Appendix A. Model parameters and their estimates for Ips typographus in Scandinavia.
Parameter |
Description |
Estimate |
W0 |
general windfall each year (smaller amounts, snow and windbreak etc, m3) |
11.43 |
kw |
windfall at big windfall events (to be multiplied with windfall randomizer, m3) |
274 |
pw |
yearly probability of big windfall event |
0.0625 |
Sadd |
susceptible trees added every year (m3) |
4 |
L |
threshold for beetle colonisation of susceptible trees (no. of beetles) |
4500 |
bw |
beetles produced from windfall (beetles per m3) |
200 |
ba |
beetles produced from colonized trees (beetles per m3) |
200 |
hs |
slope of volume regression of colonized trees if Nt>L (m3 per beetles) |
0.001621 |
a |
growthrate constant of Gompertz model |
2 |
E |
threshold of epidemic conditions (no. of beetles) |
15000 |
The parameters W0, kw, pw and Sadd were quantified by using data from the national forest inventory of Norway, the windfall taxations of the insurance company Skogbrand, forest stand measurements made by the Norwegian Forest Research Institute, and results from time series analyses of the monitoring data of Ips typographus in Norway (Økland and Berryman 2004). The added volume in the current year (Sadd) and the total volume of mature spruce trees in the current year (Vm) were considered as constants because the stand rotation practice which is dominating the Fennoscandian forest landscapes aims to keep approximately constant proportion of mature stands at the landscape level (Børset 1986).
The values of L and hs were based on the regression parameters found in the Swedish monitoring of Ips typographus populations and spruce tree colonizations (Lindelöw and Schroeder 2000). The experiments by Ogibin (1973) and Anderbrant et al. (1985) were used for estimating the parameter values of bw, ba and a. The beetle numbers per trap at outbreak level (E), which is much higher than the threshold for beetles to start colonization of susceptible trees (L), was based on the survey by Weslien et al. (1989), and the pheromone trapping records in the final years of outbreak in Norway during the 1970s (Økland and Berryman 2004).
LITERATURE CITED
Anderbrant, O., F. Schlyter, and G. Birgersson. 1985. Intraspecific competition affecting parents and offspring in the bark beetle Ips typographus. Oikos 45:89–98.
Børset, O. 1986. Skogskjøtsel II. Landbruksforlaget, Oslo, Norway.
Lindelöw, Å., and M. Schroeder. 2000. Övervakning av granbarkborre (Ips typographus) med feromonfällor och betade träd 1995-2000. Preliminär rapport. Institut för Entomologi, Swedish University of Agriculture, Uppsala, Sweden.
Ogibin, B. N. 1973. Effect of population density on fertility in Ips typographus L., Ékologiya 5:66–72.
Økland, B., and A. Berryman. 2004. Resource dynamic plays a key role in regional fluctuations of the spruce bark beetles Ips typographus. Agricultural and Forest Entomology 6:141–146.
Weslien, J., E. Annila, A. Bakke, B. Bejer, H. H. Eidmann, K. Narvestad, A. Nikula, and H. P. Ravn. 1989. Estimating risks for spruce bark beetle (Ips typographus (L.)) damage using pheromone-baited traps and trees. Scandinavian Journal of Forest Research 4:87–98.