Enhancing Native Forb Establishment and Persistence Using a Rich Seed Mixture

Establishing native forbs is crucial for invasive plant management and restoring a desirable plant community. Our objectives were to determine (1) if increasing forb seed density results in increased forb establishment; (2) if a species‐rich mixture of forbs has greater establishment and survivorship than a single species; and (3) if mixtures of forbs are more competitive with Spotted knapweed (Centaurea maculosa) than a forb monoculture. To test our first two objectives, we seeded monocultures of Purple coneflower (Echinacea angustifolia), Arrowleaf balsamroot (Balsamorhiza sagittata), Annual sunflower (Helianthus annuus), Dotted gayfeather (Liatris punctata), Western white yarrow (Achillea millefolium), Sticky geranium (Geranium viscosissimum), as well as a mixture of all forbs. Pots were seeded at 800 or 2,000 seeds/m² and watered twice or thrice weekly. The highest seed density produced the highest plant density, which averaged 4.35 plants/pot. The density of the mixture was similar to the mean density seen for individual species, and it doubled in response to the highest seed density. To test our third objective, Spotted knapweed and Purple coneflower were arranged in an addition series matrix with a maximum total density of 4,000 seeds/pot. We found that the forb mixture was seven times more competitive with Spotted knapweed than Purple coneflower alone. Using a mixture of forbs rather than a single species enhances forb establishment in various and unpredictable environments because the mixture possesses a variety of traits that may match year–year and site–site conditions. Once established, the mixture may have a greater chance of persisting than a monoculture.     

Restoring Brazilian savanna ground layer vegetation by topsoil and hay transfer

Tropical grassy biomes have been widely neglected for conservation and, after unplanned land use conversion, ecological restoration becomes urgent. The majority of interventions have been based on the misapplication of forest restoration techniques, because there are no validated techniques to restore the species‐rich ground layer. In search for innovative techniques to restore the herbaceous layer of the cerrado vegetation, we carried out an experiment based upon topsoil and hay transfer, in the state of São Paulo, Brazil. The restoration treatments were: (1) transfer of topsoil collected at the end of the dry season; (2) topsoil collected at the end of the rainy season; (3) transfer of hay collected at the end of the dry season; (4) topsoil + hay collected at the end of the dry season; and (5) control. We used an old‐growth grassland as source of material and as reference ecosystem to assess the efficacy of the restoration techniques applied to an area severely degraded after invasion by African grasses. After 211 days, hay transfer apparently inhibited germination and did not contribute to grassland vegetation recovery. Topsoil transfer, however, was effective at reintroducing herbaceous plants, including target species. The season of topsoil collection mattered: material collected at the end of the rainy season provided better results in terms of density and richness of the restored community than that from the dry season. The remaining challenge is to find sources of topsoil not invaded by exotic grasses in large enough amounts to support restoration initiatives without jeopardizing the source ecosystems.     

Frequency and Extent of Water Limitation to Primary Production in a Mesic Temperate Grassland

The frequency and extent of water limitation to aboveground net primary production (ANPP) in a mesic grassland in NE Kansas (Konza Prairie, USA) was assessed with an 8-year irrigation experiment. Since 1991, transects spanning upland and lowland sites in annually burned, ungrazed tallgrass prairie were provided with supplemental water to satisfy evapotranspirational demands. This protocol minimized water limitations during the growing season, as well as interannual variability in water stress. Irrigation of this mesic grassland increased ANPP in 6 of 8 years by an average of 26% when compared to control transects. Although interannual variation in ANPP was greater in uplands than lowlands at nominal levels of precipitation, reducing interannual variability in water availability via irrigation eliminated topographic differences; the irrigation protocol also reduced interannual variability in ANPP by as much as 40%. The addition of supplemental water enabled us to extend the relationship between annual precipitation and ANPP in grasslands to precipitation levels (average, 1153 mm; maximum, 1346 mm) similar to those experienced by more mesic grasslands that today exist only as remnants several hundred kilometers east of Kansas. This relationship was linear (r ²= 0.81), with maximum ANPP (738 g/m²) similar to values reported for sites in Illinois and Wisconsin. After 8 years of irrigation, production of the C₃ forb component was twice that in control sites. These results indicate that water limitations in grasslands at the western edge of the presettlement extent of tallgrass prairie affect ANPP in most years and that this high frequency of water limitation may lead to greater dominance of the C₄ grasses than is seen in more eastern grassland sites. Received 18 January 2000; accepted 19 July 2000.     

Effect of climate on the growth of annual rings in the main roots of perennial forbs in an Inner Mongolian semi‐arid grassland,China

Question: Is there a pattern in growth of annual rings in roots of perennial forbs in relation to climate and climate extremes in grassland ecosystems? Location: Semi‐arid grassland in Duolun (42°27′N, 116°41′E, 1380 m a.s.l.), central Inner Mongolia, China. Methods: Main roots of three perennial species, Potentilla anserina L., Cymbaria dahurica L. and Lespedeza daurica Schindl., were sampled. Cross‐sections (10–15‐μm thick) were produced from the proximal end of sampled roots using a sledge microtome. Annual growth rings in the main roots were identified and measured by differentiating between earlywood and latewood in the secondary xylem. Relationships between annual growth rings and monthly mean temperature and total monthly precipitation were identified using correlation analysis. Differences in an annual ring width to the previous and following years were examined by calculating a distinctness score. Results: The three perennial forbs showed clearly demarcated annual growth rings in all individuals and the same fluctuation patterns. Their ring widths were generally positively correlated with precipitation from April to October (except for August) and with temperature from February to June (except June for L. daurica), September to October, and the annual mean. Strong deviations of annual ring widths from their neighbour rings were observed in 1998 and 2000. The trend of absolute distinctness scores (D_m) increased significantly from 1988 to 2003, indicating an increase in the frequency of annual ring width variation. Conclusions: Annual growth rings in the main roots of three perennial forb species can be used as an indicator of the influence of climate on below‐ground grassland growth. The change in below‐ground conditions and effects on the functioning of grassland should receive more attention in future studies.     

Recovery of Greater Sage-Grouse Habitat Features in Wyoming Big Sagebrush following Prescribed Fire

The ability of prescribed fire to enhance habitat features for Greater Sage-Grouse ( Centrocercus urophasianus ) in Wyoming big sagebrush ( Artemisia tridentata wyomingensis ) in western North America is poorly understood. We evaluated recovery of habitat features important to wintering, nesting, and early brood-rearing Sage-Grouse in Wyoming big sagebrush following prescribed fire. Our case study included 1 year of preburn (1989) and 10 years of postburn data collected over 14 years (1990–2003) from control and burned study areas in the Big Desert of southeastern Idaho, U.S.A. We compared recovery and rate of change for 12 features in four categories between burned and control transects and recovery in burned transects including change in variation. Our results indicate that prescribed fire induced quantifiable changes in wintering, nesting, and early brood-rearing Sage-Grouse habitat features 14 years after fire in Wyoming big sagebrush in our study area. Specifically, grass and litter required by Sage-Grouse for nest and brood concealment recovered relatively rapidly following fire; major forb cover was similar between burned and control sites, but the rate of increase for major forb cover and richness was greater in control transects, and structurally mediated habitat features required by Sage-Grouse for food and cover in winter and for nest and brood concealment in spring recovered slowly following fire. Because shrub structural features in our study did not recover in magnitude or variability to preburn levels 14 years after fire, we recommend that managers avoid burning Wyoming big sagebrush to enhance Sage-Grouse habitat, but rather implement carefully planned treatments that maintain Sagebrush.     

Effects of bison and cattle on growth, reproduction, and abundances of five tallgrass prairie forbs

Forb populations were sampled on Kansas tallgrass prairie to examine the effects of native (bison) and domestic (cattle) ungulates on plant growth, reproduction, and species abundances. Five locally and regionally abundant native tallgrass prairie perennials, Baptisia bracteata, Oenothera speciosa, Vernonia baldwinii, Solidago missouriensis, and Salvia azurea, were selected for study. Replicate watershed-level treatments included three grazing regimes (ungrazed, grazed by cattle, and grazed by bison), and two spring fire frequencies (annually burned and burned at 4-yr intervals). The results show that forb responses to ungulates in tallgrass prairie are complex and vary significantly among plant species, ungulate species, fire regimes, and plant life history stages. Some forbs (e.g., B. bracteata, O. speciosa, and V. baldwinii) increased in growth and reproduction in grazed sites, indicating competitive release in response to selective grazing of the dominant warm-season matrix grasses. Forbs that reduced performance in grazed sites are likely negatively affected by disturbances generated by ungulate nongrazing activities, because none of the forbs studied were directly consumed by bison or cattle. Large grazers had no detectable effect on the frequency of plant damage by other herbivores or pathogens. Significant effects of grazers on patterns of flowering and seed production were not congruent with their effects on population densities, indicating that variation in sexual reproduction plays a minor role in regulating local population abundances. Furthermore, the native and domestic ungulates differ significantly in their effects on forb growth and reproduction.     

Diminishing Returns from Higher Density Restoration Seedings Suggest Trade‐offs in Pollinator Seed Mixes

Native forbs have become a more central component of restoration programs, especially because of their role in supporting crop pollinators. This study evaluates the success of different native forb mixes and seeding rates using shared goals of restoration practitioners and agroecologists, namely percent native species cover, floral resources, native diversity, and cost‐effectiveness. At 6 sites with hedgerows adjacent to agricultural lands in California's Central Valley, we planted 3 native forb seed mixes at 3 seeding rates and monitored germination, percent cover, and floral resources for 2 to 3 years. We also evaluated the cost of the mixes based on seeding rates and original seed prices. More than mix type, relative seeding rate strongly affected germination, cover, and floral resource success. The relative benefits of seeding with more species diminished at higher seeding rates, especially when cost was considered. Cover increased significantly over the years but diversity declined sharply after the first year. Increased cover of target species was mainly due to the effect of 1 dominant species Grindelia camporum, common gumplant. We summarize data from a similar forb restoration study showing that the species that dominated in our mix‐and‐rate experimental sites also attracted the greatest diversity and abundance of pollinators. These findings highlight trade‐offs and balance‐points within restoration and pollination services goals. We offer suggestions on how to weigh those trade‐offs, given particular priorities and how native forb plantings can support combined goals of pollination services and restoration.     

Growth rings in the roots of temperate forbs are robust annual markers

There is increasing interest in the analysis of annual growth rings in the secondary root xylem of perennial forbs (herb-chronology). Therefore, we need to verify whether these growth rings are always formed annually. To investigate the formation of root rings we performed common garden experiments at two distinct sites in Switzerland. We grew nine unrelated forb species from seed and subjected them to competition and clipping treatments. Anatomical developments in the roots of the individuals were tracked during five growing seasons. Across all species and treatments at least 94 % of the expected growth rings associated with full growing seasons were identifiable and the development of the anatomical patterns was consistently seasonal. While the distinctness of annual rings varied somewhat between species and sites, the treatments had no effect on the presence of annual rings. In no case were false rings developed. The results of this study demonstrate that the growth rings in the roots of northern temperate forbs represent robust annual growth increments and, hence, can reliably be used in herb-chronological studies of age- and growth-related questions in plant ecology.