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Buffering National Parks from genetic incursions

Robert Barbour
Forest Geneticist
University of Tasmania
genetic pollution Ben Lomond diagram

Figure 1. Overview of the distribution of Eucalyptus nitens plantations along the northern boundary of the Ben Lomond National Park. The estimated distributions of E. archeri and E. dalrympleana within the park are shown.

Understanding the risks of pollen-mediated gene flow from Eucalyptus nitens plantations in Tasmania represents one component of developing a sustainable forest industry. On the island of Tasmania, E. nitens represents a locally exotic species; its natural distribution comprises isolated populations across Victoria and NSW. The potential for genetic incursions into native Tasmanian eucalypt populations by this exotic species, through pollen dispersal and hybridisation, represents one area of research being conducted by the CRC. While a number of native species have been found to not be at risk due to the existence of barriers to reproduction, such as spatial isolation, flowering asynchrony and crossing incompatibility, a selection of species have been identified to be at risk. Identification has been conducted either indirectly, via assessments of reproductive and spatial compatibility, or directly through assessments of levels of hybridisation based on open-pollinated seed collections from native stands, and observations of hybrids in the wild.

A final and equally important component of the risk assessment process, however, is the conservation status of the native population. Genetic incursions into native stands that are destined for conversion to agriculture or plantations, or are of little conservation value, is not expected to be of much concern. In the case of high conservation value populations, such as rare or endangered species or those within National Parks and World Heritage Areas, genetic incursion is of concern due to its potential impacts on the integrity and long term survival of these populations and the deleterious effects on natural values. Current research by the CRC for Forestry is, consequently, focussed on key populations of high conservation value that are within pollen dispersal range from plantations.

The northeast of Tasmania, from the northern end of Ben Lomond National Park through to Scottsdale and beyond, has been an important area for E. nitens
Archeri flowering bob barbour

Figure 2. Observed flowering times of E. archeri, E. dalrympleana and E. nitens in the Blessington/Ben Lomond region of northeast Tasmania. Eucalyptus archeri and E. dalrympleana are found within the National Park, whilst E. nitens has been established in plantations close to the boundary of the Park. Eucalyptus archeri overlaps substantially with the local E. nitens plantations, whilst E. dalrympleana was not found to overlap.

plantation establishment in Tasmania. The proximity of this expansion to Ben Lomond (Figure 1), raises concerns regarding the potential off-site effects of exotic pollen movement into native forests of high conservation value. Two species from subgenus Symphyomyrtus (i.e. potentially cross-compatible with E. nitens) exist within the National Park: E. archeri and E. dalrympleana (Figure 1). Flowering time assessments of both species in the Park relative to the plantations in the valley have demonstrated that E. dalrympleana appears to display no flowering synchrony with the plantations and therefore is not at risk of genetic incursion (Figure 2). In the case of E. archeri, however, its flowering appears to overlap with that of E. nitens. In addition, artificial pollination studies testing the performance of E. archeri pollen on trees on Ben Lomond, have found that these two species are, indeed, cross-compatible, with an average level of hybridisation of 23% being found following supplementary pollination of 13 trees ("supplementary pollination" involves the placement of E. nitens pollen on open-pollinated stigma). Combined with the apparent large source/sink ratio in the size of the E. nitens compared to E. archeri populations and the position of E. archeri “down stream” from E. nitens in the prevailing northwest winds, this native population does appear to be at potential risk of genetic incursion. However, regardless of the risk of cross-pollination there may be ecological barriers which act to prevent hybrids with E. nitens establishing or reaching reproductive maturity in the wild, as has been evident for hybrids with E. ovata (see related article in Biobuzz 7). For example, Eucalyptus archeri naturally occurs at altitudes of over 980 m, but is predominantly between 1100-1200 m (Williams and Potts 1996), whereas E. nitens plantations are typically restricted to areas below 650 m altitude in Tasmania consistent with different ecological adaptive requirements.

Dave McElwee at Ben Lomond

Figure 3. Robert Barbour, Anthony Mann and David McElwee (David pictured) made the 2 hour trek up from the boundary of the Ben Lomond National Park to the tree-line, where E. archeri is found. Open-pollinated seed was collected from E. archeri and the seed is now being grown under glasshouse conditions. The resulting seedlings will be  screened morphologically for the frequency of exotic hybrids, which have been produced through pollen dispersal from E. nitens plantations established adjacent to the park.

A meeting with representatives of the Biodiversity Conservation Branch and the Threatened Species Unit of the Department of  Primary Industries & WaterForestry Tasmania, Gunns Ltd and the Forest Practices Authority was held earlier in the year to summarise the predicted risks to high conservation value populations such as the Ben Lomond E. archeri.  Current research is now focussing on direct quantification of the level of hybridisation with E. nitens pollen by collecting open-pollinated seed from the E. archeri populations closest to mature plantations (Figure 3). One particular site has been identified where the E. archeri is within 2 km of a large, recently harvested and re-established plantation. This seed is currently being germinated and grown in the glasshouses of the School of Plant Science (UTAS) for morphological detection of any exotic hybrid seedlings. Similar high conservation value populations that exist in proximity to plantations exist for E. perriniana (see related article in Biobuzz 5), as well as other Symphyomyrtus species within Mt Field National Park and the Central Plateau World Heritage Area, all of which are part of current or planned future research.

Biobuzz issue eight, March 2009