Decomposition and Invasive Species

Decomposition and Invasive Species 

Terrestial ecosystems are changed by an invasive species's litter decomposition rate.

Studies have shown than on the average, invasive species have 117% higher decomposition rate in comparison to native plants (Ehrenfeld 2010).  Generally, more litter mass is associated with higher input of elements to the soil.  

Invasive plant litter decomposes more quickly because their litter is generally of higher quality with lower carbon:nitrogen and lignin:nitrogen ratios.  Whether due to increased litter mass or increased decomposition rate, the invasive plants frequently have higher net flux of carbon to the soil (Ehrenfeld 2010).

           

There have been several studies that have shown that invasive plants have somewhat faster decomposing litter and nitrogen loss; studies have repeatedly shown faster decomposition and nitrogen cycling for both native and invasive species when they are grown together at a site growing invasive species.  The implication is that in addition to the nature of the litter, there are soil changes caused by the invasive plants that are not well-understood, but seem to favor recycling of all species.  For example, one study in Hawaii compared the invasive nitrogen-fixing tree, Falcataria molucanna, to the native tree that did not fix N₂, Metrosideros polymorpha, and found that following invasion by a Falcataria stand, the litter decomposition rates of both trees increased six times over what it had been in native soil (Hughes 2006).

                                           F. molucanna                             M. polymorpha

                                     

Garlic mustard (Alliaria petiolata) is an invasive plant that is able to suppress competition by secretion of numerous secondary compounds, such as glucosinolates, that suppress spore formation by arbuscular mycorrhizal fungi, a common symbiotic fungus of native plants (Wolf, Klironomos 2005).  Surprisingly, despite the secondary antimicrobial compounds, garlic mustard green rosette leaves consistently accelerated the decomposition of native tree litter and nitrogen immobilization, while it increased soil N and P availability, soil pH, and base cation availability.  Plant tissue volatiles and root exudates had little impact on soil properties or fungi other than AMF’s (Rodgers et al 2007).

Alliaria petiolata

                        

While you might think the larger biomass would lead to higher litterfall mass, this situation does not always occur because of other factors, such as relative carbon allocation to leaves and decomposition rate.  Florida’s invasive tree, Melaleuca, has monoterpene-rich leaves that decompose slowly.  These plant chemicals probably served a protective role against herbivores or disease in their native countries.  The oil content of trees growing in Florida is less than that found in tree of Australia (Ehrenfeld 2003).

Melaleuca quinquenervia

The preceding examples show that invasive species' litter decomposition rates change terrestrial ecosystems.                                                   

References

1. Ehrenfeld, Joan G. (2010). Ecosystem Consequences of Biological Invasions. Annual Review of Ecology, Evolution, and Systematics. 41:59-80.

2. Ehrenfeld, Joan G. (2003). Effects of Exotic Plant Invasions on Soil Nutrient Cycling Processes. Ecosystems. 6:503-523.

3. Hughes, R. Flint, Uowolo, Amanda. Impacts of Falcataria molucanna Invasion on Decomposition in Hawaiian Lowland Wet Forests: The Importance of Stand-level Controls. Ecosystems. Vol. 9:977-991.

4. Rodgers, Vikki L., et al. (2008). The Invasive species Alliaria petiolata (garlic mustard) increases soil nutrient availability in northern hardwood-conifer forests.

Oecologia. 157:459-471.

5. Wolfe, Benjamin E. and John N. Klironomos. (2005). Breaking New Ground: Soil Communities and Exotic Plant Invasion. BioScience. Vol. 53 No. 6:477-487.

Consumers and Invasive Species

Consumers and Invasive Species

Consumers are organisms (animals, bacteria, fungi) that receive energy by consuming other organisms through predation, parasitization and/or degredation, Consumers that alter the ecosystem are not limited by resource utilization requirements of producers.  By destroying biomass, consumers create an ecosystem disturbance that can later be exploited by another producer, often times allowing an invasive species to become established.  Examples of non-indigenous consumers affecting the ecosystem include plant pathogens and animals occupying a new habitat with few predators (Ecology of Biological Invasions of North America and Hawaii 1984).

The American chestnut (Castanea dentata) at one time composed almost forty percent of the forests of southern Appalachia. Beginning in the 1920’s, the fungal parasite, chestnut blight (Cryphonectria parasitica), invaded and destroyed most of the American chestnut trees by causing a typical canker, with splitting of bark in the process.  The fungus is thought to have been accidentally introduced to North America on imported Japanese nursery stock.  Since then the ecosystem has changed; after successional changes, the chestnut-oak forests became an oak complex and later a hickory-oak forest for a short-term effect (McCormick 1980).

         

     parasitica                                        O. ulmi discoloration               Scolytus brood gallery

Dutch elm disease, first reported in the U.S. in 1928, is caused by an elm bark beetle, Scolytus multistriatus, depositing the fungus, Ophiostoma ulmi, when it lays eggs.  Over the next forty years, the disease spread from New England to most of the U.S. and affected the forest ecosystem by destroying 75% of the 77 million trees (NY Times, 1989).

Rooting by feral pigs (originally introduced from Eurasia as a wild game species) at higher elevations of the Great Smokey Mountain National Park has altered the soil characteristics such as causing thinner forest floors, mixed organic and mineral soil horizons, and an increase in bare ground.  As a result, there are large concentrations of nitrogen and potassium in the soil, and nitrogen in the streams (Ecology of Biological Invasions of North America and Hawaii 1984).

The forestry industry loses about $2 billion of forestry products annually due to non-indigenous insects (Pimental 2000).  The gypsy moth (Lymantria dispar dispar), imported to start a silkworm industry, escaped and has caused great ecological and economical damage to the American forests.  Moth larva feed on tree foliage, especially leaves of oaks and birches.

       Defoliation by gypsy moth                                                                 L. dispar dispar

              

Another consumer pathogen causing ecologic and economic damage to oak forests in California and Oregon is the fungus, Phytophthora ramorum, which causes sudden oak death.  The disease is spreading rapidly to other parts of the country where it will destroy dominant tree species and alter the ecosystem (Chornesky).

  Black zone lines of P. ramorum                                             Death of an oak stand from P. ramorum

Changes to the ecosystem by invasive species acting as consumers alter the keystone and/or dominant species which in turn alters the ecosystem's flora and fauna.                                

           

 References

1. Chornesky, Elizabeth A. et al. (2005). Science Priorities for Reducing the Threat of Invasive Species to Sustainable Forestry. Bioscience. Vol 55:335-348.

2. Ecology of Biological Invasions of North America and Hawaii. (1984). Springer-Verlag: New York.  p 163-173.

3. McCormick, J. Frank, Platt, Robert B. (1980). Recovery of an Appalachian Forest Following the Chestnut Blight or Catherine Keever-You Were Right!. American Midland Naturalist. Vol104:264-273.

4. New York Times (12-5-89). [Web]. New Varieties of Elm Raise Hope of Rebirth for Devastated Tree.

5. Pimentel, David et al. (2000). Environmental and Economic Costs of Nonindigenous Species in the United States. BioScience. Vol. 50. No. 1:53-65.

Productivity and Invasive Species

Productivity and Invasive Species

All plants need carbon dioxide, water and nutrients.  If native species have evolved to utilize the resources most efficiently, then to become successful and alter the ecosystem, invasive species need to utilize resources more efficiently.  They must acquire nutrients unavailable to natives or actively produce more seeds, or at different times, than native plants (Ecology of Biological Invasions of North America and Hawaii (Vitousek) 1984).

Increased carbon acquisition, or net primary production, by invasive plants is due to their increased plant and leaf size, phenology, or growth rate.  The presence of large rhizome storage organs and associated increased carbon supply increases the biomass and furnishes photosynthate for large stem growth.  The Giant reed (Arundo donax) has a system of rhizomes that allow the stems to grow twice a high (30 feet) as competing native plants. Total plant biomass is similarly greater (Ehrenfeld 2003).

                                                                                                

In a study that compared 34 native to 30 invasive plants in Hawaii, it showed the invasive plants had large leaf areas, higher CO₂ assimilation, and lower leaf tissue construction costs than the native plants (Baruch 1999).  In successional replacement, a large invasive tree replaces the native shrubs.  In South Florida swamplands, few trees existed until the early 1900’s when the Australian tree, Melaleuca quinquenervia, was introduced to produce a forest.  This tree can grow in any soil in Florida and tolerates both drought and flooding.  Its insulated bark protects the cambium layer from fire.  While the oily leaves die in the fire, trunk buds germinate quickly and produce flowers and seeds (36,000/gram) within weeks and throughout the year. Anthropogenic disturbances for road-building and agriculture have also enabled Melaleuca to transform the wetlands to forest (Ecology and Biological Invasions of North America and Hawaii (Ewel) 1984).   Sometimes the standing crop of the individual invasive plant is not larger than the native plant, but the distribution and collective plant concentration is greater.  The invasive plant, Cheat grass or Bromus tectorum, is continuously distributed, unlike the discontinuous “islands” of native plants (Ehrenfeld 2003).

Melaleuca quinquenervia                                                        Bromus tectorum

            

Invasive plants can alter ecosystems by decreasing productivity.  Some plants adapted to drought conditions are able to concentrate salt in the soil around them, thus altering the soil community and preventing native plants from growing. Two examples are the California purple-flowering ice plant, Carpobrotus edulis, introduced for dune stabilization, but which now extends from San Francisco to Mexico (Ecology of Biological Invasions of North America and Hawaii 1984).

                   Carpobrotus edulis                                                   Halogeton glomeratus 

Saltlover, Halogeton glomeratus, of the rangelands in the western U. S. also accumulates sodium from the lower soil into the biomass and soil to alter the soil community and reduce productivity of native plants (Wolfe 2005).

References         

1. Baruch, Z., Goldstein, G. (1999). Leaf construction cost, nutrient concentration, and net CO₂ assimilation of native and invasive species in Hawaii. Oecologia. 121:183-192.

2. Ehrenfeld, Joan G. (2003). Effects of Exotic Plant Invasions on Soil Nutrient Cycling Processes. Ecosystems. 6:503-523.

3. Ecology of Biological Invasions of North America and Hawaii. (1984). Ch. 10, P.M.  Vitousek. Springer-Verlag: New York.  p 163-176.

4. Ecology of Biological Invasions of North America and Hawaii. (1984). Ch. 13, J.J. Ewel. Springer-Verlag: New York.  p 214-230.

5. Wolfe, Benjamin E. and John N. Klironomos. (2005). Breaking New Ground: Soil Communities and Exotic Plant Invasion. BioScience. Vol. 53 No. 6:477-487.