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