Treesearch

Bearclover inhabits thousands of acres of forest land in northern and central California, but little quantification of its recovery after timber harvest, site preparation, and planting is available. And the species composition and development of the ensuing plant community is largely unknown. Density, foliar cover, and height of planted ponderosa pine seedlings, bearclover, whiteleaf manzanita, forbs, and grasses were documented from 1986 through 1996 in northern California. After 11 growing seasons, bearclover and planted ponderosa pines were dominating, whiteleaf manzanita was increasing,...

Carbon dioxide reduction through urban forestry—Guidelines for professional and volunteer tree planters has been developed by the Pacific Southwest Research Station’s Western Center for Urban Forest Research and Education as a tool for utilities, urban foresters and arborists, municipalities, consultants, non-profit organizations and others to determine the effects of urban forests on atmospheric carbon dioxide (CO2) reduction. The calculation of CO2 reduction that can be made with the use of these Guidelines enables decision makers to incorporate urban forestry into their efforts to...

We studied Brown-headed Cowbird (Molothrus ater) parasitism rates in four forest types (ponderosa pine, mixed conifer, true fir, and lodgepole pine) over an elevational gradient in the southern Sierra Nevada. Cowbirds were most abundant and parasitism rates were highest at the lowest sites. All but one of 17 parasitized nests were found in the ponderosa pine type and cowbirds were detected only in ponderosa pine and mixed-conifer forest types. A hypothesis that cowbird breeding and egglaying are limited by late release of livestock at higher elevations was not rejected. Data also supported...

In foothills of the western Sierra Nevada, 31 km east of Madera, California, we studied whether Bewick's Wrens (Thryomanes bewickii) tend to be excluded from an area occupied by House Wrens (Troglodytes aedon) as reported in several studies in the eastern United States. Neither point counts from 1985 to 1997 nor spot mapping from 1989 to 1993 suggests any interaction between these species. The study period included the most prolonged drought and the most severe period of winter weather in the 64-year climatological record from the study site. House Wren abundance was significantly related...

Dusky-footed woodrat (Neotoma fuscipes) abundance is often estimated using house counts; a house typically being described as a large pile of sticks, usually built on the ground, but occasionally on tree limbs. For purposes of the count, it is sometimes assumed that each "active" house represents one woodrat. An active woodrat house is indicated by its appearance; fresh vegetative cuttings at the house and the presence of recently deposited fecal pellets. Results from our ongoing study in the foothills of the Sierra Nevada suggest that, in some habitats, house counts may not be a reliable...

A contingent valuation in-person survey of Puerto Rican households was performed from April to August 1995 to estimate their willingness-to-pay for preserving instream flows in the Río Mameyes and avoiding a dam on the Río Fajardo. Annual willingness-to-pay was $21 for each river. When expanded to the 1 million households in Puerto Rico for the 5-year period households were asked to pay, this amount increased to $110 million for the Ríos Mameyes and Fajardo. Visitors to the Río Mameyes indicated they would reduce trips by 93 percent if 10 million gallons daily were withdrawn from the...

The genus Pinus evolved about 100 million years ago, spreading from centres in eastern North America and western Europe throughout middle latitudes of the supercontinent Laurasia. Many early subsections of Pinus are recorded from fossil remains ofthis period, but it is not until the early Tertiary, when the genus was fragmented by changing global climates and continental tectonics into latitudinal refugia, that secondary centres of origin appeared. From one of these areas, now Mexico and Central America, the subsection Oocarpae is thought to have arisen. This subsection includes the...

Maxipinon (Pinus maximartinezii Rzedowski), which is confined to a single population of approximately 2000 to 2500 mature trees, covers about 400 ha in southern Zacatecas, Mexico. Genetic diversity measured by expected heterozygosity was 0.122, which is moderate for pines. However, percentage polymorphic loci was low, 30.3%. The fixation index (F) of 0.081 indicated only slight heterozygote deficiency. Mating system analysis indicated a significant but low level of selfing; the multilocus outcrossing rate, tm, was 0.816. The mean of single locus estimates, ts, was smaller (0.761), perhaps...