On the speed of plants

Author Daniel Montesinos discusses his recent Journal of Ecology article: “Fast invasives fastly become faster: Invasive plants align largely with the fast side of the plant economics spectrum.” Find out more about the plant economics spectrum and how invasive plants align largely with the fast side.

This mini-review is part of our upcoming Special Feature on: What common-garden experiments tell us about climate adaptation in plants.

When we think of “slow” plants we think of slow-growing trees, or perhaps alpine shrubs that can only grow during brief summers in between months of being covered under snow. Slow plants generally produce a small number of seeds and sometimes barely even reproduce for years (i.e. masting). When we think of “fast” plants we tend to think of, well, weeds. That is, annual plants that grow fast and can shed seeds within weeks of germination. These are plants that can complete their full life cycle even under severe and frequent disturbance. In between these two extremes there is what ecologists and plant physiologists call the ‘plant economics spectrum’; a trait and life history gradient along which plants can be conceptually aligned in order to study them and make generalisations.

The plant traits economic spectrum. Figure: Daniel Montesinos

Invasive plants generally align with the fast side of the plant’s trait economics spectrum, characterised by fast nutrient acquisition, growth, and reproduction. However, there are numerous and notable exceptions, including woody invasives. This generalization, that invasives are fast, is driven by the high occurrence of invasive ruderal species colonising nutrient‐rich disturbed habitats. Ruderal means “adapted to disturbance” or “able to grow in disturbed sites”.

Disturbance is something that humans do all too well. Farms are highly disturbed habitats, and thus it is unsurprising that weeds are intrinsically linked to them. But so are roads, railroads, cities, and most places where humans live or work. When a road is opened several things happen; habitats are broken open, trees and other vegetation are removed, and an inordinate amount of nutrients are suddenly released into the environment. Simultaneously, it is highly likely that weed seeds or propagules will be introduced. Unsurprisingly, disturbance and biological invasions usually go hand in hand, and many invasive species, at least the non-woody ones, are very well adapted to disturbance, and in fact they frequently tend to be considered weedy also their native range.

But this is not all that is going on for invasive plants. Successful invasive plants have shown a remarkable ability to rapidly adapt to the new regions where they are introduced. When exposed to new habitats or environments, numerous exotic species have been found to be able to rapidly adapt their traits at surprisingly fast rates, sometimes in less than a century. These changes predominantly involve increased resource acquisition, growth, and reproduction, aligning them even further with the fast side of the plant economics spectrum. In other words, plants that were already “fast” in their native regions, become even “faster” in the regions that they invade.

Himalayan balsam (Impatiens glandulifera) is an example of a plant that spreads quickly and has become a significant problem as an invasive species

This poses the interesting question of how “rapid” invasive plants would respond to shifting climatic conditions as a result of global change. All plants are going to experience increased selective pressures to adapt to changing and more unpredictable climates, and climate change is itself a kind of disturbance. Consequently, invasive plants are generally expected to expand their distributions both because of their ability to colonise disturbed habitats, and because of their ability to rapidly adapt to change.

Common garden experiments with invasive model systems provide valuable insights about the speed and direction of adaptive responses to different climates. The focus on invasives sometimes comes with the added benefit of knowing approximate introduction dates, which can be used to infer the speed of local adaptation. These studies are also helping us to predict general plant responses to global change, since the essential mechanisms used by invasives should be also available to the generality of plants, albeit frequently at a different “speed”. However, lest we forget that, after all, only a fraction of the numerous exotic species being introduced across the world are able to become successful in their new non‐native regions. If invasives are to provide insight about the responses of native plants to climate change, we should expect a similarly idiosyncratic divide between successful and unsuccessful natives.

Daniel Montesinos James Cook University, Australia & University of Coimbra, Portugal

Read the full article: Fast invasives fastly become faster: Invasive plants align largely with the fast side of the plant economics spectrum

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