INTRODUCTION
Some tree species, such as oaks and hickories, produce large seed crops at irregular intervals of 3 to 12 years. Seed production in these species is often synchronous over large regions (Koenig et al. 1996). This type of reproductive strategy is called masting, and though efforts have been made to determine the evolutionary significance of masting, no one theory has yet been able to account for this phenomenon (Janzen 1969, Silvertown 1980, Sork 1993).
Oak-hickory forests dominate much of eastern North America and their nuts provide an abundant, but unpredictable food source for seed-eating animals. Nut crops may provide an inexhaustible food supply one year, but no food the following year. Many birds and mammals utilize mast, but the degree to which their population biology is affected by mast availability varies greatly (Christisen and Korschgen 1955, Bock and Lepthien 1976, Ostfeld et al. 1996, Smith and Scarlett 1987). For some, a poor mast crop simply means that the animal must use other food items more than they would if there were a large mast crop (Harlow et al. 1975, Williams and Batzli 1979a). Others rely heavily on mast as a winter food source, and a poor mast crop may lead to reduced survival and perhaps poor reproductive performance (Koenig and Mumme 1987, Wolff 1996).
In turn, birds and mammals play a large role in the reproductive success of mast producing trees. Birds, mammals and insects eat a large proportion of the mast produced by a tree. Although most birds and mammals are seed predators, some cache seeds and are effective at dispersing seeds to locations favorable for germination. Thus, the relationship between mast producing trees and the animals that utilize mast is reciprocal and is an important force driving the evolution of species within the oak-hickory forest ecosystem.

 PROJECT SUMMARY
Purpose
The main purpose of my research is to examine the relationship between mast producing trees, such as oaks and hickories, and bird and mammal species that consume mast. The project has three main foci:
1. Patterns of acorn production: degree and scale of synchrony
2.  Effects of fluctuating seed crops on bird and mammal populations
3. Roles of birds and mammals in seed dispersal of mast producing trees

Study Site
My study site is located in the nature preserve area of McDowell Park on Lake Wylie in Mecklenberg County, North Carolina. The area of the park is about 400 ha, and about 70% of that area is oak-hickory forest. The site is dominated by white oak (Quercus alba) and red oak (Q. rubra) forests with pines found primarily along ridges. I have been working in cooperation with the Mecklenburg County Parks and Recreation Department and may extend the project to other parks within their system.

Funding
Initial funding for this project was provided by the USC-Lancaster Research and Productive Scholarship Grant. Funding for video and telemetry equipment was received through a grant from the South Carolina Research Institute.

Principal Investigator
I am an Assistant Professor of Biology in my 3rd year at the University of South Carolina at Lancaster. My most recent research has been in small mammal population biology during my doctoral work at Washington State University. However, this project is a return to interests that I pursued during my M.S. degree at the University of Arkansas. There, I investigated acorn use by blue jays (Cyanocitta cristata) and red-headed woodpeckers (Melanerpes erythrocephalus).
 ACORN PRODUCTION
Potentially the most important question about the effect of masting on population biology of birds and mammals remains unanswered. On what scale do trees mast? The scale on which species mast will determine how far animals will have to go to find a good mast crop. Since weather appears to have a large influence on the timing of mast crops, we might expect synchrony over large areas (Sork pers. comm.). Knowing the scale at which masting occurs is necessary to understand how birds and mammals are affected by seed crop variation. Better data on spatial patterns of mast production is needed, especially in eastern deciduous forests.
For communities that contain two or more dominant masting species another question arises. To what extent do different masting species within a community synchronize seed production? The effect of masting on the food supply of mast-eating species will be less if mast crops of different species are offset, and if there is usually a nut crop from at least one masting species. If masting species are simply responding to similar environmental cues to synchronize reproduction within the species (Norton and Kelly 1988), we might expect mixed species forests to be synchronized.

Research Question
In fall 1999 I began a long-term project dedicated to monitoring mast (primarily acorn) production on my study site. The data will be used in association with data from similar projects in South and North Carolina to examine masting patterns on several scales.
Specific questions addressed are:
1. On what scale does masting occur within nut-bearing species?
2. To what degree is masting synchronized between tree species?
The core of my research is sampling mast production during fall and winter on a yearly basis. This will provide information on the degree of intra- and inter-specific synchrony of mast production. Also, I plan to share my data with other mast production studies in the area to determine the scale at which masting occurs.

Methods
Mast Collection – My sampling design has been modeled after similar studies conducted in Missouri, South Carolina, southern Appalachia.
I currently have four 20x50m mast sampling plots on the site. There are sixty conical acorn traps on each plot. Traps are apportioned based on crown area. An average-sized tree has four traps—larger trees have more and smaller trees less based on crown area. All traps are emptied every two weeks beginning in early September, and every week, once acorns start to fall, through the end of December. Acorns from each tree are bagged together, labeled, and stored in a freezer until processing. I hope to add two more mast plots in the summer of 2001.
Mast Processing – During processing, acorn samples are separated into aborted and mature nuts, and the total of each category is recorded. Aborted nuts are then discarded. The mass of mature nuts without the cap (or husk for hickory nuts) is recorded. Nuts are then opened to determine their condition. Nut condition is classified as intact, damaged by insects, damaged by vertebrates, or damaged by unknown agents. Endosperm (edible part of acorn) is then extracted, weighed, and oven-dried for six days; dry weight is then recorded for nuts of each category.
 INFLUENCE OF MASTING ON BIRD AND MAMMAL POPULATIONS
Specialists vs. Generalists
Population fluctuations are generally greatest for species that are most specialized on mast (Watts 1969, Smith 1986, Smith and Scarlett 1987). Species that depend almost completely on mast are rare. Many birds and mammals show higher survivorship and reproduction in mast years, but are not completely dependent on mast.  Mice (Peromyscus sp.), chipmunks (Tamias striatus), red squirrels (Tamiasciurus hudsonicus), and white-tailed deer (Odocoileus virginianus) show population increases the year after a large seed crop, but may maintain populations at moderate densities in non-mast years (Harlow et al. 1975, Rusch and Reeder 1978, Ostfeld et al. 1996, Wolff 1996).
Although many animals utilize mast extensively when it is available, some are able to include higher proportions of other food items in their diet when mast crops fail. Crows (Corvus brachyrhynchos) and raccoons (Procyon lotor) are true generalists and utilize a wide variety of food items (Christisen and Korschgen 1955). Although these animals use acorns significantly when available, they are not likely to suffer greatly in years of low acorn abundance due to the diversity of their diet.
Animal mobility
Some species get around the difficulties of poor mast years by tracking mast crops. In general, birds are more mobile than mammals and can move long distances when faced with a bad mast year. Mammals are less mobile, and their populations often fluctuate with the number of seeds produced by masting trees. Mammals such as deer, squirrels, and deer mice will move from one habitat to another to find more abundant food (Gashwiler 1979, Harlow et al. 1975, Ostfeld et al. 1996), but cannot track mast crops over vast areas like birds (Smith and Balda 1979).
Research Question
I propose that the response of any particular mast-eating species to fluctuations in mast abundance will be determined by the species’ degree of specialization on mast and the relative mobility of the species. To test this hypothesis I will answer the following questions:
1. Do mobile species have better survivorship and reproduction in years of low mast abundance than less mobile species?
2. Are species that include a high proportion of mast in their winter diet more likely to show poor survival and reproduction after a poor mast?
3. Do mast-eating species switch to soft mast (fruit) in years of poor mast abundance?
Methods
In fall 1999 I began a long-term study of white-footed mice (Peromyscus leucopus) to determine how population size and demography fluctuate in relation to acorn abundance. This type of study requires many years of data to be able to identify patterns; therefore, I plan to continue acorn censusing and small mammal trapping indefinitely to establish a long-term data set. In subsequent years, I will include studies other focal species of birds and mammals differing in their degree of specialization and mobility to identify differences in their response to mast fluctuations.
I have established one 3.24 ha small mammal grid on the study site. One Sherman live trap is placed at each grid point on a 12x12 grid with 15-m spacing (144 traps total). Traps are opened in the evenings and checked in the mornings for three days. Mice are marked, weighed, aged, sexed, and released at the point of capture. Trapping sessions are run every month during the fall, once in February, and again in May.
In addition to small mammal trapping, I have placed nest boxes at 30-m intervals on the trapping grid. The 36 boxes are intended to be used by Peromyscus following the design suggested by Wolff (1996). Peromyscus commonly use nest boxes in northern forests, but the mice on my site have yet to use the nest boxes.
Over the next year, I plan to construct and put out flying squirrel boxes. These will be used for monitoring squirrel populations as well as examining the role flying squirrels play in acorn dispersal. A miniature camera system will be used to monitor nest boxes and natural nests.
 

SEED DISPERSAL
Seed production and survival are critical elements of the reproductive strategy of the tree. Though much information is available on what species eat mast seeds (Van Dersal 1940, Christisen and Korschgen 1955), little is known about the role birds and mammals play in dispersing mast. Certainly, many animals consume seeds, thus acting as seed predators and negatively effecting seed survival. But some animals store seeds in caches for later consumption or they may drop seeds on their way to cache sites. These animals are potential seed dispersers. In eastern deciduous forests, only one species has been identified as an important mast seed disperser. Blue jays store large numbers of acorns in fall, moving them long distances and often to sites favorable for germination and seedling survival. Several other species (squirrels, mice, woodpeckers, etc.) also store mast, but the degree to which these species disperse seeds has received little attention.

New Research
In the fall of 2001 I will begin an acorn dispersal study. The first part of this study will focus on acorn handling behavior of white-footed mice. Using an infrared video monitoring system I will determine how far mice move acorns, the kinds of sites they use for acorn storage, and the effect of acorn handling on the viability of the seeds. I will also use fluorescent powder tracking techniques to supplement video monitoring in determining storage sites.
I also have funding for a study on acorn dispersal by gray and flying squirrels. In this study, I will use video and radio-tracking equipment to determine seed handling and dispersal behaviors of squirrels. This work will not begin until after 2001.
 LITERATURE CITED
Bock, C. E. and L. W. Lepthien. 1976. Synchronous eruptions of boreal seed-eating birds. Am. Nat. 110: 559-571.
Christisen, D. M. and L. J. Korschgen. 1955. Acorn yields and wildlife usage in Missouri. North American Wildlife Conference 20: 337-356.
Gashwiler, J. S. 1979. Deer mouse reproduction and its relationship to the tree seed crop. Amer. Midl. Naturalist 102: 95-104.
Harlow, R. F., J. B. Whelan, H. S. Crawford and J. E. Skeen. 1975. Deer foods during years of oak mast abundance and scarcity. J. Wildl. Manage. 39: 330-336.
Janzen, D. H. 1969. Seed-eaters versus seed size, number, toxicity and dispersal. Evolution 23: 1-27.
Koenig, W. D. , J. M. H. Knops, W. J. Carmen, M. T. Stanback, and R. L. Mumme. 1996. Acorn production by oaks in central coastal California: influence of weather at three levels. Can. J. of For. Res. 26:1677-1683.
Koenig, W. D. and R. L. Mumme. 1987. Population ecology of the cooperatively breeding acorn woodpecker. Princeton, Princeton University Press.
Norton, D. A. and D. Kelly. 1988. Mast seeding over 33 years by Dacrydium cupressinum Lamb. (rimu) (Podocarpaceae) in New Zealand: the importance of economies of scale. Functional Ecology 2: 399-408.
Ostfeld, R. S., C. G. Jones and J. O. Wolff. 1996. Of mice and mast: ecological connections in eastern deciduous forests. BioScience 46: 323-329.
Rusch, D. A. and W. G. Reeder. 1978. Population ecology of Alberta red squirrels. Ecology 59: 400-420.
Silvertown, J. W. 1980. The evolutionary ecology of mast seeding in trees. Biol. J. of the Linn. Soc. 14: 235-250.
Smith, C. C. and R. P. Balda. 1979. Competition among insects, birds and mammals for conifer seeds. American Zoologist 19: 1065-1083.
Smith, K. G. 1986. Winter population dynamics of three species of mast-eating birds in the eastern United States. Wilson Bulletin 98:407-418.
Smith, K. G. and T. Scarlett. 1987. Mast production and winter populations of red-headed woodpeckers and blue jays. J. Wildl. Manage. 51: 459-467.
Sork, V. L., J. Bramble, and O. Sexton. 1993. Ecology of mast-fruiting in three species of North American deciduous oaks. Ecology 74: 528-541.
Van Dersal, W. R. 1940. Utilization of oaks by birds and mammals. J. Wildl. Manage. 4: 404-428.
Watts, C. H. S. 1969. The regulation of wood mouse (Apodemus sylvaticus) numbers in Wytham Woods, Berkshire. J. of Anim. Ecol. 38: 285-304.
Williams, J. B. and G. O. Batzli. 1979b. Competition among bark-foraging birds in central Illinois: experimental evidence. The Condor 81: 122-132.
Wolff, J. O. 1996. Population fluctuations of mast-eating rodents are correlated with production of acorns. J. of Mammal. 77:850-856.