Transcript Herbivory and predation - University of Nevada, Reno

Seminars
•
EECB seminar Thurs 4:00 PM OSN 120.
Dr. Larry Stevens, Grand Canyon
Wildlands Council. “Biogeography of the
Grand Canyon, and Colorado River
Management”.
Reading
•
Textbook Chapter 12 and 13
•
Sparrow, A., M. Friedel, and D. Tongway.
2003. Degradation and recovery processes in
arid grazing lands of central Australia part 3:
implications at landscape scale. Journal of Arid
environments 55: 349-360.
Outline
1. Case study: identifying communities and
relating to environmental conditions
2. Student case studies
3. Productivity – plants and ecosystems
4. GPP, NPP, and Efficiency
5. Global and environmental patterns of NPP
6. Production in forest VS rangeland
7. Factors influencing productivity – fire,
herbivory, nutrient pulses, etc.
8. Climate change, CO2 accumulation, and
carbon sequestration
Identification and interpretation of
community patterns
•
•
•
Using classification (TWINSPAN) to
identify wet meadow communities
Relate community classification to
environmental (hydrologic and
geomorphic) variables
Interpret impact of stream incision on
vegetation communities
Humboldt-Toiyabe National Forest
Central Nevada
San Juan Creek
Reese River
Birch Creek
Reach-scale vegetation patterns
Above-fan:
Broad valley bottom
Wet meadows
At-fan:
Narrow valley bottom
Woody riparian and
upland vegetation
Below-fan: Intermediate
valley characteristics
Woody riparian,
mesic & dry meadows
Objectives – Hydrologic Component
• Determine the dominant vegetation types & their
species associations within Kingston Meadow
• Examine relationship of vegetation types to the
current hydrologic regime within Kingston Meadow
• Evaluate any changes in vegetation associated with a
different hydrologic regime following meadow
restoration activities
Sampling Scheme
 Determine the composition, ground cover,
and biomass of the vegetation associated
with each piezometer or nested well across a
hydrologic gradient within the meadow
• 14 cross-valley transects (10 with
piezometers/wells; 4 more to adequately
sample vegetation)
• 55 sampling points (45 nested piezometers +
10 additional sampling points)
• 110 sample plots (2 subsamples per sampling
point)
Terrace Height TWINSPAN
Vegetation Cover Class Name
Big Sagebrush/Dry Meadow
Chokecherry/Woods Rose/Willow
Western Birch/Dogwood
Aspen/Woods Rose
Mesic Meadow
Wet Meadow
Streambank (Willow/Mesic Meadow)
From unpublished data and Henderson, 2001
Stream cross-sections
n
53
14
10
15
12
23
22
Mean Terrace
Height (m)
1.90 ± 0.18
1.42 ± 0.26
1.10 ± 0.36
0.91 ± 0.16
0.87 ± 0.18
0.50 ± 0.06
0.47 ± 0.04
Meadow Groundwater
Characteristics
Water Table Depth (cm)
50
0
-50
-100
-150
-200
-250
Sa
ge
y
Dr
Me
sic
ka
bra
s
Ne
Be
ak
ed
-300
Meadow Type
From Linnerooth & Chambers, 2000
Vegetation Types- Hydrology Plots
Dominate Species
Wetland
Status
Present in
Geomorphic
Plots
Carex rostrata
Carex rostrata
OBL
Carex nebrascensis
Carex nebrascensis
OBL

Mesic Graminiod
Poa pratensis
Juncus balticus
FACU
OBL

Dry/Planted
Bromus inermis
Cardex douglasii
Agropyron cristatum
NONE
FACU
NONE

Ecological type
ge
m
Sa
ea
do
w
ea
do
w
ad
ow
me
Dr
ym
sic
sce
ns
is
ros
tra
ta
bra
ne
Me
rex
Ca
Ca
rex
Depth to water table (cm)
0
-50
-100
-150
-200
-250
-300
-25
Depth to water table (cm)
0
25
50
Carex rostrata
n=2
Carex nebrascensis
n=14
a
ab
Mesic Graminiod
n=51
b
Dry
n=12
75
100
c
125
150
175
200
Mesic Graminiod
n=112
Dry/Planted
n=25
Height above streambed (cm)
175
150
Carex nebrascensis
n=42
b
125
b
100
75
50
25
0
a
Current System Dynamics
• Climate changes that occurred over 2000
years ago are still influencing system
dynamics
• Recent incision began at the end of the Little
Ice Age about 290 years ago
• The rate and magnitude has undoubtedly
been increased by human disturbance
Stream Incision: Causes
• Overgrazing in riparian zone and upland
areas within the watershed
• Roads (crossings, captures)
• Sediment “starvation” due to long-term
climate effects
Stream Incision: Causes
Corral Canyon
Barrett Canyon
Stream Incision: Causes
• Overgrazing in riparian zone and upland
areas within the watershed
• Roads (crossings, captures)
• Sediment “starvation” due to long-term
climate effects
Stream Incision: Consequences
• Lowers water table in the riparian zone
(threshold event)
• Stream flow becomes isolated from
former floodplain
• Development of inset terraces
• Invasion of more-xeric species
• Narrowing of riparian zone and loss of
riparian habitat
Barley Cr.
(Monitor Range)
San Juan Cr.
Cottonwood Creek
1994
1998
Gaining Systems
Non-Incised Meadow
Ground Surface
Water Table Surface
Incising Meadow
Ground Surface
Water Table Surface
Losing Systems
Ground Surface
Water Table Surface
Your turn…
•
•
•
List management issues/projects you
know of in range and forest ecosystems.
Which of the ecological processes or
interactions we have discussed so far do
you need to understand?
Can you make predictions or
recommendations based on your
understanding of the ecological systems?
Productivity
•
•
•
•
Energy captured by autotrophs.
GPP=total solar radiation fixed into chemical
energy via photosynthesis
NPP=GPP-respiration
Textbook Figure 12.1 = energy pathways at
primary trophic level. Solar energy is
reflected, emitted, assimilated, respired,
consumed by herbivores, turned into detritus,
or stored in standing crop/biomass.
•
Efficiency
Proportion of energy converted into plant material.
Three components:
–
–
–
Exploitation efficiency = ability to intercept light.
GPP/solar radiation X 100%. Affected by LAI, leaf
orientation, latitude, topographic location.
Assimilation efficiency = ability to convert absorbed light
into photosynthate. GPP/absorbed radiation X 100%.
Affected by CO2 absorption, temperature, light and water
availability.
Net production efficiency = capacity to convert
photosynthate into growth/reproduction rather than
respiration. NPP/GPP X 100%. Depends on temperature
and amount of non-photosynthetic biomass supported.
Net Primary Production
•
Difficult to measure accurately on large scale
because requires measures of photosynthetic
and respiration rates.
• Usually use changes in biomass over time
NPP = (wt+1- wt) +D + H
Where (wt+1- wt) is change in biomass over time
D= biomass lost to decomposition
H= biomass lost to herbivores
Net Primary Production
•
•
•
Can also use allometric means: changes in
plant size; use regression to assess.
Allometry provides measure of root
production (mini-rhizotron images)
Global scale
– Models based on climate, precipitation,
evapotranspiration
– Also – remote sensing data
Carbon balance
•
•
•
NPP-decomposition/loss to herbivores
Essentially change in standing crop over time
Important in assessing impact of vegetation
on CO2 emissions under Kyoto Protocol etc.
Relationship of biomass to
productivity
•
•
•
BAR = biomass accumulation ratio
Ratio of dry weight biomass to annual NPP.
Higher for plant communities with more longlived structure (woody plants)
Plant community
Annual
Desert
Grassland
Shrubland
Forest
BAR
1
2-10
1.3-5
3-12
20-50
Forest biomass and NPP
•
•
Productivity often strongly related to soil fertility or
texture (eg N mineralization rate in eastern US)
As community ages, ANPP changes:
–
–
–
–
Immediately following disturbance ANPP rapid and
biomass accumulates quickly
Maximum NPP and living biomass at 50-100 yrs
Leaf biomass is maximal just before canopy closure
Older forests have lower carbon balance – decomposition
and respiration/maintenance of nonphotosynthetic tissues
Rangeland biomass and NPP
•
•
•
•
Higher biomass not necessarily related to
higher NPP
In dense grasslands removal of dead or
“decadent” biomass may stimulate
productivity
Indication of coevolution of herbivores and
grasses? Ability of grasses to re-grow
photosynthetic tissue after removal =
herbivore tolerance
Grazing lawns = rapid nutrient cycling and
high productivity caused by repeated grazing
Factors affecting NPP
•
•
•
•
•
•
Light, temperature
Water (precipitation, evapotranspiration)
Carbon dioxide (high concentrations more
influential for C3 than C4)
Nutrient availability (see handout and text P326)
Herbivory – can stimulate (by reducing competition
for light) or decrease (by removing photosynthetic
tissue)
Fire – usually stimulates: release of nutrients,
removal of competition for light and water
Variable resources
•
•
•
Resources are not constant in time or space
Ecosystems are limited by a variety of
resources
Transient Maxima Hypothesis: TMH
– Explains patterns of productivity for nonequilibrium systems.
– E.g. tallgrass prairie: at equilibrium, light is
limiting (soil resources not utilized to maximum)
– When disturbed, light not limiting, productivity
increases to utilize available resources (hence
increase in productivity with fire or herbivory)
Global carbon cycle
•
•
•
•
Atmospheric carbon flux strongly affected by
human activity
Combustion of fossil fuels and clearing of
forest releases sequestered carbon into
atmosphere
Substantial changes in CO2 since industrial
revolution (from 280 ppm to >350 ppm)
Productivity of vegetation affects CO2
concentration in atmosphere