Completed Projects
These are some of the projects completed in the Mulder lab in the past decade or so, organized by theme. Other projects (e.g., older ones, ones run by graduate students that are not part of a larger project, or ones led out of other institutions) are not included here.
Theme 1: invasive plants in alaska
Non-native species are expanding rapidly in Alaska. Contributing factors include changes in climate (warmer summers with longer growth seasons, warmer winters), greater habitat created by increased fire size, frequency, and intensity, and increased human activity. What are the impacts on plant and insect communities? Several projects have explored these questions.
1. Invasions into burned sites.
As an MS student, Katie (Villano) Spellman investigated what makes burned black spruce habitat vulnerable to invasion. She conducted field surveys of burned sites and used soils collected from these sites to evaluate three invasive species: a legume (Melilotus albus, sweetclover), a forb (Hauracium aurantiacum, orange hawkweed), and a graminoid (Bromus inermis ssp. inermis, smooth brome) . You can read the results of that study here.
2. Do bryophytes affect germination and survival of invasives?
Undergraduate student Luke Ponchione followed up on Katie's work by investigating the role of bryophytes (mosses and liverworts) in making burned habitat resilient to invasion. We're hoping to publish the outcome of this work soon.
3. Where are invasive plants in interior Alaska, and why?
Recently burned forest near road systems is particularly vulnerable to invasion by non-native plants. Under a contract with the National Park Service, Katie Spellman and Christa Mulder evaluated occurrence and abundance of non-natives along roads in interior Alaska, and determined which characteristics best explained the results. You can find the results here.
Melilotus albus (white sweetclover) growing in a recently burned habitat.
Invasive plants growing in soils from a range of burned habitats.
Luke Ponchione; Seedlings growing in or through bryophyte layers
Map of burned habitat and roads surveyed for invasive plants.
4. Do invasives outcompete non-natives for pollinators services?
Some non-native plants, such as Melilotus albus (white sweetclover), produce many more flowers than do most native plants. Does this make them more attractive to native pollinators, and, if so, does this alter pollination of native plants? A set of experiments by Christa Mulder and Katie Spellman at UAF and Matt Carlson and Laura Schneller at UAA (U of Alaska Anchorage) sought out to answer these questions. You can find results in Spellman et al. 2015 and in Spellman et al. 2016.
theme 2: Phenology of northern plants
1. Overlap in flowering of white sweetclover (Melilotus albus) and two native berry species.
In interior Alaska, lowbush cranberries (Vaccinium vitis-idaea) and invasive sweetclover overlap in flowering time, creating the potential for competition for pollinators, while bog blueberries (V. uliginosum) flower before sweetclover, creating the potential for a sequential mutualism (together, they may support larger pollinator populations). All three are widespread species. Do they overlap similarly across Canada and the northern US? We used herbarium data to model how geography affects flowering time and then we used data from a citizen science project, Melibee, to validate the models built from herbarium data. Find the results in Spellman and Mulder 2016. A paper evaluating changes in flowering overlap across the continent with climate change, and shifts in risks to native plants is in the works.
2. Why aren't far northern plants changing average flowering time?
On the Cape Churchill Peninsula (northern Manitoba), summer temperature have increased for the past 75 years. Using a combination of field records and herbarium specimens, Christa Mulder (with colleagues Dave Iles and RF Rockwell) established that plants flower earlier in warm years, but that they have not increased flowering time over this period. Why not? You can find two explanations in Mulder et al. 2016. This project led to the Funky Flowers project (see Current Research).
3. Do earlier springs, warmer summers, and later autumns favor non-native species over native species?
Look around in fall in interior Alaska, and it becomes obvious that non-native species hang on to their leaves for longer than native species. But does a late fall benefit them more than native plants? What about earlier springs and longer summers? Find answers in Mulder and Spellman 2019. Further analysis of data from an associated citizen science network, Project Browndown, is still in the works.
Bees pollinating sweetclover (top) and cranberry (bottom)
Varying overlap in flowering across the continent
Saltmarsh and tundra plants on the Churchill Peninsula
Bird vetch (Vicia cracca) stays green until the leaves freeze.