GRASSLAND ECOLOGYGRASSLAND ECOLOGY

WORLD GRASSLANDSWORLD GRASSLANDS

NORTH AMERICAN GRASSLANDS REFLECTNORTH AMERICAN GRASSLANDS REFLECTWEATHER PATTERNSWEATHER PATTERNS

PRECIPITATION IS IMPORTANTPRECIPITATION IS IMPORTANT

DIFFERENTDIFFERENTGRASSLANDSGRASSLANDS

WITHWITHDIFFERENTDIFFERENT

PRECIPITATIONPRECIPITATION

GRASSLAND NET PRIMARY PRODUCTIONGRASSLAND NET PRIMARY PRODUCTION(NPP) DEPENDS ON MOISTURE(NPP) DEPENDS ON MOISTURE

SOIL TYPES CAN BE IMPORTANTSOIL TYPES CAN BE IMPORTANTWHY?WHY?

SEASONALITY OF MOISTURE ALSO IMPORTANTSEASONALITY OF MOISTURE ALSO IMPORTANT

SEASONALITY LEADS TOSEASONALITY LEADS TODIFFERENT GRASS PHOTOSYNTHETICDIFFERENT GRASS PHOTOSYNTHETIC

PATHWAYSPATHWAYS

NOT JUST WATER,NOT JUST WATER,MOISTUREMOISTUREAFFECTSAFFECTS

NITROGENNITROGENAVAILABILITYAVAILABILITY

PRODUCTION AT BISON RANGE IS NITROGEN LIMITED

Schmitz (1992) found that N - fertilization increased plantproduction more than water supplementation.

Plant production depends on soil N availability (resin bags)at microsites.

-3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

NITROGEN DEVIATIONFROM CONTROL (mg/bag)

BIO

MA

SS

DEV

IATIO

NFR

OM

CO

NTR

OL (

g-d

ry/c

ag

e)

r = 0.64, N = 21, P < 0.002

GRASSLAND:GRASSLAND:LAND OF COMMONLAND OF COMMON

DISTURBANCEDISTURBANCE

ANNUAL VARIATION IN MOISTUREANNUAL VARIATION IN MOISTURE(great)(great)

DRYNESS ANDDRYNESS ANDLIGHTNINGLIGHTNING

HERBIVORYHERBIVORY

HERBIVORY CAN BE GREATHERBIVORY CAN BE GREATIN GRASSLANDSIN GRASSLANDS

BISON RANGE HERBIVORESBISON RANGE HERBIVORES

2.5 g/m2 5.0 g/m2

Each unit of consumption = 1.25 – 1.67 units eaten

(Pre-Columbian on Great Plainsno more than 5 g/m2)

WHY?

1994

CONTRO

L

CORPSE

FRASS

HOPPER

0255075

100125

1996

CONTRO

L

CORPSE

FRASS

HOPPER

0255075

100125

1994

CONTRO

L

CORPSE

FRASS

HOPPER

0255075

100125

1996

CONTRO

L

CORPSE

FRASS

HOPPER

0255075

100125

TREATMENT

PLA

NT B

IOM

AS

S (

g/m

2)

ADDED WATER

NATURAL PRECIPITATION

TRADITIONAL VIEW OF GRASSHOPPERS

*

**

*

GRASSHOPPERS AND THE NITROGEN CYCLE

Drought Year (grasshoppers decrease plants by 43% - P < 0.03)

Normal Precipitation Year (grasshoppers do not decrease plants - P < 0.5)

LITTER POOL2.2 g/m2

LITTER POOL1.7g/m2

AVAILABLE SOIL NUTRIENT POOL1.0 g/m2

AVAILABLE SOIL NUTRIENT POOL1.7 g/m2

1.1 g/m2

0.9 g/m20.6 g/m2

0.6 g/m2

FAST CYCLE35%

SLOW CYCLE65%

FAST CYCLE50%

SLOW CYCLE50%

0.5 g/m2

0.5 g/m2

0.4 g/m2

0.5 g/m2

PLANTS(0.9 g/m2)

frass & carcasses

PLANTS(1.5 g/m2)

frass & carcasses

1994

CONTROL

CORPSE

FRASS

HOPPER02468

101996

CONTROL

CORPSE

FRASS

HOPPER02468

10

1994

CONTROL

CORPSE

FRASS

HOPPER02468

101996

CONTROL

CORPSE

FRASS

HOPPER02468

10

TREATMENT

PLA

NT –

GR

OW

ING

SEA

SO

N N

ITR

OG

EN

(mg

/g o

f re

xyn

)

A NITROGEN PERSPECTIVE FOR GRASSHOPPERS

**

**

* *

**

DENIZENS OF THE SOILDENIZENS OF THE SOILDRIVE NUTRIENT DYNAMICSDRIVE NUTRIENT DYNAMICS

Change with plant spp.Change with herbivoryChange with fireChange with drought

Different microbes = different dynamics

VERY COMPLEX DYNAMICSVERY COMPLEX DYNAMICS

HUMAN DISTURBANCEHUMAN DISTURBANCE(fire suppression, overgrazing, exotics)(fire suppression, overgrazing, exotics)

NATIONAL BISON RANGE,NATIONAL BISON RANGE,OUR LABORATORYOUR LABORATORY

MEASURING PRIMARY PRODUCTIONMEASURING PRIMARY PRODUCTION

CLIPPING TO MEASURE BIOMASS --Must separate current year’s growth from past (how?)Why dry the vegetation?Timing, plot size, number of plots?

SPECTRAL CHARACTERISTICS OF LIGHT REFLECTANCE –Why does vegetation look green?What wavelengths do chlorophyll absorb?Radiometer measures ratio of infrared to red (why?).What do you have to control for?How do you calibrate measures to biomass?Remote sensing (plane and satellite).Timing, area measured (height), number of areas?

MEASURING SPECIES COMPOSITIONMEASURING SPECIES COMPOSITION(bare ground)(bare ground)

TOE POINT AND POINT FRAME –Incidence.What is missing?Timing and how many points?

CLIPPING –Same issues as biomass measures.What does this consider?

REMOTE SENSING –Different species absorb slightly different

wavelengths.Calibration and sensitivity.Timing and how many points?

MEASURING HERBIVORYMEASURING HERBIVORYPLANT PERSPECTIVE (exclosures) –

Measure primary production with andwithout herbivores.

How large an area and how many areas?How to ensure adequate matching of exclosures

and outside areas?Does the exclosure affect plant production?

PLANT PERSPECTIVE (measure damage) –Absolute measure or index?How to calibrate to make it an absolute measure?What might you fail to consider?

ANIMAL PERSPECTIVE (compute consumption) –How many herbivores and how much does each eat?Precision?What might you fail to consider?

ANIMAL PERSPECTIVE (estimate abundance) –Index of abundance

MEASURING ABIOTIC FACTORSMEASURING ABIOTIC FACTORSSOIL TYPES –

Organic matter, sand, clay.

SOIL MOISTURE AND COMPACTION –Conductance or actual moisture?Force to penetrate?Timing and number of sites?

TEMPERATURE AND WIND –Why important?Timing?

NUTRIENTS –Measure in soil? Problem?Capture from plants? Problem?Which nutrients?Timing?

MISCELLANEOUSMISCELLANEOUS

SEED BANK –See what germinates. Problem?Flotation methods. Problem?

SOIL MICROBES –Why important?Measure activity (in situ vs. in vitro)?Identify participants (molecular techniques)?

CRYPTOPHYTES –Why important?Incidence and activity?

FIRE AND DROUGHT –How to measure (frequency and intensity)?

TOUR OF BISON RANGETOUR OF BISON RANGE

Purpose: To see what is there to help you indesigning the two class projects.

FIRST PROJECTFIRST PROJECT

Problem: Compare two adjacent sites, one with cattle andthe other without.

Goal: Learn methods. Assess sampling intensity necessaryto be confident in primary production,species composition and abiotic measures.

Product: Single group presentation, including statisticalanalysis.

Value: How much to sample at each site in thesecond exercise?

SECOND PROJECTSECOND PROJECT

Problem: Assess what might determine the presence ofdifferent plant communities at different sites.

Goal: Learn about what creates different grasslands.How to sample to address a comparative communityecology study. Apply more advanced statistics.

Product: Two group presentations (including statisticalanalysis). Can different communities be identified?How do communities differ?

Value: Learn about comparative ecology and whyplant communities may differ.