Climate, soil and biotic relationships along an annual grass invasion gradient

Results• Invasive annual grass cover was negatively correlated

with native perennial grass cover (r = -0.64). This was the strongest relationship to any of the measured abiotic or biotic variables for grasses.

• Annual grass cover was positively correlated with soil temperatures (r = 0.59), while perennial grass cover and native species diversity were negatively correlated with soil (r = -0.54) and air temperatures (r = -0.81).

• The abundances of annual forbs, shrubs and soil microbes did not have strong relationships to any climate variables.

• Structural equation modeling confirmed that the negative effect of warmer temperatures on native plants would indirectly favor the spread of annual grasses.

ConclusionOur findings indicate that biotic relationships are relatively strong in invaded sagebrush-steppe habitat, and therefore species distribution models based solely on climate variables may underestimate changes in invasive and native species’ ranges that are expected to occur with climate change in sagebrush-steppe.

• We assessed 100 climate, soil, biotic and disturbance variables associated with annual grass invasion in sagebrush-steppe across 90 field sites in eastern Oregon.

• We compared the relative correlative strength (r values) of the abundances (cover, biomass, density) of invasive and native species and diversity to each abiotic and biotic variable.

• Structural equation modeling (SEM) was used to demonstrate how multiple ecological factors can interact to influence native and invasive species abundances.

Materials and Methods

Introduction• Changes in species distributions are predicted to

follow changes in climate.

• Biotic interactions (e.g., competition) are increasingly recognized as important drivers of species distributions at micro and macroecological scales.

HYPOTHESIS: Differences between native and invasive species responses to climate may intensify competitive interactions and accelerate changes in species distributions faster than predicted from models based on climate alone.

Sheel Bansal, PhD Research Ecologist

Olympia Forestry Sciences LaboratoryOlympia, Washington 98512

[email protected]; [email protected]

This research was funded through the USDA-Agricultural Research Service Areawide Project for Ecologically-based Invasive Plant Management of Annual Grasses in the Great Basin Ecosystem

Distribution of Invasive and Native Species in Sagebrush-Steppe: The Relative Importance of Climate, Soil Properties, Biotic Interactions and Disturbance

Sheel Bansal1,2 and Roger Sheley1

1USDA Agricultural Research Service, Eastern Oregon Agricultural Research Center2USDA Forest Service, Pacific Northwest Research Station

I

litterheight

NativeSpecies

Richness

PF cover

AG density

AG seed/m2

bareground

coarsewood

rocks

invasiverichness

pH

mineral N

soil C

Plant community Plant functionalgroups

Disturbance

Ground layer

Soil physicalproperties

Soil chemicalproperties

elevation

max air T

spring precip.

shrub density

Climate/Geography

Soil biotic properties

SIR/soil C

SLA shrub

SLA tree

shrub heightPlant traits

PF height

snowfree

GWCWHC

soil N

InvasiveSpecies

Richness

nativerichness

shrub cover

AG density

AG seed/m2

BSC

litterheight

baregroundcoarsewood

sand

C: N

AUMs


Disturbance

Ground layer



latitude

min air T

AF cover

Climate/Geography


SLA AG Plant traits

litter cover

RQ

basalrespiration

PG cover

aspect AF height

rock covermineral P

silt

PerennialGrassCover

PF cover

AG cover

AG seed/m2

BSC

litterheight

roots

residentrichness

pH

mineral N

soil C

bulk density


Disturbance

Ground layer



elevation

mean soil T

spring precip.

shrub density

Climate/Geography


SIR/soil C

SLA shrub

SLA PG

shrubfootprint

Plant traits

PG height

snowfree

GWCWHC

soil N

AnnualGrassCover

invasiverichness

nativerichness

shrub density

PG density

AG seed/m2

BSC

litterheight

baregroundcoarsewood

GWC

mineral N

grazingutilization


Disturbance

Ground layer



elevation

min soil T

spring precip.

PF cover

Climate/Geography


SLA shrub

shrub heightPlant traitsAG height

total plant cover

litter cover

Abbreviations: annual grass (AG); annual forb (AF); perennial grass (PG); perennial forb (PF); specific leaf area (SLA); biological soil crust (BSC); carbon (C) to nitrogen (N) ratio (C:N); temperature (T); animal unit months (AUMs); water holding capacity (WHC); gravimetric water content (GWC); respiratory quotient (RQ); substrate-induced respiration (SIR);

Positive (blue solid lines) and negative (red dashed lines) correlative relationships between richness and abundance of invasive and native species to abiotic and biotic factors. Thicker lines correspond to higher r values

Invasives

Natives

Temperature

PG SLA

Perennial forb cover

Mineral N

Microbial biomassSoil C

Root biomass m-3

Annual grass coverPerennial grass

cover

R2 = 0.51

R2 = 0.31

R2 = 0.36

R2 = 0.29

R2 = 0.63

-0.56-0.27

-0.44

-0.60-0.45

0.33

0.50

0.21

0.59

0.48

0.20

CLIMATE

VEGETATION

SOIL

Precipitation

Resident speciesrichness

0.29

χ2 = 26.65, P = 0.23; df = 22

Solid lines with adjacent standardized coefficients indicate positive (blue) and negative (red) significant relationships; paths with precipitation were examined, but were not significant. Values of R2 are squared multiple correlations for each functional group.

SEM of integrated climate, vegetation and soil factors

5th Annual Pacific Northwest Climate Science Conference 2014