Stewart C. Sanderson

Age Structure and Expansion of Piñon-Juniper Woodlands: A Regional Perspective in the Intermountain West

Numerous studies have documented the expansion of woodlands in the Intermountain West; however, few have compared the chronology of expansion for woodlands across different geographic regions or determined the mix and extent of presettlement stands. We evaluated tree age structure and establishment for six woodlands in four ecological provinces in the central and northern Great Basin. Since 1860, the area occupied by pinon and or juniper has increased 125 to 625 percent. The increase of trees was a result of infill into shrub-steppe communities with relatively open low density stands of trees and expansion of pinon and juniper into sagebrush-steppe communities that previously did not support trees. Woodland expansion in Oregon, Utah, and Nevada were similar, but began two to three decades earlier in Idaho. The majority of woodlands are still in the early to mid phases of stand closure, which means they often support an understory of shrubs and herbaceous vegetation. This has implications for future changes that will occur within these woodlands in the next 30 to 50 years. In the absence of disturbance or management, the majority of these landscapes will become closed woodlands resulting in the loss of understory plant species and greater costs for restoration.

Cytogeography and chromosome evolution of subgenus Tridentatae of Artemisia (Asteraceae)

The subgenus Tridentatae of Artemisia (Asteraceae: Anthemideae) is composed of 11 species of various taxonomic and geographic complexities. It is centered on Artemisia tridentata with its three widespread common subspecies and two more geographically confined ones. Meiotic chromosome counts on pollen mother cells and mitotic chromosome counts on root tips were made on 364 populations ( = 3.1 plants per population). These population counts are ∼60% of all Tridentatae counts. Some are first records for taxa. The Tridentatae are a polyploid complex (x = 9) with ploidy levels from 2x to 8x, but mostly 2x (48%) and 4x (46%). Polyploidy occurs in nine of the 11 species and in many subspecies as well. Supernumerary or b chromosomes are present only at a low frequency. In the principal species, A. tridentata, 2x plants are larger than 4x ones, which are adapted to drier conditions, probably in consequence of their slower growth rates. Gigas diploidy is a phenomenon shared by some other woody genera, but is in contrast to the gigas polyploid nature of many herbaceous genera. Polyploidy occurs within populations and is essentially autoploid. Hybridization sometimes occurs at taxa interfaces in stable hybrid zones. Stable Tridentatae hybrid zones coupled with the groups inherent propensity for polyploidization has led to the establishment of a geographically and numerically large and successful complex of species.

The influence of topography on male and female fitness components of Atriplex canescens

The influence of environmental heterogeneity on components of male and female fitness is examined using Atriplex canescens growing on steep slopes and alluvium at the slope base as a model system. Female fitness is estimated as the grams of fruit produced per plant and the grams of fruit per gram leaf tissue. Male fitness is estimated as the grams of stamens produced, the number of pollen grains dispersed to a given distance, and the potential number of grams of fruit sired taking into consideration the number and distribution of mates and competing pollen donors. The influence of increased plant size on male and female fitness components, the cost of reproduction (as measured by biomass, joules and nitrogen) on a gross level and a per offspring basis are also examined. The results indicate that the female function is more limited on the slope than the male function. The efficiency of pollen dispersal (the number of pollen grains per unit donor plant volume dispersed to a given distance) is enhanced by growing on slopes. Males become less efficient at dispersing pollen as they increase in size, while the efficiency of female reproduction (grams of fruit per volume or gram leaf tissue) is unaffected by increasing plant size. The cost to a male of siring a gram of fruit is about the same as the cost to a female of producing the gram of fruit. Implications for the evolution of sexual lability and dioecy are discussed.

Are trioecy and sexual lability in Atriplex canescens genetically based?: evidence from clonal studies

Prior studies have alternatively considered floral phenotypes in Atriplex canescens as trioecious (having three sexual genders) and/or dioecious and having a “leaky genetical switch.” Clones transplanted from three populations and grown in common gardens reveal the existence of two distinctly different genetic controls regulating gender expression. In some clones gender is fixed as male (staminate) or female (pistillate), while in other clones gender varies, ranging from a mixture of male and female ramets to simultaneous hermaphrodites with various proportions of male and female flowers. For clones which vary their sex expression, variation occurs within irrigation treatments, between treatments and over time, as a consequence of the combined effects of genotype plus environment. The magnitude of sex change is also a product of the interaction of genetics and environment. Some clones have been repeatedly examined for 20 years.

Widespread Triploidy in Western North American Aspen (Populus tremuloides)

We document high rates of triploidy in aspen (Populus tremuloides) across the western USA (up to 69% of genets), and ask whether the incidence of triploidy across the species range corresponds with latitude, glacial history (as has been documented in other species), climate, or regional variance in clone size. Using a combination of microsatellite genotyping, flow cytometry, and cytology, we demonstrate that triploidy is highest in unglaciated, drought-prone regions of North America, where the largest clone sizes have been reported for this species. While we cannot completely rule out a low incidence of undetected aneuploidy, tetraploidy or duplicated loci, our evidence suggests that these phenomena are unlikely to be significant contributors to our observed patterns. We suggest that the distribution of triploid aspen is due to a positive synergy between triploidy and ecological factors driving clonality. Although triploids are expected to have low fertility, they are hypothesized to be an evolutionary link to sexual tetraploidy. Thus, interactions between clonality and polyploidy may be a broadly important component of geographic speciation patterns in perennial plants. Further, cytotypes are expected to show physiological and structural differences which may influence susceptibility to ecological factors such as drought, and we suggest that cytotype may be a significant and previously overlooked factor in recent patterns of high aspen mortality in the southwestern portion of the species range. Finally, triploidy should be carefully considered as a source of variance in genomic and ecological studies of aspen, particularly in western U.S. landscapes.

A molecular phylogenetic approach to western North America endemic Artemisia and allies (Asteraceae): Untangling the sagebrushes

PREMISE OF THE STUDY Artemisia subgenus Tridentatae plants characterize the North American Intermountain West. These are landscape-dominant constituents of important ecological communities and habitats for endemic wildlife. Together with allied species and genera (Picrothamnus and Sphaeromeria), they make up an intricate series of taxa whose limits are uncertain, likely the result of reticulate evolution. The objectives of this study were to resolve relations among Tridentatae species and their near relatives by delimiting the phylogenetic positions of subgenus Tridentatae species with particular reference to its New World geographic placement and to provide explanations for the relations of allied species and genera with the subgenus with an assessment of their current taxonomic placement. METHODS Bayesian inference and maximum parsimony analysis were based on 168 newly generated sequences (including the nuclear ITS and ETS and the plastid trnS(UGA)-trnfM(CAU) and trnS(GCU)-trnC(GCA)) and 338 previously published sequences (ITS and ETS). Genome size by flow cytometry of species from Sphaeromeria was also determined. KEY RESULTS The results support an expanded concept and reconfiguration of Tridentatae to accommodate additional endemic North American Artemisia species. The monotypic Picrothamnus and all Sphaeromeria species appear nested within subgenus Tridentatae clade. CONCLUSIONS A redefinition of subgenus Tridentatae to include other western North American endemics is supported. We propose a new circumscription of the subgenus and divide it into three sections: Tridentatae, Filifoliae, and Nebulosae. The position of the circumboreal and other North American species suggests that subgenus Artemisia is the ancestral stock for the New World endemics, including those native to South America.

Gender specialization in heterodichogamous Grayia brandegei (Chenopodiaceae): evidence for an alternative pathway to dioecy

We examined components of male and female reproductive success in protogynous and protandrous sexual morphs of the heterodichogamous and largely monoecious chenopod shrub Grayia brandegei. Percentage femaleness of flowering stalks ranged from 0 to 37.6% female ( = 15.5%) for protandrous plants and from 14 to 100% female ( = 55.8%) for protogynous plants. Functional gender estimates based on ovule production at two locations ranged from 23.0 to 31.8% female for the protandrous morph, and from 65.3 to 77.0% female for the protogynous morph. Realized gender estimates based on total seed production ranged in value from 3.6 to 16.8% female for the protandrous morph and from 76.5 to 96.4% for the protogynous morph, depending on location and year. Differences in reproductive success of the two morphs were largely due to a reduction in the female function of protandrous plants. Protogynous plants produced more female flowers per stalk and had a higher percentage of seed-filled fruits than did protandrous plants. Differences between sexual morphs were more pronounced in dry areas or years in which overall seed production was minimal. Differential seed production between morphs likely reflects temporal patchiness in environmental conditions, particularly in water availability. The significance of these findings in support of heterodichogamy as an evolutionary pathway to dioecy is discussed.

Phylogeny of Salsoleae s.l. (Chenopodiaceae) based on DNA sequence data from ITS, psbB–psbH, and rbcL, with emphasis on taxa of northwestern China

To reconstruct phylogeny and verify the monophyly of major subgroups, a total of 52 species representing almost all species of Salsoleae s.l. in China were sampled, with analysis based on three molecular markers (nrDNA ITS, cpDNA psbB–psbH and rbcL), using maximum parsimony, maximum likelihood, and Bayesian inference methods. Our molecular evidence provides strong support for the following: (1) Camphorosmeae is nested within Salsoleae s.l. instead of the previously suggested sister relationship. (2) Tribe Salsoleae s.l. is monophyletic and is composed of three monophyletic subunits, Caroxyloneae, the Kali clade, and Salsoleae s.str. (3) Climacoptera is separated from Salsola s.l. It does not form a monophyletic group but is split into two monophyletic parts, Climacoptera I and Climacoptera II. (4) Halogeton is clearly polyphyletic, as are Anabasis and the genus Salsola s.l. (5) Caroxylon, Haloxylon, Kali, and Petrosimonia are well-supported monophyletic genera. Additional evidence is needed regarding the monophyly of Halimocnemis, which remains unclear.

Mule deer-induced mortality of mountain big sagebrush

AbStMCt A fence line contrast was provided by a deer fence that bisected a mountain big sagebrush (Artend& tridkntata sap. vaseyana) community. The ~pbruab community was located on an exposed, west-fadng slope that was generally swept free of snow during the severe winters of 1982-83 and 1983-84. On the freeway side of the fence, the site was essentially free of browsing animals, while above the fence, the shrubs were exposed to concentrations of mule deer (Odocoikus hemioms). Considerable big sagebrush mortality was evident after the 2 succeusive winters of heavy snowfall. Big sagebrush mortality and partial dieback of portions of the canopy were significantly (PCO.05) higher in the portion of the community exposed to browsing. Herbaceous species composition also differed between the protected and browsed areas with a higher portion of annual species found in the browsed community. A large number of big sagebrush seedlings germinated in 1984, but failed to establish by 1986. Excessive use of native plants by native large herbivores can have lasting effects on plant communitien.

Retreating or Standing: Responses of Forest Species and Steppe Species to Climate Change in Arid Eastern Central Asia

Background The temperature in arid Eastern Central Asia is projected to increase in the future, accompanied by increased variability of precipitation. To investigate the impacts of climate change on plant species in this area, we selected two widespread species as candidates, Clematis sibirica and C. songorica, from montane coniferous forest and arid steppe habitats respectively. Methodology/Principal Findings We employed a combined approach of molecular phylogeography and species distribution modelling (SDM) to predict the future responses of these two species to climate change, utilizing evidence of responses from the past. Genetic data for C. sibirica shows a significant phylogeographical signal (N ST > F ST, P<0.05) and demographic contraction during the glacial-interglacial cycles in the Pleistocene. This forest species would likely experience range reduction, though without genetic loss, in the face of future climate change. In contrast, SDMs predict that C. songorica, a steppe species, should maintain a consistently stable potential distribution under the Last Glacial Maximum (LGM) and the future climatic conditions referring to its existing potential distribution. Molecular results indicate that the presence of significant phylogeographical signal in this steppe species is rejected and this species contains a high level of genetic differentiation among populations in cpDNA, likely benefiting from stable habitats over a lengthy time period. Conclusions/Significance Evidence from the molecular phylogeography of these two species, the forest species is more sensitive to past climate changes than the steppe species. SDMs predict that the forest species will face the challenge of potential range contraction in the future more than the steppe species. This provides a perspective on ecological management in arid Eastern Central Asia, indicating that increased attention should be paid to montane forest species, due to their high sensitivity to disturbance.