Eucalyptus Plantations

Description

Eucalyptus plantations (Eucalyptus globulus) are the most widespread forest type in Portugal: ~845,000 ha (26.2% of forest area, ~10% of the country’s total area). These are industrial monocultures for the pulp industry with a rotation cycle of 10–12 years.

From a mycological perspective, eucalyptus plantations are a poor habitat. They are often called desertos verdes (“green deserts”) due to the significant reduction in biodiversity compared to native forests.

Geographic distribution

• Main regions: northern and central Portugal
• Area: ~845,000 ha — more than cork oak (736,000 ha) or pine (714,000 ha)
• Trend: despite government reduction policies (National Forest Strategy 2006), the area continues to grow
• Since the mid-20th century, native forests (Pinus pinaster, Quercus suber) have been systematically converted to eucalyptus plantations

Why eucalyptus is a poor mushroom habitat

Allelopathic compounds

Eucalyptus releases powerful allelochemicals: benzoic acid, hydroxybenzoic acid, vanillic acid, and terpenoids. The key compound — 1,8-cineole (eucalyptol) — suppresses germination and growth of competing plants and soil microorganisms.

Acidic and hydrophobic litter

• Soils under eucalyptus are highly hydrophobic (water-repellent)
• Microorganisms struggle to decompose leaves and bark
• Low organic matter, poor soil structure
• Soil absorbs rainwater significantly worse than under native forests

Limited mycorrhizal partners

• Low colonisation of roots — both ecto- and arbuscular mycorrhizas
• Fungal diversity significantly lower than in native oak forests
• Eucalyptus was brought from Australia — European fungi “don’t recognise” this tree

Impact on biodiversity

• 66% of cases where native forests are replaced by eucalyptus lead to biodiversity loss
• Replacing large areas of native forest with monospecific plantations → homogenisation of fungal communities
• Some fungal species are found only on plots with native trees — potential bioindicators of habitat quality

What mushrooms do grow

Co-introduced Australian species

Mycorrhizal partners from Australia were unintentionally introduced alongside eucalyptus:

Native fungi on eucalyptus

A study on the Iberian Peninsula identified 26 ectomycorrhizal taxa associated with E. globulus. Only 3 were Australian; the rest were native European fungi that had formed novel associations with eucalyptus.

Some native genera colonising eucalyptus: Cortinarius, Laccaria laccata (European), Russula spp.

Saprotrophic species

• Oyster mushroom (Pleurotus ostreatus) — grows on dead eucalyptus wood
• Honey fungus (Armillaria mellea) — parasitises eucalyptus too
• Saprotrophs have limited presence due to the difficulty of decomposing eucalyptus litter

Scientific discovery: 184 species

The first mycological survey on Navigator Company land (Quinta de São Francisco) identified 184 macrofungal species, including species from eucalyptus plantations and surrounding ecosystems. Possibly over a dozen species new to science were discovered.

Ecological controversy

Replacement of native forests

• From 1958 to 1995, agricultural land and scrubland shrank dramatically, while eucalyptus plantations expanded dramatically
• Eucalyptus replaces cork oak, holm oak, and maritime pine
• 66% of replacements lead to biodiversity loss at all levels

Fire risk

Eucalyptus and pine covered ~70% of the burned area in the catastrophic Pedrógão Grande fire (2017). Eucalyptus bark rapidly conducts fire to the crown; leaves are highly flammable. By comparison, cork oak is a fire-resistant species.

Consequences for mushrooms

• Eucalyptus does not form mycorrhizas with native fungi of pine and oak forests
• Fungal species diversity is significantly lower than in native forests
• Eucalyptus litter decomposes more slowly due to essential oils
• However, arbuscular mycorrhiza (AM) can mitigate the allelopathic suppression of native trees by eucalyptus

Practical tips

1. Don’t expect a rich harvest — eucalyptus plantations are mushroom-poor
2. Look for “islands” of native trees within plantations — they harbour significantly more fungi
3. Edges and transition zones — where eucalyptus borders oak or pine forest — are the most promising areas
4. Oyster mushroom — one of the few culinarily valuable species growing on eucalyptus
5. Be cautious with unfamiliar species — Australian co-introductions may look unusual

Sources

1. Fernández-Toirán L.M. et al. — Context dependency, co-introductions, novel mutualisms, and host shifts shaped the ectomycorrhizal fungal communities of Eucalyptus globulus // Scientific Reports, 2019
2. Díez J. — Invasion biology of Australian ectomycorrhizal fungi introduced with eucalypt plantations into the Iberian Peninsula // Biological Invasions, 2005
3. Biodiversidade.com.pt — Primeiro estudo micológico identifica 184 espécies de cogumelos
4. Público — Estudo revela que eucalipto provoca «dramática redução» da biodiversidade, 2017
5. Pereira H. — Cork Oak Woodlands on the Edge // Island Press