Australasian Plant Conservation
Originally published in Australasian Plant Conservation 20(3) December 2011 - February 2012, p 8-10
Serendipity during long-term monitoring of translocation trials
Botanic Gardens of Adelaide, South Australia and School of Earth & Environmental Sciences, University of Adelaide.
An essential component of all translocation projects is the monitoring of outcomes and evaluation of processes after planting has taken place. Monitoring goals and objectives are usually formulated early in the translocation planning process based on available knowledge of the species’ biology and ecology. However, nature is rarely predictable, and occasionally unexpected and even surprising observations can be made during the course of long-term monitoring that may be missed altogether in the short-term. Such serendipitous observations may be readily explainable, or may lead to further experimentation or extended monitoring in order to understand their underlying mechanisms. I have experienced several examples of such serendipity in the course of long-term monitoring of translocation trials in South Australia, and will briefly discuss four of them here. None of these outcomes were predicted to occur in the way they did when the translocation trials were first planned or set up, and each one was revealed only after a significant period of consistent and regular monitoring.
The annual herb, Corunna daisy (Brachyscome muelleri) was introduced to a new site 1.5 km from its natural population in 1997. Early monitoring showed an abundance of seedlings emerged in their first season, fewer seedlings were found during the subsequent 2 years, and numbers swelled again in the fourth year. This observed pattern of recruitment correlated well with annual rainfall (Jusaitis et al. 2004). Subsequent annual monitoring revealed a regular cyclical pattern of recruitment with a period of 3-4 years. In each year immediately following a peak, seedling numbers fell dramatically. This longer-term cycle no longer correlates with annual rainfall, and is postulated to possibly involve dormancy-cycling phenomena in the seed. A similar synchronised recruitment pattern was observed concurrently in the natural population. This cyclic trend became evident after at least 10-15 years of observation. Ongoing monitoring will be required to confirm its repeatability and to understand its underlying mechanisms.
Prickly raspwort (Haloragis eyreana) illustrates the serendipitous discovery of an ideal microsite for translocation. The goal of this study was to examine the influence of planting-site proximity to the water table on translocation success by constructing a series of high and low crests separated by trenches. Plants were transplanted onto high and low crests to compare survival and recruitment in relation to distance from the water table. Survival was slightly higher on low crests, but the number of surviving translocants on both high and low crests declined steadily over 4 years, when none remained (Jusaitis & Freebairn 2010).
However, in year 3 a few seedling regenerants were noticed along the bottom of the trenches, and over the next 6 years the number of plants observed in trenches increased exponentially to average 18 plants/m2 by year 8. Trench plants were more likely to perenniate from year to year than crest plants. Trenches had consistently higher moisture levels and tended to have fewer weeds than crests, providing a suitable protected microsite to support successful germination and proliferation of H. eyreana.
Survival of Prostanthera eurybioides translocants in fenced and unfenced plots over 17 years. The decline in the fenced population was related to a drought event, while the steady population in fenced population suggests that grazing may assist the plant to withstand severe periods of drought.
First seedling recruits of Phebalium glandulosum observed 18 years after translocation. Photo: Manfred Jusaitis.
Monarto mintbush (Prostanthera eurybioides) illustrates an intriguing interaction of climate with herbivory. A translocation trial was set up to study the impact of herbivores on establishment (Jusaitis 2010). Seedlings were planted into replicated, paired, fenced and unfenced plots. Frequent grazing damage was observed on unfenced plants over 17 years of monitoring, although this rarely proved fatal once plants were established. By year 7, survival had stabilized at 96% (fenced) and 67% (unfenced), remaining at those levels for the next 4 years. In 2006 (year 11), the translocation site experienced its lowest rainfall on record, followed by 2 years of below average rainfall. This severe drought resulted in a dramatic loss of fenced plants, while having no effect on survival of unfenced plants.
The explanation for this unforeseen phenomenon lay in the size of unfenced plants which, due to frequent grazing, were about one third the size of fenced (ungrazed) plants. The larger size of the latter meant a larger leaf surface area, higher transpiration losses and thus increased susceptibility to water stress, compared with the smaller, unfenced, grazed plants which survived the drought. Thus, although it was tempting to abandon monitoring after the population had been stable for 5 years, the next 5 years revealed an unexpected result which suggests that this plant is far more tolerant of grazing than was first thought. Indeed, grazing may assist the plant to withstand severe periods of drought. Interestingly, the first significant recruitment of new seedlings was observed in year 14, so the drought may also have played a role in overcoming seed dormancy (Ainsley et al. 2008).
The desert Phebalium (Phebalium glandulosum ssp. macrocalyx) was translocated to a protected sanctuary to establish a secure population. A success indicator of this study was to document survival, flowering, reproduction and recruitment of the species. Survival stabilized after 3 years and survivors continued to grow over 20 years of monitoring. Flower buds were first seen on plants a year after planting, and subsequently plants flowered and set seed annually. Eleven years into the trial, the average percentage of flowers that set seed was similar in both translocated and wild populations.
The first recruitment of new individuals was observed 18 years after translocation. Most were at the 2-leaf stage, but a few larger seedlings were also found that may have emerged a year or two earlier. More new recruits were found the following year. Thus the full cycle of establishment, flowering, reproduction and recruitment took at least 16 years for these translocants. Recruitment did not require a disturbance event, and most seedlings were found clustered around the base of parent plants where shade and moisture retention provided a protected germination niche.
I hope that these brief cameos portray the importance of a long-term view when monitoring translocation trials. Each discovery made here would have been missed had monitoring ceased within the time frame of 4 years, an apparent standard for most documented translocation projects (Godefroid et al. 2011). As well as evaluating the success or failure of the translocation project, consistent long-term monitoring can also generate unexpected and surprising results that can deepen our understanding of the species and its ecology.
I would like to gratefully acknowledge Anthony Freebairn for assistance with the concept and construction of the Haloragis eyreana trial, Graham and Brenton French for allowing access to the Corunna pastoral property, and the Australian Wildlife Conservancy for allowing access to Yookamurra Sanctuary.
Ainsley, P.J., Jones, M.K. and Erickson, T.E. (2008). Overcoming physiological dormancy in Prostanthera eurybioides (Lamiaceae), a nationally endangered Australian shrub species. Australian Journal of Botany 56: 214-219.
Godefroid, S., 19 others. (2011). How successful are plant species reintroductions? Biological Conservation 144: 672-682.
Jusaitis, M. (2010). Enhancement of Monarto Mintbush populations in South Australia by translocations. In: P.S. Soorae (ed). Global Re-introduction Perspectives: Additional case-studies from around the globe, pp. 306-310. IUCN/SSC Re-introduction Specialist Group, Abu Dhabi, UAE.
Jusaitis, M. and Freebairn, A. (2010). Habitat manipulation stimulates natural regeneration of Prickly Raspwort (Haloragis eyreana) on Eyre Peninsula (South Australia). Ecological Management & Restoration 11: 81-82.
Jusaitis, M., Polomka, L. and Sorensen, B. (2004). Habitat specificity, seed germination and experimental translocation of the endangered herb Brachycome muelleri (Asteraceae). Biological Conservation 116: 251-266.