This is an excerpt from a zine, “The Troubles of ‘Invasive’ Plants.” Check out the whole project here.
By Nicole Patrice Hill & Kollibri terre Sonnenblume
Changing plant communities at the local scale are symptomatic of the changing climate globally. Patterns of temperature, precipitation and seasonal timing are shifting, and with them, the patterns of birth, growth, reproduction—and survival—of all living creatures.
One widely observed syndrome is “season creep,” in which Spring has been arriving progressively earlier in the calendar year. This does not mean that every Spring starts sooner than the year before, but that an overall trend has been observed. For example, a survey of leafing, flowering and fruiting records from 1971-2000 for 542 plant species in 21 European Union countries showed advanced timing for 78% of the plants. According to other sources, “Spring events, such as blooming, frog breeding and migrant bird arrivals, have advanced 2.3 days per decade.” Winter snow cover duration—as measured from Fall to Spring—has decreased throughout the Northern Hemisphere since 1978. The earlier the snow melts, the less water is available during the hot summer, which affects a wide range of plants, animals and other life.
Winters have been warming. For example, the average February maximum temperature in the US rose by 0.3 F per decade from 1895-2016. This general rise in the “floor” has been accompanied by an increase in “extreme” events, such as “false Springs” when temperatures warm up enough to trigger life cycle stages in a variety of species. When more “normal” weather arrives later—or another extreme event follows, but this time on the cold side—a plant can be injured or even killed. A common example is when a hot spell causes fruit trees to flower, and then a frost—even just a “normal” one—zaps the flowers, thereby taking out that year’s harvest.
When we were farmers, we experienced how extreme events affect crops. In the Spring of 2013, periods of warmer-than-average weather alternated with periods of colder-than-average weather a few times, and the transitions between them were quick, as in 36 hours. Spring greens thriving in “normal” cool temperatures would go to flower prematurely when the temperature rapidly heated up. Then, warm weather crops would stall out when the temps fell. Annual vegetable plants don’t do well with such erratic conditions and we watched helplessly as our failure rate climbed.
Nicole has observed the effects of season creep and extreme events on wild plants. In one example, in the spring of 2017, she took a camping trip across the state of Nevada with her aunties, one of whom knew the area well from over 30 years of time spent in the area tending and harvesting traditional Native American food plants. The three of them visited lower elevation patches of these native plants and observed high densities of a Biscuit Root known as Rabbit Gut (Cymopterus sp.) in foothill niches against the mountains. They saw many plants, possibly due to high rainfall the year before, but no flowering although it was the season. They mused that perhaps the plants were resting this year and would more energetically seed the next. But in 2018, when the two of them visited the same patches at the same time, they found very few plants at all, across the entire state. They wondered if the plants had broken dormancy earlier, during the false Spring in February of that year, only to be sent back to sleep by the cold weather that followed. These Biscuit Roots, although hardy and stout perennials, can only live through a certain number of aberrant events. Too many seasons of jagged temperature shifts will make their survival unlikely as the climate continues to change, in their present habitat.
For each plant species—wild or domesticated—a particular range of environmental conditions supports optimal growth and reproduction, and when these conditions are not met, all stages of plant life-cycles can be affected: germination, flowering, breaking dormancy, etc. The suffering of the plants manifests in variety of ways such as stunted growth, lower seed production, and weaker resistance to disease. In the case of human food crops, lower nutritional value can be an outcome. Conditions far enough outside the range of optimal are lethal, and the species will die off in certain locations.
Other species, however, will be well-suited to the new conditions, and will thrive as openings are made. Meanwhile, the original plants themselves might well have migrated to new areas, themselves, filling new openings there. This is a form of natural succession that has happened innumerable times in the planet’s history. The most recent globally-scaled example took place at the end of the last period of glaciation, about 11,700 years ago.
We are likely already seeing such climate-induced plant succession now. It has been observed that during the past twenty five years, plant and animal ranges have been shifting towards the poles at a rate of about six kilometers per decade.
However, this age-old, tried-and-true process is being interrupted in cases where a species is labeled “invasive” and is then exterminated by humans.
Climate change demands that we fundamentally alter our approach to relating with the rest of nature. A prerequisite would be to use way less, and take only what is needed. Continued degradation by development and expanding resource extraction is the result of what we could call an “invasive land ethic” that insists that land must be dominated. Changing this attitude is essential.
Precise predictions for the future are difficult, and many scenarios are being studied. We can say with certainty that our present trajectory is anything but stable. Under midrange global-warming scenarios, scientists at Leeds University in England found that by 2050, 15 to 37 percent of terrestrial species (plant and animal) will be “committed to extinction” in their current ranges. This points to a practical difficulty in how to proceed with conservation and restoration plans. Everyone will be needing to adapt, and whether species can adapt in place or will need to migrate and how far are hard to know.
As Alejandro E. Comacho put it, in reference to policy reform, it makes less sense to be “dedicating substantial resources to preserving and restoring a particular biological unit because it existed in one point in time if climatic conditions may make the landscape inhospitable to that unit…. Similarly, what is the ethical or scientific justification for prohibiting or removing any organism simply because it never existed in a particular location, especially if that organism is now well-matched.”
What hasn’t been widely acknowledged yet is that restoration of previous, pre-global warming plant communities is no longer possible; conditions are already too different and the rate of change is increasing too fast.
As such, indulging in “invasion biology” at this point in history is a form of climate change denialism.
In the past, climate-induced plant succession has been a fairly gradual process, taking centuries or millennia. However, in our era of increasingly rapid climate change, fewer and fewer species of plants will be able to successfully migrate. If they are to survive, they will require assistance.
Assisted migration has been finding growing support these days. In 2009, the United Nations Environment Program (UNEP) stated the possibility of necessary large-scale translocations, and that “the conservation community needs to move beyond the preservation or restoration of species and ecosystems in place as the correct approach.” The US Fish and Wildlife Service followed suit in calling for policy revisions of what constitutes native, invasive or exotic species, as well as new policies such as assisted migration to support adaptive responses to climate change. It is has become apparent within the domain of large scale policy that the complete dualism of the good native and the bad exotic is neither accurate or helpful at this point.
There are protected niches within habitats, or new habitats, that will provide conditions that these plants could have a chance to thrive in. A north slope of a mountain may buffer against early dormancy breaking. A higher elevation may provide the temperature relief needed for them to grow. Arguably, birds and other animals are already participating in this assisted migration, as they are often the agents moving plants into new areas.
Seed vaults are created, with controlled climates in order to stockpile seeds for future restoration, yet conservationists balk at the idea of planting living seed banks outside of current ranges, where plants can be adapting on their own to respond to changes. How would the cold-stored seeds, with their genetic variability frozen in time, be better suited to a new environment than plant populations that have adapted in real time to emerging circumstances and have been passing that information along for successive generations?
Assisted migration is not a new thing. It has been the way of human-plant relations for many many millennia, since well before the adoption of agriculture. It is time for us to rediscover this part of our essential connection to nature.