What is a Mast Year?
A mast year is a boom year for tree reproduction — when a population synchronously produces a massive crop of seeds or fruits, far exceeding the normal annual output. This overwhelms the animals that eat seeds (predator satiation), allowing many more seeds to survive and germinate.
How It Works
- Accumulation: Trees store resources over several low-production years.
- Trigger: A climatic cue (drought, temperature shift) synchronizes the population.
- Mass fruiting: Trees produce 10–100× more seeds than average.
- Predator satiation: Seed-eating animals cannot consume the entire crop.
- Successful recruitment: Surplus seeds germinate and establish.
Patterns
- Interval: Every 2–7 years depending on species.
- Synchrony: Populations across wide areas fruit simultaneously.
- Inter-mast years: Very low seed production — "starvation years" for seed predators.
Costa Rican Examples
Roble Encino (Quercus spp.)
Highland oaks display classic mast-year behavior, with heavy acorn crops every 3–5 years feeding Resplendent Quetzals, agoutis, and countless other species.
Almendro (Dipteryx panamensis)
Mast fruiting events are critical for Great Green Macaws, which depend on large Almendro crops for nesting season food.
Ecological Significance
- Wildlife populations: Mast years drive population booms in seed-dependent species.
- Forest regeneration: Most successful tree recruitment occurs in mast years.
- Climate sensitivity: Changes in mast timing signal climate disruption.