Rare Plant Restoration

Priscilla Crawford

Seaside Alder Background

Working with Phil Gibson, OU Departments of Biology and Botany and Microbiology, we are conducting a study on seaside alder (Alnus maritima) restoration.

To a casual observer or trout fisherman, the shrubby tree may not seem particularly special, but the seaside alder is one of Oklahoma’s rare plants, occurring only in the Clear Boggy Creek and Blue River watersheds of south-central Oklahoma. But what makes this tree extra special is the location of the nearest populations of seaside alder – the Mid-Atlantic coast and a swamp in Georgia. The seaside alder has not been found any other place in between!

Although the seaside alder was discovered in Oklahoma over 100 years ago, we know little about how and why it grows where it does and we know little about its reproduction. We have observed that, although, trees produce copious quantities of healthy seeds, we find no seedlings in the wild. The alder population is apparently persisting solely by vegetative reproduction – sending up shoots from spreading underground roots. Unfortunately, vegetative reproduction is not keeping up with tree death and populations are shrinking.

The Issue

Trees typically produce thousands of seeds each autumn, but there is no sign that seedlings survive and establish new trees. These results are perplexing because seeds will happily germinate and establish in a greenhouse. Something in the natural habitat limits seedling growth. It could be a number of things. Seeds mature and are released in the fall and subjected to harsh winter conditions on the ground before spring germination. The ground on which seeds land may not be suitable for germination. For example, seeds could land in water, on river gravel, sand bars, or riverbank soil – we don’t know which, if any, is a suitable matrix. And along a river, the seeds may fall in the wet soil near the water level, or the relatively dry soil several feet from the water’s edge. Again we don’t know what conditions are tolerable.

Experimentation

We know alder seeds will germinate and grow under the ideal conditions of a greenhouse. Now we want to discover what affects seed germination and seedling survival in nature. Unlike a greenhouse, we planned our experiment to simulate the natural conditions of seeds released in the fall. We gathered seeds in October, before they were released from the tree.

We planted seeds in pots filled with sand, gravel, or riverbank soil to represent the different substrates found along a river. We also set up different moisture levels to replicate different distances from the river edge. The pots were placed outside so that the seeds and substrate would be exposed to winter conditions similar to seeds in the wild. The warm days of spring to stimulated germination. Our preliminary results indicate that the seeds germinated best in the unshaded, gravelly pots. Seedling establishment was minimal; we were plagued by a plant disease that may have occured because of the experimental set up.

Going Onward

With the findings of this research we will move out to the native environment. Beginning in the fall of 2012, we will work with the Tishomingo National Wildlife Refuge and the Oklahoma Chapter of the Nature Conservancy in an attempt to restore the seaside alder along the Blue River and tributaries of Pennington Creek in Johnston County.