From: Bruce Sterling []
Sent: Sunday, May 21, 2000 4:48 PM
To: Viridian List
Subject: Viridian Note 00159: Biodiversity Part 2

Key concepts: human impacts on biodiversity,
Nature magazine, fires, tussock grass, salt cedar, mammoths, ticks, passenger pigeons

Attention Conservation Notice: a stark continuation of Note 00158.

Entries in the Greenhouse Disaster Symbol contest: This contest expires May 31, 2000.

Links: "Fake Ads" at their weirdest. Civil society trembles
on the neurotic brink of commodity-totalitarianism. Peculiarly humorless right-wing Starbucks effort: Incredibly offensive anti-Christian e-commerce:

Source: Nature 11 May 02000, page 234
"Consequences of Changing Biodiversity" by F. Chapin, E. Zevaleta, V. Eviner,

"Finally, the mobility of people has transported organisms across the geographical barriers that long kept the biotic regions of the Earth separated, so that many ecologically important plant and animal species of many areas have been introduced in historic time."

(...) "The introduction of the nitrogen-fixing tree Myrica faya to nitrogen-limited ecosystems in Hawaii led to a fivefold increase in nitrogen inputs to the ecosystem, which in turn changed most of the functional and structural properties of native forests.

"Introduction of the deep-rooted salt cedar (Tamarix sp.) to the Mojave and Sonoran Deserts of North America increased the water and soil solutes accessed by vegetation, enhanced productivity, and increased surface litter and salts. This inhibited the regeneration of many native species, leading to a general reduction in biodiversity.

"The perennial tussock grass, Agropyron cristatum, which was widely introduced to the northern Great Plains of North America after the 1930s 'dustbowl,' has substantially lower allocation to roots compared with native prairie grasses. Soil under A. cristatum has lower levels of available nitrogen and ~25% less total carbon than native prairie soil, so the introduction of this species resulted in an equivalent reduction of 480 X 10 (12) g of carbon stored in soils." (((This gloomy analysis makes one wonder what kind of grass stores the most carbon in soils. Why don't we plant our lawns in that stuff?)))

(...) "Several species of nutritious but flammable grasses were introduced to the Hawaiian Islands to support cattle grazing. Some of these grasses spread into protected woodlands, where they caused a 300-fold increase in the the extent of fire. (((An amazing statistic. Cro- Magnons with torches may have been the best friends that the world's prairies ever had.))) "Most of the woody plants, including some endangered species, are eliminated by fire, whereas grasses rebound quickly.

"Similar increases in the ecological role of fire resulting from grass invasions have been widely observed in the Americas, Australia and elsewhere in Oceania. The invasion of cheatgrass (Bromus tectorum) into western North America is one of the msot extensive of these invasions. Cheatgrass has increased fire frequency by a factor of more than ten in the >40 million hectares that it now dominates. (...)

(((Now for a truly weird speculation.))) "At the regional scale, an improvement in hunting technology at the end of the Pleistocene may have contributed to the loss of the Pleistocene megafauna and the widespread change from steppe grassland to tundra that occurred in Siberia 10,000 to 18,000 years ago. The resulting increase in mosses insulated the soil and led to cooler soils, less decomposition and greater sequestration of carbon in peat." (((In other words, remove the mammoths and permafrost sets in.)))

(...) "Large populations of passenger pigeons (Ectopistes migratorius) in the northeastern United States may have controlled Lyme tick-bearing mice by out- competing them for food. The loss of the passenger pigeon to nineteenth-century over-hunting may, therefore, have contributed to the rise of Lyme disease in humans in the twentieth century."

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