What types of forests are there?
Old-growth forest: Original forests that have not been disturbed for logging, road building, or development• Sometimes called primary,
ancient, virgin, or primeval forests
• 36% of world’s forest• High biodiversity
Second-growth forest:
Area which has re-grown after a major disturbance such as fire, insect, or timber harvest
60% of world’s forest
Happens by natural “succession” -small shrubs and trees followed by the larger trees
Forests Vary in Their Make-up, Age, and Origins
Tree plantation (tree farm): Planted stands of a particular tree species that are maintained, harvested, and replanted• Typically used for paper or particle board
Forests Vary in Their Make-up, Age, and Origins
What are forests good for?
Estimated annual value:
Economic services
$1.8 trillion
Ecological services
$4.7 trillion
Three major tree harvesting methods:• Selective cutting• Clear-cutting• Strip cutting• Seed tree/shelterwood
How are trees cut?
Selective Cutting:• Mature trees are
harvested individually from diverse forests
• Younger trees left to harvest later
• Reduces crowding• Removes diseased trees• Encourages growth of
younger trees
Selective cutting
Clear-cutting
Clear-cuttingClear-cutting::• Removing all trees Removing all trees
in a single pass.in a single pass.
Strip-cutting
Strip-cuttingStrip-cutting::• A type of clear cutting that A type of clear cutting that
involves clear trees along involves clear trees along the contours of the land.the contours of the land.
• Less erosionLess erosion
Other ways forests can be destroyed
Forest fire
Insect damage (mountain pine beetle in BC)
Disease (Dutch elm disease in Ottawa)
Forest fires can either benefit or harm forests• Burn away flammable ground material• Prevent larger, more destructive fires• Release valuable mineral nutrients• Stimulate new forest growth
Fire Can Threaten Forest Ecosystems
Surface fires• Usually burn leaf litter and undergrowth• May provide food in the form of vegetation that sprouts after fire
Crown fires • Extremely hot, burns whole trees, jump from treetop to treetop• Fierce and hard to control
Forest fires continued
Issues in forestry
Human activities have reduced the earth’s forest cover by as much as half.
Deforestation – temporary or permanent removal of large areas of forests• Results from unsustainable cutting of trees
Where is deforestation an issue? Developing countries – used for fuel, wood in tropical
forests used by international logging companies
Developed countries – boreal forests used for timber and paper
Unsustainable Logging is a Major Threat to Forest Ecosystems
Building roads into previously inaccessible forests paves the way for increased erosion, habitat fragmentation, loss of biodiversity, and invasion by non-native species.• For this reason, many federal wilderness areas do
not allow the construction of roads.
Poor soil in tropical forests
Run-off
Not much can grow after gain
Tropical Forests Are Disappearing Rapidly