Recovery Strategy for the Dwarf Hackberry in Canada [Final] 2011: Population and Distribution Objectives

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The designation of Dwarf Hackberry based on a decline in area, extent, and quality of habitat, less than 2 500 mature individuals in Canada, less than 1 000 in any population and an extent of occurrence less than 20 000 km2 is no longer valid based on the findings of Mills and Craig (2008). Given the naturally small area of occupancy of the species in Canada and the large gaps that occur between populations, it is neither realistic nor appropriate to expand its area of occupancy beyond 500 km2 or to focus on reducing population fragmentation. For these reasons, the main focus for the recovery of this species is to maintain existing populations and prevent declines and extirpations. The population and distribution objectives for Dwarf Hackberry are therefore:

  1. to halt the apparently steep decline in the species' population size at Point Pelee National Park and
  2. to maintain populations at the other five extant locations (Pelee Island, Lambton County, Point Anne Alvar, Stirling Slope Complex ANSI, and Salmon River Alvar ANSI [Lonsdale]) in suitable habitat.

Special focus is placed on the Point Pelee National Park population as survey information suggests that it is currently in a steep decline (Jalava et al. 2008). All other populations appear to be stable.

Key to the achievement of these population and distribution objectives over the long term is the restoration and maintenance of the natural disturbance mechanisms that provide for long term persistence of critical habitat. This is particularly true at Point Pelee National Park where the alteration of coastal processes, and potentially the suppression of fire, has contributed to aggressive plant competition and the unnaturally rapid succession of open vegetation communities suitable for Dwarf Hackberry maintenance to more closed, shaded conditions.

Efforts to update the population size and distribution data for the Dwarf Hackberry in Canada have been initiated. Recent surveys have been completed in Point Pelee National Park (Jalava et al. 2008), the Lambton County Heritage Forest (Lambton County) (Mills and Craig 2008), and one Stirling Slope Complex ANSI property (Parks Canada Agency unpub. data). Dwarf Hackberry is a nested conservation target species of the Carolinian Canada Coalition's Ausable River – Kettle Point to Pinery Conservation Action Plan (Jalava et al. 2010). A community-based biodiversity strategy for the Port Franks area of Lambton County is now in preparation (Jalava pers. comm. 2010). Dwarf Hackberry has been a key consideration in the development and implementation of management plans for Nature Conservancy of Canada sites managed by Lambton Wildlife Incorporated in this area. The species will also benefit from conservation goals and actions to improve the viability of the "beaches and shorelines" biodiversity target in the Essex Forests and Wetlands Conservation Action Plan, where it has been recognized as a significant species (Essex Forests and Wetlands Conservation Action Plan Team 2009). Communications include a web based species at risk fact sheet (Royal Ontario Museum and OMNR 2008) and messaging incorporated into programming and communications at Point Pelee National Park. The Carolinian Canada Coalition has published numerous conservation and stewardship guidance and information documents to assist landowners in the overall protection and management of species and ecosystems at risk.

In order to attain the Population and Distribution Objectives, the recovery planning approaches are summarized and ranked in Table 3 by their degree of urgency. Threats to the populations and information requirements are addressed. These approaches will be planned with due regard for negative impacts on other species.

Threat or Limitation Priority Broad Strategy to Recovery General Description of Research and Management Approaches
All High Conduct population and habitat surveys and monitoring
  • Develop a standardized population and habitat survey and monitoring protocol.
  • Identify extant, historic, and extirpated sites as well as the approximate location of unverified occurrences, plus other suitable habitats to survey for potential new populations.
  • Conduct thorough surveys of above sites every five years, including a determination of population size; distribution; health (including species and diseases detrimental to Dwarf Hackberry); reproductive status; type, quality, and extent of suitable habitat; threats and their significance; and current site management at all identified sites.
  • Incorporate citizen science where possible.
  • Develop a protocol for updating, sharing, and communicating data.
All High Communicate Best Management Practices (BMPs) and other important facts
  • Develop an information package, including BMPs, and deliver to all Dwarf Hackberry landowners to promote knowledge of the species (identification, location, and threats) and engagement in protection and recovery activities.
All High Coordinate recovery approaches
  • Develop and implement a coordinated approach to the management of Dwarf Hackberry on public lands.
Altered disturbance regimes High Mitigate erosion threats
  • Collaborate with Environment Canada, Fisheries and Oceans Canada, OMNR, Essex Region Conservation Authority, local municipalities, and others to undertake erosion mitigation measures in the Colchester to Southeast Shoal littoral cell.
    • Discourage further shoreline hardening and protection that blocks delivery of sediment into the water or prevents its transport to beaches where Dwarf Hackberry grows.
    • Remove or modify historic shoreline protection structures to mitigate their impacts to sediment delivery where possible.
All Medium Engage landowners to plan and implement protection and recovery measures.
  • Work with First Nations, stakeholder groups, land managers, and landowners to obtain funds for, plan, and implement the measures needed to protect and recover Dwarf Hackberry populations (including extirpated ones) based on prioritized needs.
  • Restore Dwarf Hackberry habitat following quarrying or sand extraction.
All Medium Encourage the use of Traditional Ecological Knowledge in decision making
  • The federal government is committed to continue to work with Walpole Island and other First Nation communities on using Traditional Ecological Knowledge to make more informed decisions in conservation.
Inappropriate logging Development Aggregate extraction Medium Implement stewardship agreements
  • Work with land trusts to establish legal or informal stewardship agreements at priority sites to ensure long-term protection of Dwarf Hackberry and its habitat from human-related impacts.
Aggregate extraction Medium Protect Dwarf Hackberry trees and habitat from resource extraction
  • Determine current and potential future impacts of resource extraction(development and/or pit and quarry expansion) on Dwarf Hackberry and its habitat.
  • Contact private landowners, permit holders, and independent road maintenance operators to discuss site protection measures and habitat restoration opportunities and encourage wise decisions.
  • Protect Dwarf Hackberry trees and habitat through provincial license agreements and permit application reviews (OMNR).
Altered disturbance regimes Plant competition Medium Vegetation management
  • Develop and implement vegetation management activities to counteract habitat succession, particularly in areas where natural disturbance regimes are impaired.
  • Where appropriate, target plants that threaten Dwarf Hackberry populations through resource competition for removal.
Snails Deer browse Medium Investigate and implement measures to manage herbivory
  • Develop and place snail exclosures at affected locations.
  • Manage White-tailed Deer according to resource and park management plans (Hutchinson et al. 1988, OMNR 1986) in sites where Dwarf Hackberry is impacted.
  • Communicate the need for such management in order to gain/maintain public support.
Bark beetles Snails Plant competition Medium Complete/refine threat assessment
  • Assess the range wide threats posed by detrimental species. Determine any underlying factors (e.g. climatic conditions, species associations) that may influence the threat.
Altered disturbance regimes Medium Research niche differentiation
  • Research niche differentiation to understand thresholds and cumulative effects of natural processes such as forest succession, canopy closure, and resource partitioning by suspected niche-competing species such as Witch Hazel and Common Juniper.
Lack of basic Information Medium Research seed dispersal
  • Determine what species disperse seeds and the patterns and mechanisms involved.
Altered disturbance regimes Medium Research fire effects
  • Research the effects of fire and fire suppression on Dwarf Hackberry habitat, its seed bank, and germination rates on trees of all age classes.
Lack of basic information Medium Research small, isolated populations
  • Determine why small, isolated populations of this self-fertile tree are not increasing in population size.
Lack of basic information Medium Research genetic differences
  • Research the genetic differences within and among populations to understand site-specific diversity and the genetic significance of each site.
All Low Population repatriation and augmentation
  • Assess the feasibility of repatriation8 of extirpated populations and population augmentation9 and implement if appropriate.
Recreational activity Low Minimize recreational impacts
  • Develop and place signage at public sites to inform users of Dwarf Hackberry presence and ways to prevent recreational impacts.
  • Direct visitor access.
  • Restore user-established trails to natural conditions, if necessary.
  • Recommend public land managers establish and/or enforce rules.
  • Recommend greater use of the Ontario Off Road Vehicle Act "Measures for Environmental Protection".
Climate change Low Reduce climate change
  • Promote and encourage activities that will slow the rate of climate change.

8 Repatriation restores a species to a location where it was formerly found, but is no longer present.

9 Augmentation adds individuals of a species to an existing population in order to increase population size.

Sutherland et al. (1994) reported that Dwarf Hackberry was found at Parkhill in Middlesex County. The origin of this information is unknown and the record does not appear to have been field checked or verified. Gartshore (pers. comm. 2009) and others have reported possible Dwarf Hackberry trees on the rim of the Niagara Gorge at the Niagara Butterfly Conservancy in Niagara Falls. Slight differences in morphology suggest that they might be escapees from the Niagara School of Horticulture (Niagara Parks Commission). Verification is required.

Additional suitable habitat may exist along the Lake Erie shore, Niagara River islands and shoreline, Lake Huron shore from Grand Bend to Kettle Point, on Pelee Island and Hastings County alvars, and the shoreline of historic Lake Iroquois in Hastings County. These areas need to be investigated for new individuals and/or populations.

Knowledge about Dwarf Hackberry ecology in Canada is the result of a single PhD thesis (Dunster 1992) that examined two populations (Point Pelee National Park and Northville/Port Franks [Lambton County]). Significant knowledge gaps remain regarding the other four populations. As such, Table 3 identifies research that is needed to complete critical habitat identification and achieve the recovery strategy objectives for Dwarf Hackberry. Knowledge gained regarding genetic differences within and between populations, in particular, will inform any restoration and augmentation activities deemed feasible.

First Nation communities have maintained local ecosystems for generations through the use of community Traditional Ecological Knowledge. It is important to work with knowledge holders as a means for species and ecosystem protection and recovery. Traditional Ecological Knowledge and western science can, together, better inform assessment, monitoring, and recovery of the ecosystems that support specific species at risk.

There are many activities that can be undertaken by landowners and land managers independently or jointly to promote Dwarf Hackberry recovery. Communication of appropriate activities and promotion and support of stewardship is key to Dwarf Hackberry recovery. Naturally occurring fire, wind throw, insect infestation, disease, and other disturbances would have maintained the open gaps and edges for Dwarf Hackberry colonization and persistence in the past. To the extent possible, such natural processes should be allowed to continue, or should be restored or mimicked. While inappropriate logging practices can threaten Dwarf Hackberry, selective harvesting using good forestry practices can also provide the critical open edge and/or forest gap conditions that promote establishment and regeneration of Dwarf Hackberry and can potentially reduce the impacts of competing species like Witch Hazel. Well-planned and carefully implemented forest management practices need to be considered in some areas, such as the Lambton County Heritage Forest (Lambton County), to promote recovery and prevent population declines (i.e. remove exotic pine plantations and restore more open habitat). It should be noted that habitat restoration activities required to address the threats of exotic and/or invasive species and/or habitat succession will result in some reduction of canopy cover. These actions, in locations where these issues have been identified as a threat(s), are deemed necessary and are not considered destruction of critical habitat, provided that the alterations promote greater use of the habitat by Dwarf Hackberry.

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