Narrative to Table 2.2 about Grasslands
• Food production: In both unmanaged and managed grasslands, plant products are considered insignificant because plant materials are harvested by herbivores, but they would be affected by biotic and abiotic factors in the same way as animal products. Management shifts decomposition and organic matter transformations toward bacterial dominance, with a reduction of faunal diversity, especially macroarthropods.
• Water quality: Water quality refers to runoff to streams. The context is essentially riparian; as in dryland systems, potential evapotranspiration exceeds precipitation. Different dynamics exist in mesic systems. Simplification of soil organisms reduces the retention of nutrients (C, N, and P) in living biomass. Nutrients released or transformed may be directed more into runoff than may percolate to the water table. Higher stocking densities introduce undesirable bacteria into runoff and reduce infiltration by compacting the soil.
• Water volume: Factors reducing evapotranspiration will be paramount in dryland systems. These include plant diversity (root depth, root architecture, and hydraulic lift), organic matter stratification and particle size distribution, and biopore formation by macrofauna.
• Other products: Fiber production (e.g., hides, carcass contents) is not an objective in managed grasslands, but a by-product. Animal production is roughly inversely proportional to population density in unmanaged grasslands (i.e., it is a function of plant production, which in turn depends on nutrient recycling and transformations by microorganisms).
• Recreation: The service rank of unmanaged grasslands for recreation is derived from both wildlife and the aesthetic value of biological diversity and landscape heterogeneity. Managed (and fenced) grasslands are harboring some wildlife, and in some areas access is given to hiking. Access to fenced land may be the subject of legal disputes, and landscape simplification or dissection reduces overall aesthetic value, but this has enormous potential for recreation in many industrialized countries.
• C sequestration: A managed grassland means it has been tilled. The C dynamics of untilled pastures are uncertain. Again, a large difference would be expected between the responses of dryland and mesic grassland systems. Accumulation of organic matter at the surface of the soil profile is greater in unmanaged systems with stratification downward and more C directed into complex long-term stable pools by fungal-dominated organisms.
• Trace gases and atmospheric regulation: The C and N fluxes of unmanaged grasslands are probably not very significant in terms of the global cycles of these elements, as out puts of greenhouse gases to the atmosphere by components of the soil organisms (fungal decomposers, nitrifiers, and denitrifiers) are restricted by corresponding sequestrators (primary producers and nitrogen fixers). Fertilizer input (chemical or animal dung) causes a large increase in both nitrification and denitrification (according to context), from which process greenhouse-forcing NOx gases are by-products. Disturbance of any kind (including compaction) strongly reduces CH4 oxidation by archaea in soils.
• Food production: A side benefit especially of unmanaged forests. Fungal fruiting bodies are a forest food product. Fungal diversity in unmanaged systems may be higher due to the higher diversity of trees and other plants than occurs in managed systems. Many species of soil invertebrates (e.g., ants) are an important food source for birds/wildlife, which in turn are important for recreation. Soil pH is a moderately important determinant of fungal diversity. Managed beech systems also produce truffles.
• Water quality and volume: Flood and erosion control. Different plant species have widely different attributes, which can affect soil water quality and quantity (evapotranspiration, different rooting depths/architecture, hydraulic lift). Soil organisms can affect water quality through production of NO3. Bioturbators affect soil physical properties, which, in conjunction with topography, affect runoff and infiltration.
• Fuel: When in the form of wood, fuel is a potentially important service of both unmanaged and managed systems. However, wood fuel may be more commonly extracted from unmanaged systems since managed systems are typically intended for fiber production.
• Biochemicals and medicines: Unmanaged forests are used extensively for bio-prospecting, particularly for microbial diversity, genes, and potentially useful products (antibiotics, yeasts, etc.) for industrial or medicinal properties. The diversity of genes, and of useful products, is likely to be related to the diversity of the forest.
• Habitat provision: Soil organisms encourage nutrient cycling for plant growth. Ecosystem engineers (e.g., earthworms) create new habitat and provide food for other animals.
• Waste disposal: Soil fungi and bacteria affect the accumulation of heavy metals in plants and indirectly into animals. Soil texture and drainage affects a system's ability to hold pollutants, pathogens, and heavy metals. However, we have ranked them with 0, as forests are not intended to be used for waste disposal.
• Biological control: Ants predate Lepidoptera pests; mycorrhizae and fungi discourage root pathogens. Water logging of soils encourages fungal pathogens such as root rot.
• Trace gases and atmospheric regulation: Soil organisms (nitrifiers, denitrifiers, methane oxidizers) are important to trace gas production and to scrubbing the atmosphere of NOx, N2O, SO2, CH4, and NHx. Soil pH, texture, and structure provide anaerobic microsites for trace gas production. Forest ecosystems are particularly important for methane oxidation. When fertilized or limed, the dynamics of emissions are changed: up to 10 percent of N fertilizers may be denitrified. There exists some doubt as to the organisms responsible for CH4 in forest ecosystems, but the organisms responsible have been identified as type II methanotrophs. Forest ecosystems are well known to act as sinks for a variety of air pollutants, such as SO2, NOx, and NHx. Diversity has been used as an indicator of aerial ecosystem pollution.
• Food production: Crop variety, rooting type, and the nature and composition of residues are critical to the quality and quantity of food service provided. Animal production is indirectly affected by the use of arable products for fodder.
• Water quality: No-till agriculture is considered to leach fewer nutrients to ground and surface water than occurs when the soil is tilled regularly. Topography is an important factor influencing water runoff, more in tilled than in non-tilled systems: soil tillage leads to exposed soil, which is sensitive to erosion.
• Water volume: Non-tillage systems have more biopores formed by earthworms than tilled systems, which benefits water storage volume. Moreover, non-tilled systems are less sensitive to topography than tilled systems because of constant surface cover. On slopes, for example, the direction of soil tillage (along or across altitude lines) is also crucial for runoff of surface water.
• Other products: A number of crop plants are used for fiber production (cotton, flax), and effects of biotic and abiotic processes are similar to those for food production.
• Waste disposal: Detoxification of waste products is lower under no-till systems because wastes cannot be incorporated, leading to volatilization from the soil surface. The role of soil biota, however, is higher than in tilled systems, where the waste may be directly introduced into the soil. In addition, under no-till systems, concentrations of intermediate toxic products and pesticides can build up in surface soil layers, along with organic matter and nutrients.
• Biological control: We define biological control as control of pathogens/weeds by another organism. Rotations in tilled conditions—through maintaining microbial activity and diversity, and through disrupting disease and arthropod cycles and also mycorrhizal networks—improve biological control more in till than in no-till monoculture. However, multi-year rotations may not be economical. Earthworms can have a negative effect on plant parasitic nematodes: for example, in India, joint management of earthworm communities and organic resources doubled tea production while regenerating degraded soils. The effect of earthworms is hypothesized to be obtained through different processes, including suppression of nematode parasites and release of plant growth promoters through enhancement of mycorrhizae. There is little known on the effects of biological agriculture and landscape management (small-scale or fragmented landscape versus large-scale landscape) on soil-borne disease management. However, whereas no-till conventional agriculture uses herbicides to control weeds, in organic agriculture (e.g., Brazil), cover-crops are used to kill weeds. Effects of GMOs are currently strongly disputed, and the potential solution of GMOs for one problem (weeds) may enhance others (more disease incidence). Therefore, we have weighed the GMO effect neutral.
• Recreation: Our concept is habitat for soil biodiversity. The key biotic aspect here is how field margins and riparian areas are managed. Field margins managed for habitat not only harbor diversity, they can also act as refuges for biological control agents, especially predatory arthropods such as beetles. Landscape aspects are important for aesthetic value and crop species matter, since some crops (e.g., corn) do not allow landscape-wide views. Riparian areas managed for habitat enhance surface and groundwater quality. On average, we assessed the recreational value of tilled and non-tilled systems to be equal, especially due to landscape effects.
• Carbon sequestration: Carbon sequestration ranks slightly higher in non-tilled than in tilled systems, because the rate of decomposition of crop residues and roots can be slightly less. When the organic matter pool is in balance, effects of C sequestration will be neutral in most cases.
• Trace gases and atmospheric regulation: Soil structure is considered under abiotic factors only, though it is clearly a product of both abiotic and biotic factors, especially macro- and microengineers that form aggregates. Specific aspects of macrofauna can alter trace gas emission, for example, denitrification can intensify in earthworm casts.
• Nutrient cycling: The microbial community and their activity are essential for nutrient cycling and are moderated by the micro-food web. Synchrony of mobilization and immobilization depends on the dynamics of the micro-food web. The shift from a bacteria-based soil food web under till to a fungal-based food web in no till triggers an associated shift in the nematode and microarthropod assemblage, and alters the micro-food web.
P-cycling is dependent on soil properties; for example, the amount and nature of clay, the nutrient content of the parent material, and soil enzymes. Cultivation (till) can decrease the enzymes (arylsulfatase and acid phosphatase) involved in S and P transformations. P uptake by mycorrhizae is variable, and is more important in no till systems.
• Other goods and services: We have not mentioned habitat provision, biochemicals and medicines, and fuel/energy in the table. These goods and services may indeed be provided by arable land, but these aspects are so context dependent that they are preferably explored in individual case studies.
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