Patterns and Controls of Net Primary Patterns and Controls of Net Primary ProductivityProductivity

Alan KnappAlan Knapp11, John Briggs, John Briggs22, , John BlairJohn Blair33, Phil , Phil FayFay44, Dave Hartnett, Dave Hartnett33, Loretta Johnson, Loretta Johnson33, Jim , Jim

KoellikerKoelliker55, Jesse Nippert, Jesse Nippert33 and and Melinda SmithMelinda Smith66

11Department of Biology, Department of Biology, –– Colorado State UniversityColorado State University22School of Life Sciences School of Life Sciences –– Arizona State UniversityArizona State University33Division of Biology Division of Biology –– KSUKSU44ARSARS--USDA USDA –– Temple, TexasTemple, Texas55Department of Biological and Agricultural Engineering Department of Biological and Agricultural Engineering -- KSUKSU66Department of Ecology & Evolutionary Biology Department of Ecology & Evolutionary Biology –– Yale UniversityYale University

> 10,000 plots and counting…

Overview:

• Highlight major accomplishments during the last 5 years• Present potential new research activities that may be incorporated into the LTER VI proposal.

Land UsePractices

ClimateChange

NutrientEnrichment

BiologicalInvasions

Tallgrass Prairie EcosystemsStructureFunction

Biotic Interactions

AlteredHydrology

Land Cover Change/Woody PlantExpansion

AlteredBiogeochemical

Cycles

• Fire• Grazing• Land use history

• Rainfall timing and amount

• Temperature

• Elevated N deposition

• Fertilization

• Exotic species introductions

Dynamics of ANPP in the context of Konza LTER and contemporary global change issues…

527.5 g/m2

406.7 g/m2

369.1 g/m2

355.2 g/m2

Abrams et al. 1986Briggs & Knapp 1995Knapp et al. 1998Briggs & Knapp 2001Nippert et al. 2006

Fire

417.1 g/m2 (all sites); range 178 - 785

Total Grass Forbs

AN

PP

(g . m

-2 . yr

-1)

0

100

200

300

400

500

annually burned unburned

*

*

*

~30% increase

Change in controls on ANPP related to land-use change

Fire exclusionAnnually burned

Woody plant encroachment

ARC

WYOKNZ

VCR

LAC

VER SEV

JOR

Site Biome type MAP/ MAT (mm/ºC)

PET (mm)

Growing season length

Arctic, AK (ARC) Tussock Tundra 291/-12.5 114 55 days Jornada, NM (JRN) Chihuahuan Desert 264/14.4 794 255 days

Konza, KS (KNZ) Tallgrass Prairie 859/12.9 793 180 days La Copita, TX (LAC) Subtropical Thorn Woodland 680/ 22.0 1448 289 days Sevilleta, NM (SEV) Chihuahuan Desert 242/13.3 747 210 days

Vernon, TX (VER) Temperate Savanna 655/17.0 1487 220 days Virginia Coast Reserve,

VA (VCR) Temperate Barrier Island 1065/ 14.2 786 245 days

Sierra Madre, WY (WYO) Sagebrush Steppe 259/ 6.2 483 100 days

SitesCHI SBS TUN SAV THW TGP ISL

ANP

P (g

/m2 )

0

200

400

600

800

1000

1200

Mea

n A

NPP

(g/m

2 )

0

200

400

600

800

1000

ShrublandGrassland

p < 0.05

Grassland∆ Change Shrublands

Mean Annual Precipitation

A

Precipitation (mm)200 400 600 800 1000 1200

Cha

nge

in A

NP

P (g

/m2 )

0

200

400

600

800

1000

1200

SAV

TUN

THWTGP

ISL

SBSCHI

B

r2 = 0.80

3-fold increase!

Long-term Irrigation Study – resource (H20) addition

• Treatments initiated in 1991

• Supplemental water added during the growing season to replicate 140 m transects (paired with control transects)

• Designed to meet plant water demand and minimize intra-annual variability in soil water deficits

Tota

l AN

PP (g

/m2 )

300

400

500

600

700

800

900

Year1992 1994 1996 1998 2000 2002 2004

PPT (mm

)

0

200

400

600

800

1000

1200

Control

Irrigated

*

*

*

**

** *

*

**

*

*

~25% ~70%

Why would the response double from the first 8 years to the next? More on this later…

12 rainfall manipulation plots (RaMPs) + non-sheltered controls

Collect, store, and reapply natural rainfall on intact prairie plots

Treatments include ambient and altered rainfall patterns

The Rainfall Manipulation Plot (RaMP) Experiment

Address the impact of changes in size and timing of growing season rainfall

Climate change

Altered rainfall patterns and soil moisturePrecipitation (m

m)0

20406080100

Soil

wat

er c

onte

nt 0

-30

cm (%

)10

20

30

40

50

DateJun Jul Aug Sep Oct

10

20

30

40

50

020406080100

Ambient Altered

Cha

nge

in S

WC

(%)

per

sam

plin

g in

terv

al

0.0

2.5

5.0

7.5

10.0Mean SWC = 24.7 ± 1.4%

P = 0.01

Mean SWC = 29.5 ± 1.2%A - Ambient rainfall treatment

B - Altered rainfall treatment

Precipitation (mm

)

0 10 20 30 40 50

Dep

th (c

m)

0-10

20-30

40-50

60-70

80-90

Root mass (% of total)

Ambient ppt timing: • “typical” seasonal

pattern

Altered ppt timing:• repeated deficits• more extreme wetting

and drying cycles

Average soil water content in top 30 cm:- reduced by 12%

Variability in soil moisture:- increased by 27%

ANPP responses to altered rainfall timing ~ 10%

Year1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

AN

PP

(g m

-2)

300

400

500

600

700

800

900

1000

1100

ambient timingaltered timing

*

* *

*

pre-treatment

Amb Alt

AN

PP

(g m

-2)

0100200300400500600700

P<0.001

Climate changeWarming treatments (~2 C) implemented in 2003 using IR lamps

Warming reduced ANPP by ~12% in 2 of 4 years

Year2003 2004 2005 2006

AN

PP

(g m

-2)

0

200

400

600

800

1000ControlWarmed

*

*

Unburned BurnedUnmowed Mowed

Significant EffectsBurn P < 0.005Nutrient P < 0.0001Nutrient x Burn P < 0.005Mow X Burn P < 0.05

Mean Aboveground Net Primary Productivity

AN

PP

(g m

-2)

0

200

400

600

800

1000

1200

Control+P +N+N+P

Nutrient Treatment

Unmowed Mowed

Nutrient (N) addition

60-125% increase

Ecosystem consequences of C4 grass invasion of a C4 grassland

Reed et al. 2005

Ecosystem consequences of invasive exoticspecies in grasslandsP. K. Baker et al. in prep.40-140% increase

Invasive species

Permanent exclosures (long-term) – Movable exclosures(2007)

Grazing – Our one gap…

Planned or new studies

• N pulse press experiment – Smith/Knapp/Blair• NutNet experiment - Smith• RaMPs grazing experiment – Knapp/Collins/Smith/Blair• Role of spring soil moisture experiment– Knapp

Where do we go from here with the core LTER ANPP measurements?

How do we continue our long-term records and still address compelling new science questions?

And with no real “new” funding?!?!

Probably don’t want to clip many more plots….But we can clip smarter and our data can be used in novel ways.May require some re-examination of how we collect our data…

Global change and chronic resource alterations

The Konza LTER Program has much to

offer….

• May be related to species changes (increased cover of Panicum virgatum) –Community response

Year1992 1994 1996 1998 2000 2002

Ave

rage

cov

er (%

)

0

20

40

60

80control

control

irrigated

irrigated

Andropogon gerardii

Panicum virgatum

Irrigation water added (mm)0 100 200 300 400 500

Stim

ulat

ion

in A

NP

P (g

/m2 )

0

100

200

300

400

500

r2 = 0.66

= 1999-2003

= 1991-1998

What would change the relationship between ANPP and precipitation in the irrigation transect study?

Physiological response

Community re-ordering

Community change

Res

pons

e

Time

Resource alteration

Physiological response

Community re-ordering

Community change

Res

pons

e

Time

Resource alteration

10-25%

30-125%

60-200%

Currently – we have adjacent measures of community change and ecosystem response

• Consider harvesting biomass by species in a targeted set of treatments to directly link community change to ANPP responses