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Since European settlement, changes in the fire regime of eastern deciduous forests of North America have led to changes in biological diversity and stand structure. These changes may be attenuated in xeric forests at the western limit of the eastern deciduous forest where woody plant species richness is low, and dominance high, due to the rigorous biotic and physical environment. Effects of fire frequency on woody plant species richness and stand structure were studied in a xeric, oak-dominated (Quercus spp.) old-growth forest in eastern Oklahoma where prescribed burning had been conducted over 20 years at frequencies ranging from zero to five fires per decade. Regeneration (stem height < 1 .4 m) cover was not affected by fire frequency. Increasing fire frequency had a strong negative effect on species richness of saplings and shrubs (stem dbh <5 cm) but no significant effect on small tree (stems 5 cm < dbh < 10 cm) and large tree (stems dbh> 10 cm) species richness. While oak sapling density was not affected by fire frequency, the density of non-oak saplings and shrubs was very high at zero and one fire per decade and strongly reduced by fire frequencies of two or more per decade. Although 20 years of treatment may not have been sufficient to show fire frequency effects on canopy trees, the effect on species composition of saplings was strong and may have long-term consequences for forest canopy composition. These results suggest that, without at least two fires per decade, tree species richness of these forests will increase and oak dominance will diminish. [ABSTRACT FROM AUTHOR]

Question: To what extent do bison serve as seed dispersers via epizoochory and endozoochory in tallgrass prairie, and does this differ by age-sex class of bison and by month? Location: Tallgrass Prairie Preserve, Osage County, Oklahoma, USA. Methods: We collected bison hair from 19 bulls, 45 cows, and 47 juveniles in fall and we collected bison dung monthly for a year. We recovered and identified seeds from hair and dung samples, and classified seeds by size and diaspore characteristics. Results: Bison hair samples contained 2768 seeds from at least 76 plant species. Several species found in hair did not feature specialized appendages for adhesive dispersal. Seed species composition differed in hair collected from bulls, cows and juveniles, possibly due to differential habitat use. Dung samples contained 7418 seeds from at least 70 species, from which graminoids accounted for 3936 seeds from 27 species. Species composition of seeds contained in dung samples differed among months, corresponding to availability. Grasses constituted about half the seeds in both dung and hair samples, but Asleraceae were more strongly represented in hair, while Scrophulariaceae and Solanaceae were more strongly represented in dung. Conclusions: We conclude that bison are potentially important dispersers of forbs as well as graminoids. A high abundance and wide diversity of seeds were found in both bison hair and dung. The great majority of seeds found undamaged in bison dung were small seeds, which agrees with the `foliage is the fruit' hypothesis. Dispersal by both epizoochory and endozoochory may play an important role in life history of many species in tallgrass prairie landscapes. [ABSTRACT FROM AUTHOR]

The biodiversity crisis demands that scientists be careful in their application of quantitative methods, because misuse of biodiversity statistics can lead to trivial but real patterns (artifacts) or to false patterns (artifictions). While misuses such as biases in taxonomic ratios, standardization by dividing by area or individuals, and the rarefaction effect have been repeatedly recognized in the literature, they continue to appear regularly in the scientific literature. Here, we illustrate (using data from North American floras and the Tallgrass Prairie Preserve in Oklahoma, USA) examples of how artifacts and artifictions can lead to misinterpretation of biodiversity patterns. We urge biogeographers and ecologists to be vigilant when using biodiversity statistics, to avoid false interpretations. [ABSTRACT FROM AUTHOR]

The 15,410 ha Tallgrass Prairie Preserve (Osage County, Oklahoma), managed by The Nature Conservancy, consists of a variety of grassland, forested, wetland, and disturbed habitats. 1,612 specimens of vascular plants collected between 1992 and 2007 were examined to obtain a vouchered flora of the preserve. The known flora consists of 763 species in 411 genera and 109 families. 12.1% of the species are not native to North America. [ABSTRACT FROM AUTHOR]

Questions: The Cross Timbers are a mosaic of savannas, grasslands and upland forests, occupying a significant portion of south-central North America. Our questions here were (1) how does a severe tornado affect the two most dominant tree species of the area Quercus marilandica and Q. stellata with respect to damage and mortality; (2) how do such patterns vary as a function of tree size? What are the implications of disturbance for codominance in species-poor systems? Location: The Cross Timbers in Oklahoma, USA. Methods: We established a 14.48-ha permanent plot following a severe tornado in 2003. We identified, numbered and tagged each tree and recorded its diameter at breast height (DBH), spatial coordinates, status (dead or alive), and damage type. We examined (1) relative abundance before and after the tornado; (2) differences in damage and mortality, and (3) the influence of tree diameter on the probability of damage and mortality for each species. Results: Differences in species identity and tree characteristics were significantly related to tree mortality following the tornado, after accounting for spatial locations. The odds of mortality were 12.0 times greater for Q. marilandica than for Q. stellata. Such greater vulnerability of Q. marilandica versus Q. stellata was also reflected in changes in density and basal area. Tree diameter clearly influenced the damage and mortality pattern in Q. stellata; larger trees sustained more damage and mortality. However, Q. marilandica did not exhibit size-dependent mortality. Conclusion: The tornado affected the two dominant species differently. The intra- and inter-specific differences in windstorm susceptibility may allow coexistence of the two species and are potentially important in the dynamics of the Cross Timbers. Species more damaged might finally benefit from the wind disturbance due to their resprouting ability. [ABSTRACT FROM AUTHOR]

Abstract: Upland oak forests in the ecotone between the eastern deciduous forest and the southern Great Plains are threatened by encroachment of eastern redcedar (Juniperus virginiana) due to fire suppression. The rapid rate of encroachment caused concern about concomitant alterations of site characteristics including nutrient cycling and the soil microbial communities (SMC) that could lead to positive feedbacks reinforcing eastern redcedar encroachment. We studied eight upland oak forests across central and western Oklahoma with stands representing three levels of encroachment: oak-dominated, eastern redcedar-dominated, and an intermediate mixture of both species. We analyzed litter chemistry (carbon, lignin, and nitrogen), soil chemistry (soil organic matter, NH4N, NO3-N, PO4, K, and pH), and profiled soil microbial communities using phospholipid fatty acid analysis (PLFA). Eastern redcedar encroachment was accompanied by reduced litter carbon along with higher levels of arbuscular mycorrhizal (AM) fungi while litter N was lower in mixed stands. However, we detected no change in soil chemistry. Our results indicate eastern redcedar encroachment in these upland oak forests reduced litter quality and altered the SMC through increases in AM fungi, a symbiont associated with eastern redcedar. These alterations may create positive soil–microbial feedbacks by reducing the fitness of the dominant oak species and facilitating rapid increase in eastern redcedar in this threatened, oak-dominated ecosystem. [Copyright &y& Elsevier]

Abstract: Viruses are most frequently discovered because they cause disease. To expand knowledge of plant-associated viruses beyond these narrow constraints, non-cultivated plants of the Tallgrass Prairie of the United States were systematically surveyed for evidence of viruses. This report discusses putative viruses of the family Secoviridae identified by the survey. Sequence analysis suggests the presence of at least six viruses in the study site, including Bean pod mottle virus, Maize chlorotic dwarf virus, three previously undescribed viruses within the subfamily Comovirinae and one unclassifiable virus. [Copyright &y& Elsevier]

Native virus-plant interactions require more understanding and their study will provide a basis from which to identify potential sources of emerging destructive viruses in crops. A novel tymovirus sequence was detected in Asclepias viridis (green milkweed), a perennial growing in a natural setting in the Tallgrass Prairie Preserve (TGPP) of Oklahoma. It was abundant within and frequent among A. viridis plants and, to varying extents, within other dicotyledonous and one grass (Panicum virgatum) species obtained from the TGPP. Extracts from A. viridis containing the sequence were infectious to a limited number of species. The virus genome was cloned and determined to be closely related to Kennedya yellow mosaic virus. The persistence of the virus within the Oklahoma A. viridis population was monitored for five successive years. Virus was present in a high percentage of plants within representative areas of the TGPP in all years and was spreading to additional plants. Virus was present in regions adjacent to the TGPP but not in plants sampled from central and south-central Oklahoma. Virus was present in the underground caudex of the plant during the winter, suggesting overwintering in this tissue. The RNA sequence encoding the virus coat protein varied considerably between individual plants (≈3%), likely due to drift rather than selection. An infectious clone was constructed and the virus was named Asclepius asymptomatic virus (AsAV) due to the absence of obvious symptoms on A. viridis. [ABSTRACT FROM AUTHOR]

Abstract: Viruses are most frequently discovered because they cause disease in organisms of importance to humans. To expand knowledge of plant-associated viruses beyond these narrow constraints, non-cultivated plants of the Tallgrass Prairie Preserve, Osage County, Oklahoma, USA were systematically surveyed for evidence of the presence of viruses. This report discusses viruses of the family Tombusviridae putatively identified by the survey. Evidence of two carmoviruses, a tombusvirus, a panicovirus and an unclassifiable tombusvirid was found. The complete genome sequence was obtained for putative TGP carmovirus 1 from the legume Lespedeza procumbens, and the virus was detected in several other plant species including the fern Pellaea atropurpurea. Phylogenetic analysis of the sequence and partial sequence of a related virus supported strongly the placement of these viruses in the genus Carmovirus. Polymorphisms in the sequences suggested existence of two populations of TGP carmovirus 1 in the study area and year-to-year variations in infection by TGP carmovirus 3. [Copyright &y& Elsevier]

Abstract: The diversity of viruses associated with non-cultivated plants was assessed from plant samples collected in the Tallgrass Prairie Preserve of northeastern Oklahoma, USA. The samples were processed to determine the sequences of nucleic acids extracted from the virus-like particle fraction of plant homogenates. Sequences from 95 specimens of 52 plant species included those of probable origin from the genomes of plants (including retroelements), bacteria, fungi, other organisms, and viruses. Virus-like sequences were identified in sequences from 25% of the specimens, coming from 19% of the plant species. Evidence of a member of the genus Tymovirus was found in 16 specimens of 6 plant species, making it the most predominant virus associated with the sampled plants. There was evidence of the presence of more than one virus in each of six specimens. [Copyright &y& Elsevier]