Climate extremes




 

 

It seems appropriate that the new year brings a deluge of rainfall. The rain washes away last year’s buildup of debris. Oncestagnant and dry creek beds flood with runoff and ensure the land is scoured.

At the same time, rain prepares the soil for new growth. Seeds deposited in late summer and autumn settle deeper into the soft earth, ready for germination when the right conditions manifest. Southern California’s winter storms hold the potential for both destruction and life.

The Santa Monica Mountains’ Mediterranean climate, which brings the winter’s torrents of rain and cool, mild temperatures to the area, is also responsible for the blazing hot summers, with many months devoid of precipitation.

While these extremes seem contrary to the often-heard advice to live in moderation, Mediterranean climates offer habitats filled with a wide variety of plant and animal species.

Only five Mediterranean climate regions exist, each on the edge of a continent near large bodies of water lying between 30 and 40 degrees latitude. Although these five regions cover only 2.25 percent of the world’s land area, they contain at least 16 percent of the Earth’s plant species.

Worldwide there are 25 recognized ecological hotspots—areas known for their rich species diversity, which is considered of critical global importance. Species that exist in these areas occur nowhere else and are threatened by human development.

Many of these hotspots lie within the zone of tropical rain forests. All five Mediterranean climatic zones fall under the hotspot designation. In proportion to the amount of land they cover, these five zones have a greater significance in the protection of global biodiversity than the entire Amazon basin and other rain forests.

Mediterranean mystique

Besides the coastal region of California, the Mediterranean climate zones are in central Chile, the Mediterranean Basin, the Cape region of South Africa and southwestern Australia. Each of these zones, with the exception of the Mediterranean Basin, is on the western side of a continent, and all of them are associated with subtropical high-pressure cells of corresponding oceans.

In the summer these highpressure cells shift poleward. The shift causes dry, sinking air to cap the surface of the marine layer, making rainfall nearly impossible and creating warm, dry summers. In the winter months, these subtropical high-pressure cells shift toward the equator, bringing rain to the Mediterranean regions and snow to high elevations.

This winter phenomenon is responsible for almost all of the year’s rainfall in these zones.

In addition to creating unique weather patterns, the high-pressure shifts play a role in the formation of the world’s deserts. Each of the Mediterranean regions is associated with a poleward desert; California’s Mediterranean region is linked to the Sonoran Desert of the southwestern United States and Mexico’s Baja California.

Learning to adapt

Although scattered around the world thousands of miles apart, all Mediterranean regions share similar characteristics. Organisms exposed to the same environmental conditions develop corresponding traits through a process called convergent evolution.

Dominant in these regions are dense evergreen shrubs with small, hard leaves. The waxy, thick, leathery leaves allow Mediterranean plants to deal with summer drought conditions and protect the plants from herbivores. In addition, these plants have a deep taproot system so they are photosynthetic year-round.

In California this region is called chaparral, in Chile “ mattoral,” in South Africa “fynbos,” in the Mediterranean Basin “maquis” and in Australia “mallee” or “kwongan.”

The habitat that embraces the deluge of winter rain is also adapted to fire tolerance. Chaparral shrubs have developed a system of recovery after their topsides have burned.

New shoots sprout from live root crowns buried underground. Another adaptation are seeds that won’t germinate unless they are stimulated by the heat of fire.

While the conditions seem inhospitable, the plants and animals of Mediterranean climates—specifically the Santa Monica Mountain chaparral—have found a home here. Rather than fighting weather extremes, they have adapted to both drought and downpour.

Perhaps in this new year we too can find a way to embrace those things that seem most uncomfortable and transform them into things most beneficial.

Meghan Walla-Murphy can be reached at the following e-mail: phoksumdo@yahoo.com.


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