DOI: 10.5061/dryad.7m0cfxq8w
title: Data from: The world's oldest man-made biological experiment

description: 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.
description: The data was collected during an initial assessment of
 environmental conditions in jar-based ecosystems on the Plain of
 Jars: Five sites, that have been cleared of unexploded
 ordnance and are therefore now safely accessible, were selected to study
 the environmental conditions inside the jars. Each site has a different
 number of available jars, depending on the size of the site and the
 condition of the jars, as many are broken and therefore unable to hold
 water. Site 1 is exposed on the plateau, with only a few trees in the
 vicinity. Ten jars from three different groups (1, 2, and 4) were studied
 at this site. Sites 2, 3, 21, and 52 are located in the forest and
 surrounded by trees. We investigated 6 jars at site 2, 6 jars at site 3,
 and 15 jars at site 52, respectively. At Site 21, two jars were sampled.
 We present here data from the samplings in November 2022 and September
 2023. At each site, jars were randomly selected during the first visit,
 but based on their ability to hold water, located via GPS, and
 photographed. The parameters measured on site depend on the sampling
 period. Documentation included measurement of water depth inside the jars,
 water temperature, and oxygen. Water samples were taken and stored in the
 dark in a fridge before being transported to Copenhagen, where they were
 stored frozen (-20°C; 2022 samples) / in a fridge (4°C, 2023 samples)
 until analysis. Laboratory measurements included alkalinity, total
 nitrogen and total phosphorus. Alkalinity was measured using Gran
 titration (Gran 1952). Total phosphorus and nitrogen were analyzed
 following Danish Standards (DS221 and DS292) using an AA3 autosampler
 (Seal Analytic). In November 2022, we also took pictures of the canopy
 right above the jars. We then used those pictures to create a binary image
 (black and white) and the percentage of black canopy was used to estimate
 canopy cover.
description: # Data from: The world's oldest man-made biological experiment
 Dataset DOI:
 [10.5061/dryad.7m0cfxq8w](https://doi.org/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](http://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.