Data from: The world's oldest man-made biological experiment

Käse, Laura 1 ; Somvongsa, Chanvilay2; Inkhavilay, Khamla2; Christensen, Claus3; Iversen, Lars 4 ; Pedersen, Ole1; Baastrup-Spohr, Lars1

Published Nov 19, 2025 on Dryad. https://doi.org/10.5061/dryad.7m0cfxq8w

Data files

Nov 19, 2025 version files 15.59 KB

Käseetal_Ecography_The_world’s_oldest_man-made_biological_experiment.csv

12.54 KB
README.md

3.05 KB

Abstract

Biological experiments are often short-lived due to logistical or resource-related challenges, and short-term observations are extrapolated to make long-term predictions. However, the effects of experimental treatments on biological communities and processes take time to develop. Consequently, the robustness of conclusions drawn from observations increases with the duration of the experiment. As a striking real-world example and scattered throughout central Laos, thousands of large stone jars have been left behind from ancient burial rituals. The most famous sites in the Xiengkhouang province are collectively referred to as the Plain of Jars. These jars form a massive biological experiment: for ~2000 years, rainwater has interacted with the geological origin of each jar to create unique yet replicated aquatic ecosystems influenced by different tree coverage. The layout of these jars, with clusters of up to several hundred jars separated by several kilometers, allows for controlled testing of multiple questions within ecology and evolution. Here, we report for the first time how these ancient mesocosms can be used to test ecosystem responses to local abiotic variation and disturbance. We show that tree cover dominates every jar ecosystem’s state, and that variations in tree cover density create gradients in O₂ and nutrient concentrations among jar ecosystems. These initial findings show that litter contribution to aquatic ecosystems leads to higher nutrient content and reduces O₂ concentration, even in systems under different long-term selection in the oldest man-made ecosystems ever analyzed. This first biological analysis provides a fundamental understanding of a unique environment and offers trajectories for future exploration.

Dataset DOI: 10.5061/dryad.7m0cfxq8w

Description of the data and file structure

Files and variables

File: Käseetal_Ecography_The_world’s_oldest_man-made_biological_experiment.csv

Description:

Variables

Jar_name_adaptedfromShewanetal.2020: Jar names adapted from the Plain of Jars Archaeological Research Project (Shewan et al., 2020).
Reference: Shewan, L., O'Reilly, D., Kemp, J., Tomko, M., Hardiman, R., Barnes, D., Michalewicz, A., Thompson, K., Fitzgerald, E., Garber, J. Turnbull, R. 2020. Plain of Jars Archaeological Research Project (www.plain-of-jars.org).
Site: Official site names (see also Shewan et al., 2020).
Sampling: Season of sampling: Dry season: November 2022, Wet season: September 2023
Samplingtime: Sampling time (November 2022 or September 2023)
Latitude / Longitude: GPS coordinates of each jar location in decimal degrees.
Coverage: Broad canopy coverage category (e.g., uncovered or covered).
Coverage2: Detailed canopy coverage category (open sky, partial tree cover, tree covered).
Canopy_%: Estimated canopy cover percentage, calculated from binary images (black/white) derived from photographs.
Jar_width1_cm: Jar width in centimeters, measured in the field.
Jar_width2_cm: Second jar width in centimeters (jar shape might be round, oval or rectangular).
Jar_height_cm: Jar height in centimeters, measured based on the maximum water depth the jar could hold. For broken jars, height was measured only up to the highest intact point, as additional height would not retain water.
potentialmaximalwatervolumed_L: Maximum potential water volume (in Liters), calculated from jar dimensions (height, width1, width2) assuming jar shape as circular cylinder (round base), elliptical cylinder (oval base) or rectangular box
waterdepth_cm: Water depth in centimeters, measured in the field.
watervolume_L: Actual water volume (in Liters), calculated from water depth and jar dimensions using the same shape assumptions as above.
Oxygen_%ofairequilibrium: Oxygen concentration expressed as a percentage of air equilibrium, measured in the field.
Temperature_C: Water temperature in degrees Celsius, measured in the field.
TotalNitrogen_microgNL-1: Total nitrogen concentration (micrograms of N per Liter).
TotalPhosphorous_microgPL-1: Total phosphorus concentration (micrograms of P per Liter).
Alkalinity_mmolL-1: Alkalinity in millimoles per liter.

Missing Data

Values that are not available in the dataset are represented as NA.

Code/software

The dataset is provided as a CSV file, which can be opened with any text editor or spreadsheet software. For data processing and analysis, we used R version 4.3.3. Details on the packages and methods applied are provided in the Supplemental Information file associated with the publication. No proprietary software is required to view the data.