1. Biology Department, Colby College, 2014
Nutrient Availability and Species Evenness Influence Productivity During Early Stages of a Tropical Forest Restoration
Julia Rogers (‘16), Emma Rosenfield (‘16), Cathy D. Collins, Susan Gagliardi, Lauren Bizzari
Biology Department, Colby College, 2014
Methods
16 plots 12x12 m cleared from the bamboo
Four replicates of each of the above treatments (Figure 1)
16 trees in each plots
Applied fertilizer five times over 2 wet seasons
Measured tree root circumference after 18 months of growth
Result 4: The effect of the diversity is dependent upon the species identity.
Background
Restorations are projects that seek to convert a degraded landscape and convert it to its original diversity and productivity. Restoration is thus one method of maintaining biodiversity in the face of anthropogenic landscape changes. In our study, we are restoring a nonnative bamboo plantation in Dominical, Costa Rica to a tropical rainforest dominated by native tree species. Because fertilizer is typically added to seedlings in tropical plantations and nutrients are central to determining plant diversity, we are exploring how nutrients and relative species abundances alter the outcome of forest restoration.
Figure 8. The effect of diversity and species on root girth (Guapinol p = ; all others, p > Error bars indicate standard error.
Results
Result 1: Root girth increased with the addition of fertilizer and with increased evenness.
Figure 2. The effect of high evenness (HE) and low evenness (LE), and fertilizer treatments on the average root girth of tropical seedlings in January of (p = ). Error bars indicate standard error.
Discussion
The interaction seen between the diversity treatments and fertilizer (figure 2) is driven by the species characteristics.
Shade-loving trees do not see as great as an effect of the fertilizer treatment as those trees that are sun-loving species (Figure 7)
This fact decreases the effect of the fertilizer in the low evenness treatments because there are shade-loving species that are dominant.
Our questions
1.What is the effect of diversity and fertilizer on the average root girth on tropical tree seedlings?
2. Is there a correlation between root girth and height?
3. Is there a different effect of diversity and fertilizer depending on the species?
4. What is the effect of diversity on each species?
Figure 2. The correlation between root girth and height by species in tropical tree seedlings in January There is a positive correlation for all species although the slopes differ.
Result 2: There is a positive correlation between height and root girth in all tree species studied.
Plot Set-Up
Figure 1a. High evenness, fertilized
Figure 1b. Low evenness, fertilized
Figure 1c. High evenness, not fertilized
Figure 1d. Low evenness, not fertilized
Figure 1. A diagram of our plot set-up. The dark backgrounds indicate fertilized plots, and different colored circles represent different tree species. Evenness is an equal distribution of species abundances.
Implications
Nutrients may be a beneficial addition to tropical forest restoration projects.
Maximizing evenness can increase biomass productivity.
Root girth may be a better indicator of the success of the restoration project than height, at an early stage.
Result 3: The effect of the nutrients is dependent upon the species.
Figure 7. The effect of nutrients on the mean root girth of trees in January 2014, per species. (Cenizaro: p = ; Kapok: p = ; all others p > 0.05) Error bars indicate standard error.
Location
Acknowledgements
I would like to thank Cat Collins, Lauren Bizzari and the rest of the lab team for their assistance with this project. I would also like to the thank the Dean of Faculty’s Students’ Special Projects Fund for the funding for this research.