Novel ecosystems
Novel ecosystems refer to ecosystems that feature new species combinations and assemblages resulting from human actions. These ecosystems emerge when physical and biological components are altered due to various factors such as species invasion, abandonment of managed lands, or environmental disturbances like fires and floods. Unlike traditional ecosystems, novel ecosystems include species that have not previously coexisted in a specific area, leading to unpredictable ecological outcomes. The rise of novel ecosystems is closely tied to human activities, such as deforestation, conversion of natural areas for agriculture, and landscape fragmentation, which have significantly modified species distributions worldwide.
Examples of novel ecosystems can be found in various regions, including areas where invasive species dominate or where formerly agricultural lands have reverted to forests with new species compositions. While some view these ecosystems as ecological challenges due to the presence of nonnative species, others see them as a natural response to environmental changes. The study of novel ecosystems provides critical insights into their ecological functions, resilience, and potential benefits, such as increased biodiversity and improved soil conditions. However, the debate continues regarding their value in conservation efforts and the implications of human-induced changes on the planet's ecosystems.
Novel Ecosystems
Category: Grassland, Tundra, and Human Biomes.
Geographic Location: Global.
Summary: Human activities affect the distribution and abundance of species, often resulting in new combinations of species that did not occur previously in a given place. This change has unpredictable consequences for the biodiversity and ecology of a place.
Novel ecosystems are defined as ecosystems that have new assemblages or combinations of species resulting directly and indirectly from human action. They are called novel, or new, because species occur in combinations and in relative abundances unlike those that occurred previously within a given biome. Another term commonly used to describe novel ecosystems is emerging ecosystems.
Novel ecosystems are formed by changes in the physical and biological components of ecosystems; by species invasion of ecosystems; and/or by the abandonment of intensively managed ecosystems, such as agricultural or urban areas.
The distribution and abundance of species can fluctuate naturally. Changes in the physical environment through disturbances such as fires, landslides, floods, and volcanic eruptions cause the removal of some or all species. The opening of space and availability of resources allows for the colonization and reestablishment of species. In fact, disturbance can play an important role in maintaining species diversity in some ecosystems, by preventing the dominance of one species to the exclusion of others.
Ecological changes that occur after a disturbance are called succession. Primary succession occurs on a landscape that has been wiped clean of its original ecosystem, such as on a lava flow or a surface recently exposed by retreating glaciers. Secondary succession occurs when there are changes in species due to a disturbance that has affected but not removed the original ecosystem, as when a fire or a fallen tree in a forest opens space for plants to colonize.
On a global scale, changes in Earth’s climate during the Pleistocene glacial and interglacial periods resulted in changing species assemblages. Species differ in their ability to adapt to changes in climate, and in their capacity to disperse or migrate in response to changes in their environment. By studying pollen records in lake cores and in sediments, scientists have found that past climatic changes resulted in new combinations of species through immigration of new species, emigration of species to a more suitable area, or extinction of those species that were unable to adapt to changing conditions. Paleoecologists call these communities no-analog communities because the resulting combinations of species have no analog in Earth’s modern history.
Novel ecosystems differ from no-analog communities and from changes in species composition during natural succession in two ways: The changes in emerging ecosystems are driven by human activities which differ from natural past climatic changes and primary succession; the communities include new species that never co-existed there before, which differs from secondary succession. In addition, no-analog communities reconstructed from past environmental data are compared with modern systems, while novel ecosystems are compared with recent historical conditions.
While the emergence of novel ecosystems depends on some environmental change that is directly or indirectly caused by human activities, novel ecosystems—unlike agricultural ecosystems—do not require human management for their maintenance. Another important element of novel ecosystems is the unpredictability of the emerging species combinations, because they do not follow the well-studied patterns of species replacement during primary or secondary succession.
Effects of Human Activity
Researchers are realizing that the influence of human activities extends all over the globe, which has led some to rename our current geologic epoch Anthropocene, for the Age of Humans. Human activities that change the landscape and species distributions include deforestation; conversion of natural forests, grasslands, and wetlands to agriculture (crops and grazing lands); and fragmentation of the landscape by urbanization. Through the domestication and trade of species, humans have deliberatively transported plant, animal, and microbial species around the world, with the result that many species now live in biomes where they never existed before and would not have been able to reach on their own.
Human activities have also caused the inadvertent movement of species around the world. For example, the spotted lanternfly, Lycorma delicatula, a species native to China, likely arrived in North America in 2012 as egg masses on a shipment of stone delivered to Pennsylvania; in less than a decade the plant hoppers were feasting on trees and other plants in eleven states. The consequence is that many species are now finding themselves in new communities, interacting with species with which they have not co-evolved.
At the same time, humans have driven many species to extinction through overhunting, disease, habitat loss, and a breakdown of biological interactions required for the survival of a species. Through the fragmentation and degradation of landscapes, humans have created barriers to the natural dispersal or movement of some species from one place to another. All these activities result in communities becoming disassembled as individual species are affected in different ways. The reestablishment of the original species is prevented by changes in the physical environment—such as loss of soil nutrients or physical habitat—or by a reduction in the original species pool, such as through the loss of a seed bank or seed source.
Effects on Ecological Processes
Much recent research has focused on studying the role of novel ecosystems and their ability to restore forest and grassland cover to human-disturbed landscapes. Some novel forests harbor native species in the understory and can include a high biodiversity of plants and animals. However, because they are new ecosystems, they are less studied, and it is often unknown how changes in composition will affect important ecological processes.
Some ecological processes that are affected by which species inhabit an ecosystem are the amount of energy and food available for higher trophic levels through photosynthesis; plant-animal interactions, which can affect pollination, seed dispersal, and germination, as well as food-web dynamics; the breakdown of dead organic matter and recycling of important plant nutrients by bacteria, fungi, and invertebrates; and water availability for plant growth through species’ effects on hydrology. The unpredictability of species combinations in novel ecosystems increases uncertainty about their continued ability to provide services that are important for humans and other organisms, such as habitat for biodiversity, watershed protection, regional climate stabilization, and carbon sequestration.
Examples of Novel Ecosystems
Examples of novel ecosystems can be found around the world. Some are relatively recent and others have been around for a long time, because humans have been modifying their environment and moving species around for thousands of years. South Africa’s fynbos shrublands are being invaded by pine species that are especially adapted to germinating rapidly after fire and thus preventing the reestablishment of the native shrub species. In Brazil, New Zealand, and parts of the United States, the introduction by humans of recurring fire and of intensive livestock grazing have caused the replacement of native forests by grasslands and shrublands.
Environmental pollution by nitrogen and other elements is changing soil chemistry in forests and grasslands in Europe and North America, allowing invasive species to outcompete those that were already present and that were better adapted to the old conditions.
In Puerto Rico, extensive deforestation for sugarcane, coffee, and cattle pasture at the beginning of the 20th century has been reversed due to changes in economic policies. This Caribbean island has experienced a threefold increase in forest cover due to the large-scale abandonment of agriculture. The emerging forests on former agricultural lands have different combinations of tree species not found before on the island. Researchers are actively studying these subtropical forests to see how ecological processes are affected by the dominance of introduced species.
Examples also exist in the aquatic world. Human control of rivers for irrigation and flood prevention has altered water and sediment flows, changing the habitat of riverine species and facilitating the introduction of nonnative fish and aquatic plants. Many important estuaries, such as San Francisco Bay in California, are now completely dominated by new species combinations, due to the confluence of ships from all parts of the world that bring along hitchhikers.
Conservation Efforts
Novel ecosystems are important because they bring attention to the extent of human influence on the environment. Many conservation practices attempt to restore ecosystems to their original condition. These efforts often fail because enough changes have happened to the ecosystem that the original species are not able to come back without intensive and expensive human assistance. Furthermore, many of these species are not able to survive and replace themselves without costly management. Often, information on the original species composition is lacking.
Novel ecosystems provide opportunities for scientists to study how ecosystems respond to environmental change. While those who value the preservation of wild nature devalue novel ecosystems because they often are dominated by nonnative, or exotic, species, others argue that novel ecosystems are nature’s way of dealing with change, by creating new combinations of species that are better adapted to the transformed environment. Novel ecosystems on soils where nutrients have been severely depleted through intensive agriculture, or on soils contaminated by industrial pollution or overfertilization, for example, harbor species that are able to tolerate extreme conditions. Over time, these species can actually improve soil conditions and facilitate the establishment of other species, some of which might have been there before the environmental change.
Controversy
There is a vigorous debate in the ecological community on the role of species that have been introduced by humans, and what place they should have in different types of ecosystems. Similar questions arise about novel ecosystems that comprise numbers of these “unwanted” species. Some argue that these ecosystems are ecological disasters, unworthy of ecological study because they are “unnatural,” and suggest that energy should be spent on studying and preserving the last wild places on Earth. Those who study novel ecosystems respond that more and more of our landscape contains these new combinations of species, and that it is important to understand how they work.
The topic of novel ecosystems provides a philosophical context for discussing the extent to which one species—humans—is modifying the planet’s surface and atmosphere, and altering the composition of ecosystems and biomes at a much faster rate than past climatic or environmental changes. Novel ecosystems suggest that, in some places, irreversible changes in physical and biological conditions may have already occurred. Emerging ecosystems provide opportunities for ecologists to study how terrestrial and aquatic communities respond to disturbances caused by human activities, changes in nutrients, and species invasions. Global warming will further drive the emergence of new combinations of species.
Bibliography
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