Réjean Gagnon

Dendroecological Analysis of Black Spruce in Lichen—Spruce Woodlands of the Closed-Crown Forest Zone in Eastern Canada

Abstract: Lichen—spruce woodlands occur in the closed-crown forest zone as a divergent type of the spruce—moss forest because of regeneration failure caused by compounded disturbances (fire, insect outbreaks, and logging). From the southern limit of distribution of lichen woodlands (47° 30′ N) to the northern limit of the closed-crown forest zone (52° 40′ N), 53 lichen woodlands were sampled for a detailed dendroecological analysis. Radial, height, and volumetric growth of black spruce (Picea mariana) trees among the woodlands varied significantly according to stand age. Growth rates were similar for all even-aged spruce trees, whereas growth rates of trees < 100 y old were significantly greater than those of trees > 100 y old. No significant differences were found in growth rates of spruces distributed along the latitudinal gradient. Spruce trees were generally small in all the woodlands studied, with only a few trees taller than 12 m. Although spruce budworm may have affected all stands, the timing and intensity of the infestations were not necessarily synchronous among the studied stands. Partial least square response (PLS) functions were calculated to evaluate the impact of climate on tree-rings with latitude. Along the 600-km transect, PLS response functions indicated that growth was strongly influenced by current and previous year climatic conditions, particularly precipitation.

17 – Relationship Between Spruce Budworm Outbreaks and Forest Dynamics in Eastern North America

This chapter focuses on the relationship between disturbances caused by native forest–defoliating insects and forest dynamics, which is recognized as an important part of the tritrophic interactions, especially for the spruce budworm system. A good model to consider in this regard is the relationship between outbreaks of spruce budworm ( Choristoneura fumiferana Clem.) and the dynamics of the boreal forest. It should be noted that predictions are based on comprehension of past events under the assumption that known variables such as climate will vary within some recognized range of fluctuations. In the context of recent climate changes that may result in unprecedented changes in temperature and aridity, things could be completely different. However, growing knowledge and understanding of the population dynamics of the insects and of the relationships between outbreaks and forest dynamics should lead to better predictions of what may occur under changing environmental conditions.

Age-Dependent Response of Migrant and Resident Aegolius Owl Species to Small Rodent Population Fluctuations in the Eastern Canadian Boreal Forest

ABSTRACT We investigated the relationship between late summer abundance of small rodents and fall migrant abundance of two nocturnal avian predators, the Boreal Owl (Aegolius funereus) and the Northern Saw-whet Owl (A. acadicus), during their fall movement/migration. In the eastern Canadian boreal forest, Boreal Owls are considered resident (with irruptive movements to the south thought to occur during periods of low prey availability), and Northern Saw-whet Owls migratory. Data on late summer abundance of small rodents collected between 1995 and 2004 were used to develop an index of prey availability. Data on the number and age of irrupting/migrating owls were collected between 1996–2004 (mid-September to late October) using audiolures and mist nets. Our study revealed strong evidence of (1) a negative relationship between the abundance of small rodents and movement of Boreal Owls and (2) a positive relationship between the abundance of small rodents and the number of migrating juveniles and second year Northern Saw-whet Owls. In the latter case, it suggests that prey availability can strongly influence breeding success of this species, which is at the northern limit of its breeding range.

Dating Black Spruce (Picea mariana) with the Awareness of its Adventitious Root System

Black spruce (Picea mariana [Mill.] B.S.R) is one of the most important species in Canada for the Pulp and Paper Industry. Despite its importance, we still have some difficulties in dating the mature trees; black spruce develops an adventitious root system, which in turn conceals the base of the stem and the root collar in the stump wood. The usual methods for dating mature trees, which consist in taking a cross section or an increment core at the base of the stem, do not consider this phenomenon, and may lead to misinterpretations about the species dynamics. The age under-estimation increases with every year since the fire, with the development of the adventitious root system and the elevation of the ground level with time. The objective of this study was to experience a new dendrochronological dating method, which permits to locate the juvenile growth rings and the root collar under the ground level, and compare the results with a conventional dating method.