Interacting effects of water input, nitrogen deposition, and fire on Coastal Sage Scrub Mike Goulden mgoulden@uci.edu

(1) How vulnerable (resilient, resistant, etc) are Southern California’s ecosystems to stress (fire, climate change, N deposition, etc)?

(2) What stress or combination of stresses poses greatest risk (where’s the Achilles heel)?

Transect Surveys

Manipulations

Eddy Flux

Santa Ana Mtns

San Jacinto Mtns Palm

Springs

Pacific

Experimental approach

Loma Ridge

•  Loma Ridge section of historic Irvine Ranch (~75 km southeast of here)

•  Currently managed by Irvine Ranch Conservancy

•  Mosaic of exotic annual grassland coastal sage evergreen oaks

•  Experiment site

•  What did this area look like 80 years ago?

•  VTM (Vegetation Type Map) survey in ~1930

•  Hand drawn – working off ~1895 topographic maps – lots of uncertainty

•  Mosaic of exotic annual grassland coastal sage evergreen oaks

•  Similar to what we see today

•  Experiment site - dominated by California sagebrush, black sage and buckwheat

1938 1977

1983 2002

CSS

GL

California sagebrush, black sage still dominate; Rhus/Malosma have increased

California sagebrush, black sage and buckwheat

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Clay Silt Sand

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Soil Texture

Loma Ridge - Soil Texture Analysis

Grassland Shrubland

Why so stable?

•! Differences in soil? Nope – same texture across border – same texture to 2-m depth

•! Constant environment? Nope – at least 4 wildfires (1948, 67, 98, 07), an order of magnitude interannual precip variation

•! Lots of ecological resiliency (at least to normal fire and precip patterns of management since 1930)

65 mph gusts *

Air T Resiliency to wildfire – an unfortunate dataset

•!Eddy covariance – measures whole ecosystem exchanges, such as photosynthesis

•!Two sites ~300 m apart on similar soil

•!Both burned in Oct 2007 Santiago wildfire

•!Fire had no (or positive) effect on grass production

•!CSS production recovered rapidly –rates of exchange 3-4 years after fire appear higher than before fire

Greater photosynthesis

Respiration

Coastal sage

Annual grassland

July Jan July Jan July Jan July Jan July Jan July

July Jan July Jan July Jan July Jan July Jan July

Greater photosynthesis

Respiration

540 mm 370 mm 212 mm 223 mm 72 mm

Santiago Fire

• Loma Ridge

• Manipulate water (+-50%) and Nitrogen (+) input for last 5 years

CSS

GL

CSS

Simulate effects of climate change on experimental plots using roofs that close/open to remove/add water - Roofs open ~97% of the time

Roofs closed 3% of the time (for big storms)

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10/1/2008 11/20/2008 1/9/2009 2/28/2009 4/19/2009 6/8/2009

Cumulative ambientCumulative dryCumulative wet

Water input for the various treatments

1/3 of the plots get extra water

1/3 of the plots get normal water

1/3 of the plots get reduced water

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Fractional  cover

Water  input  (mm  yr-­‐1)

Filaree  (Erodium  sp.)

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Fractional  cover

Water  input  (mm  yr-­‐1)

Ripgut  Brome  (Bromus  diandrus)

Grassland - Very rapid shifts in species composition

Water input (mm yr-1)

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0.4Bromus diandrus Lolium multiflorum Avena sps. Nasella pulchra Calandrinia ciliata Erodium sps. Hirschfeldia incana Vicia villosa Lupine sps.

1929-2010 median 236 mm

• Rapid changes in relative abundance – Species reordering • Species coexist at climatological precipitation (median 236 mm /yr) • Species reordering tied to traits • Favored with drought - Forbs and shorter time to flowering • Favored in wet treatments - Grasses and N fixers

Normal Nitrogen

Added Nitrogen

Reduced precipitation

Moderate risk of change to red brome grassland

Large risk of change to red brome grassland

Normal precipitation

Stable Moderate risk of change to brome grassland

Added precipitation

Stable Stable

CSS’ Achilles heel? The combination of: •  Fire (knocks shrubs back 2-3 years; no or positive effect on

grasses) •  Several dry years (soil below 0.5-1 m remains dry; hurts

shrubs, not grasses) •  Added N (accelerates grasses; only small effect on shrubs)