Dr. Catherine Potvin

Biodiversity plantation

The biodiversity plantation of SP consists of a mosaic of diversity plots established as follows: (A) monocultures planted with one of 6 different tree species, each monoculture being replicated twice. Two of the 6 species used in the monoculture are pioneers, 2 intermediates and 2 shade tolerant species; (B) 6 plots of three-species, each triplet containing one species per successional group (C) 6 six-species plots obtained by adding three species, each from a different successional group, to the existing triplets.

The 24 diversity plots were planted in July 2001 with 3 m spacing between trees, 225 trees/plot using: Luehea seemanii and Cordia alliodora (pioneers), Anacardium excelsum and Hura crepitans (light-intermediates) and Cedrela odorata and Tabebuia rosea (shade tolerants). Functional groups were classified based on relative growth rates (respectively, 9.1% and 7.0%; 5.9% and 4.9%; 2.3% and 3.4%).

The following are photos of the plantation from 2002 to 2006

The high diversity plots
The experimental design of the main plantation leaves two questions unanswered:
(1) Is the high diversity treatment relevant to the level of forest diversity?
(2) What is the importance of community composition at high diversity?

To answer these questions, Potvin and collaborators established eight additional reforestation plots in July 2003. The experiment follows a split-plot design with 3 diversity levels per plot, 6, 9 and 18 species. This high species number was chosen after estimating the diversity of plots of 45 m by 45 m in BCI (Barro Colorado Island) and is comparable to background diversity in intact forest (19 species). The high diversity experiment further compares four different mixtures of 6 and 9 species with a total of 36 species used for that experiment.

Mixture 1 - Nine Species The design allows for an explicit test of neighborhood effects.

C cycling model
We have adopted the following conceptual system model to study the cycling and accumulation of C.

According to our model, the driver of the system is photosynthetic C uptake, while C is lost either as plant or soil respiration and herbivory. C is stored in three main stocks (Ab, Bw, So) and moves between those stocks by two flows (L, FR). To meet the specific objectives of both experiments, we will quantify each term of our system's model in both the diversity plots or FACE rings (twice a year over a period of 5 years. We expect that both changes in land use and elevated CO2 will result in larger C stocks and alter C flows.

Core measurements in each of the 24 diversity plots (- collaborative work)

• 100 soil cores every ten years - Moore
• 4 randomly located 0.5m2 quadrats for above ground biomass. Biomass separated in green and brown. Twice per year (June-December) - Potvin
• 2 Randomly located 1 m2 quadrats not cut for diversity ientification. % cover per species in November - Potvin
• 4 litter traps per plot, collected monthly. Leaves identified to species and weighed - Scherer-Lorenzen
• Litter decomposition - Scherer-Lorenzen
• Nutrient pools in tree biomass – Oelmann, Scherer-Lorenzen
• Nutrient pools and fluxes in soil – Moore, Oelmann, Wilcke, Scherer-Lorenzen
• Tree growth (basal diameter (tree < 2m), diameter at breast height (tree > 2m), height, crown projection) every seedling. January - Potvin
• Tree allometry, 5 individuals per species harvested and excavated every three years - Potvin
• 10 productivity plots (50 X 50 cm) under each tower over 1 week. June and December - Potvin