Treesearch

The Forest and Rangeland Renewable Resources Planning Act of 1974 directs the Secretary of Agriculture to prepare an assessment of the nation's renewable resources and a program that will assure an adequate future supply of these resources. Responsibility for this work is assigned to the Forest Service. An inter-university symposium was held in 1976 to evaluate the first Assessment and Program. The workshop reports and the preparatory studies are summarized here, along with policy recommendations proposed.

In sexually reproducing plant species, the prevailing breeding system is of enormous importance in determining the patterns of group variation and subsequent race and species formation. The breeding system regulates the limits of the breeding population and the extent to which hybridization occurs. The breeding system in a species is governed by certain reproductive isolating mechanisms, which may be effective at many levels. One level at which isolation is operative is the interaction of pistil and pollen. In this case, pollen may be preferentially inhibited from germinating or growing in...

The molecular weight distribution of a linear homologous polymer is usually obtained empirically for any particular sample. Sample-to-sample comparisons are made in terms of the weight- or number-average molecular weights and graphic displays of the distribution curves. Such treatment generally precludes data interpretations in which a distribution can be described in terms of differing proportions of mixed populations. However, a statistical continuous univariate distribution function such as the Weibull can be applied to the molecular weight distributions measured for cellulose nitrate...

Even before weight loss in the low-temperature pyrolysis of cellulose becomes significant, the average degree of polymerization of the partially pyrolyzed samples drops sharply. The gel permeation chromatograms of nitrated derivatives of the samples can be described in terms of a small number of mixed size populations—each component fitted within reasonable limits by a Weibull distribution function. The modal value of each component is taken as an integral multiple of a "macromonomer" of nominal degree of polymerization 228.4. Thus, the data are consistent with a model in which the...

In Mediterranean climates, the shrubby plant cover and the coniferous forest above it are vulnerable to frequent large fires. The fuelbreak, a strip of land in a strategic area-such as a ridgetop-where fuel modification and often type conversion can be accomplished, is an approach to fire suppression being widely applied in the Western United States, particularly California. The fuelbreak concept and fuel modification practices have been developed extensively since the 1950's. Fuelbreak system planning is integral to land-use and fire control planning. Fuel modification practices include...

Dwarf mistletoe had no noticeable effect on trunk taper of young, dominant and codominant red firs 4 to 22 inches (10.2 to 55.9 cm) d.b.h. Also, taper was not influenced by live crown ratio of infected and uninfected trees. Trees less than 7 inches d.b.h. had significantly more taper than larger trees, irrespective of dwarf mistletoe.

The technique proposed allows interpolation of data recorded at unevenly spaced sites to a regular grid or to other sites. Known data are interpolated to an initial guess field grid of unevenly spaced rows and columns by a simple distance weighting procedure. The initial guess field is then adjusted by using a parabolic leapfrog correction and the known data. The final output is then generated by use of cubic spline interpolation on the adjusted grid. Application to test and actual data showed acceptably low root-mean-square error.

Genetic variation among loblolly pine (Pinus taeda L.) samples from a natural stand and among clones in seed orchards was analyzed using simply inherited isozyme markers. Alleles for eleven enzyme loci were found useful for genotyping trees in a natural stand in North Carolina. The pines were highly variable with as many as seven alleles per isozyme gene. On the average, close to 30 percent of the loci per tree were heterozygous. Similar levels of variability and heterozygosity were found /among the clones in two seed orchards. Such variability makes it possible to uniquely identify most,...

The pines have been more successful than most of their coniferous relatives in occupying marginal habitats at the upper and lower edges of the forest zone in western North America. Among the groups restricted to such habitats is subsection Baljourianae of Pinus, comprising the fox tail and bristlecone pines. These pines characteristically grow on cold dry sites at high elevations, and in most places have few tree associates. Perhaps because of their inaccessibility and limited economic importance, not much was known about them until E. Schulman's discovery in the mid-1950's that some...

On a short trip into the northern Olympic Mountains of Washington in the summer of 1896, Professor Charles Sprague Sargent found a fir tree that he thought might be a natural hybrid between Abies amabilis (Dougl.) Forbes and A. lasiocarpa (Hook.) Nutt. The founder and Director of the Arnold Arboretum, Sargent was generally recognized as America's preeminent dendrologist. His brief description of the putative hybrid (Sargent, 1898) is still the only report of natural hybridization between A. amabilis and any of the firs with which it grows (Klaehn & Winieski, 1962). On the same trip Sargent...