Field studies were undertaken to evaluate hoary cress (Cardaria draba (L.) Desv.) reproduction and spread in a sagebrush ecosystem. Hoary cress germination, emergence, and survival were restricted to moist environments. These conditions occurred 2 out of 8 years. Hoary cress germination under field conditions was greatest on toe slope positions and areas of soil disturbance. Number of shoots varied annually for established hoary cress populations. Shoot propagation was reduced when early spring growth was followed by frost or drought. Shoot numbers were increased when spring growth was delayed and warm, moist growing conditions occurred in May. Seed reproduction did not increase plant density in monitored populations. Established populations relied upon vegetative reproduction to sequester resources and increase plant density.

Rush skeletonweed (Chondrilla juncea L.) is an invasive, herbaceous, long-lived perennial species of Eurasian or Mediterranean origin now occurring in many locations throughout the world. In the United States, it occupies over 2.5 million ha of rangeland in the pacific Northwest and California. Despite the ecological and economic significance of this species, little is known of the ecology and life history characteristics of North American populations. The purpose of this study was to examine seed germination characteristics of 2 populations of rush skeletonweed in Idaho. Seeds from rush skeletonweed plants in southwestern Idaho were collected during the 1994 and 1995 growing seasons. Mature seeds were harvested on 6 dates between early July and early October 1994, and on 5 dates between early July and late September 1995. Fresh seeds from each harvest period were measured to determine seed weight, total germination, rate of germination, and viability (tetrazolium staining [TZ]) of non-germinating seeds. An aliquot of seeds collected in 1994 was also stored for 1 year to examine the effects of seed storage on germination. In southwestern Idaho, rush skeletonweed produces seeds continuously from mid-July through October. Seeds were capable of immediate germination without scarification or wet prechilling. Total germination generally ranged from 60 to 100% throughout the entire seed production period. Germination was also rapid, reaching 50% of total germination in less than 12 days. In general, germination was higher at the lower incubation temperature regime (20/10 degrees C), perhaps reflecting origins of this species in Mediterranean winter rainfall regions. The TZ testing indicated that 30 to 60% of non-germinating seeds were viable, suggesting that seeds may persist in the soil seed bank. Up to 60% of seeds remained viable following 1 year of storage. Stored seeds generally exhibited higher germination rates (average = 90%) than fresh seeds (average = 67%), indicating possible dormancy and afterripening effects. Germination characteristics of this species are consistent with those of other invasive alien species, and favor rapid population growth leading to community dominance.

The Ecological Index Method impacted directly on the estimation of grazing capacities in the Karoo, an arid region in South Africa. Due to inherent deficiencies in the ecological index method, index values formed a disjunct series, 10, 7, 4, and 1 and the fact that different value systems were employed to score plant species, necessitated that index values of species commonly encountered during botanical surveys be subjectively adjusted by means of a species by species comparison, forming a continuous series of index values. These index values were still subjective value judgements of the agronomic value of the Karoo plant species. The author felt that a method should be developed to objectively estimate grazing index values from certain plant variables, i.e. size, animal available dry matter production, and chemical properties of the species. The use of these properties would describe the agronomic value of the plant species, which would lead to agronomically sound current grazing capacities being estimated. The following 2 models were proposed to deal with the karoo subshrubs and the grasses of the karoo separately. Grazing index value for the karoo subshrubs = ((canopy spread cover + available forage + TDN + [K divided by (Ca + Mg)]) divided by ether extract) divided by 100, and grazing index value for the grasses = ((canopy spread cover + available forage + TDN + [K divided by (Ca + Mg)]) x ether extract) divided by 100.

Grassland of interior British Columbia are being encroached upon by Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) and ponderosa pine (Pinus ponderosa Dougl.). A pot experiment placed in the field was conducted to determine the effect of forest and grassland seedbeds on seedling emergence and early establishment of the 2 species with 2 seed collections each. For these seedbeds, structural characteristics were evaluated and the effect of seedbeds water extracts on seed germination was determined. Seedling emergence of both species was significantly reduced by Douglas-fir needles and enhanced by fescue litter and cattle manure compared to mineral soil. The rate of emergence was reduced by Douglas-fir needles and sagebrush litter, and for some collections, by ponderosa pine needles, but was always enhanced by manure compared to mineral soil. Seedling survival was generally not affected by seedbeds. Douglas-fir seedlings emerging earlier in the season survived better, and both Douglas-fir and ponderosa pine seedlings emerging earlier lived longer than these emerging later. Seed germination of ponderosa pine was not affected by the water extract while that of Douglas-fir was reduced by the water extract from sagebrush litter. Therefore, differences in seedling emergence of the 2 species among seedbeds were related more to structural than to chemical characteristics of seedbeds. Successful establishment of the 2 species in grasslands within this region likely relies on the ability of seeds to germinate early in the growing season on seedbeds in which soil moisture is conserved, as summer droughts are severe.

Forage use data can help rangeland and wildlife managers make informed decisions. However, managers need to know if forage use techniques that are commonly used to estimate ungulate herbivory under field conditions produce comparable results. The objective of this 2-year study was to directly compare forage use measurements obtained via the paired-plot method and 2 height-weight methods (using on-site height-weight curves and the pre-established United States Forest Service height-weight gauge). In June, July, and October of 1997 and 1998, we measured forage use of western wheatgrass (Pascopyrum smithii Rydb.) by cattle (Bos taurus L.) and wild ungulates, mainly elk (Cervus elaphus L.). On-site height-weight curves and the USFS gauge consistently produced lower estimates (overall means = 8 and 7%, respectively) than the paired-plot method (overall mean = 31%). Height-weight estimates did not differ (P > 0.05) when calculated with either on-site curves or the USFS gauge. Within sampling areas, paired-plot estimates were relatively more precise (mean CV = 63%) than on-site curves (mean CV = 238%) or the USFS gauge (mean CV = 271%). Selective grazing likely contributed to higher CVs for height-weight techniques. Our findings are important for rangeland and wildlife managers because the forage monitoring technique they use may influence the results obtained and, consequently, grazing management and wildlife harvest decisions. Managers should ensure that chosen monitoring techniques provide an appropriate evaluation of management goals and objectives.

The decreased carrying capacity of Argentinian Flooding Pampa rangelands through the reduction of density of C3 grasses may be partially attributed to continuous stocking. The objective of this study was to evaluated the effectiveness of rotational vs. continuous stocking to improve winter forage production by incrementing the density of Italian ryegrass (Lolium multiflorum Lam.). Under rotational stocking, ryegrass seedlings established almost 2 months earlier in the fall and tiller density was 3-fold higher in winter than under continuous stocking. Aerial net primary productivity of C3 grasses was approximately 2-fold greater under rotational compared with continuous stocking in the first and second years. This substantial increase in winter productivity supported almost 2-fold increase in stocking rate (from 0.6 to 1.0 AU ha-1).

Stocking rate directly influences the frequency and intensity of defoliation of individual plants which, in turn, impacts energy flow and plant succession in grazed ecosystems. The objective of this study was to determine the effect of stocking rate on standing crop dynamics and plant species composition of a southern mixed-grass prairie over a 7-year period (1990 through 1996). Long-term (30-year) mean precipitation has been 766 mm per year. Growing conditions were generally favorable for the study period. Yearling cattle (initial weight 216 kg, SD = 12 kg) grazed at 6 stocking rates, ranging from 23 to 51 AUD ha-1, from 14 April to 24 September (162 days). The currently suggested year-long stocking rate is 25 AUD ha-1. Herbage standing crop was measured in July and September every year while species composition was determined in July in even years. Total and dead standing crop declined as stocking rate increased but live standing crop was not related to stocking rate. Slopes of regression lines relating standing crop and stocking rate were constant over years, indicating no response for plant productivity. The major vegetation components, sideoats grama [Bouteloua curtipendula (Mich.) Torr.], shortgrasses, and forbs were not affected by stocking rate over years. Tallgrasses responded by increasing at the lower stocking rates over the study period. However, these grasses contributed less than 5% of the total standing crop. Red and purple threeawn (Aristida longiseta Steud. and A. purpurea Nutt.) increased at all stocking rates from 1990 to 1996 but the increase was greater at the lower stocking rates. This mixed-grass vegetation showed little response to stocking rate over the 7-year study period. The vegetation may have been in equilibrium with previous heavy stocking rates so that little change would be expected at those rates. Increases in grazing sensitive species at lighter stocking rates may occur over longer time intervals.