Ecological research

Our knowledge of the ecology of mesquite is very poor. This is surprising given the importance of mesquite as a weed in many tropical parts of the world, and the role a sound knowledge of ecology can provide in developing better management strategies.

Ecology can help in predicting potential spread and impact through landscapes, an important step in:

• developing management strategies
• optimising integrated control strategies
• improving management of dispersal
• selecting effective biological control agents.

It is already known that mesquite is an exceptional plant, with many adaptations that lend itself to being a highly effective invasive.

Stand out features include:

• long-lived adults: plants over 100 years old are common in the native range
• long-lived seed banks; under the right conditions seeds can remain viable under the soil for many years
• most extensive root system of any plant in the world; can access water at depths up to 80 metres, and up to 30 metres from the base of the tree, as well as upward growing roots to capture small rainfall events
• large carbohydrate stores; allows even seedlings to regrow from multiple top-kill events, such as from fire or mechanical control
• viable seeds can pass through the gut and be dispersed via animal dung
• excellent disperser; pods are highly palatable to a wide range of vertebrate herbivores including:
  • livestock (horses, cattle, sheep, goats)
  • ferals (horses, goats, pigs)
  • natives (emus, kangaroos, wallabies).

Viable seeds can pass through the gut and be dispersed in dung.

Dense infestations of mesquite can reach 20 000 plants per hectare.

New insights into ecological research was initiated by CSIRO in the Pilbara region in 1998, through the PMMC and in collaboration with DAWA, and the University of WA.

Research is ongoing, but important findings to date include:

• mesquite is very long lived, with mortalities rare among all size classes since 1998 despite prolonged drought and defoliation by the leaf-tying moth. This will have important consequences for management, and suggests that any new biological control should aim to dramatically reduce adult longevities
• mesquite seed banks in the Pilbara are surprisingly low, typically well under 50 seeds per square metre, even around cattle troughs and under dense mesquite. It is not yet known whether low seed banks are typical of mesquite, or the result of leaf-tier activity
• mesquite seedlings can emerge and become established after only a single rainfall event, once they are over ca 30 centimetres they are essentially drought-proofed
• mesquite infestations can reach very high densities, up to ca 20 000 plants per hectare. A significant proportion of those are juveniles that remain essentially quiescent until the adult canopy is removed. This has important consequences for management.

Current research reveals the ecology of different species or hybrids of mesquite in Australia is likely to differ in important respects, such as:

• reproduction
• seed bank dynamics
• responses to stresses.

Comparative ecological research commenced in 2004 in other core infestations in Australia to test this. Study sites were located within hybrid infestations (north Queensland), P. pallida infestations (north Queensland) and a P. velutina infestation (south-west Queensland).

Ultimately predictive models will be developed to predict spread and impact of different mesquite species and hybrids through landscapes, and help optimise and cost management strategies. It is intended that this research will assist in mesquite management throughout the tropics.