Avian Habitat Use in a Chronosequence of Bottomland Hardwood Forest Restoration Site

Land use change to meet economic and societal demands has negatively impacted the current state of our world's ecosystems and biodiversity. The alarming rate of landscape change and degradation has prompted ecologists to conserve intact areas and restore historical habitats in the hopes of mitigating the potential damage. As a result, restoration ecology was developed and has grown dramatically within the past couple decades. Historically, the Mississippi Alluvial Valley, provided services such as water enhancement and nutrient cycling, and the characteristic bottomland hardwood forests dominated the land cover and were suitable habitat for many organisms, especially neotropical migrants. As the Upper Mississippi Alluvial Valley was converted into agricultural fields and locks and dams were installed, many neotropical migrants had steady population declines. More recent surveys have noted that approximately two-thirds of the neotropical migrants have been declining for the past half-century. For the past two decades, the U.S. Army Corp of Engineers (USACE) has been responsible for the restoration of bottomland hardwood forests in the Upper Mississippi Valley. Using birds as model organisms, this project assessed the restoration success of this site by (1) comparing avian richness, diversity, and density among a chronosequence of forest restoration age classes to determine any significant differences in species assemblage in the chronosequence and (2) creating a predictive habitat model that assists in the formulation of appropriate recommendations for restoration planning and management in the future. I hypothesize that species richness and diversity is highest at intermediate sites since they will have habitat characteristics of both grasslands and forests and that my habitat models identifies structural variables, such vegetation height, and tree height and ground cover as significant determinants of avian presence. Our study included a chronosequence of nine restoration sites and two references in which bird surveys and vegetation surveys were completed. Avian surveys consisted of 25-m fixed radius point counts at five plots per site. Sites were visited three times for the spring and fall data collections. Spring data will continue May 2014 due to unusual flooding conditions. Within the 25-m radius, a 17.84-m radius vegetation plot was created. Tree species, tree health variables, diameter at breast height (DBH), and abundance were recorded, and the tree was tagged. Shrub stem count data was recorded in four belts within each vegetation plot, with the condition that a shrub is at least 1-m in height. The plot was divided into four belts, and five quadrats of 0.5 m2 were formed along each belt to record forb and grass cover and litter depth. Species richness, Antilog Shannon-Weiner's Diversity Index, and Simpson's Diversity Index was calculated, and the vegetation data was used in the predictive habitat modeling. I recorded 52 bird species during the spring and 79 bird species during that fall that were within the 25-m radius. Bird species richness and diversity differed among the sites, and richness and diversity generally increased as the age of the site increased. Grassland and shrubland birds did not have any significant trends for vegetation parameters. However, most open woodland birds had a significant association with DBH, and a majority of forest birds had significant associations with tree height and crown size. The observed richness and diversity values contradict several studies but may be attributed to the productivity rate of the sites chosen. Density estimates can also be enhanced through new surveying methods which would address detectability issues for naturally skittish birds. Future restoration efforts should include the planting of fast-growing trees and shrubs in order to increase structural diversity at faster rates. In addition, more sites should be acquired and restored in order to create close patches for neotropical migrants to facilitate travel. Continuing efforts in restoration and appropriate management should emphasize the causes of declines for land birds and identify them early enough to develop an appropriate management plan.