Rainfall Sites Research Articles

Eucalyptus globulus agroforestry on deep sands on the southeast coast of Western Australia: The promise and the reality

Secondary salinisation is a growing problem in Western Australia, with 1.1 Mha of agricultural and public land now affected to some extent. During the 1980s and early 1990s it was widely believed that agroforestry offered one of the best hopes for reducing the area at risk from salinisation while improving the productivity of conventional agricultural enterprises and providing new sources of income to landholders. This paper details the hydrogeology, tree water use and the productivity of Eucalyptus globulus, crops and pastures in an agroforestry system on the south coast of Western Australia with deep sandy soils and rising groundwater. The tree-belts directly occupied 10% of the catchment and the lateral spread of outer tree roots meant recharge was effectively eliminated over 20% of the catchment. However, groundwater at the site continued to rise for 13 years after the trees were planted. Sapflow and tree growth measurements showed that the trees did not access the brackish groundwater (>500 mg/L) present over most of the site. Consequently, tree growth was relatively poor (5 m 3/ha/yr for inner trees) and the estimated economic returns from pulpwood production were less than from agriculture. While the outer tree rows grew at 8 times the rate of inner rows, this was at the expense of reduced crop and pasture growth in the adjacent 15–20 m wide competition zone (CZ). If the area of the CZ where agricultural production was less than breakeven is considered, then the outer tree rows grew at a similar rate (expressed on an area basis) as the inner rows. This suggests there was no economic advantage in growing pulpwood in belts rather than blocks at this site. Thinning the trees to 125 stems/ha allowed improved crop and pasture production and reduced wind erosion in the CZ, and facilitated greater growth rates of the remaining trees. It remains to be determined whether increased economic returns from the trees will compensate for the cost of thinning and pruning. This study has shown that E. globulus is not a suitable agroforestry tree species for medium rainfall sites with deep sands and brackish groundwater, other tree species may be more suited to these sites and achieve better economic and hydrological outcomes for landholders.

The potential value of seasonal forecasts of rainfall categories—Case studies from the wheatbelt in Western Australia's Mediterranean region

Hypothetical forecasts of categories of seasonal rainfall (May–October) were evaluated in order to identify which requirements for seasonal climate forecasting are most useful in guiding decisions on both nitrogen (N) fertiliser rates, and whether or not to sow wheat, at different sites in the Mediterranean region of Western Australia. The analyses included the identification of the required number of forecast categories and their boundaries, and the quantification of effects of forecast skill (from zero to perfect) on the potential value of categorical forecasts. Simulated data from the APSIM-NWheat model were used to calculate gross margins for three soil types (clay, loam, sand) at four locations. The value of the hypothetical forecast information was calculated in terms of the additional gross margin achieved over strategies which ignore any forecasts (a “naïve forecast”). In order for the conditional distribution (based on a forecast) of gross margins to differ from the all-years distribution (based on a naïve forecast) at p ≤ 0.1, a minimum of two categories (below/above median rain) were required at the low rainfall sites Merredin and Buntine, while at the medium rainfall sites Wongan Hills and Mingenew three categories (rainfall terciles) were required. This distribution shift was significant only on the clay soil, with exception to the loam at Merredin. With a conditional N management on the clay, the average gross margin increased by 31 AUD ha −1 (+104%) at Merredin and 40 AUD ha −1 (+40%) at Buntine when a perfect two-category forecast (below/above median) was assumed. With a perfect three-category forecast (terciles) the average increase was 62 AUD ha −1 (+20%) at Wongan Hills and 60 AUD ha −1 (+18%) at Mingenew. There was no additional benefit in adjusting N fertiliser rates based on forecasts of extreme categories (i.e. the 1st, 2nd, … 8th, 9th rainfall decile) compared to forecasts of either above/below median or terciles. The minimum level of skill required for two- and three-category forecasts to be potentially valuable increased with seasonal rainfall, and was higher for a flexible than for a fixed sowing strategy. With fixed sowing on the clay soil, the threshold skill level was 13% at Merredin and 26% at Buntine in a two-category format; and 52% at Wongan Hills and 56% at Mingenew in a three-category format. At moderate levels of skill, the application of forecasts returned value at the low rainfall sites only. Given a three-category forecast with a hypothetical skill of 40%, the value was 15 AUD ha −1 when used to modify N fertiliser rates on the clay at the dry site Merredin. The same forecast had no value at the wet site Mingenew.

Three-Hour and Twenty-Four-Hour Rainstorm Ratios across the Southern United States

Atlases of extreme rainfall were produced over the past 50 years both nationally and regionally, for various applications. Quantile estimates—rainfall amounts for a given duration and return period—are often used in stormwater drainage and impoundment design, flood control, agricultural engineering, as well as in many other applications. The foundation for these atlases rests upon daily rainfall data. Past researchers determined relationships between daily rainfall frequency/magnitude relationships and 24-hour storm frequency/magnitude relationships, and then used ratios of 24-hour to shorter n-hour durations to determine storm magnitudes for durations of less than 24 hours. However, these ratios can vary geographically and the application of one averaged ratio over a large region may produce significant error into the quantile estimate maps. This research examines 14 hourly rainfall sites across the southern United States, thereby forming a transect from San Diego, to Jacksonville, Fla. Results show that the ratios between 3-hour and 24-hour rainstorms vary considerably from one climatic regime to another.

Allometric Models for Predicting Aboveground Biomass in Two Widespread Woody Plants in Hawaii

ABSTRACTAllometric models are important for quantifying biomass and carbon storage in terrestrial ecosystems. Generalized allometry exists for tropical trees, but species‐ and site‐specific models are more accurate. We developed species‐specific models to predict aboveground biomass in two of the most ubiquitous natives in Hawaiian forests and shrublands, Metrosideros polymorpha and Dodonaea viscosa. The utility of the M. polymorpha allometry for predicting biomass across a range of sites was explored by comparing size structure (diameter at breast height vs. tree height) of the trees used to develop the models against trees from four M. polymorpha‐dominated forests along a precipitation gradient (1630–2380 mm). We also compared individual tree biomass estimated with the M. polymorpha model against existing generalized equations, and the D. viscosa model with an existing species‐specific model. Our models were highly significant and displayed minimal bias. Metrosideros polymorpha size structures from the three highest precipitation sites fell well within the 95% confidence intervals for the harvested trees, indicating that the models are applicable at these sites. However, size structure in the area with the lowest precipitation differed from those in the higher rainfall sites, emphasizing that care should be taken in applying the models too widely. Existing generalized allometry differed from the M. polymorpha model by up to 88 percent, particularly at the extremes of the data range examined, underestimating biomass in small trees and overestimating in large trees. The existing D. viscosa model underestimated biomass across all sizes by a mean of 43 percent compared to our model. The species‐specific models presented here should enable more accurate estimates of biomass and carbon sequestration in Hawaiian forests and shrublands.

Production and persistence of temperate perennial grasses and legumes at five saline sites in southern Australia

Herbage production and persistence of 24 perennial legumes from 20 species and 19 perennial grasses from 10 species were measured at five sites across southern Australia that differed in annual rainfall and extent of salinity and waterlogging. At Cranbrook, Western Australia, a site with occasional waterlogging and a summer salinity [estimated by electrical conductivity (ECe)] of 6.9 dS/m in the surface 10 cm of soil, strawberry clover (Trifolium fragiferum L.) and Lotus uligonosis Schkuhr produced 2.7 t/ha in the second year and had the highest legume plant frequencies in year 3, while herbage production of L. tenuis Waldst. & Kit. ex Willd. and L. corniculatus L. was not significantly lower. No grasses produced more than 0.3 t/ha in the second year, but tall wheatgrass (Thinopyrum ponticum (Podp.) Z.-W. Liu & R.-C. Wang) was the most persistent. At Girgarre, Victoria, another site with occasional waterlogging and a summer ECe of 8.0 dS/m, phalaris (Phalaris aquatica L.) produced 8.5 t/ha in the second year, while production of tall wheatgrass and perennial ryegrass (Lolium perenne L.) was not significantly lower. Sulla (Hedysarum coronarium L.) was the only legume that produced more than 1 t/ha. Phalaris, tall wheatgrass and sulla had the highest densities in the third year. At Duranillin (Western Australia) and Keith (South Australia), which both experienced extensive winter waterlogging and had summer ECe >30 dS/m, puccinellia (Puccinellia ciliata Bor) and tall wheatgrass were the only grass or legume species that persisted beyond the first summer. Puccinellia was the only species to produce useful quantities of herbage (1.0 t/ha) in year 3 at Duranillin. No perennial grasses or legumes produced more than 0.35 t/ha in either year 2 or year 3 at Tammin, Western Australia, the lowest rainfall site (330 mm mean annual rainfall) with summer ECe of 10.9 dS/m. Genotypic differences within sites were indicated for several species, suggesting opportunities to develop cultivars better adapted to saline soils

Fertility variation and its impact on seed crops in seed production areas and a natural stand of teak in southern India

Reproductive output and fertility variation in teak were evaluated in five study sites in Western Ghats region of southern India. In four seed production areas (SPA1-4)) and a natural population (NAT) plots with 100 trees were investigated. The 40-year-old seed production areas are located in high rainfall (>2,500 mm) sites in Kerala state and the natural stand is at a drier location in Tamil Nadu. Fruit production per tree was rather high in the natural stand (1500) and quite variable in the seed production areas. SPA 4, located far south from the other sites, had the highest fruit production (almost twice that in the other study sites), high relative population size (Nr = 0.5) and predicted low genetic drift in two consecutive years. Fecundity was very low in SPAs 2 & 3 (200 fruits per tree). Reproductive output was similar in successive years except SPA 1, where the fruit production in the first year was almost five times that in the second year. Fertility variation (computed as sibling coefficient, Ψ) was in general higher in NAT and hence the relative population size was lower than in SPAs. The variation in female fertility in the natural stand was, somewhat surprisingly, similar to that in the seed production areas, while the male fertility variation was higher. In the seed production areas the male fertility variation was lower or similar to the female fertility variation. The fertility variation, Ψ was on average around 3 and correspondingly the relative effective population size, Nr = 0.36 and the variance effective number around 60. Selection for tree diameter would improve predicted diversity of the seed crop as it was positively correlated with reproductive output and negatively correlated with fertility variation among trees.

Remobilization of Dry Matter, Nitrogen and Phosphorus in Durum Wheat as Affected by Genotype and Environment

Field studies were carried out to determine dry matter (DM), nitrogen (N) and phosphorus (P) assimilation until anthesis and DM, N and P remobilization during grain filling in wheat. Twentyfive durum wheat (Triticum durum L.) varieties were grown in Tuscany at Grosseto and at Arezzo. At Grosseto 76% of DM was assimilated during pre-anthesis while at Arezzo the amount was 81%. At Grosseto 44% and at Arezzo 35% of N was accumulated until anthesis, while 33% of P was stored until anthesis in both localities. Cultivar differences in DM and N remobilization were positively related to pre-anthesis dry matter and N content at anthesis (r > 0.74). Environmental contraints on carbon, N and P availability in the plant are crucial factors in determining grain yield and N and P content in grain, affecting both accumulation and remobilization. In the low rainfall site of Grosseto, most of the grain yield originated from dry matter accumulation, while in the wetter environment of Arezzo remobilization and accumulation contributed equally to grain yield. Conversely, at Grosseto grain N content relied most on remobilization and at Arezzo remobilization and accumulation contributed equally. Finally, at Grosseto and at Arezzo accumulation of P was the main source of grain P content.

Precipitation, soil moisture, and climate database, Little River Experimental Watershed, Georgia, United States

The U.S. Department of Agriculture Agricultural Research Service Southeast Watershed Research Laboratory (SEWRL) initiated a watershed research program at the Little River Experimental Watershed in 1967. Continuous rainfall measurement across the watershed began at that time. Forty‐six precipitation gauges and three climate stations are currently in operation. Soil moisture measurements were added to 29 of the rainfall sites from 2001 to 2006. The research quantifies critical information related to long‐term and seasonal climatic relationships, hydrologic budgets for the region, water quality studies, and natural resource planning. Rainfall data from the network have been used to evaluate storm characteristics, climatic patterns, and long‐term averages for the region. Soil moisture data have been used to examine large‐scale patterns across the region and for comparison to remotely sensed data. All data are available on the SEWRL anonymous ftp site (ftp://www.tiftonars.org/).

A modelling investigation into the economic and environmental values of ‘perfect’ climate forecasts for wheat production under contrasting rainfall conditions

AbstractWith increased investment in improving climate forecasting techniques, it is essential to find ways of quantifying the maximum benefit of climate forecasts for a given industry. This paper describes an approach to quantify the value of ‘perfect’ climate forecasts to direct nitrogen management in a wheat‐cropping system at two Australian locations with contrasting annual rainfall. For annual wheat‐cropping systems, and compared with the N management based on optimal N rate derived from long‐term climatic conditions, N management based on ‘perfect’ climate forecasts can lead to an average benefit of $ 65.2/ha/year at Walbundrie (annual rainfall 560.0 mm) and $ 66.5/ha/year at Wanbi (annual rainfall 314.5 mm). Generally, the economic benefit is highest in extreme (wet and dry) years and lowest in normal years. At the high rainfall site Walbundrie, where average N‐application rate is high, the maximum yearly benefit was from significant saving through reduction in N application in driest years. At the low rainfall site Wanbi, where average N rates are low, the highest benefit was from both yield increases in the wettest years and saving of management and fertilizer cost in the driest years. Such optimized nitrogen management has little impact on excess drainage, but it can have significant impact on reduction of excess nitrogen, especially in high rainfall areas. An excess N reduction of 1314 kg N/ha at Wanbi and 1538 kg N/ha at Walbundrie can be achieved in 114 years. The significant reduction in N excess at Walbundrie may have profound environmental implications. Copyright © 2007 Royal Meteorological Society

RAINFALL AND SOILS MODIFY PLANT COMMUNITY RESPONSE TO GRAZING IN SERENGETI NATIONAL PARK

Terrestrial plant community responses to herbivory depend on resource availability, but the separate influences of different resources are difficult to study because they often correlate across natural environmental gradients. We studied the effects of excluding ungulate herbivores on plant species richness and composition, as well as available soil nitrogen (N) and phosphorus (P), across eight grassland sites in Serengeti National Park (SNP), Tanzania. These sites varied independently in rainfall and available soil N and P. Excluding herbivores decreased plant species richness at all sites and by an average of 5.4 species across all plots. Although plant species richness was a unimodal function of rainfall in both grazed and ungrazed plots, fences caused a greater decrease in plant species richness at sites of intermediate rainfall compared to sites of high or low rainfall. In terms of the relative or proportional decreases in plant species richness, excluding herbivores caused the strongest relative decreases at lower rainfall and where exclusion of herbivores increased available soil P. Herbivore exclusion increased among-plot heterogeneity in species composition but decreased coexistence of congeneric grasses. Compositional similarity between grazed and ungrazed treatments decreased with increasing rainfall due to greater forb richness in exclosures and greater sedge richness outside exclosures and was not related to effects of excluding herbivores on soil nutrients. Our results show that plant resources, especially water and P, appear to modulate the effects of herbivores on tropical grassland plant diversity and composition. We show that herbivore effects on soil P may be an important and previously unappreciated mechanism by which herbivores influence plant diversity, at least in tropical grasslands.

Provenance variation of ecologically important traits of forest trees: implications for restoration

Summary The source of seed or plant material can have profound implications for the success of restoration efforts because most species exhibit adaptive genetic variation within their range. Understanding the geographical distribution of ecologically relevant genetic variation and the environmental factors driving adaptive divergence within species will help to ensure appropriate sourcing of material for ecological restoration. We present a study of geographical variation of ecologically important traits of the forest tree jarrah Eucalyptus marginata from a 15‐year‐old provenance trial in south‐western Australia. We assessed trait variation in association with rainfall, latitude and slope position at the site of origin. Survival and stem diameter varied at the largest scale, between northern and southern jarrah forest provenances. Stem diameter also varied among rainfall zones, while latitude was a more important determinant of variation of reproductive traits (flowers and buds). None of the environmental variables accounted for significant variation of height, growth form or the presence of capsules. Slope position at the site of origin did not account for significant variation of any trait. Trees from low rainfall sites had smaller stem diameters, possibly reflecting selection for slower growth. Such a strategy could prevent drought stress and may explain why trees from the high rainfall southern jarrah forest, which showed the fastest growth, had the poorest survival at the drier northern trial site. Variation in the presence of buds and flowers among latitudinal divisions may be because of variation in flowering time, which has been observed previously among E. marginata populations. However, variation among replicate blocks within the trial suggests that the environment also strongly influences expression of these traits. Synthesis and applications. We have demonstrated divergence of several ecologically important traits in association with different types of environmental variation. Our findings support an argument for ‘habitat matching’ when sourcing material for restoration; however, differences among trait types in the distribution of variation highlight the need to consider environmental variation at a range of geographical scales. Consideration of ecologically important genetic variation within species is important and this information should be integrated into seed collection strategies for ecological restoration.

Parameter estimation and model identification for stochastic models of annual hydrological data: Is the observed record long enough?

Summary Observed hydrological records are typically not more than 100–150 years in length. This study quantifies the effect this relatively short length of data has on parameter uncertainty and model identification for two stochastic models of annual hydrological data: the common lag-one autoregressive model [AR(1)] and the two-state hidden Markov model (HMM). Both models were calibrated to synthetic data generated by different HMM and AR(1) scenarios. For the HMM the separation of the wet and dry states had a greater impact on the uncertainty than the state residence time. For the AR(1) model the uncertainty was lower than the HMM and largely independent of the persistence structure. For data lengths typical of observed data the parameter uncertainty was substantial for both models. Based on the metrics used for model identification if there was strong persistence then 100–200 years of data was required to identify both models. For weaker persistence structures typical of Australian data the length required increased to 200–500 years, well beyond observed record lengths. The analysis of six rainfall sites from across Australia showed none provided strong evidence in favour of the AR(1), HMM or an independent model. It is concluded that the limited information from observed hydrological data produces high parameter uncertainty for the AR(1) and HMM. The result is the unequivocal identification of a stochastic model to describe the underlying long-term persistence structure remains elusive. It is argued that if more complex stochastic models are proposed to represent long-term persistence they will require additional information beyond the observed hydrological data to enable their identifiability.

Changes in soil water content under annual- and perennial-based pasture systems in the wheatbelt of southern New South Wales

Nine pasture treatments differing in species composition were monitored for changes in soil water content at a depth of 0.10–1.70 m, at 2 sites (Kamarah and Junee), in the wheatbelt of eastern Australia. Treatments containing perennial species, viz. lucerne (Medicago sativa L.), phalaris (Phalaris aquatica L.), cocksfoot (Dactylis glomerata L.), mixture (lucerne + phalaris + cocksfoot), wallaby grass (Austrodanthonia richardsonii Cashmore.), and lovegrass (Eragrostis curvula (Schrader) Nees.), were sown with subterranean clover (Trifolium subterraneum L.). In addition, 3 treatments based solely on annual species were examined: subterranean clover (sown by itself and kept weed-free with herbicides), annual (sown to subterranean clover but weed invasion not controlled), and serradella (Ornithopus compressus L.). The experiment was conducted from 1994–97 at the Junee site (annual average rainfall 550 mm/year) and from 1995–97 at the Kamarah site (annual average rainfall 450 mm per year). At the higher rainfall site (Junee), there were few differences among pasture types in soil water content to 0.70 m. Below 0.70 m the soil profile was drier under all the perennial swards than under the annual pasture treatments by the end of the 4-year pasture phase. At the drier Kamarah site, where the pasture phase was shorter due to an initial sowing failure, all the perennials, except cocksfoot, dried the profile below 1.05 m. At both sites, lucerne dried the 1.05–1.70 m section of the soil profile more rapidly than the other perennials, which apparently took longer to reach this depth. At the Junee site, the soil water deficit in May (SWD(MAY), defined as field capacity (mm) – stored soil water (mm) at the beginning of May) was largest in the phalaris, mixture, lucerne, and cocksfoot treatments (155–162 mm), whereas as under a pasture of subterranean clover alone, SWD(MAY) was only 89 mm. At the drier Kamarah site, the largest SWD(MAY) was created by the lovegrass (114 mm) and lucerne (107 mm) treatments. The cocksfoot and subterranean clover treatments created the smallest SWD(MAY) at this site, at 79 and 72 mm, respectively. The study showed that currently available C3 and C4 perennial grasses can be as effective as lucerne in drying the soil profile to 1.70 m in the 450–600 mm rainfall areas of the southern NSW wheatbelt, creating a dry soil buffer to reduce the risk of deep drainage during subsequent cropping phases. As the rate at which grasses dried the profile was slower than lucerne, pastures based on perennial grasses may have to be retained longer to achieve the same level of dewatering.

Does rainfall explain variation in leaf morphology and physiology among populations of red ironbark (Eucalyptus sideroxylon subsp. tricarpa) grown in a common garden?

We investigated adaptation of leaf morphology and physiology of red ironbark (Eucalyptus sideroxylon Cunn. Ex. Wools subsp. tricarpa L.A.S. Johnson) in a common garden experiment. Fifteen populations, representing a rainfall range of 500 to 1055 mm per annum at the sites of seed collection, were grown at the same site. Because environmental variables other than rainfall did not vary significantly among populations, we were able to test if leaf morphology and physiology were related to seed-source rainfall. There were large differences among and within populations in all measured variables. Most univariate relationships with seed-source rainfall were not significant. Notable exceptions were the weak positive correlation of specific leaf area with seed-source rainfall-consistent with expectations-and the weak negative correlation of photosynthesis and stomatal conductance with seed-source rainfall-the opposite of what we predicted. In many cases, populations collected from sites of similar rainfall differed greatly in leaf morphology and physiology. Principal component analysis (PCA) reduced the 13 input variables to five principal components (PC) explaining 73.0% of the total variance in the original data. Some of the PC axes could be interpreted in terms of adaptation to drought (i.e., to seed-source rainfall), but relationships of accumulated variables (the PC axes) with seed-source rainfall were significant for only one PC axis. Hence, among red ironbark populations grown in a common garden, there was significant genetic variation in leaf morphology and physiology, but for most traits, this variation was unrelated to rainfall at the site of seed collection. This study adds to a growing body of common garden literature showing weak within-species relationships of leaf morphology and physiology with seed-source rainfall, in contrast to the consistently stronger relationships among species growing at different points along broad environmental gradients.

Growth Response of Eucalyptus regnans and Soil Changes following Periodic Fertilization

Increased demand for plantation hardwood production has resulted in the progression of Eucalyptus plantations onto soils of reasonable physical structure but low nutrient status. This study was undertaken to investigate the effects of periodic fertilization through 15 yr on stand growth and soil chemistry of a Eucalyptus regnans F. Mueller plantation on a high rainfall site in southern Tasmania. Substantial response to N fertilizer, applied as ammonium sulfate, were measured, but there was no response to P applied as single superphosphate, either alone or in combination with N. Annual applications of N fertilizer, for a period of 13 yr, at 100 kg N ha−1 yr−1 doubled volume growth from 125 to 281 m3 ha−1, at Age 19 yr. Long‐term fertilization resulted in the accumulation of nutrients within the forest floor and surface soils. Significant reductions in soil pH, from 4.5 to 3.6 in the surface soil, were associated with the highest rate of fertilization. Reductions in pH occurred with both nitrogenous and phosphatic fertilizers. Substantial reductions in exchangeable Mg concentrations in surface soils, from 258 to 71 mg kg−1 were also measured. The research highlights the balance needed between obtaining growth response and causing detrimental soil effects from long‐term fertilization.

Context‐dependent interactions between adult shrubs and seedlings in a semi‐arid shrubland

Abstract. Question: In semi‐arid systems, rainfall gradients can cause plant‐plant interactions to shift from negative to positive or vice versa. However, the importance of a second major abiotic factor, soil nutrients, has rarely been considered. We consider different combinations of both factors and ask: do net adult‐seedling interactions become less competitive and more facilitative with increasing overall abiotic harshness?Location: Succulent Karoo, Western Cape, South Africa.Methods: We examined the interactions between seedlings and adult shrubs at two sites. Sites differ in rainfall, and each contain two habitats: Nutrient‐rich mounds associated with underground termitaria and a relatively nutrient‐poor matrix. We carried out a spatial pattern analysis of community‐wide seedling‐adult associations. We then conducted field and greenhouse experiments to test the effects of soil and the presence of neighbouring shrubs on the growth and survival of six seedling species.Results: At the higher rainfall site, both competitive and facilitative effects of adults on seedlings were found but did not differ by habitat, despite the more benign conditions in the mound habitat. At the lower rainfall site, adult shrubs generally had neutral effects on seedlings in the matrix habitat. In the nutrient‐rich mound habitat, however, adult shrubs had strong and consistently competitive effects on seedlings.Conclusion: Seedling‐adult interactions could not be predicted by a simple overall gradient of abiotic harshness, demonstrating the need for more complex, mechanistic models to predict plant‐plant interactions. We suggest that rainfall and soil nutrients affect seedling‐adult relations through their interactive effects on the life‐history attributes of the species involved.

An analysis of the breakdown of paper products (toilet paper, tissues and tampons) in natural environments, Tasmania, Australia

An examination of the relative breakdown rates of unused toilet paper, facial tissues and tampons was undertaken in nine different environments typical of Tasmanian natural areas. Bags of the paper products (toilet paper, facial tissues, tampons) were buried for periods of 6, 12 and 24 months at depths of 5 and 15 cm. A nutrient solution simulating human body wastes was added to half of the samples, to test the hypothesis that the addition of nutrients would enhance the breakdown of paper products buried in the soil. Mean annual rainfall was the most important measured variable determining mean breakdown in the nutrient addition treatment between sites, with high rainfall sites (mean annual rainfall of greater than 650 mm) recording less decayed products than the drier sites (mean annual rainfall of 500–650 mm). Temperature and soil organic content were important influences on the breakdown of the unfertilised products. Toilet paper and tissues decayed more readily than tampons. Nutrient addition enhanced decay for all products across all sites. Depth of burial was not important in determining the degree to which products decayed. In alpine environments, burial under rocks at the surface did not increase the speed of decay of any product. The Western Alpine site, typical of alpine sites in the Tasmanian Wilderness World Heritage Area, showed very little decay over the two-year period, even for nutrient enhanced products. Management prescriptions should be amended to dissuade people from depositing human toilet waste in the extreme (montane to alpine) environments in western Tasmania. Tampons should continue to be carried out as currently prescribed.

Rainfall and runoff water quality of the Pang and Lambourn, tributaries of the River Thames, south-eastern England

Abstract. The water quality of rainfall and runoff is described for two catchments of two tributaries of the River Thames, the Pang and Lambourn. Rainfall chemistry is variable and concentrations of most determinands decrease with increasing volume of catch probably due to "wash out" processes. Two rainfall sites have been monitored, one for each catchment. The rainfall site on the Lambourn shows higher chemical concentrations than the one for the Pang which probably reflects higher amounts of local inputs from agricultural activity. Rainfall quality data at a long-term rainfall site on the Pang (UK National Air Quality Archive) shows chemistries similar to that for the Lambourn site, but with some clear differences. Rainfall chemistries show considerable variation on an event-to-event basis. Average water quality concentrations and flow-weighted concentrations as well as fluxes vary across the sites, typically by about 30%. Stream chemistry is much less variable due to the main source of water coming from aquifer sources of high storage. The relationship between rainfall and runoff chemistry at the catchment outlet is described in terms of the relative proportions of atmospheric and within-catchment sources. Remarkably, in view of the quantity of agricultural and sewage inputs to the streams, the catchments appear to be retaining both P and N. Keywords: water quality, nitrate, ammonium, phosphorus, ammonia, nitrogen dioxide, pH, alkalinity, nutrients, trace metals, rainfall, river, Pang, Lambourn, LOCAR

Soil disturbance by soil animals on a topoclimatic gradient

We measured the area and volume of soil disturbed by various groups of animals at three sites on a topoclimatic gradient in the Judean Desert, Israel. Both the area and volume of soil disturbed by animals correlated with the cumulative precipitation of the winter rain season. Rodent activity accounted for most of the soil disturbance at all sites except for June 2001, when the volume of soil transported to the surface by ants in the construction of nest chambers accounted for most of the soil volume moved at the intermediate rainfall site. The aggregate stability of soil ejected from animal excavations was significantly lower than that of undisturbed soil during and immediately following the winter rain season, but not during the following dry seasons. The quantities of soil moved by ants in the Judean Desert were comparable to quantities moved by ants in the Chihuahuan Desert of North America.

Uncertainty in modelled estimates of acid deposition across Wales: a GLUE approach

Abstract An uncertainty analysis of the Hull acid rain model (HARM) is presented using the Generalised Likelihood Uncertainty Estimation methodology, constrained by observations at 25 sites across Wales. It was found that no simulations could fit the 1995 observed deposition data simultaneously at all sites. To retain predictive capability, the observational constraint was relaxed, resulting in 2101 simulations that described adequately the data. HARM's predictive capability was further tested in a ‘hindcast’ to data collected at 44 sites in 1984, using the successful parameterisations for 1995. At the majority of sites, the uncertainty prediction bounds spanned the observed data satisfactorily for both 1995 and 1984, but there was a tendency for wet deposition to be overestimated at high rainfall sites and underestimated or well estimated at lower rainfall sites close to major source areas. For wet-deposited oxidised nitrogen there was systematic overestimation at most sites. It is concluded that the model could be improved to remove the systematic nature of the overestimation of wet oxidised nitrogen for Wales and to better represent the spatial pattern of all wet-deposited species considered.