Dispersal- Lesson 2

Engage:

Remind students of the trees in the woodland plot they have identified by showing them a map/aerial photo of the plot.  Tell students they are going to do an activity based on this information.  Show students a map of the location of only 1 tree species within the plot. Use a single color to represent that tree species on your map (see attached example).  The map will serve as a model of what they will do and as a visual aid to spark discussion about the differences in dispersal patterns.  Ask students to describe the dispersal pattern they see.  Tell them they are going to investigate a tree species to see how far the seeds dispersed. 

Note:  Not all the trees in your plot will be dropping seeds.  In this case, you may want to choose seedlings for students to investigate.  Alternatively you might use a stand-alone tree on your school campus that is dropping seeds.

Explore:

In order for students to visualize the dispersal pattern of their tree species in the woodland plot, students will generate their own map showing the location of a specific tree species.  Students will use the data collected from the Lesson 1, where they identified where trees were located in each plot.  The map should look something like this:

For their tree species only, students place the sticky dots on the location of their tree species based on the original woodland plot map.  This will help them visualize the dispersal of that tree within their woodland plot.  Ask students to predict what their seed types look like and how they might be dispersed. 

Field Investigation

Tell students they will be going outside to investigate seeds from their tree species.  Use attached activity sheet to guide the activity. Establish or review rules for working outside before leaving the classroom, including the signal you will use to gather them together as a group.  Once outside, ask students to find a shedding tree of their species. You should go outside beforehand and identify shedding trees to help direct students.  Remind students what a transect is and what the distance will be between each data collection point.  The distance between each data point is at the teacher discretion and depends on the size of the tree and the number of seeds.  Anywhere between 1m-5m is suggested.  Looking for shedding trees beforehand will be helpful.  Students conduct transects away from their tree and record their data on activity sheet.  Students graph their data and compare to each other.

Note:  This activity is best done in the fall.  If conducted in the spring, students might be able to find seeds left over from the year before.  See reference list for a list of shedding trees you are likely to find in spring and in fall.

Explain:

Students should have some background knowledge of how seeds are dispersed from Dispersal Lesson 1.  They should know that seed size and shape matter in how a seed is dispersed.  They should also be able to recognize that trees make a trade-off when making seeds - some make many small seeds while others make fewer large seeds.  Students also should be able to identify different types of dispersal mechanisms including wind, water, animal and human.

Students should find an average weight, using three of the seeds, to develop an understanding of the relationship between weight and distance traveled from the tree.  Trees that generate large, heavy seeds will not be dispersed by wind and, therefore, are more likely to be close to the tree.  However, seeds that are small and plentiful will, most likely, be carried farther away by wind.  When comparing graphs, students should use their knowledge of seed dispersal to explain their data.  They should use the information above to make statements about their data. For example, students who found many seeds close to the tree might make a statement such as  “there was a lack of wind that season,” or “the seeds of that tree are large and do not disperse by wind” or “the acorns from that oak were collected by animals and stored close to the tree.”

Extend: 

• Use track plates or a remote camera to investigate animal dispersal.  Attach some upholstery thread to different seeds, observe distance traveled or disappearance.  

• Set up traditional seed traps and identify the various seeds and litter.  Compare to other seed traps.  Discuss wind, rain and other variables in seed dispersal.

• Investigate the seed bank.  Dig up some soil from 2 or 3 different habitats - students can bring soil from their yard, garden or farm fields. Also include some soil from undisturbed natural habitats.  Fill up some flats with each kind of soil; water and then cover with some kind of mulch (grass clippings, plastic, paper).  Wait to germinate. 

Evaluate:  Show students pictures of a novel tree species and its seed type in its native habitat (have more than one example from different regions of the world).  Ask them to predict what the seedfall graph would look like for that species and to explain their prediction using what they know about seed size and shape.