Dwarf Hackberry

(Celtis tenuifolia)

Status: Threatened (ESA 2008, COSEWIC 2003)

Table of Contents:

Species Identification
Habitat and Biology
Threats/Reasons for Being at Risk
Conservation and Recovery Strategies
Why You Should Care
How You Can Help

Species Identification:

The Dwarf Hackberry is a small deciduous tree that grows 1-10 meters tall. It has smooth, light grey bark that becomes rigid with age; thin, hairy twigs. The leaves are grey-green, leathery, and arranged in an alternate pattern along the stem. Dwarf Hackberry leaves are also oval-shaped at the base and come to a point at the tip, and may have many or very few teeth along their edges. They have small male and female flowers that are present on the same tree and grow individually, or in groups of two or three. They have fruit that is dry, sweet, round, and dark orange in colour. The Dwarf Hackberry is distinguishable from Common Hackberry by a heart-shaped leaf base and smaller size. Common Hackberry leaves are also more narrow.

Habitat and Biology:

Dwarf Hackberry is found across much of the Eastern United States, reaching the northern end of its range in southern Ontario. The Dwarf Hackberry is now only found in six locations in Canada, all of which are in southern Ontario. The only population found in The Land Between is at the Salmon River Alvar Area of Natural Scientific Interest in Lonsdale. Fortunately, all populations except the Point Peele population are considered relatively stable.

Dwarf Hackberry is a drought-tolerant and sun-loving species that grows in open woodlands near shorelines with dry, sandy soil. They can grow in a variety of habitats including prairies, savannas, and forest edges. Dwarf Hackberry can also be found on inland sand dunes, ridge tops, and dry limestone alvars. The population in The Land Between at the Salmon River Alvar Area of Natural Scientific Interest in Lonsdale grows specifically on very dry tree barrens on limestone bedrock. Flowers emerge from May to June and are wind pollinated. Fruit eating birds are the primary source of seed dispersal but there are also many mammals that enjoy eating the fruit of Dwarf Hackberry. The Dwarf Hackberry is commonly found in areas where Common Hackberry is also found, and as a result, hybridization may occur between these two species.

Map taken from Government of Canada: https://www.canada.ca/en/environment-climate-change/services/species-risk-public-registry/cosewic-assessments-status-reports/dwarf-hackberry/chapter-4.html

Threats/ Reasons for being at Risk:

1. Human development: Habitat conversion and fragmentation as a result of human development poses a particularly strong threat to the Dwarf Hackberry population in The Land Between (Salmon River), which is currently surrounded by development in its Northeast corner. Habitat fragmentation from development results in fewer opportunities for seed dispersal and population expansion, as well as degrades nearby habitat.

2. Altered disturbance regimes: Fire suppression results in plants that grow around Dwarf Hackberry being able to grow longer and larger than they may have otherwise, allowing them to outcompete the Dwarf Hackberry for resources, and close the open canopy on which Dwarf Hackberry depends for optimal sun exposure. This threat is particularly significant to the populations in Lambton County, Pointe Pelee National Park, and Fish Point.

3. Bark beetles: Bark beetles had a significant impact on the Dwarf Hackberry population in Pointe Pelee from 1989 to 1991, causing an average 13% tree mortality rate over a three year epidemic. Bark Beetles are a native pest that burrow, lay eggs, and feed on the wood and bark of Hackberry trees, eventually causing death. With the continued effects of climate change resulting in warmer winters, a northward movement of more species of Bark Beetles from the United States is a real possibility, and could pose a threat to other Dwarf Hackberry populations in the future, including the population found in The Land Between.

4. Snails: Grazing of Dwarf Hackberry by native snails has posed a significant threat to the Pointe Peele population in the past (early 1990’s) and has the potential to do so again to all populations with the threat of climate change. Snail grazing of seedlings renders them unable to grow to maturity to contribute to the growth of the population, threatening the survival of populations impacted by the snails.

Conservation and recovery strategies:

Efforts have been made to update the data for the species population size and distribution. Dwarf Hackberry is included as a secondary conservation target in several Conservation Action Plans that are expected to benefit both the plant itself, but also the oak savanna and alvar habitats on which it depends. Objectives for Ontario’s recovery strategy include working on halting the decline of the Point Pelee population, maintaining all other Ontario populations, identifying critical habitat, halt activities that impact critical habitats, and mitigate current threats and monitor.

Why You Should Care:

One of only six remaining Dwarf Hackberry populations is located in The Land Between
Fewer than 1000 individual plants are expected to remain in all of Canada, all of which are found in Southern Ontario, one of the most heavily impacted landscapes in the country
Many of the plant communities in which Dwarf Hackberry is found are considered rare, such as oak savannas and red cedar alvars. Protection of the Dwarf Hackberry also results in protection for these incredibly rare ecosystems
The fruit of Dwarf Hackberry is favoured by many songbirds, as well as many important insects

How can you help?

Learn how to identify Dwarf Hackberry and submit observations online to The Land Between and/or to iNaturalist.
If you have Dwarf Hackberry on your property, consider removing nearby trees that are blocking light, provided they are not also Species at Risk, to allow the Dwarf Hackberry to have more sun exposure.
Volunteer with local organizations to participate in surveys or stewardship programs that protect Species at Risk.

Additional Resources:

Government of Ontario’s Dwarf Hackberry Species at Risk page
Learn to ID the Dwarf Hackberry on iNaturalist
COSEWIC 2003 Assessment and Report on the Dwarf Hackberry

Sources:

Government of Ontario. 2014. Dwarf hackberry. Retrieved from: https://www.ontario.ca/page/dwarf-hackberry

Ontario Ministry of Natural Resources. 2013. Recovery Strategy for the Dwarf Hackberry (Celtis tenuifolia) in Ontario. Ontario Recovery Strategy Series. Ontario Ministry of Natural Resources, Peterborough, Ontario. iii + 5 pp + Appendix vi + 43 pp. Adoption of Recovery Strategy for Dwarf Hackberry (Celtis tenuifolia) in Canada (Parks Canada Agency 2011). https://www.ontario.ca/page/dwarf-hackberry-recovery-strategy

COSEWIC. 2003. COSEWIC assessment and update status report on the dwarf hackberry Celtis tenuifolia in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vi + 15 pp. https://www.canada.ca/en/environment-climate-change/services/species-risk-public-registry/cosewic-assessments-status-reports/dwarf-hackberry.html