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Delta Journal
by Bob Thomas

Many people consider hackberry trees (Celtis laevigata) to be an unattractive nuisance. Though they may not be one of our most sought after ornamental species, they play an important role in nature.

Hackberries are fast growing, yet short-lived. They may grow to 20 or 30 feet tall in just a few years, but groves begin to die out between 40 and 70 years later. This is not a good trait if one wishes to line the entrance to the family plantation, but it is nice if you have built a new home on a shade-less lot.

As limbs fall and the weak trunks split with age and disease, cavities are formed that provide wonderful habitat for a variety of wildlife and other forms of life such as fungi and a host of insects. The nut-like fruit of hackberries is a wonderful wildlife attractant. During the winter, these trees are a favorite for flocks of Cedar Waxwings, one of our most beautiful birds.

One of the most unique features of hackberries is the spongy, warty outgrowth of the bark. They grow in conjunction with the tree’s lenticels, tiny pores that allow for air exchange in the bark. This very rough texture gives the trees an intriguing appearance and provides a myriad of nooks and crannies for tiny critters to live.

It is not uncommon to find dense stands of hackberry in the Mississippi River Delta. They do quite well in alkaline soils and seem to be unaffected by alternating periods of drought and deluge. During plant succession, the gradual replacement of one plant community by another over time, a hackberry dominated forest appears to precede the final step in the delta region - live oaks.

The Audubon Louisiana Nature Center’s forest is a good example of this hackberry transition (called a “seral stage”). Before 1914, the site where LNC is located was a brackish marsh. It was drained to make way for future development and plant succession began. Marsh vegetation gave way to a wave of new plant invasions, each changing the soil as it went through its life processes and unknowingly preparing it so that yet other species could grow and prosper. After a number of years, hackberries gained a foot-hold. They gradually became more numerous, displacing other species. Before Katrina, some 91 years later, the forest was 90% hackberry and 10% a mixture of live oak, elm, maple, and many understory plants. The oak trees were rather stunted, stretching for light above the hackberry canopy. As hackberries fell, more light hit the ground and the oaks begin to expand their growth.

LNC hackberries were suffering from two major afflictions. They were susceptible to a root fungus (Hypoxylon) that appeared around the base of the tree as a black, crusty growth. This fungus didn”t appear to interfere with normal life processes and, other than the fungal growth, the trees appeared healthy. However, the fungus weakened the roots and, following a wind storm, the tree may be found toppled over. Inspection of the root-base revealed a break between roots and trunk that was so clean that it appeared to have been done with a chain-saw!

The other problem faced by local hackberries is infestation by Jumping Plant Lice. These are tiny leaf-hoppers that suck the juices from the leaves. Healthy trees can support a thriving colony of these insects, but over-infestation will lead to yellowing leaves, defoliation, and often the death of whole limbs of leaves. The plant lice look like miniature cicadas, having a total length of about a tenth of an inch. Their most obvious sign is the presence of tiny white circular shields on the under-surface of leaves. These are produced when the larvae pupate, thus undergoing changes that result in the adult stage. When infestations are high, vast numbers of these “scales” may accumulate under hackberries as the plant lice metamorphose en masse. Some locals call these piles of white flakes “summer snow”.