The post provided by Emilie Champagne
This post refers to the article Forage diversity, type and abundance influence winter resource selection by white‐tailed deer by Emilie Champagne, André Dumont, Jean‐Pierre Tremblay and Steeve D. Côté, published in the Journal of Vegetation Science: https://onlinelibrary.wiley.com/doi/abs/10.1111/jvs.12643.
This is the story of a major fieldwork problem and a desesperate Ph.D. student, with the academic happy ending: an article.
It was the second year of my Ph.D. project. My team of assistants and I were set to collect data in a new region, never exploited by my supervisors nor by me. Our objective was to determine how diversity in plant communities influenced browsing on white pine (Pinus strobus) by white-tailed deer (Odocoileus virginianus). The core of my thesis related to the effects of neighbouring plants on browsing (i.e. associational effects). Most of my thesis’ data were collected on Anticosti Island (Québec, Canada), where plant diversity is very low because of deer overbrowsing in a boreal forest (Potvin et al. 2003; Tremblay et al. 2006). By measuring browsing in the Outaouais region, we would be able to test the effects of plant diversity on browsing, as this is one of the most diverse regions for plants in Québec. Although many studies had investigated the relationship between diversity and invertebrate herbivores (Kambach et al. 2016; Moreira et al. 2016), few had investigated the relationship with large herbivores, especially in natural environments. Is was most probably a question of scale: it is easier to manipulate the composition of patches of plants for invertebrates than to do the same thing for cervids.
With the help of my co-author (A. Dumont), we had selected a white pine plantation site. It was a small area (less than 1 km2), where we could do an almost complete mapping of the stems. The first day in the field, we found the site easily and saw that there were plenty of pines within deer’s reach. Several plants presented signs of browsing in the area. Browsing studies are often characterized by a lot of ‘non-event’, so it was an encouraging sign! My goal for this first day was to train my assistants, which is an essential task. Measuring browsing is not complicated, but it does require a bit of training and lots of rigour. We had done an entire morning of work, finished two complete plots, when I realized there was a problem.
These were not white pines, but rather red pines (Pinus rubens). Now those two species are easy to discriminate, but I was so concentrated on training my assistants that I had not realized my mistake. A bit anxiously, I told my assistants to wait, while I walked the site, in a quest of white pines. Not a white pine in sight. Both white and red pines were supposedly planted on that site, but for an unknown reason, only red pines remained. And, more tragically for my project, red pines are not browsed by deer. I will never know whether it was a mistake on the forest map or whether deer had completely browsed the poor white pine, but the result was the same: no data to collect.
For an experienced researcher, this could be a minor issue. For a Ph.D. student, it was a panicking event. I frantically tried to contact my supervisor, in a region with low cell phone coverage, but he was unreachable. I then turned to my collaborator, who suggested contacting a forestry technician working at the nearby office. With his invaluable help, I was able to obtain detailed maps of the region. I selected 13 forest stands that had received a forestry treatment in the last 23 years, and planned a new sampling design. I would use transects in all those stands, and each time we encountered a white pine, we would set a circular plot around it.
We found the new design plan easy to follow, and we completed fieldwork without any more trouble. Buried under the more pressing needs of other chapters of my thesis, it took me months to analyze the data and a couple of years to have a manuscript. My misfortune was forgotten by almost everyone, and even for me, the adventure felt like an old story. The results brought me an additional surprise. I was expecting results similar to the previous studies, where browsing by moose (Alces alces) increases with plant diversity (Vehviläinen & Koricheva 2006; Milligan & Koricheva 2013). In my data, however, browsing by deer decreased with diversity indices such as the Shannon index, although browsing did increase with plant richness. By using multivariate analyses (principal component analysis) and an index of plant selection, it became clearer that herbivore choice was influenced by the relative abundance of species. We measured diversity using indices, such as the richness or the Shannon index, but herbivores do not perceive the environment in this manner. To them, the identity and relative abundance of the different plant resources is what matters. The key message of this article is that while diversity indices are interesting proxies for several ecological functions, they might not be as useful in plant-herbivore interactions.
If my original sampling plan had worked, I would have sampled one forest stand very precisely. That would have been interesting, but I am quite sure that diversity would have been lower than in the realized sampling plan. The results would also have been less representative of the entire area. In the end, I am not sure we would have learned as much. Perhaps more importantly for my personal development, I learned how to react to unexpected issues. So, to all the early career researchers reading this…please, don’t panic!
- Kambach, S., Kühn, I., Castagneyrol, B. & Bruelheide, H. (2016). The impact of tree diversity on different aspects of insect herbivory along a global temperature gradient – a meta-analysis. Plos One, 11, e0165815. https://doi.org/10.1371/journal.pone.0165815
- Milligan, H.T. & Koricheva, J. (2013). Effects of tree species richness and composition on moose winter browsing damage and foraging selectivity: an experimental study. Journal of Animal Ecology, 82, 739-748. https://doi.org/10.1111/1365-2656.12049
- Moreira, X., Abdala-Roberts, L., Rasmann, S., Castagneyrol, B. & Mooney, K.A. (2016). Plant diversity effects on insect herbivores and their natural enemies: current thinking, recent findings, and future directions. Current Opinion in Insect Science, 14, 1-7.
- Potvin, F., Beaupré, P. & Laprise, G. (2003). The eradication of balsam fir stands by white-tailed deer on Anticosti Island, Québec: a 150-year process. Ecoscience, 10, 487-495. https://doi.org/10.1080/11956860.2003.11682796
- Tremblay, J.-P., Huot, J. & Potvin, F. (2006). Divergent nonlinear responses of the boreal forest field layer along an experimental gradient of deer densities. Oecologia, 150, 78-88. https://doi.org/10.1007/s00442-006-0504-2
- Vehviläinen, H. & Koricheva, J. (2006). Moose and vole browsing patterns in experimentally assembled pure and mixed forest stands. Ecography, 29, 497-506. https://doi.org/10.1111/j.0906-7590.2006.04457.x
Emilie Champagne is a specialist of plant-herbivore relationships. She completed a PhD in biology at Université Laval (Canada) in 2017 and is currently the recipient of a Mitacs Accelerate fellowship, resulting from a partnership between Université Laval, Ouranos and Ministère des Forêts, de la Faune et