Biology Department

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Examining the Relationship Between Black Walnut and Spicebush

(Juglans nigra and Lindera benzoin: A Case for Associational Resistance?)

The purpose of this experiment is to better understand the relationship between black walnut (Juglans nigra) and spicebush (Lindera benzoin) - most notably how herbivory of spicebush is affected by black walnut.

STATE THE PROBLEM :

Herbivory on spicebush (L. benzoin) tends to be limited when growing in close proximity to black walnut (J. nigra).

MAKE OBSERVATIONS:

  • Spicebush (L. benzoin) growing under or near black walnut (J. nigra) trees shows limited signs of herbivory.
  • Spicebush (L. benzoin) growing in sun and spicebush (L. benzoin) growing in shade have similar herbivory - more away from walnut trees and less when close to walnut.

Background Information (What questions were you trying to answer?):

  • Is there a significant reduction in herbivory when spicebush (L. benzoin) grows under black walnut (J. nigra)?
  • Can the addition of allelopathic chemicals to the soil reduce herbivory in spicebush (L. benzoin)?
  • Can the addition of allelopathic chemicals to spicebush (L. benzoin) leaves reduce herbivory?

FORM A HYPOTHESIS :

  • Proximity to black walnut (J. nigra) is positively correlated with herbivory.
  • Uptake of juglone or other chemicals from the surrounding soil makes spicebush (L. benzoin) less susceptible to herbivory.
  • Throughfall from black walnut (J. nigra) directly onto spicebush (L. benzoin) leaves will reduces growth rate of herbivores.

EXPERIMENT:

Materials:

  • wheeled measuring tape
  • Al Tags
  • flagging tape (orange)
  • light meter
  • plotless sampling prism
  • CIAS - computer image analysis software
  • juglone solution
  • walnut hull solution
  • small paintbrush (2 or more)
  • 30 ziplock bags
  • 30 early instar Epimesis larva
  • balance

Method:

  1. Make four transects with ten spicebush plants along each transect line. (Be sure to choose areas with variable populations of black walnut trees)
    1. Two transect sites were found at Raker Biological Field Station and Wildlife Sanctuary and two sites were created at Graver Arboretum.
    2. Using a wheeled measuring tape, walk out in a straight line about 40 meters. Every four meters, look for the nearest spicebush plant and tag it using an Al Tag and orange flagging tape.
  2. Collect data about each plant throughout the summer
      1. Closest black walnut (meters)
      2. Closest hickory (meters) –hickory also produces small amounts of juglone
      3. What species of plant was directly over the spicebush plant
      4. Approximate diameter of plant
      5. Gender
      6. Llight readings on 3 different sunny days (using a light meter)
      7. Count the number of walnut and hickory around each plant that were close or large (use a plotless sampling prism)
      8. Number of leaves with herbivory from 4 stems
      9. Average leaf area eaten per plant based on 8 leaves (use CIAS)

Example of a Graph

DRAW A CONCLUSION :

Analysis of Data:

Both of these graphs show no real correlation. I would like the graph to have a positive or negative slope, but both of these just have a horizontal slope so I will continue to work with data and make graphs and hopefully some variables will be closely positively or negatively correlated like the hypothetical example below.

Conclusion:

Both a field experiment and a lab feeding trial support the trend that herbivory is reduced under black walnut (J. nigras ). While leaf origin affected larval performance, leaf area consumed did not vary and experimental additions did not replicate this pattern. A broader assessment of the interaction of walnut and spicebush chemistry, including soil-mediated affects may yield more insight into this relationship. I do not believe walnut/spicebush interactions are as important a factor in this system as other top-down controlling factors like predation of caterpillars by insects and birds. A third experiment that I attempted was ruined because 29 out of 30 caterpillars were eaten by yellow jackets. Unfortunately, there were not enough larvae to repeat the experiment.

Experimental set-up of failed Experiment 3

 

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This material is based upon work supported by the National Science Foundation under Grant No. 0442049.

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.