Category Archives: Agriculture

More trees than we thought on Earth

Agriculture, Biology, Earth Science

Do you know how many trees there are on Earth?

The previous estimate in 2008 was 400 billion, or 61 trees for every person.

Here, a new study used satellite imagery and tree counts on the ground to calculate there are 3 trillion trees on Earth.

This is 7 times the previous estimate and equates to 422 trees for every person.

The distribution around the world is determined by climate and human activity.

Highest tree density is in northern boreal and tundra forests (e.g. Scandinavia, North America), as well as tropical areas, which contain 43% of the planet’s trees.

But it’s not all good news.  15 billion trees are being cut down each year and we have lost nearly half of the World’s trees since farming began around 12,000 years ago.

 

Do you want more information?

Background

Trees are essential components of many diverse ecosystems around the world.

They provide shelter, carbon sequestration, oxygen production, food, water quality control and protection against erosion, amongst other benefits.

However, their usefulness for construction timber and fires (cooking, warmth), as well as competition for farming land, means they have been cleared by humans for thousands of years.

Knowing how many trees there are in the world and where they are would help policy makers manage the world’s forests against competing pressures.

A previous estimate of 400 billion trees in 2008 was thrown into doubt when a later study found 390 billion trees in the Amazon basin alone.

So how many trees are there in the world?

Materials and Methods

This study used 429,775 ground-source measurements, as well as satellite imagery, of tree density from every continent on Earth (except Antarctica) to generate a global map of forest trees.  This provided a global tree density map at 1 km2 resolution.  Trees were defined as plants with woody stems larger than 10 cm in diameter at breast height.

Results

This study estimates there are 3.04 trillion trees in the world, equating to 422 trees for each of the 7.2 billion people on Earth.

This is 7 times the previous estimate of 400 billion trees (in 2008), and is also more than the number of stars in the Milky Way galaxy.

1.39 trillion trees (46%) are in tropical and subtropical regions, 0.74 trillion (24%) in boreal regions and 0.61 trillion (22%) in temperate regions.

Tree density generally increases with temperature, with moist, warm conditions optimal for tree growth.

A negative relationship between tree density and moisture availability was discovered.  It is most likely due to competition for productive land between forests and farming.

Current global forest clearing rates are estimated to be 15.3 billion trees or 192,000 km2 cleared each year, with the highest being in tropical regions.

Since the onset of human civilisation and farming (around 12,000), it is estimated that Earth’s tree numbers have fallen by 45.8%.

Discussion

It is hoped this survey of tree numbers will help policy makers manage the forests better, especially against powerful competing interests like agriculture and timber industries.

Article

Mapping tree density at a global scale

Crowther et al., 2015 Nature 525: 201-5

Keywords

Science, Earth, World, planet, biology, ecosystem, tree, forest, rainforest, plant, agriculture, timber, wood, tropical, boreal

Subject

ST1-8ES, ACSSU019, ST1-9ES, ACSSU032, ST1-11LW, ACSSU211, ST2-8ES, ACSSU075, ST2-11LW, ACSSU073, SC4-13ES, ACSSU116, SC5-13ES, ACSSU189

Top fuel fish drives up prices

Agriculture

Do you know why some fish are more expensive to buy than others?

It’s largely due to the amount of diesel fuel used by fishing vessels to catch them.

Robert Parker from the University of Tasmania analysed fuel records of over 1,600 fishing boats from around the world to determine which seafood requires the most diesel fuel (hence most expensive).

The most fuel efficient (least amount of diesel) are the pelagic (surface water) fish, such as anchovies, sardines and tuna.

The least fuel efficient are crustaceans, such as prawns and crayfish which use ~100 times more diesel than pelagic fish.

High diesel use is mostly due to dragging heavy nets and travelling long distances out to sea to catch the fish.

Seafoods that use the most diesel and produce the most greenhouse gases tend to be the most expensive to buy.

 

Do you want more information?

Background

Seafood is the most heavily traded commodity in the world.

It employs ~260 million people and is worth ~US$100 billion annually.

It contributes ~17% of animal protein consumption in the world.

Many species are expensive because of high costs of catching them.

The largest cost is diesel needed to drive the fishing vessels (30-50%).

So which types of seafood need the most diesel?

Materials and Methods

Robert Parker from the University of Tasmania analysed fuel records of over 1,600 fishing vessels from around the world since 1990 and matched them to the type of seafood caught (meta-analysis).

Results

The order of diesel-efficient seafood species are (most to least):

  • Small pelagic fish (e.g. anchovies, sardines, mackerel)(average 71 L diesel per tonne fish). Easily caught in light surrounding nets not far from shore, therefore boats don’t need to travel far).
  • Large pelagic fish (e.g. tuna)(434 L/t). Caught using light surrounding nets but need to travel further out to sea.
  • Molluscs (e.g. scallops)(525 L/t). Scooped up in heavy dredges.
  • Salmon (886 L/t). Trolling with hook and line over long distances.
  • Flatfish (e.g. sole, flounder)(2827 L/t). Trawlers drag a heavy metal beam along the sea floor to disturb the flatfish and catch them in a net. Uses a lot of fuel.
  • Crustaceans (e.g. prawns, lobster)(2923 L/t). Uses heavy pots, traps and trawls. Boats travel large distances for these relatively scarce species. Especially inefficient in Oceania (~4,000 L/t).

Discussion

Diesel fuel efficiency has improved over the past 2 decades, mostly due to fish stocks recovering from previous over-fishing (laws introduced to protect them), meaning that boats don’t have to travel as far out to sea.

Seafood is far more fuel efficient and has less greenhouse gas emissions than beef production, which is by far the most energy demanding and worst for the environment.

Article

Fuel consumption of global fishing fleets: current understanding and knowledge gaps

Parker and Tyedmers, 2014 Fish and Fisheries (DOI: 10.1111/faf.12087)

Further Reading

See BOSH – Cows are worst livestock for the environment for a comparison of greenhouse gas emissions for different types of livestock.

http://bosh.net.au/cows-are-worst-livestock-for-the-environment/

Keywords

Seafood, fish, mollusc, crustacean, ocean, sea, marine, fishing, boat, vessel, trawl, trolling, trawler, prawn, lobster, crayfish, greenhouse, gas, emission, climate, diesel, fuel, energy

Subject

Science, Agriculture, ST1-11LW, ACSSU211, ST1-9ES, ACSSU032, ST2-11LW, ACSSU073, SC4-15LW, ACSSU112, SC5-14LW, ACSSU176

Cows are worst livestock for the environment

Agriculture

Did you know that cows are by far the worst livestock for the environment?

Beef uses 28x more land, 11x more irrigated water, 5x more greenhouse gas emissions and 6x more nitrogen fertilizers than other livestock.

Crops use even less.

We could help the environment by eating less beef and more pigs and chickens.

 

Do you want more information?

Background

Farming is a relatively efficient and necessary way to feed humans.

However, it is undoubtedly bad for the natural environment. It causes:

* 1/5th greenhouse gas emissions (including methane from animal farts)

* Clears land, trees and removes habitats for native animals

* Fertilizers are a major source of water pollution

* Competes with biodiversity and contributes to species extinctions

One strategy to improve the situation is to get farmers, governments and consumers to prioritise more sustainable products.

So what is the most/least environmentally friendly livestock?

Materials and Methods

This study compared the 5 major animal-based food products: beef, pork, poultry, dairy, eggs (together provide 96% of animal-based foods).

They measured 4 environmental factors: land usage, water irrigation, nitrogen fertilizer use and greenhouse gas emissions.

Based on US government data from 2000-2010, although conclusions are generalisable to many other countries, including Australia.

Results

Beef is much more damaging to the environment that pork, poultry, dairy and eggs, which are all similar to each other.

Beef uses 28x more land, 11x more irrigated water, 5x more greenhouse gas emissions, 6x more nitrogen fertilizers

Plant crops (potatoes, wheat, rice) use even less resources than the pork, poultry, dairy and egg products.

Feeding each US person with the 5 animal products listed here requires ~12,000m2 of land, ~150m3 or irrigation water and ~1.1 tons of greenhouse gas emissions per year.

Discussion

The reason beef is more environmentally damaging than other animals is due to its basic biology: It is less efficient at converting resources and energy into food for human consumption.

Beef is the second most popular animal-based food product in the US (behind dairy). If consumers would shift from beef to pork or poultry, it would greatly benefit the environment.

This information could also be used to change governmental farming policies and agricultural technology/practice to reduce the environmental impact of farming.

Article

Land irrigation water, greenhouse gas and reactive nitrogen burdens of meat, eggs and dairy production in the United States

Eshel et al., 2014 Proc. Natl. Acad. Sci. USA 111:11996-12001

Keywords

Farm, farming, agriculture, livestock, crops, food, animal, plant, population, economics, environment, pollution, fertilizer, land, irrigation, water, greenhouse, gas

Subject

Science, Agriculture, ST1-9ES, ACSSU032, SC4-15LW, ACSSU112, SC5-13ES, ACSSU189, SC5-15LW, ACSSU176