Shocking study: Insects are also declining in forests

In recent years, the dwindling number of insects has become a cause for concern, particularly in agricultural areas where the decline is well documented. However, less attention has been given to insect populations in forests, with most studies focusing on species considered pests. 

A new study led by the Technical University Darmstadt, in collaboration with the Technical University Munich and other researchers, has now revealed that many insect species in German forests are also experiencing a decline. The findings, published in the scientific journal Communications Biology, came as a surprise to the researchers.

Central European forests have gained increased public attention for their role in climate mitigation, as well as the widespread forest damage caused by hot and dry summers. Forest ecosystems are vital for various animal species, including insects, which are often viewed as pests in forest environments. While the population trends of pest insects have been well-studied, there is limited knowledge about the many other fascinating insect species found in forests.

The study examined the population trends of 1,805 insect species in German forests from 2008 to 2017. Contrary to the researchers’ expectations, the number of individuals in the majority of the studied species has declined over time. 

This decline was particularly surprising when compared to agricultural lands, where changes in land use and intensification, such as the use of more effective pesticides and increased cultivation of corn, have been documented. Such disturbances are not typically present in forests.

The decline in forest species was particularly pronounced among larger and more abundant species. While herbivorous insects saw a slight increase in species numbers, all other feeding types, including predators and deadwood decomposers, experienced significant declines.

The study, conducted as part of the Biodiversity Exploratories project funded by the German Research Foundation (DFG) since 2006, analyzed three regions: the Hainich National Park, the UNESCO Biosphere Reserve Schorfheide-Chorin, and the UNESCO Biosphere Reserve Swabian Alb. 

The researchers found that insect losses were greater in forests with a high proportion of conifers, such as spruce and pine, which are not native to the study areas. In contrast, losses were lower in native beech forests. Additionally, the declines were less severe in unmanaged protected forests compared to intensively managed forests.

According to study lead author Dr. Michael Staab, more than 60 percent of the studied insect species have been declining. “This will very likely have an impact on all organisms in our forests as food webs may be altered.” 

Future research will be necessary to understand how climate change-related factors, such as increasing drought and changes in native forests, will affect insect population trends.

Professor Nico Blüthgen, head of the Ecological Networks Group, emphasized the significance of these findings: “Our forests are undergoing drastic changes due to the climate crisis. We are currently trying to understand how this affects insect populations.” 

The study suggests that targeted forest management, including promoting a more natural tree species composition and reducing tree harvest, could help mitigate the decline in insect populations in forests.

Insects play a critical role in Earth’s ecosystems, contributing to their overall health, stability, and functioning. They serve various essential functions, including:

1. Pollination: Many insects, such as bees, butterflies, and moths, are vital pollinators, transferring pollen from one flower to another, facilitating plant reproduction. Approximately 75% of the world’s flowering plants and around 35% of global food crops depend on insect pollination. This process is crucial for maintaining plant biodiversity and ensuring food security.
2. Decomposition and nutrient cycling: Insects like beetles, ants, and termites contribute to the decomposition of dead plants, animals, and other organic matter. They break down complex organic compounds into simpler forms, enriching the soil with nutrients that promote plant growth. This process of nutrient cycling is essential for maintaining soil fertility and overall ecosystem functioning.
3. Food source: Insects are a crucial food source for many animals, including birds, mammals, reptiles, amphibians, and other invertebrates. They are a significant link in the food chain, transferring energy and nutrients from plants to higher trophic levels. A decline in insect populations can lead to a cascade of negative effects on the organisms that rely on them for sustenance.
4. Pest control: Many insect species, such as ladybugs and parasitic wasps, are natural predators of agricultural pests. These beneficial insects help to control pest populations and reduce the need for chemical pesticides, promoting sustainable agriculture and reducing the environmental impact of farming practices.
5. Seed dispersal: Some insects, like ants, play a crucial role in seed dispersal. They transport seeds away from the parent plant, increasing the chances of successful germination and promoting plant diversity.
6. Indicator species: Insects are sensitive to changes in their environment and can serve as bioindicators, reflecting the overall health of an ecosystem. Monitoring insect populations can help identify environmental disturbances and inform conservation efforts.

In summary, insects are crucial to Earth’s ecosystems because they contribute to pollination, decomposition, nutrient cycling, and pest control, serve as a primary food source for many animals, and function as bioindicators of ecosystem health. A decline in insect populations could have far-reaching consequences for the health and stability of global ecosystems, making it essential to understand and address the factors contributing to their decline.

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