Jodi Johnson-Maynard

Ph.D. 1999

Address:

Department of Plant, Soil & Entomological Sciences
University of Idaho
Moscow, ID

Dissertation Title:

Biogeochemical Processes and Soil Formation Across a Chaparral Biosequence

Currently:

Assistant Professor, Department of Plant, Soil & Entomological Sciences
http://www.ag.uidaho.edu/pses/People/fac_pages/p_fac_maynard.htm

Publications from Dissertation Research:

Johnson-Maynard, J.L., R.C. Graham, L. Wu, and P.J. Shouse. 2002. Modification of soil structural and hydraulic properties after 50 years of imposed chaparral and pine vegetation. Geoderma 110:227-240.
Johnson-Maynard, J.L., P.J. Shouse, R.C. Graham, P. Castiglione, and S.A. Quideau. 2004. Microclimate and pedogenic implications in a 50-year-old chaparral and pine biosequence. Soil Sci. Soc. Am. J. 68:876-884

Photo of Jodi hand sorting soil under scrub oak to obtain estimates of earthworm density

Vegetation has a profound influence on soil processes. Understanding the role of vegetation as part of a functioning ecosystem is increasingly important as shifts in vegetation are more common due to urban sprawl, fire suppression, and logging.

Jodi's research focused on the influence of vegetation on biogeochemical processes, microclimate, and the development of physical properties important to water movement.

Photo of the lysimeters at the San Dimas Experimental Forest before planting of native species

In 1946, a biosequence was created when several types of native chaparral and one pine species were planted in a series of earthen-walled "lysimeters" (5.3 x 5.3 x 5.3 2.1m deep). Today, this biosequence provides the rare opportunity to quantitatively assess the effect of vegetation on soil processes.

Morphologically, soil profiles forming under scrub oak and Coulter pine represent the end-members of the biosequence. A thick (7 cm) dark, A horizon has formed under oak. Under pine the soil has a thicker O horizon, a thin (1 cm) A horizon, and a weakly developed clay-enriched (argillic) horizon.

Photo of some earthworms collected at the site

Earthworms, which have a large effect on soil processes, are abundant under scrub oak, but absent under pine. Under scrub oak earthworms:

Mixed organic matter into mineral soil, causing a thicker A horizon with greater porosity, saturated hydraulic conductivity, and available water holding capacity.
Mixed mineral soil and prevented formation of argillic horizon.
Increased the decomposition rate of litter and biocycling of essential elements.

Charts showing calcium and potassium data for precipitation, throughfall, litter leachate and in the soil at three depths (10, 35, and 65 cm). Under Oak the Ca and K levels are significantly higher in the litter. Under pine the K levels are significantly higher in the litter

Large amounts of K and Ca are released from the litter layer under oak. These elements are quickly taken up by the plant or incorporated into mineral structures (data represent the mean annual concentration for two years of data)

Charts showing temperature an volumetric water contents for lysimeter soils under oak and pine

Average monthly soil temperature (10 cm) and volumetric water contents under Coulter pine and scrub oak.

Despite differences in soil physical, chemical and morphological properties under oak and pine, microclimatic conditions are very similar. This indicates that earthworm burrowing and biocycling have had a greater effect on soil processes than the microclimate created under each species.