1. INTRODUCTION Ecology 270 students investigated the age and size distribution, abundance, and mortality patterns of Eastern white pines in a mixed-species stand in Range Pond State Park, Poland, Maine. Although pines tolerate poor soils, they are shade intolerant and need open canopy to get established. White pines are frequently early colonizers of disturbed sites. In New England, typical pine growth averages 8-10 yr to breast height (1.37 m), and then about 30-40 cm/yr thereafter. Pine age is easily determined because they produce a whorl of branches each year at the apical meristem as well as an annual growth ring in the stem. Growth form (shape of tree, relationship of height and stem diameter) is very responsive to light availability; open-grown trees are bushy and look squat whereas trees grown in high densities and under canopies or in shade of other trees tend to be skinny and tall, with foliage concentrated at the top of the stem (Fig. 1). Range Pond State Park (fig. 2) was established in 1970, and since that time there has been no management interventions or cutting in the area. Although records of land use in the park area are not available, USGS aerial photographs from 1949 and 1964 provide some information about changes to the landscape prior to 1970 (fig. 3). In 2003, Bio 270 students conducted a similar study at this site and noted a high mortality of white pines whose stems remain intact and upright. The presence of these stems offered us an unusual opportunity to study the patterns of mortality in the population and how that mortality has altered the local neighborhood environment of the living trees. The goal of this study was to describe the characteristics of the white pine population along Plains Road, Range Pond State Park, and to analyze recent mortality patterns to deduce past and present environmental and biological factors influencing the growth and development of the population, and to predict future dynamics within the stand. ABSTRACT The purpose of this investigation was to describe patterns of age, size, spacing, and mortality of an Eastern white pine stand in Range Pond State Park. All living pines within a 28 m x 36 m plot were measured for age, stem diameter, height, and distance to nearest neighbors (live or dead). Standing dead pines were measured for stem diameter, categorized by height relative to the main canopy height, and assigned to mortality classes based upon the degree of deterioration of the tree. Historical land use of the site was determined by examination of aerial photographs dating back to 1949. The canopy is predominately white pine with a few red maple trees. In contrast, saplings in the understory were primarily red oak, red maple and American beech. The average live pine germinated in 1957 and is now 47 years old (range of 24-67 years); 91% of the population is between 36 and 52 years. The average height of live pines was 19 m with a mean diameter of 28.36 cm at 1.37m (breast height) and a vertical growth rate of nearly one half meter per year (41 cm). Live pine population density in the plot was 556 trees/hectare, yet when the dead standing pine trees are included, density more than triples to 1,796 trees/hectare. Recruitment of white pine was low within the plot and adjacent areas. These seedlings and saplings showed distinct growth suppression: eight years of vertical growth for the average recruit (46 cm) is equivalent to one year of the average tree established in the canopy. The majority of white pines within the plot were dead (69%); the degree of bark and branches deterioration allowed us to compare their relative time since death, from this it seemed evident that mortality occurred first for smallest canopy trees. Furthermore, spatial distribution of white pines within the plot was determined to be random for current and recent past pre- mortality populations, with a significant positive correlation between live stem diameter and mean distance to two nearest live white pine neighbors. Analysis of aerial photographs from 1949 and 1964 indicate the harvesting of mature trees which opened the canopy and allowed white pine, a shade intolerant species, to colonize the site and grow well. Current canopy structure is well developed and light has once again become limited as evidenced by strong suppression of the recent recruits into the understory. We conclude that over the past half a century the availability of light, and more recently patterns of precipitation and drought have greatly influenced the dynamics of the eastern white pine population. MATERIALS AND METHODS Site Description The stand studied was located at W 70° 21’31’’ N 44° 02’44.1’’ along Plains Road, on the northeastern side of Range Pond State Park in Poland, Maine. The site is relatively flat and dry, and the stand appeared relatively homogenous throughout. The soil is characterized as Adams Series sandy loam, a well drained, nutrient-poor soil. White pines, most of which were dead, dominated the study area. Hardwood species such as maple, sugar maple, beech and oak were also present, mostly as saplings, in the area. Sampling Plan White pines were sampled within a 28 m x 36 m plot (1008 m 2 ) located approximately 20 m from the Plains Road so as to avoid edge effects. All white pine (live or dead) 1.37 m or taller were measured for: DBH: stem diameter at breast height (1.37 m), Stem height (LIVE: determined by percent slope triangulation using an Abney level; DEAD: categorized by height class – see criteria). Age, as determined either by counting the annual branch whorls or from a stem core to count the growth rings (dead trees could not be aged). Mortality class: live, or categorized based upon the degree of decomposition (see criteria) Recruitment: For seedling and sapling pines, not otherwise measured, the stem height and age were determined. Spacing and Spatial Distribution: The average distance to the two nearest neighbor (NND) pines (live or dead) was measured for all white pine trees (live or dead); for live pines, the average distance to the two living pine neighbors was also determined. In addition, an index of dispersion was calculated based upon the distance to the nearest neighbor for live trees only, and for all trees to ascertain whether the mortality of pines had altered the spatial distribution pattern for surviving trees. Mortality Class Criteria 1. Live tree (green needles visible) 2. Tree holds needles (brown) or small twigs; bark intact 3. Most twigs gone, but major branches are still present; more than 50% of main trunk bark is intact. 4. Less than 50% of the main trunk bark is intact or a significant portion of the tree top is missing. 5. Tree leaning to the point that it is being partially supported by another tree. Figure 1. Growth form of pines under A) crowded conditions and B) open field grown conditions. 1. Tree top intact, in highest local canopy level. 7. Indeterminate due to condition of tree. Height Class Criteria (dead pines and hardwoods) Figure 9. Stem diameter at breast height as a function of average distance to nearest neighbor for live Eastern white pine. The relationship indicates that increasing space between trees leads to a larger stem diameter, suggesting that trees spaced farther apart do more secondary growth. There was a random distribution of white pines within the plot for recent and current populations of pines. Dashed line = 95% CI for slope of best fit line. Figure 10. >80 % of the hardwoods were recently established and sapling sized individuals have a DBH of less than 4cm. There are relatively few canopy and subcanopy sized trees. This would indicate the stand is in an early successional stage typical of New England mixed pine-hardwood forests. More than likely the climax forest will be dominated by hardwoods and not pines. Figure 4. Age structure of the Eastern white pine population on the study plot is based on the year the tree was established. Two major age groups have been identified. The younger trees established after a majority of the initial forest, from 1949, were cut, and were believed to grow in conditions with high light availability. The younger trees, however, would have been subject to greater limitation of light as it had to establish itself under the cover of the older trees. Primary growth rates where higher among the young trees in order to reach canopy height. Figure 7. A) Averaged annual increase in stem height (height/age) vs. current age. Younger trees have done proportionally more primary growth per year over their life times (Inset; MW U = 105, p = 0.003) which is a growth pattern typical of shaded or crowded understory pines. B) Typical view of pines within the plot showing internode distances consistent with this pattern of growth. Figure 8. Seedling and sapling pines were primarily located along the border between the plot and Plains Road. The relationship indicates that these trees are being suppressed due to low light availability. Typical early growth of white pines in New England is 8-10 years to a height of 1.37m (Breast height). Figure 3. Aerial photographs of Range Pond State Park area A) circa 1949 and B) 1964. Red box indicates position of current study plot. Between 1949 and 1964 there was harvesting of previous mature trees as indicated by the prominence of the row of trees along the road, highlighted in the green box. Population Characteristics Figure 2. Topographical map of Range Pond State Area. The plot (yellow box) is located 14 km SW of Lewiston, Maine, United States (North 44°2’, 41”; West 21°31’4”). Photos courtesy of the U.S. Geological Survey (http://terraserver-usa.com). Figure 5. A) Height frequency and B) DBH frequency of live pines. The highest local canopy was approximately 19-21 m. Figure 11. The frequency of dead white pines (Pinus strobus) among mortality classes. N=122 trees. A majority of dead pines were classified as having severe deterioration with 50% or less of main trunk bark intact (class 3 and 4) or being partially support by a neighboring tree (class 5). Figure 12. Both A) height class and B) stem diameter at breast height of dead pines across mortality classes indicate that smaller pines have a more advanced state of decomposition suggesting that they died longer ago. Growth Characteristics AB Mortality Patterns The overall mortality of pines was 69% of the standing stems and was concentrated among smaller trees. AB Hardwood Characteristics Why the Mortality? Shade intolerance of white pines Sandy low nutrient soil with poor moisture retention Lower than average precipitation and periodic, severe droughts over last 30 years (Fig. 13) Figure 13. A) Drought index and B) precipitation data from Maine, 1900 to present. A B Other species occurring at low densities included American beech, red oak, red maple, yellow birch, ash. The overall density of all hardwood species in the plot was 1,349 trees/hectare, roughly 2.5x the density of live pines. The overall live pine density in the plot is currently 556 trees/hectare. AB Individual growth appears to be a function of light availability and spacing. Acknowledgements We appreciate the help from all the students in the 2003 Bio 270 class for taking the time and effort to obtain the data needed. Thanks also to Sharon Kinsman for guidance and help over the course of the study. A special thanks to Greg Anderson for his technological support, time, and chocolate! Thanks to the class TA’s for their help out in the field and back in the lab. We gratefully acknowledge the Maine Sate Department of Conservation, Bureau of Parks and Lands, for allowing access to Range Pond State Park. The USDA Service Office in Lewiston for allowing to their collection of aerial photos for which were most helpful. Age, Size, Spacing, Density, and Mortality Patterns of an Eastern White Pine (Pinus strobus) Stand in Range Pond State Park, Poland, Maine Brian Dupee, Katie King, Hallie Preston, and Lissa Moses (left to right) Bio 270 Ecology Bates College