# Spatial Variations in Seed Germination Traits of White Spruce (Picea glauca) and Black Spruce (P. mariana) Across the Canadian Boreal Forest

## TL;DR

This study examines how seed germination of two spruce species varies across the Canadian boreal forest, finding differences in temperature requirements and germination times.

## Contribution

The study provides new insights into spatial germination traits of Picea glauca and P. mariana, linking them to geographic and climatic variables.

## Key findings

- P. glauca has a broader base temperature range for germination compared to P. mariana.
- Thermal time requirements for germination are higher in P. glauca than in P. mariana.
- Latitudinal temperature variables strongly influence germination traits more than precipitation or evaporation.

## Abstract

This study focuses on the spatial variation in seed germination characteristics of Picea glauca and P. mariana, prominent and widespread species within the Canadian boreal forest. The main objective was to determine seed germination requirements of geographically distinct seed collections of P. glauca and P. mariana. A total of 73 collections of P. glauca and 62 collections of P. mariana were selected across Canada and tested for germination under various temperatures. Base temperature (Tb) and thermal time required to reach 50% germination (TH50) were derived from thermal model parameters for all seed collections. Correlation analyses between seed germination traits, geographic, and climatic variables were conducted. Base temperatures for germination of P. glauca ranged from 5.2 to 11.9 °C while P. mariana had base temperatures ranging from 6.2 to 12.8 °C, indicating a broader temperature range for the former to initiate germination. Optimal germination temperatures ranged from 15 to 20 °C for P. glauca and from 17.5 to 30 °C for P. mariana. Thermal time requirements for 50% germination were higher for P. glauca than for P. mariana, indicating that the former takes longer to germinate under the same temperature conditions. Latitudinal-related variables such as temperature of sites had a stronger influence on germination relative to precipitation or potential evaporation and affected seed viability, final germination and germination capacity of all seed sources. Seed viability was lower in northern seed collections and germination capacity was diminished at lower temperatures for both species. The results from this study can be built into models predicting shifts in boreal forest species under climate change.