In The Subalpine Conifer Forests of Colorado, Will Fallen Trees

Affect The Percent Cover of Understory Vaccinium Shrubs?

Alex RobertsonVegetation Ecology

2013

IntroFrom a study on windows of opportunity for

Vaccinium species, Eriksson and Fröborg (1996) found that decaying wood is a highly favorable substrate for Vaccinium species.

Would their findings hold true in Colorado’s subalpine forest with fallen Engelmann spruce (Picea engelmannii) and Subalpine fir (Abies lasiocarpa).

Fallen trees offer a potential window of opportunity for understory growth.

HypothesisPredict that the percent cover of understory species will be

greater around fallen trees.Reasons:

More organic matter available Greater access to sunlightIncreased moisture content

Methods1. 50(m) x 50(m) plot with at least 5

fallen trees.2. Fallen trees DBH > 10(cm).3. Point frame method at top and

bottom of each fallen tree4. Record number of contact points

and species name.5. Record location of sample sites6. Random location of 10 sampling

sites where no fallen trees are present. Being sure to stay within the 50(m) x 50(m) plot.

7. Point frame method at each random location.

Sample SiteKey:• Fallen tree =• Sampling location = (fallen trees)• Sampling location =

(open areas)

   

           

top     trun

k

               top

   

                  top 

                 trunk

 

           

top     trun

k

 

                   

                   

 top    trunk

     trunk

       

                   

                   

50 (m)

50 (m

)

Results• P-value = 0.5499 > 0.05,

so I cannot reject my null hypothesis.

• There is no significant relationship between Vaccinium percent cover for these two sites.

• Standard Error for Fallen = 0.068

• Standard Error for Open Area = 0.062

Fallen0.26

0.27

0.28

0.29

0.3

0.31

0.32

0.33

0.34

0.336

0.288

Average % Cover

Open AreaA

vera

ge P

erce

nt C

over

Average Percent Cover of Vaccinium myrtillus Between Fallen Trees and Open Space

Results• Samples taken by fallen trees

reveal greater average percent cover at the top, compared to the trunk of the tree.

• P-value = 0.057 > 0.05• T-test of the samples reveal

that there is no significant difference in percent cover between these sites, but close.

• Standard error for the trunk = 0.072

• Standard error for the top = 0.109

Trunk0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.248

0.424

Top

Average Percent Cover of Vaccinium at Trunk and Top of Fallen Trees

Ave

rage

Per

cent

Cov

er

Discussion• Eriksson and Fröborg (1996)

found that decaying wood is a favorable substrate for Vaccinium, but my findings do not adhere to their results.

• Window of opportunity must align in time with Vaccinium fruiting and seed dispersal.

• Would other species present in the understory provide different results?

• What is the relationship among Vaccinium percent cover for fallen trees between the trunk and top of the tree.

Summary“The occurrence of decaying wood is spatially

unpredictable in coniferous forests but at least in natural or semi natural forests not temporally unpredictable” (Eriksson, Fröborg 1996).

Need to consider the timing of seed dispersal for understory species in relation to windows of opportunity and percent cover of the forest floor.

Fallen trees alone are not enough to increase percent cover for Vaccinium myrtillus.

References"Comprehensive Report Association - Abies Lasiocarpa - Picea

Engelmannii / Vaccinium Myrtillus Forest." Comprehensive Report Association - Abies Lasiocarpa - Picea Engelmannii / Vaccinium Myrtillus Forest. Nature Serve, n.d. Web. 17 July 2013.

Eriksson, Ove, and Heléne Fröborg. ""Windows of Opportunity" for Recruitment in Long-lived Clonal Plants: Experimental Studies of Seedling Establishment in Vaccinium Shrubs." Botany 74.9 (1996): 1369-374. Print.

"Standard Error." Definition. N.p., n.d. Web. 17 July 2013."Window Of Opportunity." Definition. N.p., n.d. Web. 17 July

2013.

Appendix I

1 2 3 4 5 6 7 8 9 100

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Fallen

Open Area

Sample Number

Per

cent

Cov

er

Percent Cover of Vaccinium myrtillus in CO Subalpine Conifer Forest

• High variability in percent cover for Vaccinium myrtillus throughout all sampling sites