Evaluation of a Demonstration Management Project in a White Pine (Evaluation of a Demonstration Management Project in a White Pine (Pinus strobusPinus strobus)-Dominated Stand in )-Dominated Stand in Range Pond State Park, Poland, Maine: Stand Characteristics Before and After a Selective HarvestRange Pond State Park, Poland, Maine: Stand Characteristics Before and After a Selective Harvest

Bio 270 Ecology and Evolution – Winter 2007 – Bates CollegeBio 270 Ecology and Evolution – Winter 2007 – Bates College

AbstractAbstract

IntroductionIntroduction

MethodsMethods ConclusionsConclusions

ResultsResults

References CitedReferences Cited

AcknowledgementsAcknowledgements

A white pine-dominated forest located in Range Pond State Park along Plains Road has been the subject of study by Bio 270 (Ecology) since 2003. The stand was characterized by fairly even age (45-55 years) and size (18-23 m tall, 25-45 cm stem diameters), a random spatial distribution of stems, and a stand density of 408 living pines per hectare. Initial studies on the site indicated there was a high mortality rate – approximately 60-65% - among the mature trees (Bio 270, unpublished data, 2003-2004.) Accurate mortality estimates were possible because a majority of the dead stems were still standing at the time of the studies. Size and decomposition characteristics of the dead trees indicated that most of the mortality had occurred in the recent past. Subsequent studies strongly suggested that the cause of mortality was a combination of factors: poor soil quality on the site (Adams series sandy loam with poor water retention characteristics), a series of drought years during the 90’s which led to “white pine decline”, and the Ice Storm of 1998. Similar patterns of mortality have been documented in other parts of southern Maine (http://extension.unh.edu/forestry/Docs/livingsto.pdf.)

In 2005, the State of Maine, Department of Conservation, Bureau of Parks and Lands identified Range Pond State Park as one of several demonstration sites for intensive management of state park forests to improve the forest quality and wildlife habitats, enrich visitor experiences by creating or improving interpretative trail systems, and to generate revenue to help fund park maintenance and operations. At Range Pond State Park, our study site (Fig. 1) is situated in one of the management areas, and in spring of 2006, the stand was selectively harvested. Because we had data characterizing the stand immediately prior to the harvest, we were in an excellent position to evaluate the effect of the harvest on stand characteristics and to determine whether the management activities would meet the intended goals for this site which included, 1) removal of deadwood, 2) thinning the stand to give it a more old-growth, late-successional appearance, 3) improve the growth of the remaining live population, and, 4) improve establishment and growth of seedling pines in the stand. In late January 2007, the Bio 270 (Ecology and Evolution) class from Bates College collected population data for both the mature pines and seedlings to determine post-harvest characteristics of the stand and to evaluate the subsequent effect of the harvest on seedling growth and recruitment.

A previously studied white pine-dominated stand in Range Pond State Park was studied in January 2007 to determine the effects of an prescribed management selective harvest (spring 2006) on population characteristics of the mature pine, and growth and recruitment of pine seedlings. Live pines in an established 30 x 40 m plot were measured for age and size, spacing, and spatial distribution. Dead trees were characterized by size only. Seedlings were measured for age, height, annual increments of primary growth, and density in four, paired, low and high-density 2.32m2 quadrats. Data collected in 2007 were contrasted with similar data from 2006 collected prior to the harvest. The harvest removed 52% of the dead pine stems and 31% of the life pines in the plot. Although the mean age of living pines was shifted approximately 4 years older (48 YO in 2006 vs. 52 YO in 2007), the harvest did not alter the mean size of trees. The mean distance to the nearest two neighbors among live pines increased from 3.1 m in 2006 to 4.5 m in 2007. The spatial distribution of trees was random before and after the harvest, although the Index of Aggregation has shifted slightly toward a more regular distribution. Seedling growth has yet to respond to the release, but a significant increase in age 1 seedlings was observed following the harvest. Growth responses in mature and seedling pines should become more detectable in subsequent years. The new characteristics of the population and the increased seedling establishment indicate that the management activities have moved the stand characteristics in a direction toward the stated goals.

Sampling was carried out in January 2007, in a previously studied 30 x 40 plot, located along the northeast boundary of the park on Plains Road (Fig. 1). All living white pine of 1.37 m (breast height) and taller (n = 33 in 2007) were measured for age, height, stem diameter at breast height (DBH), and the distances to their two nearest neighbor pines. Dead pines were categorized in height classes relative to the local canopy height (Fig. 2) and measured for DBH. Stand density was calculated, and using the nearest neighbor data, the spatial distribution of stems was determined based on an Index of Aggregation using nearest neighbor data (Clark and Evans 1956). Results from 2007 were contrasted with the data collected in 2006 (pre-harvest) from the same plot to assess the changes to the population characteristics using frequency analyses and comparative hypothesis tests (ANOVA, t-tests). Four, paired seedling quadrats (1.52 x 1.52 m) – one of high seedling density and one low – were arbitrarily placed in and around the main plot. One pair was located out of the harvest zone and served as a non-harvest area control for growth and recruitment analyses. All pine seedlings within each qaudrat were measured for age, height, and individual internode lengths (for specific primary growth history analysis.)

Figure 2. Height categories used to classify heights of dead white pines relative to local average canopy height (~21-23 m in 2007).

Age and Size Structure: Age and Size Structure: Live PinesLive Pines

Seedling Recruitment and Seedling Recruitment and GrowthGrowth

Spacing and Spatial Spacing and Spatial DistributionDistribution

Size Structure: Dead PinesSize Structure: Dead Pines

Bormann, F. H. 1965. Changes in the growth pattern of white pine trees undergoing suppression. Ecology 46(3):269-277.

Clark, P.J. and Evans, F.C. 1954. Distance to nearest neighbor as a measure of spatial relationships in populations. Ecology 35: 445-453.

Lancaster, K.F. and W.B.Leak. 1978. A silvicultural guide for white pine in the northeast. Forest Service Tech. Rpt. NE-41 1978. U.S Dept. of Agriculture. 13 pp.

http://extension.unh.edu/forestry/Docs/livingsto.pdf : Presentation based on joint research by U-Maine Forestry Department, Maine Forest Service, SWOAM, the U.S. Forest Service, and S.W. Cole Engineering, Inc. addressing white pine decline in Maine. Livingston, W.H., Granger, G., Fires, M., Trial, H., Struble, D., Steinman, J. and S. Howell. December 2005.

Figure 3. Typical stand appearance (A) prior to the harvestand (B) after the harvest.

32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 780

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2006 n = 44 trees 2007 n = 29 trees

Figure 4. Age distribution of white pines in 2006 (pre-harvest) and 2007(post-harvest). The harvest, while it primarily removed younger trees (40-44 yo),removed trees across all age classes. The presence of the two older trees in2007 is likely due to error in re-establishing the plot. The average age of trees in theplot has shifted from 48 YO in 2006 to 52 YO in 2007 (unpaired t-test, p = 0.0229)as a result of the harvest.

Age Class

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10 12 14 16 18 20 22 24 260

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202006 n = 46 trees2007 n = 34 trees

Figure 5. Height frequency of white pines in 2006 and 2007. The harvest targetedshorter, subcanopy trees. Sampling error associated with height measurementlikely explains the "increase" in pines in the 20 m category in 2007 - these are mostlikely the same trees that appear as 22 m trees in 2006. Height was determined bypercent slope triangulation using an Abney level. Overall, the harvest had no effect onmean height in the stand which is approximately 19.4 m.

Height Class (m)

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5 10 15 20 25 30 35 40 45 50 550

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2006 n = 49 trees

2007 n = 34 trees

Figure 6. Stem diameter at breast height (DBH) of white pines in 2006 and2007. The harvest removed approximately 1/3rd of the trees across all sizecategories with no change in mean DBH overall (~31.7 cm). Breast heightis 1.37 m (4.5 ft) above ground.

DBH Class (cm)

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25 2006 n = 58 trees 2007 n = 31 trees

Figure 7. Height class frequency of dead pines before and after theharvest. The harvest removed most of the stems of 10 m and taller.Note also the sharp increase in the number of fallen or leaning stemsin the post-harvest sample (class 1). Mean canopy height at time ofharvest was approximately 19-21 m.

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Figure 8. Stem diameter frequency among dead pines before andafter the harvest. The harvest removed all dead stems above 20 cmdiameter.

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Pre-mortality ca.'92 Post-mortality ca. '98 Post-harvest ca. '070

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Figure 9. Canopy appearance in the study area (A) prior to natural mortality ca.1992, (B) after the natural mortality ca. 1998, and (C) following the 2006 harvest.(D) Mean distance ( SEM) to the two nearest neighbor white pines correspondingto the timepoints in A-C. "Pre-mortality" represents the spacing of all stems (liveand dead) in the 2006 sample."Post-mortality" reflects the condition of live stemsin 2006 prior to the harvest, but after accounting for natural mortality. "Post-harvest"is the spacing of live pine trees at present, following the May 2006 harvest. Allmeans significantly different (Kruskal-Wallis test, p < 0.0001)

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1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.50

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252006 n = 49 trees

2007 n = 33 trees

Figure 10. Frequency of the mean distance to the two nearest neighbor whitepines before (2006) and after the harvest (2007). The harvest dramaticallyincreased the average spacing among trees and improved canopy openness.nearest neighbor distances averaged ~3.0 m in 2006 and 4.5 m in 2007.

Mean Nearest Neighbor Distance (m)

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Figure 11. An older seedling patch associated with a canopy gap created by natural mortality in the stand. Seedlings germinated in 2006 post-harvest are now found throughout the site.

The most obvious effects of the harvest in 2006 were to open the forest and to increase the spacing (NND) among the mature trees (Fig. 3). Age and size of mature pines became more even; mean age among survivors increased whereas average size of pines was unchanged (Table 1). Overall stem density was reduced by 31% (live pines) and 52% (dead pines).

The harvest altered the age structure by removing many younger trees (ages 41-45) and cropping all other age groups(Fig 4). Distribution of heights was much more uniform after the harvest (Fig. 5) whereas the distribution of stem diameterremained relatively unchanged (Fig. 6).

The number of dead pine stems was reduced by 52%and of those removed, most were the larger canopy and sub-canopy sized trees (Fig. 7). Stem diameter frequency analysis indicates that all stems over 23 cm were removed as well as a majority of stems 7-18 cm diameter (Fig. 8)

The presence of virtually all dead pines as standing stems in 2006, following many years of mortality, permitted us to compare spacing of trees for pre-mortality,post-mortality, and post-harvest conditions. Aerial photos of the study area thatcorrespond to these different stand conditions clearly show an increase in canopyopenness over time (Fig. 9 A-C). Further, absolute spacing of trees (NND) increased significantly at each stage (Fig. 9 D). The range of nearest neighbor distances also increased dramatically as a result of the harvest (Fig. 10).

Due to the recruitment strategy (gap invaders) and natural thinning processes characteristic of white pine populations, there is a tendency for spatial arrangements of the trees to progress from being somewhat clumped, to being randomly arrayed, to being more uniformly arrayed (old growth stands, low density of stems). We calculated an Index of Aggregation (Clark and Evans 1954) based on the closest nearest neighbordistance for pre-mortality, post-mortality, and post-harvest stand conditions to see if the spatial distribution had changed over time. In all conditions, the spatial arrangement of pine stems was found to be random (Table 2), although post-harvest, the Index tended slightly in a direction toward uniform.

Seedling plots of high density were sampled throughout the study area and were clearly associated with older gaps in the canopy dating back to the late ’90’s (Fig. 11). Prior to the harvest, few seedlings were found outside of these patches. Seedling establishment patterns clearly show that since the harvest, most new seedlings are found outside the older gaps (low density plots), and that a surge in seedling establishment has occurred since the harvest (Fig. 12) throughout the stand. Seedlings in the stand allexhibit suppressed growth (Bormann 1965) (Fig. 13) and as yet, do not show an expected primary growth response to the opening of the canopy (Fig. 14).

Future Future StudiesStudies

The management plans initial goal of altering the population structure and density to increase spacing and open the canopy has been achieved. The population of mature pines is more uniform in all aspects than prior to the harvest.

Decreased canopy density should, in the near term, lead to better growth among the surviving pines as competitionfor light at the canopy level is reduced and penetration of light to the forest floor is increased. We would expect to detect improved and more uniform secondary growth (stem diameter and foliage density) within a few years. Planned follow-up thinning harvests in 10-15 years should help maintain and promote good growth in the pines.

The many dead stems and snags that remain in the stand should provide enhanced wildlife habitat (e.g., bird perches).

The removal of most of the large, dead trees improves the aesthetic appearance of the stand, and will improve safety for park visitors.

Seedling recruitment may have been improved as a directresult of thinning the stand and opening the canopy; establishment of age 1 seedlings throughout the stand supports this. Seedling densities in subsequent years should continue to increase if so.

Growth response to release among seedlings is not yetdetectable. We anticipate that measurable improvements in primary growth increments, indexed to mean growth over 2003-2005, will be found among current age 6-9 YO seedlings as early as 2008. Follow-up canopy thinning in future years will be needed to maintain improved growth of younger trees.

The effect of seedling density (high density vs. low densityplots) on primary growth is not yet clear. Nor were differences between uncut and cut over areas. Because the seedlings mustadapt to the new conditions, and because a large number are in their early slow growth phase, growth differences related to population density and canopy density may only become detectable after a few more years of growth.

The Ecology and Evolution class (Bio 270) from Bates College will continue to monitor the white pine population characteristics into the foreseeable future. The results from our 2007 sample will serve as the baseline for measuring changes in growth patterns among the mature and seedling segments of the population. Because we expect to see improved secondary growth, we will begin monitoring the height/DBH ratio and basal area, and compare them against data from 2003 – 2007.

Much of our attention will shift to following the seedling population recruitment and growth patterns in relation to cut vs. uncut areas, population density, and age. We anticipate that both recruitment and growth will increase within the next few years as the seedlings shift away from suppressed growth patterns and realize their biological growth potential as stand conditions improve.

The Biology Department of Bates College and the students and staff of Bio 270 gratefully acknowledge the Maine Department of Conservation, Bureau of Parks and Lands, and Range Pond State Park personnel for permission and encouragement to carry out these studies. All students of Bio 270 from 2003 to 2006 are thanked for their commitment to this study and their contributions. This poster was prepared by Greg Anderson based on the 2007 Bio 270 class study.

Figure 1. Location of study site in Range Pond State Park. Inset color aerial photo shows current stand appearance. (Aerial photo courtesy of Eben Sypitkowski, Bates College, Dept. of Biology.)

1 2 3 4 5 6 7 8 90

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Figure 13. Age-specific average annual increment of primary (height) growth(mean height/age ratio SD) of white pine seedlings in January 2007. Samplesize is given as the number over each mean. The data indicate that post-5 YOseedlings exhibit suppressed growth. Growth through age 5 seems to beindependent of local conditions. Seedlings growing under good conditions shouldattain 1.37 m (4.5 feet) height within 7-10 years in New England and may average30-35 cm (1 foot) per year thereafter (Lancaster and Leak 1978). The 7-9 YOseedlings on this site are approximately 0.55 - 0.65 m tall and average just over 7cm/year primary growth (red dashed line). The expected effect of the release willbe increased annual primary growth in all seedlings of age 6 and older.

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Figure 12. White pine seedling recruitment patterns in (A) oldgaps (high density plots) and (B) younger gaps (low densityplots). Low density plots were sited in areas that, prior to the2006 harvest, were subject to a more dense canopy cover. Thelarger relative recruitment of seedlings in low density plots mayindicate that the increased canopy openness is allowing moreseedlings to become established. The actual density (#/m2) ofage 1 seedlings is given above the 2006 year bars in eachgraph.

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Age 6 Age 7 Age 8 Age 90

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Figure 14. The 2006 primary leader length (mean SEM, n givenabove error bar) as a percentage of the mean of primary growthinternodes for 2003-2005 by seedling age class. The seedlings seemto be not yet responding to release in the first growing season after thecut. Interpretation of Age 9 growth is limited by small sample size.Ages 6-8 show no significant differences among the means(Kruskal-Wallis test, p = 0.7867; Age 9 data were excluded from theanalysis due to small sample size).

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