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.