What is a Nurse Tree?
A nurse tree is a species that creates favorable conditions for the establishment of other, often more valuable or shade-tolerant species. By providing shade, wind protection, improved soil, and sometimes mycorrhizal connections, nurse trees accelerate forest recovery.
How Nurse Trees Help
- Shade: Reduce temperature extremes and photo-inhibition stress on seedlings.
- Moisture: Lower evapotranspiration under the canopy, keeping soil moist.
- Wind protection: Buffer young trees from desiccating or damaging winds.
- Soil improvement: Add organic matter and fix nitrogen (in legumes).
- Mycorrhizal networks: Share fungal connections that transfer nutrients to seedlings.
Costa Rican Examples
Guarumo (Cecropia obtusifolia)
The classic nurse tree — colonizes gaps rapidly, providing shade that allows slower-growing species like Almendro and Guapinol to establish beneath it before it is eventually overtopped.
Madero Negro (Gliricidia sepium)
Nitrogen-fixing legume widely used in reforestation as a nurse species for cacao, coffee, and valuable timber species.
Pochote (Pachira quinata)
Used in mixed plantations to shelter slower-growing mahogany and cedar seedlings from direct sun and wind.
Nurse Trees in Reforestation
Costa Rican reforestation programs commonly use nurse tree strategies:
- Plantation enrichment: Plant pioneers first, then introduce target species beneath them.
- Living fences: Border plantings that shade and protect adjacent restoration zones.
- Temporal sequence: Nurse trees are allowed to grow 1–2 years before target species are interplanted.
Practical Significance
- Lower mortality: Seedling survival rates can double under nurse tree canopy.
- Faster succession: Nurse trees compress decades of natural succession into years.
- Economic efficiency: Cheaper than artificial shade structures in large-scale restoration.