By Michael Renton
As climate changes, some plant species will start to die out in areas where climate becomes unsuited for them. Individual plants will not be able to move to find new areas where climate is more suitable, of course, but through seed dispersal, some species may be able to establish new colonies in areas that become suitable. In this way, the species or population may be able to survive by moving through the landscape and thus ‘keeping up’ with climate change. But this will be made more difficult if the landscape is fragmented by agriculture, or if the species has poor seed dispersal. Which species will be able to move fast enough, and which will lag behind? Can we do anything to help them? The answer to these questions can be provided by PPunCC.
PPunCC (Plant Persistence under Climate Change) is a new model that predicts the likelihood of plant species being able to move through fragmented landscapes fast enough to keep up with changing climates. The image at the top shows a ‘birds-eye-view’ of a fragmented landscape. There is a climate gradient from dry in the east (right) to wetter in the west (left). Here we are simulating one species that likes a relatively dry climate. At the beginning, the climate in the far east is suitable for this species, but over time the climate becomes drier, and the part of the landscape suitable for the plant moves towards the west. Red areas are unsuitable for the species, because they have the wrong soil type, or are cleared for agriculture or urbanisation. Orange cells are suitable in terms of soil and land use, but do not currently have any of the species growing there, probably because the climate is too wet or dry, while white and yellow cells have a population of the species. The lighter the cell, the more populated it is. Can you see the population moving across the landscape over time? The middle plot shows the total population at different points along the gradient as time changes, and the bottom plot shows the total population size over time.
This species is one of the lucky ones. It moves fast enough to survive. But we simulated thousands of different types of plants with different characteristics, and found that the future was not bright for many of them. Trees fared particularly badly; few were predicted to move fast enough to keep up with the changing climate, mainly because of the relatively long time they need to establish, mature, and produce seed. In the top PPUNCC image, notice that there is a kind of orange path through he landscape. This shows an example where we have simulated some targeted restoration to produce a corridor through the unsuitable landscape. Such targeted restoration does increase the number of species predicted to survive, but not by a huge amount. This warns us that we may need to consider options like assisted migration or translocation of species if we don’t want to lose our most vulnerable plant species.