Data collection
Monthly, from June to August 2006, we measured light intensity
(photosynthetically active radiation; PAR) within each of the 49 plots
using a LI-COR L1–250A light meter (µmol s-1n-2; LI-COR Biosciences, Lincoln, USA). Each plot was
divided into nine equal squares in a 3 x 3 grid, with three measurements
taken in the center of each plot row, directly above the canopy, and
nine measurements taken at ground-level in each square (Fig. 1). We
calculated the percentage of light penetration based on the mean light
intensity at ground-level for each of the nine locations in the plot and
the mean above-canopy light intensity measured above each plot row
[100 × (ground-level light intensity / above-canopy light
intensity)].
From June to August 2006, we collected abundance data by quantifying the
number of rooted units per species in each plot (i.e., ramets, Schamp et
al. 2016), and determined plot-level species richness from these
abundance data. We monitored plot-level abundance biweekly, which was
further classified into two census types: total abundance of each
species (including all rooted units in a plot, both reproductive and
nonreproductive), and flowering abundance of each species (including
only reproductive rooted units in a plot). Species maximum height (cm)
data were collected for all species in the dataset from specimens
measured at the study site (not in sample plots) and in nearby
old-fields at the Queen’s University Biological Station. The number of
values recorded per species ranged between 5-20, and the largest value
per species was used as the maximum height for that species.