Charlie D. Clements

Use of Fluorescent Pigments in Studies of Seed Caching by Rodents

We describe a new technique for locating seeds cached by rodents that offers practical and logistical advantages over previous methods. The new technique uses ultraviolet illumination and seeds marked with powdered fluorescent pigments, which transfer readily between surfaces upon contact and have been applied successfully for other research on small mammals. We used the technique at a field site in the Great Basin Desert of western Nevada to test and verify the prediction that seed-caching, heteromyid rodents would transport a preferred seed type longer distances to make caches in a habitat where this seed is rare relative to an adjacent habitat. We also tested two variations of our seed-tracking technique. The first uses only marked seeds and allows an investigator to locate rodent scatterhoards by searching systematically for pigment spots on the ground surface. The second technique requires rodents to harvest pigmented seeds from a bait station that also is laced with pigments, so that the animals leave pigmented footprints when transporting the seeds. Significantly more seed caches were located, and the caches were located at significantly longer distances from the seed source by following footprints with the second technique. Moreover, the footprint trails provided a detailed record of paths traversed by rodents during seed transport, they revealed locations of rodent burrows where seeds are stored in larders, and they made it easier to find scatterboards.

A viewpoint: rangeland health and mule deer habitat.

The Lassen interstate mule deer (Odocoileus hemionus) herd ranges from the northwestern area of Nevada to the northeastern corner of California along the western rim of the Great Basin. This mule deer herd serves as a model for what has happened in terms of population dynamics for many Intermountain west mule deer populations. Before contact with Europeans the populations were apparently very restricted. After the introduction of domestic livestock there has been significant impacts on the relative abundance of shrubs versus perennial grasses. Mule deer herds underwent tremendous expansion which peaked in the 1950s. Recent mule deer population numbers in the Lassen interstate herd have sharply declined. These population dynamics can be related to several habitat changes that reflect increased frequencies of wildfires in lower elevational sites as shrubs became old and decadent. Lack of fire in the higher elevations resulted in decadent/senscent old shrub stands. Invasion by exotic annual grasses in lower elevational sites. In certain environments, sharply improved range condition due to grazing management systems. The increase in coniferous woodlands, which may reflect changes in climate and/or atmospheric gases, combined with the lack of fire significantly negatively impact the Lassen Interstate mule deer herd. Identifying the specific aspect of winter, transitional, and/or summer habitat, in terms of dietary deficiency, that are most closely related to the decline in mule deer numbers is a highly significant problem facing wildlife and range managers.

Influence of nitrogen on antelope bitterbrush seedling establishment

Nitrogen enrichment, immobilization, or inhibition of nitrification were used to investigate the influence of available nitrogen on the seedling recruitment of antelope bitterbrush (Purshia tridentata [Pursh] DC) and annual grass competition. The influence of nitrogen enrichment on antelope bitterbrush seedling recruitment depended on the form of nitrogen applied. Ammonium sulfate applications markedly enhanced growth of herbaceous annuals resulting in the loss of all antelope bitterbrush seedlings the first growing season. Enrichment with calcium nitrate marginally enhanced growth of herbaceous annuals and enhanced the growth of antelope bitterbrush seedlings. Immobilization of nitrogen with carbon (sucrose) applications suppressed the growth of herbaceous annuals and produced large, vigorous antelope bitterbrush seedlings. Similar results were obtained by inhibiting nitrification with applications of nitrapyrin or combining nitrapyrin and carbon applications.

Germination of seeds of big and bottlebrush squirreltail.

Bottlebrush squirreltail [Elymus elymoides (Raf.) Swezey] and big squirreltail [E, multisetus (J. G. Smith) Burtt Davy] are short-lived perennial bunchgrasses found on rangelands from the Pacific Coast to the Great Plains and from Canada to Mexico. They are highly variable species with several subspecies described for bottlebrush squirreltail. In many rangeland communities, bottlebrush squirreltail is the transitional dominant native grass in secondary successional communities. There is considerable interest in using squirreltail species in rangeland restoration seedings, but problems with seed collection (disarticulating rachis) have kept seed prices very high. Recently, grass geneticists have begun to develop lines of squirreltail for release as pre-varietal germplasm. Our purpose was to compare the germination at a wide range of constant or alternating temperatures of squirreltail seeds from developmental lines and material collected from native stands. Big and bottlebrush squirreltail seeds (caryopses) germinated over a wide range of temperatures. Seeds of bottlebrush squirreltail produced from the same stand in 3 different years had remarkably similar germination temperature profiles. The greatest variation in germination among accessions occurred at very cold and cold categories of seedbed temperatures. These differences may be very significant in the establishment of seedlings in the field. There was no one temperature regime that always supported optimum germination for all of the squirreltail accessions tested. The regimes most frequently supporting optimum germination were 15/20 and 15/25° C. The seeds of big and bottlebrush squirreltail tested do not have the ecological amplitude of seeds of the competitive exotic weed cheatgrass (Bromus tectorum L.), but they come close.

Germination of seeds of Tamarix ramosissima

The germination of seeds of saltcedar (Tamarix ramosissima Ledeb.) was compared at a wide range of constant or alternating temperatures from 0 through 40° C. Germination temperature profiles were developed for seeds of saltcedar collected from the Walker River Delta in western Nevada over a 3 year period. Germination occurred over a wide range of temperatures. For 2 of the 3 years of testing, maximum germination observed was 98 or 100 %, indicating the seed lots were highly viable. Germination ranged from 0 to 6% at very cold seedbed temperatures, but jumped to 39 to 43% at cold seedbed temperatures. There was very little difference in germination between moderate and warmer seedbed temperatures. No single temperature always supported optimum germination. The temperatures that most frequently supported optima were 10/20 (10° C for 16 hours and 20° C for 8 hours in each 24 hour period), 10/25, 15/20, and 35° C. Mid summer collections of saltcedar seeds were much more variable in germination response compared to annually repeated late spring collections from the Walker River Delta. Available soil moisture apparently is an important factor in the germinability of saltcedar seeds collected in mid summer. Temperature regimes that supported optimum germination for the Walker River Delta accession of seed collected in mid summer, tended to occur at higher temperatures than for seeds collected from the same stand in late spring. Comparison of the saltcedar profile with germination temperature profiles of seeds of tree willow (Salix lutea Nutt.), coyote willow (S. exigua Nutt.), or Fremont cottonwood (Populus fremontii S. Watson) revealed that germination of saltcedar seeds was equal in the number of regimes with some germination, mean of optima, and maximum observed germination. For all other germination characteristics measured, saltcedar is lower and sometimes distinctly lower than for seeds of the native woody species.

Influence of rodent predation on antelope bitter- brush seedlings

Antelope bitterbrush (Purshia tridentata(Pursh) DC) is the most important browse species on many mule deer (Odocoileus hemionus) ranges. California-Nevada interstate mule deer herds are critically dependent on antelope bitterbrush stands, in which many of these stands have been and are currently exhibiting little recruitment. Lassen is the only established cultivar of antelope bitterbrush. Rodent predation on Lassen antelope bitterbrush seedlings was studied in burned and unburned antelope bitterbrush communities in northeastern California during 1993. Rodent population densities were 15/ha and 14/ha in the burned and unburned habitats, respectfully. Rodent compositions consisted of the Ords kangaroo rat (Dipodomys ordii), deer mouse (Peromyscus maniculatus), and the Great Basin pocket mouse (Perognathus parvus). Rodents significantly decreased antelope bitterbrush recruitment through grazing and disturbance of antelope bitterbrush seedlings. Ords kangaroo rats preyed on higher numbers of antelope bitterbrush seedlings than did the other 2 common rodent species.

Purple Loosestrife (Lythrum salicaria) Seed Germination1

Abstract: Purple loosestrife is an invasive, exotic perennial weed of wetlands throughout much of the United States and Canada. Once established, it forms dense colonies to the near exclusion of more desirable vegetation. Established plants are prolific seed producers. Our purpose was to investigate the germination of purple loosestrife seeds at a wide range of constant or alternating temperatures from 0 through 40 C. Purple loosestrife seeds germinate over a wide range of temperatures. We define optimum germination as not less than the maximum observed minus its confidence interval at the 0.01 level of probability. Optimum germination occurred over a considerable range of temperatures: Only 10, 15, or 20 C for 16 h alternating in each 24 h with 35 C for 8 h always supported optimum germination. Wide ranges in diurnal temperature fluctuations were conducive to maximum germination. These ranged from a maximum of 35 degrees with 0/35 C to 5 degrees with 30/35 C. No one constant temperature supported optimum germination. Nomenclature: Purple loosestrife, Lythrum salicaria L #3 LYTSA. Additional index words: Wetlands, seed and seedbed ecology, diurnal temperatures.

Germination-Temperature Profiles for Achenes of Yellow Starthistle (Centaurea solstitialis)1

Yellow starthistle is an annual that is dependent on achene production, dispersal, and germination for stand renewal. Our purpose in this study was to determine the temperature relations for germination of achenes of this species. Germination temperature profiles were developed for achenes of yellow starthistle collected from 15 sites in California, Nevada, and Oregon. Each profile consisted of achene germination at 55 constant or alternating temperatures from 0 through 40 C. A total of 85 germination temperature profiles were developed by using the germination data to construct quadratic response surfaces through regression analysis. For most profiles, germination occurred at all the temperature regimes except a constant 40 C. This includes a constant 0 C and 0 alternating with 40 C. Rarely, there was no germination at 35 C and 35 C alternating with 40 C. The only evidence of afterripening requirements for achenes of yellow starthistle that we noted occurred at very cold temperature regimes. At those temperatures, the germination of dark-colored achenes without pappus increased 3 mo after harvest, and decreased for light-colored achenes with a pappus. No single temperature regime always supported optimum germination when all the profiles were combined. The most frequent optima was 2/20 C. Comparing all profiles for the Davis, CA, accession, there were 5 regimes (5 and 10 C cold periods alternating with 15 through 25 C warm periods) that always supported optimum germination. Light-colored achenes with pappus tended to have optimal germination at colder temperatures, and the dark-colored achenes at higher temperatures when seeds were tested immediately after harvest. Nomenclature: Alfalfa, Medicago sativa L. #3 MEDSA; tocalote, Centaurea melitensis L.; yellow starthistle, Centaurea solstitialis L. # CENSO. Additional index words: Seedbed ecology, seedbed temperatures, optimum germination, invasive species.

Exotic and Invasive Herbaceous Range Weeds

T here is a considerable body of terminology developed during the 20th century concerning range weed control. This terminology was developed so individuals concerned with herbaceous range weeds could communicate. Nothing is more boring than terminology, but in the case of range weed control, if everyone gets on the same page in terminology, an artificially cloudy subject becomes much clearer. A weed is simply a plant growing in a site where it is not desired. You can make up your own standards for what constitutes desirability. It may be forage production, nutritional quality, or season of growth or have little to do with forage characteristics. Watershed protection, chance of ignition and rate of spread of wildfires, and wildlife habitat are all plant characteristics that influence individual perception of plant desirability. A weed may be a desirable plant in one location and a weed in another. For example, in the salt deserts of Nevada, desert salt grass is a desirable forage species in alkaline/saline habitats surrounding playas. It is virtually the only herbaceous forage species adapted to grow in such environments. In the irrigated alfalfa fields of Nevada, it is considered a serious herbaceous weed.

Germination of seeds of Fremont cottonwood.

Fremont cottonwood (Populus fremontii S. Watson) is the most important cottonwood species of the southwestern United States. It is usually found in riparian areas of desert riverine systems. Often it is the only tree species in such environments. Lack of Fremont cottonwood seedling recruitment is of concern in many areas. This is especially an issue in river systems infested with the exotic saltceder (Tamarix ramosissima Ledeb.). The proposed suppression of saltceder with a biological control agent, raises the question of the spontaneous recruitment of Fremont cottonwood seedlings if competition is reduced from exotic woody species. Several studies have stressed that geomorphologic-hydrologic conditions in riparian habitats control safesites for Fremont and other cottonwood species seed germination and seedling establishment. Our purpose was to investigate the physiological amplitude for Fremont cottonwood seeds to germinate under a wide range of constant or alternating temperatures. Immediately after dispersal the seeds of Fremont cottonwood are highly germinable. In each of the 3 years that seeds were collected multiple temperature regimes supported 100% germination. Optimum germination averaged over 90%. At moderate to high warm period temperatures, most germination that will occur does so during the first week after imbibition of moisture. Temperature regimes that supported optimum germination at least once ranged from 0/5 C to 25/40 C. The regimes that always supported optimum germination were in 2 distinct group: 2/25 and 2/30 C; and a wider dispersed group with 15, 25, or 25 C cold period temperatures and 25, 30, or 35 C warm period temperatures. There was one outlier at 10/15 C. Fremont cottonwood seeds are highly and rapidly germinable at a wide range of temperatures. DOI:10.2458/azu_jrm_v56i6_young2