Canopy stratification, age structure, and development of multicohort stands of eastern white pine, eastern hemlock, and red spruce

Abstract

The causes of canopy stratification were investigated in five mixed stands of red spruce (Picearubens Sarg.), hemlock (Tsugacanadensis (L.) Carr.), and white pine (Pinusstrobus L.) in eastern Maine. All species were present in all crown classes; however, there was a clear pattern of pine dominance and eventual emergence. Red spruce was prevalent in the middle stratum, and hemlock most common in the lower strata. Canopy stratification was caused by interspecific differences in shade tolerance and height growth, and by multicohort structures. The multicohort structures developed as a result of episodic partial disturbances such as spruce budworm (Choristoneurafumiferana Clemens) outbreaks and partial harvesting that both initiated regeneration and released previously suppressed trees of older, surviving cohorts. Spatial and temporal variability in disturbances created extremely variable patterns of competition among cohorts, resulting in a more complex developmental pattern than would be found in a single-cohort model involving stand-replacing disturbances.

Density and population structure of the natural regeneration of Scots pine (Pinus sylvestris L.) in the High Ebro Basin (Northern Spain)

“…Complex stand structures and continuos age distributions due to episodic partial disturbances have been also found in mixed-species stands [9]. In contrast, in cases of severe disturbances, like a fire, the occupation of all the growing space in the first twothree years and the non viability of later settlers have been reported.…”

Développement d’un outil de classification de la structure des peuplements et comparaison de deux territoires de la pessière à mousses du Québec

“…On reconnaît en fait que la structure diamétrale est amenée à changer avec le temps écoulé depuis le dernier feu (Knowles et Grant 1983, Lorimer et Krug 1983, Groot et Horton 1994, Linder 1998. Ces changements sont généralement associés aux perturbations secondaires et à la sénescence des arbres, qui engendrent une dynamique par trouées en l'absence de feu (Heinselman 1981, Fajvan et Seymour 1993, Hofgaard 1993, Kneeshaw et Bergeron 1998, McCarthy 2001. Les chablis et les épidémies d'insectes sont des perturbations importantes sur le territoire de la Côte-Nord (Blais 1983, Ruel 2000.…”

“…Les peuplements ayant subi une telle perturbation dans un passé récent présen-tent généralement une structure régulière, alors que les peuplements dont la dernière perturbation majeure est survenue il y a plus longtemps présenteraient une structure davantage irrégulière ou une distribution en « J » inversé (Oliver et Larson 1996, Smith et al 1997. Parmi les autres facteurs reconnus pour exercer une influence sur la structure des peuplements, on compte les perturbations secondaires, telles que les épidémies d'insectes et les petits chablis, qui favoriseraient la formation de structures irrégulières en l'absence prolongée de feux (Heinselman 1981, Hunter 1990, Fajvan et Seymour 1993. En outre, les caractéristiques du milieu physique (dépôt, drainage, topographie, relief, climat) influencent la composition des peuplements et pourraient également affecter leur structure ou encore la rapidité avec laquelle ils changent de structure (Lindenmayer et al 1999, Bebi et al 2001.…”

Spatial dynamics of late successional species under Pinus nigra stands in the northern Apennines (Italy)

“…In particular, for plots 2 and 3 un-modifiable factors, such as micro morphology [6], soil characteristics or long-term disturbance with effect on soil or canopy structure (large gaps) could have caused the observed clumped distribution of NR formed by several uneven-aged groups of saplings [18]. On the contrary, in the plot 1 short-term disturbances, such as tree mortality with sudden and temporary canopy openings or litter removal could explain the observed clumped pattern made up by several even-aged groups of saplings [18].…”

“…For instance, the irregularity of climate conditions, especially the annual rainfall variations were reported by Oliver and Larson [38] as the main factor triggering the NR process. However, many other factors such as the irregularity of seed production, the annual changes in seed eaters population and pathogens diffusion could account for the interannual variation in NR [18].…”