Alarmingly, says Dr McFadyen, extreme weather events are likely to become more common as climate change progresses. But for many weeds, that’s great news. ‘In the tropics, cyclones often break open the canopy of a forest and let in new light to the normally dim forest floor – that’s just perfect for weeds.’
‘For thousands of years the local native plants have supplied the only seed available. This meant, given time, that the forest always returned to near-original condition.’ But now, says Dr McFadyen, thanks to people and vehicles, there are often seeds of new foreign species lying around in small numbers ready to out-compete the local plants in the grab for space and light. Birds and animals may also bring in these new seeds from towns and farmland. ‘Suddenly’, says Dr McFadyen, ‘the invaders get the break they need’.
…Fire risk is also predicted to increase greatly under climate change scenarios, and favours weeds by ‘clearing the decks’ of competitors, says Dr McFadyen. And while fires may burn up many tons of weed seed, and favour the germination of some fire-adapted native species, it also provides the perfect seed bed for weed seeds.
…Drought also tips the scales in favour of weeds. If climate change does result in more frequent and more severe droughts, then weeds will again be the first to benefit. ‘If the drought kills off all the competitors, whether these are crops or pasture grasses, then when the rains finally come the weeds will do what they do best – invade bare ground and grab all the moisture!’, says Dr McFadyen.
‘Those invaders able to cope with drier conditions, and able to quickly move their seed around, (eg parthenium weed, or serrated tussock) will be the weeds we’ll be battling tomorrow’, she says.
Finally, floods can help weeds get a toehold in conditions they like. Climate scientists are predicting more floods – as we are already seeing in the north - as rainfall conditions become more variable. Once again, this will suit the weeds nicely.
…'Whether it’s cyclones, fire, drought or flood, weeds are set to become the big winners from climate change’, she says. ‘Extreme vigilance and early action by landholders, agencies and individuals are the keys to keeping these species under control.’ ‘Changing climate is new territory for farmers and other land managers, and they will need all the information and understanding that science can provide if they are to stay ahead in the weed war’, says Dr McFadyen.
It is critical that public and private stakeholders join forces and invest wisely in building a new knowledge base, she says. ‘This is the only way we will equip ourselves to meet the new weed challenge now emerging from climate change.’
Forest fire shot by Todd Heitkamp, Riverton, Wyoming acting meteorologist-in-charge, NOAA, Wikimedia Commons