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Tuesday, 6 March 2007
The Invisible World of Alien Species in Deciduous Forest Soils
Topic: Deciduous Forest

www.invaders.nv.blm.gov


What is an alien species?

No, it is not some large green slimy being with a big head and weird eyes traveling down from Mars to destroy our planet. It is, however, just as frightening. An alien species or invasive species, is a "species that has been moved into an area and reproduced so aggressively that it has replaced some of the original species." (www.speciesatrisk.gc.ca/glossary e.cfm) Alien species come from our very own planet and attack our very own species. They can be in our lakes and streams, parks and nurseries, or even our own backyards.

Why do we care?

Alien species have the overwhelming potential to destroy habitats, convert them into completely new ecosystems, or cause mass extinctions of native species. Next to habitat destruction, invasive species are the most important cause of species endangerment and extinction. Historically, we have associated invasive species as only being significantly detrimental in island communities. In island communities, invasive species out compete the native species for resources. There are no natural predators that have been able to evolve to suppress their numbers, thus they take over. On islands or island like areas, native species have no where to escape to and no new possible niches to occupy, thus they go extinct. The effects of alien species are often times not even seen, however. Now, we are discovering the invisible "bottom-up" invasions of alien species in non-island ecosystems, such as the effects of invasive species in the soils of deciduous forests.

Invasive Species in Deciduous Forests: (A Hypothesis)

In 1990, scientist Vitousek proposed the possibility of a positive feedback loop caused by invasive species changes in soil composition. He suggested that by changing the natural soil ecology, invasive species could not only cause the acceleration of their own growth, but perhaps even promote further growth by other invasive species.

An experiment was constructed to prove how invasive plants could effect soil composition and how these changes in soil characteristics could affect the natural ecological community. In the experiment, two dominant alien species, Berberis Thunbergii and Microstegium Vimineum, were studied in the under story of three highly infested New Jersey parks, Morristown Natural Historical Park, Worthington State Forest, and Allumuchy State Park. The ancient soils of these three deciduous forests are considered a peinobiome. The lands were never covered by the ocean since they were part of the old Gondwana shield and thus they have suffered from long term leaching and are extremely nutrient poor.

The Experiment:

An experiment was conducted to prove how invasive plants could effect soil composition and how these changes in soil characteristics could effect the natural ecological community. In the experiment, two dominant alien species, Berberis Thunbergii and Microstegium Vimineum, were studied in the under story of three highly infested New Jersey parks, Morristown Natural Historical Park, Worthington State Forest, and Allumuchy State Park. Berberis Thunbergii is a woody shrub with dense surface roots. It was used often as an ornamental plant in the late 1800s and thus is found frequently in abandoned farm lands. Microstegium Vimineum is a C4 grass that forms continuous lawns in the under story.

The results of the experiment revealed that the soil below the invasive plants had significantly higher pH than the soil found below native species. The NH4 concentration studied between March and June under Berberis had increased probably due to the early leaf growth of Berberis. The NO3 soil concentrations below both invasive species were also increased for the entire year studied. As the season progressed, the net nitrification rates had increased, thus by midsummer most of the mineralization in the soil below the exotics, was due to nitrification. This high level of nitrification is unusual and detrimental to native plants, like Vaccinium, who have become adept to peinobiome soils. By midsummer, the soils below Vaccinium are found to have higher nitrification rates, however, ammonification also increases. The ammonification increase contributes the largest portion of the soils net mineralization and keeps the soil acidic unlike nitrification.

Berberis Thunbergii (www.habitas.org.uk)

Microstegium Vimineum (www.dnr.wi.gov)

The increased root density of Berberis might contribute to its higher pH.

Soil respiration in the soils below the exotics also increased, adding further nutrients to the soil. Root biomass probably is partially responsible for this as well.

The litter decomposition under Berberis is extremely fast. In fact, up to 90% of the initial plant material is decomposed every year. 17% of the nitrogen remains in the litter after decomposition, thus again increasing the nitrogen nutrient concentration in the normally nutrient poor soil. Microstegium litter decomposes about 40%-60% in the first, but very little after that. The decomposed litter, however, contains almost all of its original nitrogen.

Conclusion:

Deciduous Forest plant species are perfectly evolved and adept to growing in highly nutrient poor soils. Invasive species, like Berberis Thunbergii and Microstegium Vimineum are altering the natural characteristics of deciduous soils, making them more prone to further, successful invasions. The result could mean the loss of the entire deciduous forest ecosystem.


Posted by planet/bruinsavannahs at 12:01 AM PST
Updated: Wednesday, 14 March 2007 11:50 PM PDT
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Monday, 5 March 2007
The Human Impact on Temperate Deciduous Forests
Deforestation and Its Consequences:
Deforestation in temperate deciduous forests has obviously had a large impact on the species composition of the zonobiome. However, the adverse effects of deforestation and logging are far graver than would be expected solely based on the amount of land lost to agricultural purposes. This is because agriculture and grazing require a relatively flat grassland, which interrupts the continuous distribution of the deciduous forest.

These sparse areas of forest vegetation, in which humans live side-by-side with the forest, also contain many invasive species of plant life. Such alien plants have been introduced by humans, intentionally or otherwise, severely altering the natural pattern of the forest vegetation. These factors, taken as a whole, dramatically increase the prevalence of fire (a typically periodic event in temperature deciduous forests) in areas already lacking a high forest density. Thus, fires, while typically rejuvenating to the ecosystem as a whole, are now occurring so frequently that they pose a threat to many of the forest?s remaining animal species.


Centris Bees: A Genus in Danger
A notable example of a type of animal whose distribution has been hindered by the deforestation and its subsequent increase in fire frequency are bees of the genus Centris, who utterly depend on the forest and its resources for their survival. Aside from the pollen and nectar they must acquire from flowering plants in the forest, bees have an increased reliance on the structure and composition of the forest to maintain optimal survival conditions. That is, Centris bees create nests in deadwood portions of tree holes and in protected sites near the ground, both of which are destroyed by frequent fires. Additionally, fires also scorch oil-producing plants, which female bees use to maintain the young cells growing in their nests. Excessive fires decrease the amount of oil produced by these plants, limiting the ability of the bees to offer sustenance to their young.

Thus, as a whole, the increased frequency of fires due to deforestation has had drastic consequences on the distribution of Centris bees, whose populations over the past 2 decades have declined by almost 90% in temperate deciduous forests.




Alien Species: A Threat to Forest Diversity
In addition to changing the distribution of the vegetation in temperate deciduous forests, humans have further impacted these ecosystems by introducing alien species, both accidentally and intentionally.

African Honey Bees:
Over the last 2 decades, Mayans in the Yucatan region have imported the aggressive African honey bees as a substitute to the native stingless bees. The African bees produce higher quantities of quality honey, making them a more valuable resource to residents of this region who invest in the honey market.

However, the introduction of a new species has not been without its costs. As a result, there has been a breakdown in the diversity of stingless bees, to a point where they are now rare in the Yucatan, that correlates directly to the presence of the African honey bees. The breakdown of stingless bee populations has been caused by the aggressive nature of the African bees, who attack the passive native bees, thus lowering their diversity.

Red Fire Ants:
On the other hand, some alien species are introduced into foreign environments unintentionally, as is the case with the red imported fire ant, Solenopsis invicta. Over the last 60 years, this species of ants has increased dramatically in North America. However, this has come at a cost, as the presence of fire ants has led to a decreased diversity of other species of ants. Moreover, in the presence of the fire ants, the co-occurrence of many ant species has been random. This is because the invasive ants, foreign to their new habitat, fail to acknowledge the domains of other ant species. Instead, they inhabit land randomly, leading to aggressive behavior between ants that would otherwise not have occurred.



Conclusion:
The presence of invasive species can drastically affect the species composition of native plants and animals, leading to an imbalance in the native species distribution as the indigenous flora and fauna greatly decreased in diversity.


Posted by planet/bruinsavannahs at 12:01 AM PST
Updated: Thursday, 15 March 2007 12:32 AM PDT
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Sunday, 4 March 2007
Sources/Works Cited
Plant productivity and soil nitrogen as a function of grazing, migration and fire in an African savanna
RICARDO M. HOLDO, ROBERT D. HOLT, MICHAEL B. COUGHENOUR, MARK E. RITCHIE (2007)
Journal of Ecology 95 (1), 115?128.

Ecology of a Grazing Ecosystem: The Serengeti
S. J. McNaughton
Ecological Monographs, Vol. 55, No. 3. (Sep., 1985), pp. 259-294.

Grazing as an Optimization Process: Grass-Ungulate Relationships in the Serengeti
S. J. McNaughton
The American Naturalist, Vol. 113, No. 5. (May, 1979), pp. 691-703.

Thornbush invasion in a savanna ecosystem in eastern Botswana
J. A. van Vegten
Plant Ecology, Vol. 56, No. 1. (April, 1984), pp. 3-7.

The Brazilian Cerrado Vegetation and Threats to its Biodiversity
J. A. RATTER, J. F. RIBEIRO and S. BRIDGEWATER
Annals of Botany, Vol. 80, No.3, pp. 223-230

Cerrado
World Wildlife Federation
http://www.worldwildlife.org/wildworld/profiles/terrestrial/nt/nt0704_full.html

Biodiversity Hotspots- Cerrado
http://www.biodiversityhotspots.org/xp/Hotspots/cerrado/index.xml

Breckle, S.W. "Walter's Vegetation of the Earth". Berlin: Springer-Verlag, 2002.

Longcore, Travis. "Geography 108 Lecture Series: World Vegetation". Univeristy of California, Los Angeles: Winter 2007.

Changes in Soil Functions Following Invasions of Exotic Understory Plants in Deciduous Forests (in Invited Feature: Invasive Species and the Soil)
Joan G. Ehrenfeld; Peter Kourtev; Weize Huang
Ecological Applications, Vol. 11, No. 5. (Oct., 2001), pp. 1287-1300.

Biogeographic Effects of Red Fire Ant Invasion
A.E Arnett, N.J Gotelli
Ecology Letters, Vol. 3, No. 4. (200), pp. 257?261.

Nesting-Habitat Preferences of Selected Centris Bee Species in Costa Rican Dry Forest
J.F Barthell, G.W Frankie, S.B Vinson
Biotropica, Vol. 25, No. 3. (1993), pp. 322-333.


Posted by planet/bruinsavannahs at 12:01 AM PST
Updated: Thursday, 15 March 2007 1:09 AM PDT
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