Arbre à noix longues

The species is 'scattered' or 'sporadic' in its habitats but may occasionally form small pure groups (Broders et al. 2015).  Small isolated pockets are found in the south of the range, and subpopulations in Wisconsin, Michingan, Ontario and Quebec are considered disjunct (Coladonato 1991). The species is rarely dominant, but in some sites is co-dominant with an overall low abundance (Michler et al. 2006).

Population is subject to a high rate of decline. This is a consequence of infection of trees by the fungus Ophiognomonia clavigignenti-juglandacearum, commonly known as butternut canker (Broders et al. 2015, NatureServe 2018). This fungal pest was first reported in 1967 and the population of butternut has continued to decline since its invasion. In some states up to 91% of trees can be infected, putting them at risk of death (McIlwrick et al. 2000). Seven midwestern states recorded a decline in butternut trees of 23% (Michler et al. 2006) while Wisconsin recorded a loss of between 27 and 92% by 1992 (Michler et al. 2006). Flickinger (2015) reports a decrease in number of butternut trees from 1.4 million individuals to 84,000 individuals, a 94% decline. In general, the average loss across reporting states is around 80% (McIlwrick et al. 2000). The species is also subject to decline in its Canadian range at a similar rate.

Despite this decline the species is still present in habitat as infected individuals, uninfected saplings, mature putative resistant trees (McIlwrick et al. 2000). The species currently maintains good genetic diversity and there is some natural resistance to O. clavigignenti-juglandacearum (Ross-Davis et al. 2008). Other causes of population decline are due to habitat loss, poor regeneration and genetic dilution (Parks et al. 2013).

The species produces seed from 20 to 60 years old, hence generation length is given as 40 years. Therefore, across three generations looking from 1967 to 2067 it is estimated that the population will experience decline between 50 and 80%. There has been a historical reduction of up to 80% based on the loss of trees due to butternut canker, and the variable rate this has occurred across the range. There is a high rate of infection and high rate of mortality of the tree. Decline will continue into the future as O. clavigignenti-juglandacearum is present across the entire species range and there is no known remedy (Parks et al. 2013). Decline over the next 100 years could also be as much as 80%, considering a conservative estimate.