Torreya Guardians generally doesn't try to find and document seed production of horticultural plantings on other continents. But the article above offers some important observations.
BACKGROUND: "... It was brought here by the curator of the collections Antoine Kort around 1910 from a nursery close to the Italian Lago Maggiore. The plant grows in south-facing ground at the edge of the estate, close to the historic Vangeertenhof. A good ten years ago, the surrounding plants were removed so that this very special tree could get a full quota of light and air. A low wall protects the base of the trunk from bright sunlight and strong winds. Since then, the circumference of the tree has almost doubled. Another superb example of this cultivar grows in the Allard Arboretum in Angers (France)."
ACADEMIC PAPERS ON IMPORTANCE OF OBSERVING HORTICULTURAL PLANTINGS
• Garden Plants Get a Head Start on Climate Change, by Sebastiann Van der Veken et al., May 2008, in Frontiers in Ecology and the Environment.
EXCERPTS: Conservation biologists are concerned that climate change will cause widespread extinctions because limited capacity for migration could compromise species' ability to adjust to geographic shifts in habitat condition. However, commercial plant nurseries may provide a head start for northward range shifts among some plant species. To investigate this possibility, we compared the natural ranges of 357 native European plant species with their commercial ranges, based on 246 plant nurseries throughout Europe. In 73% of native species, commercial northern range limits exceeded natural northern range limits, with a mean difference of approx. 1,000 km. With migration rates of 0.1 to 5 km per year required for geographic ranges to track climate change over the next century, we expect nurseries and gardens to provide a substantial head start on such migration for many native plants. While conservation biologists actively debate whether we should intentionally provide "assisted migration", it is clear that we have already done so for a large number of species. ... ... Of the 534 ornamental species sold in Britain during the 19th century and examined by Dehnen-Schmutz et al. (2007), 27% were subsequently found growing outside of cultivation, and 30% of these had established populations, clearly demonstrating the potential for horticultural plants to spread into non-cultivated habitats (see Sullivan et al.2005).
• The role of botanical gardens in climate change research, by Richard B. Primack and Abraham J. Miller-Rushing, 2009, Tansley Review in New Phytologist.
EXCERPTS: Botanical gardens have a unique set of resources that allows them to host important climate change research projects not easily undertaken elsewhere. These resources include controlled growing conditions, living collections with broad taxonomic representation, meticulous record-keeping, networks spanning wide geographic areas, and knowledgeable staff. Indeed, botanical gardens have already contributed significantly to our understanding of biological responses to climate change, particularly the effects of temperature on the timing of flowering and leaf-out.... The evidence reviewed here shows that botanical gardens can serve as particularly valuable sources of long-term data to describe how plants are responding to climate change.... Of special concern, we suggest that species be monitored to determine whether previously hardy species are no longer able to grow at particular botanical gardens. Additionally, researchers should note species that were previously difficult to grow at a site that are able to thrive in the changing climatic conditions.
• "Plants' native distributions do not reflect climatic tolerance", by Tierney Bocsi et al., 2016, Diversity and Distributions
EXCERPTS: In an era of rapid climate change, conservation biogeography often focuses in particular on risks to rare native species. Our analyses suggest that species native ranges often underestimate their climatic tolerance.... Most species have not been broadly introduced outside of their native ranges. As a result, our understanding of climatic tolerance limits for the bulk of species can only be inferred from occurrences within their native ranges. Accordingly, ecological forecasting studies assessing extinction risk and supporting conservation planning are typically based on native occurrences.
Our results show that native range data strongly underestimate the climatic conditions where many species could occur. The vast majority (86%) of species had adventive occurrences in climate conditions that were not encompassed by native range distribution data. Range models expanded substantially when adventive occurrences were included, and particularly when those adventive occurrences had novel climate conditions.
 |
|
LEFT: Fraser Fir, how adventive occurence expands ecological niche. (All maps in Supplement)
|
Thus, the broader range models are likely due to expansion of the realized niche rather than a model response to the addition of more data points. The corresponding expansion of niche models by 35% geographically suggests that an assumption of climatic equilibrium in the native range may be optimistic for many native species.... This study supports the findings of Early & Sax (2014) that niche shifts are similarly prevalent amongst non-invasive species. This accumulation of evidence strongly suggests that the native distribution of a species is a poor proxy for climatic tolerance. Moreover, our results suggest a pattern of greater niche expansion amongst plant species with smaller native range sizes.... Many species would already be able to successfully establish outside of their native ranges, even before climate changes. The latter finding could support conservation strategies like managed relocation, particularly for slow-growing, long-lived species like trees that might require planting well in advance of shifting climate conditions. Given that many plant species appear limited by dispersal ability, it is unlikely that they will be able to keep up with climate change unaided.
• "Limited Range-Filling Among Endemic Forest Herbs of Eastern North America and Its Implications for Conservation With Climate Change" - by Stephanie K. Erlandson, Jesse Bellemare, and David A. Moeller, 8 December 2021, Frontiers in Ecology and Evolution.
EXCERPTS: Species with low dispersal and poor range-filling capacity may be especially threatened by modern climate change because they are unlikely to migrate quickly enough to keep pace with changing climate (Thomas, 2011). In some cases, their realized and potential distributions might shift apart entirely, exposing them to high risk of extinction (Sax et al., 2013). In this context, many endemics might be particularly susceptible, as their distributions often reflect past marginalization by climate change (e.g., Pleistocene glaciations), and their current distributions are often restricted to unusual habitats (high elevations, north slopes) in southern areas that are surrounded by warmer, unsuitable habitat (Ohlemüller et al., 2008). Conservation of such endemics may require assisted migration (McLachlan et al., 2007). However, in the case of endemic forest herbs of the Southern Appalachian Mountains, it has been unclear whether suitable habitat already exists outside their native ranges. Our models based on current climates predicted suitable habitat north of the range margins of three endemics, suggesting that assisted migration could be successful currently and that single, larger-scale translocations might be feasible, rather than “many small steps” moving incrementally northward over decades... Notably, Diphylleia cymosa and Shortia galacifolia are known to survive, reproduce, and recruit new adults in parts of New England where they have been transplanted decades ago, making these patterns plausible (J. Bellemare, pers. obs.).
... In the case of the endemics investigated here, our Last Glacial Maxium projections suggest that they could have persisted near their present-day distributions in the Southern Appalachian Mountains (SAM) even during the colder climatic conditions of the Pleistocene. This pattern is consistent with horticultural observations that narrow endemics of the SAM often survive and reproduce in gardens far to the north. However, this Pleistocene context might not suggest a similar likelihood for pre-existing tolerance to the significantly warmer conditions projected for the future given that they would be unprecedented in the recent geological past. In the absence of rapid evolution or preexisting tolerances, poleward migration might be necessary for the long-term survival of the endemic species investigated here. However, natural dispersal to northern areas for endemic species may be particularly unlikely, given their apparent lack of substantial northward migration during the Holocene.... Given the severity of reductions in suitable habitat within the range and the disjunct nature of suitable habitat outside the range, assisted migration may be an important strategy for long-term conservation (Hoegh-Guldberg et al., 2008)... Our results suggest a history of dispersal limitation following the last glacial maximum along with an environmental barrier to northward migration. Conservation of endemic species would likely require intervention and assisted migration to suitable habitat in northern New England and Canada.
• "Climatic criteria for successful introduction of Quercus species identified by use of Arboretum data", by Corrie Lynn Madsen et al., March 2021, in Forestry.
EXCERPTS: Climate change is projected to have a major influence on forest tree populations and composition. Translocation of species outside their historic range has been suggested to maintain healthy forests and tree species. The introduction of exotic species into botanical gardens and arboretums worldwide demonstrates the ability of many trees to grow outside their natural habitat and may play an important part in avoiding climate driven extinction if grown in a matching climate. However, it remains to be determined which climatic factors are the most important predictors of climatic match. In this study we use information from the arboretum in Horsholm, Denmark, to analyse differences in performance of translocated Oak (Quercus) and show how data from tree collections can be used to predict success of assisted migration.
... We find that arboretum data contain biogeographic information that may help interpret factors involved in climatic adaptation, and assist in selecting suitable source areas for assisted migration. The full potentials can only be realized, however, if data from several arboreta are combined. Here we determined criteria for successful migration under current conditions, but what will they be under future conditions? Establishing a network of collections ('metacollections' as coined by Dosmann 2006) across Europe or the world would make it possible to expand the scope of analyses considerably by verifying whether the same parameters are decisive for success under different conditions, and by allowing more detailed studies of individual species or genera. This could potentially lead to a new understanding of assisted migration under climate change.
• "Reconsideration of the native range of the Chinese Swamp Cypress
(Glyptostrobus pensilis) based on new insights from historic,
remnant and planted populations", by Jinlog Zhang and Gunter A Fischer, 2021, Global Ecology and Conservation.
EXCERPTS: ... Tree populations in human-modifed landscapes are usually considered less important compared to "natural" or "wild" populations and consequently are rarely collected comprehensively during scientific plant surveys. Indeed, no matter whether the species were planted to enhance natural populations, used for ex situ conservation or as roadside trees in cities, their potential importance to conservation is underestimated. In fact, if trees are planted in habitats with comparatively low anthropogenic disturbance such as nature reserves or in greening projects in rural areas, such as roadsides, highway slopes, edges of agricultural fields or gallery forests along streams and rivers, the species may start to reproduce and spread by themselves. Nonetheless, such planted tree stands, even when they are located within the species historic and/or present native range, are usually considered cultivated and not 'natural' or 'wild'. If such stands are able to reproduce and grow without human assistance over a longer period of time, then they could be considered as 'rewilded' under the concept of Carver et al. (2021).... For a rare and undercollected species, which has experienced a significant decline in range size and habitat degradation, taking historical records such as buried ancient trees and "planted" trees would supplement the museum collections and hence improve species distribution modelling. Based on the output of species distribution modelling, we argue that the native range of the Chinese Swamp Cypress should be much broader. Consequently, naturalized or rewilded populations within the modelled range should be considered native and receive adequate protection.
• "Home gardens contribute to conservation of the critically endangered Wollemi Pine: Evaluation of a botanic garden-led horticultural release programme", by Catherine A. Offord and Heidi C. Zimmer, 26 July 2023, in Plants People Planet.
EXCERPTS: Botanic gardens play a leading role in conserving plant species worldwide. Wollemi Pine, a critically endangered species described as new to science in 1994, has been the subject of botanic garden-led conservation efforts, including widespread horticultural cultivation. An online survey found that gardeners hold a wealth of knowledge on the response of Wollemi Pine to local environmental conditions and horticultural regimes and a high level of awareness of the importance of plant conservation. This information could increase the success of future ex situ conservation efforts, such as the development of a genetically diverse, globally dispersed metacollection of Wollemi Pines.... This programme is likely to have contributed to the protection of wild populations from illegal visitation and potentially harmful harvesting (NSW Department of Environment and Conservation, 2006) while, at the same time, enabling people to experience caring for a Wollemi Pine of their own.... In our study, Wollemi Pines were reported to grow mostly in moderate climates: neither too hot, cold, wet, nor dry, in what might be described as 'a goldilocks zone'.
... This study highlights the role that botanic gardens and home gardeners can play in altering the global distribution of a threatened species. The Wollemi Pine is a special case because it is valued neither for food nor timber but rather for its story, conservation, and iconic status. This study demonstrates that it is feasible to establish Wollemi Pines in many parts of the world and under different climates and cultural regimes, which can help conserve this species in the face of climate change and other threats.... Despite its limited genetic diversity, the commercial distribution of the Wollemi Pine has clearly contributed to important conservation outcomes such as global awareness raising, developing a sense of custodianship/connection and building horticultural know-how.
Contact Connie Barlow OR
Contact Fred Bess
Return to HOME PAGE
Annotated List of Papers/Reports Online re Assisted Migration
