Site BiodiversiTREE (US)


Experiment
BiodiversiTREE@SERC was established in 2013 with the goal of examining how diversity both within and among tree species influences local and landscape level processes, including above and belowground productivity, soil nutrient retention, soil carbon turnover, resistance to herbivory, and water quality. In addition, most of the experimental site is a self-contained watershed that has been intensively studied by Smithsonian scientists for over 30 years. Phase I of the experiment replants 13 hectares of the watershed that have been in continuous corn agriculture since 1978, with a similarly long period of monitoring water quantity/quality from an instrumented weir (WS108). This provides an opportunity to examine how reforestation impacts watershed quality. In addition, corn is a C4 plant with a different isotopic carbon signature than C3 trees. Thus, by tracking changes in soil carbon isotopes through time, we can estimate the quantity, turnover and movement of carbon in the soil as the land returns to forest.

overview BiodiversiTREE
Squares depict experimental plots and are drawn to scale. Yellow squares outlined in black were planted in 2013, and white-outlined squares will be planted in 2014. Watershed WS108 is delineated with thick black lines. The white circle indicates a water-sampling weir at the base of WS108.


Basic design
The experimental design addresses four fundamental questions:

1. Does tree species diversity impact forest productivity and ecosystem function?

BiodiversiTREE@SERC utilizes a classic diversity-ecosystem function manipulation, whereby 16 tree species are planted into monoculture plots (n=2 plots per species), 4-species plots (n=19), or 12-species plots (n=19). Each plot is 35 m x 35 m in size, and density is held constant at 255 trees/plot (hexagonal grid spacing with 2.4 m between trees). The pool of species includes 14 canopy and 2 sub-canopy tree species, including 16 of the top 20 species by basal area in local forests. For comparison, natural patterns of species diversity in similarly-sized plots range from 1-13 species. Thus, our experimental manipulation of 12 species spans the natural gradient of species diversity found in local forests.
We will monitor tree survival and growth over time, focusing on a core of n=143 trees in the center of each plot. To account for edge effects, each plot has a buffer strip of 112 trees in a 2.4 m band that will not be sampled.

2. Is functional diversity important?

To address this question, each of our 4-spp plots is arranged on a gradient of all arbuscular mycorrhizal species, all ectomycorrhizal species, or every combination therein. Thus, these plots all have the same species richness and density, but varying levels of functional diversity defined by the relationship between trees that associate with arbuscular versus ectomycorrhizal fungi. The former are typically early successional species living in more mesic environments, whereas the latter are typically climax species living in areas where litter and soil nutrients are more recalcitrant.

3. How will species and population sources respond to climate change?

For each species, we used seed sources that derived from both mid-Atlantic populations (similar in latitude to the experimental location), and more southern populations (Florida and Georgia, two USDA growing bands to the south). Each provenance is represented equally in each plot where that species located. This approach opens up avenues of future research into how both species and populations within a species respond to a changing climate.

4. How does tree diversity impact water quality and quantity?

As the forest becomes established, we can observe, in real-time, how water discharge changes by monitoring the weirs at the base of BiodiversiTREE@SERC and compare these data with discharges over the past 20 years. We expect that replacing cropland with tree plots will increase evapotranspiration, decreasing the amount and variability of water discharge, and that the cessation of fertilizer application will likely decrease nitrogen (especially dissolved nitrate) discharge. Understanding the time lag between reduction in N inputs to the watershed and reduction of N discharges to the watershed is important for predicting the effects of nutrient management practices in watersheds. Eventually the goal is to connect plot-level measurements of water quality to landscape-level measurements.



Site characteristics

Location Edgewater, MD, USA
Area 13 ha
No of plots 75
No of trees planted 17 850
Planting date April 2013
Former land use corn agriculture
Altitude 7-28 m
Soil type loamy fluviomarine deposits
Species pool Acer rubrum, Carpinus caroliniana, Carya alba, Carya glabra, Cornus florida, Fagus grandifolia, Fraxinus pennsylvica, Liriodendron tulipifera, Liquidambar styraciflua, Nyssa sylvatica, Platanus occidentalis, Quercus alba, Quercus falcata, Quercus rubra, Quercus velutina, Ulmus americana



Site maintenance

The site was in relatively long-term no-till corn agriculture until the year before planting. Prior to planting, corn stubble was mowed, but no other alterations were made. In the first year, we have mowed between trees to reduce the height of competing vegetation and hand-removed volunteer tree species with a machete. Trees are individually caged to protect them from deer browsing.



Research

First data were collected on the timing of bud break and leaf out for each species. Work is now proceeding to characterize the baseline soil nutrient conditions, carbon pools, and invertebrate fauna. In year 1 we will also assess insect damage, initial height, and initial transplant survival.



Extra information

For more information on the BiodiversiTREE experiment, please e-mail the contact person:

Contact person Dr. John D. Parker


photo planting
planting of the experiment (April 2013)