Why are Wisconsin’s pine barrens disappearing?

By Allison Cauvin, Masters student, Wildlife Ecology & Conservation Dept. 

Dr. Daijiang Li has attempted to solve a fifty year-old mystery. Rather, he’s tried to consolidate data taken fifty years ago and compare it to trends he’s noticing in the present day pine barrens of Wisconsin. Pine barrens are dry, sandy, nutrient-poor habitats that were once fairly frequent in Wisconsin. Typically, they contained species such as jack pine and northern pin oak. However, these sandy, open habitats have essentially disappeared over the past fifty years, with over 98% of their area lost. Dr. Li has sought to answer science’s most prevailing question: why?

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Pine barren habitat; Photo by Eric Epstein, WDNR

Dr. Li began his career at the Yunnan University in Kunming, China studying Ecology. He also obtained a Master’s degree in Restoration Ecology at Sun Yat-Sen University in Guanzhou before coming to America to complete his Ph.D. at University of Wisconsin-Madison with the Waller Lab Group. He also attained another MS in bioinformatics there during this time. He is now currently fulfilling a post-doctoral position with the University of Florida’s Wildlife Ecology and Conservation department. According to Dr. Li, his main research interests include understanding how communities of organisms change over time, and what the consequences of these changes are. This is what led him to begin investigating the disappearance of the pine barren habitats in Wisconsin.

All Li had to go on was a survey conducted by a biologist named John Habeck on these pine barren communities over fifty years ago. Using this fifty year-old data, he was able to pinpoint some very specific environmental changes that have happened to the pine barrens in this span of time. When Dr. Li analyzed the data from these communities, he discovered that the pine barrens hadn’t been subjected to fire for more than fifty years. Because of this, he believed that the suppression of wildfires was the primary reason the pine barrens were disappearing. Wildfires, when they occur, are typically treated as an emergency situation and immediately extinguished. However, these natural events are important for clearing out old foliage and opening up the canopy for low-lying plants. Without these natural disturbances, low-lying plants suffer and the entire species structure of the community is shuffled up.

Given that fire had been suppressed in pine barrens and surrounding areas for decades, Dr. Li hypothesized that the species composition of the pine barren communities had shifted to favor more shade-tolerant, but fire-intolerant, species, as opposed to the open-air species typical of the pine barren habitat. In addition, he sought to understand if the biodiversity within each community, and the larger pine barren region, had decreased due to these compositional shifts. Essentially, he was concerned that because fire had been suppressed in the region, it was losing valuable species to encroachment by other exotic species. And, finally, Dr. Li believed that this encroachment meant that each site was losing its unique habitat characteristics in a process called biotic homogenization.

In order to investigate, Li revisited the sites Habeck had surveyed in 1958. Expanding upon Habeck’s original sampling techniques, Li measured characteristics such as canopy cover, the presence of vascular plant species, and the species and diameter at breast height of each tree and sapling within the sampling area. He grouped closely related species together and identified those species that were considered introduced or ‘exotic’ to the pine barren habitat and Wisconsin region for further analysis. What Li found was that there were definitive “winners” and “losers” in the changing pine barren community structure. As fire suppression had prevented the opening of the canopy, cover had increased dramatically. Therefore, “winners” were typically shade-tolerant species such as ferns or woody species, while “losers” tended to be species that were suited to open-air environments (i.e. forbs) and had historically colonized the pine barren habitat.

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Pine barrens habitat; photo by Eric Epstein

However, Li was surprised to find that biodiversity at each site and among the pine barren region had actually increased. In each sampling site, overstory canopy species richness had increased by 29%, while understory exotic and native species richness had also experienced gains. What he found was that each site had been colonized by so many new plant species that it was increasing the total plant species found there, and therefore increasing the overall biodiversity. Essentially, more species were present in these pine barren communities now than there were in the past. However, the bulk of these species were the shade-tolerant winners that were not naturally found in the pine barren habitats. Additionally, Li discovered that the differences in species found among these sites had decreased, and biotic homogenization was indeed occurring. This means that each site was losing its unique biotic characteristics and was becoming more like every other site.

Dr. Li’s work is important in understanding why these pine barren habitats are disappearing. Fire suppression has changed the habitats and landscape, making conditions for shade-tolerant, “winner” plant species more favorable. And, in a process that can only be likened to gentrification, as these new species move in to these pine barren habitats, each site loses those factors that once made it unique. However, this study has implications far beyond the disappearing pine barrens. Dr. Li’s study has provided a model for how habitats and communities change over time in response to environmental stresses. We look forward to seeing what he will accomplish here at the University of Florida.

To learn more about Dr. Li’s work on the pine barrens, and his other research, please visit his web page here.