Other ways we MESS with the Land!

1. Overgrazing

• When livestock eat too much plant cover on rangelands, impeding plant regrowth

• The contrast between ungrazed and overgrazed land on either side of a fenceline can be striking.

Figure 8.22

Overgrazing

• Overgrazing can set in motion a series of positive feedback loops.

Figure 8.21

Overgrazing• Livestock graze on grasslands and cleared forest slopes– 65% of drylands are grasslands

• Land is often overgrazed– Barren land is eroded and degraded

• In the 1800s American buffalo (bison) were slaughtered– Rangelands stocked with cattle were overgrazed– Leading to erosion and growth of unpalatable plants

• U.S. western rangelands produce less than 50% of the forage they produced before commercial grazing– Yet 20% of rangelands remain overstocked

Degraded rangelands• The National Public Lands Grazing Campaign

documents harmful effects of livestock grazing – Competition of livestock with native animals for food– One-third of endangered species are in danger due to

cattle-raising practices (predator control, fire suppression)

– Wooded zones along streams are trampled and polluted– Polluted streams make fish species the fastest-

disappearing wildlife group• Desertification impacts 85% of North America’s

drylands– The most widespread cause is livestock grazing

Public lands• Overgrazing occurs because rangelands are public

lands– Tragedy of the commons: the incentive is for all to keep

grazing, even though the range is being overgrazed• The U.S. Bureau of Land Management (BLM) and

Forest Service leases grazing rights on 2 million km2 of land– Federal land is owned by taxpayers– Animal unit = one cow-calf pair or five sheep– The grazing fee ($1.35/animal unit/month) is 10% what

would be paid on private land

Why are rangelands overgrazed?• The 1934 Taylor Grazing Act prohibits reducing

grazing levels or keeps grazing fees below market level– The U.S. government lost $115 million in 2004– $500 million more was lost in ecological costs (to

watersheds, streams, wildlife, endangered species)• When Congress and the BLM try to raise fees,

western congressmen threaten to cut the BLM budget

Solutions to overgrazing• Better management could restore rangelands– Benefiting wildlife and cattle production

• Conservation Stewardship Program (NRCS)– Provides information and support to land-owning ranchers to

burn woody plants, reseed land, rotate cattle• The government could buy up some of the 26,000

permits– Retire rangelands– Generously pay ranchers for their permits– Use the land for wildlife, recreation, watershed protection

2. Deforestation• Porous, humus-rich forest soil efficiently holds and

recycles nutrients– Also absorbs and holds water

• Converting a forested hillside to grassland doubles the amount of runoff and increases nutrient leaching

• When forests are cut and soils are left exposed– Topsoil becomes saturated with water and slides off

the slope– Subsoil continues to erode

Forests are cut at alarming rates• 13 million hectares (32 million acres) are cut per year– Mostly in developing countries

• Cutting tropical rain forests causes acute problems– Heavy rains have leached soils of minerals– Parent material is already maximally weathered– So tropical soils (oxisols) lack nutrients

• Clearing rain forests washes away the thin layer of humus– Leaving only the nutrient-poor subsoil– Very poor for agriculture

Animal agriculture: Livestock and poultry

•Consumption of meat has risen faster than population over the past several decades.

Figure 9.15

3. Feedlot agriculture•Increased meat consumption has led to animals being raised in feedlots (factory farms), huge pens that deliver energy-rich food to animals housed at extremely high densities.

Figure 9.16

Feedlot agriculture: Environmental impacts

•Immense amount of waste produced, polluting air and water nearby

•Intense usage of chemicals (antibiotics, steroids, hormones), some of which persist in environment

•However, if all these animals were grazing on rangeland, how much more natural land would be converted for agriculture?

Food choices = energy choices

•Energy is lost at each trophic level.

•When we eat meat from a cow fed on grain, most of the grain’s energy has already been spent on the cow’s metabolism.

•Eating meat is therefore very energy inefficient.

Grain feed input for animal output

•Some animal food products can be produced with less input of grain feed than others.

Figure 9.17

Land and water input for animal output

•Some animal food products can be produced with less input of land and water than others.

Figure 9.18

4. Aquaculture

•The raising of aquatic organisms for food in controlled environments

•Provides 1/3 of world’s fish for consumption

•220 species being farmed

•The fastest growing type of food production

Aquaculture

•Fish make up half of aquacultural production. Molluscs and plants each make up nearly 1/4.

•Global aquaculture has been doubling about every 7 years.

Figure 9.19

Benefits of aquaculture•Provides reliable protein source for people, increases food security

•Can be small-scale, local, and sustainable

•Reduces fishing pressure on wild stocks, and eliminates bycatch

•Uses fewer fossil fuels than fishing

•Can be very energy efficient

Environmental impacts of aquaculture•Density of animals leads to disease, antibiotic use, risks to food security.

•It can generate large amounts of waste.

•Often animals are fed grain, which is not energy efficient.

•Sometimes animals are fed fish meal from wild-caught fish.

•Farmed animals may escape into the wild and interbreed with, compete with, or spread disease to wild animals.

Environmental impacts of aquaculture

•Transgenic salmon (top) can compete with or spread disease to wild salmon (bottom) when they escape from fish farms.

Figure 9.20

Highly efficient

High yield in smallvolume of water

Increased yieldsthrough cross-breeding and genetic engineering

Can reduce over-harvesting of conventional fisheries

Little use of fuel

Profit not tied to price of oil

High profits

Advantages

Large inputs of land, feed, And water needed

Produces large and concentrated outputs of waste

Destroys mangrove forests

Increased grain productionneeded to feed some species

Fish can be killed by pesticide runoff from nearby cropland

Dense populations vulnerable to disease

Tanks too contaminated touse after about 5 years

Disadvantages

Trade-OffsAquaculture

5. Fish Harvesting

Spotter airplane

Fish farmingin cage

Trawlerfishing

Purse-seinefishing

sonartrawl flaptrawllines

trawl bag

Long line fishing

lines withhooks

Drift-net fishing

fish caughtby gills

float buoy

fish school

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World Fish Catch Per Person

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Problems and consequences• Problem

– Overgrazing

– Water Pollution• Slaughter• Wastes• Riparian grazing

– Land use• Fencing, deforestation

– Uses more water

• Consequence– Desertification, erosion nutrient loss

– Groundwater contamination, ^BOD, Eutrophication, etc

– Habitat loss & fragmentation, decreased biodiversity

– Water shortages / depletion