Johannes (Jean) M H Knops
Johannes "Jean" Knops
Professor

Ph.D. Arizona State, 1994
Contact Information
211A Manter
402.310.3904

 

Research Interests


I am broadly interested in all areas of ecology but especially in the interface between plant population, community, and ecosystem ecology. Biotic interactions, resource availability, and species pools interact to govern the assembly, diversity, and functioning of plant communities. This understanding is key to predicting future changes in ecosystems since biotic interactions, resource availability, and species pool change as a result of global change. Secondly, I am interested in feedbacks through nutrient cycling and density-dependent biotic processes that influence the composition, diversity and the functioning of plant communities. Thirdly, I am interested in understanding the impacts of management and human-induced global changes on biodiversity and ecosystem function and applying this understanding to the conservation and restoration of native plant communities.

I think that changes in biodiversity, either through local extinction or biological invasions, is the single most important and dramatic problem in contemporary ecology, and to understand these changes we need to place community ecology in the context of population and ecosystem processes. I also think that this is essential to study the mechanisms that control species diversity as a way to predict the consequences of global change on diversity. I am interested in testing and developing mechanisms of what controls biodiversity using experimental and observational studies of plant communities in combination with mathematical and statistical models and simulations.

My approach has been to combine observational data with well-replicated field experiments using a theoretical framework. Some of the questions that I am currently working on are:

1. How biodiversity in plant communities changes over successional time and how this links with ecosystem carbon and nitrogen cycling

2.The relative importance of biotic and abiotic processes that structure biodiversity and that control successional changes in plant communities

3. How changes in the environment, such as elevated CO2, fire, nitrogen additions, herbivory and species pools, drive changes in community composition and what the consequences of these changes are for ecosystem dynamics

4. How invasive plant species differ from natives, and which traits translate into a competitive advantage and what the consequence of an invasion is for ecosystem dynamics

5. The effects of nutrient limitation for diversity, stability and composition of grassland ecosystems.

6. The interactive effects of carbon dioxide, nitrogen deposition and plant diversity on primary productivity decomposition and soil organic carbon and nitrogen pools

7. Carbon sequestration, methane and NO2 fluxes in natural and agricultural ecosystems

8. Lastly, I am working with Dr. Koenig on a long-term project to determine which factors influence acorn productivity and oak masting. We are using a 29-year database of acorn productivity of 250 individual trees at a site to determine which factors influence the variability both in time and space that we observe. We expanded our monitoring to 16 additional sites within California. This will allow us to better address regional and statewide scaling issues.

Publications


  • Kochsiek, A.E. & J.M.H. Knops. 2009. Impacts of maize decomposition on the litter carbon balance in irrigated and rainfed no-till agricultural systems. Agricultural and Forest Meteorology, in press.
  • Miles, EK & JMH Knops. 2009. Shifting dominance from native C4 to non-native C3 grasses: Relationships to community diversity. Oikos, in press.
  • Laungani, R & JMH Knops. 2009. Species-driven changes in nitrogen cycling can control plant invasions. Proceedings of the National Academy of Sciences 106:12400-124005.
  • Miles, EK & JMH Knops. 2009. Grassland compositional change in relation to the identity of the dominant matrix-forming grasses. Plant ecology and diversity, in press.
  • Knops, J.M.H. & K.L. Bradley. 2009. Soil carbon and nitrogen accumulation and vertical distribution across a 74-year chronosequence. Soil Science Society of America Journal 73: 2096 – 2104.
  • Bakker, E.S., J.M.H. Knops, D.G. Milchunas, M.E. Ritchie & H. Olff. 2009. Cross-site comparison of herbivore impact on nitrogen availability in grasslands: the role of plant nitrogen concentration. Oikos 118: 1613-1622.
  • Koenig, W.D., J.M.H. Knops, W. Carmen & D. Sage. 2009. No trade-off between seed size and number in the valley oak Quercus lobata. American Naturalist 173:682-688.
  • Knops, J.M.H., W.D. Koenig & W. Carmen. 2007. A negative correlation between growth and reproduction does not imply a tradeoff between growth and reproduction in California oaks. Proceedings of the National Academy of Sciences: 104: 16982-16985.
  • Knops, J.M.H., S. Naeem & P. Reich. 2007. The impact of elevated CO2, increased nitrogen availability and biodiversity on plant tissue quality and decomposition. Global Change Biology 13: 1960-1973.
  • Knops, J.M.H. 2006. Fire does not alter vegetation in infertile prairie. Oecologia 150: 477-483.
  • Reich, P.B., S.E. Hobbie, T. Lee, D.S. Ellsworth, J.B. West, D. Tilman, J.M.H. Knops, S. Naeem & J. Trost. 2006. Nitrogen limitation constrains sustainability of ecosystem response to CO2. Nature 440: 922-925.
  • Kennedy, T., S. Naeem, K. Howe, J.M.H. Knops, D. Tilman & P. Reich. 2002. Biodiversity as a barrier to ecological invasion. Nature 417: 636-639
  • Knops, J.M.H., K.L. Bradley & D.A. Wedin. 2002. Mechanisms of species impacts on ecosystem nitrogen cycling. Ecology Letters 5: 454-466
  • Tilman, D., P. Reich, J. Knops, D. Wedin, T. Mielke & C. Lehman. 2001. Diversity and productivity in a long-term grassland experiment. Science 294: 843-845.
  • Knops, J.M.H. & D. Tilman. 2000. Dynamics of soil nitrogen and carbon accumulation for 61 years after agricultural abandonment. Ecology, 81: 88-98.
  • Koenig, W.D. & J.M.H. Knops. 1998. Geographic variation in mast-seeding of boreal trees. Nature 396: 225-226
  • Tilman, D., J. Knops, D. Wedin, P. Reich, M. Ritchie & E. Siemann. 1997. The influence of functional diversity and composition on ecosystem processes. Science 277: 1300-1302.
  • Knops, J.M.H., T.H. Nash III & W.H. Schlesinger. 1996. The influence of epiphytic lichens on the nutrient cycling of an oak woodland. Ecological Monographs 66:159-179.
  • Tilman, D., D. Wedin & J. Knops. 1996 Productivity and sustainability influenced by biodiversity in grassland ecosystems. Nature 379: 718-720.