Page 661 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 19 ecosystem essentials 625
▲Figure 19.1.2 Native grasses after a prescribed fire, South Africa. impala graze on the new grasses a year after a prescribed fire in kruger national Park in 2010. [navashni govender, SanParks/ naSa.]
▲Figure 19.1.3 Prescribed burn, Algonquin Provincial Park, Ontario. Prescribed burns help to maintain integrity of this ecosystem in the Boreal forest. [Janet Foster/getty images.]
Today, following the principles of fire ecology, fire specialists worldwide use controlled ground fires, deliber- ately set to prevent undergrowth ac- cumulation and maintain ecosystem health. These controlled “cool fires” remove fuel and prevent catastrophic and destructive “hot fires” that burn through the forest crown. in grasslands, frequent fires prevent the growth of woody species that would compete for light, moisture, and other resources. Scientists and forest managers use pre- scribed burns in grasslands to control invasive species and restore natural habitat (Figure 19.1.3).
Wildfire and Climate Change
With ongoing climate change, the wildfire threat is worsening. Scientists have linked record wildfires in the western United States since 2000 to increased spring and summer temperatures and an earlier spring snow- melt. Perhaps more important is the fact that these climatic changes are occurring after 150 years or more of fire suppression across the United States. lightning-caused fires related to more intense weather systems are also on the increase in some regions. in June 2013, the West Fork Complex fire, ignited by lightning, burned explosively through the rugged terrain of southwest Colorado, fuelled by forests
desiccated from drought and from exten- sive die-off caused by spruce beetle.
The destruction caused by wildfires
is increasing as urban development en- croaches on forests, putting homes at risk and threatening public safety. in 2013, the most destructive fire in Colorado’s history burned over 500 homes north of Colorado Springs. Wildfires have devas- tated communities in southern California, especially those developed in the “wilds” of chaparral country. in 2007, fire de- stroyed more than 2000 homes in that region and burned over 200 000 acres
in two dozen wildfires. This is part of the overall pattern continuing today.
▲Figure 19.18 Primary succession. Plants establishing on recently cooled lava flows from the kıˉlauea volcano in Hawai‘i illustrate pri- mary succession. [Bobbé Christopherson.]
animals having niches that differ from those of the pre- vious community colonize the area; species assemblages may shift as soil develops, habitats change, and the com- munity matures.
Most of the areas affected by the Mount St. Helens eruption and blast in 1980, which burned or blew down about 38450 hectares of trees, underwent secondary suc- cession (Figure 19.19). Some soils, young trees, and plants were protected under ash and snow, so community de- velopment began almost immediately after the event. The areas completely destroyed near the Mount St. Helens volcano and those buried beneath the massive landslide north of the mountain became candidates for primary succession.
Traditionally, communities of plants and animals were thought to pass through several successional