- Cooperative Forestry & Pest Management

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1 PRONG BNDER j - Cooperative Forestry & Pest Management SD 4-4 Pr 3.. g3- Report July 983 PERMANENT MOUNTAN PNE BEETLE POPULATON TREND PLOTS: AN UPDATE, 983 by Kenneth E. Gibson ABSTRACT For the fourth year since their establishment, the six permanent plot locations in Montana were revisited following beetle flight in 982. Beetle populations remained low in five of the six areas. Only in the Murr Creek plots did newly attacked trees represent an epidemic beetle population. n the Centennial Valley location, several plots had been logged. Growth and phloem thickness data were collected from Murr Creek, Boulder Creek, and Dunsire Creek in an effort to explain why beetle numbers are not building in these areas as rapidly as we had anticipated. nsufficient data has been collected, as yet, to reach meaningful conclusions. n NTRODUCTON Following beetle flight in 982, we once again visited the six areas in the State containing permanent mountain pine beetle trend plots. These plots, 3 in each of the six areas, were established in July 979 (Gibson et al. 98). n 979, and each year since, the plots have been monitored after beetle flight (Gibson 98, 982). Plots were originally established in areas of lodgepole pine which were then uninfested, or with low populations, but which we considered to be high risk for beetle infestation--based on criteria described by Amman et al. (977). Our intent is to follow the course of the infestation over stands of known preoutbreak characteristics. We expect that impact data collected from the beginning to the end of the infestation will enhance management recommendations for lodgepole pine stands threatened by mountain pine beetle. While beetle populations have not yet developed in some areas to the extent we anticipated, any information regarding the failure of stands to support beetle outbreaks will be valuable. Such information may assist us in our attempts to refine risk rating systems. United States Forest Northern RO. Box 7669 Department of Service Region Missoula, Montana Agriculture 5987

2 RESULTS AND DSCUSSON To date, beetle populations still are not developing in some areas as we expected (based on the risk-rating criteria we used). n other areas, the infestation has apparently peaked and is beginning to wane. Most notable of those areas is Centennial Valley, where trees per acre attacked have steadily declined since 979. n 982, no new attacks were observed there. n addition, four of the previously heavily attacked plots were logged sometime before our evaluation in 982. Data compiled from the 3 plots in that area (tables and 2) indicate the beetle did have a decimating effect on those lodgepole pine stands. Though only 3 percent of the trees over 5 inches d.b.h. were killed, those trees represented 85 percent of the volume. That explains, at least in part, the decline of the infestation since its peak in 979. Slightly more than '5 green trees per acre over 5 inches d.b.h. remain; however, they are in the smaller diameter classes and represent only 34 board feet volume per acre. Beetle populations are expected to remain endemic in those stands for the next several years. The Madison River plots have also shown a consistent decline in new attacks for the past 4 years--having peaked in 978. Though only 8 percent of the lodgepole pine greater than 5 inches d.b.h. was killed, those few trees represented 6 percent of the lodgepole volume in the stands. No new attacks were observed in those plots in 982 and, as in the Centennial Valley plots, those green trees remaining are of sufficiently small diameters (mostly 5-8 inches d.b.h.) that adequate food supplies for sustained beetle populations may no longer exist. The data collected from the Murr Creek/North Fork Murr Creek plots indicate that while numbers of newly attacked trees have remained fairly constant for the past 3 years, many susceptible trees remain. All of the characteristics we usually associate with high risk for mountain pine beetle attack in lodgepole pine are present in most of these stands: age is about years, average diameter approximately inches, and elevation-latitude (4,4 feet; 48 N) factor is in the high-risk range. Some factor or set of factors must be keeping beetle populations relatively low in these stands. t could be that the beetles are just taking an abnormally long time to build up. Amman (982) has stated that epidemics in a given stand usually last 5 to 7 years. Last year, 982, was the sixth consecutive year we have measured annual mortality above what is usually considered epidemic conditions (> tree per acre). Some infestations have been known to persist for years in a low epidemic/high endemic condition (W. E. Cole, pers. comm.). Such longstanding infestations are largely unexplained.

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5 4 Explaining the low infestation level in the final three plot areas is even more difficult. n all three areas--boulder Creek, Dunsire Creek, 4) and Spotted Bear--the infestations have been at endemic levels or below for most of the past 4 years. No new attacks were observed in either the Boulder Creek or Dunsire Creek plots in 982. n the 3 plots at Spotted Bear, two new attacks were recorded--one on each of two plots. Risk-rating criteria described by Amman et al. (977) identify Spotted Bear and Dunsire Creek as high risk for beetle attack and Boulder Creek as moderate: Area Average d.b.h. LPP li >5 inches Avg. AS...q Elevation/latitude Spotted Bear 8.5 inches 4,'/47 5'. Dunsire Creek 9.3 inches -/ 2 4,4'/48 2' Boulder Cree 7.8 inches - 5 4,8'/48 5' / These are average diameters for all lodgepole over 5 inches in the 3 plots. Many trees, and all those for which growth and phloem thickness were measured, vary from to 2 inches d.b.h. t may be that beetle populations are still building in those areas, and the trees may yet be attacked. nfestations have existed,however, in areas near those stands for several years. Thus, it seems that stand characteristics other than those normally associated with "high risk" are influencing these stands' susceptibility to the beetle. n 982, began collecting growth rate and phloem thickness data in these areas--from both infested and uninfested trees--in an effort to determine if these factors may be contributing to the low beetle populations found there. As yet, insufficient data have been collected to reach meaningful conclusions. plan to continue collecting that information in 983. When we established these permanent plots, our intent was to gather impact data through the course of an infestation. nfestations of epidemic proportions have not yet developed in three of the six areas. f those stands remain uninfested, or if infestations take an abnormally long time to build there, and we are able to identify the stand characteristics responsible, we may be able to refine our risk-rating systems. That informtion, too, will be of great importance to the land manager.

6 REFERENCES Amman, G. D The mountain pine beetle--identification, biology, causes of outbreaks, and entomological research needs. n Proceedings of the Joint Canada/USA workshop on Mountain Pine Beetle Related Problems in Western North America, D. R. MacDonald and D. A. Graham, Cochairman. Environ. Canada, Can. For. Serv., Victoria, B.C. pp Amman, G. D., M. D. McGregor, D. B. Cahill, and W. H. Klein Guidelines for reducing losses of lodgepole pine to the mountain pine beetle in unmanaged stands in the Rocky Mountains. USDA, For. Serv., nt. For. & Range Exp. Stn., Ogden, UT. Gen. Tech. Rpt. NT-36, 9 pp. Gibson, K. E Permanent mountain pine beetle population trend plots: an update 982. USDA For. Serv., Northern Region, S&PF, CFPM Rpt. 82-9, 5 pp. Gibson, K. E. 98. Permanent mountain pine beetle population trend plots: an update, 98. USDA For. Serv., Northern Region, S&PF, FPM Rpt. 8-4, 4 pp. Gibson, K. E., M. D. McGregor, and D. D. Bennett. 98. Establishment report: Permanent mountain pine beetle trend plots, Montana, 979. USDA For. Serv., Northern Region, S&PF, FPM Rpt. 8-8, 4 pp. 4