AIM & BACKGROUND

 We invite you to join a new global research network – the Disturbance and Recovery Across Global Grasslands (DRAGNet) – aimed at assessing the generality of factors influencing disturbance recovery and community assembly in herbaceous-dominated ecosystems. This network builds from a decade of highly successful collaborative research by Nutrient Network, but examines a new set of theoretically-motivated questions about the effects and interactions between two pervasive global changes, land disturbance and elemental nutrient supply.

DRAGNet will quantify plant community assembly dynamics and and ecosystem recovery under a wide range of biotic and abiotic conditions, and test whether assembly, recovery rate, or trajectory in herbaceous-dominated plant communities interacts with environmental nutrient enrichment.

This experiment is timely and relevant, as physical disturbances are among the most pervasive impacts of humans on Earth (Ellis 2011; Higgins 2017). Habitat loss via land conversion for agriculture is a leading cause of extinction (Pimm et al. 1995), and biodiversity in grassland systems is particularly affected by land use change (Newbold et al. 2016). Even small-scale disturbances by feral pigs can have long-term impacts on grasslands (Cushman et al. 2004). Although disturbances are an important driver of community dynamics and assembly (Chase 2003; Turner 2010), they now occur concurrent with other human impacts including climate change and nutrient deposition (Steffen et al. 2015).

GOALS

The four primary goals of DRAGNet are to: 
  1. Quantify community assembly, vegetation, recovery rates, and trajectories of change after disturbances across a wide variety of herbaceous-dominated sites under ambient and elevated nutrient supply. 
  2. Determine the relative importance of local and regional processes for community assembly by pairing theoretical models with core and additional "add-on" seed bank/seed rain data. 
  3. Quantify community resistance to, and resilience after, short-term nutrient addition
  4. Gain insights into the reproducibility of ecological experiments by leveraging plot-level data from sites already participating in NutNet and replicating the same treatments (control and nutrients) in different starting years. 

DESIGN & IMPLEMENTATION

Our detailed protocols are described on our website.  The DRAGNet experiment will consist of a set of 3 completely randomized blocks (within-site spatial replicates), each with five, 5 x 5 m plots receiving one of 5 treatments: 1. Long-term nutrient addition; 1. Physical disturbance (annual removal of standing vegetation, litter, rhizomes and tilling of the soil); 3. Nutrient addition combined with disturbance; 4. Short-term nutrient addition; or 5. No treatments (controls). The core response variables will be plant species composition, aboveground plant biomass, light intercepted by the plant canopy, and soil chemistry. The sampling protocols are identical to the NutNet experiment, but will also include sampling for an optional seed-bank and seed-rain study. The design has built-in flexibility for site-level or regional add-on studies such as trapping insects, measuring plant traits, or tracking small mammal granivory.
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The time and effort to disturb the plots  will vary among sites, depending on vegetation, soils, etc. However, post-disturbance field sampling, plant sorting, and data entry generally requires about 1-3 days for 2-3 people. The design also is modular; a one-time pre-treatment sampling (“observational dataset”) has proven extremely valuable for addressing a wide variety of questions, as well. We cannot provide funds for this project, but we have designed it to be inexpensive (see Time and Financial Costs under Protocol). For example, maintenance of the nutrient treatment plots is only the cost of fertilizer (about $50 per year for US participants). 

TIMING

DATA SHARING
​Sites may join at any time, but to be eligible for the first round of “opt-out” papers (papers that include all participants by default), sites must establish their plots and collect baseline data no later than December 2022. We hope that sites will maintain their experiment for at least ten years, but we have designed the experiment to provide opportunities for meaningful experimental contributions on shorter timelines.
​Our guidelines for network participation are the same as NutNet. The collaborative nature of DRAGNet requires that all scientists must be willing to share their core data with others in the network. We request that collaborators send us their site’s core data within 3 months of collection. All network members can access the network data thereafter, following network guidelines. Our goal is for project data to go into the public domain three years after collection or upon first publication.

BENEFITS
One of the greatest advantages of contributing to DRAGNet, besides the collection of data comparable across continents, will be interactions by yourself and your lab with a collaborative network. In addition to many opportunities for coauthorhsip on DRAGNet publications, participants will be welcome to collaborate on research that uses over a decade of NutNet data from more than 100 sites around the world. DRAGNet also provides an experimental platform with capacity to answer research questions not yet envisioned, either via “add-on” studies that require new measurements, or with analyses of core data.

References

Borer, E.T., Grace, J.B., Harpole, W.S., MacDougall, A.S. & Seabloom, E.W. (2017). A decade of insights into grassland ecosystem responses to global environmental change. Nat. Ecol. Evol., 1, 1–7

Cushman, J., Trisha A. Tierney, & Jean M. Hinds. 2004. Variable Effects of Feral Pig Disturbances on Native and Exotic Plants in a California Grassland. Ecological Applications, 14(6), 1746-1756

Ellis, E.C. (2011). Anthropogenic transformation of the terrestrial biosphere. Philos. Trans. R. Soc. A Math. Phys. Eng. Sci., 369, 1010–1035 Higgins, S.I. (2017). Ecosystem assembly: A mission for terrestiral Earth system science. Ecosystems, 20, 69–77

Newbold, T., Hudson, L.W., Arnell, A.P., Contu, S., De Palma, A., Ferrier, S., et al. (2016). Has land use pushed terrestrial biodiversity beyond the planetary boundary? A global assessment. Science (80-. )., 354, 288–291

Pimm, S.L., Russell, G.J., Gittleman, J.L. & Brooks, T.M. (1995). The future of biodiversity. Science (80-. )., 269, 347–350

Steffen, W., Richardson, K., Rockstrom, J., Cornell, S.E., Fetzer, I., Bennett, E.M., et al. (2015). Planetary boundaries: Guiding human development on a changing planet. Science (80-. )., 347, 737–747

Turner, M.G. (2010). Disturbance and landscape dynamics in a changing world. Ecology, 91, 2833–2849