Landscape Genetics of Eastern White Pine (Pinus strobus)
Eastern white pine (Pinus strobus) is one of the most valuable tree species in North America. Before the arrival of European settlers, the landscape of central and southern Ontario was dominated by stands of eastern white pine (Wilson & Gray, 2001). However, after more than a century of intense logging, this pristine landscape exists only in photographs. The wood of eastern white pine is light, straight-grained, and easily worked. In the 18th century, this tree was highly valued for these properties. It was logged heavily to create the masts and booms of British Royal Navy ships, for building materials, and furniture (Wilson & Gray, 2001).
A past study estimated that the current eastern white pine coverage in the Great Lakes and boreal forest regions of Ontario are 50% and 35% respectively of what they were in the pre-settlement landscape (Quinby, 1993). This over-harvesting has resulted in the reduction of seed sources, making it difficult for population regeneration to occur. Buchert et al. (1994), using allozyme analysis, reported a loss of 25% in the mean number of alleles in a partially harvested old-growth stand of white pine in Ontario. The same results were obtained when microsatellite analysis was applied to the same study area (Rajora et al., 2000).
In Canada, the current distribution of eastern white pine occurs across the Great Lakes region of central and southern Ontario, across southern Quebec into the Maritime Provinces, and into Newfoundland. Its American range includes the states of New York and New Jersey, Minnesota, northeastern Iowa, Illinois, Ohio, Pennsylvania, northern Georgia, and northwestern South Carolina (Abrams, 2001).
Eastern white pine trees can live to be over 400 years old. Trees can grow up to a height of 53 metres and a diameter of 1.2 metres. White pine is monoecious, meaning that each individual tree possesses separated male and female reproductive structures. The seeds of white pine are located in cones, which mature over a two year period. Cone production begins at 5-10 years of age, but good seed years do not occur until the tree is over 20 years of age, and only every 3-5 years after that, although seeds are produced annually. The primary method of seed dispersal is by wind, which can send a seed traveling 60+ metres from the source within a stand of trees, and up to 220 metres in the open. However, animals also play a minor role in seed dispersal. Mice and voles create caches of white pine seeds just beneath the soil, and caches that are not revisited usually produce seedlings (Wilson & Gray, 2001).
Eastern white pine is of great ecological importance. White-winged crossbills, pileated woodpeckers, lynx, flying squirrels, and bald eagles all depend on white pine for various things, including protection from predators, shelter, and food. The white-winged crossbill (Loxia leucoptera) possesses a bill that is specialized for opening the cones of conifers. Dead and dying trees provide sites for cavity nesting species such as hibernating black bears and woodpeckers (Green, 1992). Squirrels, chipmunks, and mice feed on the seeds and soft needles. Several animals including rabbits feed on the outer bark.
The eastern white pine project is part of a larger multi-species study with the Ontario Living Legacy Trust. This larger study focuses on the ddevelopment of landscape genetics as a novel management tool for Ontario’s parks and heritage sites. Landscape genetics includes a genetic component, the use of molecular markers to examine population demographics and evolutionary processes, as well as a Geographical Information Systems (G.I.S.) component, the database systems responsible for the organization, modeling, analysis and presentation of geographically referenced genetic data. Objectives of this study include identifying landscape variables that promote or reduce dispersal within and among multi-use habitats, as well as to investigate the effects of different degrees of fragmentation on multiple indicator species including eastern white pine, moose, fishers, and northern flying squirrel. The study will assess the impact of parks, specifically Algonquin Provincial Park, on surrounding areas and smaller adjacent parks and multi-use areas that differ significantly with respect to forest cover and forest composition. Landscape variables (e.g. habitat quality, geographic isolation, heterogeneity and anthropogenic development) will be compared directly to genetic profiles to identify causal factors limiting or promoting connectivity around park systems.
Eastern white pine sample sites include Algonquin Park and different land-use areas surrounding the park, including smaller provincial parks, primary heritage sites, conservation areas and other non-designated regions. Study sites outside the park are chosen based on the amount of white pine forest cover. Thirty or more meristem (bud), needle, or cambium samples will be obtained for each sample site.
Genetic analysis of the eastern white pine will include 20-30 microsatellite loci per profile. Plants have three independent genomes: the nuclear, chloroplast, and mitochondrial genomes (Dong & Wagner, 1994). In plants, chloroplast and mitochondrial genomes exhibit different patterns of genetic differentiation compared to the nuclear genome due to their uniparental mode of inheritance (Powell et al., 1995). In Pinus, the chloroplast genome is inherited paternally through pollen, while the mitochondrial genome is inherited maternally through seeds. Since both the chloroplast and mitochondrial genomes do not recombine, variants will accumulate in a uniparental lineage, and can therefore provide information about the history of populations.
The summarized genotypes and landscape maps will be stored as GIS layers in the Land Information Ontario (LIO) warehouse. Land-use and natural resource managers will have secure on-line access to these maps through the NRDPFC website. This information will ultimately help to define practical conservation units for each species included in the study. Also, the level of variation across Ontario will help in determining what spatial scale is appropriate to aim conservation efforts in order to preserve local adaptations, which is important in reforestation initiatives for eastern white pine.
The establishment of a working GIS database also has important forensics applications. Unknown White Pine samples can be profiled and linked to a geographic area as a probable source of origin. This will aid in the enforcement of current logging restrictions, as well as provide stronger evidence to prosecute offenders.
Abrams, M.D. 2001. Eastern white pine versatility in the presettlement forest. BioScience 51:967-979.
Buchert, G.P., Rajora, O.P., Hood, J.V., and B.P. Dancik. 1996. Effects of harvesting on genetic diversity in old-growth eastern white pine in Ontario, Canada. Cons. Bio. 11(3):747-755.
Dong, J., and D.B. Wagner. 1994. Paternally inherited chloroplast polymorphism in Pinus: estimation of diversity and population subdivision, and tests of disequilibrium with a maternally inherited mitochondrial polymorphism. Genetics 136:1187-1194.
Green, J.C. 1992. “Ecological features of white pine stands for wildlife”: in White Pine Symposium Proceedings; Minnesota, USA.
Powell, W., Morgante, M., McDevitt, R., Vendramin, G.G., and J.A. Rafalski. 1995. Polymorphic simple sequence repeat regions in chloroplast genomes: applications to the population genetics of pines. Proc. Natl. Acad. Sci. USA 92:7759-7763.
Quinby, P.A. 1993. Old-growth eastern white pine forest: an endangered ecosystem. Forest Landscape Baselines No. 2.
Rajora, O.P., Rahman, M.H., Buchert, G.P., and B.P. Dancik. 2000. Microsatellite DNA analysis of genetic efforts of harvesting in old-growth eastern white pine (Pinus strobus) in Ontario, Canada. Mol. Ecol. 9:339-348.
Wilson, S., and T. Gray. 2001. Fact Sheet #3: White Pine Forests; in Forestry in Ontario. Natural Conservancy of Canada, Toronto, Ontario.