Land Use Change and Current Forest Structure at Howard Falls Land Trust in Northwestern Pennsylvania

Nicholas Baldwin, Ottavio Borgia, Ryan Hnida, Richard Kirby, Melissa Normandeau, Thomas Norway, Andrea Pace, Alyssa Piper, Michael Ritner, Philip Schreiber, Allison Swan, and

Karen S. Eisenhart (Edinboro University, Dept. of Geosciences)

Abstract It is well known that Pennsylvania experienced a dramatic change in land use from agriculture to forest cover during the twentieth century. The purpose of this research project was to determine and analyze the change in land use on the Howard Falls Land Trust property in Erie County, Pennsylvania. We used aerial photographs from 1939, 1959, 1969 and 1992 along with tree cores to estimate the minimum age of forest patches. We subsampled the stand structure of seven plots that are currently forested, and collected tree cores from the largest trees in 5 of the 7 plots for age determination. The property experienced dramatic changes in land use between 1939 and 1992. In 1939, 43% of the land trust area was cultivated and 23% was forested. By 1992, 63% was forested and only 17% was cultivated. We identified forest patches that ranged in age from at least 25 years old to more than 75 years. Considering all seven field plots, tree species richness was 10 (for DBH > 10cm); however, like other studies of post-agriculture landscapes in the eastern U.S., Acer rubrum (red maple) dominated the tree density and basal area in all sampled plots. Few studies of this type have been conducted in Northwest Pennsylvania and this project is the first in Erie County. Our study suggests the Howard Falls Land Trust property is typical for the eastern deciduous forest region.

1992196919591939

2005 color orthophoto

Objectives:•Use air photos and tree cores to estimate time-since-agricultural-abandonment of landscape patches in the Howard Falls landscape.•Collect tree data to characterize patch structure of select plots.•Determine diameter-frequency distribution of each plot.

Study site:The study site (Map 1) is located in Erie County, Pennsylvania at Howard Falls Land Trust. The site is relatively flat and features a gorge on the western extent of the property. Geographically, it falls in the transition between Hemlock-white pine-northern hardwoods and Beech-maple forests as described by Braun (Delcourt & Delcourt, 2000). The region was previously glaciated leaving behind poorly-drained glacial tills, primarily Mill silt loam and Venango silt loam. The climate region is humid continental, with annual precipitation ranging from 94 cm to 109 cm and experiences lake effect snow throughout the winter (Soil Survey, 2013).

Field Sampling:Each sampled plot was 50 m x 8 m. All trees in the plot that were 2.5 cm diameter or larger were recorded individually by species and diameter.

Forest Species Richness and Dominance:•Considering all plots, tree species richness was 10: Acer rubrum (red maple), Fraxinus americana (white ash), Prunus serotina (black cherry), Acer saccharum (sugar maple), Nyssa sylvatica (black gum), Amelanchier arborea (service berry), Quercus rubra (red oak), Fagus grandifolia (American beech), Populus tremuloides (trembling aspen), and Magnolia acuminata (cucumber magnolia). •Acer rubrum dominated both tree density and basal area in all plots. Fraxinus americana is the second most abundant tree species, but occurs only in the younger sites (Figure 1). •Average basal area for the plots is 35 m2/ha and average tree density is .12/m2 (Figure1).

References:Abrams, M. D. (1998). The Red Maple Paradox. BioScience 48: 355-364.Delcourt, H. R., & Delcourt, P. A. (2000). Eastern Deciduous Forests. In Barbour & Billings, North American Terrestrial Vegetation (pp. 358-382).Dyer, J. M. (2009). Land-Use Legacies in a Central Appalachian Forest: Differential Response of Trees and Herbs to Historic Agricultural Practices. Applied Vegetation Science 13:195-206.Whitney, G. G., & DeCant, J. P. (2003). Physical and Historical Determinants of the Pre-and Post-Settlement Forests of Northwestern Pennsylvania. Canadian Journal of Forest Research 33: 1683-1697.Soil Survey Erie County Pennsylvania. (1960). Series 1957, No. 9, United States Department of Agriculture. Archived at www.nrcs.usda.gov.Web Soil Survey. (2013). Web Soil Survey, Natural Resources Conservation Service. Retrieved from websoilsurvey.sc.egov.usda.gov.

Figure 1. Aerial photo of Howard Falls Land Trust. Pie charts are positioned at sampled plot locations and show relative density of the dominant tree species. Plot label indicates estimated minimum age using tree cores, except for plots 4 and 7 where tree cores were not collected. Bar charts show the diameter distribution of all live and dead standing trees at the indicated plots.

Map 2. Penn Pilot aerial photos illustrated against land use categories.

Plot 1Min Age

45

Plot 2Min Age

52

Plot 3Min Age

50

Plot 4Min Age

55(Air Photo Estimate)

Plot 5Min Age

50 Plot 6

Min Age65

Plot 7Min Age

55(Air Photo Estimate)

Estimating Time-Since-Abandonment:•Land use was classified as agriculture, transitional from agriculture to forest, or forest using air photos from 1939, 1959, 1969, and 1992 (Map 2) (following Dyer, 2009). Minimum forest age was estimated based on the earliest known date of transition to forest.•Tree cores were extracted from near the base of at least 10 of the largest trees in five forest patches (see Fig. 1). Cores were mounted, sanded, counted, and cross-dated. The age of the oldest cores at each sampled plot was used to estimate minimum stand age.

Figure 2. Colored polygons in top maps show land use classifications for each aerial photo year. Land use maps for each year were intersected to create a map of forest patches. The resulting forest patch map has been overlaid on the land use maps for each year. The graph below the maps shows percent land use in each classification for each aerial photo year.

Conclusion:In northwestern Pennsylvania, as in other regions of the Eastern Deciduous Forest, Acer rubrum expresses opportunistic establishment and growth following a variety of disturbances (Abrams, 1998). This has resulted in Acer rubrum becoming the dominant species in many young forests (Abrams, 1998). Agricultural areas on the Howard Falls property were allowed to go fallow varying from 44 to 63 years ago, with no statistically significant difference in species richness or Acer rubrum relative density. Acer rubrum is expected post-agriculture as noted above, but species diversity may increase with time (Hibbs, 1983). Our study does not show an increase in diversity in the older stands, however, the oldest stand sampled was only 65 years. Future work will include sampling of older forest areas identified using air photos.

Figure 3. Student counting tree rings and close up of tree core sample under microscope

Figure 4. Students collecting tree seedling data.

Howard Falls Location

Map 1. Locator map of Erie County

Acknowledgements:Funding and Logistical Support: Howard Falls Land Trust and Edinboro University of Geosciences; Field Lab Assistance: Students in GEOG 525 Forest Geography and Conservation;Tree Core Mounts: Mark Wickenheiser