Vegetation patterns and wrack-initiated disturbance in a nontidal brackish marsh in North Carolina / by David Bryant Knowles.
| Author/creator | Knowles, David B. author. |
| Other author | Brinson, Mark M., degree supervisor. |
| Other author | East Carolina University. Department of Biology. |
| Format | Theses and dissertations |
| Production | 1989. |
| Description | vii, 134 leaves, 2 unnumbered leaves of plates : illustrations ; 28 cm |
| Supplemental Content | Access via ScholarShip |
| Subjects |
| Summary | Disturbance by wrack provides one explanation for the mosaic pattern evident in the plant community of a nontidal marsh dominated by Juncus roemerianus Scheele, within the Cedar Island National Wildlife Refuge, North Carolina. The changes in species composition and community structure are, in part, a response to a gradient of decreasing hydroperiod and salinity from the shoreline to the interior. This gradient, however, does not adequately explain the abrupt changes in species dominance found in portions of the marsh. Wrack (mats of dead J. roemerianus leaves deposited by storm surge) can cause mortality of the covered vegetation. This is believed to initiate a disturbance/succession cycle in which the disturbed site is colonized by the more invasive species from the patch periphery, through the spreading and tiller production of surviving rhizomes, and by seedling establishment, where conditions permit. Eventual domination of the patch by J. roemerianus may occur in the absence of subsequent disturbance, but the successional cycle may require decades before J. roemerianus regains dominance. In order to investigate the disturbance/succession cycle, five objectives were addressed: (1) an analysis of plant community composition to examine the expression of wrack initiated disturbance, (2) an examination of the spatial and temporal distribution of wrack over 30 years using high altitude photograph interpretation, (3) the creation and manipulation of wracks to determine the survival of underlying vegetation, (4) a measurement of vegetative colonization of the created disturbance patches and in natural, vegetated disturbance patches, and (5) an evaluation of the viability of the soil seed bank. The marsh can be divided into three major vegetation zones. Community species composition changes from nearly monotypic stands of J. roemerianus in Zone 1, nearest the shoreline, to mixed stands in the two interior zones (Zones 2 and 3) where J. roemerianus may be dominant, absent, or subdominant to Spartina patens (Aiton) Muhl., Distichlis spicata Greene, Fimbristvlis spadicea Vahl., and Panicum virgatum L. |
| Summary | In Zone 3, species diversity is greatest (28 species) including the shrub, Myrica cerifera L. The distribution and effect of wrack varied among the three vegetation zones. Wracks are more frequently deposited in Zone 1 and vegetation mortality was more rapid and complete than in Zones 2 and 3. Wracks are usually smaller in Zone 1 (avg. 590 m2) than the wracks deposited in Zone 2 (avg. 871 m2) and Zone 3 (avg. 1,509 m2 ) . Storm events capable of wrack deposition in the two interior zones occur at intervals of approximately 3.3 years. Vegetative colonization was minimal after 1.5 year of monitoring. D. spicata was the only species capable of rapid colonization of disturbance patches via extended stolon production. However, the abundance of this species in the peripheral vegetation is a primary factor governing the effective colonization of the patch. Vegetative colonization by S. patens, J. roemerianus. and P. virgatum was from the lateral spreading of surviving rhizomes. Over 3 years, the ingrowth of J. roemerianus into patches occupied by dense stands of S. patens was not discernible. For the seed bank experiment, soil samples were collected from each vegetation zone. In the greenhouse, four treatments were imposed: flooded or drawdown with either fresh or salt water (maintained at 20, 10, and 5 ppt. for Zones 1, 2, and 3, respectively). After 5 months, no seedlings appeared in the flooded treatments. In the drawdown treatments maintained with saline water, J. roemerianus germination was significantly reduced in Zone 1 soil sample only. Pluchea purpuraseens (Swartz) DC. and Cyperus spp. germination was significantly reduced in the saline treatments from Zones 1 and 2 samples but not in Zone 3. |
| General note | Submitted to the faculty of the Department of Biology. |
| General note | Advisor: Mark M. Brinson |
| Dissertation note | M.S. East Carolina University 1989 |
| Bibliography note | Includes bibliographical references (leaves 126-134). |
| Funding information | "This research was funded, in part, through a cooperative agreement (No. 14-16-0009-85-963) between the U.S. Fish and Wildlife Service and East Carolina University."--Page iii |
| Genre/form | Academic theses. |
| Genre/form | Academic theses. |
| Genre/form | Thèses et écrits académiques. |
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