How to Read the Vegetation & Productivity Map
This map summarizes vegetation productivity, vegetation density, and seasonal production within a 500 km radius around each selected site.
The values are area-weighted averages calculated from the land grid cells contained within each analysis window. The circles are standardized statistical comparison areas. They do not represent reconstructed settlement territories, hunting ranges, or cultural boundaries.
| Variable | What It Measures | How to Interpret It | Important Limitation |
|---|---|---|---|
| Annual NPP | Annual net primary productivity | Higher values indicate greater annual plant production per unit area. | It does not directly measure edible plants, herbivore abundance, or human carrying capacity. |
| Annual Mean LAI | Average leaf area index | Higher values indicate denser vegetation or more leaf cover. | Dense vegetation is not necessarily more suitable for large grazing animals. |
| Productive Months | Estimated duration of meaningful plant production | Higher values indicate a longer productive season. | A longer productive season does not necessarily mean greater total production. |
| Peak-Quarter NPP | NPP during the most productive consecutive three months | Higher values indicate stronger production during the peak growing season. | The displayed unit should be verified against the original data and calculation method. |
| Lowest-Quarter NPP | NPP during the least productive consecutive three months | Values near zero indicate a strong winter or dry-season production bottleneck. | Zero may represent a true absence of production or a data-processing issue. |
| Analysis Window Area | Land area included in the regional calculation | It shows the actual area represented by the regional statistics. | It is not a reconstructed settlement territory, hunting range, or cultural boundary. |
Annual NPP
NPP, or Net Primary Productivity, is the amount of organic carbon accumulated by plants after subtracting the carbon used for plant respiration from total photosynthetic production.
The unit is:
g C m⁻² yr⁻¹
This represents the number of grams of carbon newly accumulated by vegetation per square metre per year.
For Tianyuan Cave at 30 ka BP:
269.4 g C m⁻² yr⁻¹
This means that vegetation within the 500 km analysis window accumulated an estimated average of 269.4 grams of carbon per square metre during that year.
How to interpret Annual NPP
- Higher NPP indicates greater annual plant production.
- Lower NPP may reflect colder temperatures, drier conditions, or a shorter growing season.
- Declining NPP through time indicates weakening plant productivity.
- Comparisons between regions show differences in plant production per unit area.
NPP is not equivalent to:
- the amount of edible vegetation available to humans;
- actual herbivore abundance;
- the density of huntable animals;
- winter-accessible forage;
- human population size or carrying capacity.
NPP provides information about the foundation of the terrestrial food web, but it does not directly measure human or animal populations.
Annual Mean Leaf Area Index
LAI, or Leaf Area Index, represents the total leaf area above one square metre of ground.
For Tianyuan Cave at 30 ka BP:
LAI 1.59
This indicates approximately 1.59 square metres of leaf surface above each square metre of ground within the analysis window.
Because LAI is a ratio of area to area, it is technically dimensionless. It may be displayed simply as:
LAI 1.59 or 1.59 m²/m²
How to interpret LAI
- Higher LAI indicates denser vegetation or more leaf cover.
- Lower LAI indicates sparse vegetation or limited leaf cover.
- Declining LAI may indicate vegetation thinning, forest opening, or deteriorating growing conditions.
- Declining NPP and LAI together provide stronger evidence of weakening vegetation.
LAI describes vegetation structure and density, whereas NPP describes the amount of new plant production over a given period.
Reading NPP and LAI together
| NPP | LAI | Possible Environmental Interpretation |
|---|---|---|
| High | High | Dense and productive forest |
| High | Low | Rapid seasonal production in relatively open vegetation |
| Low | High | Leafy but slowly growing cold-climate forest |
| Low | Low | Sparse tundra, cold grassland, or desert-like vegetation |
A high LAI was not necessarily favourable for large herbivores. Open grasslands with somewhat lower LAI may have provided better habitat for mobile grazing animals such as horses, bison, and mammoths than dense forests.
Productive Months
Productive months estimates the part of the year during which meaningful plant production could occur.
For Tianyuan Cave at 30 ka BP:
5.8 months
This indicates an average productive period of approximately 5.8 months within the analysis window.
The decimal does not mean that every location experienced exactly 5.8 consecutive productive months. It may result from averaging values across multiple land grid cells within the 500 km analysis window.
How to interpret Productive Months
- Higher values indicate a longer productive season.
- Lower values indicate that production was concentrated within a shorter seasonal window.
- A decrease of 0.5 months corresponds to approximately 15 days.
- A decrease of 0.9 months corresponds to approximately 27 days.
Productive months must be interpreted together with NPP:
- Long productive season and high NPP: long and productive growing season
- Long productive season and low NPP: prolonged but weak production
- Short productive season and high peak-quarter NPP: short but intense production window
- Short productive season and low NPP: strong seasonal and productivity constraints
At high-latitude sites such as Yana, a short productive season could still support a concentrated pulse of summer vegetation used seasonally by mobile herbivores.
Peak-Quarter NPP
Peak-quarter NPP represents the cumulative net primary productivity during the most productive consecutive three-month period of the year.
For each grid cell, NPP values are summed across every possible sequence of three consecutive months. The three-month period with the highest cumulative value is then selected. Because the three monthly values are added rather than averaged, the unit is:
g C m⁻² per 3 months
For Tianyuan Cave at 30 ka BP:
Peak-quarter NPP: 175.632 g C m⁻² per 3 months
Peak-quarter NPP was therefore approximately 65.2% of annual NPP:
Within the 500 km Tianyuan analysis window, the average amount of NPP accumulated during each grid cell’s most productive consecutive three-month period was approximately 65.2% of the annual NPP average. This indicates that plant production was strongly concentrated within a relatively short seasonal window.
How to interpret Peak-Quarter NPP
- Higher values indicate greater cumulative plant production during the most productive part of the year.
- A high ratio of peak-quarter NPP to annual NPP indicates strong seasonal concentration.
- A decline in both annual NPP and peak-quarter NPP indicates weakening annual and peak-season productivity.
- High peak-quarter NPP combined with few productive months indicates a short but relatively intense production season.
Unit note
The map currently displays:
g C m⁻² month⁻¹
Lowest-quarter NPP
Lowest-quarter NPP represents the cumulative net primary productivity during the least productive consecutive three-month period of the year.
For each grid cell, monthly NPP values are summed across 12 possible sequences of three consecutive months. The three-month period with the lowest cumulative value is then selected.
The unit is:
g C m⁻² per 3 months
This indicates that, under the corrected model values, the Tianyuan analysis window contained a seasonal production bottleneck during which cumulative plant productivity was effectively zero for three consecutive months.
How to Interpret Lowest-Quarter NPP
- Values near zero indicate a severe winter or dry-season production bottleneck.
- A value of zero indicates that corrected modelled NPP was effectively absent during the least productive consecutive three-month period.
- Higher values indicate that some plant production continued throughout the least productive season.
- A large difference between peak- and lowest-quarter NPP indicates strong seasonality.
- Lowest-quarter NPP should be interpreted together with annual NPP, peak-quarter NPP, and productive months.
Interpretation Limitation
A value of 0.0 does not constitute direct observational evidence that all photosynthesis completely stopped throughout the natural landscape.
It indicates that, at the spatial resolution of the model and after applying the negative-value correction rule, the reconstructed NPP reached an effectively non-productive winter bottleneck for three consecutive months. Small-scale plant activity below the model’s spatial or numerical resolution may not be represented.
Analysis Window Area
For Tianyuan Cave, the map shows:
784,191 km²
Each circle represents a statistical analysis window with a radius of 500 km. The theoretical area of a complete 500 km radius circle is:
he small difference may result from raster resolution, land masks, coastline boundaries, or the area-weighting method.
The analysis window does not represent:
- the territory occupied by the site’s inhabitants;
- the actual hunting range of a human group;
- a reconstructed archaeological culture area;
- the distance regularly travelled by individuals.
Example: Tianyuan Cave at 30 ka BP
The Tianyuan analysis window at 30 ka BP can be summarized as follows:
- Annual NPP: 269.4 — higher productivity than northern Siberia, although productivity was declining over the longer term.
- Annual mean LAI: 1.59 — moderately dense vegetation, possibly representing relatively open vegetation or a forest–grassland mosaic.
- Productive months: 5.8 — a substantially longer productive season than in northern Siberia.
- Peak-quarter NPP: 175.6 — approximately 65% of annual production may have been concentrated in the most productive three months.
- Lowest-quarter NPP: 0.0 — plant production may have effectively stopped during the least productive season.
- Analysis window area: 784,191 km² — the land area represented by the standardized 500 km statistical window.
A cautious overall interpretation would be:
At 30 ka BP, the Tianyuan region had a longer productive season and higher plant productivity than northern Siberia. However, production remained strongly seasonal, while longer-term drying and declining vegetation productivity were making the regional environment increasingly unstable.
Environmental indicators provide ecological context. They are not direct evidence of human movement, settlement density, hunting behaviour, or population size.
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
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