In 1988 our initial expectation for the Woodland Conservation Area was that, with the cessation of grazing and its management for conservation, that the native plant species would increase in abundance. Certainly tree and shrub cover increased noticeably over a 10 year period, but this only involved a few tree species and the shrub species, Bursaria spinosa, Blackthorn, which was mainly from previously suppressed individuals - areas that were previously devoid of shrubs are still relatively shrub free nearly 20 years later.
Changes in the relative abundance of native groundcover species (and these make up over 80% of the plant species) have been much less obvious. Native species that were regarded as Frequent species in 1988 were still Frequent species in 2000 (an exception is the grass Bothriochloa macra which appears to change in response to changing structure), while a few less common species have increased in abundance e.g. the fern Cheilanthes sieberi.
See our image galleries of groundcover species in the woodland.
Undisturbed woodland plots 1988-2004
Five of our 5 x 5 m monitoring plots (four plots from September 2002) were left essentially undisturbed over the 16 year period from December 1988 to November 2004. Undisturbed plots were those kept unslashed, unburnt, un-grazed by domestic stock, and unfenced - allowing access by rabbits from 1991, and kangaroos from 2000. These are essentially control plots and represent the basic management treatment for the conservation area.
The figure below shows the mean species richness measures for these plots. Native species richness was high initially with 32 species per plot, but fluctuated over the initial 14 year period, generally dropping no more than 25% of the initial measure, and returning to similar high levels after 15 and 16 years. The exception was a major slump to 16 species (a 50% drop on the initial figure) in November 2002 during an exceptionally very hot dry period. Native species richness the following year recovered to 32 species per plot.
Exotic species richness declined over the 16 year period from 16 species to 7 species, and dropped to 3 species in the very dry 2002.
Gaps in recording years however could mask fluctuations but there does appear to be a trend in decrease of exotic species over the period. Many of these species would remain in the soil seed bank or as rootstocks as is indicated by the immediate response in 2003 after the dry conditions of 2002.
The first five years - will the weeds go?
With the grazing or slashing regime lifted, we expected the native groundcover plants to increase in abundance and begin to dominate. While some native species were widespread and common in 1988, many native species had very localised populations often of only a few plants occupying an area of a few square metres. Species such as Pimelea spicata, Daviesia ulicifolia, Sorghum leiocladum, Vernonia cinerea, Calotis lappaceus, Ranunculus lappaceus and Ranunculus sessiliflorus were all very restricted and we expected to see an increase in their abundance and distribution.
During the five years from 1988 however the main changes in species abundance were among the exotic species and many of these weedy species, after an initial increase, decreased or virtually disappeared. These included *Petrorhagia nanteillei, *Vulpia bromoides, *Silene gallica, *Lepidium species [they reappeared after drought], *Polycarpon tetraphyllum, *Soliva sessilis, *Stachys arvensis, *Linum trigynum, *Centaurium tenuiflorum and *Verbascum virgatum. These species were generally short-lived species, with many of the exotics being weedy annual species and are part of a group of species that we called Short-term (<5 years) responders. Data from our plots showed that species of this group decreased in frequency during the first 5 years (between 1988 and 1993), and continued to decrease further in the following 10 years.
Many are common weeds in rural sites. Presumably these species benefited from the open conditions created by slashing and grazing, and particularly in the years immediately following but were unable to establish or persist as longer-lived herb species became more abundant, and the perennial grasses grew taller.
Short-term (< 5 years) responders also include some short-lived ephemeral native species e.g. Daucus glochidiatus, Fimbristylis dichotoma and Ranunculus sessiliflorus, and short-lived perennials e.g. Geranium homeanum, Oxalis perennans , as would be expected, but also perennial species with rootstocks e.g. Sida corrugata.
Most of these native species have long-lived soil seedbanks and reappear periodically during wet seasonal conditions, particularly where groundcover has been depleted by drought or disturbance.
The next ten years 1993-2002
During the first 5 years some species increased in frequency, but subsequently, between 1993 and 2002, decreased in frequency. These species appeared to respond best to conditions 5-10 years after grazing/slashing ceased. Medium term (5 -10 years) responders are herbs and monocots, including a particularly high component of exotic herbs. They also include annuals e.g. Wahlenbergia gracilis, *Sonchus oleraceus, *Conyza sumatrensis, and short-lived species e.g. Senecio quadridentatus, *Senecio madagascariensis, *Anagallis arvensis and perennial species with rootstocks e.g. Asperula conferta, Pimelea spicata. These species appear to be taller growing species that are susceptible to regular slashing or grazing but respond to open conditions. We have called these Medium-term (5-10 years) responders.
A third group of species either increased in frequency or at least remained relatively stable over the 14 year time span. These Long-term (> 10 years) responders are mostly native species, herbs and monocots but also includes the tree and shrub component of the woodland. Perennial species with rootstocks are a major component e.g. Dichondra repens, Brunoniella australis, Aristida ramosa, Cheilanthes sieberi, but there are also some relatively shortlived species that establish in the absence of disturbance, e.g. Solanum prinophyllum, Oplismenus imbecillis, Crassula sieberiana.
Species persistence - changes in species present over 12 years (1988-2000) in 8 permanent plots (total area 0.2 ha).
( ) = inconclusive due to ID problems or seasonal effects. Disappearing species are not necessarily gone from the woodland.
| |
Native species |
Exotic species |
| Species disappearing within first 5 years |
2(2)
Daucus glochidiatus
Fimbristylis dichotoma
(Polygala japonica)
(Solenogyne bellioides) |
10
*Leontodon taraxicoides
*Lepidium spp.
*Petrorhagia nanteuilii
*Plantago myosuros
*Polycarpon tetraphyllum
*Silene gallica
*Soliva sessilis
*Stachys arvensis
*Verbascum virgatum
*Vulpia bromoides |
| Species disappearing within 8 years |
2(1)
Juncus subsecundus
Wahlenbergia communis
(Solenogyne dominii) |
6
*Centaurium tenuiflorum
*Ciclospermum leptophyllum
*Medicago lupulina
*Paronychia brasiliana
*Romulea rosea
*Taraxacum officinale |
| Species present after 12 years |
54 = 78% |
19 = 48% |
| New species appearing during 12 years |
4(4)
Eremophila debile
Oplismenus imbecillus
Rumex brownii
Cotula australis
(Lachnagrostis filiformis)
(Carex breviculmis)
(Dodonaea viscosa)
(Stackhousia viminea) |
5
*Briza subaristata
*Hypericum perforatum
*Modiola caroliniana
*Trifolium spp.
*Solanum nigrum |
| TOTAL |
69 |
40 |
Asterisk * indicates exotic species naturalised at the Australian Botanic Garden.