ECOSYSTEM TYPES

ECOSYSTEM TYPES

What process helps in restoring forests?

Afforestation establishes tree cover on land that has long been non-forested or substantially degraded, and it can help restore forest functions such as carbon storage, erosion control, water regulation, habitat provision, and microclimate moderation. Closely related reforestation restores trees to recently cleared forest land; the two terms are sometimes distinguished in forestry statistics. Successful ecological restoration requires more than planting any trees. Native species, appropriate genetic sources, soil condition, hydrology, fire regime, landscape connectivity, and the needs of local communities determine whether a resilient forest develops. Diverse natural regeneration may outperform a single-species plantation for biodiversity and long-term stability. Deforestation removes forest cover, urbanization converts land to built surfaces, and desertification degrades dryland productivity, so none represents a restorative process. By adding woody vegetation and enabling succession, afforestation can rebuild biomass and facilitate colonization by other organisms. However, planting trees in natural grasslands or peatlands can damage native ecosystems and carbon stores. The term applies when establishment is ecologically suitable for the site and directed toward recovering tree-dominated land functions.

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 2-3

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ECOSYSTEM TYPES

Which ecosystem is least productive?

Deserts generally have the lowest primary productivity among the terrestrial ecosystems listed because water availability sharply limits photosynthesis, leaf area, and the length of active growth. Rainfall is sparse and unpredictable, and evaporation may exceed precipitation. Plants often remain widely spaced and invest resources in water storage, conservative metabolism, or extensive roots rather than continuous rapid growth. Productivity can surge briefly after rain, but annual net primary production remains low. Forests maintain much larger leaf area and biomass where temperature and water permit; grasslands receive enough seasonal moisture to support a continuous herb layer; and wetlands often achieve high productivity because water and nutrients are available, although nutrient-poor bogs are exceptions. Tundra can rival or fall below some deserts, but it is not among these choices. “Least productive” also depends on measurement: productivity per unit area differs from total global production, and some coastal deserts receive fog that supports local growth. Under the standard biome comparison intended here, chronic aridity makes desert the strongest match for low ecosystem productivity.

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 2-3

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ECOSYSTEM TYPES

What does eutrophication cause?

Eutrophication is enrichment of water with nutrients, especially phosphorus in many fresh waters and nitrogen in many coastal systems. The added nutrients remove a growth limitation on phytoplankton or cyanobacteria, allowing rapid population increase that appears as an algal bloom. Dense blooms reduce water clarity and shade submerged vegetation. When algal cells die, bacteria decompose the organic matter and consume dissolved oxygen; stratified bottom waters may then become hypoxic or anoxic. Fish kills, loss of oxygen-sensitive species, toxin-producing cyanobacteria, unpleasant odours, and altered food webs may follow. Nutrient enrichment can initially increase biomass or the abundance of a few species, but it does not reliably boost biodiversity and often reduces it through dominance and oxygen stress. Clear water and higher oxygen are therefore opposite to the common late consequences. Natural eutrophication occurs slowly as basins age, whereas fertilizer, manure, sewage, and urban runoff can accelerate it dramatically. The bloom is the immediate visible response because nutrient supply raises photosynthetic growth before decomposition generates oxygen depletion.

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 2-3

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ECOSYSTEM TYPES

Where is photosynthetic activity highest in lakes?

The littoral zone is the shallow lake margin where sunlight reaches the bottom, allowing rooted macrophytes, attached algae, and phytoplankton to photosynthesize. Plants occupy both the sediment and water column, creating a large photosynthetic surface and structurally complex habitat. Nutrients arrive from shoreline soils, runoff, decomposing vegetation, and sediment recycling, while wave action and animal activity can return them to the water. Consequently, areal primary production is often especially high in the littoral region. The profundal zone lies below effective light penetration and is dominated by respiration and decomposition. The aphotic zone likewise lacks enough light for net photosynthesis. “Benthic” means the bottom habitat at any depth; a sunlit littoral bottom can be productive, but deep benthic sediment cannot be treated as uniformly photosynthetic. In large lakes, the open-water limnetic zone may contribute more total production because of its area, so “highest” depends on scale. Among the listed zones, however, littoral water best combines abundant light, rooted vegetation, periphyton, and nutrient access, explaining the keyed choice.

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 2-3

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ECOSYSTEM TYPES

Which grassland has scattered trees?

A savanna is a tropical or subtropical grassland in which a continuous or nearly continuous herbaceous layer coexists with scattered trees and shrubs. Seasonal rainfall supplies enough water for some woody plants but not enough, or not consistently enough, to maintain a closed forest canopy. Fire and grazing are equally important: grasses can regrow from protected basal tissues, whereas frequent burning and herbivory limit many tree seedlings. Adult trees often have deep roots, thick bark, small leaves, or drought-deciduous foliage. The balance among rainfall, fire, soil, herbivores, and human land use controls tree density, so savannas grade from open grassland to woodland. Temperate prairies may contain occasional trees but are defined by cold winters and are typically more continuously treeless. Tundra is too cold for substantial tree growth, while “prairie” is a temperate grassland type. Scattered woody vegetation above a grass-dominated ground layer is therefore the characteristic structural signature of savanna, produced by seasonal water limitation and recurring disturbance.

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 2-3

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ECOSYSTEM TYPES

What organisms float on water surface?

Neuston are organisms that live at or immediately adjacent to the air-water interface. Some rest on top of the surface film, termed epineuston, while others occupy its underside, termed hyponeuston. Examples include water striders, floating microbial communities, certain algae, fish eggs, larvae, and small invertebrates. Surface tension creates a specialized habitat, and strong gradients in light, temperature, oxygen, and chemicals distinguish it from deeper water. Wind can aggregate neuston into slicks, while ultraviolet radiation and pollutants concentrated at the surface impose stress. Benthos live on or within the bottom; periphyton grow attached to submerged substrates; and nekton actively swim through the water column. The everyday verb “float” can also describe plankton, which drift with currents throughout the water, but among the terms listed, neuston specifically refers to life associated with the water surface. Their position lets some species obtain atmospheric oxygen or exploit floating food, yet also exposes them to waves and desiccation. Occupation of the surface microlayer is therefore the decisive feature.

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 2-3

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What defines a fen wetland?

A fen is a peat-forming wetland supplied by groundwater or mineral-rich surface water in addition to precipitation. Water moving through soil and rock carries dissolved calcium, magnesium, bicarbonate, and other ions, making most fens less acidic and more nutrient-rich than rain-fed bogs. Some are neutral or alkaline, especially in limestone regions, although mildly acidic fens also occur; groundwater influence is more fundamental than a universally high pH. Sedges, grasses, brown mosses, and specialized flowering plants commonly dominate, and peat accumulates because saturation restricts oxygen and slows decomposition. Bogs are mainly ombrotrophic, receiving water from rain, and are usually acidic and nutrient-poor. Wetlands with mineral soil and trees are more commonly called swamps, while shallow rocky conditions do not define a fen. The keyed description combines the usual chemical tendency—alkaline conditions—with the causal hydrology—groundwater feeding. That water source explains the greater mineral availability, distinctive vegetation, and generally higher productivity of fens compared with bogs.

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 2-3

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ECOSYSTEM TYPES

What type of forest grows after disturbance?

A secondary forest develops after a disturbance removes or damages an earlier forest but leaves a biological legacy, especially soil. Fire, storms, logging, shifting cultivation, or abandoned farmland can initiate this recovery. Seeds in the soil, surviving roots and stumps, nearby seed sources, microbes, nutrients, and existing soil structure allow vegetation to return faster than during primary succession on newly exposed rock. Early colonists are often fast-growing, light-demanding herbs, shrubs, and trees. As their canopy develops, shade, litter, soil moisture, and competition change, allowing more shade-tolerant species to establish. A primary forest is usually one that has not experienced recent major human clearing and has developed over a long period; “climax forest” is an older equilibrium concept, not the general name for post-disturbance regrowth. Mangrove forest is defined by intertidal habitat and salt tolerance, not by successional origin. Secondary forests can recover substantial biomass and biodiversity, but their composition may differ for decades or longer. Retained soil and propagules are therefore the mechanism linking disturbance to secondary forest formation.

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 2-3

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ECOSYSTEM TYPES

Which water body is brackish and tidal?

An estuary is a partly enclosed coastal water body where river water mixes with seawater and tidal action influences water level and circulation. Mixing produces brackish water, whose salinity lies between fresh and fully marine conditions and often varies over each tide, season, and position along the estuary. Density differences can create a salt wedge or partial stratification, while tidal currents transport sediments, oxygen, nutrients, plankton, and organisms. Estuaries support salt marshes, mangroves, mudflats, seagrass beds, nursery grounds, and productive detrital food webs. A river is primarily flowing fresh water, although its mouth may enter an estuary. Lakes and ponds are inland standing waters and normally lack regular marine tides and salt mixing. Some coastal lagoons also become brackish, but estuary specifically captures the combined river-sea connection and tidal forcing stated here. Organisms living there must tolerate rapid changes in salinity and turbidity. Thus, “brackish and tidal” identifies the physical mixing process that distinguishes an estuary from ordinary freshwater bodies.

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 2-3

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ECOSYSTEM TYPES

What describes the neritic zone?

The neritic zone is the shallow marine water extending from the low-tide margin to the edge of the continental shelf. Its exact offshore width varies because continental shelves may be narrow or hundreds of kilometres broad, but depth commonly remains below about 200 metres. Sunlight can reach much or all of this water column, while rivers, coastal runoff, sediment resuspension, and upwelling often supply nutrients. These conditions support phytoplankton, seaweeds, seagrasses, benthic invertebrates, fishes, and many commercial fisheries. The neritic zone is not simply the shoreline: the intertidal region is periodically exposed, whereas neritic water remains marine and overlies the shelf. Beyond the shelf break lies the oceanic zone over deep open ocean. “Deep ocean” therefore describes neither its position nor typical depth, and “open sea” is too broad. By linking a horizontal marine region to the underlying continental shelf, the definition also explains its generally high productivity: shallow illumination and land-derived or mixed nutrients are more available than in many offshore surface waters.

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 2-3

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Which oceanic zone has highest biodiversity?

The epipelagic zone, extending from the surface to roughly 200 metres, generally supports the greatest biodiversity among the listed open-ocean depth zones because it receives enough light for photosynthesis. Phytoplankton convert solar energy and inorganic nutrients into organic matter, forming the energetic base for zooplankton, fishes, turtles, marine mammals, and numerous predators. Warm temperatures, relatively high oxygen, wave-driven mixing, and habitat variation near fronts and floating structures further expand ecological opportunities. Much of the ocean’s primary production occurs here, although nutrient-poor subtropical gyres can be locally unproductive. The mesopelagic contains many species and enormous animal biomass, but light is insufficient for net primary production and its food supply largely originates above. Bathypelagic and abyssopelagic waters are colder, darker, and more food-limited, so abundance and typical species richness decline with depth. “Highest biodiversity” depends on spatial scale and habitat definition—coral reefs and benthic margins can exceed pelagic waters—but within the four vertical pelagic zones offered, the sunlit epipelagic has the strongest and most diverse food web.

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 2-3

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ECOSYSTEM TYPES

Which ecosystem receives

Deserts are commonly defined by chronic water limitation, and many receive less than about 250 millimetres of precipitation per year. Low rainfall, often combined with high evaporation, prevents continuous tree cover and limits primary productivity. Desert organisms show water-conserving adaptations: plants may use CAM photosynthesis, reduced leaves, succulent tissues, deep or widespread roots, and rapid life cycles after rain; animals may be nocturnal, burrowing, or produce concentrated urine. Not all deserts are hot. Polar and high-altitude deserts can be cold, demonstrating that aridity rather than temperature is the essential criterion. Rainforests and temperate forests need substantially more moisture to maintain closed canopies, while grasslands generally receive intermediate precipitation, often with seasonal drought and fire. The 250-millimetre boundary is approximate because rainfall variability, soil properties, and potential evapotranspiration also determine biological water availability. Even so, among the listed ecosystems, desert most closely matches this annual precipitation threshold. Sparse vegetation then reinforces low productivity and exposes soil to wind and episodic water erosion.

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 2-3

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