Chapter 10: Forest Ecosystems

In Order to Grow a Forest

  • Temperature- some trees are cold adapted and some are not
  • Air (carbon hydrogen, oxygen, nitrogen)- the need of clean air is required for trees
  • Light (photosynthesis)
  • Water
  • Soil

Forests Create, Store and Mobilize Nutrients and Water

They are living just like humans

  • Photosynthesis
  • Mycorrhizal associations
  • Soil interactions
  • Nutrients
  • Transpiration stream

Photosynthesis

  • In the presence of light and energy, we have a carbon capture which is converted into glucose, which is converted into other chemicals through water

Fungal Symbiosis

Mycorrhizae: They are specific type of fungi that form associations with plants. This is an important symbiosis for forests to be dominant

  • Symbiotic relationship between plants and fungi
  • Plants get increased surface area for nutrient absorption; fungus gets carbohydrates
  • Mycorrhizae critical to plant success; productivity
  • Benefit for plants is that the fungus increases the surface for absorption, which is why a lot of nutrient and water can be absorbed by the plant. In return, the fungus gets carbon compounds
  • Fungi cannot photosynthesis, but they get benefit by providing this surface increase by getting carbon compounds
  • Ectomycorrhizae: fungus forms a sheath around root

Transpiration Stream

A Necessary evil

  • To transport water, water must be lost- plants open up to gain water, however, at the same time they lose water from their leaf.
  • Capillary action= moves H20 2-3m
  • Rest= evaporation
  • When we deforest an area, it contributes to climate change
  • It affects the water flow in the specific area, and a huge change in temperature regulation etc

Mature forests are complex ecosystems because they create microclimates and microenvironments for the plants underneath them

Trees Provide Many Ecological Services

  • Trees have crucial link in nutrient and water cycles
  • They stabilize soil and prevent erosion
  • Trees slow runoff and lessen or prevent flooding
  • They store carbon, release oxygen, and moderate climate

Forests are Economically Valuable Because They Provide Benefits Such as Fuel, Shelter, Transportation (ships), Paper

  • Softwood= timber harvested from coniferous trees
  • Hardwood= timber which is harvested from deciduous trees
  • NTFPs= non-timber forest products, such as medicinal, herbal, decorative, and edible products
  • Forests are home to many people today, especially to indigenous people
  • In conclusion forests are really important and we need to understand more about them and preserve them

Forests are defined partly on the basis of their structure: Closed (trees are together) vs. open canopy (trees wide apart from each other)

3 Major Types of Forest Biome

Boreal (taiga) Forest

  • They are fairly dry. They experience cold winters. They have low precipitation because most of the water gets locked up in winter. Their soil is very shallow and acidic because soil processes are very slow.
  • Vegetation in boreal forests is usually conifers or mosses
  • Boreal forests are closed canopy
  • They are conifers which make them cold tolerant
  • They have low light penetration: understory limited
  • They depend heavily on mycorrhizae (fungi)
  • Boreal forests tend to make the ground very acidic

Tropical Rainforest

·        Forests which are very diverse with species

  • They have relatively constant temperature and no freezing temperatures
  • They have annual rainfall of 2-3m
  • They have extremely high productivity
  • They consist of variation degree of seasonality
  • They have high light penetration unlike Boreal forests
  • Their canopy is multilayered, continuous; little light penetration
  • Tropical rain forest compete intensively for light; vines, epiphytes, bromeliads
  • Tropical rainforest have soil which is very nutrient-poor and acidic
  • They have rapid decomposition(rotting); rapid leaching (downward movement of soils) (laterite soils)

Since most primary production is in canopy, most species are canopy specialists; unlike in other biomes, most mammal herbivores are arboreal in these forest

Temperate deciduous forests

  • They are mid-latitude forests which are usually located in Europe, eastern China, and eastern North America
  • Deciduous trees- they lose their leaves each fall and remain dormant (undeveloped) during winter
  • They have seasonal variation
  • The precipitation for deciduous forests is more than boreal forests, but less than tropical rain forests
  • Soil is fertile (rich) and has organic material because in deciduous forests, decomposition (rotting) is slow. Decaying litter
  • Canopy: it allows some light to penetrate; well-developed understory
  • Forests today have become very vulnerable to logging, which is affecting the environment by cutting down trees.
  • MacMillan Bloedel organization responded to this with reforms
  • They phased out clear-cutting because clear-cutting is very damaging to the ecosystem
  • There was a commitment to try to protect old-growth
  • They did selective logging to preserve where forest habitats and streams were
  • They invited scientists to monitor progress so that they can make report and see change. Able to help and indicate what’s good and bad through reports
  • They developed non-timber sources of revenue such as tourism, other forest products and carbon offsets (trading of carbon offset in the global market)

Deforestation is not new because it’s a principle form of land conversion. In the earlier days, it was common to clear forests for farmers, which is considered one of the first human environmental impacts. Deforestation is visible for thousands of years, even during civilization. Deforestation for agriculture purposes back in the day

Deforestation has Proximate and Root Causes

Proximate: Mechanism causes

  • Slash-and-burn agriculture
  • Clearcut logging- mechanism by which you deforest
  • Pollution- a lot of forests are dying due to pollution which is caused by mechanism
  • Fuelwood use

Ultimate (root): Main causes 

  • Poverty
  • Debt
  • Bad policies
  • Environmental change
  • Agriculture is the major cause of conversion of forests
  • Swidden agriculture also known as slash and burn agriculture which support only a couple of years of crop production; they are abandoned later on to restore fertility
  • 7 years are required to replenish soil in original clearings to support crops or forests
  • It is bad to deforest tropical forests because their biomasses are the major storage area of nutrients, rather than soils. Therefore when you cut down tropical forests, there is not much of support by the soils which do not have nutrients. Since there are no nutrients in the soil but are in the biomass, they cannot support the rain forest
  • Deforestation in temperate area is not as problematic because their nutrients are stored in the soils. If trees are cut in temperate forests, they tend to generate faster than rainforests
  • Deforestation is proceeding rapidly today in many developing nations because of its economic benefits

Plantation Forestry has Grown in North America

  • Reforestation is the planting of trees after logging
  • Afforestation is the planting of trees in areas which haven’t been forested for a long time
  • Even-aged trees are all trees that are the same age

Timber Harvesting

  • Pros of clear cutting is that it is cost-efficient
  • Cons of clear cutting is that it destroys age structure which is crucial (this links back to population where there are age pyramids and how they describe population of not only people, but trees as well. Because there is only old age population and not young, it will be hard to replenish the age structure without younger trees), ecosystem functions, and tends to lead to erosion
  • Rather than cutting down trees in the same agriculture and age, it is better to do it selectively, thus leading to selective harvest
  • Pros of selective harvest is that it can mimic natural disturbance and maintains ecosystem function and resilience (toughness)
  • Cons of selective harvest is that it is expensive
  • Shelter woods help the growth of smaller trees, which is why people tend not to cut them

Maximum Sustainable Yield:

  • MSY (maximum sustainable yield) refers to maximum resource extraction without reducing the resource
  • Populations grow most rapidly at an intermediate (middle) size
  • Population size has to be maintained below carrying capacity
  • In the graphs above, the growth rate is slow when there are not many individuals
  • The rate slows down because it is getting to carrying capacity as it is running out of resources
  • Half way of carrying capacity is when the population grows the fastest because there are a lot of individuals reproducing even when there are resources running out. Therefore, being in half of the carrying capacity in an environment is the best place for growth of population

Adaptive and ecosystem-based management are guiding principles for managing the harvesting of resources, in order to minimize impacts on ecosystems and ecological processes.

  • Adaptive management is when:
  • You access and design a management scheme for harvesting resources
  • You implement that design and monitor it
  • You let other scientists evaluate this design, and make adjustments according to these evaluations. Then you access your design again
  • Fire suppression allows fuel accumulation (suppression of fire allows fuel to build up)
  • Climate change and housing development near forests increase fire risk (development of houses near forests and climate change increase the risks of fires)
  • Prescribed burns are burning areas of forests under careful controlled conditions to reduce built-up fuel loads
  • Sustainable forestry has started to gain ground today
  • Sustainable forestry certification: only products which are produced sustainably can be certified

Habitat protection can be compatible (friendly) with sustainable human activities (it is not impossible to have sustainable activities because we can harvest our forests and we can manage our ecosystems)

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