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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.
Outline1. Case study: identifying communities and
relating to environmental conditions2. Student case studies3. Productivity – plants and ecosystems 4. GPP, NPP, and Efficiency5. Global and environmental patterns of
NPP6. Production in forest VS rangeland7. 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 ForestCentral NevadaSan Juan Creek
Reese River
Birch Creek
Reach-scale vegetation patterns
Above-fan:Broad valley bottomWet meadows
At-fan:Narrow valley bottomWoody riparian andupland vegetation
Below-fan: Intermediatevalley characteristicsWoody 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 nBig Sagebrush/Dry Meadow 53 1.90 ± 0.18Chokecherry/Woods Rose/Willow 14 1.42 ± 0.26Western Birch/Dogwood 10 1.10 ± 0.36Aspen/Woods Rose 15 0.91 ± 0.16Mesic Meadow 12 0.87 ± 0.18Wet Meadow 23 0.50 ± 0.06Streambank (Willow/Mesic Meadow) 22 0.47 ± 0.04
Mean Terrace Height (m)
From unpublished data and Henderson, 2001Stream cross-sections
Bea
ked
Neb
rask
a
Mes
ic
Dry
Sag
e
Wat
er T
able
Dep
th (
cm)
-300
-250
-200
-150
-100
-50
0
50
Meadow Type
Meadow GroundwaterCharacteristics
From Linnerooth & Chambers, 2000
Vegetation Types- Hydrology Plots
Dominate SpeciesWetland 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
De
pth
to w
ate
r ta
ble
(cm
)
-25
0
25
50
75
100
125
150
175
aab
b
c
Carex rostratan=2
Carex nebrascensisn=14
Mesic Graminiodn=51
Dryn=12
Hei
ght a
bove
str
eam
bed
(cm
)
0
25
50
75
100
125
150
175
200
Carex nebrascensisn=42
Mesic Graminiodn=112
Dry/Plantedn=25
a
b
b
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
Barrett CanyonCorral Canyon
Stream Incision: Causes
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
Incising Meadow
Ground SurfaceWater Table Surface
Non-Incised Meadow
Ground SurfaceWater Table Surface
Gaining Systems
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 timeNPP = (wt+1- wt) +D + H
Where (wt+1- wt) is change in biomass over time
D= biomass lost to decompositionH= 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
long-lived structure (woody plants)
Plant community BAR
Annual 1
Desert 2-10
Grassland 1.3-5
Shrubland 3-12
Forest 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 non-equilibrium 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