Edward Charles Morris

Summary: Restoration of degraded former Cumberland Plain Woodland by planting of native trees and shrubs was undertaken by Greening Australia (NSW) on the Cumberland Plain, west of Sydney, Australia, from the mid‐1990s. Our study examined the success of this restoration in stands of two ages using species composition as the criterion. The starting point (pasture) and the target (reference woodland) were sampled to document the extent of progress of species composition from pasture through young (3–5 years) and old (9–11 years) restoration stands to reference woodland across three sites at two surveys. Comparisons showed restored stands of both ages differed significantly from pasture, and from each other, showing decreasing similarity between the restoration stands and pasture at all sites. Despite this, species composition in restored stands at all three sites was still significantly different from reference sites, showing that none had achieved the target reference state after 11 years. The trajectory of restored sites between the two surveys was not towards the reference state. Restoration resulted in the establishment of 20 (71%) of the planted species. Recruits from five planted species were found. A further 40 unplanted native ground layer species were found in restoration. Structurally, tree cover increased with time since restoration and was higher in the restored sites. Ground cover, which was very high in pasture was lower in some restored sites. The majority of the unplanted native species were resprouters, and their presence in the above‐ground vegetation was most likely by vegetative resprouting from the bud‐and‐tuber bank as ground cover was lower with the increase in tree cover and shade. Tree and shrub planting by itself has not yet progressed the restored areas to the species composition of reference sites. Additional tools will be needed to assist restoration, specifically the addition of re‐seeder native plants not able to persist through vegetative resprouting after restoration. Measures to control the burden of weeds present in the pasture seed bank are also required.

Summary: Revegetation of abandoned pasture by planting tree and shrub species has been undertaken in western Sydney to restore Cumberland Plain Woodland. This study investigated the germinable soil seed bank of pastures, revegetated areas and remnants to assess the potential of the seed bank to contribute to Cumberland Plain Woodland restoration. Soil cores were taken, air dried, sieved and spread out in germination trays. Half of the samples were subjected to a fire treatment, with the other half as controls. The size of the germinable seed bank was 9,400–9,500 m⁻² in the pasture and revegetated areas, and 3,000 m⁻² in the remnant. Exotics, mainly forbs, dominated the seed bank in pasture and revegetated areas, with more than half the number of species and three quarters the number of seedlings. Numbers of native species and seedlings were half to one quarter of exotics in the pasture and revegetated areas. In remnants, native species outnumbered exotics, but numbers of native and exotic seedlings were approximately equal. Numbers of native shrub species and seedlings were low, and seedlings of one native tree appeared. There was some recruitment of seedlings from planted shrub species in the revegetated area. Only native species (numbers of species; seedling numbers) increased after the burn treatment; numbers of exotic species and seedlings were already high in the control and did not increase further after burning. Species composition was significantly affected by vegetation type, and by fire. The seed banks of the pasture and revegetated areas were very similar to each other, and both were most dissimilar to the remnant. The soil seed bank of the pasture had a heavy burden of exotic weeds, the majority forbs with the seeder fire response, and lacked the propagules of native species. The revegetated area was the same, as the revegetation method used planted only trees and some shrubs and did not address the problems of the weed seed abundance and propagule limitation of natives.

Cleared areas in Scheyville National Park, New South Wales, that formerly supported Cumberland Plain Woodland (CPW) now have a long unburnt mixed native and exotic grassland. To test whether re-introducing fire to these sites would benefit native species composition, and drive it towards that of neighbouring remnant woodland, an experiment was established in three grassy areas (grassy blocks) with prior agricultural land use, and one block in a remnant woodland. Replicate plots were established within blocks, and assigned to a repeat fire treatment, or unburnt controls. Plots in the fire treatment were burnt on all blocks in 2001, and in the grassy blocks only in 2005. Although the two fires did not result in recruitment of new native species on the grassy blocks, the successive fires had other beneficial effects. More native species were apparent in the above-ground vegetation on burnt than unburnt plots after both fires, and more summer-growing native grasses were apparent above ground and increased in abundance after the second fire. The large flush of exotic forbs that appeared after the first fire was not repeated after the second fire; many of these forbs had an obligate seeder fire response, and the short inter-fire interval may not have allowed replenishment of their seed bank. Burning did not result in recruitment of new native species in the grassy areas, and did not make the grassy areas more similar to the woodland in species composition. In the woodland, the first fire did not significantly affect species composition. Re-instating fire to degraded grassy sites will not by itself return the site to good quality CPW in the short term, but may contribute positively in the longer term through beneficial effects on natives and adverse effects on exotics.

Grassy woodlands worldwide are vertically structured by trees, a ground layer of grasses and forbs, and a variable mid-storey. In Western Sydney’s Cumberland Plain Woodland this mid-storey is increasingly dominated by the prickly shrub Bursaria spinosa Cav. subsp. spinosa. We investigated whether tree and shrub vegetation affects species richness and composition of ground layer microhabitats in this woodland, and whether fire frequency directly affects the ground layer in addition to any indirect effects via overstorey vegetation. Replicate sites were located in areas that had burnt with a frequency that was high, moderate or low. All sites had a similar time since last fire. Three microhabitats (open, under Bursaria, around tree) within each site were sampled for species richness and composition of native and exotic species. Native species richness was not significantly affected by either microhabitat or fire frequency, for total species, grasses or forbs; however the relative abundance of native grasses decreased significantly as fire frequency declined, while the relative abundance of native forbs increased. Exotic species richness was lowest at high fire frequency and significantly higher at low fire frequency. Species composition was significantly affected by both microhabitat and fire frequency combining independently. Planned burning at relatively short intervals can help managers retain grassy habitat for open patch species, habitat for ground layer species that do best under frequent fire, and a robust Themeda triandra Forssk. sward antagonistic to weeds.

Our study investigated the effects of fire frequency on the tree and grass components of Cumberland Plain Woodland, an endangered grassy eucalypt woodland in eastern Australia. We located three sites within each of three fire frequency classes (high, moderate, low) based on fire history and a similar time since last fire. For trees, we asked whether fire frequency affected density, eucalypt population structure, basal area and spatial patterning. For grasses, we tested for fire frequency effects on total abundance and the abundance of two common species. Density of trees was not significantly affected by fire frequency for juveniles, saplings or adult trees and neither was basal area per hectare. Features of a recruitment bottleneck model were present for eucalypts. There was a large pool of suppressed juveniles making up more than half the population at each fire frequency. Saplings were the smallest group and were susceptible to fire‐induced stem mortality, with particularly low numbers relative to juveniles and small trees where fire was frequent or intense. Despite this difference in sapling mortality, numbers of small trees did not differ with fire frequency. Saplings could transition to small trees in equal numbers if they did so more quickly at high than at lower fire frequencies, and if recruitment of saplings into the tree layer was controlled independently of fire frequency. The size hierarchy of small to medium eucalypt trees was homogeneous over eight of the nine sites, spatial patterning of adult trees was random tending to regular, and mean tree size decreased with density at all sites. These features of eucalypt population structure are indicative of possible resource competition which could regulate tree recruitment. Total grass cover index was high across all fire frequencies, with Themeda triandra dominating at high and moderate fire frequencies and Microlaena stipoides at low fire frequency.

Summary: A restoration trial of grassy woodland on former agricultural land applied carbon at a standard rate (840 g C/m²/year) and at a high rate (4,200 g C/m²/year), to test whether further benefits to native plants and suppression of exotics would emerge. Carbon addition at the high rate reduced plant cover further than the standard rate but led to severe loss of plant species; it also reduced soil pH. Soil Al, Fe and Mn levels increased across the gradient of C addition, which would be consistent with the reduction in soil pH for Al and Mn, and a decrease in soil redox potential for Mn and Fe. Nutrient analysis of leaf tissue confirmed that uptake of Fe and Mn increased over the range of C addition, with the concentration of Mn in the high carbon treatment exceeding the threshold for toxicity for a range of species. The soil and plant tissue data are consistent with the induction of increased soil acidity and of stronger reducing conditions in the soil by high level of carbon addition and localised soil flooding. Plant uptake of Mn to toxic levels occurred subsequently, leading to negative effects on plants; aluminium phytotoxicity may also have occurred.

This study reports on a trial of methods to overcome barriers to restoration of degraded Cumberland Plain woodland. Soil scalping was compared with fire or slashing to remove existing canopy. Fire and slashing were combined with soil carbon addition at two levels, to reduce soil nitrate. Native seed was added to overcome a lack of native propagules. Treatments, applied to 2 × 2 m plots, consisted of a control; scalped; fire and slash treatments without carbon addition; fire and slash treatments at the low and the high carbon addition levels; and a further fire and a slash treatment at the low carbon level with no native seed added, to give 10 treatments in total. Scalping eliminated the existing canopy and reduced weed seed and bud banks allowing native species (and some colonising exotics) to establish by 33 months. Rapid re-growth in the fire treatment resulted in plant canopy abundance returning to control levels by 12 months, and native species richness on burnt plots remained similar to the control. Canopy abundance in the slash treatment remained lower than in the controls for 20 months, and native species richness increased by then. Carbon addition reduced canopy re-growth in both fire and slash treatments: in the fire-low carbon plots with added native seed, native species richness was double that of the controls by 20 months. This increase did not occur on slash-low carbon plots. The highest level of carbon addition had negative effects on plant growth and survival, resulting in the lowest native species richness. The non-scalping treatments had little effect on exotic species richness in the absence of carbon or small negative effects if combined with carbon.

Seeds of some eastern Australian Grevillea species show the characteristics of non-deep physiological dormancy, which is broken by exposure to heat shock and/or smoke. The current study tested whether the restrictive effect of the seed coat on germination was localized to specific regions, whether the fire cues affected the growth potential of the embryo, the mechanical strength of the seed coat itself, and the anatomy of fracturing of the seed coat. Removal of the micropylar seed coat allowed germination, while retaining it in place restricted germination. The growth potential of the embryo was increased by exposure to heat shock or to smoke, and increased the most if exposed to both cues. Estimation of the minimum force required by embryos to germinate from intact seeds suggested that this force was reduced for seeds treated with fire cues. The fire cues did not affect the resistance of the seed coat to compressive force when tested after 24 h of imbibition. Fracturing of the seed coat occurred between cell walls, except for the palisade layer, where fracturing occurred across palisade and sclerenchyma cells. While the micropylar end of the seed coat imposes dormancy, most likely by mechanical constraint, heat shock and smoke overcome dormancy by increasing the embryo's growth potential and possibly weakening the seed coat, either directly or via the embryo.