Modeling fire hazards for the maintenance of long-term forest inventory plots in Alberta, Canada

Long-term forest inventory plots provide important data for forest research and management. Maintaining such sites is a challenge as they are vulnerable to numerous unforeseeable anthropogenic and natural disturbances. This is particular so given the ongoing global change and the resultant risks of intensified disturbances. Of these disturbances, fire is the most important regime that dictates the dynamics of northern forests. However, little is known about how fire may threaten the forest inventory plots in the region. To address this question, we compiled data on forest fires occurred over the past six decades for permanent sample plots in Alberta, Canada. We employed the Cox proportional hazards model to quantify the effects of stand conditions and climate on the fire hazards of these plots. The results showed that 17% of the plots were burned, and they had an average 28.7-year lifespan, and more recently established plots suffered higher fire hazards. Our model predicted that 15% of the plots in Alberta would be disturbed due to fire 30 years after plot establishment, and that prediction increased to 35% after 50 years. The plots located in the Boreal ecoregion suffered 2.85 and 3.36 times higher fire risk than those in the Foothills and Rocky Mountain ecoregions, respectively. Tree species richness and density of deciduous trees of the plots were found to reduce their fire hazards, while mean annual temperature increased the hazards. By 2050, the mean fire hazards of the plots are projected to be 1.63 times higher than the current level as global warming persists, posing a great threat to the long-term maintenance of forest inventory plots.