Plant Talk

Using Plants as Calendars

Posted in Plant Science on October 25, 2023, by Michael J. Balick & Gregory M. Plunkett

Michael J. Balick, Ph.D., is Vice President for Botanical Science and Director and Senior Philecology Curator of the Institute of Economic Botany, and Gregory M. Plunkett, Ph.D. is Director and Curator of the Cullman Program for Molecular Systematics at The New York Botanical Garden.

Three juxtaposed images of flowers in red, white, and purple

Species of “calendar plants” used in southern Vanuatu as indicators for various agricultural, hunting, and other activities include (left to right) Metrosideros vitiensis, Urena lobata, and Hedycarya dorstenioides. Photos by Gregory M. Plunkett, Ph.D., and Wayne Law, Ph.D.

The New York Botanical Garden’s long-term project, Plants and People of Vanuatu, has just published a very interesting and timely paper that comprehensively records how Pacific islanders use plants as time indicators to guide such essential activities as when to hunt and fish for certain animals and the best time to plant various crops. In this paper, “Calendar Plants in Southern Vanuatu,” just published in the peer-reviewed research journal Economic Botany, we documented 111 species of what are called “calendar plants.” The study was based in Tafea, the southernmost province of the Southwestern Pacific nation of Vanuatu. Nearly 130 local Ni-Vanuatu (Indigenous people from Vanuatu) contributed knowledge to this paper.

Our team—which included researchers from the Botanical Garden, VinUniversity in Vietnam, Vanuatu Department of Forests, Vanuatu Cultural Center, in partnership with local communities—noted in the paper that, unlike standard reckonings of days and weeks, calendar plants are “flexible frameworks” because they adapt their fruiting and flowering times to changes in the local climate, an important quality that could provide greater resilience in the face of global climate change.

One important reason for documenting and disseminating this Indigenous knowledge is the role calendar plants can play in fostering resilience to global climate change. An advantage of using plants as guides to various activities is that they can adapt to changes in local weather. For example, in one area of Tanna, precipitation was much higher in 2022 than normal, and a number of calendar plants gave their signals later than usual. That meant people planted their gardens later than they normally do, and the crops did well. As we write in the paper, “Rather than conducting a particular agricultural activity on the same…date each year, calendar plants serve as reliable guides as they respond to peculiarities in weather that also affect crop plants.”

Of the 111 plant species that serve as environmental or cultural time-cues, most (66 species) involve plant signals that are guides to hunting birds and fruit bats because a large number of flowering and fruiting plants are food sources for these animals. We also documented plant species that are cues for agricultural activities, such as planting and harvesting crops, gathering wild plants and fungi, and fishing for or harvesting various marine species.

Among speakers of the Nafe language on Tanna, for example, the flowering of a plant they call nawawa (Metrosideros vitiensis, a shrub or tree in the myrtle family of plants) means that taro, a root vegetable that is a food staple in the region, is ready to be harvested. In some cases, we found that the same plant can indicate different things to more than one Indigenous group. When speakers of Netwar language in western Tanna see the sprouting seedlings of Urena lobata, they know that it is time to plant various crops. On Aneityum, however, the appearance of the plant’s delicate flowers and its fruit indicates that the cyclone season has passed.

Even neighboring peoples on the same island can find dramatically different associations with a plant’s annual development and the ecosystem of their local area. On Tanna, speakers of the Naka language know that it is a good time to hunt birds when fruit appears on the plant they call negapup (Hedycarya dorstenioides, a tropical tree or shrub). The island’s Nafe speakers watch for the same plant, which they call kapuapu, to flower, a signal that sea urchins are fat and ready to be harvested.

Some calendar plants play a role in the sustainable management of marine life. On Aneityum, for example, when the leaves of Terminalia catappa, a large tropical tree, change colors and fall from the tree, people know that it is time for lobsters to be harvested, a period that lasts about a month and half. Traditionally, people used this environmental cue to begin and end the harvest of lobsters, allowing the populations to recover during the remainder of the year. As the paper points out, “elders have observed that abandonment of this practice has led to overharvesting of lobster populations on Aneityum, and the depletion of this important food source.”

This change of practice is one example of how traditional knowledge of calendar plants is eroding, a trend we find troubling. It is critical that such information is recorded and revitalized before Indigenous knowledge systems decline even further. Such knowledge systems have relevance for other nations grappling with climate change. Languages are key repositories of the knowledge that helps instill resilience in communities. As part of our interviews with community members, we sometimes made audio and video recordings, which our team has used to create a series of “Talking Dictionaries” that help to preserve names, pronunciations, and uses of plants, fish, birds, and other animals.

The project is part of the effort by the Garden’s International Plant Science Center to study and preserve plants, fungi, ethnobotanical and ethnomedical knowledge, cultural practices, and plant-related language information in many regions of the world. That includes poorly studied nations such as Vanuatu, which is not only a hotspot of biodiversity but also the most linguistically dense country in the world, with an estimated 138 languages spoken by a population of 319,000.

“Calendar Plants in Southern Vanuatu” is available here.

A Plant Talk post about how the Plants and People of Vanuatu team documented the use of plants in centuries-old “weather magic” rituals and other practices intended to understand and even influence the weather can be found here.

In addition to The New York Botanical Garden and the Vanuatu Department of Forests, the calendar plant research was supported by the U.S. National Science Foundation (Grants DEB 1555657, 1555675, and 1555793), Velux Stiftung (Grant 1288), the Marisla Foundation, the National Geographic Society, the Christensen Fund, the Gildea Foundation, and the Silicon Valley Community Trust.


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