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How are the forests changing over time?

Iesha Brooks, Stephany Cook, Grace Harsha, Jamie Oriez, Vanessa Fox

Introduction

The DePauw Nature Park provides a home to many species of plants and animals. The park also serves as a valuable resource for students and Greencastle community members as a place to conduct research, learn about ecology, engage in recreational activities, and appreciate its beauty and history. Prior research started in 2008 by Vanessa Fox and students measured forest structure and composition. In 2015, we continued the project to study the change in forest structure and composition over time.

research questions

  • How has the forest changed in the past eight years?
  • Are there differences in composition among the trees, saplings, and seedlings? 
  • Are there differences in survival, regeneration, and recruitment among tree species?
  • How will the forests change in the future?

Study sites

We collected data in two sites in the DePauw Nature Park:  Quarry Hillside and Quarry South.  Quarry Hillside is located on a steep hill just above the Rail Trail.  Quarry South is located at the south end of the Nature Park.  The area of both sites combined is 3.7 hectares, which is equivalent to the area of seven football fields.

Methods

Plots were initially set up in 2008. Each plot is 10m x 10m. Within each plot, we identified, mapped, tagged and measured the diameter of all trees, saplings, and shrubs that were ≥ 1.0 cm dbh (diameter at breast height, 1.38 m from the ground). We remeasured all trees and saplings in 2015. We also measured the diameter and height of all seedlings. We documented growth, survival, and recruitment of new trees into the population. We identified, tagged, measured, and mapped 2,020 trees, 6,125 saplings, and 7,874 seedlings from 2008 to 2015.

Are there differences in composition among the trees, saplings, and seedlings?  Yes

Trees:  Sugar maple is most abundant.  Elm, cherry and walnut are also common.  Red oak, sassafras, and ash are less common.  Buckeye was rare.  Red oak and buckeye are the largest in diameter.  Sugar maple and elm are smaller in diameter.  Saplings:  Sugar maple is most abundant.  Elm, ash, and buckeye are also common.  Red oak and walnut are almost entirely absent.  The “other” category includes pawpaw, spicebush, and grape.  Seedlings:  Ash is most abundant, followed by sassafras, elm, and buckeye.  Cherry, walnut, and red oak are very uncommon. 

Are there differences in survival , regeneration, and recruitment among tree species? Yes

Sugar maple is dominant among the trees and saplings but is less common among the seedlings.  Sugar maple trees have very high survival.  Elm is common among the trees and has moderate recruitment and regeneration.  However, elm trees have high mortality.  30% of elm trees died over a seven-year period.  Cherry, walnut, and red oak are common among the trees but have almost no regeneration or recruitment.  Ash  is not common among the trees but is superabundant among the seedlings.  Ash trees have high survival.  Buckeye is rare among the trees but is abundant among the saplings and seedlings.  Buckeye saplings have very high survival. 

How will the forests change in the future?

Sugar maple will probably continue to dominate the forests in the DePauw Nature Park.  Sugar maple has high survival, and modest recruitment and regeneration.  Cherry, walnut, and red oak trees have high survival, but if these trees die, they are unlikely to replace themselves.  Ash trees have high survival and very high recruitment and regeneration.  There are currently no signs of infection by the emerald ash borer, but this pest has killed ash trees on DePauw’s main campus and has the potential to move in and wipe out the ash trees in the Nature Park.  If this happens, the ecological niche occupied by ash will most likely be filled by sugar maple.  Elm trees seem to have a shorter life span and higher mortality than other tree species, but elm trees will continue to exist in the forests because of their moderate regeneration and recruitment.  Buckeye will continue to exist in the understory given their high abundance and survival.  Our results are typical of patterns seen in other studies of forest structure and composition in eastern deciduous forests.