Kakadu National Park Landscape Symposia Series 2007–2009

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4.3 Conclusion

Compared to other national parks and reserves in Australia, Kakadu has a relatively low number of weeds. However, the Park still faces major challenges in controlling or eradicating the weed species that are presently found in the Park and preventing invasion by new weeds. The continuation of rigorous surveillance and control programs by dedicated weeds teams and other Parks staff will assist in achieving this goal.

References

Bayliss P, van Dam R, Boyden J & Walden D 2006. Ecological risk assessment of Magela floodplain to differentiate mining and non-mining impacts. In eriss research summary 2004–2005. eds Evans KG, Rovis-Hermann J, Webb A & Jones DR, Supervising Scientist Report 189, Supervising Scientist, Darwin NT, 172–185.

Director of National Parks 2007. Kakadu National Park Management Plan 2007–2014. Department of the Environment and Water Resources, Canberra, Australia.

5 The need for weed data

D Walden^⁸

5.1 Data for decisions

The purpose of this paper and the preceding symposium presentation is to summarise the important role data/knowledge plays in terms of strategic planning, prioritising, and implementation of control. This paper does not detail the methods of weed data collection, nor does it present available data and other knowledge of the species of concern as this has been addressed in the literature. Thus, the information presented does not follow the original focus questions, and is not necessarily specific to Kakadu National Park (KNP). Some aspects of this topic and others related to KNP are discussed in Walden and Gardener (2008), which also includes an extensive bibliography that is largely specific to KNP weed issues. Comprehensive guidelines for weed data collection in the Northern Territory (Weeds Management Branch NRETA 2007), survey and mapping techniques (McNaught et al 2006) and guidelines for the development of local weed management plans (Cooperative Research Centre for Australian Weed Management 2008) are readily accessible.

Weeds are very social creatures and rarely come to a party in ones or twos. Thus the land manager is usually faced with a host of species, all with differing degrees of actual impact (often unquantified) and perceived impact (ie by various stakeholders). Other confounding parameters include (but are not limited to) differing environmental ranges, spread rates and spread pathways. The control methods vary between species as does the knowledge base of control mechanisms and biology of the individual species. The manager must carefully address the following questions, the latter of which is often overlooked when planning strategies and allocating resources.

‘How much will it cost to reduce the impact of the infestation to a socially acceptable level?’

‘How much will it cost to maintain the infestation at that level in perpetuity?’

Resources for weed control are always limiting, so species priority has to be determined in conjunction with realistic, achievable and sustainable targets. Determination of these priorities and targets relies on comprehensive and objective data on weed impacts, distribution and spread which also enables outcomes of weed research and control to be measured. Obtaining this data and the subsequent research is typically resource intensive and it may be many years before a ‘profile’ of the weed is established. McNaught et al (2006) summarise the need for weed data as follows:

‘You can’t manage what you can’t measure’

There is often a perception that if weeds are being sprayed with herbicide, burnt or physically removed, then there will ultimately be an impact on the problem. However, if the extent of the problem is an estimation at best, or the spread rate is faster than the control rate, or the method lacks the efficacy to prevent regrowth the following season (ie from the soil seed bank), then the resources employed have been largely wasted. On the other hand, if the manager is armed with knowledge of the attributes listed in Table 1 for example, this information can influence how the control strategy is approached.

Table 1 Some attributes of weeds where data/knowledge can greatly influence control approach

Attribute	Comments
Flowering ‘window’, peak flowering times and time to maturation	Targeting control at these times can prevent seeding of the next generation
Seed germination period, germination factors, longevity of seeds in the soil	Relevant to the above. Some germination factors eg fire can be controlled. Longevity crucial to follow-up control
Invasion rates and key pathways	Important for modelling spread. Some pathways can often be removed or minimised
Hydroperiod and inundation levels	Good indicator of habitat preference. Can sometimes be used as a control tool eg drowning following spraying or cutting (timing is critical)
Local topography, soil type, soil moisture and pH, nutrient requirements	Often indicators of habitat preference. If the plant is particularly sensitive to change in these – maybe used as a control tool
Salinity tolerance	Indicator of habitat preference. Given the right circumstances, introduction of saline water could be used for control
Associated plant communities and competition and shade tolerances	Essential information when planting competition species. Can also be indicators of habitat preference
Response to fire	Fire can be a powerful control tool or a powerful facilitator of weed spread. Knowledge of this attribute is essential for determining which.
Allelopathic capabilities	Chemicals and other factors that weeds use to reduce competition. Knowing how these work can be particularly useful for post control rehabilitation using native species
Potential pathogens	Essential knowledge when considering biological control which for some species is the only long-term option

Mapping is perhaps the most important component when planning a weed management strategy. Monitoring the success of control by regularly updating maps and revisiting sites will provide the necessary feedback to assess the need for adapting the strategy if required. This is often referred to as ‘adaptive management’ (or systematic learning by doing), and can be achieved using experimental plot trials. Systematic records of weed infestations can help support the understanding of:

What weed is found, where and when
Changes in area and density over time
The effect of land management practices and weed management programs

With the rapid progression of technologies such as Global Positioning Systems (GPS), Geographic Information System (GIS) and a wide variety of remote sensing techniques eg satellite imagery, maps are becoming more prolific, more accurate, more accessible and often less expensive than previously.

Accurate and regularly updated maps and databases enable the manager to:

Assess the size/extent of the problem
Detect satellite infestations (if possible given the method)
Determine rates of spread
Divide the problem into manageable portions
Identify the threat to significant habitats
Audit and monitor the success of control programs
Communicate results in a spatially explicit, comprehensible way

To avoid duplicating information and discussion on the need and applications of weed mapping issues, see Boyden et al 2010 in this publication for details and examples for application to weeds of high resolution satellite imagery in Kakadu National Park.

The control cost figures presented at the symposium as derived for several species in KNP were presented at the KNP Landscape change symposium in April 2007 (see Internal Report 532 – http://www.environment.gov.au/ssd/publications/ir/532.html) and are not included in this paper.