ENVIRON 102 Chapter Notes - Chapter 14: Insular Biogeography, Carbon Cycle, Soil Fertility
10 May 2018
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Chapter 14: Forests (all)
14.1 The Values of Forests
Ecosystem Services: Forests prevent floods and provide clean water, recreation, and inspiration.
Forest ecosystem services (not monetized but are extremely valuable)
o Purify and regulate water
o Withdraw and store carbon from the atmosphere
o Conserve biological diversity
o Primary habitat for 60-80% of all terrestrial species
o Source of beauty and inspiration to humans
▪ Ecotourism
Play a role in the hydrologic cycle
o Roots absorb large quantities of water and evaporates via the leaves (transpiration)
o Forest litter slows the flow of water across land
Forests store a lot of carbon
o Process of photosynthesis – plants remove carbon dioxide from the atmosphere
o Amount of carbon stored reduced by deforestation
Wood Products: The woods extracted from Earth’s forests is primarily used for fuel, paper, and building
materials.
Wood consumption – 53% for fuel, 31% for construction and wood products, and 16% for paper
Fuel from wood
o Burned into fuel or made into charcoal
o Only provides about 7% of energy for humans
o Burned to heat homes for developing countries
o Charcoal is more effective than wood
▪ Produces 2 times more heat
▪ Not impervious to termites
▪ Releases less smoke but does release pollutants (ex: carbon monoxide)
Building materials and solid wood products
o Most wood is harvested from old-grown trees
Paper production
o Wood cut into small chips, chemically digested (by lignin) into pulp
o Fibers are washed, dried, and then pressed into large roles of paper
o Significant impact on air and water quality
o Easy to recycle paper
Non-Wood Forest Products: Hundreds of non-wood commodities come from forests.
Non-wood commodities – over $17 billion in international trade
o Ex: honey, gum, rattan and bamboo, cork, forest nuts, mushrooms, essential oils, and raw
materials that make pharmaceuticals
14.2 Forest Growth
Three levels of forest growth – individual trees, communities of trees called forest stands, large
forested landscapes
The Life History of a Tree: Wood supports the vertical growth of trees.
(1) Seed: embryo embedded in nutritive tissue ad surrounded by a protective coat
o Trees classified by type of seed:
▪ Conifer seeds grow in cones
▪ Angiosperm seeds grow in flowers and are eventually surrounded by fruit
(2) Seed is mature, disperses, and germinates
o Seed germinates: shoot extends up from seed and roots grow into soil
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▪ Primary growth: upward and downward growth from rapid cell division
o Carbohydrates for germination comes nutritive tissue in seed
(3) Carbohydrates for continued growth comes from photosynthesis in leaves
o Phloem: thin layer of specialized tissue that transports carbohydrates down the stem to the
roots
(4) Tree roots absorb water and mineral nutrients from soil and transport them up stem through
xylem (specialized tissue)
o Growth by additional layers of xylem that causes increase in diameter – secondary growth
The Life History of a Forest Stand: Communities of trees develop through four stages that differ in structure
and species composition.
After a disturbance, forest goes through 4 stages of succession
(1) Establishment stage: tree seedlings germinate on the recently cleared ground
o Quick growth because of abundance of light and soil resources
o Growing trees begin to close in on one another – creates canopy of shade
o Competition causes some trees to die and other trees more slowly
(2) Thinning stage: largest trees continue to grow and total biomass in forest continues to increase
but number of trees decrease
o Trees are more widely spaced and even-aged
(3) Transition stage (aka gap phase): increased light and reduced competition for soil resources
allow tree seedlings to become established in the gaps
o Diversity of ecosystem increases – growth of shade-tolerant trees
o Uneven-aged
(4) Old-growth stage: large, old trees and abundant standing and fallen woody debris
o Diversity of herbs and animals – rich soils, favorable moisture, temperature
Succession in tropical climates – less than 5 years
o Longer in temperate evergreen and deciduous forests
o Cooler climates – may take several hundred years
The Life History of a Forested Landscape: Landscapes are a mosaic of patches representing different stages
of forest stand development.
More biodiversity in transition and old-growth forests
Net primary production and other ecosystem processes determined by arrangement and relative
abundance of patches in different stages
o Patches in establishment stage
▪ Store little carbon, lower net primary production
▪ May be subject to erosion and nutrient loss
o Stands in the thinning stage
▪ Trees rapidly taking up nutrients; increasing storage of carbon
▪ High net ecosystem production
Minimum dynamic area: area necessary to maintain all different patch types and populations of
their associated species, given the typical patterns of disturbance
Irregular disturbances – large minimum dynamic area
Regular disturbances – small minimum dynamic area
14.3 Deforestation
Deforestation: the removal of forest cover to an extent that allows alternative land uses
o Humans replace a forest with something else
Historical Change: The pace of deforestation is quickening.
Between 2000 and 2010, about 130,000 km3 was deforested
o Annual net loss of 52,000 km3 taking into account replanting artificially/naturally
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Ecosystem services: forests prevent floods and provide clean water, recreation, and inspiration. Play a role in the hydrologic cycle. Wood products: the woods extracted from earth"s forests is primarily used for fuel, paper, and building materials. Wood consumption 53% for fuel, 31% for construction and wood products, and 16% for paper. Building materials and solid wood products: most wood is harvested from old-grown trees. Paper production: wood cut into small chips, chemically digested (by lignin) into pulp, fibers are washed, dried, and then pressed into large roles of paper, significant impact on air and water quality, easy to recycle paper. Non-wood forest products: hundreds of non-wood commodities come from forests: ex: honey, gum, rattan and bamboo, cork, forest nuts, mushrooms, essential oils, and raw. Non-wood commodities over billion in international trade. Three levels of forest growth individual trees, communities of trees called forest stands, large. The life history of a tree: wood supports the vertical growth of trees.
