Juglans nigra

Black Walnut

Physical Traits & Growth

Typical max. heightiMaximum height in typical conditions, in metres. Full data also shows maximum achievable height in exceptional conditions.:
50m 1
32m 5
Rarely more than 30m 6
31m 7

Max. canopy widthiLikely maximum horizontal width of the canopy, in metres:
Globular, more conical when young 1
At least 8m 2
Domed crown 3

Size of shadowiSize of shadow based on a fully grown tree, categorised as low, medium or high: Moderate (292 sqm)

Canopy densityiShading intensity of the canopy when in full leaf. Categorised from open to dense.: Moderate 1

Leaf emergenceiTime of leaf emergence, categorised as very early, early, late, or evergreen: Late (May to Nov 1)

Growth rateiHow quickly the tree grows during establishment. Categorised as low, moderate or high, with very high used in exceptional cases.: Moderate 1 to high 9

LongevityiExpected lifespan of the tree: Unknown

Management & Systems

Typical systemsiCommon agroforestry or silvicultural systems where this species is used:
Arable or pasture, lowland 1
Lowland 2

Approach to silvicultureiCoppicing and pollarding ability: Can be coppiced and pollarded 1

Establishment requirementsiCommon requirements to establish the tree:
Formative pruning usually necessary 6
Benefits from weed control 1

Management requirementsiCommon long-term management needs such as pruning. Categorised as low, moderate or high.:
Minimal or no pruning 1
High pruning required for timber 2

Pruning timeiOptimal season for pruning: Summer or winter (mid) 1

Black Walnut, Reading, UK / Tom Staton / https://creativecommons.org/licenses/by-sa/4.0/deed.en

Products & Economy

Food productsiCommon food products such as fruits and nuts: Nuts 3, but difficult to remove shell 2

Wood productsiCommon wood products, including timber, turnery, and pulp:
High-value timber 125
Max YC 12 4
Hybrids available with improved vigour (e.g. NG23) but likely lower value 2

BiomassiCommon biomass products such as fuelwood: –

Speciality productsiOther speciality and niche products: Dye, oil 5

Time until market (food)iNumber of years until the tree produces food products: 10 years for commercial nut cropping 2

Time until market (timber)iNumber of years until the tree produces wood products: 60 years 5

Ecology & Utility

Nutrient and organic matter accumulationiRough estimate of soil-improving properties, with larger and deeper-rooting trees predicted to have higher value. Categorised as low, moderate or high.: High – deep roots and moderate canopy area

Nitrogen fixationiNitrogen-fixing properties, categorised as yes or no: No

High carbon sequestrationiAll trees sequester carbon, but faster-growing, larger trees generally have higher sequestration potential.:
Short-term (20 years): Moderate
Medium-term (40 years): Moderate
Long-term (60 years): Relatively low

Native status in the UKiCategorised as native, long-established, or recent introduction.: Recent introduction (neophyte) – naturalised 1

High wildlife valueiMost trees are likely to be of some value to wildlife, but some trees are of generally higher value to various wildlife groups:
Relatively low 5
Highest value for mycorrhizal fungi and leaf litter 5

Pollinators

Flowering period (pollinator benefit)iTypical flowering months: May-Jun 2

High pollen and nectar value for pollinatorsiValue of flowers to pollinators: Low

Susceptibility & Risks

Risk of toxicity to livestockiReported potential toxicity to livestock, categorised as yes or no. Toxicity is complex and often context-specific.: High risk of toxicity to horses from wood shavings and potentially from leaf ingestion, and to all animals from mouldy walnuts 10

Risks to farming operationsiOther risks such as suckering roots, very large tree size, secondary host for aphids, and flammability:
High allergenicity from pollen 2
Highly allelopathic to many other plants 4, especially to small fruit and legume crops 7

Disease susceptibilityiSusceptibility of the tree (not tree products) to diseases, e.g. fungal and bacterial disease:
Moderate
Susceptible to walnut-leaf blotch 3
May be susceptible to walnut leaf spot, walnut leaf blotch, honey fungus and coral spot 6

Invertebrate pest susceptibilityiSusceptibility of the tree (not tree products) to invertebrate pests, e.g. aphids and other insects:
Moderate
May be susceptible to aphids and walnut blister mite 6

Vertebrate damage susceptibilityiSusceptibility of the tree (not tree products) to vertebrate pests, e.g. squirrels and deer:
High
Highly susceptible to squirrel damage 8
Susceptible to browsing by deer and rabbits 10