The scientists in this study wanted to collect samples of the different bees and butterflies living in the study area. Because the scientists could not collect every bee and butterfly that lived there, they designed a method to collect bees and butterflies that would represent the whole population. The scientists decided to use pan traps, which are shallow bowls filled with soapy water, to collect the pollinators (figure 1). They used yellow, blue, and white bowls and put those bowls on wire stands so they stood above the ground. Why do you think the scientists chose this method?

The scientists chose this method because of earlier research on different ways to collect pollinator samples. Most scientific research builds on the findings of earlier research. In this case, other scientists had tested what kinds of traps were best at catching pollinators, what color pan traps were best, which traps were best in which types of environments, and whether ground traps or elevated traps were better. The scientists in this study used this previous research to choose the best method to collect the data they needed for their experiment.

Diversity can be important to an ecosystem. Biodiversity is the existence of different kinds of plants and animals in an environment. Habitat diversity is the existence of different types of habitat in an environment. Scientists hypothesize that the more habitat diversity there is in a given environment, the more biodiversity there will be in that environment, too. Why do you think this might or might not be the case?

Think about a typical preschool or kindergarten classroom. Often, these classrooms have a variety of centers that children can visit. These classrooms might include a center for dress-up, one with a play kitchen, one with blocks, and another with art supplies. The more centers there are, the fewer children there may be at each center. Also, children may be more likely to find something they enjoy doing when they can choose from a variety of centers to visit.

Like centers in a classroom, many different types of habitat in an environment mean that each species may find its own niche in the environment. They may not have to compete with as many other plants or animals to occupy that space. The environment can support many kinds of plants and animals in finding food and shelter (figure 2).

Another reason more habitat diversity can lead to more biodiversity is that diverse habitats can provide refuge when other places in that environment are damaged, changed, or difficult to reach. In the classroom centers example, if the kitchen center is broken and children cannot play there anymore, other centers are available where the children can play. In an ecosystem, if one habitat is damaged by something like a fire, other places in that ecosystem may be available where animals can seek refuge and find food and water.

Fire can also be an important source of habitat diversity. Fire can burn with different temperatures, in different locations, and at different times. This fire diversity can lead to habitat diversity. You will read more about fire diversity in the following study. Scientists in this study wanted to know how habitat diversity, largely created by fire diversity, impacts pollinator diversity.

The Coastal Plain of the southeastern United States has one of the highest fire frequencies in North America (figure 3). Many more fires start in this region every year than in the Western United States.

Before humans began suppressing wildland fires, many of these landscapes burned regularly. These fires supported healthy and diverse ecosystems. Fire would start from a lightning strike or be intentionally set by humans who understood its benefits and behavior, and the fire would spread until it ran out of fuel or was put out by rain or another water source.

These fires would clear away shrubs, grasses, other plants, and fallen trees and branches, resulting in an open forest landscape. An open forest is characterized by widely spaced trees and a low or absent understory of shorter plants.

Some plants even need fire to grow. For these species, fire can remove competing plants, stimulate growth, or cause seeds to sprout.

After many years of preventing or putting out all fires in wildland areas, more and more people are beginning to understand how some fires can be good for the ecosystem.

Land managers use prescribed fire to help keep forests healthy and prevent large, destructive wildfires. A prescribed fire, also known as a prescribed burn, is the controlled use of fire under specific weather conditions to restore health to an ecosystem that depends on fire. A prescribed burn is conducted by trained professionals who consider many factors before starting a fire (figure 4).

Areas that experience fire can experience a variety of fire conditions, even in places where most of the fires are prescribed. Within a forest, one area can burn every year, while another place in that same forest may go several years between fires. One area may burn in the early spring while another area burns later in the fall. One area may experience a severe crown fire that destroys many trees while another area experiences a less destructive ground fire (click on “Fuels and Fire” in the sidebar). The variety of fires in an area is known as pyrodiversity (pī rō dǝ vǝr sǝ tē).

Scientists hypothesize that pyrodiversity may lead to biodiversity in an ecosystem. If different parts of a forest burn at different times and at different intensities, plants may grow back at different rates. Different plants may grow in different areas. The diversity of plants may result in a diversity of animals who rely on those different plants for food.

Pyrodiversity may also allow animals to seek shelter in unburned places during a fire. Many studies have been conducted on how pyrodiversity affects plants and animals, but fewer studies have been done on how pyrodiversity affects insects, and specifically pollinators.

The scientists in this study wanted to know how pyrodiversity affects bee and butterfly numbers and diversity in an open pine forest in Florida that experiences regular prescribed burns.

Fire needs heat, oxygen, and fuel to burn. Forests contain many different fuel sources. Grass, leaves, needles, shrubs, trees, and fallen limbs are some of the fuels in a forest. Two of the elements that determine what kind of fire burns in a forest are the type and placement of the fuel.

Below are three types of fire that occur in a forest:

The scientists conducted their study at Tall Timbers Research Station (TTRS) in Florida. The research station has many burn units. A burn unit is a section of the property that is managed by prescribed burns. The research station manages these burn units for research purposes and for conservation.

Prescribed burns occur from the late winter to the early summer. Some burn units are burned every year, but most units are burned every 2 years. The frequent burns result in open stands of loblolly pines (figure 5).

An open stand is characterized by widely spaced trees and a low or absent understory of shorter plants. These open stands are much like the open stands of longleaf pine that used to grow in this region before farming and logging changed the ecosystem.

Because of the frequent burns, fires in this region are typically low-severity surface fires. A low-severity fire is a fire with a limited effect on trees, understory plants, and the soil. In a low-severity fire, fewer than 30 percent of the trees are killed.

Scientists in this study selected 26 sampling locations within TTRS (figure 6). At each sampling location, they placed a row of three bowls (one yellow, one blue, and one white), each 5 meters apart (see “Thinking About Science”). The bowls were filled with soapy water to trap insect pollinators and were held 30 centimeters above the ground on wire stands. The bowls were used for 3 days each month from February to September in 2017. Scientists collected and identified each captured bee and butterfly.

Scientists also collected plant data at each sampling location. They marked a 10-meter square around each sampling location. Inside that square, they gathered data on plant height, the amount of bare ground, and the number of plant species present. They also took a picture of the sky above each bowl at each sampling site to measure the amount of canopy cover in that area (figure 7).

Because TTRS has been used for research on prescribed fire for over 100 years, the scientists had a lot of data about the fires at TTRS. They looked at circular areas with a radius of 250 meters around each sampling location (figure 8). They gathered fire history data from 2007 to 2017 for each of the circles. The scientists recorded how many different fires occurred at the location, how big the fires were, and how often they occurred. They also recorded the percentage of area burned at each sampling site in 2017, the year the pollinator samples were collected.

The scientists gathered fire history data from 2007 to 2017 for each of the circles. They recorded how many different fires occurred at the location, how big the fires were, and how often they occurred. They also recorded the percentage of area burned at each sampling site in 2017, the year the pollinator samples were collected.

The scientists collected 3,735 bees of 70 different species and 371 butterflies of 30 different species. When the scientists analyzed the data, they found that, in general, sampling locations that experienced greater pyrodiversity had more diverse and abundant bees and butterflies. While this finding was true for most of the bee and butterfly species they sampled, a few species of bees declined in number in areas with greater pyrodiversity.

The same was true of sampling locations that had more area that burned in 2017. In general, the locations with more burned area in 2017 had a greater number of bees and butterflies than other locations (figure 9). However, some individual species of bees showed a decline in numbers in areas with recent burns.

Areas that burned more frequently tended to have less bee and butterfly diversity and abundance, though butterflies seemed to be impacted more by more frequent fires (figure 10). However, not all species followed this general trend. Some species of bees declined in number when fires were more frequent, but the opposite was true of a few species as well. Those bees were present in greater numbers in areas with more frequent fires.

Open canopy areas had higher numbers of bees. The number and variety of bees and butterflies varied with different amounts and kinds of plants growing at the sampling sites.

In general, the scientists’ findings strongly support the hypothesis that high pyrodiversity will contribute to high biodiversity for insect pollinators like bees and butterflies. Locations that experienced a variety of smaller burns on different burn schedules had a higher number of bees and butterflies as well as a greater variety of species.

This abundance and variety may be because these areas have more resources available that are close to the nesting sites of many of the bees. More bee and butterfly species may be successful in areas with varied burns because they may not have to travel very far to find a location in the forest that did not burn and has available food.

However, when fires were too frequent, bees and butterflies were less abundant and fewer species were present. When fires occur too frequently, flowering plants may not be able to grow enough between fires to provide food for pollinators. More frequent fires may destroy more plants that butterflies live on during their immature stages. Also, more frequent fires may not give pollinators enough time to rebuild nests and raise young before the next fire comes.

Even though bees and butterflies generally increased in abundance and diversity in areas with high pyrodiversity, some individual species did not. Because individual species were impacted differently by fire conditions, there may not be one fire management strategy that works for all bees and butterflies.

In general, though, efforts to increase pyrodiversity will benefit the majority of insect pollinators like bees and butterflies.

Adapted from Ulyshen, M.D.; Hiers, J.K.; Pokswinksi, S.M.; Fair, C. 2022. Pyrodiversity promotes pollinator diversity in a fire-adapted landscape. Frontiers in Ecology and the Environment. 20(2): 78–83.