if a spruce interacts with soil that has been previously conditioned by
spruce, that plant will die. But if the soil has been conditioned by pine,
ash, or Ailanthus species, the spruce will survive.
The directions for setup are as follows:
(1) Split the class so that there are equal numbers of plant and
soil players (Figure 1A). Clear enough space in the room so
that plant and soil players can stand in two opposing lines
with no obstacles between the groups (Figure 1B). Soil
players each receive one blank notecard and paperclip.
Include a pile of paper cutouts of the different plant species
(3× the total amount of plant players for each species) to
serve as the species pool, as well as a separate discard pile
for when plants die and are not returned to the species pool.
(2) Each plant player randomly draws one species from the species
pool and returns to the line of opposing soil players. Record
the abundance of each plant species in the community at this
initial time point (T0). These abundances are recorded on multiple graphs (one graph for each time point; Figure 2A). Note:
the game can be purposefully set at different levels of diversity
After setup, the gameplay begins:
(3) Plant players approach a random soil player to begin the
conditioning phase that determines how plants change
the physical, chemical, and biotic components of their
soils on the basis of traits related to their identity. For
example, ash leaves have lower ratios of carbon (C) to
nitrogen (N) than spruce needles, which affects the qual-
ity of litter inputs to the soil and structures decomposer
communities. To simulate conditioning, plant players
hand their species to soil players, and soil players paper-
clip the species behind their soil card to hide the species
that conditioned them.
(4) Plant players then randomly draw another species from the
species pool, form a new line opposing the now conditioned soil players, and interact with a random soil player.
It is important that plant players do not know the conditioned status of soil players before interacting with them
(just as tree seedlings cannot preferentially choose more
hospitable soil locations in a forest). In this interaction,
plants approach soils and show their species identity; in
Live Live Live
Die Die Live
Die Live Live Live
Live Live Live
Live Live Live
Assign plant & soil players
Plants ‘condition’ soils
Plants & soils interact
Figure 1. How to perform the activity. (A) The flow diagram outlines the general approach to the activity. The game is based on many
random one-on-one interactions between plant and soil players. (B) The outcomes of plant–soil interactions depend on the mode and
identities of both plant and soil players. Plants that live remain matched with their soils (players stand next to one another; gray arrows).
Plants that die discard their species, draw a new species from the species pool, and interact with any unmatched soil. In negative mode,
plants die when they interact with soils conditioned by the same species ( i.e., survival occurs when plants and soils are mismatched). In
positive mode, select one plant species that will have positive interactions (e.g., Ailanthus species marked with asterisks). This species
survives in all soil types, and no other species can survive in Ailanthus-conditioned soil. Plant species’ abundances are recorded once all
plants are living to show how the species’ abundance and community richness are shaped by plant–soil interactions.