Recovery Strategy for the Dwarf Hackberry in Canada [Final] 2011: Population and Distribution Objectives
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mature individuals in Canada, less than 1 000 in any population and an extent of occurrence less than 20 000 km2 is no longer valid based on the findings of Mills and Craig (2008).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:
- to halt the apparently steep decline in the species' population size at Point Pelee National Park and
- 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 |
|
All | High | Communicate Best Management Practices (BMPs) and other important facts |
|
All | High | Coordinate recovery approaches |
|
Altered disturbance regimes | High | Mitigate erosion threats |
|
All | Medium | Engage landowners to plan and implement protection and recovery measures. |
|
All | Medium | Encourage the use of Traditional Ecological Knowledge in decision making |
|
Inappropriate logging Development Aggregate extraction | Medium | Implement stewardship agreements |
|
Aggregate extraction | Medium | Protect Dwarf Hackberry trees and habitat from resource extraction |
|
Altered disturbance regimes Plant competition | Medium | Vegetation management |
|
Snails Deer browse | Medium | Investigate and implement measures to manage herbivory |
|
Bark beetles Snails Plant competition | Medium | Complete/refine threat assessment |
|
Altered disturbance regimes | Medium | Research niche differentiation |
|
Lack of basic Information | Medium | Research seed dispersal |
|
Altered disturbance regimes | Medium | Research fire effects |
|
Lack of basic information | Medium | Research small, isolated populations |
|
Lack of basic information | Medium | Research genetic differences |
|
All | Low | Population repatriation and augmentation | |
Recreational activity | Low | Minimize recreational impacts |
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Climate change | Low | Reduce 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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