In a short span of time, human activity has led to a 68% average decline of animal species since 1970. While this is a crisis in and of itself, fewer birds, elephants, and insects will also mean fewer plants in the near and far future. About half of all plant species worldwide rely on animals to distribute their seeds. And with conditions of plant habitats shifting due to climate change, the movement of their seeds is more important than ever. A new study in Science finds that the decline of mammals and birds caused by people and development has already reduced plants’ ability to adapt to the changing climate by 60%.

Why This Matters

Plant and animal life exists in ecosystems that developed together, so changes to parts of the system ripple out much more broadly. Wildlife and plants are already on the move because of climate change -- but without animals, many plants will be stranded in an environment they can no longer grow in because it’s too hot or too salty or too dry. This can "trigger a frightening feedback loop," as Vox writes. "If some tree and plant species wither because they can no longer hitch a ride on wildlife, that could worsen climate change, which makes it harder for both plants and animals to survive.”

Double Human Impact

The study shows one many ways that short- and long-term human impacts are harming the planet. Change in land use -- such as a grassland becoming farmland or a forest being cleared for development -- is one of the biggest drivers of biodiversity loss. These short-term changes immediately destroy the habitats of local plant and animal species. The ongoing, long-term threat of climate change is a multiplier that will further destabilize ecosystems.

There's also the feedback loop mentioned above: when plants die, whether from deforestation or climate change, the planet loses some of its carbon store. Less stored carbon means more climate change -- which, in turn, can kill off more plants.

"We're only beginning to really quantitatively wrestle with that vicious cycle," Rice University ecologist Evan Fricke, the lead author of the study, told Vox.