Introduction
1 . Background & Rationale
White spruce (Picea glauca) is known as one of the most widely distributed and most commercially valuable native boreal forest species in North America, which across Canada and Alaska to the northern United States. In Canada, white spruce comprises roughly a quarter of Canadian forest inventory. In Alberta Province, Canada, white spruce is one of the most valuable commercial tree species, which accounts for around 30% of the local total forest inventory and 48% of the volume of coniferous growing stock(Power & Gills, 2006). Besides high commercial value, white spruce also plays a significant role in the local ecological system. A wide variety of wildlife species including moose, caribou, woodpeckers, and northern hawk owls use white spruce communities as habitat.
Meanwhile, the distribution, growth, and establishment of white spruce is estimated to be affected by climate change. With warmer climatic condition, some studies recommended that white spruce populations may expand their current region into areas formerly covered by permafrost or move northward and higher elevation (Davis & Shaw, 2001; Payette & Filion, 1985). Numerical model of white spruce niche is needed as one important guidance of site selection for the future plantation.
Beside estimating potential consequences of global warming on white spruce habitat, modeling the niche could provide evolutionary insights of the modeled species. Until now, the origin of white spruce in Yukon Territory is still not clear. Numerous studies have seen Beringia as a refugium for arctic herbs and shrubs, but little is known about the role of this refugium for trees. A study by Brubaker et al. (2005) based on fossil pollen records supports a glacial refugium for boreal Larix in eastern Beringia, and Pinus pumila in Western Beringia. In 1937, Eric Hulten in his book proposed that the ice-free region of Beringia as the glacial refuge for the Alaska and Yukon boreal tree species during the last glaciation. Since then, a few paleoecological research have tempted to testify this theory and/or suggest alternative theories(E.g., Brubaker et al., 2005; Hopkins, 1972; Ritchie & MacDonald, 1986). For instance, by sequencing chloroplast DNA(cpDNA) , Anderson et al.(2006) compared the haplotype diversity of white spruce populations and concluded that the current Yukon white spruce populations are originated from bidirectional migration(one from Alaska, the other from eastern US). Building species distribution model for white spruce can be necessary to resolve this controversy by identifying possible species spatial patterns during the glacial period. Understanding white spruce migration processes could guide us estimating tree responses to anthropogenic warming.
2. Objectives
In this project, by building SDM of white spruce we hope to determine the ecological niche of the species based on climatic factors. Then the niche can be used to map the species distribution for assessing their distribution change in temporary scales. Modeling the past(distribution in the periods of 21,000, 14,000, 11,000, 6,000 years before present(BP)) can provide unique evolutionary insight of our modeled species migration history.
In this study, we will :
1. Using SDM to verify whether there was Beringian Refugium for white spruce during the last glacial maximum(LGM);
2. to uncover the post-glacial migrate pathways of white spruce;
3. Expected results
The ideal model has good performance of identifying the suitability of white spruce habitat and estimate the probability of the species occurrence given by certain climatic condition. However, if the climatic factors are not the primary drivers of the species presence, it is difficult for the model to make high accuracy predictions. In that case, biotic factors like interactions among species or/and environmental factors (other than climate) should be added in the model as predictors. If the predictions match the paleorecords, the model can properly present the ecological niche of the species and the make reliable predictions.
If the Beringia can be served as one refugium for white spruce, refuge population should have relatively high genetic diversity and unique alleles; Also, Beringia region should have suitable climate for white spruce to survive at 21000 years ago before present.