Chestnut Forests

Description

Chestnut groves — soutos — are among Portugal’s most productive mushroom habitats. The European chestnut (Castanea sativa) forms ectomycorrhiza with dozens of fungal species, creating an exceptionally rich fungal community. A scientific study in Bragança recorded 73 macrofungal species in a single chestnut grove, of which 82% were mycorrhizal.

Before the arrival of potatoes from the New World, chestnuts were the dietary staple of northern regions — the tree was called árvore do pão (“bread tree”). Today, chestnuts and mushrooms are the two great “gifts of the forest” in autumn Trás-os-Montes.

Geographic distribution

Main regions

• Trás-os-Montes — the main chestnut region: 75.8% of all chestnut plantations, ~23,000 ha, ~85% of national chestnut production
• Beira Alta — includes the PDO zone “Castanha dos Soutos da Lapa”
• Serra da Estrela — chestnuts on mountain slopes
• Marvão (Alentejo) — a southern isolated population, ~550 ha, PDO “Castanha de Marvão”

Growing conditions

• Soils: acidic to slightly acidic (pH 5–6.5), well-drained
• Climate: humid Atlantic, cooler than the south
• Altitude: 400–900 m
• Total area: ~42,000 ha (reduced from ~80,000 ha due to disease)

Characteristic mushrooms

Edible species

Chestnut forests are among the best places for gathering prized edible mushrooms. Average mushroom income: ~134 EUR/ha/year.

Scientific data

A study by IPB (Bragança Polytechnic Institute, 2002–2005) in the Oleiros chestnut grove identified:

Most numerous genera: Russula (12 species), Inocybe (9), Lactarius (7), Tricholoma (6), Boletus (5), Cortinarius (5), Amanita (5).

11 of 73 species exhibit dual-season fruiting (spring + autumn) — a unique feature of chestnut forests.

Dangerous species

• Deadly webcap (Cortinarius orellanus) — also found in chestnut forests

Seasonality

The peak mushroom season coincides with Magusto — the traditional roast chestnut festival held on St Martin’s Day (November 11).

Mycorrhizal networks

Chestnut forests support rich Common Mycorrhizal Networks (CMN):

• A teaspoon of healthy forest soil contains up to 100 metres of fungal hyphae
• Trees allocate up to 30% of photosynthesised carbon to their mycorrhizal partners
• Through the networks, trees exchange sugars, water and signalling molecules
• Mother trees can nourish young seedlings via the mycorrhizal network
• Chestnut groves serve as biodiversity bridges for ecosystem recovery after fires

Read more: Mycorrhiza

Threats

Ink disease (Doença da Tinta)

Caused by Phytophthora cinnamomi (oomycete). Introduced to Portugal in 1838. Reduced chestnut forest area by nearly half — from 80,000 to ~42,000 ha. Symptoms: chlorosis → defoliation → crown dieback → tree death.

Notably, a project in Marvão has launched mycorrhization of 53 ha of chestnuts with Boletus spp. — mycorrhizal fungi protect roots from Phytophthora.

Chestnut blight (Cancro do Castanheiro)

Caused by Cryphonectria parasitica — an invasive pathogen. First detected in Portugal in 1989. Found in 56.5% of surveyed groves. The only effective control method is biological control through hypovirulence (infecting the pathogen with a hypovirus).

Practical tips

1. Best regions: Bragança, Vinhais, Valpaços, Chaves (Trás-os-Montes)
2. Best time to visit: late October – early November (peak season + Magusto)
3. Look under old trees — centuries-old chestnuts support the richest mycorrhizal networks
4. Spring visit — a second chance: Boletus aereus, Cantharellus cibarius, Calocybe gambosa
5. Stay alert: Amanita phalloides grows in the same spots as edible species

Sources

1. Baptista P. et al. — Diversity and fruiting pattern of macrofungi associated with chestnut (Castanea sativa) in the Trás-os-Montes region // Fungal Ecology, 2009
2. CCRES — Cogumelos silvestres em Portugal
3. DGADR — Produtos Tradicionais Portugueses: Cogumelos Silvestres
4. INIAV — Portuguese Castanea sativa Genetic Resources
5. Gouveia E. et al. — Cancro do Castanheiro em Trás-os-Montes // IPB Bragança