André Michaux International Symposium

Magnolia Research






Big Leaf Magnolia (Magnolia macrophylla Michaux) has the largest size simple leaf of any North American tree. Its geographic range includes the southeastern U.S. In North Carolina it is predominantly found in Gaston County, located in the western Piedmont region of the state. André Michaux first described this species from a population site in Gaston County in 1789. This is a preliminary study of a larger research project to better understand the ecology of M. macrophylla. This preliminary study includes data from six population sites sampled during the last two growing seasons. Initial data show a significant correlation of M. macrophylla with mesic habitats. There is a significant correlation between the presence of M. macrophylla and Fagus grandiflora at these sites. There is also evidence of recent disturbance at most of the study sites. It appears that disturbance may be an important factor in the success and/or establishment of M. macrophylla populations. 

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Magnolia macrophylla Michaux (Big-Leaf Magnolia) has the largest sized leaf diameter of any simple leaf tree species in North America. Its range extends from North Carolina westward to southeast Kentucky and south through Tennessee, Alabama and Louisiana. Approximately 95% of the populations in N.C. are in Gaston County, with only a few widely scattered populations in other sections of the state (NC Natural Heritage Program 1998). In fact, Michaux first described it from an extant population in Gaston County, NC in 1789 (Williams 1999). The historical distribution of M. macrophylla and factors that have contributed to its localized distribution pattern, are not well understood. In addition, only one known previous study (Doyle unpubl. Thesis 1989) on the ecology of this species has been conducted. Magnolia macrophylla has generally been described as inhabiting sheltered coves or valleys protected from strong winds. Its leaves are often 50-76 cm long and 23-26 cm broad. The flowers are large as well, measuring 32-46 cm in diameter and bloom from April to early June (Thein 1974).  

To better understand the ecology and distribution pattern of Magnolia macrophylla, a study was initiated in the spring of 2000 to collect data from several large populations sites within Gaston County, NC. The objective of this study focuses on providing baseline information on the species ecology of M. macrophylla and its current status in Gaston County, NC. 

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Six populations were sampled using a total of 205 5m2 contiguous quadrats. Within each quadrat data were collected for each of the following: total number of Magnolia macrophylla individuals and a corresponding diameter at breast height measurement (dbh) for each, a list of all associate woody species and a designation of whether they were tree or sapling size, and a total cover class value for all vegetation. DBH values were assigned as follows:

1 = dbh>5 in.,

2 = dbh>2 in.<5 in.,

3 = dbh<2 in.

Cover class values were as follows:

50 – 100% = 5,

25– 49% = 4,

11 – 24% = 3,

1 – 10% = 2,

<1% = 1.

The presence or absence of flowers/fruits on individuals of M. macrophylla was also recorded. In addition, aspect and soil series data for each population were ascertained. Chi-Square analyses were performed on the data. 

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Magnolia macrophylla and Associate Species 

Among associates within sampled quadrats with Magnolia macrophylla, Fagus grandifolia is the most significant associate species (P = .012). Of the 177 quadrats sampled with M. macrophylla, 81 (46%) contained at least one individual of F. grandiflora. Liriodendron tulipera is also significantly correlated with M. macrophylla within the sampled quadrats (P = .048). Of the 177 quadrats with M. macrophylla, 66 ( 37%) contained at least one individual of L. tulipfera (Fig. 1). 

Figure 1. Species occurrence

Presence of Fruit/Flowers and DBH Values of M. macrophylla 

Of the Magnolia macrophylla individuals with a dbh value of 1, 41% possessed flower/fruit structures. Only 8% of individuals with a dbh value of 2 possessed flowers/fruits. No flower/fruit structures were observed on individuals with a dbh value of 3 (Fig. 2).  

Figure 2. Occurrence of Flower/Fruit Structures

Slope/Aspect Features  

The six populations were located on moderate to severe north facing slopes. Soils series from each study site were of similar taxonomic groupings.  

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Of the associate species found within quadrats with Magnolia macrophylla, only Fagus grandifolia and Liriodendron tulipfera are significantly correlated. Doyle’s (1989) study documented F. grandifolia as an important associate species in Mill Creek Forest in Pearl River County, Mississippi. Also, the slope and aspect positions for these population sites are consistent with historical descriptions of M. macrophylla populations (Raynal 1938, Sargent 1947). The population sites meet the critera for classification as Mesic Mixed Hardwood Forest (Piedmont Subtype). These sites are often along slopes and ravines, which may be north facing and steep. The soils are deep, well drained and often acidic. They are characterized as often having uneven-aged members and reproduction which occurs in canopy gaps (Schafale and Weakly 1990). Doyle (1989) describes a “clumping ” in the landscape of M. macrophylla seedlings as a result of apparent vegetative reproduction from surrounding root systems. This was also my observation among my study sites. Initial observations suggest increased asexual propagation from root systems of M. macrophylla in both canopy gaps and areas of less intense competition from other species. Much of the county, including portions of these sites, experienced the creation of canopy gaps due to tree loss during Hurricane Hugo in 1989. This might suggest the necessity of periodic disturbance mechanisms within a M. macrophylla population site to optimally sustain it. The author hopes that further research will yield a better understanding of the ecology of this species.  

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Literature Cited 

Doyle, A.M. 1989. Unpubl. Honor Thesis. Magnolia Macrophylla: Population structure, reproductive strategies and the disturbance regime of Mill Creek Forest. Tulane University.

 N.C. Natural Heritage program records for Magnolia macrophylla sites. 1998. North Carolina Dept. of Environment and Natural Resources. 

Raynal, C.E. 1938. Bigleaf magnolia. American Forests. 44:204-240. 

Sargent, C.S. 1947. The silva of North America. Vol. I. Peter Smith. New York. 

Schafale, M.P. and A.S. Weakly. 1990. Classification of the natural communities of N.C. Third Approximation.

Thein, L.B. 1974. Floral biology of magnolia. Amer. J. Bot. 61 (10): 1037-1045. 

Williams, C. 1999. Andre Michaux and the discovery of Magnolia macrophylla in North Carolina. Castanea 64(1):

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Acknowledgement for Grant Support 

Blumenthal Foundation of Charlotte, NC 

Fidelity National Bank of Atlanta 

Berlin America Co. 



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