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Butternut Tree

  • Butternut (Juglans cinerea) is a medium to large, deciduous tree of the walnut family reaching a height of up to 30 m. Its leaves are densely hairy, alternate, and composed of 11-17 pinnately-arranged, stalkless leaflets. The twigs are stout and hairy with a central pith divided into chambers. The Butternut fruit is a sticky-hairy, egg-shaped husk enclosing a single two-chambered nut within a hard, jagged-ridged shell.
  • Butternut is a shade-intolerant deciduous tree that rarely lives more than 100 years. It flowers from April to June with separate male and female flowers on the same tree maturing at different times to encourage out-crossing. It is wind-pollinated and can hybridize with Japanese, English, Little and Manchurian walnuts. The fruit matures in September and October in the year of pollination. Seed bearing starts about age 20 and peaks at age 30 to 60. Generation time is estimated at 45 years, the median of this range. Pollen may be disseminated over distances exceeding 1 km.
  • Butternut occurs primarily in neutral to calcareous soils of pH 5.5 to 8, often in regions with underlying limestone, and is generally absent from acidic regions. It tends to reach greatest abundance in rich well-drained mesic loams in floodplains, streambanks, terraces and ravine slopes, but can occur in a wide range of other situations. In closed-canopy stands, it must be in the overstory to thrive. Seedling establishment, growth and survival to maturity are most frequent in stand openings, riparian zones and forest edges.
  • Butternut occurs across much of the central and eastern United States and small portions of southeastern Canada, occurring south to Arkansas, Mississippi, Alabama and Georgia. Within this latitudinal range, the species occurs in all states west to Minnesota, Iowa and Missouri. Butternut’s native Canadian range is restricted to southern Ontario and Quebec (primarily south of the area bounded by Georgian Bay, the Ottawa Valley and the Quebec City region), and western and southern portions of New Brunswick.

Status

  • COSEWIC: Designated Endangered in November 2003. Status re-examined and confirmed in April 2017.
  • Reasons for designation: The species was formerly a significant source of wood for cabinetry and instrument making and continue to hold cultural significance for some Indigenous communities in eastern Canada. The fungal disease Butternut Canker has infected almost all Canadian trees, causing rapid mortality, and is projected to cause a near 100% decline from the pre-canker population of this species within one generation. There is evidence that some trees may be showing resistance. Ornamental introductions in Manitoba, Nova Scotia, and Prince Edward Island are not included in the assessment.
  • In Canada, Butternut Canker was first detected in Quebec in 1990, Ontario in 1991, and New Brunswick in 1997. It now occurs throughout Butternut’s native range, affecting nearly all trees in Ontario and Quebec and 70+% of trees in New Brunswick.

Threats

Direct, from highest impact to least, as per IUCN Threats Calculator)

  • Invasive Non-native Pathogen: Butternut Canker
  • Habitat Conversion
  • Logging and Wood Harvesting
  • Introduced Genetic Material: Hybridization with Japanese Walnut

Less Significant Threats (Unknown rating)

  • Problematic Native Species: White-tailed Deer
  • Climate Change

What additional limiting factors are relevant?

  • Low Genetic Diversity
  • High Levels of Seed Predation 

Significant Threats:

  • Pathogen that causes butternut canker Fungal infection of butternut causes necrosis of cambial tissue which may eventually disrupt nutrient flow. It may take trees more than 40 years to die, but in many cases, death has rapidly followed infection. Mortality after infection appears to be directly related to the size of the tree due to the girdling effect of the cankers as they grow and coalesce. As larger trees disappear from the landscape, average time-to-mortality following infection will become shorter and shorter. Following dieback, this species does not leave live root sprouts, usually does not leave viable seed, and stem cankers damage the commercial value of the wood. Once killed the trees rarely sprout and when they do, the sprouts are not known to reach any appreciable size or produce seed (Ostry unpubl.data). Butternut canker is transmitted from tree-to-tree by asexually produced spores (pycnidiospores) carried by wind and rain droplets/aerosol (Tisserat and Kuntz 1983). The fungus can also survive in infected seed stratified at 4°C for up to 18 months (Schultz 2003). Beetles, including some long-horned beetles (Cerambycidae) and weevils (Curculionidae), are known to play a role in fungal transmission (Halik and Bergdahl 2002).
  • However, in anticipation of mortality from the disease, in some areas, the threat of harvesting may be a more immediate threat than the canker itself. Harvesting of butternut by landowners in anticipation of mortality has already been documented in the U.S. (Ostry and Pijut 2000) and an increased incidence of butternut is already evident in the market (e.g. at log auctions) in Ontario (Boysen unpubl. data). The harvesting of non-infected and putatively resistant trees may reduce genetic diversity. If genetic resistance exists, it appears to be rare and should be preserved on the chance that it may contribute to the recovery of the species.

Actions Completed/Underway in New Brunswick

  • New Brunswick. A butternut conservation strategy was developed by the New Brunswick Gene Conservation Working Group (Nielsen et al. 2003). The Working Group identified knowledge gaps and set goals to identify and locate butternut populations in the province; assess the frequency of canker infection and estimate mortality; develop ex situ storage methods, and examine the genetic diversity of butternut and check for the presence of hybrids.
  • An educational program was also set up by Natural Resources Canada, Canadian Forest Service (Atlantic Region) and the New Brunswick Federation of Woodlot Owners to enable woodlot owners to identify the tree and symptoms of butternut canker disease
  • A database was set up by the Canadian Forest Service (Atlantic Forestry Centre) to maintain information provided by the public on location and health of trees.
  • Ex situ (off-site) conservation initiatives were undertaken by the National Tree Seed Centre in order to preserve valuable butternut germplasm (e.g. embryonic axes, buds and cells).
  • One plot has been established by the CFS Atlantic Forestry Centre to monitor development of the disease over time, and additional areas have been surveyed.
  • Research conducted by the Canadian Forest Service in 2004, 2007, and 2008 confirmed the presence of butternut canker at new locations in New Brunswick, expanding the known range of canker over 100km south of the original location
  • Research conducted by the Canadian Forest Service in 2004, 2007, and 2008 confirmed the presence of butternut canker at new locations in New Brunswick, expanding the known range of canker over 100km south of the original location
  • New Brunswick Department of Natural Resources obtains information that assists in determining butternut range in the province through three ongoing core programs (Photo Interpretation, Forest Development Survey and Permanent Sample Plots). They also sponsored a butternut canker workshop in 2004

Knowledge Gaps

In all provinces, information is still required to assess the distribution and abundance of butternut itself, the disease incidence and severity, and to identify putatively resistant trees. Data collection and management should be standardized to facilitate inter-jurisdictional cooperation and comparisons, by following the common protocol developed by specialists with NRCan’s Canadian Forest Service forestry centers and with the natural resource departments of Ontario, Quebec and New Brunswick in February 2007. The network of Conservation Data Centres currently in place can play a major role; however, more detailed databases that hold disease assessment and monitoring information are also required. Knowing whether or not resistance to butternut canker exists, and if indeed it does, the mechanisms of resistance (e.g. genetic (G), environmental (E), and/or both (GxE), are also crucial elements necessary for recovery success. Many questions pertinent to long-term butternut survival (e.g. what are ecologically functioning population levels?) remain unknown.

Rationale For Recovery Feasibility

Based on the following four criteria outlined by the Government of Canada (2009), there are unknowns regarding the feasibility of recovery of the butternut. At present, it is unknown if trees exist in Canada which are resistant to the butternut canker, yet this information is key to the recovery of this species and will be important in determining recovery feasibility over the long term for butternut. Therefore, in keeping with the precautionary principle, this recovery strategy has been prepared as per section 41(1) of SARA, as would be done when recovery is determined to be feasible. This recovery strategy addresses the unknowns surrounding the feasibility of recovery.

  1. Individuals of the wildlife species that are capable of reproduction are available now or in the foreseeable future to sustain the population or improve its abundance. YES
  2. Sufficient suitable habitat is available to support the species or could be made available through habitat management or restoration. YES
  3. The primary threats to the species or its habitat (including threats outside Canada) can be avoided or mitigated. UNKNOWN
  4. Recovery techniques exist to achieve the population and distribution objectives or can be expected to be developed within a reasonable timeframe. UNKNOWN

As individuals and habitat are still plentiful for butternut across its range, the recovery of butternut will largely depend on the identification of a canker-resistant strain of the species, from either Canada or the United States, the conservation of genetic material, and a program to restore a viable population that can fulfill butternut’s ecological function.

Recovery

Long Term Recovery Goal (> 20 years)

  • Ensure conditions that will allow for the restoration of viable, ecologically functioning, and broadly distributed populations within its current range in Canada.
  • Restoration of viable populations requires the presence of disease-free butternut stands or trees. At present, the conditions required to achieve and ensure disease-free populations are unknown. Thus it is not possible at this time to further quantify the recovery goal or population and distribution objectives.

Short Term Objectives

  • Develop stewardship and outreach products informing Canadians of the identification, conservation status, conservation mechanisms and management of butternut and on the identification, assessment and management of butternut canker.
  • Identify local populations of butternut across its native range and maintain them through focused stewardship in order to increase the likelihood of finding individuals which show resistance to the canker (due to environmental or genetic factors, or a combination thereof).
  • Where the disease is widespread, select, graft and archive at least ten putatively resistant trees in each eco-district in support of a future breeding and/or vegetative propagation program to produce resistant trees for restoration, and in support of future critical habitat identification.
  • Address priority knowledge gaps and research necessary for implementing recovery activities (including research into disease resistance and level of adaptive genetic variation, as well as environmental factors that limit the spread of the disease).
References:
  • Environment Canada. 2010. Recovery Strategy for the Butternut (Juglans cinerea) in Canada.
  • Species at Risk Act Recovery Strategy Series. Environment Canada, Ottawa vii + 24 pp.[2]