Transcript Document
Temperate Forests Temperate forests are found primarily in North America and Eurasia. Successional Dynamics In temperate forests, ecological succession is a critically important factor in determining biodiversity. What is biotic succession? Ecosystems undergo fundamental changes during the successional process. Early in succession, nutrients may decline in the soil. Colonization by plants may move slowly. When coverage is more or less complete, biomass may accumulate more rapidly. During this period, nutrients also accumulate rapidly. Late in the successional process, nutrients may be tied up in dead plant material and less available to the ecosystem. Species composition of plants and animals may change dramatically during succession. Generally, the greatest diversity is found during the middle stages. Under some conditions, particularly when major disturbances are rare, “oldgrowth forests” can develop. Many specialized animal species, like the northern spotted owl, are found in oldgrowth forests. This makes them a particularly critical habitat, and the subject of many debates regarding conservation. Spotted owls have a home range of 800 to 2000 hectares in old-growth forests. Old-growth timber is valued at over $10,000 per hectare. So, preserving habitat for 500 pairs of owls involves how much timber? About $4 billion dollars worth If successional changes bring large changes in the dominant species, there are often species that are adapted to different stages of the successional process. Organisms that are adapted to particular successional stages often have distinctive characteristics. Early Successional Species Mule deer – Odocoileus hemionus Late Successional Species Woodland caribou Rangifer tarandus Early Successional Species Ruffed grouse – Bonasa umbellus Late Successional Species Spruce grouse – Canachites canadensis Early Successional Species Mourning dove – Zenaida macroura Late Successional Species Passenger pigeon – Ectopistes migratorius Human Impacts Logging Conversion to other use Fragmentation Invading species Overprotection of ungulates Air pollution Virtually no virgin deciduous forests remain, and most coniferous forests have been cut one or more times. Managing Succession Must consider: 1. Amount of habitat in different stages. 2. Size and location of areas in these stages. 3. Nature and intensity of human use. Many species require habitat in late successional stages. Red-cockaded woodpecker requires large pine trees, infected by a type of fungal disease called “red heart” disease. This disease enables the woodpecker to excavate nest chambers. Requires special management practices. Managing Fire Relationships In many areas, protecting forests from fires has led to dramatic changes in the nature of the forest. In many areas, the policy is now to allow natural fires to burn. (Let Burn Policy) Klamath National Forest - Fire and Aviation, Wildland Fire Use This policy backfired in Yellowstone National Park in 1988. Forest fires burned about 36% of the Park and surrounding areas. $125 million was spent trying to stop the fires. Global climate changes may have dramatic effects on distribution of temperate forests. An exam question: What do you think the criteria should be for determining how much old-growth forest is preserved in western North America?