Lecture 5: Land use change at a global scale Flashcards
Lecture aims
1.Define land cover and land use
2.Discuss how human activities influence land cover globally
3.Evaluate recent and ongoing trends in land-use change with respect to (a) drivers and (b) impacts
4.Discuss how negative impacts of agriculture can be ameliorated
Land cover definition
Land cover is what physically covers the Earth’s surface
Natural:
Abiotic: rocks, rivers, sea etc.
Biotic assemblages: plants and animals
Anthropomorphic:
Abiotic: urban structures
Biotic assemblages: farm animals and crops
Biome definition
How do we classify and map land cover?
We usually classify and talk about land cover in terms of biomes
This encompasses the geography, climate, soil, vegetation and biotic assemblages that we think of as characterising the main global differences in land cover
Biome = a group of ecosystems in a geographic region that are subject to similar climatic conditions and which share a similar range of vegetation structures, biotic diversity, and soil types
(compiled from multiple sources)
E.g. Whittaker biomes: One of the classic early systems (1962) for defining biomes was the Whittaker biomes, which delineated biomes based on broad vegetation classes mapped onto just two climate variables
In 2001 WWF developed a classification scheme which remains popular.
It is similar to Whittaker’s biomes but more detailed
We start with biogeographic realms – broadly about shared evolutionary history, so related to tectonic plates and within that we have 14 biomes.
Within the biomes there are also ecoregions (not depicted here)
Terrestrial ecoregions are:
“relatively large units of land containing a distinct assemblage of natural communities and species, with boundaries that approximate the original extent of natural communities prior to major land-use change” Olson et al. (2001) Bioscience
^ Prior to major land-use change -> we have an explicit exclusion of human influence here, so this is not depicting current reality
Land use and land cover mapping
Land use cover was traditionally mapped from the ground up, ignoring human influence:
The benefit perhaps is that it can include complex & detailed concepts, such as the biotic assemblages beyond just vegetation
Now it is common to map from above, including human influences:
^ This is done using satellite data, because it is ~equally available everywhere and can be collected repeatedly over time. Although some of the nuances of biotic assemblages will be missed this method includes all physical structures that give a clear signal in satellite imagery
^This approach forces us to consider human-made features, including buildings and agricultural land
Maps of land use and land cover for reference
*WorldCover provides the first global land cover products for 2020 and 2021 at 10 m resolution, developed and validated in near-real time based on Sentinel-1 and Sentinel-2 data
* Human influence is represented by cropland and built-up areas, and actually a lot of the grassland and shrubland is livestock pasture
*We have similar data available for the UK over many years, produced by UKCEH:
*Also based on satellite data but use land cover categories matched to UK Biodiversity Action Plan (BAP) Broad Habitats
*Looks like there is lots of green and brown, but most of this is grazing land for sheep
*There’s also a lot of dark green for coniferous woodland, but most of this is non-native conifer plantations for timber e.g. larch and Sitka spruce
No natural habitat in the UK
Key definitions
Definitions
Land cover:
describes the physical structures on the Earth’s surface:
E.g. water, bare rock, forests, grassland
May include human influence e.g. buildings
Land use describes how people use the land:
Typically, land use influences land cover
Land use change:
describes changes in land use over time
What about the human component of land use cover?
As biomes are defined based on climate and vegetation rather than using satellite imagery, in a map of biomes we are looking at land cover without human influence:
see map at:
https://atlas-for-the-end-of-the-world.com/world_maps/world_maps_biomes.html
Paper by Ellis & Ramankutty (2008) Frontiers in Ecology and the Environment)
suggested anthromes as an alternative, displaying anthropogenic biomes such as villages, agriculture and ‘wildlands’
^ Wildlands are areas free form human influence shown in dark green: see: https://atlas-for-the-end-of-the-world.com/world_maps/world_maps_anthromes.html
Types of anthrome
DENSE SETTLEMENTS
urban
dense settlements
VILLAGES
cropped and pastoral villages
pastoral villages
rainfed mosaic villages
AGRICULTURAL SETTLEMENTS
residential irrigated cropland
residential rainfed mosaic
populated rainfed croplands
remote croplands
RANGELAND SETTLEMENTS
residential rangelands
populated rangelands
remote rangelands
FORESTED
populated forests
remote forests
WILDLANDS
wild forests
sparse trees
barren
How humans influence land cover globally
Humans have been influencing land cover for a long time, at least since we developed agriculture
Before agriculture, humans were using fire to manage habitats for food and humans contributed to extinctions of megaufauna when they colonised new land masses
see timeline in notes
fire used to clear land originally due to the fact that plants that generate after fire are more palatable
By 10,000 BCE, all human societies employed varying degrees of ecologically transformative land use practices
see Ellis et al 2021 PNAS:
*Burning, hunting, species propagation, domestication, cultivation, and others that have left long-term legacies across the terrestrial biosphere
*This paper uses the same anthromes that we saw earlier, to recognise the many ways in which humans use and influence land
*Earlier on in human society, most of the world was uninhabited wildlands and cultured lands, where people lived without intensive land use practices – they impacted the land cover, but not necessarily negatively
By 2017 CE, more than 80% of the terrestrial biosphere was transformed by human populations and land use: 51% in Intensive anthromes, 30% Cultured, and just 19% in Wildlands (Ellis et al 2021)
example: The Mayan city of Caracol dates to 12000BC - Clearly, the Maya impacted land cover tremendously by building these amazing structures and cultivating food to feed its population of over 100,000 people
Global land use for food production
see ourworldindata graph in notes
*Nearly half of the Earth’s habitable land is used for agriculture
*80% of that is used for livestock vs. only 16% used for crops
^ That 80% accounts for only 17% of global calorie supply – we get more calories from the cropland
Both cropland and grazing land have increased a lot in the last few centuries, but grazing land occupies a much larger area:
see land use over the long-term, world
Ourworldindata HYDE 2023
Change in land use is reflected in the distribution of mammal biomass globally, which is now mostly livestock:
See Bar-On et al 2018 PNAS
& Ourworldindata distribution of mammals on Earth 2015
when we consider the biomass of all life on Earth, livestock and humans make up a large portion of the animal biomass
*Not just about land area used by humans – it’s also important to think about efficiency of land use
*Land use per person significantly decreased in the last 70 years due to the green revolution (ourworldindata; agricultural land use per person HYDE 2023)
*However population size also grew massively alongside the much higher yields
Agricultural intensification and the green revolution:
*1700 to 1900 = industrial revolution & internal combustion engine -> mechanised farming
*1920s -> hybrid seeds & monocultures
*1940s WW2 = funding & infrastructure for chemistry (e.g. explosives) -> nitrogen fertiliser & pesticides
*1950s onwards (post war) -> agricultural subsidies & irrigation
*Hybrid seeds were created by self-pollinating crops with desirable traits to increase yields
*World wars also played a significant role
*Fertiliser & pesticides were often by-products of wartime innovations (for poisons and bombs) and infrastructure
*Also, post-wars, many governments wanted to improve food security and therefore supported farmers through agricultural subsidies & support for irrigation
This fueled the green revolution
Recent and ongoing trends in land-use change with respect to drivers of conversion to agricultural land
What drives conversion of land to agriculture?
see world population growth 1700-2100
(Ourworldindata HYDE/UN 2022)
Increasing global population undoubtedly fuels land conversion – more people need more space to live and, more importantly, more space to feed themselves
BUT, population growth rate has already peaks (in the 60s) and is now declining
Not just about population size – patterns of consumption matter
* Richer nations have higher per capita caloric demand: Tilman et al. (2011) PNAS
Richer nations also have a higher per capita protein demand: As countries become wealthier, people eat more meat – we already saw that livestock take up a much larger portion of land use globally than cropland
*As countries become wealthier, per capita consumption increases
*We obviously want poorer nations to develop to improve health and wellbeing, but wealthier nations are undoubtedly consuming more than they need
Land arable agriculture is a low proportion of most countries. The land we are using to meet protein demands is making up the largest share:
Recent and ongoing trends in land-use change with respect to the environmental impacts of agriculture
Biodiversity loss: see chart from BBC in notes from WWF 2018:
*Habitat loss is the single biggest threat to biodiversity and has been for a long time
*Most of this habitat loss is through conversion to agriculture
Huge declines in species richness caused at a local scale in response to land conversion:
Newbold et al 2015 (Nature)
species richness decline in pasture and cropland
Greenhouse gas emissions
Agriculture is a major contributor:
A variety of sources, from the CO2 released when land is first converted, to the CO2 released by farm vehicles & crop burning, the methane released by cow farts, manure and rice paddies, and the nitrous oxide released from over-application of nitrogen fertiliser
Pollution:
*Pollution of waterways in particular is a serious problem
*Pesticides are toxic and excess fertiliser runs off causing excess nutrients to end up in surrounding waterways through surface run-off, sub-surface leaching and even through rainfall. Resulting in eutrophication
Disruption to hydrology:
*70% of global freshwater withdrawals are devoted to irrigation
*Poor management of water application as well as nutrients
*This can lead to waterlogged soils in some places, and loss of water elsewhere
*Waterlogging results primarily from inadequate drainage and over-irrigation and, to a lesser extent, from seepage from canals and ditches
*Waterlogging can also cause salinization due to the accumulations of soluble salts
How negative impacts of agriculture can be ameliorated
Priority is to halt expansion of agricultural land:
*Land is converted to meet caloric demand, so o halt the expansion of agricultural land, we need to: Decrease demand & Increase supply on existing agricultural land
*Particularly urgent as 70% new agricultural land is now coming at the expense of tropical forests, without adding much to global food production
Decrease excessive calorie consumption and decrease excessive meat consumption:
see UN/Lancet video: diet of the future:
https://www.youtube.com/live/RD4u9L_jd8g?feature=shared
How can we increase calorie availability?
*Close the diet gap – use crops for human food > animal fodder or biofuel
*Close the yield gap – grow more food in the same area
^see Foley et al (2011) Nature
*Decrease food waste
*There are lots of calories produced that are never eaten
*In developed countries, waste is mainly by retail and the consumer
*In developing countries, waste is in the field and on the way to consumer
^see FAO infographic in notes
see FAO 2023 chart:
*1.76 billion ha of land was spared from conversion due to improvements in crop yield
*There were still obvious problems with this intensification in terms of environmental impacts, so we need to intensify in a smarter way
Food for thought: what about agricultural land abandonment?
Perpiña Castillo et al. (2021) Environmental Modelling & Software
*In many parts of the world, marginal farmland was brought into production post-war and is now very difficult to make a living on, especially with subsidy reform
*This could and has led to widespread land abandonment in many places across Europe
*Could we ameliorate the negative impacts of agriculture through restoration of abandoned farmland?
