Howea forsteriana in Lord Howe Island, Australia. Credit William J. Baker

Palm trees most abundant in tropical forests in the Americas

Palm trees are more than five times more numerous in tropical forests in the Americas than in comparable Asian and African forests, a new study shows.

Many palms were already known to prefer land with a good groundwater supply, and the new study confirms that palm trees are more plentiful in wetter areas with less fertile soils and shallower groundwater.

Characteristics of palm trees differ from those of other tropical trees in many ways.

The new study, led by Uppsala University (Sweden) and University of Campinas (Brazil), surveyed the numbers of palms in tropical rainforests around the globe.

The proportion of palm trees is important to include in calculations of forests’ potential carbon storage and in estimates of forested areas’ sensitivity to climate change.

“To get a better understanding of tropical forests and reduce uncertainty about carbon balance in these ecosystems during climate change, we summarised data to show how the number of palms vary around the world compared with other tree species,” said Bob Muscarella, of Uppsala University

Palm trees are iconic tropical forest plants.

However, postcard images of coconut palms leaning over white sandy beaches do not capture the stunning diversity of palms and their importance to humans and ecosystems.

Co-author Dr Ted Feldpausch, of the Global Systems Institute at the University of Exeter, said: “Understanding how the distribution of palms varies and the susceptibility of palms to changing climate is important for global livelihoods.

“Many different species of palms are used by people throughout the tropics as sources of food and fibre for crafts and construction.

“For example, protein and oil-rich species such as açaí (Euterpe oleracea) are used in drinks.

“Species that are eaten include the peach palm (Bactris gasipaes) fruit and the delicacy heart of palm harvested from the stem of several species of palm.”

In some areas, palms are also entirely dominant and form natural monocultures.

Palms are among the most common tree species in the Amazon rainforest, but in some tropical areas they are unusual, or conspicuously absent.

Before this study, variation in numbers of palm trees among tropical regions had not been quantified.

Drawing from existing networks of forest plots, the researchers compiled a huge database of 2,548 plots and then quantified palm numbers relative to other tree species in the sample plots.

Tropical rainforests are often seen as synonymous with biodiversity.

However, this diversity is not evenly distributed, and most plants in a given area belong to only a handful of species.

More than half of the total biomass in the Amazon rainforest is distributed among fewer than 300 tree species – including several species of palms.

“Understanding the dominant species in tropical forests is crucial to recognising how these forests function and how vulnerable they’re going to be to disturbances and climate change in the future,” Muscarella said.

Being monocotyledons (the seed produces only one first leaf, or cotyledon), palms are more closely related to grasses than to the deciduous trees of the tropics, for instance.

Palms therefore differ in many fundamental ways, in anatomy and physiology, from other tropical trees.

These differences may have far-reaching implications when it comes to estimating uptake and storage (sequestration) of carbon in tropical forests, as well as their resilience to climate change.

The new study provides knowledge with a vital bearing on further research into both of these aspects.

“Impressive levels of palm abundance do not come as a surprise to many tropical forest researchers,” said Thaise Emilio, of the University of Campinas.

“Days of work may be necessary to measure all the palms of a single hectare in some places in the middle of Amazon.

“However, a fair representation of palms in studies of tropical forests functioning is yet to come.

“Showing where and when palms must be considered is a major contribution of our new study.”

The paper, published in the journal Global Ecology and Biogeography, is entitled: “The global abundance of tree palms.”

Date: 6 July 2020