Climate Change: The End of Plant Diversity?
How moisture availability controls plant diversity
Climate change is altering moisture availability across the tropics, which is both crucial for plant life and for plant diversity. Current climate models indicate that rising temperatures will cause a reduction in rainfall. As temperature increases so do forest fires, since harsh sun, wind, and prescribed burning dry forests out increasing susceptibility for further burning. Smoke can also hang over forest canopies and suppress rainfall. Tropical forests often generate much of its own rainfall through use of the water cycle. The effects of climate change lessen a forest’s ability to generate rainfall, which will increase forest degradation and loss of diversity that is needed for plant survival.
Overall, plant diversity has been found to decrease in drier years and increase in wetter years. In a search to discover why, researchers hypothesized that moisture availability may increase the survival of species that need more water and suppress the growth of abundant species, allowing for more diversity to take place.
Seedlings that are more abundant in moist environments have greater survival rates in the first year of life than other plant species due to their innate tolerance. Many tropical plants have an innate tolerance to higher water levels because they are genetically able to function better in wetter conditions than other plants. Plants that lack this tolerance are often less adaptable to their environment and are less likely to survive in heavier rainfall. Tropical plant species with an innate tolerance do contribute to plant diversity, but they do not have a significant effect on the greater diversity of seedlings in wetter seasons. The lack of a significant effect indicates that there are more variables that affect plant diversity than just a natural tolerance for heavier rainfall.
The majority of tropical plants are more likely to survive conditions with too much water than in a drought. The more water there is the less competitive plants have to be with each other. Therefore, the majority of tropical seedlings are more likely to survive. Consequently, ecosystems also have greater diversity the more moisture that is available to them since it helps various species to thrive.
Plants tend to be less diverse when there are a higher number of conspecifics, which are plants with similar characteristics or of the same species. The presence of many conspecifics enhances already abundant species and suppresses growth of rarer species. When there are only a few abundant species in an ecosystem those species can spread and take resources away from plants that are less in number. Plants have a lower chance to survive when their ecosystems are less diverse because then they have less adaptability to the environment.
Soil moisture conditions and conspecific environments also affect organisms that prey upon tropical plants. When there is more soil moisture available, tropical insect activity increases and fungi increase their dispersal, growth, and infection rates of plants. Plant predators do more damage to plant growth when seedlings are planted with conspecific neighbors. Even when wetter seasons increase the number of organisms preying on plants, it still increases diversity. Predators often help to keep abundant populations in check, which keeps diversity present in the ecosystem.
Predator and prey relationships to maintain diversity and plant survival depend on the availability of soil moisture to organisms in tropical forests. Climate change alters the amount of soil moisture available and is responsible for drier seasons, which will alter these interactions and harm plant diversity. Without tropical plant diversity the whole forest ecosystem suffers.
