Treesearch

The pines and other groups of temperate forest trees often fail to conform to widely accepted principles of plant evolution that are based primarily on observations of herbaceous plants. For example, interpreters of plant evolution tend to equate the fertility or sterility of inter specific hybrids with the magnitude of the genetically controlled reproductive barriers limiting the production of hybrids. This tendency has been articulated by Grant (1958, p. 353): "This is assuming that incompatibility barriers and sterility barriers, two distinct phenomena in the physiological sense, tend...

A number of factors have been suggested as affecting reproductive success in gulls. In this study we have attempted to isolate the effect of human disturbance on breeding success. We held other factors such as age of birds, terrain, and density of colony as constant as was practicable with a varied colony environment. There have been several previous discussions of the possible effect of human disturbance on the breeding success of birds. However, no study has documented this effect with controls. Reid (1968) found that in the Adélie Penguin (Pygoscelis adeliae) "banding and close observati...

In direct-seeding trials on the Challenge Experimental Forest, Yuba County, California, 27 combinations of seeding rates, aspect, and site treatment were tested. The best results were obtained on northerly aspects on unburned mechanically disturbed seedbeds with a high proportion of exposed mineral soil when seed application rates were high. Sowing at least 1 pound of seed per acre (1.12 kg per ha) consistently resulted in 400 or more seedlings per acre (988 seedlings per ha). Baiting for rodent control and attempted seed covering by "dragging" did not improve results. If regeneration...

Timely and appropriate use of air tankers in firefighting can bring high returns, but their misuse can be expensive when measured in operating and other costs. An allocation model has been developed for identifying superior strategies-for air tanker initial attack, and for choosing an optimum set of allocations among airbases. Data are presented for a representative initial attack allocation area and strategies are computed for alternative budget levels. Although designed for determining day-to-day operating rules, the model is flexible enough to be applied to policy questions concerning...

The winter home of a bird, although vitally important in the study of adaptations, has received little attention as compared to various aspects of breeding. During the fall and winter much mortality occurs and may be the limiting factor in many populations (Mac Arthur 1971). We will explore the process of site fixation onto the winter quarters and its implications to the population.

The effect of thinning on growth rate and quality of a 6-year-old Eucalyptus saligna Sm. stand on Maui, Hawaii, was studied by testing three levels of thinning from below: 100, 85, and 70 sq ft per acre (23, 19.5, and 16 sq m/ha). The stand had an average basal area of 102 sq ft per acre (23 sq m/ha). Initial spacing was about 10 by 10 feet. During the next 6 years, no significant differences in growth response were found among the three treatments. Basal area increased to an average of 144 sq ft per acre (33 sq m/ha) at age 12, and the average height of dominant and codominant trees...

In a two-stage stratified procedure for sampling herbage yield, plots are stratified by a pin frame in stage one, and clipped. In stage two, clippings from selected plots are sorted, dried, and weighed. Sample size and distribution of plots between the two stages are determined by equations. A way to compute the effect of number of pins on the variance of estimated herbage yield has been developed. It was tested by using a sampling budget and a simulated population of Bromus mollis (soft chess), and worked reasonably well with other annual plant populations. But application to other plant...

The effects of clipping California-poppy (Eschscholzia californica Cham.) at various growth stages on plant survival, flowering, herbage yield, and root production were studied at the San Joaquin Experimental Range, in central California. Plants were clipped once to a 2-cm stubble at one of six stages. Through the early reproductive stage, a single clipping had little effect, but clipping at either the start or peak of vernal flowering reduced the display of spring flowers. Other factors studied were not significantly affected.

A tripod-supported boom sprayer was developed and used to spray herbicides on shrubs up to 15 feet tall on experimental plots where use of other spray equipment was not feasible. A pneumatic pressurized sprayer with 10 diaphragm nozzles, geometrically spaced along the outer 20 feet (6.1 m) of a 25-foot (7.6-m) boom, distributed the spray uniformly. Brush leaves were well covered with droplets of relatively uniform size at low dosages. The volume of spray applied per acre could be readily changed from plot to plot by varying the number of revolutions of the boom over the circular plot. Each...

Redwood Creek drains a 280 square mile basin which is located in a region of high winter rainfall and high natural rates of erosion. Forests of commercial quality formerly covered about 238 square miles of the basin. Parklands, including a portion of Redwood National Park, occupy approximately 10% of the lower basin and include, amount other values, several of the world's tallest trees.