What is a Snag?
A snag is a standing dead tree — one that has died but remains upright as it slowly decays. Far from being wasted space, snags are ecological powerhouses: they provide food, shelter, and nesting sites for hundreds of species.
Ecological Roles
Nesting Habitat
- Primary cavity nesters: Woodpeckers excavate holes in soft snag wood.
- Secondary cavity users: Parrots, owls, bats, and small mammals move into abandoned cavities.
- Bee and wasp nests: Hollow chambers host pollinator colonies.
Food Source
- Decaying snag wood teems with beetle larvae, termites, and other invertebrates.
- Woodpeckers, anteaters, and bark-gleaning birds forage on snags.
- Fungi fruiting on snags feed insects and small mammals.
Perch Sites
- Raptors use snag tops as hunting perches.
- Kingfishers perch on riverside snags to spot fish below.
Snag Stages
- Recently dead: Bark intact, hard wood — primary cavity excavation begins.
- Decay stage 1: Bark loosening, heartwood softening — cavity nesters active.
- Decay stage 2: Bark fallen, soft wood — more cavities, fungi fruiting.
- Hollow stage: Trunk largely hollow — large cavity users (macaws, kinkajous).
- Collapse: Snag falls, becoming a nurse log on the forest floor.
Costa Rican Context
Almendro Snags
Dead Almendro trees are critical nesting sites for the endangered Great Green Macaw — their large, durable trunks form cavities that persist for decades.
Why It Matters
- Biodiversity: A single old snag can support dozens of species simultaneously.
- Forest management: Retaining snags in managed forests and plantations dramatically increases wildlife value.
- Urban ecology: Dead trees in parks and gardens are valuable if they pose no safety risk.