Treesearch

Summary - Vegetation helps stabilize forested slopes by providing root strength and by modifying the saturated soil water regime. Plant roots can anchor through the soil mass into fractures in bedrock, can cross zones of weakness to more stable soil, and can provide interlocking long fibrous binders within a weak soil mass. In Mediterranean-type climates, having warm, dry summers, forest evapotranspiration can develop a substantial soil moisture deficit which can reduce both piezometric head and slope mass. Pore water pressures change seasonally in response to precipitation and are often...

Abstract - Stream channel recovery from recent large floods in northern California involves a sequence of processes, including degradation of streambeds to stable levels, narrowing of channels, and accentuation of riffle-pool sequences. Most channels have degraded but remain widened because hillslope encroachment and establishment of riparian groves conducive to sediment deposition have not yet caused streambanks to accrete. The deepening of pools depends on streambed degradation, channel narrowing, and introduction of scouring agents, such as large organic debris, that were removed by...

Abstract - The nature of sediment production from logging roads and the effect of the resulting sediment on salmonid spawning success in the Clearwater River drainage have been studied for eight years. The study includes intensive and extensive analyses of field situations, supplemented by several controlled experiments. It was found that significant amounts (15-25 percent) of fine sediments (less than 0.85 mm diameter material) are accumulaing in spawning gravels of some heavily roaded tributary basins. This accumulation is highest in basins where the road area exceeds 2.5 percent of the...

Abstract - Discharge measurements at nine gauging stations in northern California and southern Oregon document episodes of channel bed aggradation lasting 5 to 15 years after the flood of December 1964 to January 1965. Bed elevations rose 1 to 4 m, then gradually declined to a stable level at or above the pre-flood level. Seven gauging sections widened by 7 to 105 per cent during the aggradation episodes. Channels formed within aggraded material narrowed during degradation; in one case, the pre-flood width was attained. Eroded streambanks formed in non-alluvial material rarely advanced...

Four examples illustrate the potential for practical use of isozyme analyses in applied breeding programs. These include identifying parent trees and clones, seed sources, and parentage of controlled crosses, and evaluating the effectiveness of different procedures involving open-pollination to produce seed of specific crosses. The improved ability to assess the true identity of parents, seed stocks, and controlled crosses justifies the added expense resulting from the use of isozyme analyses in applied tree-breeding programs.

Patterns of genetic variation were studied in three populations of ponderosa pine in Colorado by using electrophoretically variable protein loci. Significant genetic differences were found between separate clusters of trees and between age classes within populations. In addition, data indicate that differential cone production and differential animal damage have genetic components. These results suggest that many diverse phenomena can affect allele frequencies within populations and may contribute to the high levels of genetic variability detected within populations of this species.

Genetic variation at 21 to 25 loci in extracts of individual megagametophytes was surveyed in Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco), Sitka spruce (Picea sitchensis [Bong.] Carr.) and lodgepole pine (Pinus contorta ssp. latifolia [Engelm.] Critchfield). The overall mean proportion of polymorphic loci was 61.19 percent, and the overall mean heterozygosity per individual was 15.81 percent. Sitka spruce was on the low side and interior Douglas-fir on the high side of overall mean genetic variation. Distribution of loci relative to frequency of heterozygotes was rather even for...

Data from isozyme analyses are being used to help answer many basic biological questions about forest insect pests and to provide information for a variety of other purposes as well. This paper summarizes the uses of isozymes in quality control of laboratory insect colonies, in studies of insecticide response, as markers of insect parasitoids, and in investigations of species relationships and population differentiation, including patterns of dispersal.

Isozymes of female gametophyte tissue were analyzed for allelic variation in knobcone, lodgepole, loblolly, Jeffrey, and sugar pines and in Douglas-fir. Linkage was studied in the five pines. The average number of alleles and average herozygosity per enzyme locus were estimated. Knobcone pine ranked lowest among the six species in number of alleles and average heterozygosity; loblolly pine and Douglas-fir ranked highest. Numerous linkages were identified, and one chromosome segment contained between one-fourth and one-third of all loci examined. Linked loci had a consistent gene order in...

Genetic data are an essential prerequisite for analysing the genetic structure of tree populations. The isozyme technique is the best currently available method for obtaining such data. Despite several shortcomings, isozyme data directly evaluate the genetic resources of forest trees, and can thus be used to monitor and manipulate these resources. For example, preliminary isozyme data indicate that domestication of cultivated species has generally reduced variation within populations. Geographic differences among natural populations are less evident in trees than in herbaceous plants, but...