Differential effect of drought regimes on the seedling performance of six floodplain grassland species.

The performance of seedlings is crucial for the survival and persistence of plant populations. Although drought frequently occurs in floodplains and can cause seedling mortality, studies on the effects of drought on seedlings of floodplain grasslands are scarce. We tested the hypotheses that drought reduces aboveground biomass, total biomass, plant height, number of leaves, leaf area and specific leaf area (SLA), and increases root biomass and root-mass fraction (RMF) and that seedlings from species of wet floodplain grasslands are more affected by drought than species of dry grasslands. In a greenhouse study, we exposed seedlings of three confamilial pairs of species (Pimpinella saxifraga, Selinum carvifolia, Veronica teucrium, Veronica maritima, Sanguisorba minor, Sanguisorba officinalis) to increasing drought treatments. Within each plant family, one species is characteristic of wet and one of dry floodplain grasslands, confamilial in order to avoid phylogenetic bias of the results. In accordance with our hypotheses, drought conditions reduced aboveground biomass, total biomass, plant height, number of leaves and leaf area. Contrary to our hypotheses, drought conditions increased SLA and decreased root biomass and RMF of seedlings. Beyond the effects of the families, the results were species-specific (V. maritima being the most sensitive species) and habitat-specific. Species indicative of wet floodplain grasslands appear to be more sensitive to drought than species indicative of dry grasslands. Because of species- and habitat-specific responses to reduced water availability, future drought periods due to climate change may severely affect some species from dry and wet habitats, while others may be unaffected.

Soil vs. canopy seed storage and plant species coexistence in species-rich Australian shrublands.

The fire-prone shrublands of southwestern Australia are renowned for their high plant species diversity and prominence of canopy seed storage (serotiny). We compared species richness, abundance, and life history attributes for soil and canopy seed banks in relation to extant vegetation among four sites with different substrate conditions and high species turnover (50-80%) to identify whether this unusual community-level organization of seed storage might contribute to maintenance of high species richness. Soil seed bank (SSB) densities were low to moderate (233-1435 seeds/m2) compared with densities for other Mediterranean-type vegetation and were lowest for sites with highest canopy seed bank (CSB) species richness and lowest nutrient availability, but not richness or abundance of resprouters. Annuals were infrequent in the lowest nutrient sites, but there was no evidence that small SSB size was due to low seed inputs or a trade-off between seed production/storage and seed size in response to low nutrient availability. Sorensen's similarity between SSB and extant vegetation was 26-43% but increased to 54-57% when the CSB was included, representing levels higher than reported for most other ecosystems. Resprouting species were well represented in both the SSB and CSB, and there was no evidence for lower seed production in resprouters than in non-sprouters overall. The SSB and CSB held no species in common and were characterized by markedly different seed dispersal attributes, with winged or small seeds in the CSB and seeds dispersed by ants, birds, and wind (though none with wings) in the SSB. There was no evidence of spatial differentiation in the distribution of seeds of SSB species between vegetated and open microsites that might facilitate species coexistence, but most woody non-sprouters showed aggregation at scales of 1-2 m, implying limited seed dispersal. High similarity between overall seed bank (SSB + CSB) and extant species composition, high number of resprouting species, and seed dispersal processes before (SSB) and after fire (CSB) leading to differential spatial aggregation of post-fire recruits from the two seed bank types may buffer species composition against rapid change and provide a mechanism for maintaining species coexistence at the local scale.

A comparison of actual and apparent lumbar lordosis in black and white adult females.

The purposes of this study were to investigate differences in lumbar lordosis in black and white adult females and to explain the clinical impression that blacks have a greater lordosis than whites. An actual lumbosacral lordosis angle (ALS) was measured from a standing right lateral lumbosacral radiograph using the angle formed from the intersection of lines drawn across the top of the second lumbar vertebral body (L2) and across the top of the sacrum. An actual lumbo-lumbar angle (ALL) was measured in the same manner, except the second line was drawn across the bottom of the fifth vertebral body (L5). To determine whether gluteal prominence gives a false impression of increased lumbar lordosis, an apparent lordosis (APL) measurement was taken, measuring the distance from the subject's greater trochanter to the most posterior aspect of the buttocks. No significant differences were found in ALS or ALL between 25 black and 27 white adult female subjects (ALS, P = 0.26; ALL, P = 0.41). Significant differences were found between black and white APL, with blacks demonstrating a larger APL than whites (P less than 0.01). A high correlation was noted between ALS and ALL in both blacks (0.70, P less than 0.01) and whites (0.77, P less than 0.01). The investigators therefore contend that the clinician's assumption that blacks have a greater lordosis than whites is based on an apparent increased lordosis due to more prominent buttocks (APL).

Investigation of the validity of postural evaluation skills in assessing lumbar lordosis using photographs of clothed subjects.

Data for this study was collected at the 1988 Texas Physical Therapy Association Annual Conference with approval through the state Research Committee. The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or reflecting the views of the Army, the Department of Defense, or the US. Government. The purpose of this study was to evaluate the validity of physical therapists' visual postural evaluation skills in assessing lumbar lordosis using photographs of clothed subjects compared to actual radiographic measurements. The study also addressed the efficacy of the use of a plumb line in postural assessment. Forty-eight physical therapists (raters) participated. After completing a demographic questionnaire, raters were given a set of pictures showing sagittal views of three subjects and asked to rank order the subjects from most to least amount of lumbar lordosis. Raters were then given a second set of pictures with different subjects to evaluate. During this second trial, raters were given a plastic overlay with a hairline to use as a plumb line. Each rater evaluated one set of subjects with 7-8 degrees of difference in lordosis and one set with 13- 14 degrees of difference as measured radiographically. The raters' rank order of the pictures was interpreted as either correct or incorrect. For 96 trials, 9 responses were correct for an accuracy rate of 9.3%. The use of the hairline as a plumb line did not improve the raters' accuracy. A chi-square test showed no relationship between ratings except under circumstances related to the gluteal prominence body contour. The strongest trend in interrater reliability identified was that the raters' perception of increased lordosis may have been influenced by gluteal prominence. The results indicate low validity in assessing relative amounts of lumbar lordosis using photographs of clothed subjects. This preliminary study indicates the need for more research in this area using both pictures and live subjects. J Orthop Sports Phys Ther 1990;12(1):24-29.

Investigation of the flexible ruler as a noninvasive measure of lumbar lordosis in black and white adult female sample populations.

The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or reflecting the views of the Army, the Department of Defense, or the U.S. Government. The purpose of this study was to investigate the validity of the flexible ruler as a noninvasive measure of lumbar lordosis in black and white adult females. The bony landmarks of the second lumbar vertebra (L2) and the intersection of the posterior superior iliac spines (PSIS) were palpated and marked on 45 adult females (21 blacks, 24 whites). Potential subjects with a previous history of activity-limiting low-back pain, spinal surgery, or spinal anomaly were excluded from the study. A lateral lumbosacral roentgenograph was taken of each subject, and an actual (skeletal) lumbosacral lordosis angle (ALS) was calculated from the roentgenograph. A flexible ruler was then molded to the contour of the subject's lumbosacral spine, and the previously marked L2 and PSIS intersection bony landmarks were located on the flexible ruler. The flexible ruler lordosis angle (FRA) was then calculated and correlated to the subject's ALS. The criterion validity of the flexible ruler as a measure of actual lumbosacral lordosis was poor (Pearsons' Correlation Coefficient = 0.30, N = 45). Because of the poor criterion validity of the flexible ruler compared to roentgenographically confirmed lumbar lordosis, the flexible ruler has questionable clinical value in the assessment of lumbar lordosis. J Orthop Sports Phys Ther 1989;11(1):3-7.

Vegetative reproduction capacities of floodplain willows--cutting response to competition and biomass loss.

While several studies on regeneration in Salicaceae have focused on seedling recruitment, little is known about factors controlling their vegetative reproduction. In two greenhouse experiments, we studied the response of floodplain willows (Salix fragilis, S. viminalis, S. triandra) to competition with Poa trivialis, and to shoot and root removal when planted as vegetative cuttings. In the first experiment, growth performance variables were analysed in relation to full competition, shoot competition, root competition and control, taking into account two different water levels. After 9 weeks, shoots were removed and the resprouting capacity of the bare cuttings was recorded. In the second experiment, the cutting performance of the three floodplain and an additional two fen willow species (S. cinerea, S. aurita) was compared when grown in three different soil compositions and with two different water levels. After 9 weeks, shoot and root biomass was removed and the bare cuttings were replanted to test their ability to resprout. Cutting performance and secondary resprouting were negatively affected by full and shoot competition while root competition had no or weak effects. The floodplain species performed better than the fen species in all soil types and water levels. Secondary resprouting capacity was also higher in the floodplain species, which showed an additional strong positive response to the previous waterlogging treatment. The results contribute to understanding of the vegetative regeneration ecology of floodplain willows, and suggest that the use of vegetative plantings in restoration plantings could be an effective strategy for recovering floodplain forests.