2.6 Environmental Effects of Trade

Trade routes didn't just carry silks and spices—they transported living things that transformed environments across Afro-Eurasia. Between 1200 and 1450 CE, as caravans crossed deserts and ships sailed distant seas, they carried seeds, plants, animals, and unfortunately, disease-causing microorganisms. These biological exchanges had profound and lasting effects on human societies and natural environments. Some of these transfers, like new food crops, brought tremendous benefits. Others, like the devastating bubonic plague, caused immense suffering. Together, they show how greater connectivity changed not just human cultures but the natural world as well.

The Spread of Crops and Food Plants

As merchants traveled across Afro-Eurasia, they brought useful plants with them. New food crops changed diets, farming practices, and even landscapes in the regions where they were introduced.

Bananas in Africa

Bananas transformed agriculture and diet across much of Africa after their introduction from Southeast Asia. Though they had arrived in East Africa before this period, they continued to spread and gain importance between 1200 and 1450.

Bananas offered several advantages to African farmers:

• They produced more calories per acre than most traditional African crops
• They grew well in tropical forest regions where other crops struggled
• They could be harvested year-round, providing a steady food supply
• Different varieties could be eaten fresh, cooked, or made into beer
• They required less labor than grain crops once established

The impact of bananas on African societies was significant and far-reaching. Villages in forest regions could now support larger populations thanks to this productive crop. Banana cultivation spread gradually from East Africa into the Central African rainforests, carried by traders and migrants.

In forest regions from Uganda to the Congo Basin, bananas became dietary staples. Communities developed specialized cultivation techniques suited to local conditions. The increased food security provided by banana cultivation allowed some forest communities to develop more complex political organizations and trading networks.

New Rice Varieties in East Asia

Rice had been grown in East Asia for thousands of years, but the introduction of new, faster-growing varieties during this period significantly boosted food production. These new types of rice spread primarily from southern China into Korea, Japan, and other parts of East Asia.

Champa rice, originally from Vietnam, brought several benefits to farmers:

• It matured in just 60 days (compared to 100+ days for older varieties)
• It could be grown in drier conditions with less irrigation
• Farmers could plant two or even three crops each year instead of just one
• It was more resistant to drought and certain pests
• It could grow in higher elevations where traditional rice varieties couldn't thrive

The introduction of these improved rice varieties had profound effects on East Asian societies:

Food production skyrocketed, especially during China's Southern Song dynasty. The population grew dramatically as more food became available. More people could live in cities since fewer farmers could produce more food. Government tax revenue increased as rice harvests grew larger. Agricultural expansion moved into hilly areas previously considered unsuitable for farming.

By allowing multiple harvests per year, these new rice varieties also created changes in seasonal labor patterns. Farmers developed new irrigation systems and terracing techniques to maximize production of these valuable rice strains. Regional trading networks expanded to move surplus rice from productive areas to cities and less fertile regions.

Citrus in the Mediterranean

Citrus fruits—including lemons, oranges, and bitter oranges—spread throughout the Mediterranean region during this period, fundamentally changing both agriculture and cuisine. Originally from Southeast Asia, these fruits had moved gradually westward for centuries.

Muslim agricultural practices helped spread citrus across the Mediterranean:

• Islamic agricultural texts included detailed instructions for citrus cultivation
• Sophisticated irrigation systems made citrus growing possible in drier regions
• Muslim-ruled Sicily and Spain became major centers of citrus production
• Specialized gardens called "paradises" featured oranges as ornamental and food plants
• New grafting techniques allowed for better fruit quality and adaptation to local conditions

Citrus fruits brought multiple benefits to Mediterranean communities:

The fruits added valuable vitamin C to local diets, improving nutrition and health. Preserved lemons and oranges could be stored for use throughout the year. Citrus oils and extracts were used in perfumes and medicines. Citrus orchards became profitable commercial enterprises, especially near trading ports. The fruits inspired new culinary traditions that are still central to Mediterranean cooking today.

As Christian kingdoms conquered Muslim territories in Spain and Sicily, they maintained and expanded citrus cultivation. By 1450, oranges and lemons were common in gardens throughout southern Europe. The distinctive scent of orange blossoms became associated with regions like Valencia and Sicily, where orchards transformed both the landscape and the economy.

Spread of Disease and the Black Death

While the exchange of crops brought many benefits, the same networks that carried useful plants also transmitted deadly pathogens. The most devastating example was the bubonic plague, which caused the pandemic known as the Black Death.

The Black Death Pandemic

The bubonic plague erupted into the deadliest pandemic of the pre-modern world in the 1340s. It likely originated in Central or East Asia before spreading rapidly along trade routes.

The disease moved along established trade networks:

• It traveled the Silk Roads from Central Asia to the Black Sea region
• From Crimean ports, it spread by ship throughout the Mediterranean
• Merchant vessels carried it to European port cities
• Overland trade routes spread it into the Middle East and North Africa
• It even reached as far as sub-Saharan Africa along caravan routes

The plague was caused by the bacterium Yersinia pestis, carried by fleas that lived on rats. As infected rats traveled on ships and in caravans, they brought the disease to new populations with no immunity.

The pandemic's impact was catastrophic and wide-ranging:

• Between 1346 and 1353, it killed an estimated 75-200 million people
• Some regions lost 30-60% of their entire population
• Cities were especially hard-hit due to crowded conditions
• Some villages and small towns were completely abandoned
• Trade temporarily collapsed in many regions as people feared contact

The Black Death transformed societies across Afro-Eurasia:

Labor shortages after the plague led to higher wages for surviving workers. The massive death toll weakened traditional social structures and religious institutions. Some regions took decades or even centuries to recover their pre-plague population levels. Religious explanations for the disaster ranged from divine punishment to poisoning by marginalized groups. Medical theories and practices were questioned as traditional remedies failed to stop the disease.

Other Disease Exchanges

While the Black Death was the most dramatic example, other diseases also spread along trade routes during this period, though with less severe consequences.

Various diseases moved between regions:

• Smallpox spread along trade routes in Africa, affecting new populations
• Measles moved into previously isolated communities as trade connections grew
• Influenza strains traveled with merchants and diplomats
• Malaria expanded its range as agricultural patterns changed
• Waterborne diseases spread through growing urban centers connected to trade

Disease exchanges often accompanied human migration:

• Merchant communities carried diseases between trading cities
• Military campaigns spread illnesses between regions
• Pilgrimages to religious centers became vectors for disease transmission
• Refugees fleeing conflicts or environmental disasters carried pathogens to new areas
• Growing cities attracted migrants who brought unfamiliar diseases

The impacts of these disease exchanges varied:

• Previously isolated populations often suffered most severely
• Some diseases became endemic (constantly present) in newly affected regions
• Knowledge of treatments sometimes followed disease pathways
• Quarantine practices developed in some areas, especially after the Black Death
• Trade sometimes declined temporarily when disease outbreaks occurred

Environmental Impacts Beyond Crops and Disease

The increasing connections across Afro-Eurasia had other environmental consequences beyond the movement of crops and diseases.

Animal species moved along with human travelers:

• Horses from Central Asia were imported to India and Southeast Asia
• New cattle breeds spread through trade corridors
• Sheep varieties moved between different pastoral regions
• Domesticated animals sometimes escaped to become invasive species
• Animal diseases followed similar paths to human diseases

Landscape changes accompanied the spread of new crops:

• Forests were cleared for expanding agriculture
• Irrigation systems altered water flow patterns
• Terracing transformed hillsides for farming
• Urban growth around trading centers changed local environments
• Mining for trade goods scarred landscapes and polluted waterways

The intensification of trade sometimes led to resource depletion:

• Valuable timber was harvested for shipbuilding
• Fuel wood was consumed in growing quantities for metalworking
• Overgrazing occurred along major caravan routes
• Some luxury goods (like certain spices or animals) became harder to find
• Water resources were strained around major urban centers

The environmental exchanges of the period between 1200 and 1450 CE demonstrate how human connections can have far-reaching ecological consequences. The movement of plants, animals, and microorganisms across traditional boundaries created new environmental relationships that continue to shape our world today. These exchanges—both beneficial and harmful—remind us that globalization has deep historical roots and profound environmental dimensions.