Why don’t all plants grow everywhere across the world?

Why do some plant species grow and flourish only in certain places, while their close relatives take root in faraway landscapes? Scientists have wrestled with this mystery for years, hoping to understand how nature sets its limits.

A global investigation of nearly 270,000 seed plant species sheds new light on the environmental and historical factors that decide where vegetation can prosper.

The research was led by an international team that examined climate data, soil conditions, and ancient geologic events spanning millions of years. The break apart of the supercontinent Pangea due to plate tectonics is one significant event which saw a drastic change in plant life.

The investigation’s central findings trace back to work by Dr. Lirong Cai from the University of Göttingen and the German Centre for Integrative Biodiversity Research (iDiv), who served as a key figure in this study.

Plants grow in some places only

Many scientists argue that biodiversity is shaped by more than just random spread or occasional migration.

Climate, soil composition, and geographical barriers are thought to play a strong part in keeping certain plant groups confined to specific locations. In turn, the locations become a place for unique plants to thrive.

Researchers have also turned to phylogenetic methods that track family trees over deep timescales. This approach helps reveal when a plant group encountered new conditions or broke past a barrier into another region.

Climate and soil affect plant growth

Temperature and moisture have long been recognized as strong regulators of distribution, influencing growth and survival.

Some species can endure extreme cold, drought, or humidity better than others. This paves the way for plant growth to flourish or can restrict them to smaller pockets.

Shifts in habitat conditions can push certain lineages to adapt over time. Others may fail to survive these changes, leaving them behind as evidence of how vital the environment can be.

What stops the spread of plants?

Physical structures such as mountains, deserts, and vast oceans block species from expanding at certain stages. Younger plant lineages often get stranded, while older ones might have had more time to grow and overcome these obstacles.

Older plants are more accustomed to harsh weather and soil conditions. Not only have older plants had more time to grow than younger plants, older plants are familiar with the structures around them.

This familiarity gives older plant species an advantage which allows the plant to continue to grow without becoming trapped due to terrain or physical structures.

“These findings reveal a fundamental process in nature. Given enough time, plants can overcome the barriers of vast distances and geography, but they often remain limited by the environments they encounter,” said Dr. Cai.

Shifting continents changed plant paths

Continents drifted into different positions between 20 and 50 million years ago, opening or closing routes that influenced plant travel.

This rearrangement had moderate impacts on long-term distribution, though it was more pronounced within that window of shifting plates.

Some groups of plants managed to traverse newly connected landmasses, while others remained clustered where they first took root. The lasting effect of those movements is still visible in the distribution patterns seen today.

Ancient plants spread more

Genetic evidence confirms that dispersal barriers remain tough to conquer in the short run, even though ancient lineages managed to spread widely over longer intervals.

Oceanic gaps and hostile climates slow down or halt these botanical journeys. Unfortunately, some plants cannot survive and spread in specific environments.

Because of this, environmental filtering stays a constant factor. Where the temperature or moisture swings too far from a species’ tolerance, the plants refuse to grow or venture there, no matter how long they have existed.

Future research directions

Ecologists see value in integrating more detailed geological reconstructions with modern species data. Climate fluctuations, like those in the past Ice Ages, also carry clues about how quickly species can respond or shift their homes.

A broader understanding may inspire efforts to protect fragile habitats. Some zones remain high-risk for plant extinctions if conditions change faster than species can grow or adapt.

The study is published in Nature Ecology & Evolution.

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