Principle – Ecological Integrity

Criterion- Genetic Diversity

Indicator – Population sizes and reproductive success are adequate to maintain levels of genetic diversity.

Box B: Definition:

Genetic diversity is essential to allow adaptation to environmental change. Genetic diversity refers to the variety of genes coding for particular traits present in populations. Most temperate forest trees are outcrossing with long distance dispersion of gametes, resulting in high levels of genetic variability within populations but often little differentiation between neighboring populations. Other forest species have different genetic strategies and structures. Almost all forest species develop specific adaptations under spatially different environmental conditions, and these adaptations are maintained by natural selection. Important factors in maintaining adequate levels of genetic diversity to allow for continued adaptation to environmental change are population size and reproductive success (Namkoong et al, submitted).

Box D: Applicability to Different Landowners. Explain any differences:

Monitoring population size, and especially making periodic genetic diversity measurements is more applicable to large landowners than small ones. All landowners generally monitor regeneration. Larger landowners and government agencies can coordinate genetic monitoring programs, to develop baseline date where it is lacking and provide periodic measures of genetic diversity.

Box E: Overlap.

CIFOR 2.4.5 (T1) 1.2.2

Notes:

Maintaining adequate population sizes to ensure maintenance of genetic diversity is best done at tenure level, though both larger and smaller scales are important as well. The scale is finer than regional, however.

Notes:

The indicator is diagnostic in that it provides information about the expected genetic state of the forest today, but it is stronger as a predictive tool. As population size decreases, and if it remains small for several generations, the incidence of inbreeding and genetic drift increases, reducing the genetic diversity, reproductive success and adaptive potential.

Notes:

The indicator primarily describes composition. Genetic diversity measures describe the state of populations. Changing levels of genetic diversity affect genetic processes and function of the system.

Box I: Underlying Concepts:

Genetic diversity is an essential component of sustainable forest management. Genetic diversity is the basis of evolution and thus is essential for adaptive response to environmental change. Genetic diversity of forest species varies from almost zero to very high levels. Most tree species are at the high end with relatively high levels of both genetic diversity and genetic load. This means that tree species not only have high adaptive potential, but consequences of loss of genetic diversity, if accompanied by inbreeding in small populations, are generally directly deleterious.

The plight of butternut in North America, offers an example of the importance of maintaining large genetically diverse populations of trees. Butternut has been seriously challenged by an exotic disease, which is very rapidly killing trees everywhere throughout the species range. The progress of the pathogen known as butternut canker is so fast that there is no time for the species to develop new resistance. The only chance that the species has for survival is if there is existing "preadapted variation" that gives some small proportion of the species resistance to the pathogen.

Red spruce is an example of a late-successional species that very likely has lost genetic variability as a result of past inappropriate forestry practices. Estimates put the current extent of the species at 1/5^th of its historical distribution and frequency in the United States. Clear cutting red spruces appears to result in relatively high levels of hybrids among regeneration when black spruce pollen sources are available. Thus populations have been lost in some areas and gene pools have been changed by hybridization in others.

Direct measures of genetic diversity would be preferable to the indirect estimate provided by population size, but the methods required to produce direct genetic diversity measures are not routinely used by forest managers. Hence a proxy is essential until genetic monitoring becomes more widely applied. The proxy measure that is likely to be generally most reliable is population size.

Namkoong et al. (1997) discussed population size as a verifier for genetic diversity. They pointed out that effective population size is a recognized indicator of the changes that lead to reduced genetic diversity. The estimation of effective population size is difficult, however, particularly where populations are heterogeneous in terms of age structure. Estimates of numbers of mature individuals, presumably contributing to the mating pool, are much more easily acquired from inventory data. The use of simple population size of mature individuals instead of effective population size necessitates increasing the number several-fold because the assumptions that mating is random and all mature individuals have equal opportunity to contribute genes to future generations are rarely true in nature.

Ledig (1992) pointed out that most harvest practices still result in dramatic swings in population size and age class structure. Leaving low numbers of parents in a seed tree cut may be result in elevated levels of inbreeding reducing survival, growth and fecundity of the offspring. In addition to ensuring that population size is sufficient and that the population achieves reproductive success, as indicated by surviving natural regeneration, density of seed trees retained after a partial cut, must be sufficient to avoid increasing natural inbreeding level.

From the perspective of long term sustainability, it cannot be assumed that plantations will always be followed by plantations, thus the genetic composition of the plantations must be sufficiently diverse and locally adapted to result in viable natural regeneration. When genetically improved material is extensively planted, buffers separating plantations from natural populations of the same species will protect the genetic diversity of these populations.

Population size, coupled with reproductive success, is a proxy for genetic diversity because except in cases where species are being assessed for genetic diversity under prevalent forest harvesting regimes, data is neither available nor quickly attainable on the comparative diversity levels themselves.

Box J: Relevance to Sustainable/Unsustainable Management:

From CCFM:

"The genetic diversity of Canada’s forests is truly an inheritance from previous generations, and we are responsible for passing it on unimpaired to future generations. Conserving genetic diversity is key to ensuring that species retain their capacity to evolve and adapt to change. It sustains the productive capacity and resilience of forest ecosystems, and it can be viewed as the fundamental basis of the diversity of all species and the ecosystems of which they are a part.

Sustainable forest management requires a commitment by forest agencies to conserve locally or regionally adapted populations of Canada’s major commercial tree species using a combination of in situ and ex situ approaches. It also requires special conservation measures for rare and endangered vegetation species.

Conserving and managing genetic diversity is a key element in operational forest management planning. Foresters must consider genetic diversity in planning for natural regeneration. In white pine stands, for example, it has been found the "seed tree" cuts (i.e. where only a few widely spaced mature trees remain in harvested areas) do not allow sufficient cross—pollination to avoid inbreeding and serious growth loss in seedlings. Other silvicultural systems, such as shelterwood cuts, are now preferred for this species."

From Namkoong, et al. (submitted to CIFOR):

"Genetic variation is required for species to have successfully met the challenges of the past and to survive and reproduce under current environmental conditions. Conservation of genetic diversity is also a necessary precondition for the future evolution and adaptability of local populations and of the entire species (e.g. Newman and Pilson, 1997). Thus, conservation of genetic diversity is a necessary element in the maintenance of all other levels of biodiversity that we value for their existence and utility. However, genetic diversity is difficult to measure directly and is often cryptic in its effects on population and ecosystem dynamics. Hence its loss is easy to ignore – until it is too late to restore, thus threatening the capacity of species and ecosystems to adapt to changing environments. Genetic erosion ultimately induces species extinction and ecosystem loss, and eliminates the possibility of using genetic variation for economic gain and ecological restoration.

Box K: Measurement Methods – red spruce, tree improvement

In evaluating genetic indicators, first the target species and populations must be identified. In general the species that are chosen should be sensitive to forestry practices that are being carried out or other human induced perturbation in the region. Likewise for the choice of populations: the populations must be located in areas where the effects of the identified disturbance are occurring.

The choice of species for assessment should not be limited to those for which the most information is available but instead should be based on an evaluation of the likely effects of past and present forestry practices on the native tree species. This could be done as follows:

4. Categorize species including those with little or no commercial value, according to silvics and habitat requirements; eg. shade tolerant, shade intolerant, moisture requirement, etc.; and by range and frequency reduction or expansion in study area compared to reference (historical) levels.
5. List forestry intervention methods including proportion of study area treated by each method, and predict impact on the basis of silvics, habitat requirements, range and frequency of the species. Identify any additional human-caused or naturally occurring environmental changes that may be impacting populations of forest species. Check with local experts.
6. Identify those species that are expected to be impacted by the forestry practices.

Considerations in determining whether or not the evolutionary potential of a species is impacted by forestry practices:

1. Is the range or frequency of the species decreasing? Have populations become isolated?
2. Does the cutting practice suit the silvics of the species; e.g. does the predominant harvest method provide for the shade conditions required by the species?
3. Is regeneration adequate to maintain population size?
4. Are sufficient numbers of seed trees left on site (at least 10 per acre) to avoid inbreeding?

4. Among those species that are known or suspected to be susceptible to genetic change as a result of forest practices, choose several representing different impacts. For example, the assessor might choose one species that is undergoing intensive selection in a tree improvement program, one or more species of little commercial value that have substantially declined in the study area, and one or more species that do not respond well to the prevalent harvesting practices.
5. Much of the required information should be available from standard inventories. Sampling must be done in reference populations as well as those impacted by forest harvesting. Reference populations should be managed to reflect natural condition as much as possible. In most areas, this means no active intervention. In fire prone areas, it means management allows or even sets fires to maintain the species and habitat conditions natural for the site.
6. Permanent sample plot data in combined with aerial photo interpretation can be extrapolated to provide population numbers of tree species in various size classes, including established regeneration, per unit area. Data collection could be modified to include any other forst vegetation.
7. If possible, actual genetic diversity parameters should be measured and monitored over time for all commercial species and others of special concern. It is especially important to initiate comparative genetic diversity monitoring when population sizes are declining.
8. Monitor genetic diversity directly through a combination of isozyme analysis and common garden testing to ensure that the genetic variance is not being reduced for sets of selectively neutral and adaptive traits to ensure that the genetic variance is not being reduced for sets of selectively neutral and adaptive traits. Reference populations must be sampled as well as populations that may be impacted by forestry practices or other human induced stressors.
9. Monitoring of populations throughout the range of a number of species known or suspected to be susceptible to human-induced impacts would include populations in reference "natural" areas and populations in areas of active forest management.
10. A good general review of standard measures for describing genetic diversity using isozymes is provided by Berg and Hamrick (1997).

In the southwest Idaho study area, a useful set of tree species to evaluate would be:

Ponderosa pine - plantation species with breeding program, though small, also harvested primarily using partial cuts,

western larch - at the southern limit of the species range, regeneration problems

trembling aspen - primarily clonal, reduced in frequency compared with historical levels; population size must be estimated on the basis of number of clones, not individual trees.

whitebark pine - possibly endangered by the spread of the introduced pathogen, white pine blister rust and the reduction in fire frequency.

Box L: Data Required:

Data required includes inventory data, records of harvesting methods, species frequency, regeneration success – generally obtainable from local forest management agencies.

Monitoring genetic diversity, requires isozyme data collected for at least 20 loci with sample sizes of 50-60 individuals from a range of populations.

Box M: Data Used for the North American Test:

Data for the Boise test is sketchy. There are genetic data available for the commercially important tree species for example short-term common garden experiments conducted by Rehfeldt (1989,1991,1994) and others. However the genetic studies provide baseline information about genetic variability of the species and are not designed to monitor genetic changes as a result of forest harvesting practices.

Information regarding baseline genetic diversity estimates was obtained for some species from the relevant literature and from discussions with geneticists in the area. There is some pertinent data for whitebark pine, showing genetic diversity estimates on the basis of isozymes (Hamrick and Jorgensen 1997).

The best source of data on population size and reproductive success for the national forests is from permanent sample plots, which can be presented by age class including seedlings, species, and habitat type. For the portions of the Boise and Payette National Forests included in the study area, data were from approximately 6000 permanent sample plots. This is not generally available in a spatial format, so population size estimates have to be based on average numbers of trees per acre for particular habitat type strata.

Box N: Example Results:

Baseline levels of genetic variation are high for all the commercial species in the area. No data were found for genetic diversity of aspen in Idaho, and there are no available genetic data to show effects (if any) of forestry practices, in comparison with reference levels of genetic diversity.

Adequate population size varies among species, depending on natural levels of variability and population structure. However, maintaining an effective population size of at least 500 is prudent (Lande and Barrowclough 1987; Frankel and Soule ,1981). Lynch (1996) recommended an effective population size of 1000 to ensure no losses in genetic diversity. The actual census population size is generally several times the effective population size. Thus maintaining interbreeding population sizes of at least 2000 reproductively mature individuals should ensure that there is no net loss in genetic diversity. The expert systems used for seed transfer guidelines (Rehfeldt 1994) could be used to identify the minimum number of populations required in a management area. A minimum of three populations per "zone" should provide a reasonable safety margin.

Because of timing of the request, the specific inventory data required to evaluate population sizes were not available for this test. However, in discussions with practicioners in the state, the following assessment was made:

Ponderosa pine – there are no population size concerns for this species. As a result of fire suppression, the species dynamics have been changed somewhat, but the cover type area may be increasing at this time as a result of reforestation and afforestation, emphasizing this species.

Aspen – this species has declined and continues to do so; it should be monitored over time, both population numbers and direct genetic diversity.

Western larch – regeneration is very poor for this species, some reforestation efforts are underway. The species has low successional amplitude compared to other conifers harvested in the area, and does not respond well to partial cut management. Population sizes and genetic diversity should be monitored.

Whitebark pine – this species is not impacted by forest harvest, though fire suppression is considered to negatively impact its regenerative ability, by creating conditions for fire-susceptible shade tolerant competitors (McCaughey and Schmidt 1990). The greatest challenge for whitebark pine is the exotic white pine blister rust, which has devastated populations, often in conjunction with mountain pine beetle (Kendall and Arno 1990). It is important that genetic diversity, numbers of reproductively mature trees and reproductive success be monitored in the shrinking populations of this species.

Box O: Assessing the Practicality:

The population size and regeneration components of this indicator can be tracked over time relatively easily and inexpensively. Baseline information exists by which to monitor genetic changes over time and this monitoring should be initiated by management agencies.

Box P: Assessing the Information Value :

This indicator, especially when monitored over time will provide useful information to managers and other stakeholders. If the indicator drops, targeted genetic studies should be initiated to track potential genetic consequences.

Strengths – population size and reproductive success are measurable. They provide a reasonable proxy for the genetic information that we are really interested in generating.

Weakness – unless direct genetic monitoring is initiated, the indicator does not provide a direct measure of the genetic variability.

Box R: Did you rewrite or revise to a new indicator. If so what?

This is a new indicator.

Box S: References :

• Brussard, P.F. 1990. The role of genetic diversity in whitebark pine conservation. In Proceedings of the Symposium on Whitebark Pine ecosystems: ecology and management of a high-mountain resource, Bozeman , MT, March 29-31, 1989, pp. 315-318.
• Canadian Council of Forest Ministers. 1997. Criteria & Indicators of Sustainable Forest Management in Canada. Technical Report. Cat. Fo75-3/6-1997E, ISBN 0-662-25623-9. Natural Resources Canada–Canadian Forest Service 8th floor, 580 Booth Street,Ottawa ON
• Frankel, O.H. and M.E. Soule. 1981. Conservation and Evolution. Cambridge University Press, Cambridge, U.S. 327 pp.
• Hamrick, J. and Jorgensen. 1997. CJFR
• Kendall, K.C. and S. F. Arno. 1990. Whitebark pine – an important but endangered wildlife resource. In Proceedings of the Symposium on Whitebark Pine ecosystems: ecology and management of a high-mountain resource, Bozeman , MT, March 29-31, 1989, pp 264-273.
• Lande, R. and G. Barrowclough. 1987. Effective population size, genetic variation, and their use in population management. In: Soule, M.E. (Ed.) Viable Populations for Conservation. Cambridge University Press. Cambridge, U.S, pp. 87-123.
• Ledig, F.T. 1992. Human impacts on genetic diversity in forest ecosystems. OIKOS 63:87-108
• Lynch, M. 1996. A quantitative-genetic perspective on conservation issues. In: Avise, J.C. and J.L. Hamrick. (Eds) Conservation Genetics: Case Histories from Nature. Chapman & Hall, NewYork, pp. 471-501.
• Namkoong,G., T. Boyle, Y. El-Kassaby, G. Eriksson, H.-R. Gregorius, H.Joly, A. Kremer, O. Savolainen, R. Wickneswari, A. Young, M. Zeh-Nlo, and R. Prabhu. Criteria and indicators for assessing the sustainability of forest management: conseration nof genetic diversity. AMBIO. (submitted 1997)
• Newman, D. and D. Pilson. 1997. Increased probility of extinction due to decreased genetic effective population size: experimental populations of Clarkia pulchella. Evolution 51: 354-362.
• Refeldt, G.E. 1989. Ecological adaptations in Douglas-fir (Pseudotsuga menziesii var. glauca): a synthesis. For. Ecol. Manage., 28: 203-215
• Rehfeldt, G.E. 1991. Gene resource management: using models of genetic variation in silviculture. In: Proc. Genetics/Silviculture Workshop. Aug. 27-31,1990,Wenatchee, Washington. USDA, Forest Service, pp 31-44.
• Rehfeldt, G.E. 1991. A model of genetic variation for pinus ponderosa in the Inland Northwest (U.S.A.): applications in gene resource management. Can. J. For. Res. 21: 1491-1500
• Rehfeldt, G.E. 1994. Adaptations of Picea engelmannii populations to the heterogeneous environments of the Intermountain West. Can. J. Bot. 72: 1197-1208

Please record your notes on evaluating the indicator here.