Unit 5 – Land and Water Use

AP Environmental Science (APES)

18-19 Class Periods

10-15% AP Exam Weighting

5.1 The Tragedy of the Commons

Overview

The Tragedy of the Commons is a concept describing how individually rational people acting in their own self-interest can deplete a shared resource, ultimately harming everyone. Named by ecologist Garrett Hardin (1968), this principle explains why common resources (fisheries, forests, groundwater, atmosphere, rangelands) are often overexploited despite everyone benefiting from their sustainable use.

For the AP Environmental Science exam, you must understand why this occurs, provide examples, and recognize solutions to prevent commons depletion.

Why Does Tragedy of the Commons Occur?

Individual Incentive vs. Collective Good

The Problem: Each person gets full personal benefit from exploiting the resource, but the cost of degradation is shared among everyone.

Example - Shared Pasture: If a rancher adds one more cow, HE gets the benefit of that cow's milk/meat, but the cost of overgrazing is spread among all users. Result: everyone adds more animals until pasture is destroyed
Example - Fishery: Fisher who catches more fish gets more profit, but depletion affects all fishers equally. Result: fish populations crash as everyone overfishes
Example - Atmosphere: Corporations that pollute save money on cleanup, but air pollution affects everyone. Result: atmospheric CO₂ keeps rising

Key Features of Commons Depletion

Open Access: No owner; anyone can use the resource
Nonexcludability: Difficult/impossible to prevent others from using
Limited Supply: Resource is finite; overuse reduces availability
Rational Individual Behavior: Each person rationally acts to maximize personal benefit
Collective Irrationality: Result is catastrophic for everyone

Real-World Examples

Fisheries: Overfishing has collapsed major stocks (Atlantic cod, bluefin tuna); fish populations crash despite everyone losing livelihood
Groundwater Aquifers: Farmers pump aquifers faster than recharge rate; water table drops; wells run dry; everyone loses water access
Forests: Open-access forests are clearcut by anyone with chainsaw; forest disappears despite everyone wanting trees
Atmosphere (Climate): Each nation/company burns fossil fuels for profit; costs of climate change shared globally; CO₂ keeps rising
Rangelands: Herders add more animals to maximize profit; overgrazing destroys pasture; desertification; entire ecosystem collapses
Wildlife: Passenger pigeons hunted to extinction; some whale species nearly extinct; bison nearly exterminated

Solutions to Prevent Commons Depletion

Privatization: Convert common resource to private property; owner has incentive to manage sustainably (works for some resources but not all)
Government Regulation: Set quotas, licenses, hunting seasons; enforce limits through penalties (fishing quotas, hunting licenses)
Community Management: Local groups self-regulate commons (community forests, water user associations)
International Agreements: Treaties and protocols to manage shared resources (CITES for endangered species, Montreal Protocol for ozone, whaling moratoriums)
Economic Incentives: Carbon taxes, cap-and-trade systems, payments for ecosystem services
Technology: Monitoring systems, enforcement technology, sustainable alternatives
Education/Culture: Shift values toward sustainability and long-term thinking

⚠️ Common Pitfall: Don't confuse "common resource" with "government property." Commons are UNOWNED or SHARED, not state-owned. The tragedy occurs because of open access and lack of individual responsibility. Solutions vary by resource type - what works for fisheries may not work for atmosphere. Privatization doesn't work for global commons (atmosphere, oceans).

5.2 Clearcutting

Overview

Clearcutting is a harvesting method where ALL trees are removed from a forest in one operation, leaving bare ground. It's the most profitable but most damaging timber harvest method. Understanding clearcutting impacts is crucial for Unit 5 as it exemplifies unsustainable land use with major ecological and economic consequences.

For the AP Environmental Science exam, you must know the process, its environmental impacts, economic benefits, and sustainable alternatives.

What is Clearcutting?

Process

All trees removed regardless of size or species
Entire forest canopy stripped in one operation
Heavy machinery compacts remaining soil
Slash (branches, bark) often burned or left to rot

Why Use Clearcutting?

Most Profitable: Maximizes timber volume harvested per hectare; minimizes labor costs
Most Efficient: Fastest way to harvest; large equipment can work quickly
Short-Term Gain: Companies maximize immediate returns; little concern for long-term sustainability
Easy Access: No need for selective harvesting expertise

Environmental Impacts of Clearcutting

Soil Erosion: Exposed soil washes away in heavy rains; topsoil loss reduces fertility for regrowth
Water Pollution: Sediment-laden runoff clouds waterways; covers stream substrate smothering aquatic life
Habitat Loss: Destroys shelter for wildlife; fragmentation isolates populations; many species require forest interior
Biodiversity Decline: Loss of plant diversity; collapse of associated insect, bird, mammal populations
Hydrological Changes: Increased runoff, flooding, stream scouring; reduced infiltration; lower water table; drought stress on remaining plants
Nutrient Loss: Removal of biomass takes nutrients; ash from slash burning can acidify soil
Microclimate Changes: Loss of shade increases temperature extremes; wind damage to remaining vegetation
Carbon Release: Reduced carbon sequestration; decomposition of slash releases CO₂

Recovery After Clearcutting

Pioneer Species: Fast-growing, shade-intolerant species colonize first (weeds, grasses, shrubs)
Mono-Plantations: Often replanted with single species (often non-native) instead of diverse native forest
Long Recovery: Can take 200+ years for old-growth forest characteristics to return; often never fully recovered
Perpetual Fragmentation: Rotation cycles (30-40 years) mean forest never reaches maturity; never regains old-growth characteristics
Loss of Old-Growth: Species requiring old-growth forests (spotted owls, northern flying squirrels) disappear; entire ecosystems lost

Sustainable Alternatives

Selective Cutting: Remove individual trees or small groups; maintains forest structure and biodiversity
Shelterwood Cutting: Remove trees in stages; provides shade and shelter for regeneration
Variable Retention: Retain 10-30% of forest structure; reduce erosion and maintain habitat
No-cut/Protection: Designate old-growth reserves; protect remaining ancient forests
Reforestation with Native Species: Plant diverse native species instead of monocultures

💡 Exam Tip: Clearcutting is the MOST profitable harvest method but most damaging. Leads to soil erosion, water pollution, habitat loss, biodiversity decline. Takes 200+ years to recover old-growth characteristics (or never). Sustainable alternatives maintain forest while producing timber. Be able to compare environmental impacts of different harvest methods!

5.3 The Green Revolution

Overview

The Green Revolution (1960s-1980s) was a dramatic increase in agricultural productivity due to new technology, crop varieties, fertilizers, pesticides, and irrigation. It prevented global famine and increased food supply, but also created significant environmental problems. Understanding its successes and failures is essential for AP exam questions about agriculture and sustainability.

For the AP Environmental Science exam, you must know the technologies involved, the benefits, the environmental impacts, and regional variations.

Technologies of the Green Revolution

1. High-Yield Crop Varieties (HYVs)

Selective Breeding: Developed crops with higher grain/fruit yield, shorter growing season, disease resistance
Famous Breeder: Norman Borlaug ("Father of Green Revolution"); developed dwarf wheat varieties
Key Crops: High-yield rice, wheat, corn (maize) varieties
Result: Dramatically increased calorie production per hectare; multiple harvests per year possible

2. Synthetic Fertilizers

Nitrogen Fertilizers: Haber-Bosch Process enables mass production of ammonia; allows massive nitrogen application
Phosphorus Fertilizers: Mined from phosphate deposits; applied to supplement soil
Effect: Increased nutrient availability; higher yields; reduced soil depletion from continuous cropping
Problem: Excess runoff causes eutrophication; water pollution

3. Pesticides and Herbicides

Chemical Pest Control: Synthetic pesticides (DDT, organophosphates, pyrethroids) kill crop-damaging insects
Herbicides: Chemical weedkillers increase crop yield by reducing competition
Effect: Dramatically increased yields; reduced crop losses to pests
Problems: Pesticide resistance, bioaccumulation, nontarget species killed, ecosystem disruption

4. Irrigation Technology

Water Management: Dams, canals, pumps; enables agriculture in semi-arid regions
Multiple Cropping: Reliable water supply allows 2-3 harvests per year instead of one
Effect: Turned marginal lands into productive agricultural areas
Problems: Aquifer depletion, salinization, water conflicts, ecosystem degradation

Success and Positive Impacts

Prevented Famine: Averted global food crisis predicted by 1960s; fed billions of additional people
Increased Yields: 2-3x increase in crop production; more food per hectare
Reduced Hunger: Lower food prices; more people have access to adequate nutrition
Economic Development: Increased agricultural surplus enabled investment in other sectors
Preserved Forests: By increasing productivity on existing farmland, reduced need to clear additional forests (though this benefit is debated)
Poverty Reduction: Economic growth from agricultural surplus helped lift people out of poverty

Negative Environmental Impacts

Soil Degradation: Monocultures deplete soil; erosion increases; organic matter declines
Water Pollution: Excess fertilizer runoff causes eutrophication; pesticide contamination
Aquifer Depletion: Over-irrigation drains groundwater faster than recharge (Ogallala Aquifer, Indus River)
Biodiversity Loss: Monocultures replace diverse wild plants; pesticides kill nontarget insects, birds, soil organisms
Pest Resistance: Heavy pesticide use selects for resistant insects; pest control becomes less effective over time
Salinization: Excessive irrigation deposits salts in soil; reduces productivity; creates unusable land
Energy Intensive: Fertilizer production requires fossil fuels; petroleum-based agriculture increases carbon emissions
Loss of Genetic Diversity: Traditional crop varieties abandoned; genetic heritage lost; vulnerability to new pests/diseases
Farmer Dependence: Small farmers dependent on expensive inputs (seeds, fertilizer, pesticides); debt and vulnerability

⚠️ Common Pitfall: The Green Revolution was SUCCESSFUL in increasing food production but NOT sustainable! Don't confuse "more food" with "good for environment." It prevented famine BUT caused significant environmental damage. Positive: averted hunger crisis. Negative: water depletion, soil degradation, pollution, biodiversity loss. It's a tradeoff that MUST be understood for AP exam.

5.4 Impacts of Agricultural Practices

Overview

Agricultural practices have profound impacts on environmental quality. Modern intensive agriculture, while productive, creates multiple environmental problems including soil degradation, water pollution, habitat loss, and climate impacts.

For the AP Environmental Science exam, you must understand how different farming practices affect ecosystems and recognize sustainable alternatives.

Major Environmental Impacts

Soil-Related Impacts

Erosion: Tilling breaks soil structure; monocultures lack diverse roots; topsoil washes away (1 billion metric tons/year globally)
Compaction: Heavy machinery compacts soil; reduces water infiltration and air spaces for roots and organisms
Salinization: Excessive irrigation accumulates salts in soil; renders land unusable
Depletion: Continuous cropping removes nutrients; soil organic matter declines; requires ever-increasing fertilizer inputs
Loss of Structure: Monocultures reduce soil aggregation; makes soil more vulnerable to erosion

Water-Related Impacts

Nutrient Runoff: Excess nitrogen and phosphorus cause eutrophication; dead zones in estuaries and coastal areas (Gulf of Mexico dead zone ~15,000 km²)
Pesticide Contamination: Pesticide residues in groundwater; bioaccumulate in aquatic food chains
Aquifer Depletion: Over-irrigation drains groundwater; wells run dry; agricultural collapse when aquifer is exhausted
Runoff Volume: Loss of vegetation and soil infiltration increases surface runoff; flooding, stream erosion, sedimentation
Water Diversion: Massive amounts diverted for irrigation; rivers run dry before reaching ocean (Aral Sea case study)

Biodiversity Impacts

Habitat Loss: Agricultural conversion destroys native ecosystems; major driver of species extinction
Pesticide Effects: Kill nontarget insects; reduce food for birds and other wildlife; cause population crashes
Genetic Erosion: Traditional crop varieties replaced by monocultures; genetic diversity loss
Pollinator Decline: Neonicotinoid pesticides harm honeybees, butterflies, and wild pollinators; threatens food production

Climate Impacts

Greenhouse Gas Emissions: Fertilizer production (Haber-Bosch Process) energy-intensive; fossil fuel inputs; methane from livestock and rice paddies
Carbon Release: Tilling releases soil carbon; deforestation for agriculture eliminates carbon sinks
Agriculture = 14-18% of global emissions: Major contributor to climate change
Feedback Loop: Climate change (drought, floods) threatens agricultural productivity; agriculture accelerates climate change

💡 Exam Tip: Agriculture affects MULTIPLE environmental systems simultaneously: soil (erosion, degradation), water (pollution, depletion), biodiversity (habitat loss), and climate (emissions). Be able to explain connections between practices and impacts. Major dead zones from agricultural nutrient runoff. Pesticides harm nontarget species. Fertilizer production energy-intensive. Irrigation depletes aquifers.

5.5 Irrigation Methods

Overview

Irrigation is artificial water application to land for agricultural production. Different irrigation methods have varying efficiency, cost, and environmental impacts. Understanding these methods is crucial for understanding water use and sustainability in agriculture.

For the AP Environmental Science exam, you must know different irrigation methods, their efficiency, advantages, and disadvantages.

Types of Irrigation Methods

1. Flood Irrigation (Furrow/Basin)

Method: Water diverted into furrows or basins; gravity flows across field
Efficiency: 40-50% (much water evaporates or infiltrates deeper than roots)
Advantages: Low cost; uses simple technology; works on slopes
Disadvantages: Wasteful; poor water distribution; causes waterlogging and salinization
Best for: Cereal crops, fruits in developing regions

2. Sprinkler Irrigation (Center Pivot)

Method: Water sprayed through overhead sprinklers; mimics rainfall
Efficiency: 60-80% (less water lost than flood; some evaporation)
Advantages: Better water distribution; works on uneven terrain; uniform application
Disadvantages: High cost; energy-intensive (pumping); wind affects distribution; evaporation losses
Best for: Corn, wheat, vegetables in developed regions

3. Drip Irrigation (Trickle)

Method: Water delivered directly to plant roots through perforated tubes; minimal distribution loss
Efficiency: 90%+ (highest efficiency); minimal evaporation; water goes directly to roots
Advantages: Most water-efficient; reduces weed growth; can deliver fertilizer; precise application
Disadvantages: Highest initial cost; maintenance required; can clog with sediment or salt
Best for: High-value crops (vegetables, fruits) in water-scarce regions; Israel uses drip extensively

Irrigation Efficiency Comparison

Method	Efficiency	Cost	Water Loss
Flood	40-50%	Low	High (evap + seepage)
Sprinkler	60-80%	High	Moderate (evaporation)
Drip	90%+	Very High	Minimal

💡 Exam Tip: Drip irrigation is MOST efficient (90%+) but MOST expensive. Flood irrigation is cheapest but wasteful (40-50%). Sprinkler is middle ground. Agriculture uses 70% of freshwater globally; irrigation is major water use. Efficiency improvements can reduce agricultural water demand significantly. Know tradeoffs between cost and efficiency!

5.6 Pest Control Methods

Overview

Pest control methods range from chemical pesticides to biological controls to cultural practices. Each has tradeoffs between effectiveness, cost, and environmental impact. Understanding these methods is essential for discussing sustainable agriculture.

For the AP Environmental Science exam, you must know different pest control approaches, their advantages, disadvantages, and impacts.

Types of Pest Control

1. Chemical Pesticides (Synthetic)

Advantages: Fast-acting; effective immediately; broad spectrum kills many pests; relatively inexpensive
Disadvantages: Kills nontarget organisms; pesticide resistance develops; bioaccumulation; water contamination; health risks to applicators
Types: Organophosphates, pyrethroids, neonicotinoids, carbamates
Issues: Honeybee/pollinator decline linked to neonicotinoids; DDT bioaccumulation nearly caused bald eagle extinction

2. Biological Controls

Natural Enemies: Introduce predators, parasites, or pathogens of pests (ladybugs eat aphids; parasitic wasps)
Advantages: Self-sustaining once established; target-specific; no chemical residues; long-term solution
Disadvantages: Slower than chemicals; may not completely eliminate pest; introduced species can become invasive
Examples: Cane toads (failed - became invasive), Australian lady beetles controlling pests, Bacillus thuringiensis (Bt) bacteria kills caterpillars

3. Cultural Controls (Mechanical)

Methods: Crop rotation, intercropping, hand-picking, row covers, trap crops, timing plantings
Advantages: Minimal environmental impact; no chemical residues; low cost
Disadvantages: Labor-intensive; less effective for large-scale monocultures; slower results
Examples: Crop rotation prevents pest buildup; intercropping confuses pests; timing prevents pest emergence

4. Genetic Engineering (GMO Pest Control)

Bt Crops: Insert Bacillus thuringiensis toxin genes; plants produce insecticide; kills caterpillars that eat crop
Advantages: Reduces pesticide spraying; targeted at specific pests; effective
Disadvantages: Resistance developing; impacts nontarget organisms; genetic escape concerns; consumer acceptance issues
Concerns: Bt resistance in bollworms already appearing; potential impacts on monarch butterfly larvae

⚠️ Common Pitfall: Chemical pesticides are FASTEST but create resistance and environmental damage. Biological controls are SLOWER but sustainable. Different approaches work best in different contexts. Integrated Pest Management (IPM) combines multiple strategies. Know tradeoffs between effectiveness, cost, and environmental impact. Neonicotinoid pesticides linked to pollinator decline = major exam topic!

5.7 Meat Production Methods

Overview

Meat production has significant environmental impacts including land use, water consumption, feed production, and greenhouse gas emissions. Different production systems (conventional feedlots vs. pasture-based) have different environmental footprints.

For the AP Environmental Science exam, you must understand different production methods and their environmental impacts.

Production Systems

1. Conventional Feedlots (Concentrated Animal Feeding Operations - CAFOs)

System: Thousands of animals confined in small spaces; fed grain from elsewhere; highly efficient at converting feed to meat
Advantages: Efficient land use; rapid growth; low-cost production; consistent supply
Environmental Impacts: Massive waste accumulation (manure); water and air pollution; requires large grain input; methane emissions
Animal Welfare: Crowded conditions; disease risk; stress
Current System: Dominant in U.S.; 95% of beef, chicken, pork from CAFOs

2. Pasture-Based Systems

System: Animals graze on pasture; feed themselves; more extensive use of land
Advantages: Better animal welfare; lower pollution concentration; maintains vegetation; carbon sequestration in soil; biodiverse pastures
Disadvantages: Requires more land; slower growth; higher labor costs; less efficient resource use; risk of overgrazing
Sustainability: Can be sustainable if managed well; risk of degradation with overstocking
Growing Trend: "Grass-fed beef," regenerative grazing practices gaining popularity

Environmental Impact Comparison

Land Use: Feedlots - minimal; Pasture - extensive (major driver of deforestation in Amazon for cattle ranching)
Water Use: Feedlots - high (grain irrigation); Pasture - lower but depends on rainfall
Pollution: Feedlots - concentrated waste; water pollution; air pollution; Pasture - dispersed; less acute pollution
Feed Efficiency: Feedlots - ~7 kg grain per 1 kg beef; Pasture - variable
Greenhouse Gases: Both produce methane; feedlots have grain production emissions; pasture-based may sequester carbon
Resource Demand: Livestock uses 77% of farmland but produces 18% of calories globally; major land use impact

💡 Exam Tip: Feedlots = efficient production but concentrated pollution. Pasture = extensive land use but better welfare/sustainability. Cattle ranching major driver of Amazon deforestation. Livestock uses 77% of farmland but provides only 18% of calories - inefficient protein conversion. Methane from cattle = major climate impact. Know both systems' tradeoffs!

5.8 Impacts of Overfishing

Overview

Overfishing occurs when fish are harvested faster than populations can reproduce, leading to population collapse. This is classic tragedy of the commons - individual fishers maximize catch while shared resource depletes. Impacts include ecosystem collapse, economic crisis, food security threats, and biodiversity loss.

For the AP Environmental Science exam, you must understand overfishing causes, impacts, and solutions (fishery management).

Causes of Overfishing

Open Access Fisheries: No ownership; anyone can fish; no incentive for individual restraint (tragedy of commons)
Advanced Technology: Industrial fishing vessels (factory ships) can catch enormous quantities; sonar locates fish; large nets capture everything
Economic Pressure: Fishing communities need income; subsidies encourage overexpansion of fishing fleets
Global Demand: Increasing seafood consumption; fish prices high; incentivizes extraction
Lack of Enforcement: International waters have limited regulation; illegal fishing hard to prevent

Impacts of Overfishing

Population Collapse

Atlantic Cod: Once abundant; overfished from 1960s-1990s; population crashed 95%; fishing moratorium imposed; slow recovery
Bluefin Tuna: Overfished for sushi market; Mediterranean population down 90%
Shark Finning: 73-100 million sharks killed annually; populations declining; ecosystem impacts (apex predator loss)
Status: 90% of major fish stocks fully exploited or overfished

Ecosystem Effects

Trophic Cascade: Removal of top predators allows prey to proliferate; disrupts food web
Bycatch: Non-target species killed; endangered species affected; dolphins, sea turtles, seabirds die in fishing nets
Habitat Damage: Bottom trawling destroys seafloor ecosystems; takes decades to recover
Biodiversity Loss: Genetic diversity within fish populations reduced; evolution of smaller-sized fish
Regime Shift: Overfishing can cause permanent shift to different ecosystem state; alternative stable states

Economic and Social Impacts

Fishing Industry Collapse: When stocks crash, fisheries close; communities dependent on fishing lose income
Food Security: Over 1 billion people depend on fish as primary protein; overfishing threatens food security
Unemployment: Fishing communities face economic hardship; difficult to transition to other industries
Price Increase: Scarcer fish = higher prices; particularly impacts poor populations

Solutions to Prevent Overfishing

Fishing Quotas: Limit total catch; distribute as individual transferable quotas (ITQs)
Marine Protected Areas: Establish no-take zones where fishing prohibited; allows population recovery
Fishing Moratoriums: Temporarily close fisheries (e.g., Atlantic cod moratorium 1992)
Gear Restrictions: Limit fishing methods (prohibit bottom trawling, shark finning); reduce bycatch
International Agreements: Treaties managing shared fish stocks; enforcement across national boundaries
Aquaculture: Fish farming reduces pressure on wild stocks (but has its own problems)
Reduce Consumption: Lower seafood demand reduces fishing pressure

💡 Exam Tip: Overfishing = perfect example of tragedy of commons. Atlantic cod collapse iconic example. 90% of fish stocks fully exploited/overfished. Impacts: population collapse, ecosystem disruption, bycatch, food insecurity. Solutions: quotas, MPAs, international agreements. Know cases like bluefin tuna, shark finning. Bycatch includes endangered species!

5.9 Impacts of Mining

Overview

Mining extraction of minerals from earth has severe environmental impacts including habitat destruction, water pollution, air pollution, and acid mine drainage. Mining is often in biodiverse regions; impacts persist long after mining ceases.

For the AP Environmental Science exam, you must understand mining processes, environmental impacts, and restoration challenges.

Types of Mining and Impacts

1. Surface Mining (Open-pit, Mountaintop Removal)

Process: Remove overburden (top layers); extract ore; leaves massive holes/scars
Impacts: Habitat destruction; erosion; water pollution; visual blight; dust
Mountaintop Removal (coal): Blasts off mountain tops; deposits waste in valleys; devastates Appalachian ecosystems
Recovery: Difficult; often leaves permanent scars; biodiversity rarely fully recovers

2. Subsurface Mining (Underground)

Process: Underground tunnels; less surface disturbance; more expensive and dangerous
Impacts: Subsidence (ground collapse); tailings (mine waste) dumped; acid mine drainage; water contamination
Acid Mine Drainage: Water oxidizes sulfide minerals; becomes highly acidic; contaminates waterways for decades

3. Placer Mining

Process: Extract minerals from stream beds/sediments; panning, sluicing, dredging
Impacts: Stream channel disruption; habitat destruction; sedimentation; mercury pollution (gold mining)
Common: Gold mining often uses mercury; contaminates waterways and food chains

Major Environmental Impacts

Habitat Destruction: Mining in biodiverse regions (tropics, mountains); fragments ecosystems
Water Pollution: Heavy metals (lead, mercury, cadmium, copper) contaminate water; bioaccumulate; toxic to aquatic life and humans
Acid Mine Drainage: Low-pH water persists years/decades after mining closes; kills aquatic life; corrosive infrastructure
Air Pollution: Dust particles; particulate matter; respiratory health impacts
Tailings Ponds: Massive waste repositories; can rupture (Mount Polley 2014); contaminate waterways
Biodiversity Loss: Species in mining areas often endemic (found nowhere else); extinction risk
Indigenous Impacts: Mining often on indigenous lands; violates rights; destroys traditional resources

Reclamation and Restoration

Challenges: Highly disturbed sites; contamination persists; restoration expensive and difficult
Attempts: Replanting, water treatment, capping; often only partially successful
Reality: Most abandoned mines never fully reclaimed; long-term environmental liability
Better Approach: Prevention (more efficient recycling, reduce consumption); protect remaining pristine areas from mining

💡 Exam Tip: Mining = severe, long-lasting environmental damage. Habitat destruction (often in biodiversity hotspots); water pollution (heavy metals, acid mine drainage); air pollution; tailings dams risk. Acid mine drainage persists for decades+ after mining ends. Impacts often on indigenous lands. Prevention better than remediation. Know mountaintop removal impacts Appalachia!

5.10 Impacts of Urbanization

Overview

Urbanization (conversion of land to urban/suburban areas) is rapid global trend. 55% of humans now live in cities (projected 68% by 2050). Urbanization impacts habitat, water, air, soil, and creates environmental justice issues.

For the AP Environmental Science exam, you must know urbanization impacts and sustainable city planning approaches.

Environmental Impacts of Urbanization

Habitat Loss

Direct Loss: Forests, wetlands, grasslands replaced with buildings, roads, parking lots
Fragmentation: Remaining habitat broken into isolated patches; prevents species movement
Edge Effects: Urban-habitat boundary creates altered microclimates, increased predation, pollution
Result: Biodiversity loss; extinction of species requiring large territories

Water Impacts

Stormwater Runoff: Impervious surfaces (asphalt, concrete) prevent infiltration; increased surface runoff; flooding; erosion
Pollution: Urban runoff carries oils, heavy metals, salts, fertilizers; contaminates waterways
Altered Hydrology: Changed precipitation patterns; reduced aquifer recharge; lower water tables; thermal pollution from urban heat
Wetland Loss: Wetlands drained for development; lost water filtration and storage capacity
Water Demand: Cities consume vast water quantities; strain on water supplies

Air Quality

Emissions: Vehicles, industry, heating produce air pollution; smog in cities
Health Impacts: Air pollution causes respiratory diseases, cancer, premature death
Heat Islands: Paved surfaces absorb heat; cities warmer than surrounding areas; increases energy use, stress on wildlife
Particulate Matter: Fine particles penetrate lungs; health risks from dust, vehicle emissions

Soil and Waste

Soil Burial: Native soils covered by buildings, roads; soil services lost; limited green space
Contamination: Industrial legacy pollution; brownfields; soil testing required before redevelopment
Waste Generation: Urban areas generate massive waste volumes; landfills overflow; recycling insufficient
Urban Agriculture Loss: Fertile farmland converted to urban sprawl; reduced local food production

Social/Environmental Justice

Unequal Exposure: Pollution concentrated in low-income neighborhoods; minorities disproportionately affected
Landfills/Refineries: Located near poor communities; health disparities
Green Space Access: Wealthy neighborhoods have parks; poor areas lack green spaces; health and recreation disparities
Gentrification: Environmental improvements (parks, green spaces) can lead to rising property values; poor residents displaced

💡 Exam Tip: Urbanization = habitat loss (fragmentation, edge effects); stormwater runoff (pollution, flooding); air quality (emissions, heat islands); waste generation; environmental justice issues. Urban runoff is major nonpoint source pollution. Heat islands increase energy use and stress wildlife. Green infrastructure reduces runoff. Urban agriculture and green roofs help. Know sprawl vs. dense urban planning tradeoffs!

5.11 Ecological Footprints

Definition and Calculation

Ecological Footprint is the land area required to sustain an individual's or nation's consumption and absorb their wastes. Measured in global hectares (gha) - standardized productive land.

Formula considerations: Food production, energy use, transportation, goods/services consumption, waste disposal

Key Facts

Average American Footprint: ~8 gha (uses resources/creates waste equivalent to ~8 hectares of productive land)
Global Average: ~2.7 gha per person
Earth's Biocapacity: ~1.6 gha per person (sustainable level)
Overshoot: Humanity uses ~1.7 Earths-worth of resources; unsustainable
Variation: Rich nations have large footprints; poor nations have small footprints; global inequality
Components: Built-up land, cropland, forest, fishing grounds, carbon footprint (land to absorb CO₂)

Reducing Ecological Footprint

Reduce consumption (buy less)
Choose local/plant-based foods
Reduce energy use (renewable energy, efficiency)
Use public transportation
Recycle and reuse
Support sustainable businesses

💡 Exam Tip: Ecological footprint measures sustainability of consumption. Americans use 5x sustainable level. Global overshoot means we're using 1.7 Earths. If everyone lived like Americans, would need 4-5 Earths. Know components: cropland, forest, fishing grounds, built-up, carbon footprint. Reduction strategies matter for sustainability!

5.12 Introduction to Sustainability

Definition and Principles

Sustainability is the ability to meet present needs without compromising the ability of future generations to meet their needs. It requires balancing three interconnected systems: environmental protection, social equity, and economic prosperity (often called the "triple bottom line" or "three pillars").

Three Pillars of Sustainability

Environmental (Planet): Protect ecosystems, biodiversity, air/water quality, climate stability; maintain renewable resources; manage waste responsibly
Social (People): Ensure equity and justice; meet basic human needs (food, water, shelter, health, education); protect worker rights; respect cultural heritage; community participation in decisions
Economic (Profit): Support livelihoods and prosperity; business viability; long-term economic growth; fair wages; financial stability without depleting resources

Key Sustainability Concepts

Carrying Capacity: Maximum population/resource use an ecosystem can support indefinitely; exceeding this leads to degradation
Regeneration vs. Depletion: Renewable resources (forest, fishery, aquifer) sustainable if harvested at rate ≤ regeneration rate; non-renewables (oil, minerals) require recycling/alternatives or eventually run out
Planetary Boundaries: Nine critical Earth system processes with safe operating limits (climate change, biodiversity loss, nitrogen/phosphorus cycles, etc.); currently exceeded in several
Intergenerational Equity: Current generation has responsibility to leave resources/functioning ecosystems for future generations
Intragenerational Equity: Fair distribution of resources among current population; addressing poverty and inequality
Cradle-to-Cradle Thinking: Design products/systems for reuse/recycling (circular economy) rather than linear take-make-dispose model
Precautionary Principle: When activity raises threat of harm, precautions should be taken even before cause-effect fully established

Paths to Sustainability

Reduce Consumption: Voluntary simplification; challenging "more is better" mentality; slower, localized economies
Renewable Energy Transition: Replace fossil fuels with solar, wind, geothermal, hydroelectric; essential for climate stability
Circular Economy: Design out waste; keep materials in use (reuse, repair, recycle); eliminate concept of "waste"
Regenerative Practices: Go beyond "no harm"; actively restore/improve ecosystems (regenerative agriculture, forest restoration)
Green Infrastructure: Nature-based solutions (wetlands, forests, green spaces) instead of gray infrastructure (concrete, pipes)
Local Self-Reliance: Strengthen local food systems, energy production, manufacturing; reduce transportation, build community resilience
Technology Innovation: Efficiency improvements, clean energy, carbon capture, alternative materials
Policy and Governance: Carbon pricing, renewable energy mandates, conservation regulations, international agreements

Challenges to Achieving Sustainability

Economic Incentives: Short-term profits often prioritized over long-term sustainability; externalities (pollution costs) not reflected in prices
Population and Consumption: Growing population + rising per-capita consumption in developing nations strains resources
Infrastructure Lock-in: Existing systems (fossil fuel energy, automobile-dependent cities) resistant to change; massive capital invested
Political Inaction: Short election cycles; fossil fuel industry lobbying; lack of political will for difficult changes
Inequality: Rich nations resist restricting consumption; poor nations rightfully claim right to develop; global cooperation difficult
Tragedy of the Commons: Individual rational behavior leads to collective harm; difficult to regulate global commons (atmosphere, oceans)

💡 Exam Tip: Sustainability = balance environmental protection, social equity, economic viability (three pillars). Regeneration rate must exceed harvest rate for renewables. Carrying capacity limits growth. Planetary boundaries exceeded. Circular economy replaces linear model. Intergenerational equity = responsibility to future generations. Know pathways: renewable energy, reduce consumption, circular economy, local resilience. Barriers: short-term economics, population growth, political inaction.

5.13 Methods to Reduce Urban Runoff

Understanding Urban Runoff

Urban runoff is precipitation that flows over impervious surfaces (roads, roofs, parking lots) directly into storm drains and waterways. Rapid, concentrated runoff causes flooding, stream erosion, and carries pollutants (oils, heavy metals, sediments, fertilizers) into aquatic ecosystems. Green infrastructure mimics natural water infiltration and filtering.

Green Infrastructure Technologies

1. Green Roofs (Living Roofs)

System: Vegetation and growing medium installed on building rooftops; retains 40-80% of annual rainfall
How it works: Vegetation intercepts rainfall; soil stores water; excess slowly drains or evaporates
Co-benefits: Insulates buildings (reduces HVAC costs 20-30%); extends roof lifespan; provides habitat; reduces urban heat island; beautifies cityscape; improves air quality
Challenges: High installation cost ($10-25/sq ft); structural requirements; maintenance needed; weight of system
Best for: Commercial buildings, apartment complexes; cities with significant rainfall

2. Rain Gardens and Bioswales

System: Shallow, depressed gardens designed to capture and filter stormwater runoff; planted with water-tolerant native plants
How it works: Runoff collects in depression; infiltrates through soil layers; vegetation roots and soil microbes filter pollutants; excess water either infiltrates to groundwater or slowly drains
Co-benefits: Removes 90%+ of pollutants; recharges groundwater; supports biodiversity; reduces flooding/erosion downstream; attractive landscaping
Challenges: Requires space; needs proper soil; may attract mosquitoes if poorly maintained; requires plant selection for local climate
Best for: Residential properties, parking lots, street medians; anywhere runoff accumulates

3. Permeable/Porous Pavement

System: Road, parking lot, or walkway surfaces that allow water infiltration through material; water drains into underlying reservoir and soil
Types: Permeable concrete, porous asphalt, pervious pavers, grid pavers with grass infill
How it works: Water passes through surface voids; underlying gravel/sand filters pollutants; water percolates to groundwater or is stored in base layer
Co-benefits: Eliminates surface ponding/flooding; recharges groundwater; reduces heat island effect; removes pollutants; quieter than regular pavement (water absorbs sound)
Challenges: Higher initial cost (20-50% more); clogging concerns if not maintained; durability questions in freeze-thaw climates
Best for: Parking lots, sidewalks, low-traffic roads, residential areas

4. Constructed Wetlands

System: Engineered wetlands built to treat stormwater; shallow ponds/marshes with vegetation, gravel, soil
How it works: Stormwater flows slowly through wetland; plants and soil organisms filter/degrade pollutants; long residence time allows settling of sediments; denitrification reduces nitrogen
Co-benefits: Removes 90%+ of pollutants; provides wildlife habitat; aesthetic value; can support biodiversity; resilient to extreme weather
Challenges: Requires significant land area (not available everywhere); mosquito management; regular maintenance
Best for: Industrial sites, large commercial properties, parks, areas with dedicated land

5. Stormwater Detention/Retention Ponds

Detention: Temporary storage basin; water held for hours to days; then released to waterways
Retention: Permanent water feature; water stored indefinitely; infiltrates or evaporates; may become pond/wetland
How it works: During storms, runoff diverted to basin; slows flow; sediments settle; pollutants adsorb to soil particles; reduces peak flows downstream
Co-benefits: Prevents downstream flooding; sediment removal (40-70% removal); provides habitat; recreational use (ponds); water supply (retention)
Challenges: Requires land; mosquito breeding potential; sediment accumulation requires maintenance; may not remove all pollutants
Best for: Parking lots, residential subdivisions, commercial areas; standard practice in many jurisdictions

6. Street Trees and Urban Forests

System: Strategic planting of native trees in urban areas, especially street corridors and parks
How it works: Tree canopy intercepts 10-40% of rainfall during storms; water stored on leaves and evaporates; infiltration through root zone; reduced runoff 20-50%
Co-benefits: Reduces heat island effect (shade, evapotranspiration); air quality improvement; carbon sequestration; wildlife habitat; property value increase; mental health/recreation
Challenges: Slow to establish (years to mature); requires irrigation initially; compacted soil reduces root growth; damage from construction/pollution
Best for: All urban areas; especially streets, parks, schoolyards

Integrated Approach to Urban Stormwater Management

Best practice: Combine multiple green infrastructure techniques at landscape scale to manage stormwater holistically. "Sponge cities" concept - make cities permeable, resilient to flooding.

Multi-Level Approach:

Building Level: Green roofs, downspout rain barrels, rain gardens in yards
Street/Block Level: Permeable pavements, street trees, bioswales, pocket parks
Neighborhood/Watershed Level: Detention/retention basins, constructed wetlands, riparian restoration
City Level: Urban forest strategy, green infrastructure standards, financing mechanisms
Regional Level: Watershed-based stormwater planning, agricultural best management practices

💡 Exam Tip: Urban runoff = major nonpoint source pollution. Green infrastructure reduces runoff, filters pollutants, recharges groundwater, reduces flooding. Green roofs intercept 40-80% rainfall; rain gardens remove 90%+ pollutants; permeable pavement eliminates surface ponding; constructed wetlands provide habitat while treating water. Multiple technologies work together. Know each method's pros/cons and best applications!

5.14 Integrated Pest Management (IPM)

Definition and Philosophy

Integrated Pest Management (IPM) is a holistic approach combining multiple pest control strategies to maintain pest populations below economically damaging levels while minimizing environmental and health risks. Rather than automatically applying pesticides, IPM uses pesticides as last resort after trying other methods.

Key philosophy: Manage pests, don't eradicate them. Some pest presence acceptable if economic damage threshold not exceeded.

Core IPM Principles and Components

1. Monitoring and Thresholds

Monitor pest populations: Regular scouting to count/identify pests and beneficial insects
Economic Threshold: Pre-determined pest population level at which damage losses exceed control costs; treatment triggered only when threshold exceeded
Action Threshold: Slightly lower threshold; triggers preventive measures before economic damage occurs
Decision Tools: Degree-day models, weather data, pest traps help predict pest emergence and timing of controls
Benefit: Prevents unnecessary/costly pesticide applications; reduces costs 30-50%; protects beneficial insects

2. Cultural Controls (Priority #1)

Crop Rotation: Alternating different crops breaks pest life cycles; pests adapted to specific crops can't survive if crop changes
Sanitation: Remove plant debris, fallen fruit, weeds that harbor pests; sterilize tools to prevent disease spread
Resistant Varieties: Plant crop varieties with genetic resistance/tolerance to pests and diseases
Timing: Plant/harvest dates adjusted to avoid pest emergence; example: early planting escapes late-season pest pressure
Spacing and Density: Proper plant spacing improves air circulation; reduces disease; facilitates pest management
Trap Crops: Plant sacrificial crops that attract pests away from main crop; pests concentrate on trap crop instead
Mechanical: Hand-picking, row covers (prevent insect access), traps, barriers, pruning infested branches

3. Biological Controls (Priority #2)

Natural Enemies: Introduce predators, parasites, or pathogens that feed on target pests
Examples: Ladybugs eat aphids (one ladybug eats 60-100 aphids/day); parasitic wasps lay eggs in insect pests (waste management); Bacillus thuringiensis (Bt) bacterium kills caterpillars; spiders are excellent predators
Conservation Biocontrol: Protect/encourage existing beneficial insects; minimize pesticide use (kills beneficials too); provide habitat (flowering plants, water)
Advantages: Self-sustaining; no chemical residues; pest-specific; reduces pesticide costs long-term
Disadvantages: Slower action than chemicals; may not completely eliminate pest; biological control can fail if natural enemies themselves decline
Pest Resistance Avoidance: Biological controls less likely to develop pest resistance compared to chemicals

4. Chemical Controls (Priority #3 - Last Resort)

Selection: Use ONLY when cultural and biological controls insufficient; choose pesticide with narrowest spectrum (targets specific pest, not beneficial insects)
Least Toxic Options: Organic-approved pesticides when possible (neem, insecticidal soaps, sulfur); botanical pesticides (pyrethrin from chrysanthemum flowers)
Application Timing: Apply pesticides only when threshold reached; use proper timing to catch vulnerable pest life stage (e.g., spray when eggs hatch)
Rotation: Alternate pesticide classes/modes of action to prevent resistance development; never use same pesticide repeatedly
Precision: Apply only to affected areas; avoid drift to non-target areas; use rates recommended on label
Safety: Follow label directions; use protective equipment; avoid applicator exposure and nontarget damage
Documentation: Record all pesticide applications (date, product, rate, target); helps identify patterns and resistance issues

IPM Decision Framework (Sequential Decision Making)

Step 1: Scout and Monitor - Identify pests, count populations, assess damage
Step 2: Compare to Threshold - Is pest population above action/economic threshold?
Step 3: If Below Threshold - Continue monitoring; no action needed; pest populations naturally fluctuate
Step 4: If Above Threshold - Implement controls in priority order:
a) Cultural controls first (easiest, cheapest, safest)
b) Biological controls if available and effective
c) Chemical controls only if other methods fail or too slow
Step 5: Evaluate Effectiveness - Did population drop below threshold? Adjust strategy if needed

Benefits of IPM vs. Chemical-Only Approach

Factor	IPM Approach	Chemical-Only
Pesticide Use	30-50% reduction	Maximum spraying
Resistance Development	Slow (rotation of methods)	Fast (same chemical)
Cost	Lower ($50-150/acre)	Variable (depends on pest)
Beneficial Insects	Protected, abundant	Killed (collateral damage)
Pollinator Health	Protected	Harmed (esp. neonicotinoids)
Applicator Health	Safer (less exposure)	Higher risk
Environmental Pollution	Reduced	High
Long-term Sustainability	Sustainable	Unsustainable

💡 Exam Tip: IPM = sequential decision-making, not chemical-first. Priorities: (1) Monitor/thresholds, (2) Cultural controls, (3) Biological controls, (4) Chemicals. Reduces pesticide use 30-50% while maintaining productivity. Prevents resistance development. Protects beneficials/pollinators. More labor-intensive than blanket spraying but cheaper long-term. Know framework and specific examples of each control type!

5.15 Sustainable Agriculture

Definition and Goals

Sustainable agriculture integrates environmental, social, and economic goals to produce sufficient food/fiber indefinitely while maintaining soil health, water quality, biodiversity, and farmer viability. It moves away from exploitative linear models toward regenerative practices that restore ecosystem functions.

Goals of Sustainable Agriculture

Environmental: Protect soil, water, air; maintain biodiversity; reduce chemical inputs; sequester carbon; adapt to climate change
Economic: Ensure profitability; reduce input costs; diversify income streams; fair prices for farmers; viability for multi-generational farms
Social: Fair labor practices; safe working conditions; support rural communities; food security; cultural preservation
Food Production: Sufficient yields to feed population; nutrient-dense food; reduced food waste

Key Sustainable Practices

1. Crop Rotation

System: Plant different crops in sequence (Year 1: corn, Year 2: soybeans, Year 3: wheat, Year 4: hay/clover)
Benefits: Legumes (peas, beans, clover) fix nitrogen, enriching soil; breaks pest/disease cycles; reduces pesticide need; improves soil structure; uses different root depths
Challenges: Requires planning; less intensive land use than monocultures; market uncertainty
Result: Reduced synthetic fertilizer need 50-70%; healthier soil; stable pest populations

2. Cover Crops

System: Plant vegetation (legumes, grains, grasses) during off-season when main crop absent
Benefits: Prevents erosion; adds organic matter; nitrogen fixation (legumes); breaks pest cycles; improves water infiltration; reduces weeds
Examples: Winter rye, clover, alfalfa, hairy vetch
Cost: Seed cost low; reduces need for synthetic fertilizer/erosion control

3. Reduced/No-Till Farming

System: Minimize or eliminate soil tilling; leave crop residue in place; plant new crop directly into previous crop residue
Benefits: Prevents soil erosion; maintains soil structure; preserves soil organisms; reduces fuel/labor; sequesters more carbon; retains soil moisture
Challenges: Requires specialized equipment; initial learning curve; relies more on cover crops/herbicides (may offset some sustainability gains if herbicide-heavy)
Result: Soil health improves; erosion drops 90%+; long-term productivity maintained

4. Agroforestry

System: Integrate trees with crops and/or livestock; trees provide shade, windbreak, nitrogen fixation, fruit/nuts
Examples: Alley cropping (rows of trees with crops between); silvopasture (trees in pastures for shade); forest farming (shade-tolerant crops under tree canopy)
Benefits: Diversified income (timber, nuts, fruit, crops); improved microclimate; increased biodiversity; soil improvement; resilience to climate extremes
Challenges: Long-term investment; complex management; initial productivity loss while trees establish

5. Organic Farming

System: Prohibited inputs: synthetic pesticides, fertilizers, antibiotics, GMOs; uses biological/mechanical controls and natural fertilizers
Benefits: No synthetic chemical residues; supports biodiversity; carbon sequestration; soil health; healthier for ecosystems and applicators
Challenges: Lower yields (10-20% lower than conventional); higher labor costs; certification requirements; market premium needed for profitability
Certification: USDA organic certification ensures no synthetic chemicals; premium prices (20-30% higher) offset some costs
Growing Market: Organic agriculture fastest-growing sector; consumer demand increasing; premiums support farmer viability

6. Polyculture (Multiple Crops)

System: Grow multiple crops together instead of monocultures; intercrops provide complementary benefits
Examples: "Three sisters" - corn + beans + squash (nitrogen fixation, support, ground cover); alley cropping; multistory cropping
Benefits: Pest/disease suppression (diversity confuses pests); improved soil fertility (legumes + others); efficient resource use; food diversity; resilience
Challenges: More complex management; markets designed for monocultures; harvest/processing more difficult
Result: More biodiverse, resilient, stable farms mimicking natural ecosystems

7. Precision Agriculture (Site-Specific Management)

System: Use GPS, drones, sensors, and data analysis to apply inputs (water, fertilizer, pesticides) precisely where needed
Benefits: Reduces input use 20-40%; improves yields; minimizes environmental impact; data-driven decisions; cost savings long-term
Technologies: Variable rate application, drone monitoring, soil sensors, weather integration
Challenge: High initial cost; requires tech expertise; data privacy concerns

Sustainable Approaches: Broader Context

Regenerative Agriculture: Goes beyond sustainability to actively restore soil health, increase carbon, improve biodiversity (composting, minimal disturbance, diverse rotations)
Farm Diversification: Multiple products (crops, livestock, agritourism) spread economic risk; reduce monoculture vulnerability
Local Food Systems: Direct-to-consumer sales (farmers markets, CSA); reduce transportation; build community; fair prices for farmers
Soil Health: Central to all sustainable approaches; healthy soil produces healthy food, sequesters carbon, retains water, supports biodiversity
Adaptive Management: Monitor results; adjust practices based on outcomes; continuous improvement

💡 Exam Tip: Sustainable agriculture balances production, profitability, and environmental protection. Crop rotation replenishes nitrogen, breaks pest cycles. Cover crops prevent erosion, add organic matter. No-till preserves soil. Agroforestry diversifies income. Organic eliminates synthetic chemicals. Polyculture mimics natural diversity. Precision ag reduces waste. Each practice has tradeoffs; combining multiple methods most effective. Know specific benefits and challenges of each approach!

5.16 Aquaculture

Definition and Overview

Aquaculture is the farming (cultivation) of aquatic organisms - fish, shellfish, crustaceans, mollusks - in controlled environments like ponds, tanks, cages, raceways. It's the fastest-growing animal food production sector globally, expanding 8-10% annually. Aquaculture now produces ~50% of seafood for human consumption.

Types of Aquaculture

Freshwater Aquaculture: Ponds, tanks, raceways (fish farms); tilapia, carp, salmon, catfish; lower environmental impact than marine
Marine Aquaculture: Cages/pens in coastal waters; salmon, sea bass, shrimp, oysters; higher impact on marine ecosystems
Integrated Multi-Trophic Aquaculture (IMTA): Combination of fish, shellfish, seaweed; waste from one species feeds another; more sustainable
Recirculating Systems: Intensive indoor operations with water recycling; minimal environmental footprint but high energy/capital costs

Advantages of Aquaculture

Reduces Wild Fishery Pressure: Farming reduces demand for wild-caught fish; prevents overfishing of marine stocks; critical as wild fisheries declining
Efficient Protein Production: Fish convert feed to body mass efficiently (1.5-2 kg feed per 1 kg fish vs. 5-7 kg for beef); sustainable protein source
Food Security: Produces protein in quantity needed for growing human population; makes seafood accessible to more people
Economic Development: Job creation in coastal/rural areas; export income for developing nations; farmer profitability
Controlled Production: Year-round production independent of seasons; predictable supply; consistent product quality
Research Opportunities: Selective breeding for disease resistance, growth rate, feed efficiency

Environmental Disadvantages of Aquaculture

Fish Waste and Pollution

Waste Production: Farmed fish produce feces and uneaten feed that settles under cages; creates benthic (sea floor) dead zones
Nutrient Eutrophication: Excess nitrogen/phosphorus causes algal blooms in surrounding waters; oxygen depletion; aquatic life die-offs
Sediment Buildup: Organic matter accumulates under farm cages; smothers benthic communities; harmful bacteria proliferate
Coastal Impact: Nearshore farms have highest impact; some regions restrict expansion due to pollution concerns

Escapes and Invasiveness

Cage Breaches: Farm fish escape during storms, accidents, or deliberate release; establish in wild populations
Genetic Contamination: Escaped farmed fish interbreed with wild relatives; introduce farmed genetics (weaker adaptation to wild conditions)
Competition/Predation: Escaped fish compete with wild fish for food/habitat; may predate on native species
Examples: Atlantic salmon farms in Pacific cause ecological disruption; farmed tilapia become invasive in many regions
Prevention: Better cage design, regular inspections, sterile triploid fish (prevents reproduction if escaped)

Disease and Parasite Pressure

Crowding Stress: High stocking densities stress fish; reduce immunity; increase disease susceptibility
Sea Lice: Parasitic copepods infest farmed fish; escape to wild salmon, causing high mortality in wild populations
Antibiotic Use: Antibiotics administered to treat/prevent disease; resistance develops; residues in environment; affects wild microbiomes
Pathogen Spread: Diseases/parasites can transmit from farms to wild populations through water movement
Solution: Better farm hygiene, selective breeding for disease resistance, reduce stocking density

Feed Requirements

Feed Conversion Ratio: Takes 1.5-2 kg of feed to produce 1 kg of farmed fish (better than terrestrial animals but not zero impact)
Fish Meal/Oil: Many farms use fish meal (ground wild-caught fish) and fish oil; perpetuates fishery pressure on wild stocks
Unsustainable Loop: Farming salmon/carnivorous fish requires wild-caught forage fish; can undermine overfishing concerns if 2-3 wild fish needed for each farmed fish
Solution: Plant-based feeds (soy, algae) developing; shellfish/herbivorous fish (no feed needed) are more sustainable
Emerging:** Lab-cultured fish feed reduces wild-fish dependency

Making Aquaculture More Sustainable

Best Farmed Species: Filter-feeders (shellfish, mussels, oysters) require no external feed; actually filter water improving clarity; minimal environmental impact
Integrated Multi-Trophic Aquaculture: Combine fish with seaweed, shellfish; waste products utilized; mimics ecosystem functions
Inland Recirculation Systems: Indoor farms with water recycling; eliminate wastewater/escapes; higher capital/energy but smaller footprint
Certification Programs: ASC (Aquaculture Stewardship Council) standards; consumers can identify sustainably farmed seafood
Herbivorous/Omnivorous Species: Fish that don't require fish meal (tilapia, carp) more sustainable than salmon
Offshore Farming: Locate farms in open ocean with strong water movement; better dispersal of waste; reduced local impact

💡 Exam Tip: Aquaculture = growing sector but environmental concerns real. Advantages: reduces wild fishery pressure, efficient protein, food security. Disadvantages: fish waste pollution, escapes/invasiveness, disease/parasite spread, feed requirements (especially carnivorous species). Shellfish most sustainable. IMTA mimics natural systems. Certification (ASC) identifies sustainable farmed seafood. Know tradeoffs: solves one problem (overfishing) but creates others (pollution, escapes)!

5.17 Sustainable Forestry

Definition and Principles

Sustainable forestry (also called responsible forestry or forest stewardship) harvests timber at rates ≤ forest growth rates, maintaining forest ecosystem functions, biodiversity, and carbon storage. It balances timber production with environmental protection and social needs.

Core Principles of Sustainable Forestry

Harvest ≤ Growth: Annual timber harvest cannot exceed annual forest growth; maintains standing biomass and carbon storage
Ecosystem Function: Maintain forest structure, microhabitats, soil health, water cycles; don't just count board feet of timber
Biodiversity Protection: Preserve species habitat requirements; protect old-growth characteristics where possible
Long-term Perspective: Manage for perpetual productivity; think in terms of generations, not quarterly profits
Community Benefits: Support rural livelihoods; meet local needs (firewood, medicine); respect indigenous rights
Adaptive Management: Monitor outcomes; adjust practices based on results

Sustainable Harvest Methods

1. Selective Cutting

System: Remove individual trees or small groups; maintains forest canopy continuity and structural complexity
Process: Identify target trees (large/mature/lower-value species); harvest with minimal impact on remaining trees; leave smaller trees to grow
Benefits: Maintains forest appearance, habitat, ecosystem services; continuous production; lower erosion risk; reduces flooding
Challenges: More expensive than clearcutting (selective labor); lower timber volume per harvest; requires skilled workers; market bias toward clear timber from clearcutting
Harvest Rate: Typically 25-50% of trees removed per cycle (20-40 year cycles)

2. Shelterwood Cutting

System: Remove trees in 2-3 stages over 5-10 years; provides shade and shelter for regeneration; transition to new cohort
Process: First cut removes some mature trees (still 40-60% remain); new trees establish in shade. Second cut removes more shelter trees as young trees grow. Final cut removes remaining shelter trees once young forest established
Benefits: Maintains canopy shade; promotes natural regeneration; reduces erosion; preserves habitat during transition; protects soil from extreme conditions
Challenges: Longer rotation; complex logistics; requires careful planning and skilled management
Result: More natural-looking regeneration; better habitat than clearcut; more resilient young forest

3. Variable Retention Harvesting

System: Retain 10-30% of forest structure (scattered trees, clumps, wildlife trees); remove remaining for timber
Benefits: Intermediate between selective and clearcutting; maintains some structural complexity; reduces soil erosion; provides habitat refugia; faster regeneration than selective (shorter rotation)
Challenges: Retained trees susceptible to windthrow (blown over); need careful placement
Use: Gaining popularity as compromise between productivity and conservation; research ongoing on optimal retention levels
Result: Biodiversity and forest services maintained while providing reasonable timber harvest

4. Clearcutting (Not Sustainable)

Difference: Clearcutting removes ALL trees; not considered sustainable forestry despite being most common industrial practice
Why Not Sustainable: Takes 200+ years to regain old-growth characteristics; ecosystem functions temporarily lost; biodiversity crash; often regenerated with monocultures not diverse native forest
Context: Some foresters argue clearcut + replant rotation is necessary for short rotation timber supply; others argue not truly sustainable because old-growth functions lost
Conservation Perspective: Clearcutting incompatible with biodiversity protection; sustainable forestry must preserve old-growth where it exists

Additional Sustainable Forestry Practices

Old-Growth Forest Protection

Reserve System: Designate certain forests as no-cut reserves; preserve remaining old-growth (5-10% of original remains in many regions)
Biodiversity Value: Old-growth forests provide unique habitat for species requiring large trees, late-successional characteristics, old-growth microenvironments
Carbon Storage: Old-growth stores massive carbon; climate mitigation value
Challenge: Pressure to harvest remaining old-growth for profits; conservation lands must be legally protected long-term

Native Species Reforestation

System: After harvest, replant with diverse native species rather than monocultures; matches original forest composition
Benefits: Supports native biodiversity; ecosystem resilience; disease/pest resistance better than monocultures
Challenges: More expensive than pine monoculture; slower growth to harvestable size; market challenges
Reality: Industrial plantations usually monocultures; sustainable forestry should prioritize native diversity

Certification and Third-Party Verification

FSC (Forest Stewardship Council): International certification verifying forests managed sustainably; consumers can identify certified wood products
PEFC (Programme for Endorsement of Forest Certification): Alternative certification standard
Benefits: Market premium (15-20%+) for certified sustainable wood; incentivizes better practices; consumer choice
Limitations: Certification costs money; small/poor forests can't afford certification; greenwashing risk (certification standards vary)
Growth: FSC forests increasing; certification creating market incentive for sustainability

Sustainable Forestry vs. Clearcutting: Comparison

Factor	Sustainable Methods	Clearcutting
Forest Structure	Maintained	Destroyed
Biodiversity	Protected/maintained	Dramatically reduced
Soil Health	Preserved	Exposed to erosion
Water Quality	Protected	Damaged (runoff/erosion)
Carbon Storage	Maintained	Released (carbon spike)
Timber Yield	Moderate/sustainable	Maximum (short-term)
Recovery Time	Ongoing (structure maintained)	200+ years (old-growth)
Cost	Higher (selective labor)	Lower (machinery)
Sustainability	Perpetual	Not sustainable

💡 Exam Tip: Sustainable forestry = selective cutting, shelterwood, variable retention (10-30% retained trees). Harvest ≤ growth. Maintains biodiversity, soil, water, carbon storage. Clearcutting NOT sustainable (200+ years to recover old-growth). Old-growth reserves essential for biodiversity/carbon. Native species reforestation > monocultures. FSC certification provides market incentive. Know methods, benefits, and why clearcutting not sustainable!

🎯 Unit 5 Key Takeaways for AP Exam Success

✓ Must-Know Concepts

Tragedy of the Commons
Clearcutting impacts
Green Revolution pros/cons
Agricultural impacts
Irrigation efficiency methods
Pest control approaches
Overfishing/bycatch
Mining environmental damage
Urbanization impacts
Ecological footprints

⚠️ Common Mistakes to Avoid

Green Revolution only positive (ignore negatives!)
Clearcutting = recovery to old-growth (FALSE!)
Drip irrigation not most efficient (it is!)
Chemical pesticides only solution
Overfishing affects only fishers
Mining damage can be fully remediated
Americans' footprint is sustainable
IPM not practical at scale
Aquaculture has no environmental impacts

📚 Study Strategies for Unit 5

Create comparison tables for land use impacts (clearcutting vs. sustainable forestry; feedlots vs. pasture; chemical pesticides vs. biological controls). Make timelines showing Green Revolution spread. Diagram fishery collapse and recovery. Calculate your own ecological footprint (online tools). Map urbanization impacts (habitat loss, stormwater runoff, urban heat islands). Understand sustainability as balancing environmental, economic, social factors. Know specific examples: Atlantic cod collapse, mountaintop removal, acid mine drainage, overfishing impacts.