Roles of weathered bedrock and soil in seasonal water relations of Pinus Jeffreyi and Arctostaphylos patula

In the southern Sierra Nevada, California, relatively thin soils overlie granitic bedrock that is weathered to depths of several metres. The weathered granitic bedrock is porous and has a plant-available water capacity of 0.124 m3·m–3, compared with 0.196 m3·m–3 for the overlying soil. Roots confined within bedrock joint fractures access this rock-held water, especially during late summer when overlying soils are dry. We sought to determine seasonal soil and bedrock water changes in a Jeffrey pine (Pinus jeffreyi Grev & Balf.) plantation and to examine concurrent effects on the water relations of Jeffrey pine and greenleaf manzanita (Arctostaphylos patula Greene). In 1996, plant-available water in the 75 cm thick soil was depleted by late June, with soil water potential (ψsoil) <–2.2 MPa, but below 75 cm, bedrock water potential (ψbedrock) was still > –2.2 MPa. Thus, the bedrock, not the soil, supplied water to plants for the remainder of the dry season. Higher values of, and smaller fluctuations in, seasonal predawn pressure potential (ψpredawn) for Jeffrey pine indicated that it is deeply rooted, whereas active roots of greenleaf manzanita were interpreted to be mostly within the upper 100 cm. The extra rooting volume supplied by weathered bedrock is especially important to pine relative to manzanita.

Spray deposition within plant canopies

Spray deposition was measured within canopies of bracken fern (Pteridium aquilinum) and greenleaf manzanita (Arctostaphylos patula) following ground application of a spray mixture containing water a fluorescent tracer and surfactant A high proportion of spray (3538) reached the ground through manzanita canopies whereas only 113 reached the ground through a bracken canopy Spray deposition was closely linked to the quantity of foliage projected on a plane normal to the trajectory of droplets passing through the canopy Droplets that had trajectories with a significant horizontal velocity component were more effectively captured because of an increase in the quantity of foliage in their path

Development of a Shrub-Fern-Ponderosa Pine Community Eleven Years After Site Preparation and Release

Vegetation management can direct trends in early plant development and species succession and through various treatments achieve specific combinations of species desired by the ecosystem manager. Density and development of several plant species were studied in an area in northern California that was planted with 1-yr-oldponderosa pine (Pinus ponderosa var. ponderosa) seedlings in 1986 and treated with three herbicides (Velpar L, Garlon 4, Escort) in fall 1986 and spring 1987. Abundant species in the new plantation were bush chinquapin (Chrysolepis sempervirens) that regenerated from root crowns, greenleaf manzanita (Arctostaphylos patula)from seed, and bracken fern (Pteridium aquilinum var. pubescens )from rhizomes. After 11 growing seasons, chinquapin sprouts in the control averaged more than 15,900/ac, manzanita seedlings over 16,400/ac, and bracken fronds 11,400/ac. Mean ponderosa pine diameter (5.1 in.), height (12.9 ft), and crown diameter (7.6 ft) were significantly greater in the Velpar treatment than in the control. Additional information is presented on plant diversity, the onset of statistically significant differences among treatments for pine, and the makeup of the plant community in the near future. West. J. Appl. For. 14(4):194-199.

ARTHROPODS ASSOCIATED WITH A MANZANITA GALL INDUCED BY THE APHID TAMALIA COWENI (COCKERELL) (HOMOPTERA: APHIDIDAE)

Galls induced by the aphid Tamalia coweni (Cockerell) were sampled from greenleaf manzanita (Arctostaphylos patula E. Greene) in Shasta County, California. Thirty galls from each of four sites were collected over a 5-year period (1990–1994) at roughly weekly intervals (N = 5010). The contents of each gall were examined and recorded. Excluding T. coweni, 25 taxa were encountered representing eight arthropod orders: Acari, Thysanoptera, Hemiptera, Neuroptera, Coleoptera, Diptera, Lepidoptera, and Hymenoptera. All play a minor role in the gall community with the exception of two species of Diptera. The data suggest that Leucopis sp. and Heringia sp. are obligatory predators of T. coweni and coexist by partitioning the aphid resource with different exploitation strategies. Heringia sp. has a relatively low infestation rate (10.8%) but is a superior competitor. Leucopis sp. compensates for its inability to compete effectively with Heringia sp. by maintaining a higher infestation rate (41.4%).

Response of Young Ponderosa Pines, Shrubs, and Ferns to Three Release Treatments

One-year-old Sierra chinkapin (Castanopsis sempervirens) sprouts, greenleaf manzanita (Arctostaphylos patula var. platyphylla) seedlings, and new fronds of bracken fern (Pteridium aquilinum var. pubescens), present in a 1-yr-old ponderosa pine (Pinus ponderosa var. ponderosa) plantation in northern California, were treated once with one of three herbicides (Velpar L, Escort, and Garlon 4) in fall 1986 and spring 1987 and their density and development compared among treatments and to a control. After 6 growing seasons, chinkapin sprouts in the control averaged more than 16,000 per acre, manzanita seedlings over 19,000, and bracken ferns more than 13,000 per acre. After 6 growing seasons, mean ponderosa pine diameter ranged from 2.03 in. in the Velpar treatment to 1.28 in. in the control. Cover of combined shrubs, also after six seasons, was about 3% with Velpar, 7% with Garlon, 20% with Escort, and 51% in the control. Bracken fern cover was greatest (13%) where foliage-active Garlon reduced competing shrubs, and least in the soil-active Velpar treatment (2%) and the control (3%), where heavy competition from shrubs precluded establishment. West. J. Appl. For. 9(1):24-28.

Impact of Shrub Sprout Competition on Douglas-fir Seedling Development

In 1983, 1-0 container-grown Douglas-fir (Pseudotsuga menziesii) seedlings were planted on a site subject to summer drought under three levels of sprout competition from greenleaf manzanita (Arctostaphylos patula) and canyon live oak (Quercus chrysolepis). Seedlings were planted with 0.25-m-tall dead sprouts, mature shrubs slashed just before planting, or 1-m tall sprouts, which represent an increasing order of competition. After 3 years, Douglas-fir survival did not differ significantly among levels of competition. However, percentage cover of competing shrubs was negatively correlated with conifer root and shoot biomass. Under the least competition, root biomass increased 25 times and shoot biomass 103 times over dry weight at planting, but dry weights in other treatments increased <5 times. Douglas-fir seedling growth did not increase significantly following shrub removal when vigorous sprouting occurred during the first year. After 3 years, however, competitor cover in the minimum-competition plots was less than 15%, and conifer biomass had increased exponentially. West. J. Appl. For. 4(3):89-92, July 1989.

Effect of Physiological Status and Growth of Ponderosa Pine (Pinus ponderosa) and Greenleaf Manzanita (Arctostaphylos patula) on Herbicide Selectivity

Correlations between herbicide damage and several physiological factors were examined in the field for ponderosa pine (Pinus ponderosaDougl. ex P&C Lawson) and greenleaf manzanita (Arctostaphylos patulaGreene). Pine injury caused by 2,4-D [(2,4-dichlorophenoxy) acetic acid], glyphosate [N-(phosphonomethyl) glycine], or triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid]} was compared to leader growth rate, needle growth rate, predawn xylem potential, daytime xylem potential, and photo synthetic rate occurring on the dates of herbicide application. Shrub injury for each of the three herbicides was compared to predawn xylem potential, daytime xylem potential, and photo synthetic rates. Both species exhibited less injury from herbicide applications made at the end of September than from any applications made from April through October. Comparison of factors highly correlated to herbicide damage indicates that highest herbicide selectivity occurs when pine has ceased growing, the xylem potential of the pine is relatively low (high water stress), and the xylem potential of the manzanita is relatively high.