Land use changes a major factor in biodiversity loss

provided by Colorado State University

report in a March issue of the journal Science is the first systematic look at how biodiversity is likely to be impacted by several agents of human-caused global change and global warming and climate change aren't necessarily the principal factors.

In the article, researchers look at what factors affect biodiversity, what kinds of habitats are susceptible to those factors and what may happen to biodiversity between now and 2100. The article's 19 authors, from the United States, Latin America, Europe and Australia, include two Colorado State University faculty members, Diana Wall, director of Colorado State's Natural Resource Ecology Laboratory, and N. LeRoy Poff, assistant professor of biology.

Global warming and climate change aren't necessarily the principal factors in the loss of biodiversity anticipated over the next century, Poff said. Nitrogen deposition and particularly land-use change and the introduction of nonnative species can play a significant role in some ecosystems. "For most ecological systems, land-use change is more important than climate change within the next 50-100 years," said Poff, a specialist in freshwater ecosystems. "If climate change were to just go away tomorrow, land-use change will still drive down biodiversity.

"We have to think about ways to reduce land-use change and biotic introductions in order not to exacerbate what happens when climate change is thrown into the mix."

The researchers identified five primary influences, or "drivers," in global change that in turn affect biodiversity: global atmospheric carbon dioxide, climate change, biotic change (the introduction of new species to an ecosystem), nitrogen deposition and land-use change (for example, development, and agricultural and forestry practices). They then identified 10 terrestrial biological communities, called "biomes," and tried to assess how sensitive each was to a particular driver. The biomes included alpine, arctic, boreal forest, deserts, grasslands, Mediterranean systems, Northern temperate forest, savanna, Southern temperate forest and tropical forests. The researchers also examined freshwater ecosystems, both lakes and running water, and soil.

Poff said biotic exchange is a much greater threat to freshwater systems, particularly lakes, than to terrestrial biomes. Aquatic species have typically evolved in relatively isolated habitats, and introduction of a new species often produces stress on the food chain or some other aspect of native species' existence. Freshwater ecosystems are very sensitive to poor land-use practices, Poff said, because as low points on the landscape, they accumulate damaging silt and excess nutrients from runoff.

The earth's surface wasn't the only focus of the study. Wall, a professor of rangeland ecosystems and a specialist in soil biodiversity and microscopic invertebrates, said below-ground species, from bacteria to worms, currently are most harshly effected by land-use change.

"That's because soil is usually torn up," she said. "It's taken perhaps a hundred years to form an inch of soil, and whether we're digging a ditch or cultivating a garden, we're disturbing that ecosystem, the habitat for thousands of species."

Of the global change drivers, carbon dioxide levels are probably the hardest to assess in terms of their direct influence on soil biodiversity, Wall said. Nonetheless, the indirect effects through plants of increased carbon dioxide concentrations may be significant, she said.

On land, the researchers found, Mediterranean-climate and grassland ecosystems will probably experience the greatest proportional change in biodiversity because all five factors affect them. Northern temperate ecosystems will likely experience the least biodiversity change, primarily because they've already been so extensively affected by major land-use change. The most land-use change will occur in tropical forests and the temperate forests of South America and the least in arctic and alpine biomes.

Climate change will affect high latitudes the most. It will produce the fewest changes in the tropics and have intermediate effects in other biomes. Nitrogen deposition is greatest near northern cities in temperate zones and least in the arctic and southern temperate forests. Overall, land-use change seems to be the dominant driver, although in some biomes land-use and climate change have relatively little effect. In freshwater systems, land-use change has the most effect on rivers, while biotic exchange has the most affect on lakes. However, Poff said, this knowledge suggests directions biodiversity is to be preserved to the greatest extent possible.

"The hopeful message from this is that if we care about biodiversity, we can examine land-use, help mitigate climate change and save species," he said.