Ninety years of change on the TGB Osborn Vegetation Reserve, Koonamore: a unique research opportunity

The TGB Osborn Vegetation Reserve, on Koonamore station in the NE pastoral area of South Australia, is the longest-running vegetation monitoring project of its type in Australia. In 1925, a 4-km2 rectangle in a heavily overgrazed area was fenced to exclude rabbits and sheep, and permanent quadrats and photo-points set up to record changes. The area is predominantly chenopod shrubland, with an open woodland tree layer. After the initial elimination of rabbits, control slackened and rabbit numbers increased until the 1970s, when intense elimination efforts resumed, together with the arrival of myxomatosis and rabbit haemorrhagic disease viruses. Consequently, the reserve has had 50 years without sheep, followed by 40 years virtually without either sheep or rabbits. Changes over that time have been very striking, and they have been recorded regularly via mapped quadrats and photopoints. The objective of this paper is to highlight opportunities for making use of this database for researching several interesting ecological questions.

DEVELOPING AGE-SIZE RELATIONSHIPS FOR LONG LIVED TREE SPECIES

Calculating the age of trees is often desirable in vegetation studies, but is sometimes difficult. In arid areas in particular, tree rings may not be annual, and growth may be related more to rainfall than annual cycles. A relationship between age and trunk circumference was developed for two species, Acacia aneura and Myoporum platycarpum, based on measurements of trees of known age (<80 years) growing on permanent quadrats on the Koonamore Reserve, in semi-arid South Australia. Extrapolation beyond the known ages was made by finding the maximum girth of mature trees in a larger population and using this to estimate an asymptote to which the curve is constrained to approach. We envisage that the techniques developed here could be applied to other species of a similar nature, those for which there is no relationship between number of tree rings and age.

Regeneration of Agathis australis and associated species in a native bush stand on Limestone Downs

A predator-proof fence enclosing 270 m2 of predominantly kauri (Agathis australis) bush on Limestone Downs was erected in February 2004. Regeneration of A. australis and other seed-dispersed species was monitored in permanent quadrats laid out within and immediately outside the enclosure. The quantity of viable A. australis seed entering the enclosure by natural dispersal and extent of viable A. australis seed within the soil seed bank were measured. Two thirds of the viable seed dispersed was lost, probably through mammalian predation. Eleven species were found in the soil seed bank. No viable A. australis seed was found in the soil seed bank. Seed rain was the source of viable A. australis seed. Regeneration of A. australis was greater within the protected environment of the predator-proof fence. There was a decline in seedling numbers between May 2007 and April 2008 both inside and outside the predator-proof fence suggesting that predation was not the only factor influencing seedling survival. Keywords: Agathis australis, Xcluderâ„¢ fence, seed predation, seedling survival, regeneration, seed rain

An Emergence Model for Wild Oat (Avena fatua)

Wild oat is an economically important annual weed throughout small grain producing regions of the United States and Canada. Timely and more accurate control of wild oat may be developed if there is a better understanding of its emergence patterns. The objectives of this research were to evaluate the emergence pattern of wild oat and determine if emergence could be predicted using soil growing degree days (GDD) and/or hydrothermal time (HTT). Research plots were established at Crookston, MN, and Fargo, ND, in 2002 and 2003. On a weekly basis, naturally emerging seedlings were counted and removed from six 0.37-m2permanent quadrats randomly distributed in a wild oat–infested area. This process was repeated until no additional emergence was observed. Wild oat emergence began between May 1 and May 15 at both locations and in both years and continued for 4 to 6 wk. Base soil temperature and soil water potential associated with wild oat emergence were determined to be 1 C and −0.6 MPa, respectively. Seedling emergence was correlated with GDD and HTT but not calendar days (P = 0.15). A Weibull function was fitted to cumulative wild oat emergence and GDD and HTT. The models for GDD (n= 22,r2= 0.93, root mean square error [RMSE] = 10.7) and HTT (n= 22,r2= 0.92, RMSE = 11.2) closely fit observed emergence patterns. The latter model is the first to use HTT to predict wild oat emergence under field conditions. Both models can aid in the future study of wild oat emergence and assist growers and agricultural professionals with planning timely and more accurate wild oat control.

Influence of Planting Date and Microsite on Weed Dynamics in Sugarcane in Sri Lanka

Experiments were conducted in Sri Lanka to compare weed seedling emergence in three sugarcane plots of 0.1 ha planted in October 1995, January 1996, and April 1996. In each plot, weed seedling emergence was monitored for 20 wk in five permanent quadrats on each of three microsites: on ridges, in furrows, and on adjacent fallow land. Soil moisture (0 to 5 cm) and soil temperature (at 2.5 cm) were also recorded. Only crowfootgrass, swamp millet, and guineagrass (all grasses) occurred in all nine planting time-by-microsite combinations. About half of all seedlings emerging over the three planting times were swamp millet, and the next most frequent species was tropic ageratum. The composition of the emerged flora was similar on ridges and in furrows, but more seedlings emerged in the furrows than on the ridges. The highest number of emerged seedlings and of species occurred on adjacent fallow land. The major factor influencing seedling emergence appeared to be soil moisture.

Twenty years of post-fire plant succession in a "cerrado", São Carlos, SP, Brazil

Secondary succession in degraded areas is little studied, especially where long-term observation of evolutionary processes is concerned. The aim of this work was to follow the qualitative and quantitative changes in vegetation throughout the regeneration process after fire in a cerrado with forest physionomy. The area under study is a reserve on CPPSE-EMBRAPA's farm, São Carlos region of São Paulo State, Brazil. In 1981, an especially destructive fire eliminated the aerial part of the vegetation and litter. From that time, the vegetation in three permanent quadrats of 2 x 20 m was recorded for twenty years. The results demonstrated the rapid growth of herbs, shrubs, climbers and trees successively, with a great species richness and, after a certain time, a decline in density at a rate similar to the initial recovery. Both the soil seed bank and sprouting subterranean organs played important parts in the recovery of the vegetation. Three phases were observed in the plant succession: plant growth, followed by intraspecific competition with a reduction in the number of individuals and finally interspecific competition with the disappearance of some species from the quadrats. The different populations behaved similarly and the rise and fall in density of each species over time reflected their ecological role.

Long-term changes in vegetation, gradual and episodic, on the TGB Osborn Vegetation Reserve, Koonamore, South Australia (1926 - 2002)

The TGB Osborn Vegetation Reserve at Koonamore, South Australia, is a 390-ha exclosure in semi-arid chenopod shrubland. The area was heavily overgrazed in 1925 when it was fenced to exclude sheep. Permanent quadrats and photopoints have been maintained to the present. Feral rabbits were sometimes numerous until the mid-1970s but have since been controlled. The records represent 50 years without sheep grazing, followed by 26 years without either sheep or rabbits. Dramatic seedling establishment events have occurred since 1978 for the following species: Acacia aneura Benth., Myoporum platycarpum R.Br., Senna artemesioides subsp. coriacea Randell, S. artemesioides subsp. petiolaris Randell, Acacia burkittii Benth., Dodonaea attenuata A.Cunn., Eremophila longifolia (R.Br.) F.Muell., E. sturtii R.Br. and Maireana pyramidata (Benth.) Paul G.Wilson. However, the chenopod shrubs Atriplex vesicaria Benth. and A. stipitata Benth. increased earlier and did not respond in the same way to episodic rainfall events or rabbit control. Numbers of Alectryon oleifolius (Desf.) S.T.Reynolds and Casuarina pauper F.Muell. ex L.A.S.Johnson have remained almost unchanged, whereas Maireana sedifolia (F.Muell.) Paul G.Wilson and M. astrotricha (L.Johnson) Paul G.Wilson have shown a very gradual increase over time. The data show evidence for both episodic and gradual change among different species.

Persistence of dead trees and fallen timber in the arid zone: 76 years of data from the T.G.B. Osborn Vegetation Reserve, Koonamore, South Australia

Very little information is available about how long dead trees remain standing, or fallen logs persist, in the Australian arid zone. Data on dead timber longevity were extracted from records of both permanent quadrats and photopoints on the T.G.B. Osborn Vegetation Reserve on Koonamore Station, South Australia. Two species were examined, Acacia aneura (mulga) and Myoporum platycarpum (false sandalwood, sugarwood). Some individuals of mulga are capable of standing dead for over 75 years, while dead M. platycarpum may stand for over 60 years. Dead Myoporum trees remained standing for an average of 31.2 � 5.7 years, fallen trunks persisted for 38.4 � 3.7 years. Standing dead A. aneura persisted on average for 40.0 � 3.7 years, fallen trunks for 22.4� 6.3 years. These figures are almost certainly underestimates. The reasons why are discussed and some comparisons made with temperate forests and tropical mangroves.