Dyers woad (Isatis tinctoria L.) is a noxious weed on northern Utah rangelands. Chemical and mechanical means of control are unsuitable for rangelands. A potential alternative, biological control, is difficult due to a lack of basic ecological information. To remedy this, some aspects of the population biology and autecolgy of dyers woad were studied. The feasibility of controlling dyers woad by early spring grazing was also investigated via clipping experiments. A population study followed the survivorship of experimentally established populations over two years. Fall germinating individuals (1984) overwintered as rosettes twice and all survivors reproduced successfully. Spring germinating individuals (1985) overwintered as rosettes only once and 87% seeded the subsequent spring. Thus, on a good condition {high seral) foothill rangeland, dyers woad behaved predominantly as a biennial. Peak mortality in both fall and spring populations coincided with summer drought. The population size of dyers woad was constricted at two stages: (i) germination and establishment, and (ii) young rosette. The risk of mortality mortality in young rosettes was 77%. Dyers woad should be targeted for biological control at this vulnerable stage of growth. The seed dispersal pattern of dyers woad was best described by a negative exponential model of the type logy= a+ bx; (r = .78, a= 1.92, and b = -0.02). Ninety-five percent of a11 fruits were deposited within 54cm of mother plants. The root system of dyers woad was predominantly a taproot with some lateral sin the upper 30cm of the soil. There was little difference between mapped taproot and total mapped root lengths of rosette and mature plants. Significant mortality and reduction in reproductive performance occurred only by clipping, on or after 23 May 1984, at 60% or 90% intensity. Clipping twice, at either intensity, before 23 May had no effect on dyers woad. Sheep utilization of dyers woad ceased after mid-May, and had no significant effect on its mortality, percent flowering, and fruit production. Sheep grazing on dyers woad did not occur when much impact on mortality or seed production could be expected. The stocking re qui red to restrict dyers woad will result in range deterioration. More host-specific biological control agents should be tried.

Two perennial species of wild geranium (Geranium nervosum Rydb. and G. richardsonii Fisch, and Trautv, [Geraniaceae]) which grow throughout the mountainous regions of western North America were studied to determine the factors influencing the life stage development and distribution of these plants. Attempts were also made to provide some information to assist in the taxonomy of this genus. Geranium richardsonii is found in wet meadows and along streambanks throughout its distribution, Geranium nervosum frequents rocky hillsides and drier meadows throughout its range. Seeds of Q. nervosum had 65o/, germination in the stratification pretreatment. Geranium richardsoniiseeds required scarification to reach 60% germination, Both species germinated in excess of 80% when scarified and stratified. Overwinter survival experiments indicated that Q. richardsonii could survive only in a wet meadow environment while G. nervosum could survive and establish in ail three environments examined, wet meadow, dry hillside, and aspen (Populus tremuloides) grove. Both G. richarasonii and Q. nervosum appeared to be limited by the same environmental factors although the degree of response was different. The seedling stage was the most responsive to environmental stress. Both Q. richardsonii and Q. nervosum seedlings had an optimum temperature range for survival of 20-25°C although they could and did adapt to lower temperatures. Seedlings of neither species could survive soil water potentials (Ψs) of -10 bars or lower. The adult stage of both species was more tolerant of stress and G. nervosum adults could survive (Ψs) of -25 to -30 bars. Geranium richardsonii was less tolerant and appeared to Ψs limited by both Ψs and temperature in its distribution at the Forestry Field Station. The critical factors influencing the distribution G. nervosum and Q. richardsonii were similiar but the species reacted to them in different ways. Geranium richardsonii was able to survive in environments that were highly saturated with water and under heavy cover. Geranium nervosum, although limited by temperatures above 32°C, was able to live in drier conditions by virtue of a tap root system. Hence, although the distribution of these two species was similiar, they were seperated by their response to environmental conditions.