Treesearch

The Chisos Mountain hedgehog cactus (Echinocereus chisoensis, Cactaceae) is a narrow endemic restricted to an approximately 100 square mile area in Big Bend National Park, Texas. It was listed as threatened in 1987 as Echinocereus chisoensis var. chisoensis. An investigation of the reproductive biology and pollination ecology conducted in 1999 and 2000 revealed the taxon to be homogamous, self-incompatible, xenogamous, and heavily dependent upon the cactus oligolectic bee, Diadasia rinconis (Anthophoridae) for pollination. Despite infrequent bee visitation, fruit set from open pollination...

Many noxious weed infestations are initiated or increased by soil disturbance. With the recent emphasis on reintroduction of fire into natural ecosystems there has been increased interest in the effects of noxious weeds following fires. This paper discusses the effects of fire on Flagstaff pennyroyal, a Forest Service Region 3 sensitive plant, and the subsequent infestation of the project area by Dalmatian toadflax (Linaria genistfolia ssp. dalmatica).

Small populations are threatened with deterministic and stochastic events that can drive the number of individuals below a critical threshold for survival. Long-term studies allow us to increase our understanding of processes required for their conservation. In the past 7 years, the population of the federally endangered Holy Ghost ipomopsis (Ipomopsis sancti-spiritus) in Holy Ghost Canyon has fluctuated widely from 2047 to 372 plants. Metapopulation analysis of average Leslie matrices suggested that I. sancti-spiritus has a high probability of extinction; 60 percent of the demographic...

The existence of the endangered shrub Purshia subintegra may be threatened by hybridization with the more common P. stansburiana. In the Verde Valley, the range of the rare P. subintegra overlaps with the range of P. stansburiana, allowing introgression to occur. Although P. subintegra and P. stansburiana have many distinguishing characteristics, there are plants in the Verde Valley that have a combination of characteristics, making them difficult to identify. Using discriminant function analysis, we found that the parents and introgressed forms had detectable morphological differences...

Surveys for Paradine plains cactus (Pediocactus paradinei B. W. Benson) conducted for the Kaibab National Forest, North Kaibab Ranger District in 1992-94 qualitatively showed a fairly substantial population of scattered individuals in the pinyon-juniper woodland, and indicated that there might be a correlation between plant distribution and dripline of trees. This project was initiated in 1999 to test that possibility. Field surveys in July of 2000 showed an apparent sharp decrease in numbers of cacti since 1994, probably due to conditions caused by a drought from 1998 to the summer of...

Four listed plants on the Arizona Strip are being monitored for various population characteristics. Pediocactus sileri Engelm. L. Benson and P. bradyi L. Benson have been monitored since 1985-86, Asclepias welshii N & P Holmgren since 1989, and Cycladenia humilis Benth. var. jonesii Welsh & Atwood since 1993. The two pediocactus species were monitored in plots where each cactus was tagged, measured for height or width, and mapped; how many cactus fruited and the mortality rate were also noted. Asclepias welshii plants were counted and mapped, and each stem was checked for follicles....

Siler's pincushion cactus (Pediocuctus sileri) occurs primarily on Bureau of Land Management (BLM) lands in Washington and Kane Counties in southwestern Utah and across the border in northwestern Arizona. This 5 year (1993-1997) monitoring study was set up as a challenge cost-share project between Red Butte Garden and the Utah State BLM Office in Salt Lake City. A permanent study plot was established about 10 miles east of Kanab, in Kane County, to annually monitor growth, reproduction, recruitment, mortality, and threats to the species. The cactus grew an average of 0.42 cm in height and...

Twenty-six native orchid species occur in Arizona, and 14 are considered rare with fewer than 100 occurrences in the state. The author is conducting three studies covering four of the wild orchids: Stenorrhynchos michuacanum, Hexalectris revoluta, Malaxis porphyry, and M. tenuis. The studies are ongoing so only interim results are available. Interim results indicate that plants of S. michuacanum and H. revoluta do not bloom every year, and in the latter case do not come up every year. The study on Malaxis is looking at recovery rates in damaged habitat, but is still in its first year.

This study on Platanthera zothecina (alcove bog orchid) was initiated by the National Park Service after a recent threatened and endangered species survey at Navajo National Monument. It is listed as Category 2 (species of special concern) by the U.S. Fish and Wildlife Service, and Category 3 (likely to become endangered) by the Navajo Nation. Because P. zothecina is a fairly new taxon, and little is known about its ecology, this baseline study documents population size, number of basal leaves, flowering plant height, number of flowers, and fruit set rates for a 2-year period (1999 and...

Samples from three isolated populations of the dwarf bear-poppy (Arctomecon humilis Cov.) demonstrate that both flower pollination (fruit set) and seed set per fruit decline as interplant distances increase and the number of flowers per plant declines. Interplant distance and number of flowers per plant tend to interact with reproduction. Seed set per plant is most impaired on plants that produce few flowers and are far from other flowering, conspecific individuals. Such data warn that the number of surviving individuals alone is not a safe criterion for evaluating reproductive health of a...