Ana səhifə

Plant Community Ecology Course Packet, bio 390 Fall 2010

Yüklə 1.08 Mb.
ölçüsü1.08 Mb.
  1   2

Plant Community Ecology Course Packet, BIO 390

Fall 2010
Dr. Julie Korb

2445 Berndt Hall



Description Page #'s
Syllabus 3-5

Class Schedule 6-7

Article Discussion Guidelines 8

Common Trees in the Southwest 9-10

In-Class Activities:

Article Discussion Questions Week #1 11-12

Article Discussion Questions Week #2 13-14

Pinyon-Juniper Worksheet 15-16

Mixed Conifer Worksheet 17-18

Subalpine Worksheet 19-21

Releve Info 22-25

Animas City Mountain Species List 26-28

Plant Interaction Exercise 29-40

Dendrochrono logy 41-43

BIO 390: Plant Community Ecology

Fort Lewis College-Fall 2010

Class Schedule: T/R 11:15-12:35 p.m. Rm# Berndt 235, BH #570

Instructor: Julie Korb, Ph.D.

Office: 2445 Berndt Hall phone: 382-6905

Office Hours: T 10:15-11:10 R 1:25-2:35 or by appt.

Required Texts: There are no required texts for this course. This course does require a lot of reading of peer-reviewed journal articles that will be located on the O drive under Korb in a folder labeled Plant Community Ecology.
Course Objectives: This course will introduce students to major themes/theories and current data analysis techniques in plant community ecology. This course will emphasize biotic and abiotic variables that affect the distribution and abundance of plant species including natural and anthropogenic disturbances. We will use native ecosystems in southwestern Colorado, field collection data, and current scientific literature to explore these topics.
Class Format: It is imperative for you to be at class in order to learn the course material and to receive a good grade. This class will focus on using a variety of learning techniques. Generally, the first half of the class period will be spent on lectures and the latter half of the class period will be dedicated to group discussions/active learning exercises.
Reading Assignments: All reading assignments are assigned to prepare you for each class period and therefore you should do your weekly assignments BEFORE you come to class. I will draw information from class readings each day and thus it is necessary that you will have read your assignment so you will be able to participate in class discussion.
Laboratory Format: There is no laboratory associated with this class. We will however have a required one-day field trip on Sept. 4th starting at 9 am until 4:00 pm to collect data that we will analyze in class. We will meet at parking facilities (Physical Plant) near the SW Center. Please dress appropriately by wearing suitable clothes and shoes, bringing a rain jacket, water, lunch and a notebook.
Evaluation: You will have numerous opportunities to demonstrate your knowledge of plant community ecology including written exams, oral presentations, group discussion participation, and assignments. Grading will be done on a point system.

Evaluation Format Points Percentage

Exams (2) @ 100 pts 200 25.0%

Discussion Article Leader 100 12.5%

Group Discussion Participation 100 12.5%

All Day Field Trip 50 6.25%

PC-Ord Assignments 100 12.5%

Class Assignments (various points/

assignments) 50 6.25%

Final Presentation 100 12.5%

Final Exam (plant competition) 100 12.5%

800 points total 100%
Midterm grades: Midterm grades will based up one exam, ½ group discussion participation, all day field trip and class assignments. If you receive a failing midterm grade you will be asked to withdraw from the course.


Exams: No make-up exams will be allowed without prior instructor permission or a note from a physician. Exams during the semester will cover the material since the first of the semester or the previous exam. The final exam consists of take-home essay questions.
Discussion Article Leader: Each student will be required to give a 10 minute summary presentation on a peer-reviewed article related to plant community ecology. Students will sign up for the article the first week of class. This summary presentation will lead into a discussion of the article facilitated by the same student presenting the summary presentation. You will be required to email your classmates with a list of questions a week before your presentation and discussion of the article. This will allow you to further develop your skills in scientific reading, interpretation, and presentation. Please see attached discussion article information in course packet for further details.
Group Discussion Participation: Throughout the semester will we have both small and large group discussions regarding class lecture material and reading assignments. These discussions will provide you with the opportunity to explore ecological concepts more in-depth with your classmates and myself. For your group discussion grade, you need to be present on discussion days. If you are absent, it will result in a zero for your group discussion grade for that day. If you are present you will receive 5 points, if you talk you will receive another 5 points for the day.
Final Presentation: Each student will give a 12 minute final presentation in Powerpoint with 3 minutes for discussion based on a topic of the student’s choice related to plant community ecology. Students must pick one theory/major theme of plant community ecology (e.g., continuum concept, intermediate disturbance hypothesis, competition regulation, stress gradient hypothesis, succession theory, facilitation, niche differences, life-history traits, novel weapons hypothesis, etc.) and illustrate how the theory/major theme has been advanced/supported through plant community ecology research and design a study to further test the theory/major theme based on current literature. You must cite at least four scientific articles for this presentation and tie the various research articles into one cohesive presentation. You will be graded on your oral presentation skills, Powerpoint presentation slides, and most importantly the content of the presentation. For content you need to include: 1) one theory/major theme, 2) define the theory/theme, 3) discuss current status of theory/theme based on the current literature—minimum of 4 scientific articles, and 4) design study to further test the theory/major theme based on current literature.
Final Word: Enjoy this course. Although learning a new subject is challenging at times, it is also FUN. If you have problems with anything regarding this course please come visit me during my office hours or make an appointment at a time convenient for both of us. I am looking forward to an exciting semester learning about the plant community ecology!
Students with Disabilities:
“"Fort Lewis College is committed to providing all students a liberal arts education through a personalized learning environment. If you think you have or you do have a documented disability which will need reasonable academic accommodations, please call, Dian Jenkins, the Coordinator of Disability Service, 280 Noble Hall, 247-7459, for an appointment as soon as possible."

Course Syllabus (tentative schedule subject to change)

Topics (subject to revision)


Assignment Due

Class: Week of August 30

T: Course overview & syllabus , Intro to Plant Ecology

R: Intro to Plant Community Ecology/ Article Discussion

Kelly and Goulden 2008 (plant migration, climate change, gradients)

R: Reading Questions

FIELD TRIP: September 4th


Plant Community Data Collection

Class: Week of September 6

T/R: Gradient Analysis/Pattern
& Process R: Article Discussion/Intro PC-Ord

Lortie et al. 2004 (neutral and niche theory, plant interactions)

R: Reading Questions

Class: Week of September 13

T/R: Plant Life History Traits

R: Article Discussion/Lab: PC-Ord

Fukami et al. 2005 (assembly rules, alternative states, succession); Craine 2005 (plant strategies, competition, stress)

R: Reading Questions

Class: Week of September 20

T/R: Competition/Facilitation

R: Lab: Start Plant Competition Greenhouse Experiment

Plant Competition lab handout

Class: Week of September 27
T: Competition/Facilitation continued

Callaway et al. 2002 (facilitation, environmental stress); Maestre et al. 2009 (competition/facilitation)

T: Reading Questions

T:Dr. Jeffrey Mitton, Pine Beetle Outbreak NH 125 7 pm


Class: Week of October 4

T/R: Disturbance and Succession

R: Article Discussion/Lab: PC-Ord

Connell and Slatyer 1977 (successional theory); Davis et al. 2000 (invasions, resource availability, disturbance)

R: Reading Questions

Class: Week of October 11

T/R: Fire Ecology: Pinyon-Juniper

R: Article Discussion/Lab: PC-Ord

Callaway et al. 2008 (novel weapons hypothesis, invasions, mycorrhizae)

R: Reading Questions

Worksheet (in class)

Class: Week of October 18

T/R: Fire Ecology: Ponderosa Pine/Mixed Conifer

R: Article Discussion/Lab: PC-Ord

Fule et al. 2009 (reference conditions, fire ecology, restoration)

Reading Questions

Worksheet (in class)

Class: Week of October 25

T/R: Fire Ecology: Subalpine

R: Dendrochronology

Scheonnegal et al. 2007 (fire ecology, climate change, dendrochronology)

T: Reading Questions,

Worksheet (in class)

R: PC-Ord report

Class: Week of November 1

T: Restoration & Article Discussion


Palmer et al. 1997 (restoration, community ecology theory); Suding et al. 2004 (alternative states, feedback loops, restoration)

T: Reading Questions

Class: Week of November 8

T/R: Diversity, Abundance, Rarity

R: Article Discussion; complete plant competition greenhouse lab

Loreau et al. 2001 (biodiversity/ecosystem functioning); Levine & HilleRisLambers 2009 (niche differences, biodiversity)

R: Reading Questions

Class: Week of November 15
T/R: Climate Change & Plants/Alpine; Article Discussion
R: Video

Kikvidze et al. 2005 (competition, facilitation, environmental stress, climate change)

T: Reading Questions

R: Video Worksheet

Class: Week of November 22

NO CLASS-Happy Thanksgiving!

Class: Week of November 29

Student Presentations

T/R: Powerpoint Presentation

Class: Week of December 6

No Class—credit for field trip

Final Exam: December 15th MONDAY @ 4:30-6:30 pm

Plant Competition Report

Presentation of Discussion Articles
About 1/4 of this course will be spent evaluating and discussing papers from the primary literature. This is a critical skill that students must develop. You need to develop the ability to figure out the good, bad, useful and useless parts of each paper. You also need to be able to clearly communicate this to others and to defend your thoughts. This critical thinking, along with clear enunciation of ideas, is arguably one of the most important skills to get out of your upper division courses within your major. These skills will also be invaluable for your own writing, as well as for editing and reviewing.
I want the following questions addressed when papers are presented in class:
1. What is the stated purpose of this paper?

2. What general approach or methods are used to accomplish that purpose?

3. Are the data sufficient and clearly presented?

4. What are the primary stated conclusions?

These first four points are obvious exercises in reading. More importantly, I want you to be able to apply your critical thinking:
5. Is the main question important (not to be confused with interesting)? Why, why not? (e.g., does it tie back to any theory in plant community ecology)?

6. Go back and compare the stated purpose of the paper (#1) with the main conclusions (#4). Do they match?

7. Do the data support the conclusions? Would another approach have been better? Are the data over-interpreted or is the interpretation just wrong?

8. What overall contribution does this paper make to community ecology? (can be the same as question #5)

9. What new questions are raised and what further work is suggested by this study, either directly or indirectly?

Adapted from



(Juniperus scopulorum) Rocky Mountain Juniper: Berries: less than or about 1/4 inch across, often pale blue or pale greenish-blue. Usually two seeds in each berry, sometimes one or three. Trunk: Usually single trunk. Bark: often has reddish-brown color in places; Tree Characteristics : branches slender and elongate.

(Juniperus osteosperma) Utah Juniper: Berries: more than 1/4 inch across and often reddish-brown, berries dry and mealy inside. Needles: yellow-grey. Bark: grey with abundant long shreddy fibers.

(Juniperus monosperma) Oneseed Juniper: Berries: 1/8 to 1/4 inch across with one seed, dark-blue, reddish-brown or copper colored, juicy inside. Needles: often grey-green. Trunk: Often has several trunks.


All pines have needles in bundles of two or more. Spruce and fir tree needles are single.

(Pinus ponderosa) Ponderosa Pine: Needles: over 3 1/2 inches long and in bundles of two or three) Bark: dark brown/black when young; orange when old-growth; thick made up of jigsaw puzzle segments. Habitat: Typically found on south-facing slopes between 7000-9000 ft).

(Pinus edulis) Pinyon Pine: Needles : in bundles of two, rarely three, usually 1 to 1 1/2 inches long. Cones: 1-2 inches; fall soon after maturity; Tree Characteristics: Tree often stubby, robust, and under 30 feet high. Habitat: Typical of lower elevations (below 7500 feet) and on dry sites, in arid forests.

(Pinus contorta) Lodgepole Pine: Needles: in bundles of two, usually 1 1/2 to 2 1/2 inches long. Cones: 1 inch; cones persist for several years past maturity; Tree Characteristics : Tree usually tall and straight with slender trunk. This tree is not found naturally in the Southwest; it has been planted in revegetation efforts.

(Pinus flexilis) Limber Pine: Needles: in bundles of five, usually 1 1/2 to 3 inches long. Cones: no bristles on cones, mature cones very pale brown and 3 to 10 inches long. Tree Characteristics : Trunk branched; not straight; Habitat: usually found on exposed or rocky and windy sites.

(Pinus strobiformis) Southwestern Pine (Mexican White Pine): Needles: in bundles of five, usually 1 1/2 to 3 inches long; very few minute teeth near apex; Cones: no bristles on cones, mature cones very pale brown and 3 to 10 inches long. Tree Characteristics: tree form upright and straight:

(Pinus aristata) Bristlecone Pine: Needles : in bundles of five, usually 1 to 1 1/2 inches long; speckled with white resin drops; strongly curved; Cones: a long, slender bristle on the tip of each cone scale; cones less than 3 1/2 inches long.


All spruces have single, four-sided needles (square in cross-section). Cones are lightweight and cone scales are thin and papery. The cones hang downward and fall intact from the tree after the seeds are mature. Cones with forked papery strips between the cone scales are not spruces but rather Douglas-fir.

(Picea engelmannii) Engelmann Spruce: Needles: square in cross-section and 1.0 inch in length or less; needles often fairly stiff and sharp pointed. Cones: mature cones 2.5 inches or less in length; usually 1.5 to 2.0 inches.

(Picea pungens) Colorado Blue Spruce: Needles: square in cross-section and usually over 1 inch in length; needles stiff and very sharp; pungent odor when crushed; Cones: mature cones over 2.5 inches in length; often about 3 inches. Bark: almost always grey.


All true fir trees have flat, soft needles about an inch or two long, and upright resinous cones on top branches which disintegrate on the tree after one season with the scales and seeds falling to the ground and an upright spike remaining on the branch. NOTE: The Douglas-Fir is not a Fir at all but is listed here only because of name similarity

(Abies lasiocarpa) Subalpine Fir: Bark: thin Needles: soft and flattened, 1 to 1 3/4 inches long on lower branches except shorter near treeline. Tree Characteristics: forms tall, narrow, spire-like trees, the narrowest trees of the Rocky Mountain forests.

(Abies arizonica) Corkbark Fir: Bark: thick and soft or corky and broken into ridges, in color grey, ash-white, creamy-white, or pale- yellowish. Habitat: It is found only in the southern half of Colorado and northern New Mexico.

(Abies concolor) White Fir : Bark: thick and grooved when older, checkered, spongy under hand pressure; Needles flattened and soft, 1 3/4 to 3 inches long on lower branches; attachment to branch looks like a suction-cup; blue-green color. Habitat: Found below 10,000 feet, in the mountains of central and southern Colorado and of northern New Mexico.

(Pseudotsuga menziesii) Douglas Fir: Needles: short flat soft needles, only 3/4 to 1 1/2 inch long that have a pedicle (leaf stalk); Cones: pale brown, and only 1 to 3 inches long, dry papery scales with papery three-pointed bracts, hang down from the branch, and fall intact from the tree.

Discussion Questions: Week 1

  1. Before reading the article, describe in your own words how you think plant communities will respond to climate change?

  1. Examine the figure below. Which, if any of the diagrams (it can be a combination of any of them) represents what you described in question 1?

Fig. 1. Types of distributional change for species on an elevation gradient, resulting from changes in

growth, establishment, decline, and/or mortality: ‘‘Lean,’’ where the range remains constant but the

central tendency shifts, as highlighted in a new study (13); ‘‘March,’’ where the entire distribution and its

range moves upslope (5); and ‘‘Crash,’’ where mortality is widespread across the range (10). These types

are not mutually exclusive and could occur in various combinations or sequences to affect distribution

range, central tendancy, and/or skewness.

  1. Which of the diagrams represents what Kelly and Goulden (2008) found in their research in Southern California over a 30 year period?

  1. How might the findings from Kelly and Goulden (2008) be applicable to plant communities in southwestern Colorado?

  1. The authors state four reasons their findings can be attributed to climate change. What are these four reasons and do you agree with them? Why or why not?

  1. What would you suggest for future research to expand upon the findings of this study?

Discussion Questions Week 2

  1. Explain the figure below. Is there anything in the figure that should be removed or added?

  1. What makes the “Integrated Community Concept” unique from Clements’ organismic concept or Gleason’s individualistic concept? Do you agree that the IC concept is a stronger theory for understanding the structure and function of ecological systems? Explain your response.

  1. How does neutral theory and niche theory fit into the IC concept? Describe both of these theories.

  1. Why is the IC concept important to consider when thinking about plant community responses to climate change? How, if at all, do the results from Kelly and Goulden (2008) relate to the IC concept?

  1. What is a research study that could be conducted in southwest Colorado to test the IC concept and its applicability to climate change?

Pinyon-Juniper Class Exercise

Pinyon juniper forests vary in their distribution across elevations (4500-8500 ft).

Answer the following questions regarding their distribution patterns.

1) In the above diagram draw in the elevation bands for the pinyon-juniper forest life zone. Is there a difference between north and south facing slopes? Why or why not? Why do pinyon-juniper forests only grow between 4500 and 8500 ft? Hint: what are the limiting climatic factors?

2) Pinyon pine and Utah juniper are NOT evenly distributed across the elevation gradient range for pinyon-juniper forests. Which of the two species would be found higher in elevation? ___________________ Lower in elevation?___________________
What physical characteristics for these two species led you to your conclusions—adaptations to different climatic environments?

3) Density and basal area are also NOT evenly distributed across the elevation gradient range for pinyon-juniper forests. Where would density be the highest and why? Where would basal area be the highest and why?

4) Fire is one of the major disturbance agents in pinyon-juniper forests. Is fire behavior similar in intensity and frequency across the elevation gradient? Fill in the fire behavior triangle below and think about how these three variables would influence fire behavior and how they would vary across the elevation gradient. Specifically, look at the leg of the triangle that you graphed in question #1.

Fire Behavior Triangle

Mixed Conifer Class Exercise

  1. There are two types of mixed conifer in the Southwest: warm, dry mixed conifer and cool, wet mixed conifer. How is it possible for these two different vegetation types to grow near each other when their names describing their environment are so different? In the diagram below draw in the elevation bands for these two types of mixed conifer.

  1. What tree species is the indicator species for warm, dry mixed conifer? ____________________ What adaptations/characteristics allows this species to prefer warm, dry areas over cool, west areas?

  1. Using the LEGO set, create a warm, dry mixed conifer forest prior to Euro-American settlement (~1880). When doing this think about the types of tree species (species richness), density (trees/acre) and biomass (basal area/acre). Also, think about the fire regime for warm, dry mixed conifer.

What species did you include?

What was the density (low, medium, high)?
What was the diversity of tree diameters--basal area (lots of small trees, lots of large trees, mixture)?

Using the LEGO set again, create a warm, dry mixed conifer forest after Euro-American settlement. What impacts did fire suppression, grazing, and logging of old-growth trees have on the forest structure?

What species did you include?
What was the density (low, medium, high)?

What was the diversity of tree diameters--basal area (lots of small trees, lots of large trees, mixture)?

  1. Using the LEGO set, create a cool, wet mixed conifer forest prior to Euro-American settlement (~1880). When doing this, think about the types of tree species (species richness), density (trees/acre) and biomass (basal area/acre). Also, think about the fire regime for cool, wet mixed conifer.

What species did you include?

What was the density (low, medium, high)?
What was the diversity of tree diameters--basal area (lots of small trees, lots of large trees, mixture)?
Using the LEGO set again, create a cool, wet mixed conifer forest now after Euro-American settlement. What impacts did fire suppression, grazing, and logging of old-growth trees have on the forest structure?
What species did you include?
What was the density (low, medium, high)?
What was the diversity of tree diameters--basal area (lots of small trees, lots of large trees, mixture)?

  1. Fire is one of the major disturbances in mixed conifer forests. Is fire behavior similar in intensity and frequency across the elevation gradient for the two different types of mixed conifer (warm, dry and cool, wet)?

Subalpine Class Exercise

  1. In the diagram below draw in the elevation band for the subalpine. Note, how does this influence tree line? Where would you first see signs of climate change impacting tree line?

  1. The subalpine is dominated by two tree species: subalpine fir and Engelmann spruce. Look at the photographs and think about traits for the other common conifers we have already discussed in class and list four adaptations for each species (some of them can be the same for both species).

Subalpine Fir



Engelmann Spruce



  1. What other tree species that we have already talked about might also occur in the subalpine vegetation zone? What adaptations do these species have to live at higher elevations (colder and wetter than lower elevations)?

  1. What type of forest stand structure did the subalpine have prior to Euro-American settlement? When describing this think about the types of tree species (species richness), density (trees/acre—low, medium, high) and biomass (basal area/acre-- lots of small trees, lots of large trees, mixture)?

  1. What type of forest stand structure did the subalpine have after Euro-American settlement? When describing this think about the types of tree species (species richness), density (trees/acre—low, medium, high) and biomass (basal area/acre-- lots of small trees, lots of large trees, mixture)?

  1. Fire is one of the major disturbance agents in the subalpine vegetation zone. Fill in the fire behavior triangle below and think about how these three variables would influence the fire regime for subalpine forests. List the fire regime for subalpine forests and the variables that influence it.

Fire Behavior Triangle

  1. What other natural disturbances play a role in the dynamics of subalpine forests? How are these similar and dissimilar to fire?

Relevé Approach to Vegetation Sampling
The relevé approach to vegetation sampling was developed by Braun-Blanquet for application to table analysis for vegetation classification. The primary goal of the relevé approach is to acquire a complete species list from each sample site. If other quantitative site and soil information is collected, the information can also be used for ordination analysis.
Reconnaissance and Entitation

Reconnaissance is essential. The better your initial knowledge of an area, the better the subsequent sampling will be. This reconnaissance phase should include the establishment of the apparent relations of various vegetation types with topography, history, geology, soil conditions and major disturbance factors (animals, fire, floods, etc.)

The entitation process subjectively subdivides the vegetation into recognizable entities or vegetation types. The types defined during this process are a starting point for analysis of the vegetation. During analysis of the data some of these units will likely be subdivided or eliminated (e.g. they represent transition communities).
Sample Site Requirements for a Relevé

The Braun-Blanquet approach is based on centralized replicate sampling. Plot locations are chosen in the central areas of homogeneous stands of vegetation and numerous replicate samples are collected from other similar sites.

Each sample should satisfy the following criteria:

  1. Homogeneity of the vegetation canopy

  2. Homogeneity of the soil and other site factors

  3. Large enough area to contain all the species in the community

  4. Should be recognizable as a unit that can be repeated in other areas of the landscape

If the data are to be analyzed using probability statistics, the selection of the sample sites must be done randomly within an area of homogenous vegetation (e.g. stratified random sampling approach)

If the data are to be analyzed using ordination methods, then it is necessary to collect environmental and soils information at each sample site and plant cover estimates.
Plot Size

There are two main methods for determining plot size: the minimal area technique or using tables based upon previous investigators’ experience.

Minimal area

The minimum mapping area is determined by finding the point where the species-area curve levels off. Nested plots are used to create this curve. In each plot, a complete species list is created. Additional plots are added until only one or no new species in the larger nested plots are found. The species-area curve does not level off in tropical and other complex communities.

Published Tables

The following table is the minimum-area guideline (m2) that has been published by Westhoff and van der Maarel (1978) for various community types. Only a portion of the table is shown.

Pastures 5-10

Alpine Meadows 10-50

Chaparral 10-100

Scrub Communities 25-100

Temperate Deciduous Forest 100-500

Mixed Forest 200-800

Tropical Secondary Rainforest 20-1000
Data to Collect
Site Factors

You should describe the site as completely as possible using a consistent set of quantitative variables that can be used in an ordination analysis.


The soil-vegetation relationship is fundamental to understanding vegetation patterns. Some recommended soil analyses include pH, percent soil moisture, soil texture, percent organic matter, soil nutrients (N, P, K) and other physical and chemical characteristics.

Plant Species

You should collect a specimen of every unknown plant species for later verification. Collect the complete plant including roots, stems, leaves, flowers and fruits. Cover estimates should be made for each species. Cover estimates can either be exact aerial estimates or cover-abundance classes can be used. The disadvantage of using cover-abundance classes is that it is not possible to determine the average cover of a species for a group of plots (the average score however can be averaged).

Braun-Blanquet Cover Estimate Scale

R =rare, <<1% cover

+ =common, but < 1% cover

1 =1-5% cover

2 =6-25% cover

3 =25.1-50% cover

4 =50.1-75% cover

5 =75.1-100% cover

Size of Plots-Minimal Area Method

Cover Class Tables

Common Plants of Animas Mountain Trail

(partial list)


Abies concolor (White fir)

Juniperus osteosperma (Utah Juniper)

Juniperus scopulorum (Rocky Mountain Juniper)

Pinus edulis (Pinyon Pine)

Pinus ponderosa (Ponderosa Pine)

Pseudotsuga menziesii (Douglas-fir)

Ulmus pumila (Chinese Elm)


Amelanchier alnifolia (Utah Serviceberry)

Ceanothus fendleri (Buckbrush)

Cercocarpus montanus (Mountain Mahogany)

Fendlera rupicola (Cliff Fendlerbush)

Fragaria virginiana (Wild Strawberry)

Gutierrezia sarothrae (Broom Snakeweed)

Juniperus communis (Common Juniper)

Mahonia repens (Oregon Grape)

Peraphyllum ramosissimum (Squawapple)

Quercus gambelii (Gambel Oak)

Rhus trilobata (Threeleaf Sumac)

Rosa woodsii (Wild Rose)

Symphoricarpos rotundifolius (Snowberry)


Achnatherum hymenoides (Indian Ricegrass)

Agropyron cristatum (Crested Wheatgrass)

Aristida purpurea (Three Awn)

Bouteloua gracilis (Blue Grama)

Bromopsis inermis (Smooth Brome)

Bromus tectorum (Cheat Grass)

Elymus elymoides (Squirrel-tail)

Festuca arizonica

Festuca thurburi

Hesperostipa comata (Needle-and-thread)

Koeleria macrantha (June Grass)

Muhlenbergia wrightii (Spike Muhley)

Pascopyrum smithii (Western Wheatgrass)

Poa fendleriana (Muttongrass)

Poa pratensis (Kentucky Bluegrass)

Sporobolus cryptandrus (Dropseed)


Achillea lanulosa (Yarrow)

Agoseris glauca (Pale Agoseris)

Allium acuminatum (Tapertip Onion)

Allium cernuum (Nodding Onion)

Alyssum alyssoides (Pale Allysum)

Androsace septentrionalis (Rock Jasmine)

Antennaria parvifolia (Pussytoes)

Arabis drummondii (Drummond’s Rockcress)

Artemisia franserioides (Sage)

Artemisia frigida (Silver Sage)

Asclepias subverticillata (Whorled Milkweed)

Astragalus coltonii (Milkvetch)

Bahia dissecta (Ragleaf Bahia)

Calochortus nuttallii (Sego-lily)

Castilleja linariifolia (Paintbrush)

Chenopodium fremontii (Fremont Goosefoot)

Circium tracyi (Thistle)

Comandra umbellata (Bastard-Toadflax)

Convolvulus arvense (Field Bindweed)

Conyza canadensis (Horseweed)

Corallorhiza maculate (Summer Coralroot)

Delphinium nuttallianum (Larkspur)

Erigeron divergens (Fleabane)

Erigeron flagellaris (Fleabane)

Erigeron speciosus

Eriogonum racemosum (Whorled-buckwheat)

Erodium cicutarium (Crane’s Bill)

Galium septentrionale (Bedstraw)

Gaura coccinea (ButterflyWeed)

Gayophytum diffusum ssp. parviflorum (Spreading Groundsmoke)

Gilia aggregata (Scarlet Gilia)

Grindelia squarrosa (Gumweed)

Helianthus rigidus

Heliomeris multiflora (Showy Goldeneye)

Heterotheca villosa (Goldenaster)

Hieracium fendleri (Yellow Hawkweed)

Holodiscus dumosus (Rock Spiraea)

Lactuca serriola (False Dandelion)

Lactuca serriola (Prickly-lettuce)

Lepidotheca suaveolens (Pineapple Weed)

Lithospermum multiflorum (Showy Puccoon)

Lotus wrightii (Deer Vetch)

Lupinus ammophilus (Lupine)

Lupinus kingii (Lupine)

Machaeranthera canescens

Medicago lupulina (Black Medic)

Melilotus officinalis (Yellow Sweet-clover)

Opuntia polyacantha (Prickly Pear)

Opuntia whipplei (Rat-tailed Cholla)

Oreocarpa bakeri

Orthocarpus luteus

Packera neomexicana (Groundsel)

Penstemon barbatus (Beardlip Penstemon)

Penstemon linarioides

Penstemon rigens

Penstemon strictus (Rocky Mountain Penstemon)

Penstemon strictus (Rocky Mountain Penstemon)

Polygonum aviculare (Knotweed)

Psoralidium tenuiflorum

Pseudocymopterus montanus (Mountain Parsley)

Pterogonum alatum

Schoenocrambe linifolia (Skeleton Mustard)

Solidago simplex (Goldenrod)

Sphaeralcea coccinea (Globe Mallow)

Taraxacum officinale (Dandelion)

Thalictrum fendleri (Meadowrue)

Thalpsi montana (Candytuft)

Tragopogon pratensis (Salsify)

Thermopsis montanus

Verbascum thapsus (Mullein)

Vicia americana (American Vetch)

Virgulus faclcatus

Wyethia arizonica (Mule’s Ears)

Yucca angustissima (Narrow Leaf Yucca)

Yucca baccata (Datil Yucca)

Plant Interaction Lab


Competition in plants may be thought of as “those hardships which are caused by the proximity of neighbors” (Harper 1961). Hardships may be due to the decreased availability of light, water, or nutrients to any individual plant when its canopy or root area overlaps with that of another individual. Therefore, the degree of crowding in an area will have an important effect on the amount of overlap between individuals and the mean growth of individuals in an area. Competition may be within a species (intraspecific) or between individuals of different species (interspecific). Differences in growth form (shape of leaves and arrangement on stem), root depth, development rate, daily pattern of water and nutrient uptake from the soil, and photosynthetic pathway may all influence the magnitude of competition.

In this exercise, you will be measuring the effect of competitor density on the growth of plants. You will be able to design your own experiment to test hypotheses about expected differences in competitive effects between species under different environmental conditions. You will carry out the experiment in the greenhouse.


During this laboratory exercise you will

  • Generate hypotheses regarding the outcome of competition between two plant species.

  • Design and conduct and experiment to test competition between two potential plant competitors.

  • Learn how to perform a regression analysis and how to compare the slopes of two regression equations.

  • Discover some of the many adaptations that allow plants to survive conditions of differing temperature and moisture.


The effect of intraspecific competition in plant populations is usually examined by planting the species over a range of densities. The most common result is that the mean weight per plant decreases as density increases (Figure 1) so that total yield (weight per area) approaches some constant value (Figure 2). This result of diminishing returns is called the Law of Final Yield (Harper 1977). We can think of this constant yield as the carrying capacity (in terms of biomass) of the environment. Carrying capacity is the number, or mass, of individuals that can be supported by a particular environment at any one time. Graphs such as figures 1 and 2, can be used to approximate the optimal planting density for a particular crop – the density beyond which total yield no longer increases.

You may have noticed that the mean weight per plant decreases in a non-linear fashion as plant density increases. This non-linear relationship is difficult to analyze statistically. If, however, we transform the non-linear relationship into a linear relationship, we can analyze the results using a simple linear regression. A transformation is simply a mathematical manipulation of one or both measured variables. The best transformation in this situation involves calculating the reciprocal of mean plant weight (1/w). The reciprocal of mean plant weight is related to plant density in a linear fashion (Figure 3) according to the following formula:
1/w = a + b·D

Plant Density

Fig. 3
here w = mean plant weight, D = density, a = reciprocal of the maximum mean plant weight, and b = coefficient of competition. This formula is called the reciprocal yield equation. A large (positive) value of b (steep slope) implies a strong competitive effect.
Most plants, however, do not live in a monoculture but experience interspecific competition from a number of other species. Even crops must share their environment with various weed species. To examine the effects of interspecific competition, you can use an experimental design similar to the one described above for intraspecific competition. In this case, you have two species, an indicator species (i) and a competitor species (j). If you keep the density of species i constant and vary the density of species j, you will be able to measure the effect of species j on species i. This type of experiment is referred to as an additive design because competitors are added to indicators so that the total density of the mixture increases (Harper 1977).

If the density of the indicator species is kept low enough so that intraspecific competition is weak or non-existent, we can use the reciprocal yield equation to describe interspecific competition only. In this situation, w = mean of the indicator species, D = density of the competitor species, a = reciprocal weight of the indicator when no competitors are present (D=0), and b = competitive effect of species j on species i.

Using the above design and analysis, students in each laboratory section will conduct experiments to test hypotheses about the interaction between two likely competitors. The plant species available in this exercise were chosen because they are potential competitors under natural conditions.

SAMPLE EXperiments

Students will get in groups of two and will conduct two experiments, each consisting of 5 density treatments. A single treatment consists of one indicator species and one competitor species grown in a single pot. Each treatment will be replicated three times. Therefore, there you will need 15 pots for each experiment. You can design experiments to test different combination of species or the same combination under different environmental conditions. Some suggested designs are given below.

  1. Compare intensity of competition (b) for two competitor species on a single indicator species. Choose your species so that you can develop hypotheses about which species should be the strongest competitor from knowledge of its morphology or physiology. For example, you could compare several species of similar growth form but different seed size. If you include the same species as both indicator and competitor, you can compare the intensity of intraspecific to interspecific competition.

  2. Compare the intensity of competition for two indicator species with the same competitor species. Again, choose species so that you can develop hypotheses about likely outcomes.

  3. Compare the same species pair, reversing which one is the indicator and which the competitor. Is one species a stronger competitor than the other?

  4. Compare the same species pair under various resource levels. Do different levels of fertilizer or water alter the intensity of competition (b)? What might be the outcome of competition between a legume and grass under low and high nitrogen fertilization? What might be the difference between a C3 and C4 grass with mycorrhizae additions?

species selection

There are two main groups for species selection: eight grass species and two legume species will be available for experimentation that are cultivars or native mid-elevational species to SW Colorado which include: four grass species, two legume species and four forb species (see lists below). Consider the specific adaptations of each species (growth form, seed size, nutrition, and photosynthetic pathway) as you design your experiments. The seeds of the various species vary in size. How might seed size affect competition? The legumes are nitrogen fixers. They have symbiotic bacteria (Rhizobium) in root nodules. These bacteria convert atmospheric nitrogen into a form utilizable by the plant. How might this affect the outcome of competition with a non-nitrogen fixing species or another legume? Millet is the least closely related grass species. It has a C4 photosynthetic pathway whereas most of the other species have a C3 pathway. The C4 pathway allows a plant to photosynthesize more efficiently in hot, dry environments. Does millet have an advantage when light is high and soil moisture low? Lastly some of these plants are allelopathic. Allelopathic plants have the ability to release chemicals that suppress some other plant species growing around them by processes such as reduced seed germination or seedling growth. How would this effect competition?

Cultivar Species Mix

Legume C-pathway Allelopathy

Family Fabaceae

Red clover (Trifolium pratense) yes 3 no

Alfalfa (Medicago sativa) yes 3 no

Family Legumacae

Green Pea (Pisum sativum) yes 3 no
Family Poaceae

Subfamily Pooideae

Oats (Avena fatua) no 3 no

Rye (Secale cereale) no 3 yes

Subfamily Panicoideae

Millet (Pennisetum spicatum) no 4 no

Sorghum (Sorghum sp.) no 4 yes
Family Solanaceae

Tomato (Lycopersicon sp.) no 3 no

Green pepper (Capsicum annuum) no 3 no

Southwest Colorado Native Mid-Elevation Species Mix

Legume C-pathway Allelopathy

Family Fabaceae

Lupinus argenteus yes 3 no

Oxytropis lambertii yes 3 no

Family Poaceae

Pascopyrum smithii no 3 no

Bouteloau gracilis no 4 no

Elymus elymoides no 3 no

Muhlenbergia wrightii no 4 no
Family Scrophulariaceae

Castilleja linariifolia no 3 yes

Family Onagraceae

Epilobium angustifolium no 3 no
Family Asteraceae

Artemisia ludoviciana no 3 no

Erigeron speciosus no 3 no


planting procedure

  1. Prepare 15 four-inch pots for each experiment. Use tape to label each pot with indicator name, competitor name, competitor density, replicate number, and treatment (fertilizer, mycorrhizae). Remember that there should be 5 density treatments with 3 replicates each. Fill each pot with soil to the inner rim.

  2. Calculate seeding rate. For best results, you should have 2 indicator plants per pot. Competitor plant densities should be 0, 4, 8, and 16. Because all seed will not germinate, you should plant at least 3 indicator seeds in each pot (you can thin the plots after they germinate if needed). Plant 0, 6, 11, and 20 competitor seeds in appropriate pots.

  3. Plant seeds by distributing them evenly across the soil surface. Plant at a depth of 3 times the seed size. Place a straw or toothpick next to each indicator seed. This will help you find the plants after the competitor species germinate as many of them look similar.

  4. Put all pots for one experiment in two plastic trays (set 1 and set 2). Label tray with treatment (“fertilizer”, “mycorrhizae”), if needed. Randomly place pots in trays.

  5. Check the pots every week for germination of indicators and later for their survival. If more seeds than expected germinate, thin plants to appropriate density.


All plants will be harvested and weighed after 7 weeks. Students should harvest their plants only.

  1. Carefully pull each plant out of the soil, removing the indicators first.

  2. Count the number of surviving indicators and competitors.

  3. Note reproductive stage of plants (flower, seeds) and numbers for each species. Also note anything else unique you see about your plants before you harvest them.

  4. Clip the roots from each plant (shoots) and measure the total length (cm) and wet weight (g) of all indicators and competitors for the roots and shoots. Place in drying oven at 65 ºC for 24 hours and reweigh to get dry weight (g) of the roots and shoots.


  1. Calculate the reciprocal mean plant weight (1/w) for the indicator species in each pot. Use dry weight.

  2. Create two graphs for each experiment. On the first, plot 1/w against final competitor density. On the second, plot 1/w against final competitor weight. Each group should create four graphs.

  3. Perform a regression analysis and calculate the reciprocal yield equation for each experiment.

  4. Compare the slopes of the two reciprocal yield equations (b1 vs b2).

  5. Calculate the Root Weight Fraction for all of the species in both experiments. RWF=root dry weight/total dry weight. Compare the RWF among species and experiments.

  6. Calculate average root and shoot lengths (cm) and create figures with means and standard error of means. Run statistics. Also calculate averages for any reproductive stage data you gathered and present means and SEMs.


  1. What hypotheses were you testing in your experiments? What reasoning led you to develop these hypotheses?

  2. Did your results support your hypothesis? What conclusions can you draw?

  3. What abiotic or biotic factors in nature might change the competitive outcome you observed? How could you design a similar test in the field?

  4. What plant community ecology theories are supported and/or refuted or simply are relevant to your experiments?

  5. How would you improve this study to expand its scope or to better address your initial hypotheses?

  1   2

Verilənlər bazası müəlliflik hüququ ilə müdafiə olunur © 2016
rəhbərliyinə müraciət