As I discussed in the previous post, there is a great deal of evidence for change in phenology and other plant characteristics as a result of climate change. Here I want to consider other types of specimen information related to environmental change that can improve our understanding. For example, long-term herbarium data reveal a decline in temperate-water algae at its southern range (Riera et al., 2015). On dry land, a massive analysis of a database with two million specimens from a network of 35 Californian herbariums revealed that species are moving northward, but not at the same rate. In particular, animal populations are adjusting to temperature rise more rapidly than plants. This isn’t surprising, but it means that food webs are likely to be disrupted. In a very different kind of study, Swedish researchers compared photosynthesis products in 100-year-old herbarium specimens versus recently collected ones and detected a difference in the balance between photorespiration and photosynthesis. Again, it is not surprising that there was discovered an increase in photosynthesis relative to photorespiration; this would be expected as CO2 levels rise, but it does provide a very different type of evidence, thus strengthening the climate-change argument.
Unfortunately, there are many other environmental problems. Specimens can supply crucial data in these areas as well. Ecologists employed niche modeling tools combined with herbarium occurrence records to estimate the global invasive potential of each of 10 species of parasitic witchweeds in the family Orobanchaceae (Mohamed et al., 2006). Results show that these notorious weeds have significant invasive potential not only in tropical and subtropical areas, but in temperate ones as well. There have already been a number of large-scale control and eradication efforts, and perhaps these predications will lead to earlier and more effective interventions. A number of European groups have studied the genetics of the ragweed, Ambrosia artemisiifolia, which is native to the Americas but is now widespread in Europe. By comparing genes in old herbarium specimens and more recent collections in Italy, France, and Spain, geneticists are beginning to be able to identify more recent populations, and those that have interbred with older ones. It is fascinating how such comparisons can fill in stories about species movements in ways that just looking at more recent collections can’t (Chun et al., 2010).
Not only invasions can be tracked with specimens but infestations as well. The most spectacular story, at least from the viewpoint of someone of Irish descent like myself, is the discovery of the strain of Phytophthora infestans responsible for the potato late blight that caused the famine in Ireland in the mid-1840s (Goss, et al., 2014). It was possible to retrieve specimens of the pathogen from Kew herbarium sheets of potato plants collected in Ireland at the time. DNA sequencing indicates the origin of the pathogen was from a Mexican strain rather than an Andean one. This is significant not only for solving a historical puzzle but for understanding how these pathogens spread from their areas of origin. Since phytophthora remains the leading cause of potato crop destruction, the study is important for the future as well.
The larva of the moth Cameraria ohridella is a leaf-miner feeding on horse chestnut trees in Europe. It was first noted in Austria in 1984 and was declared a new species in 1986. It’s now becoming more and more common throughout Europe, but where it originated was something of a mystery. One place to look for clues would be in herbaria, and when horse chestnut specimens at several European collections were examined, horse chestnut leaf damage by this species was found on leaves in the Kew herbarium collected from natural populations in Greece as early as 1879. This is a significant finding, but who knows what more searches may turn up. The authors note: “This case history demonstrates that herbaria are greatly underutilized in studies of insect–plant interactions, herbivore biodiversity, and invasive species’ origins” (Lees et al., 2011, p. 322).
The types of research I’ve been discussing are why large-scale digitization of specimens has been funded. Herbarium sheets supply data on environmental change that just can’t be acquired in any other way. Herbaria are also used by many who are not doing research, but rather are involved in creating and enforcing environmental regulations at the federal, state, and local levels. For example, the Centre for Mined Land Rehabilitation in Australia maintains a herbarium to aid in the assessment of the environmental effects of mining and of successes in rehabilitating disturbed lands. Plant identification is crucial to this work, and there is nothing better than vouchered specimens for the purpose.
Mark Elvin of the US Fish and Wildlife Service, who is involved in conserving aquatic plant species, notes that digitization of specimens has improved the basis for decision making related to the laws and regulations that the service administers including the Endangered Species Act and the Convention on International Trade in Endangered Species (CITES). With digitization, information can be obtained faster, and more thorough data searches can be done. Willem Coetzer (2012) reports from South Africa that herbaria there are involved in projects dealing with bioregional planning, developing sustainable harvesting programs, preparing environmental impact assessments, and doing ecological niche modeling. The same could be said for many herbaria worldwide, and as more data becomes available online these uses will only grow more important.
It might seem at this point that there couldn’t be any further ways that herbaria can be useful, but that’s just not the case. In the next post, I’ll finish up this review by looking to other fields that are beginning to see herbaria as mines of information and inspiration.
Chun, Y. J., Fumanal, B., Laitung, B., & Bretagnolle, F. (2010). Gene flow and population admixture as the primary post-invasion processes in common ragweed (Ambrosia artemisiifolia) populations in France. New Phytologist, 185(4), 1100–1107.
Coetzer, W. (2012). A new era for specimen databases and biodiversity information management in South Africa. Biodiversity Informatics, 8(1). Retrieved from https://journals.ku.edu/index.php/jbi/article/view/4263.
Goss, E. M., Tabima, J. F., Cooke, D. E. L., Restrepo, S., Fry, W. E., Forbes, G. A., … Grünwald, N. J. (2014). The Irish potato famine pathogen Phytophthora infestans originated in central Mexico rather than the Andes. Proceedings of the National Academy of Sciences, 111(24), 8791-8796.
Lees, D. C., Lack, H. W., Rougerie, R., Hernandez-Lopez, A., Raus, T., Avtzis, N. D., … Lopez-Vaamonde, C. (2011). Tracking origins of invasive herbivores through herbaria and archival DNA: The case of the horse-chestnut leaf miner. Frontiers in Ecology and the Environment, 9(6), 322–328.
Mohamed, K. I., Papes, M., Williams, R., Benz, B. W., & Peterson, A. T. (2006). Global invasive potential of 10 parasitic witchweeds and related Orobanchaceae. Ambio, 35(6), 281–8.
Riera, R., Sangil, C., & Sansón, M. (2015). Long-term herbarium data reveal the decline of a temperate-water algae at its southern range. Estuarine, Coastal and Shelf Science, 165, 159-165.