Implications of future climate- and land-change scenarios on grassland bird abundance and biodiversity in the Upper Missouri River Basin

Landscape Ecology - Over the past decades, numerous threats from climate- and land-use change to ecosystems have been identified. Grassland ecosystems are among the most endangered in the world and...     

Mechanisms of drought response in Thuja occidentalis L. II. Post-conditioning water stress and stress relief

We examined the extent of osmotic adjustment and the changes in relative water content (RWC) and transpiration rate (i.e., relative stomatal function) that occur in water-deficit-conditioned 6-year-old Thuja occidentalis L. (eastern white cedar) trees in response to a severe drought. Trees conditioned by successive cycles of mild or moderate nonlethal water stress (conditioning) and nonconditioned trees were exposed to drought (i.e., -2.0 MPa predawn water potential) to determine if water deficit conditioning enhanced tolerance to further drought stress. Following drought, all trees were well watered for 11 days to evaluate how quickly osmotic potential, RWC and transpiration rate returned to preconditioning values. Both nonconditioned trees and mildly conditioned trees exhibited similar responses to drought, whereas moderately conditioned trees maintained higher water potentials and transpiration rates were 38% lower. Both conditioned and nonconditioned trees exhibited a similar degree of osmotic adjustment (-0.39 MPa) in response to drought relative to the well-watered control trees. The well-watered control trees, nonconditioned trees and mildly conditioned trees had similar leaf RWCs that were about 3% lower than those of the moderately conditioned trees. Following the 11-day stress relief, there were no significant differences in osmotic potential between the well-watered control trees and any of the drought-treated trees. Daily transpiration rates and water potential integrals (WPI) of all drought-treated trees approached those of the well-watered control trees during the stress relief period. However, the relationship between cumulative transpiration and WPI showed that previous exposure to drought stress reduced transpiration rates. Leaf RWC of the moderately conditioned trees remained slightly higher than that of the nonconditioned and mildly conditioned trees.     

The relative efficacy of herbicides for the control of Deschampsia flexuosa (L.) Trin. in woodland establishment in the UK

Deschampsia flexuosa is a commonly occurring calcifuge grasswhich can be detrimental to tree regeneration. In the work reportedhere, two experiments using pot-grown plants and one field experimentwere set up to investigate the relative efficacy of variousherbicides in controlling D. flexuosa. Cycloxydim, glyphosateand imazapyr applied in the summer killed virtually all pot-grownplants of D. flexuosa within 1 year of treatment. Hexazinoneand propyzamide were also effective at the recommended doses.Mixture B enhanced the efficacy of several herbicide treatmentsbut pre-spraying plant moisture stress had no effect on subsequentherbicide activity. Cycloxydim and imazapyr applied in springor summer gave excellent long-term control in the field. Itis concluded that if non-chemical approaches such as canopymanipulation or cultivation fail to give adequate control ofD. flexuosa and herbicide use becomes necessary to allow treeregeneration, then cycloxydim applied at 0.45 kg a.i. ha^–1appears to be an effective alternative to the use of more broad-spectrumproducts, and gives very good tree tolerance. If herbicide useis required prior to tree establishment, glyphosate may be acheaper option and will control a broader spectrum of weeds,although it is slightly less effective than cycloxydim on D.flexuosa.     

Comparison of image and rapid field assessments of riparian zone condition in Australian tropical savannas

Suitable methods for measuring and monitoring the condition of riparian environments are being investigated by government agencies responsible for maintaining these environments in Australia. The objective of this work was to compare two riparian condition assessment approaches, the Tropical Rapid Appraisal of Riparian Condition (TRARC) method developed for rapid on-ground assessment of the environmental condition of savanna riparian zones and an image based riparian condition monitoring scheme. Measurements derived from these two approaches were compared and correlated. The sample representativeness of the TRARC method was evaluated and the cost-effectiveness and suitability for multi-temporal analysis of the two approaches were assessed. Two high spatial resolution multi-spectral QuickBird satellite images captured in 2004 and 2005 and coincident field data covering sections of the Daly River in the Northern Territory, Australia were used in this work. Both field and image data were processed to map indicators of riparian zone condition including percentage canopy cover, organic litter on the ground, canopy continuity, tree clearing, bank stability, and flood damage. Spectral vegetation indices, image segmentation, and supervised classification were used to produce riparian health indicator maps. QuickBird image data were used to examine if the spatial distribution of TRARC transects provided a representative sample of ground based estimates of riparian health indicators. Covering approximately 3% of the study area, the sample mean of the TRARC estimates of individual indicators of riparian zone condition were in most cases within 20% of the global mean derived from the whole imaged riparian area. The cost-effectiveness of the image based approach was compared to that of the ground based TRARC method. Results showed that the TRARC method was more cost-effective at spatial scales from 1 km to 200 km of river in relatively homogeneous riparian zones along rivers with only one channel, while image based assessment becomes more feasible at regional scales (200–2000 km of river). A change detection analysis demonstrated that image data can provide detailed information on gradual change, while the TRARC method is less suited for multi-temporal analysis due to the ranked data format, which inhibits precise detection of change. However, results from both methods were considered to complement each other for single date assessment of riparian zones if used at appropriate spatial scales.     

Genetic variability in antibiotic resistance to the greenbug Schizaphis graminum in Hordeum chilense

Hordeum chilense (Roem. et Schult), a native grass of South America, is a source of antixenotic and antibiotic resistance to the greenbug Schizaphis graminum Rondani. The genetic and environmental components of the variability in antibiotic resistance shown by H. chilense were determined by measuring the developmental time, the length of adult life, fecundity and intrinsic rate of population increase of green-bugs reared on this host. The aphids belonged to a clone of biotype C. Plants were cloned to reduce the incidence of environmental variability. Different plant characters appeared to prolong aphid developmental time and reduce the length of adult life and total fecundity. The broad sense heritability and the genetic variability of these plant characters were different. The plant character that affected aphid development appears to differ from that affecting fecundity.     

Identification of levels of resistance to cassava root rot disease (<Emphasis Type="Italic">Botryodiplodia theobromae</Emphasis>) in African landraces and improved germplasm using <Emphasis Type="Italic">in vitro</Emphasis> inoculation method

Cassava root rot disease is an increasing problem in Africa where yield losses of about 80% have been recorded. We evaluated 290 African landraces and 306 improved genotypes from the germplasm collections of the International Institute of Tropical Agriculture (IITA), for sources of resistance using root slice laboratory assay. Disease severity was assessed quantitatively by direct percentage estimation (PS) and by use of a rating scale (RS). Both methods of assessment were compared for identification of variability in the germplasm, and genotypes were classified into response groups using an enlarged rank-sum method that combined the PS and RS assessments. The two scoring methods revealed continuous variation (P < 0.001) for resistance in the sets of germplasm. Disease assessments based on PS and RS were highly correlated in both the improved germplasm (r = 0.75) and the landraces (r = 0.72). Based on PS assessment, 50 improved genotypes (16.3%) and 53 landraces (18.3%) showed significantly lower disease scores than the resistant control. The rank-sum method separated each set of collections into highly resistant, resistant, moderately resistant, moderately susceptible, susceptible and highly susceptible groups. Fifty-nine improved genotypes (16.4%) and 61 African landraces (16.9%) were identified as either highly resistant or resistant. Generally, these genotypes exhibited resistance by limiting the growth of the pathogen (reduced amount of invaded surface area). This type of rate-reducing resistance is highly heritable and a quantitative trait which can be harnessed in breeding. Genotypes subsets were identified for further studies into the genetic basis of resistance to root rot disease.     

Global forest systems: An uncertain response to atmospheric pollutants and global climate change?

Forest systems cover more than 4.1×10⁹ ha of the Earth's land area. The future response and feedbacks of forest systems to atmospheric pollutants and projected climate change may be significant. Boreal, temperate and tropical forest systems play a prominent role in carbon (C), nitrogen (N) and sulfur (S) biogeochemical cycles at regional and global scales. The timing and magnitude of future changes in forest systems will depend on environmental factors such as a changing global climate, an accumulation of CO₂ in the atmosphere, and increase global mineralization of nutrients such as N and S. The interactive effects of all these factors on the world's forest regions are complex and not intuitively obvious and are likely to differ among geographic regions. Although the potential effects of some atmospheric pollutants on forest systems have been observed or simulated, large uncertainty exists in our ability to project future forest distribution, composition and productivity under transient or nontransient global climate change scenarios. The potential to manage and adapt forests to future global environmental conditions varies widely among nations. Mitigation practices, such as liming or fertilization to ameliorate excess NO_x or SO_x or forest management to sequester CO₂ are now being applied in selected nations worldwide.The U.S. Government's right to a non-exclusive, royalty free licence in and to any copyright is acknowledged.     

Comparative evaluation of the contributions of soil physicochemical properties to variations in the yields of four major staple food crops in eastern Nigeria

The contributions of soil variables to the variations in the yields of cassava (Manihot esculenta), yam (Dioscorea rotundata), maize (Zea mays) and pigeon pea (Cajanus cajan) were evaluated over 2 years in this study. The data were from three replicates of two randomized complete block design experiments sited in a newly cleared forest and on previously cultivated land both in Nsukka, eastern Nigeria. The 28 soil physicochemical properties and six crop yield parameters measured were partitioned between location and year before applying a stepwise regression procedure to analyze them.

The study showed that soil variables accounted for >70% of the variation in cassava root yields and harvest index. Both soil physical and chemical properties contributed but the former (particularly macroporosity, microporosity, total porosity and bulk density) contributed most. Selected soil variables also accounted for >70% of the variation in yam tuber yield and shape index of tubers especially in 1998. In both crop years chemical properties appeared to dominate over the physical ones. Soil variables accounted for between 51 and 99% of the variation in maize grain and stover yields. The only exception was the figure of 44% obtained at the forest location in 1998. Soil pH, total exchangeable acidity and microporosity were particularly important contributors to the variations in both maize yield parameters. The contributions of soil variables to pigeon pea yield parameters were low (<50%) except in 1999 at the forest location where seven soil variables accounted for over 85% variation in seed yield.

It was obvious generally from the study that soil variables were important determinants of yield variations in the four crops. It was also shown that physical properties should always be included in this kind of analysis. Also the number of soil variables which were of significance generally increased when the level of soil properties was low, as was the case with the cultivated site versus forest site, and 1999 versus 1998 analysis. Thus increasing the number of soil variables used and partitioning them into more homogeneous units helped to improve the results obtained using the procedure.