Megabiome composition (major groups + Other)
How to Read the Megabiome Map
This map shows how reconstructed potential vegetation changed across major Eurasian regions from the late MIS 3 to the early MIS 2.
A statistical analysis window with a radius of 500 km was defined around each archaeological site. Land grid cells within each window were classified by megabiome, and the area share of each category was then calculated.
The circles shown on the map do not represent reconstructed settlement territories or hunting ranges. They are standardized statistical windows used to compare environmental conditions across regions.
Biome and Megabiome
Biome
A biome is a categorical classification of potential vegetation and climate, such as forest, grassland, shrubland, tundra, or desert.
Biome identifies the type of environment, not the amount of plant production.
For example, two regions classified as Boreal forest may differ substantially in:
- vegetation density;
- annual plant productivity;
- growing-season length;
- moisture availability;
- snow depth; and
- winter forage accessibility.
The same biome classification does not mean that two regions had the same ecological productivity.
Megabiome
A megabiome combines several detailed biomes into broader ecological categories. It makes long-term regional and large-scale spatial patterns easier to compare, although some detailed vegetation differences are lost during aggregation.
For clarity, the map and graph display only five categories:
- Boreal forest
- Grassland
- Tundra
- Tundra-steppe
- Other
The Five Categories Shown in the Graph
Boreal Forest
Boreal forest represents northern forest environments dominated largely by cold-adapted trees, including conifers and other cool-climate species.
Boreal forests may have provided humans with:
- wood;
- fuel;
- shelter;
- construction materials;
- plant resources; and
- small-animal resources.
Dense forest, however, may have restricted visibility and movement for some large, herd-forming grazing animals compared with open environments.
How to interpret it
- Increasing share: boreal forest environments expanded within the analysis window.
- Decreasing share: forest may have been replaced by more open environments.
- Stable share: the forest category remained spatially extensive, but its productivity may still have changed.
Even when the Boreal forest share remains high, declining NPP and LAI may indicate weakening plant productivity and vegetation density within the forest environment.
Grassland
Grassland represents open environments dominated by grasses and other herbaceous plants.
These environments could support mobile herbivores such as horses, bison, and some reindeer populations. However, a Grassland classification does not necessarily indicate a lush or highly productive steppe.
Its ecological value depends on:
- plant productivity;
- growing-season length;
- precipitation;
- snow depth;
- winter forage accessibility; and
- vegetation density.
How to interpret it
- Increasing share: herbaceous open environments expanded.
- Increase combined with forest decline: forest barriers may have weakened and open habitats may have become more connected.
- Increase combined with declining NPP: grassland area expanded while forage production per unit area may have decreased.
- High NPP and a long productive season: the grassland may have been relatively productive.
Grassland expansion should not automatically be interpreted as evidence of increasing animal abundance or improving human living conditions.
Tundra
Tundra represents cold, treeless environments in which tree growth is severely restricted.
Typical vegetation may include:
- sedges;
- mosses;
- lichens;
- low shrubs; and
- short herbaceous plants.
Tundra generally has a short growing season and low annual productivity. However, it may still provide seasonal forage for mobile herbivores such as reindeer.
How to interpret it
- Increasing share: cold open environments expanded.
- Increase combined with Boreal forest decline: forest may have shifted toward treeless cold environments.
- Increase combined with fewer productive months: cooling and shortening growing seasons may have occurred together.
- Increase combined with Tundra-steppe decline: relatively steppe-like open environments may have shifted toward colder tundra.
Tundra expansion does not mean that animals and humans were completely unable to use the region. Seasonal production and winter forage accessibility must also be considered.
Tundra-Steppe
Tundra-steppe is a cold, open environment combining tundra vegetation with dry steppe vegetation.
It is closely associated with discussions of the Ice Age mammoth steppe, but it was not one uniform grassland extending unchanged across Eurasia.
Regional conditions differed in:
- grass, sedge, and shrub composition;
- vegetation density;
- soil moisture;
- snow conditions;
- productive-season length;
- summer productivity; and
- seasonal availability to herbivores.
How to interpret it
- Increasing share: cold but steppe-like open environments expanded.
- Increase together with Tundra: forest may have declined while cold open environments expanded.
- Increase relative to Grassland: the environment may have shifted toward colder or drier steppe conditions.
- High Peak-quarter NPP: production may have been concentrated within a short summer season.
- Low annual NPP: the environment may have been extensive but sparsely vegetated and weakly productive.
A large Tundra-steppe area does not by itself demonstrate high mammoth or herbivore density.
Other
Other is a visualization category combining megabiomes that are not displayed separately in the graph.
Depending on the region and period, it may include:
- Temperate forest
- Cool forest
- Savanna / woodland
- Shrubland
- Desert
- Barren
- Land ice
Other is not a single ecological environment. It is used to simplify the graph and make changes in the four principal categories easier to see.
How to Read the Stacked Bar Graph
Each bar represents the megabiome composition of the selected region at a particular date.
The vertical axis shows the percentage of land within the 500 km analysis window.
The total of each bar equals 100%.
For example, one date may show:
- Boreal forest: 4%
- Grassland: 0%
- Tundra: 51.5%
- Tundra-steppe: 26.8%
- Other: 17.7%
This does not mean that the entire analysis window consisted of one environment. It means that different megabiomes occupied those proportions of the window.
Reading a single bar
For each bar, ask:
- Which category occupied the largest area?
- Which category ranked second?
- Did one category dominate strongly?
- Were several categories present in similar proportions?
- What was the balance between forest and open environments?
Reading change through time
Comparing bars from left to right shows:
- forest expansion or decline;
- changes in Grassland and Tundra-steppe;
- tundra expansion;
- periods of rapid ecological restructuring;
- persistence of particular environments; and
- repeated shifts between forest and open environments.
A large movement in the boundaries between coloured sections indicates substantial change in environmental composition.
Dominant Megabiome
The Dominant Megabiome is the megabiome occupying the largest share of the selected region at a particular date.
For Yana at 30 ka BP:
Dominant Megabiome: Tundra
Dominant Megabiome Percent: 51.5%
This means that approximately 51.5% of the 500 km Yana analysis window was classified as Tundra, making it the largest individual category.
Important qualification
The dominant megabiome does not describe the entire analysis window.
The remaining 48.5% contained other environments, including Tundra-steppe, Boreal forest, Barren land, and Desert.
An appropriate statement is:
At 30 ka BP, Tundra was the largest megabiome in the Yana analysis window, covering approximately 51.5% of its land area.
Closed Forest
Closed Forest is a derived indicator combining the area shares of relatively closed forest megabiomes.
It includes:
- Temperate forest
- Cool forest
- Boreal forest
For Yana at 30 ka BP:
Closed Forest: 4.0%
At this date, Boreal forest covered approximately 4.0% of the window, while the other closed-forest categories were effectively absent.
How to interpret it
- High value: forest environments occupied a large part of the analysis window.
- Low value: open environments predominated.
- Decline through time: possible weakening of forest barriers or landscape opening.
- Increase through time: possible forest expansion or recovery.
Closed Forest does not directly measure tree density or wood production. It measures the percentage of the analysis window classified within closed-forest megabiomes.
Core Steppe
Core Steppe represents the combined share of principal steppe-like open environments.
It includes:
- Grassland
- Tundra-steppe
For Yana at 30 ka BP:
Core Steppe: 26.8%
Because Grassland was effectively absent at Yana, this value was almost entirely derived from the 26.8% Tundra-steppe share.
How to interpret it
- High value: steppe-like open environments were extensive.
- Increase combined with Closed Forest decline: forest may have contracted while open steppe habitats expanded.
- High together with Cold Open: cold open environments dominated much of the region.
- High but accompanied by low NPP: the steppe may have been extensive but sparsely vegetated and weakly productive.
- High Peak-quarter NPP: production may have been concentrated within a short seasonal window.
Core Steppe does not directly measure herbivore abundance or available forage.
Cold Open
Cold Open combines cold environments that were treeless, sparsely vegetated, or nearly vegetation-free.
In this map, it primarily includes:
- Tundra
- Barren
For Yana at 30 ka BP:
Therefore:
Cold Open: 68.7%
This means that approximately 68.7% of the Yana analysis window consisted of tundra or sparsely vegetated cold open ground.
Tundra-steppe is included in Core Steppe and is not counted again in Cold Open.
How to interpret it
- High value: cold open environments were extensive.
- High Cold Open and low Closed Forest: the landscape was predominantly open and largely treeless.
- Increase driven by Barren: may indicate stronger vegetation scarcity rather than tundra expansion alone.
- Increase driven by Tundra: indicates expansion of treeless cold environments.
An increase in Cold Open was not necessarily favourable for herbivores. Greater openness could coincide with lower productivity, reduced animal density, and longer seasonal movements.
Megabiome Turnover
Megabiome Turnover summarizes how much the proportional composition of megabiomes changed between two consecutive dates.
It is calculated by summing the absolute changes in the area shares of all categories and dividing the result by two:
where:
- pi,t is the area share of category i at the current date;
- pi,t−1 is its area share at the previous date.
Values generally range from 0 to 1.
Basic interpretation
| Turnover | Interpretation |
|---|---|
| Near 0 | Megabiome composition changed very little |
| Increasing value | Larger proportions of the analysis window changed categories |
| Near 1 | Composition was almost completely replaced by different categories |
For Yana at 30 ka BP:
Megabiome Turnover: 0.078
This indicates that the compositional change from 32 to 30 ka BP was equivalent to approximately 7.8% of the analysis window changing from one megabiome category to another.
The principal changes were:
- increasing Tundra-steppe;
- decreasing Tundra;
- decreasing Barren; and
- a small increase in Boreal forest.
The value of 0.078 does not indicate simple environmental deterioration. It describes the degree to which parts of the landscape shifted from tundra and barren environments toward Tundra-steppe and Boreal forest.
Important qualification
High turnover does not automatically indicate environmental deterioration. It indicates substantial change in the proportional composition of environmental categories.
Both of the following could produce high turnover:
- forest declining while tundra expands;
- tundra declining while grassland or forest expands.
The direction of change must therefore be determined from the individual category shares.
The first date in a time series has no preceding date for comparison. Its turnover may be shown as zero or excluded from calculation. This does not mean that no environmental change occurred before that date.
Interpretation Example: Yana RHS at 30 ka BP
| Display Category | Area Share | Composition |
|---|---|---|
| Boreal forest | 4.0% | Boreal forest |
| Grassland | 0.0% | Grassland |
| Tundra | 51.5% | Tundra |
| Tundra-steppe | 26.8% | Tundra-steppe |
| Other | 17.7% | Barren 17.2% + Desert 0.5% |
The result can be summarized as follows:
At 30 ka BP, Tundra was the largest megabiome in the Yana analysis window, covering approximately 51.5% of its land area. Tundra-steppe accounted for approximately 26.8%, while Boreal forest covered only about 4.0%. Other accounted for approximately 17.7%, consisting mainly of Barren land and a small Desert component. The region was therefore dominated by cold open environments, although Tundra-steppe remained present across more than one-quarter of the analysis window.
The derived indicators shown on the map card can be read as follows:
- Dominant Megabiome 51.5%: the share occupied by Tundra, the largest category
- Closed Forest 4.0%: the combined share of closed-forest environments
- Core Steppe 26.8%: the combined share of Grassland and Tundra-steppe
- Cold Open 68.7%: the combined share of Tundra and Barren
- Megabiome Turnover 0.078: the magnitude of compositional change since 32 ka BP
These results do not indicate that Yana was a warm or continuously productive refuge. They show a low-forest landscape dominated by cold open environments.
However, the presence of Tundra-steppe and a short summer production window may have allowed mobile herbivores to use the region seasonally. Humans may then have exploited these seasonal opportunities through clothing, shelter, storage, cooperation, and knowledge of animal movement.
Data source. Beyer, R. M., Krapp, M., & Manica, A. (2020). High-resolution terrestrial climate, bioclimate and vegetation for the last 120,000 years. Scientific Data, 7, 236. https://doi.org/10.1038/s41597-020-0552-1
Watch the accompanying video
For a guided interpretation of the reconstructed temperature patterns and their archaeological context, watch the accompanying video on our YouTube channel