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Plant monitoring project tracks competition for pollinators

Katie Spellman and Christa Mulder want to know which plants bees like best. The University of Alaska Fairbanks research team is asking whether invasive weeds are better at attracting pollinators than native species. Seeds of these invasive weeds hang onto tire treads or hitch a ride on pant legs to find new territories. The problem with this kind of opportunism is that these plants have a combination of traits that allow them to outcompete native species.

During research for her master’s project, Spellman investigated the movement of invasive plant species into areas burned by a record-breaking amount of wildfires in 2004.

“I noticed white sweetclover, or Melilotus albus, was the most abundant species along roadsides near the burns and that the sweet clover patches were just buzzing with bees," said Spellman, a student in the UAF College of Natural Science and Mathematics." We thought maybe these pollinators were being distracted from the native plants flowering at the same time.”

Blueberries and lowbush cranberries come back vigorously after fires, but they require insect pollination to produce fruit. Avid berry pickers themselves, Spellman and her advisor, Mulder, wondered whether the invasive white sweetclover might affect the berry production. “We set up a big experiment where we added flowering sweetclover – very carefully so as to not start an invasion – to blueberry and lowbush cranberry patches and looked at how the pollination and berry production changed in those patches.”

The researchers found that the relationship between the invasive plants and pollination changed depending on how far away the berry plant was from the invasive plant patch. The berry plants were more likely to be visited by pollinators and were more successful at producing berries if they grew very close to the sweetclover, but the berry plants that were further away were getting less pollen and had less fruit production.

“What this means is that the invasive plants are acting like a magnet,” Spellman said. “Our experiments helped us understand the interaction between invasive plants and berries when they are flowering at exactly the same time. What we didn't know was which parts of Alaska actually had long periods of flowering overlap.”

For answers, the researchers turned to the herbarium at the University of Alaska Museum of the North and to citizen scientist volunteers.

“We needed to know when blueberry and cranberry flower in different parts of Alaska and how the flowering is related to climate,” Mulder said. “We used the herbarium collections as a way to get information from the past.”

People collect plants for the herbarium when they are in flower and easiest to identify. Each specimen is associated with a location and a date and can be linked to historical climate data from the nearest climate station.

“These pressed and dried plant specimens are prepared on archival paper to give them a lifespan of centuries,” collection manager Jordan Metzgar said. “The herbarium has more than 22,000 lichens, mosses and vascular plants that thoroughly characterize the flora of Alaska and adjacent regions of Canada and the Russian Far East. The specimens can also be accessed in the online database, Arctos.”

This archive gave the researchers a good idea of when cranberry, blueberry and white sweet clover flowered in the past. The museum also has historical specimens dating back to the late 1800s. To get an idea of the phenophase (the flowering developmental stage), the researchers counted all the flower buds and open flowers, along with both unripe and ripe fruits on all the herbarium specimens they could get their hands on. They also needed to know how berry and sweetclover flowering overlaps in the present, so they turned to citizen science by asking volunteers to adopt five blueberry, lowbush cranberry or white sweetclover plants and watch them as they progress from bud to fruit.

“Each week volunteers visit their plants and count the numbers of buds, flowers, or fruit just like we did with the herbarium specimens,” Spellman said. “Then we can use mathematical models to predict which parts of Alaska have the greatest overlap in flowering and which berry-picking habitats will be most vulnerable in the future under different climate change scenarios.”

Last summer, 89 volunteers monitored 50 different sites across Alaska.

Spellman and Mulder found that cranberry typically has a longer period of overlap with white sweet clover than blueberry does. This kind of data can hint at which berry-picking regions could be most vulnerable to the effects of invasive plants.

Spellman and Mulder held volunteer trainings in May to give people the skills to identify the plants and the different phenological phases, set up a monitoring site and enter data. Formal and informal educators who want to get involved in a plant monitoring project can take a one-credit professional development course with UAF Summer Sessions called "Invasive Plants of Alaska for Educators" from June 24-26.

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