Integrating forest disturbance of nun moth into process-based growth modelling Authors M. Gutsch, A. Degenhardt, M. Wenk, C. Kollas, P. Lasch-Born, F. Suckow
Project WAHYKLAS – Forest health adaptation strategies to mitigate increasing harmful organisms in climate vulnerable regions under increasing restrictions PIK Research Domain II: Climate Impacts & Vulnerabilities
Introduction
Implementation
We integrated an existing model approach of several biotic disturbance impacts into the processbased forest stand model 4C. In this framework, insects and pathogens are clustered upon their damaging action and abstracted on the level of functional groups (e.g. defoliators). Here the validation of the extended model is based on observed impacts of a nun moth (Lymantria monacha, Linnaeus, 1758) gradation (2004) in two pine stands in Brandenburg, Germany. Another validation is shown on a second poster by Kollas et al: Mistletoeinduced growth reductions at the Nonnenkahlfraß, Lausitzer Rundschau 11. April 2012 forest stand scale.
Biotic disturbances were implemented into the model 4C using the general framework proposed by Dietze and Matthes (2014) (Fig. 1). Concerning defoliation events the implemented algorithms work as follows: • Based on the disturbance year, the start of disturbance (day of year), the percent foliage loss the consumed leaf mass is removed from the crown and added to the litter • Allocation of assimilated carbon at the end of the year to root, stem and foliage • Additional carbon provided by the NSC-storage pool to compensate the reduced assimilation (due to defoliation) Functional group Impact Defoliator % foliage loss Xylem clogger % reduction in water supply rate % increase in transpiration Xylem feeder % carbon reduction Phloem feeder % carbon reduction Root damage % increase in turnover rate Stem rot % increase in stem mortality
Fig. 1 General concept of implementing biotic disturbances into process-based forest growth modelling after Dietze and Matthes (2014) .
Data and Simulation Observed tree ring data were available for two pine stands (age 51 and 68 in 2004) located in the northeast of Germany (Brandenburg) with nun moth outbreak in 2003 . The data set encompass increment cores, diameter at breast height (2004), left foliage cover (2004) of 58 and 33 tree individuals, respectively. 4C-Simulations were conducted with two theoretical pine stands matching age and diameter of the two real pine stands. The analysis encompassed 6 simulation runs with defoliation in 2003, start of foliage loss at day 153 and six levels of foliage loss (100, 90,…,50%). Observed and simulated data of the two pine stands were pooled together in the analysis due to high correspondence between the two stands.
Fig. 2 Mean relative radial growth (with respect to the median of 2000-2009) of simulated and observed trees. Vertical segments show the standard deviation of all simulated and observed trees.
Fig. 3 Probability of radial growth decrease below 10% of average radial growth. Curves show the mean probability for all simulated and observed trees.
Results The simulated relative radial growth show high accordance to the observed curve (Fig. 2). The observed radial growth shows a time lag of one year in its response to the defoliation. This cannot be captured by the model, were the highest decrease of radial growth is in the disturbance year itself (Fig. 2). The sensitivity of the decrease of the relative radial growth due to different levels of left foliage cover after the disturbance was reproduced well by the model (Fig 3.). In addition, the extended model 4C also depicts well the recovery of the radial growth after the disturbance (Fig. 4).
Fig. 4 Number of years needed to recover the relative radial growth to 90% of the median radial growth between 2000-2009.
Conclusion and Outlook The amended model 4C shows plausible growth responses simulating a severe defoliation. This was validated with tree ring data of two pine stands in the northeast of Germany. The validation has to be extended by other disturbance events from other regions. This would enable simulation studies at larger scale to analyse effects concerning timber yield losses with scenarios of biotic disturbances. The implementation also allows coupling 4C with explicit biotic disturbance models. cited Reference: M.C. Dietze and J.H. Matthes, Ecology Letters (2014) 17: 1418–1426
Contact Dr. M. Gutsch Telegrafenberg A62 | 14473 Potsdam
[email protected] Gefördert durch das Bundesministerium für Ernährung und Landwirtschaft und das Bundesministerium für Umwelt, Naturschutz, Bau und Reaktorsicherheit aufgrund eines Beschlusses des Deutschen Bundestages.
