Female cones typically expand from buds in the spring, remaining small, closed, and often reddish in color for the first year. Pollination occurs the second year, after which cones expand rapidly, turning green in color and then brown as they mature. Cones can begin to open in fall of this second year, but seeds may release throughout winter. Cones begin to fall from trees soon after, but, depending on species, may remain on tree for years.
Our cone counts record an estimate of the number of cones seen through binoculars together with the fraction of the crown that the count represents. This is the basis for a binomial likelihood in model fitting, binom(yc|n, p), with known y (cone count), c (seeds per cone), and p (canopy fraction) and unknown n. We count both the number of green, unopened cones that will open this year and the brown cones that opened last year. The count of cones opened last year is a minimum count, because some cones may have already fallen.
Cones have two seeds per bract. To obtain seeds per cone, cones are sampled from multiple individuals and locations and counted.
P. contorta can produce both serotinous cones, which remain closed and attached to the stem until opened by heat during fire, and non-serotinous cones, the latter opening in autumn and releasing seeds like most other species. The proportions of serotinous and non-serotinous cones varies by individual tree. For this species, we record each individual as serotinous, non-serotinous, or mixed.
Seed predation begins in the canopy, where squirrels dismember them and song birds can extract seeds after cones open and before seeds are dispersed. Uncertainty in the model has to allow for variation in seeds per cone, in addition to cone production and seed dispersal. Due to canopy predation, seed trap counts are conservative.