Marginal Grassland Research Articles

Species diversity in dryland and irrigated agroecosystems and marginal grassland ecosystem in dry tropics

This study was carried out to compare composition, density and diversity of species between dryland and irrigated agroecosystems and between agroecosystems and the marginal grassland ecosystem in dry tropics. Main management characteristics of these ecosystems are: (1) Dryland cropping, low fertilizer input, rainfed (no irrigation) and seed sown rice; (2) Irrigated cropping, high fertilizer, water (irrigation) inputs, flooded rice by transplanting; (3) Grassland, post-rainy season herbage removal and light grazing. All ecosystems showed comparable number (12–14) of species in winter, but in the rainy season higher number of species (21) were recorded in the grassland ecosystem. The species composition of the grassland was entirely different from both agroecosystems (similarity <1%). Dryland and irrigated agroecosystems showed only 25% and 38% similarity with each other during winter and rainy cropping seasons, respectively. Occurrence of few grasses (e.g., Cynodon dactylon, Dichanthium annulatum and Sporobolus diander) in the agroecosystems depends on the propagules dispersed from the marginal grassland. The change from dryland to irrigated agroecosystem involved elimination of 4–5 species during both cropping seasons and simultaneous recruitment of 2 new species in winter and 6 species in rainy season. In both agroecosystems, forbs (C3 type) dominated over graminoids (C4 type) during winter season but the dominance was reversed during the warm, rainy season. During winter some forbs were abundant in both agroecosystems due to their tolerance to widely varying moisture conditions (e.g., Chenopodium album), others were dominant in either drier soil conditions (e.g., Anagallis arvensis in dryland) or wet conditions (e.g., Melilotus indica and Phalaris minor in irrigated). Higher species diversity occurred in the grassland relative to both agroecosystems. The seasonal trends of species diversity and species evenness were broadly similar in both agroecosystems but irrigated agroecosystem exhibited relatively higher species diversity. The changes in species composition and species diversity in agroecosystems are mainly attributed to differences in water management. The water management in irrigated agroecosystem tends to reduce weed diversity but leads to the dominance of some potentially noxious weeds (e.g., Phalaris minor).

Estimation of global river transport of sediments and associated particulate C, N, and P

This paper presents a multiple linear regression model developed for describing global river export of sediments (suspended solids, TSS) to coastal seas, and approaches for estimating organic carbon, nitrogen, and phosphorous transported as particulate matter (POC, PN, and PP) associated with sediments. The model, with river‐basin spatial scale and a 1‐year temporal scale, is based on five factors with a significant influence on TSS yields (the extent of marginal grassland and wetland rice, Fournier precipitation, Fournier slope, and lithology), and accounts for sediment trapping in reservoirs. The model generates predictions within a factor of 4 for 80% of the 124 rivers in the data set. It is a robust model which was cross‐validated by using training and validation sets of data, and validated against independent data. In addition, Monte Carlo simulations were used to deal with uncertainties in the model coefficients for the five model factors. The global river export of TSS calculated thus is 19 Pg yr−1 with a 95% confidence interval of 11–27 Pg yr−1 when accounting for sediment trapping in regulated rivers. Associated POC, PN, and PP export is 197 Tg yr−1 (as C), 30 Tg yr−1 (N), and 9 Tg yr−1 (P), respectively. The global sediment trapping included in these estimates is 13%. Most particulate nutrients are transported by rivers to the Pacific (∼37% of global particulate nutrient export), Atlantic (28–29%), and Indian (∼20%) oceans, and the major source regions are Asia (∼50% of global particulate nutrient export), South America (∼20%), and Africa (12%).

Effects of age, cohort and individual on breeding performance in the Lapwing Vanellus vanellus

The breeding performance of individually colour‐ringed Lapwings Vanellus vanellus was studied on marginal grassland in Upper Teesdale, County Durham (UK), from 1992 to 1995. Contrary to many studies of birds, female age had only a minor effect on breeding performance: yearling females produced eggs on average 5% smaller than those of adults. In contrast, the average productivity of male Lapwings was estimated to increase by around 40% between one and two years of age, and by a further 10% between two and three years of age. This was because of a 40% increase in the proportion of males that bred between one and two years of age, and of an increase in mating success with age coupled with a higher breeding success for polygynous males. The likelihood of breeding for male Lapwings was affected by year of hatching. More than half of those males that hatched in 1990, and which were present in both 1993 and 1994, did not breed. It was suggested that this was due to environmental effects experienced by these males as chicks, resulting in reduced success in securing a breeding territory later in life. Individual female Lapwings showed a high degree of consistency between years in both laying date and egg size, and those that raised up to two young in 1993 raised approximately the same number in 1994. However, females producing more than two young in 1993 raised significantly fewer in 1994, perhaps suggesting a cost of reproduction.

N, K and P deficiency in chronosequential cut summer-dry grasslands on gley podzol after the cessation of fertilizer application

With the intensification of agricultural practices, formerly species rich marginal grassland communities of high botanical value in the Netherlands have been fertilized or manured since the first part of the twentieth century. This type of land use resulted in a dramatic decrease of the original plant species-richness. In the early 1970's yearly nutrient input to many of these grasslands was ceased as a nature management practice, while hay-cropping was continued. This type of grassland management is carried out to decrease overall nutrient supplying ability of the soil to plant cover in order to restore their original high botanical richness. The effect of this management on the type and the extent of nutrient deficiency was studied by comparing the short-term shoot responsiveness of undisturbed turfs to added nutrients and the nutrient status of fieldgrown dominants of four hay-field communities which were not fertilized for 3, 7, 20 or 25 years. Contrary to expectation, hay-cropping without input of additional nutrients did not impose an increase of species-richness of grassland on gley podzol. During early vegetation change strong inadequacy of N supply and moderate inadequacy of K supply by the soil regulate (shoot) growth. P-deficiency was not established. Prolonged discontinuation of fertilizer application caused concomitant inadequate supplies of N, K and P. In the last field (25 years unfertilized), nutrient deficiencies could not be detected by shoot growth responses to added nutrients but only by a low nutrient status. It appeared that during this type of vegetation change N-deficiency is the most pronounced and that K-deficiency developes much more rapidly than P-deficiency. The strong decline in total aerial pool sizes of N, K and P also emphasizes these simultaneously occurring shifts. We conclude that cut grassland composition on gley podzol soil is regulated by co-deficiencies of at least the soil phytoavailable macronutrients nitrogen, potassium and phosphorus. The absence of change in plant species number is likely not regulated by the nutrient supplying ability of the soil. Seed dispersal from elsewhere seems to be the most important factor.

Agricultural intensification and the loss of habitat, species and amenity in British grasslands: a review of historical change and assessment of future prospects†

AbstractGrassland in Britain is a plagioclimax vegetation type. All lies on land originally cleared from forest and, without some form of management, would revert to forest through a process of natural succession. Traditionally managed, unsown grasslands nonetheless resemble more natural grasslands in other parts of the world and contain a substantial proportion of our native flora and fauna. They are also often important for recreational activities. Agricultural intensification over a long period has led to a loss in their extent, species and amenity. Reconciling agricultural and environmental objectives in grassland management is very difficult because increased fertility and production invariably leads to species loss. Current overcapacity in the agricultural industry is leading to the switching of some agricultural support from food production to countryside management. As a result some arable and intensively managed grass is being managed more extensively. However future production technologies may be so efficient that very many fewer stock are required with the result that much marginal grassland may revert once again to forest.

The effects of improvement of upland, marginal grasslands on the breeding success of Lapwings Vanellus vanellus and other waders

Data on the breeding success of Lapwings Vanellus vanellus on unimproved and improved grassland, with comparative data for arable land, were obtained from a study on 760 Lapwing clutches. The study was undertaken in the Eden Valley, Cumbria, and Teesdale, Co. Durham, between 1985 and 1987. First clutches were larger on unimproved grassland with a mean of 3.73 eggs compared to 3.61 eggs on improved grassland. In contrast, replacement clutches were larger on improved areas (3.90 eggs) than on unimproved (3.47 eggs). On average, 40% of eggs laid on unimproved pastures hatched compared to only 17% on improved pastures. No significant difference in hatching success was found between unimproved and improved meadows with 32% and 22% of eggs hatching, respectively. Overall, 73% of unsuccessful first clutches were replaced on unimproved pastures, whereas on meadows and improved pastures combined, only 32% were replaced. Survival of small chicks was highest on unimproved areas. Production on unimproved areas was sufficient to replace adult losses and so maintain numbers, whereas on improved land production was too low to maintain existing breeding densities. Hatching success on unimproved areas was similar for the four species of wader considered. On improved areas, Redshank hatching success was relatively high, with 54% of pairs producing chicks, compared to 35% for Lapwing and 23% for Curlew.

The effects of improvement of upland, marginal grasslands on the distribution and density of breeding wading birds (Charadriiformes) in northern England

Abstract Agricultural improvement of grasslands, at the upper altitudinal limit of agricultural practice, subsequently referred to as the uplands, has progressed rapidly in recent years. The impact on breeding wading birds (Charadriiformes) was assessed in the years 1985–1987 by comparing the densities and species of waders using improved and unimproved grasslands in northern England. Improvement (drainage, inorganic fertilizing and, in some cases, reseeding) resulted in the virtual disappearance of snipe Gallinago gallinago and marked reductions in the density of, and in the proportion of fields used by, redshank Tringa totanus , curlew Numenius arquata and lapwing Vanellus vanellus . In contrast, oystercatchers Haematopus ostralegus have started to nest on improved grasslands in areas where they have not previously bred. Thus the species composition on unimproved grasslands have changed following improvement. It is evident that within large areas containing many fields, the overall density of waders has declined as the percentage of fields that have been improved in the post-war period increased. This suggests waders have not simply redistributed themselves between improved and unimproved fields but rather that there has been a marked, overall decline in the numbers of waders in areas where improvement has taken place.

Modeling the long-term effects of fuelwood harvests on Pinyon-Juniper Woodlands

In the Southwestern United States, increasing demand for firewood has quickly promoted pinyon-juniper woodlands to commercial status. Slow recovery rates for pinyon and juniper and inadequate mensuration data present significant obstacles to predictive management efforts. Many National Forest districts have witnessed continued fuel use for at least the past 100 years. To explore the need for long-term analysis at the district level, we have developed FORMAN I, a computer simulation written in FORTRAN IV that models prolonged fuel harvesting and its impact on pinyon-juniper woodlands. The technique is well-suited for historical analyses and we comply with an initial application that involves the suggested impact of prehistoric peoples on a marginal woodland in Chaco Canyon, New Mexico. To accentuate the significance of the simulation, we have deliberately overestimated woodland parameters while maintaining conservative annual rates for firewood procurement. A low-density woodland (less than 14.8 cords/ha) is completely depleted within 200 years when subjected to tenth-through-twelfth century estimates of human demography for the canyon. Interesting conclusions are drawn from the lack of pinyon-juniper recovery at Chaco over the past millennium. Traditional assumptions, such as the pristine state of Southwestern vegetation prior to historic settlement and subsequent invasion of marginal grasslands by pinyon and juniper, are questioned.

Behavioral and trophic plasticity of juvenileTilapia mossambica in utilization of the unstable littoral habitat

JuvenileTilapia mossambica Peters (2.5–10.0 cm standard length) in Lake Sibaya, South Africa, move daily from deep offshore waters to shallow (<0.5 m) littoral areas where they feed for several hours and then return to deep water. The timing of these movements varies in response to changing physical and biological features of the littoral environment. During this study (December 1973 – February 1976), lake level rose more than 1 m. At the start of the study, littoral areas visited by juvenileT. mossambica were free of vegetation and debris, but at higher lake levels trees and brush from the eroding shoreline were common in nearshore littoral waters. When the littoral zone was free of debris, juvenileT. mossambica visited nearshore waters only during daylight hours. After a 0.65 m rise in lake level and considerable accumulation of debris, these fish were abundant in the littoral zone only at night. This reversal can be attributed to efforts by juvenileT. mossambica to avoid their principal predator, the catfishClarias gariepinus. At low lake levelC. gariepinus ventured into the littoral only at night but at higher lake levels this predator was found within flooded vegetation during the day. When further increases in lake level flooded marginal grasslands, juvenileT. mossambica abandoned the littoral zone in favor of this newly created eulittoral habitat where potential fish predators did not occur. With the change in habitat, the diet changed from benthic detrital aggregate to periphyton. These observations suggest the importance of behavioral and throphic plasticity in the ability of tilapia to utilize unstable habitats.