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Adaptations Help Illustrate Importance of Biodiversity

Arkansas Natural Heritage Commission - Thursday, November 30, 2017

by Bill Holimon

Protection and restoration of open pine ecosystems (woodlands dominated by large pine trees spaced about 50 feet apart with sparse mid-story and shrub layers and a rich herbaceous layer) in the Coastal Plain of southern Arkansas has been a high priority of the ANHC and partners for over two decades. One of the two pines within this ecosystem, shortleaf (Pinus echinata), has the largest range of any of the pines in the southeastern United States.

Historically, shortleaf pine was far more common across the region; but forests with a major shortleaf pine component have decreased by nearly half in just the past 20 years and by much more when compared to the 1800s. These declines followed decades of timber management and changes in fire regimes that have favored loblolly pine (Pinus taeda) over shortleaf. Both pine species are native to the state and the ANHC has been working at Warren Prairie Natural Area (WPNA), located in southeastern Arkansas, to restore shortleaf pine numbers so that the tree is better represented, which increases the biological diversity of the natural area.

Is the restoration working? Dr. Don Bragg, Research Forester with the U.S. Forest Service, found encouraging evidence during a recent work day at WPNA. Don found several small clumps of shortleaf pine seedlings (top photo) scattered throughout a restoration tract. Mature trees of both pine species are well adapted to fire, but only shortleaf pine seedlings survive fire, thanks to its early development of a crook.

Within the first 3 months of sprouting, the top couple of inches of the shortleaf pine’s stem turns and grows horizontally through the soil abruptly turning up and creating a basal crook. There are special cells at the location where the stem turns up (photo at left with red arrow) which typically remain dormant – unless the aboveground portion of the tree is killed by a fire or some other means. Those cells are insulated from fire by the soil and will sprout a new stem or stems when the aboveground portion is killed. The equivalent portion of loblolly seedlings are aboveground and would be exposed to the fire, making them more vulnerable to harm. This gives shortleaf pine a competitive advantage over loblolly in these frequently burned (every 2-3 years) open pine ecosystems. In the photo at right, Don demonstrates to a group of volunteers and ANHC staff the difference in the roots of shortleaf and loblolly pine seedlings at WPNA.

Why was Don so excited? It turns out that only large, mature trees occur in most areas where shortleaf pine is a major component of the forests. This means that there are no young shortleaf pine trees in those areas to replace older trees when they die. This is partly due to changes in the fire regime that have resulted in canopy closure across shortleaf’s range. Shortleaf is shade intolerant, especially the younger trees. Loblolly pine is a more prolific seed producer and grows more quickly over the first several years, typically outcompeting shortleaf in the absence of fire. Scattered patches of shortleaf seedlings are common at WPNA and they represent future persistence of this otherwise quickly declining species.

With their crooked ways, some shortleaf seedlings will eventually escape fire and grow into large trees. In years of higher rainfall when prescribed fires are conducted, loblolly pine seedlings escape fire in the lower, wetter areas of WPNA. In this way, both native pine species flourish in a more natural frequency and manner.

Above photos

Top left, group photo: Don Bragg discusses shortleaf pine ecology and conservation to a group of volunteers from Little Rock Zoo staff and ANHC staff at Warren Prairie Natural Area. A small patch of shortleaf pine seedlings occurs at bottom, right-side of the base of the pine tree. Zoo staff painted white lines around each of the red-cockaded woodpecker cavity trees to increase the ease of finding those trees for management and monitoring purposes.

Above left (with red arrow): Bill Pickens identifies the basal crook of shortleaf pine. The arrow indicates the location at which the plant will re-sprout if the above-ground portion of it is killed by fire or other means. Photo by Bill Pickens.

Bottom right: Don demonstrates the difference in root morphology (form and structure) of shortleaf (left) and loblolly (right) pine seedlings he plucked from the ground at Warren Prairie Natural Area.

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