Pondberry: Modest But Mysteriousby Zoë Hoyle
A team of researchers from the SRS Center for Bottomland Hardwoods Research are working with the U.S Army Corps of Engineers (Army Corps) and the U.S. Fish and Wildlife Service (USFWS) to learn as much as they can about the biology and ecology of pondberry, an endangered plant with significant remaining populations in the Lower Mississippi Alluvial Valley (LMAV).
Pondberry is a rarely seen woody plant that grows in seasonally flooded forests and on the edges of sinks and ponds. Growing up to 6 feet tall, pondberry plants consist of many stems that are connected underground. The small yellow flowers bloom in the very early spring before the plant itselfand most other plantsleaf out. The red berries appear in the fall in clusters where secondary stems meet the main stems. A member of the Lauraceae family, pondberry most closely resembles spicebush. About 36 populations of the plant remain in sites across seven Southern States, with the majority in the LMAV. The plant has recently been discovered in Alabama.
Pondberry was listed as endangered in 1986. A large part of its habitat disappeared when forests were cut for timber or for conversion to agricultural fields, and as wetlands were drained or flooded. “Pondberry has always been a rare plant,” says Margaret Devall, SRS research ecologist who leads her unit’s efforts to understand the plant’s reproductive biology and was the first in the unit to work on it in 1997. “We still know very little about the ecology, physiology, even genetics of pondberryand, more importantly, we don’t know what is required to sustain the populations we still have.”
When Push Comes to Shove
Pondberry studies got underway bigtime when flood measures proposed for the southern part of the Delta region of Mississippi raised questions about the survival of the plant in the Delta National Forest. USFWS biologists were concerned about the persistence of pondberry populations. Though populations of the plant are scattered across seven States, one of the largest populations is on the Delta National Forest. Over 5 years, some $5 million has been devoted to collaborative studies on the biological and ecological factors that may affect the survival of pondberry. This is likely the largest single study funded for an endangered plant in the Southeast. As collaborators in the study, SRS researchers set up permanent plots in the Delta National Forest and others on nearby sites to monitor environmental factors. They are also investigating the role of flooding and light availability on pondberry at a large-scale impoundment facility, and have set up greenhouse studies to look at competition, seed germination, and storage, as well as seed persistence in a seed bank. Together, they take an integrated approach to pondberry, looking at ecology, insect predators, fungal pathogens, physiological responses to light availability and flooding, population genetics, seed physiology, and seed dispersal.
The Mystery of Dispersal
Pondberry has two modes of reproduction. The plant seems to reproduce mostly by shooting up new stemscalled stolonsfrom the rootstock. These clonal stems (meaning they all have exactly the same genetic material) flower at around 2 to 3 years of age, and live for only a few years. The plant bears seed-containing fruit, but it is rare to find a seedling near existing populations. This brings up two questions: How are new populations of pondberry established? If by seed, how are the seeds dispersed?
Existing populations of pondberry are so far apart that some researchers speculate that the seeds were once spread by floods. Because so little was known about how pondberry seeds were carried to new locations, SRS researchers submitted a proposal to the Army Corps to try to catch seed dispersers on tape. They set up five video cameras with infrared illuminators to record a pondberry population in the Delta National Forest from late fall until all the fruits had disappeared in late December. Various birds and other creatures appeared on the tapebut whether animals such as the Louisiana black bear are primary dispersers is still unknown.
To look at dispersal by birds, Paul Hamel, Carl Smith, and fellow SRS researchers selected fruiting pondberry colonies on the Delta National Forest and set up a series of 1-hour observation periods to record the species of birds seen near the pondberry colony, perched on a pondberry plant, or actually eating a pondberry fruit. They observed 82 different species of birds in the colony area, and 12 species perched on the plant. Of these, the hermit thrush and northern cardinal were observed actually eating pondberry fruit. Hermit thrushes swallow the entire fruit, so are unlikely to drop seeds in the immediate area. This makes them a good candidate for local dispersal of seeds, but the birds move relatively small distances in the winter and are not likely to carry seeds across the open space between forest patches.
Dispersal, or its lack, could severely limit future populations of pondberry, since many of the existing populations are in small wooded areas surrounded by agricultural fields that limit further clonal colonization. “In the past the seeds could also have been dispersed by floodwaters, but flooding is controlled in these areas,” says Devall. “Without human intervention, it is unlikely that new pondberry colonies will appear to replace those lost to habitat alteration or destruction.”
With a small grant from the National Wildlife Federation, center scientists Devall and Nathan Schiff have investigated introducing pondberry to new sites. Colonies on protected sites have done well, but private landowners are reluctant to plant endangered species on their land. Reintroduction is also not a solution for the USFWS, which is more interested in how to protect the naturally occurring populations of pondberry. In addition to those mentioned in the article, SRS researchers involved in the pondberry project are: Kristina Connor, Craig Echt, Emile Gardiner, Tracy Hawkins, Ted Leininger, Brian Lockhart, and Dan Wilson.
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