For several decades now there have been warnings that we are getting ever closer to the limits of our planet’s ability to support us. One example that sticks in my mind is that at our current rate of destruction and consumption, we need something like four planets to sustain us. Scientifically accurate or not, it is a stark warning that things need to change.
Another report was published this week that, again, warns us that we are pushing our planet too hard. The report found that across the majority of the Earth, the abundance of plants and animals has fallen below a ‘safe’ level. When levels of biodiversity fall too low, ecosystems become less resilient and, in extreme cases, may even cease to function.
For the study, researchers were investigating ‘biotic intactness’. An intact area had suffered minimal losses of biodiversity. If the average proportion of natural biodiversity remaining in local ecosystems had reduced by more than 10%, the area was described as being in the ‘danger zone’. Although the 10% figure is fairly arbitrary, it is based on the Planetary Boundaries framework which, amongst other things, attempts to establish a safe limit to the amount of biodiversity that can be lost whilst retaining key ecosystem functions.
By using over 2 million records for nearly 40,000 terrestrial species, scientists modelled the response of biodiversity to human land use. Using this information they could then estimate the extent and spatial patterns of changes in local biodiversity.
The study found that, overall, across 58% of the terrestrial surface, biotic intactness had declined by more than 10%. In fact globally, the average decline is close to 15%. Unsurprisingly, the most significant declines are associated with areas of human population. Biotic intactness also varied with habitat type. Whilst grassland biomes and biodiversity hotspots tended to have the most prominent declines, northern tundras and boreal forest ecosystems are still relatively intact.
Ecosystems provide a huge range of services to humans. To name but a few they can store carbon, improve air quality and regulate climate. When we develop land to build houses, create new transport links and farm, we reduce local biodiversity which has huge impacts on the ecosystem. Although species may not be going extinct, reduced abundance can lead to diminished ecosystem services.
Another study this week provided a great example of how land use is affecting the ecosystem. Using nest cameras, researchers found that bald eagle parents were feeding their young less than twice a day – almost half of what chicks received in other areas. The amount of food also declined over time, despite chicks growing larger. The study concluded that the Florida Bay ecosystem is collapsing and unable to support the eagles. It is thought that land development in the Everglades has disrupted the flow of fresh water to the bay, resulting in high salt concentrations. This has killed sea grasses, releasing sediments that trigger algal blooms. As a result, many fish that eagles depend on for food have been killed.
I was initially surprised that only half of the planet has seen losses of more than 10%. However, it is important to consider that this study only accounts for land use and does not consider the impacts of climate change, both now and in the future. A loss of 10% does not tell us much about the state of the ecosystem either. Some ecosystems will be much more resilient to loss of biodiversity than others.
Although this study tells us more of what we already know, it is yet another warning that nature’s pulse is slowing.
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