ If moose browsing causes a shift in dominance
from hardwoods to conifers across adjacent
areas, we should expect corresponding
changes in soil nutrient availability over the
landscape.

Results:
What did Pastor conclude?

Tested hypothesis…
◦ Moose causing patterns.

Alternative hypotheses?
◦
◦
◦
◦
◦
◦

Slope
Aspect
Fire
Bedrock
Geology
Beavers
No differences in nitrogen availability or
consumption due to slope or aspect.
◦ Spatial patterns not caused by topographic relief.
◦ Nor other factors.
What did Pastor conclude?

Conclusion:
◦ Patterns are a result of dynamic interactions
between moose foraging and plant
communities.
◦ Uncommonly strong impact for a large
mammal.
◦ This patterns has occurred in less than 50
generations.