A Comparison of Carbon Cycling and the Surface Energy Balance Between Native Perennial and Exotic Annual Grass Ecosystems in Northern Coastal California

Laurie Koteen1, John Harte1,2, Dennis Baldocchi2, Carla D’Antonio3, Ted Hehn2

1Energy and Resources Group, UC Berkeley, 2Dept. of Environmental Science, Policy and Management, UC Berkeley, 3Dept. of Ecology, Evolution and Marine Biology, UC Santa Barbara

AbstractThis research is a comparative look at the cycling of carbon, water and energy in native perennial and exotic annual grass ecosystems. California’s native perennial grasses have been almost completely replaced by exotic annual grasses across the state’s ten million acres of grassland habitat. The comparison is being carried out at two field sites in Marin County, California where remnant perennial grass communities are found on the same soils and slopes as exotic annual grasses. This research makes use of a number of biogeochemical and micro-meteorological methods. The primary objectives are:

1. To observe and understand the biotic and abiotic processes that affect the cycling and storage of carbon, water and energy among the soil, plants and the atmosphere in native perennial and exotic annual grass ecosystems in northern coastal California.

2. To apply our observations towards understanding ways that changing ecosystems affect surface climate and meteorology, and how they may impact the magnitude and direction of global climate change.

We have set up research plots at each of the two field sites, in locations of relatively pure native perennial and exotic annual grass communities. In each plot, we are measuring plant and soil carbon storage, above and belowground annual productivity and rates of tissue turnover, soil temperature, soil moisture and soil respiration, to understand the mechanisms by which differences in ecosystem carbon storage arise.

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Native grass 1 = Agrostis densiflora, Native grass 2 = Festuca rubra, Native grass 3 = Mix of Bromus carinatus, Nassella pulchra and Danthonia californica, Native grass 4 = Elymus glaucus and Bromus carinatus Exotic grass 1 = mix of exotic grasses from Tennessee Valley field site, Exotic grass 2 – mix of exotic grasses from Bolinas Lagoon Preserve field site.

Acknowledgements: We would like to thank the the Kearney Foundation for Soil Science, the NASA Earth Systems Science Graduate Student Fellowship Program, the Energy and Resources Group at UC Berkeley, and the Berkeley Atmospheric Science Center for support for this research.

At Tennesse Valley, in the Golden Gate National Recreation Area, we have also established two sets of micro-meteorological sensors: one in the annual and one in the perennial- dominated grassland. We use the surface renewal and the eddy covariance methods to measure the components of the surface energy balance.

Soil Carbon in Depth Increments Native (Agrostis and Festuca) vs. Mixed Exotic Grasses from Tennessee

Valley, Marin County

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Annual Aboveground Productivity for Two Sites in Marin county, California (kg.m-2), 2003-2004

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Overview of a typical native grass plot. Observe, soil temperature probes, litter decomposition bags, and soil respiration collars.

We hypothesize that differing lifecycle strategies between annual and perennial grass species have led to key differences in plant morphology, phenology and tissue quality that, in turn, impact material exchange at the land surface. Long-lived perennial species produce deep roots, have a bunchy structure, construct complex tissues and transpire over most of the year. By contrast, annual species are shallow-rooted, evenly-distributed, build tissues to last a single wet season, and die with the onset of summer drought. We expect that these structural and functional differences have led to differences in the cycling of carbon, energy and water by affecting soil temperature, soil moisture, radiation capture and energy partitioning into latent and sensible heat fluxes.

Total Root Biomass In Two Native (Festuca rubra and Agrostis densiflora ) and an Exotic (Mixed Species) Grass Community, in kg.m-3 Tennessee Valley, Winter 2003 -

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Total Root Biomass in kg.m-3 for two Native grass (Festuca rubra and Agrostis densiflora ) and an Exotic Grass Community,

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Native Grasses and Exotic Grasses change in color and morphology over the course of the year. a. Native grasses (Spring), b. Exotic Grasses (Spring), c. Native grasses (Summer), d. Exotic grasses (Summer).

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Tennessee Valley Soil Moisture Festuca (native grass)

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Tennessee Valley Soil Moisture Exotic Grasses

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Micro-meteorological station among Native Perennial Grasses,Tennessee Valley, Marin County, CA.

To determine the surface energy balance components, weUse both the Surface Renewal Method and the EddyCovariance Methods. The Surface Renewal Method is a robust alternative to the more commonly used, but moreexpensive technique for determining surface fluxes.

Surface Renewal and Eddy Covariance Methods for Estimating Sensible Heat Flux at the Vaira Ranch, Day 346, 2001. Baldocchi, pers. comm.

Schematic of Changes in Native andExotic Grasses with the seasons. NativeGrasses (left) and Exotic Grasses (right.)

Some Preliminary Results

Soil carbon at the Tennessee Valley field site. At some depths, there is greater storage under the native grasses. This is most pronounced at lower soil depths, where the root system for exotic annual grasses is scarce and well-developed under native perennial grasses.

Soil Moisture Profile under the native perennial grasses (left) and exotic annual grasses (right.) The top soil layers are driest underthe annual grasses. In contrast, the bottom soil layers becomethe driest under the native perennial grasses during the onset of summer drought, as depicted here.

Preliminary latent Heat flux is found to be similar for annual and Perennial grasses. However, we estimate that transpiration is higherUnder perennial grasses and evaporation higher under annuals. The Data set for the perennial grasses started in February 2004. The dataset for the annual grasses began in June 2004.

Albedo for annual and perennial grasses. The data set for perennial grasses began February 2004. Data set for annuals began in June 2004.

Preliminary sensible heat flux for annual and perennial grasses. The data set for perennial grasses began February 2004. Data set for annuals began in June 2004.

Root biomass at the Tennessee Valley site at Period of minimum (winter) and maximum (summer) root biomass.