Survey of threatened plant species in South East Queensland biogeographical region queensland cra/rfa steering committee survey of threatened plant species in
|
|  Yüklə 1.26 Mb.
|
3.12 dodonaea rupicola C.T. White3.12.1 SummaryDodonaea rupicola is only known from the South East Queensland Biogeographical Region. It has a distributional range of approximately 10 km in the area between Caboolture and Beerwah. It is known from 4 populations; 3 are within areas gazetted for conservation purposes; 1 is within State Forest lands but in an area with no commercial timber values. The total area of occupancy is approximately 17 hectares. The largest known population is within Glasshouse Mountains National Park. D. rupicola occurs on low rocky hillslopes on shallow, acidic, silty clay loam to loams which are generally well drained. The vegetation community varies in structure from open shrubland to tall woodlands. The potential threats to the survival of D. rupicola arise from human interference with the environment. These threats are an inappropriate fire regime and the invasion of weed species. 3.12.2 Species background, description and identificationDodonaea belongs in the family Sapindaceae and is predominantly an Australian genus with 60 of the 69 species currently recognised endemic to Australia. The genus is well distributed in all states and grows mostly in shrubland, woodland and open forest communities (West 1984). A few species are used as ornamental plants in horticulture, fodder in meat production and a pollen source for honey production (Lazarides and Hince 1993). The colourful fruits of the genus resemble the fruits of Humulus lupulus (hops) which is used in the brewing industry. The common name Hopbush is applied to Dodonaea because of this resemblance, although these genera are not in any way closely related (Closs 1993). Dodonaea rupicola C.T. White was formally described in 1926 from material collected on Saddleback Mountain, approximately 48 km north of Brisbane (White 1926). The botanical description of Dodonaea rupicola is as follows: Dioecious spreading shrub 0.6-1 m high. Branchlets terete to slightly angular, covered in spreading long soft white hairs. Leaves imparipinnate 1.5-3.5 cm long (excluding petiole); petiole 3-8 mm long, densely covered with spreading long soft white hairs; rachis 1-1.5 mm broad, winged. Lateral leaflets 10-18, opposite, oblong to oblanceolate, 4-9.5 mm long, 2-4 mm wide, dark to olive-green above, paler below, densely covered with long spreading hairs, margin entire or sometimes undulate, recurved or revolute, apex acute, midvein prominent below, impressed above; terminal leaflet lobe-like, otherwise as in lateral leaflets, Inflorescence a panicle composed of monads to botryoids, terminal. Flowers unisexual, pedicels 2-2.5 mm long covered with spreading long soft white hairs. Sepals 4, lanceolate or sometimes ovate-lanceolate, 2.5-4 mm long, 1-1.5 mm wide, acute, persistent, mostly covered with long spreading soft white hairs. Petals absent. Stamens 8, approximately equal in length to the sepals. Ovary 4-carpellate, obovate, ca 1-1.5 mm diameter, densely covered with long spreading white hairs. Capsule 4-winged, dehiscent, transverse-elliptic in lateral view, 7.5-9 mm long, 12-15 mm diameter, densely covered with long spreading hairs, red-brown at maturity; wing extending 3-4 mm beyond body of carpel, margin undulate, extending from base to apex of carpel. Seed 2-4, lenticular, approximately 2 mm diameter, black, dull, aril absent (West 1984) (see Plate 6). D. rupicola is closely related to and resembles the more widespread species D. vestita but can be distinguished by the larger leaves, the shorter pedicels, the shorter filaments and anthers and the smaller fruits. Details of these differences are presented in Table 3.12.1. Table 3.12.1. Characters distinguishing Dodonaea rupicola and Dodonaea vestita.
3.12.3 Current conservation statusDodonaea rupicola is presently listed on the schedule of the Queensland Nature Conservation Act 1992 as “vulnerable wildlife”. The species has been assigned a national conservation status of V (vulnerable) by ANZECC (1993). It is also listed on Schedule 1 Part 2 (vulnerable) of the Commonwealth Endangered Species Protection Act 1992. 3.12.4 Distribution and abundanceA compilation of Queensland Herbarium records of D. rupicola is presented in Appendix 1.11. D. rupicola is represented in the herbarium by twelve specimens. Three of the records lack sufficient information to relocate the collection site. The first collection with adequate information was made in 1926 from Saddleback Mountain just north of Caboolture. Another seven specimens have been collected from this site with the last collection made in 1974. A second locality was recorded in 1977 when it was found on Wild Horse Mountain approximately 10 km north of Mt Saddleback, near Beerburrum. Recent field work has confirmed that D. rupicola is still present on Wildhorse and Saddleback Mountains. A third population has been located on a peak beside Tibrogargan some 5 km WNW of Wildhorse Mountain. This peak is locally known as Mt Cooee. Site data for all three localities is presented in Appendix 2.3. Other potential locations searched include the slopes of Mt Tibberoowuccum, Mt Miketeebumulgrai and the low hills between Mt Beerburrum, Mt Tibberoowuccum and Mt Tibrogargan. Other areas that warrant further searching include Round Mountain and Tunbubudla. As far as can be ascertained, the current distribution pattern is natural and is not related to habitat reduction or fragmentation from human activity. The sites on Saddleback Mountain and Mt Cooee are within areas gazetted for conservation purposes under the control of the Queensland Department of Environment while the Wildhorse Mountain site is part of State Forest lands (State Forest Park No. 24) managed from the Department of Primary Industries, Forestry. The plants on Wildhorse and Saddleback Mountains were scattered over a relatively large area. These areas were systematically searched and direct counts of individuals were undertaken to obtain a measure of present population size. There are 2 sites on Mt Cooee. The population at site 1 on the crest of the mountain was estimated using 50 random quadrats along a 100 m transect through the population. At site 2 on the north west lower slope of the mountain the population was counted. The population data is presented in Table 3.12.2. Table 3.12.2. Estimated abundance, area of occupancy and land tenure for DODONAEA RUPICOLA sites. Where abundance was estimated by random transect sampling a mean with lower and upper 95% confidence limits are given. N.P. = National Park; S.F. = State Forest.
The population estimate for Mt Cooee site 1 of 42650 plants is has an extremely large standard error, making the estimate of little value. D. rupicola was observed to be very variable in its density through the habitat. The number of individuals in a 4 m2 quadrat varied from 1 to 196 revealing a extreme patchy distribution. Within the 50 quadrats 853 plants were recorded. Although the population estimate on Mt Cooee is unreliable, it is still evident that the majority of the presently known population occurs on Mt Cooee. From field observations of the population it is considered that a more reasonable population size estimate would be between 10000-20000 individuals. However this needs to be confirmed with more critical sampling of the site. The populations on Mt Cooee and Mt Saddleback are in legally gazetted conservation reserves and are relatively undisturbed. The other population on Wild Horse Mountain is within State Forest and has been impacted on by development of an access road to the lookout on the summit and the construction of a telecommunication tower half way up the slope. It is difficult to obtain an understanding of the age structure of a population from a brief survey. However, measurements of plant heights to the nearest 5 cm were used as a guide to the age structure within the population on Mt Cooee. The heights were grouped into classes of 5 cm intervals. Plants that were flowering or had evidence of recently flowering were also noted. A summary of this data is presented in Figure 3.12.1. The heights range from 5 to 140 cm with the most common size class 32.5-37.5 cm. There is a large proportion of individuals in the smaller size classes with more than 50% of the sample less the 47.5 cm high, although there is a lack of individuals in the smallest size classes (less than 4 % less than 12.5 cm ). There has been a high level of recruitment in the past but this does not appear to be occurring at the present time. It could be suggested the recruitment is not a continuous event but occurs as discrete events triggered by some unknown factor. Thirty-seven percent of the plants sampled were flowering or had just flowered. Flowering had occurred over a wide range of size classes. The smallest size class with flowering individuals was 17.5-22.5 cm tall. Figure 3.12.1: size class distribution of dodonaea rupicola population at mt cooee site 1. 
3.12.5 HabitatThe sites are situated on low isolated hills on crests and moderately to steeply inclined slopes of varying aspects and at elevations between 40-160 m above sea level. There are large areas of rock outcrop at three of the known sites. The soils on the rocky sites are shallow, well drained, black loams with a high organic content and a pH 5.3-5.7. The soils on the more wooded areas are greyish yellow brown to dull yellow brown, silty clay loams to sandy loams with a pH 5.7-5.9. The geology is mapped as Tertiary trachyte, comendite, trachyrhyolite, mangerite, syenite. The vegetation community in which D. rupicola is found varies in structure from open shrubland on the rocky outcrops to tall woodlands on the areas where the soils are deeper. The common species present in the shrublands included Acacia hubbardiana, Xanthorrhoea latifolia, Leptospermum microcarpum, Calytrix tetragona and Lophostemon confertus. The common tree species in the woodland sites are Eucalyptus tindaliae, Corymbia trachyphloia and E. crebra. The Mt Saddleback site is undisturbed apart from an old quarry site on the edge of the population. The quarry has been allowed to naturally regenerate. D. rupicola is one of the species that has colonised the quarry floor. The exotic weeds Melinis minutiflora, Lantana camara and Melinis repens are present near the summit of the mountain but are presently not a dominant part of the vegetation. The is no human disturbance at either of the sites on Mt Cooee (Plate 5), although site 3 is near the National Park boundary and adjacent to the firebreak along the park boundary. Lantana camara is present but not dominant within these sites. On Wildhorse Mountain there is a public lookout at the summit. Access is by a concrete vehicular track that leads from the carpark at the base of the mountain to the summit. There is also a telecommunication tower approximately halfway up the mountain on the south western side with a track leading to it from the concrete track. Both tracks dissect the habitat of D. rupicola. A number of exotic weed species were observed around the lookout on the summit and on the disturbed soil at the edge of the concreted track. These included: Conyza sumatrensis, Ageratum houstonianum, Baccharis halimifolia, Cenchrus echinatus, Lantana camara, Melinis repens, M. minutiflora, Richardia brasiliensis and Pennisetum sp.. 3.12.6 Life history and ecologyThere have been no studies into the biology or autecology of Dodonaea rupicola. The majority of the following information is extrapolated from our understanding of other species of Dodonaea. D. rupicola is known to have been cultivated by members of The Society for Growing Australian Plants (Closs 1993). Most species of Dodonaea can be propagated from seed or cuttings. For the best strike rate cuttings are best taken from semi-hardwood (Dixon 1993, Closs 1993). Seeds usually require pretreatment by soaking in very hot water prior to sowing. Elliot and Jones (1984) report the germination is fairly rapid for most species with seedlings often appearing after 14 days, but they can take up to 7 weeks to germinate. Dodonaea rupicola is a dioecious perennial shrub with an unknown life span. The main method of reproduction is by sexually produced seeds. D. rupicola has been recorded flowering in April, June, November and December and fruiting in April, June, August, September and December. All species of Dodonaea are considered to be wind pollinated (West 1993). Pollen seems to be released only under climatic conditions favourable for wind pollination to be successful, ie. warm, dry and usually windy days (West 1993). The light dry fruits are 4-celled and winged. However, the fruit does not appear to assist in the dispersal of the seed as the fruits dehisce tardily at maturity which occurs within 1 or 2 months of flowering. The number of seeds maturing on each plant varies greatly (West 1984). The levels of seed viability are unknown. Many Dodonaea species exhibit parthenocarpy (ie. the development of seedless fruits). The seeds of most species of Dodonaea appear to be released from the fruit largely in a dormant state (Closs 1993). The seed dormancy mechanism is not understood. However, the dormancy appears to be broken by the treatment of the seed with heat (Closs 1993). This suggests that the dormancy is due to seed coat impermeability. With these seed characteristics D. rupicola would accumulate a persistent soil seed bank during inter-fire periods. The longevity of such a soil-stored seed bank is unknown. Plants of D. rupicola are suspected to be fire-sensitive and killed by fire. There is no evidence to suggest that it is capable of regenerating from the rootstock. In the past on Wildhorse Mt D. rupicola has been observed prior to fire to be an uncommon species in the shrub layer but after fire it has become a common species in the understorey (B. Stark pers. comm.). Seedling recruitment may be promoted by fire in the habitat. Consequently, estimates of plant abundance at sites should not be used to assess conservation success at sites unless such estimates are continually made over time or related to the age of the population since it was last burnt. 3.12.7 ThreatsWith our limited knowledge of the species it is difficult to determine the stability of the populations and what possible threats there are to the long term existence of Dodonaea rupicola in the wild. However extinction of all three populations seems highly unlikely within the next few decades, especially with the majority of the known population within existing conservation reserves in the Glasshouse Mountain National Park. Anecdotal evidence suggests that fire plays a role in the maintenance of the population levels of D. rupicola in its habitat. However the lack of ecological information about this species makes it impossible to assess what would be an appropriate level of frequency and intensity for the long term benefit of the species. If fires are too frequent, the plants will have insufficient time to build-up a soil seedbank to replace plants that are killed in the fire, and this will lead to population declines. If fires are too infrequent then adult plants will become senescent and the soil seedbank may decline to the point where there are insufficient levels of fecundity to maintain population levels. Therefore inappropriate fire regimes are a potential threat to the species. A number of exotic weed species have been recorded from Wildhorse Mountain and also from the relatively undisturbed habitat of Saddleback Mountain. There is the potential for these exotic plant species to encroach on the habitat of D. rupicola. The impact that such a weed species invasion could have on D. rupicola is unknown. However, it can be assumed that weeds would change the vegetation structure and lead to increased competition for available habitat resources. Therefore another potential threat to the species is the invasion of weed species into the habitat. 3.12.8 Management, Research and Conservation MeasuresAppropriate management practices need to be put into place to ensure the long-term survival of D. rupicola in the wild. However, management presupposes knowledge about the effect of decisions on the species. There is a need to establish monitoring projects to determine the impact of particular management decisions. Information on the effect of fire on the population dynamics of this species is required. More detailed data on reproductive ecology is required especially in relation to seed germination. This needs to be understood in the long term if successful management techniques are to be developed for the effective conservation of the species. Although weeds are not a current threat their level and distribution should be monitored within the habitat of D. rupicola. Dodonaea rupicola assessed against the IUCN (1994) criteria for threatened wildlife falls into the category of Vulnerable, ie. is facing a high risk of extinction in the wild in the medium-term future, as defined by criteria D.2. Its population is characterised by an acute restriction in its area of occupancy (typically less than 100 km2) or in the number of locations (typically less than 5). The present status of Vulnerable for D. rupicola is considered to be appropriate. |