Nikolai Knapp

Research

Since 2021, I am working at the Thuenen Institute of Forest Ecosystems, where I am responsible for the coordination and data analysis of the German crown condition survey ( WZE ) within the ICP forests monitoring program. My research is about modeling tree vitality and mortality by integrating field data, remote sensing, machine learning and process models.

Personal Thuenen website

WZE data visualization

From 2015 to 2021 at UFZ, my main research focus was on the following topics:

My research interest is about linking the fields of remote sensing and forest modelling. Lidar and radar remote sensing allow us to measure forest structures at large scales. Dynamic forest models, like FORMIND , provide tools to study the processes behind the structures. Combining both improves our understanding of how canopy height structure is related to above ground biomass and carbon dynamics. The focus lies on tropical forests. They play an important role in the global carbon cycle, but they are structurally complex and less well covered by inventories compared to other ecosystems.

Project: Biotrop-X

In this context, I also work on the question of how distributions of different forest attributes, such as biomass, growth and mortality, vary with spatial scale. I use forest models of different complexities to investigate how model parameters can be upscaled to obtain coarse-scale simulation results, which are consistent with aggregated fine-scale simulation results. Upscaling and complexity reduction are important for reducing the computational demand of ecological models.

Project: Reduced Complexity Models (RedMod)

FORMIND simulation Lidar simulation

Publications

• Bauer, L., Knapp, N., Fischer, R. (2021):
  Mapping Amazon forest productivity by fusing GEDI lidar waveforms with an individual-based forest model
  Remote Sens. 13 (22), art. 4540 10.3390/rs13224540
• Bruening, J.M., Fischer, R., Bohn, F.J., Armston, J., Armstrong, A.H., Knapp, N., Tang, H., Huth, A., Dubayah, R. (2021):
  Challenges to aboveground biomass prediction from waveform lidar
  Environ. Res. Lett. 16 (12), art. 125013 10.1088/1748-9326/ac3cec
• Cao, Y., Ball, J.G.C., Coomes, D.A., Steinmeier, L., Knapp, N., Wilkes, P., Disney, M., Calders, K., Burt, A., Lin, Y., Jackson, T.D. (2023):
  Benchmarking airborne laser scanning tree segmentation algorithms in broadleaf forests shows high accuracy only for canopy trees
  Int. J. Appl. Earth Obs. Geoinf. 123 , art. 103490 10.1016/j.jag.2023.103490
• Duncanson, L., Kellner, J.R., Armston, J., Dubayah, R., Minor, D.M., Hancock, S., Healey, S.P., Patterson, P.L., Saarela, S., Marselis, S., Silva, C.E., Bruening, J., Goetz, S.J., Tang, H., Hofton, M., Blair, B., Luthcke, S., Fatoyinbo, L., Abernethy, K., Alonso, A., Andersen, H.-E., Aplin, P., Baker, T.R., Barbier, N., Bastin, J.F., Biber, P., Boeckx, P., Bogaert, J., Boschetti, L., Brehm Boucher, P., Boyd, D.S., Burslem, D.F.R.P., Calvo-Rodriguez, S., Chave, J., Chazdon, R.L., Clark, D.B., Clark, D.A., Cohen, W.B., Coomes, D.A., Corona, P., Cushman, K.C., Cutler, M.E.J., Dalling, J.W., Dalponte, M., Dash, J., de-Miguel, S., Deng, S., Woods Ellis, P., Erasmus, B., Fekety, P.A., Fernandez-Landa, A., Ferraz, A., Fischer, R., Fisher, A.G., García-Abril, A., Gobakken, T., Hacker, J.M., Heurich, M., Hill, R.A., Hopkinson, C., Huang, H., Hubbell, S.P., Hudak, A.T., Huth, A., Imbach, B., Jeffery, K.J., Katoh, M., Kearsley, E., Kenfack, D., Kljun, N., Knapp, N., Král, K., Krůček, M., Labrière, N., Lewis, S.L., Longo, M., Lucas, R.M., Main, R., Manzanera, J.A., Vásquez Martínez, R., Mathieu, R., Memiaghe, H., Meyer, V., Monteagudo Mendoza, A., Monerris, A., Montesano, P., Morsdorf, F., Næsset, E., Naidoo, L., Nilus, R., O’Brien, M., Orwig, D.A., Papathanassiou, K., Parker, G., Philipson, C., Phillips, O.L., Pisek, J., Poulsen, J.R., Pretzsch, H., Rüdiger, C., Saatchi, S., Sanchez-Azofeifa, A., Sanchez-Lopez, N., Scholes, R., Silva, C.A., Simard, M., Skidmore, A., Stereńczak, K., Tanase, M., Torresan, C., Valbuena, R., Verbeeck, H., Vrska, T., Wessels, K., White, J.C., White, L.J.T., Zahabu, E., Zgraggen, C. (2022):
  Aboveground biomass density models for NASA’s Global Ecosystem Dynamics Investigation (GEDI) lidar mission
  Remote Sens. Environ. 270 , art. 112845 10.1016/j.rse.2021.112845
• Fischer, R., Bohn, F., Dantas de Paula, M., Dislich, C., Groeneveld, J., Gutiérrez, A.G., Kazmierczak, M., Knapp, N., Lehmann, S., Paulick, S., Pütz, S., Rödig, E., Taubert, F., Köhler, P., Huth, A. (2016):
  Lessons learned from applying a forest gap model to understand ecosystem and carbon dynamics of complex tropical forests
  Ecol. Model. 326 , 124 - 133 10.1016/j.ecolmodel.2015.11.018
• Fischer, R., Knapp, N., Bohn, F., Huth, A. (2019):
  Remote sensing measurements of forest structure types for ecosystem service mapping
  In: Schröter, M., Bonn, A., Klotz, S., Seppelt, R., Baessler, C. (eds.)
  Atlas of ecosystem services : drivers, risks, and societal responses
  Springer International Publishing, Cham, p. 63 - 67 10.1007/978-3-319-96229-0_11
• Fischer, R., Knapp, N., Bohn, F., Shugart, H.H., Huth, A. (2019):
  The relevance of forest structure for biomass and productivity in temperate forests: New perspectives for remote sensing
  Surv. Geophys. 40 (4), 709 - 734 10.1007/s10712-019-09519-x
• Getzin, S., Fischer, R., Knapp, N., Huth, A. (2017):
  Using airborne LiDAR to assess spatial heterogeneity in forest structure on Mount Kilimanjaro
  Landsc. Ecol. 32 (9), 1881 - 1894 10.1007/s10980-017-0550-7
• Gonzalez-Akre, E., Piponiot, C., Lepore, M., Herrmann, V., Lutz, J.A., Baltzer, J.L., Dick, C., Gilbert, G.S., He, F., Heym, M., Huerta, A.I., Jansen, P., Johnson, D.J., Knapp, N., Kral, K., Lin, D., Malhi, Y., McMahon, S., Myers, J.A., Orwig, D., Rodríguez-Hernández, D.I., Russo, S., Shue, J., Wang, X., Wolf, A., Yang, T., Davies, S.J., Anderson-Teixeira, K.J. (2022):
  allodb: An R package for biomass estimation at globally distributed extratropical forest plots
  Methods Ecol. Evol. 13 (2), 330 - 338 10.1111/2041-210X.13756
• Knapp, N. (2019):
  Remote sensing of forests: analyzing biomass stocks, changes and variability with empirical data and simulations
  Dissertation, Universität Osnabrück
  PhD Dissertation 3/2019
  Helmholtz-Zentrum für Umweltforschung - UFZ, Leipzig, XI, 161 pp.
• Knapp, N., Attinger, S., Huth, A. (2022):
  A question of scale: modeling biomass, gain and mortality distributions of a tropical forest
  Biogeosciences 19 (20), 4929 - 4944 10.5194/bg-19-4929-2022
• Knapp, N., Fischer, R., Cazcarra-Bes, V., Huth, A. (2020):
  Structure metrics to generalize biomass estimation from lidar across forest types from different continents
  Remote Sens. Environ. 237 , art. 111597 10.1016/j.rse.2019.111597
• Knapp, N., Fischer, R., Huth, A. (2018):
  Linking lidar and forest modeling to assess biomass estimation across scales and disturbance states
  Remote Sens. Environ. 205 , 199 - 209 10.1016/j.rse.2017.11.018
• Knapp, N., Huth, A., Fischer, R. (2021):
  Tree crowns cause border effects in area-based biomass estimations from remote sensing
  Remote Sens. 13 (8), art. 1592 10.3390/rs13081592
• Knapp, N., Huth, A., Kugler, F., Papathanassiou, K., Condit, R., Hubbell, S.P., Fischer, R. (2018):
  Model-assisted estimation of tropical forest biomass change: a comparison of approaches
  Remote Sens. 10 (5), art. 731 10.3390/rs10050731
• Rödig, E., Knapp, N., Fischer, R., Bohn, F.J., Dubayah, R., Tang, H., Huth, A. (2019):
  From small-scale forest structure to Amazon-wide carbon estimates
  Nat. Commun. 10 , art. 5088 10.1038/s41467-019-13063-y
• Shugart, H.H., Asner, G.P., Fischer, R., Huth, A., Knapp, N., Le Toan, T., Shuman, J.K. (2015):
  Computer and remote-sensing infrastructure to enhance large-scale testing of individual-based forest models
  Front. Ecol. Environ. 13 (9), 503 - 511 10.1890/140327
• Taubert, F., Fischer, R., Knapp, N., Huth, A. (2021):
  Deriving tree size distributions of tropical forests from lidar
  Remote Sens. 13 (1), art. 131 10.3390/rs13010131

CV

Teaching

• UFZ Winterschool Ecological Modelling :
  Grid- and individual-based dynamic models and C++ programming
• Collection & Analysis of Lidar Data , HNE Eberswalde:

  Lidar and spatial data processing in R