Performing Woodland Rehabilitation

Intact, high-quality woodland capable of effective natural regeneration is becoming scarce across the Northern Tablelands, placing pressure on what woodland remains to provide habitat and ecosystem services for the greater landscape. It is for this reason that any woodland regeneration or rehabilitation project must prioritise at conserving what woodland remains, ensuring that at least some woodland will remain into the future. In most cases, large-scale rehabilitation or revegetation projects are prohibitively expensive, when factoring fencing, tube-stock, labour and surveying costs into account. For this primary reason, we strongly recommend that natural regeneration be prioritised in every instance where a canopy of healthy trees is present, relying only on assisted revegetation when no canopy is present or when the infilling of trees, shrubs, or herbs would be advantageous for improving structure within the existing woodland.

In the previous section you assessed your woodland for health and condition, we will use this in the following sections to inform initially where regenerative works can be best targeted considering the resources available. To decide where to start, it is worthwhile considering the following points

• If you have ‘high or moderate quality’ woodland present, look to improve and maintain this status. Keeping this woodland in good condition is necessary for any future projects. Furthermore, maintaining a condition of good quality is always more cost-effective than having to rehabilitate woodland from a degraded state.

• Always look to work with larger woodland patches than small, fragmented or scattered paddock trees. Natural regeneration is increasingly more likely where there are woodlands of increasing size, particularly if in reasonable condition. However, maintaining small patches is also necessary, particularly when considering improving connectivity across the landscape.

• Prioritise woodland along creeks, drainage lines, or riparian zones first

• Prioritise secondly woodland on ridge lines or in elevated regions, as these zones often work as important habitats for fauna and flora

• Patches of woodland that are clumped rather than divisioned into linear strips (laneways or windbreaks), are less likely to be affected by edge effects (wind, drought, storms).

• If the woodland presents even moderate quality or condition, in most cases it is more effective to rehabilitate or regenerate this woodland than resorting to the planting of new patches.

Performing natural regeneration

Effective techniques to restore woodland TECs on the New England Tablelands are already broadly known: destock to reduce grazing pressure, control invasive exotic weeds, rip the soil mechanically, and plant tube-stock. These techniques are prohibitively expensive when applied at landscape scales, and their uptake to date has been insufficient to restore the TECs. Therefore, we focus on developing cost-effective ways to increase natural regeneration in these TECs.

Rehabilitating any habitat from a degraded state requires strategic, well-timed intervention, observant monitoring, and a consistent methodical approach to obtain desired results. The following methodology is a starting point and a guide, working from first principles required for natural regeneration to occur. The following methodology is framed within a six-stage approach; Identify, Enclose, Monitor, Modify, Manage, Expand.

1. Identify:
   Where canopy remains, identify those mature trees with above average canopy health, focusing on canopies with minimal dieback and those trees with the greatest projected foliar cover i.e.; largest canopies.

2. Enclose:
   For natural regeneration to occur, these trees will require enclosure in stock-proof fencing, forming an ‘island’ from the surrounding grazed paddock. Aim to group as many individual healthy trees as possible, remembering that seed-fall and germination of new seedlings will only occur within the drip-line of the tree plus 10 to 20 meters. Fertiliser application should not occur within these ‘island’ patches, and no closer than 20 meters from the perimeter fence.

3. Monitor:
   Monitoring of adult trees within the enclosed ‘island’ for flower and bud development will be necessary. This can be done with a set of binoculars aimed at the growing tips of branches. For details in identifying the stage development of fruit, please consult the resource section concerning species.

4. Modify:
   Prior to seed-fall from mature fruit, it may be useful to attention two primary factors that directly influence germination;

   1. Removal or reduction of competitive ground cover (particularly of exotic weeds or pasture). This may be achieved through high intensity grazing for short periods.

   2. Scarification of the soil surface layer. This may be achieved with a surface cultivation tool (harrow, disc, rake). The aim here is not to remove all vegetation cover so to increase the potential of erosion, but to break the top surface layer of soil (O-horizon) so seed to soil contact is increased.

   3. Timing the above two activities prior to the onset of an approaching weather system or wetter seasonal period (such as a La Niña event), pre-seed-fall.

   Considering the unlikely nature that these events will perfectly line up, it is imperative that continued observations are conducted so to determine the best timing for a crash grazing event. Seed-fall can be a slow, ongoing event that lasts months, therefore it is important to observe when your fruits are a) mature, b) raining seed, and c) when might be the next series of rain dumping storm events to stimulate germination.

5. Manage:
   Post-seed-fall, monitor for germinating seedlings. As heavy competition from exotic pasture species reduces the growth rate of seedlings, reduction of competing exotic grasses can aid in seedlings becoming established. Once a lignotuber has formed (typically a year post germination), short intense ‘crash’ grazing may be beneficial to reduce competition from exotic weeds and pasture species. The term crash grazing here refers to high stock density for limited periods (usually one to two days), aiming for stock to remove weed species and grass cover before the browsing of seedlings occurs. Where grass density is minimal or there is a higher proportion of native to exotic grasses, the previous approach is likely unnecessary.

6. Expand:
   When the first succession of recruits have reached waist height, remove the outer exclusion fence and install adjacent to the woodland island, starting from step 1 again. This ‘flip-block’ approach allows for the gradual expansion of woodland outwards while maintaining some grazing production within the vicinity.

Performing assisted revegetation

The success of plantings is strongly dependent on four critical factors,

1. Species selection, favouring local provenance and nursery stock quality

2. Location and size (width) of tree-lane or island patch

3. Pre-planting ground preparation

4. Maintenance and upkeep

Species selection for assisted revegetation plantings should be directed by the current remnant vegetation growing on or adjacent to the proposed site for planting. Along with species selection, the quality of planting stock also plays a large hand in the overall success of an assisted revegetation project. Planting hardened-off, mature saplings, ideally 9 to 12 months old typically results in higher success rates. Where possible, sourcing seedlings grown from local provenance seed is preferable.

The location and size (width) of tree lanes, shelter belts, or vegetation islands is a critical factors to assess. Three-row tree lanes are no longer recommended as narrow tree lanes are susceptible to edge effects including impacts from heavy wind and drought. Minimum width of 10 m or 5 tree rows is commonly advised, however, we would recommend increasing this to at least 20 m or 7 to 10 rows when considering the long-term health of tree shelter belts in a fragmented landscape.

Pre-plating ground preparation through the use of single or multiple tined sub-surface ripping implements, along with the removal of immediate surface vegetation is necessary so to assure young seedlings have suitable conditions. This ground preparation is best undertaken several months before planting and/or timed prior to the onset of wet weather season. Planting should be targeted around favourable weather conditions, ideally after a rainfall event. For the northern-tablelands region, two suitable planting windows generally occur in Autumn (March-May to avoid hot, drying summer winds) and Spring (August – October to avoid heavy frosts), however, this is not a hard-set rule and when forecasts are indicating wetter periods, this can be a determining factor.

Maintenance and upkeep of plantings is a necessary task to ensure seedlings have consistent conditions favourable for establishment. This typically includes removal or reduction of weeds, along with maintaining adequate soil moisture, the first three to four months being the most critical up until 6 months to a year post planting. This can be aided through the use of mulch or artificial weed-matting that excludes invasive grasses from smothering the seedlings.

References

Benson, J.S. & Ashby, E.M. (2000) Vegetation of the Guyra 1:100 000 map sheet New England Bioregion, New South Wales. Cunninghamia 6(3): 747-872

Goldney, D. C., & Wakefield, S. (1997). Save the bush toolkit. Environmental Studies Unit, Charles Sturt University.

Rawlings, K., Freudenberger, D., & Carr, D. (2010). A guide to managing box gum grassy woodlands. Commonwealth of Australia.

McIntyre, S., McIntyre, S., McIvor, J. G., & Heard, K. M. (Eds.). (2004). Managing & conserving grassy woodlands. CSIRO PUBLISHING.