SLIDE 1
FRAP 2003
Californiarangelandstatus,structureandfunc2on ValerieEviner,UCDavis - - PowerPoint PPT Presentation
Californiarangelandstatus,structureandfunc2on ValerieEviner,UCDavis - - PowerPoint PPT Presentation
Californiarangelandstatus,structureandfunc2on ValerieEviner,UCDavis Million acres Rangeland 57 Area Availablefor 41 Grazing AreaGrazed 34 FRAP2003 Grasslands
SLIDE 2
SLIDE 3
Grasslands (including within hardwood woodlands) provide over 2/3
- f CA livestock
forage
FRAP 2003
SLIDE 4
SLIDE 5
States
Exo2c annual grassland (grasses and forbs) Na2ve grassland (grasses and forbs) “New” exo2cs ‐ Medusahead
‐ Goatgrass
‐ Yellow starthistle Oak woodland Oak savanna Shrubs
SLIDE 6
Major driver of func?on/ composi?on
- Timing of
precipita?on and warm temperatures
- Variability in
precipita?on
- Past 20 years, 6‐8
fold annual varia?on in precipita?on
- At least 8 mul?‐
year droughts since 1900
Summer Fall Winter Early Spring Late Spring
a
Precipitation Temperature
Summer
Climate
Wet-up
Summer Fall Winter Early Spring Late Spring Summer
Aboveground Belowground
Plant growth rate b
Wet-up
Biswell 1956, Eviner & Firestone 2007
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Factors influencing produc?on and states and transi?ons
- Precipita2on‐ amount, seasonality
- Soil‐ nutrients (N,P, S), water
- Grazing‐ ?ming, intensity, frequency, type, dura?on
– Also herbivory by: grasshoppers, elk, deer
- Fire‐ ?ming, intensity, frequency, type
- Soil disturbance by animals (gophers, ground squirrels,
feral pigs, earthworms) e.g. pocket gophers turn over en?re soil surface every 3‐15 years
- Granivory‐ voles, mice, ants
- Pathogens‐ barley yellow dwarf virus, sudden oak death
- Compe??on between plant groups
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Plant community Nitrogen availability Other Key determinants
- f impacts
Fire Spring burning o[en increases forbs in short‐term Short‐term increase in nitrogen availability Short‐term erosion Timing Frequency Soil disturbance by mammals O[en increases forbs in short‐term poten?al to increase annual exo?cs Short‐term increase in nitrogen availability, soil carbon release Short‐term erosion Timing Frequency Grazing Generally increase na?ve annual forbs Varied impacts on: exo?c grasses, na?ve grasses, produc?vity No impact to slight increase in N pools, cycling Redistribu?on Compac?on Alter small mammal ac?vity Trampling of thatch Increase root alloca?on Timing Frequency Dura?on Intensity Grazer Type Weather Vegeta?on type Grazing exclusion Increased thatch can: ‐ Decrease produc?on ‐ Decrease forbs (2‐ fold) ‐ Increase fire ‐ Increase goatgrass
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States alter func?on
Exo2c annual grassland (grasses and forbs) Na2ve grassland (grasses and forbs) “New” exo2cs ‐ Medusahead
‐ Goatgrass
‐ Yellow starthistle Oak woodland Oak savanna Shrubs
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Annual state is “weird”
- Mediterranean climate‐ cool season grasses dominate
- Invaders are early successional in their na?ve range,
stable state in CA (this is gedng increasingly common throughout W. US rangelands)
- Standard rangeland assessments don’t work in CA‐
annual is considered “degraded” state
Westoby et al. 1989
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Need different frameworks to assess annual func?on
Exo2c annual grassland (grasses and forbs) Na2ve grassland (grasses and forbs) “New” exo2cs ‐ Medusahead
‐ Goatgrass
‐ Yellow starthistle Oak woodland Oak savanna Shrubs
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Future challenges
- Invasive species
- Temperature Change
– increased temperature, 2‐4 fold increases in frequency of heat stress days
- Precipita?on Change
– Mean annual precipita?on predic?ons
- Northern California‐ 0‐18% decrease (Greatest decrease in the Central Valley
and North Coast)
- Southern California‐ 26% decrease to 8% increase
– Seasonality
- Shorter growing seasons (most decreases in late spring/summer)
- Moderate winter decreases‐ but less frequent, more intense storms
- Spring/fall precipita?on not well‐modeled (but likely most important for vegeta?on
composi?on) – Annual variability will increase
- 1.5‐2.5 fold increase in frequency of cri?cally dry years
- Increased El Nino frequency
- Nitrogen deposi?on‐ increase invasion
- Land use change
– Projected to lose 750,000 acres of rangeland by 2040‐2100)
- Increased expecta?ons of what rangelands should deliver