Competitive interactions in sub-boreal birch–spruce forests differ on opposing slope aspects

Green, D. Scott; Hawkins, Chris

doi:10.1016/j.foreco.2005.03.051

Cited by 15 publications

(7 citation statements)

References 32 publications

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“…At this age the deciduous trees are 3 to 4 m taller than the spruce and cast shade for at least this distance (Lieffers et al 2002). Green and Hawkins (2005) found that plots up to 5 m in radius were better for measurement of competitive status of a subject tree. Lieffers et al (2002) found the present FTG criteria were poorly linked to simulated light levels available to spruce.…”

Section: Discussionmentioning

confidence: 88%

Free-to-grow regeneration standards are poorly linked to growth of spruce in boreal mixedwoods

Lieffers¹,

Stadt²,

Zhang³

2007

The Forestry Chronicle

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For public lands in Canada, the free-to-grow (FTG) standards are part of regulatory surveys of post-harvest juvenile stands that are designed to assess the level of competition on conifer trees. In this paper we analyzed two data sets to test the ability of FTG standards to predict growth of white spruce saplings. Using data from juvenile permanent sample plots, FTG was assessed at age 13 and subsequent diameter increment and height increment were assessed in the measurement interval after year 18. If the growth of trees was adjusted for differences in height at age 13, FTG status made no difference in predicting subsequent growth. A second data set from operational regeneration surveys of 49, 13-year-old boreal mixedwood stands was also evaluated for evidence of competition across a range of cutblock with different percentages of plots classed as FTG. There was no evidence of an increase in variation in size or growth of leading trees in stands when the plots in a cutblock were evenly split between FTG and not-FTG trees, compared to cutblocks with either few plots FTG or nearly all plots FTG. Height attained at year 13 was a sufficient indicator of future growth. Key words: regeneration, standard, free, grow, productivity, mixedwoods

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Section: Discussionmentioning

confidence: 88%

Free-to-grow regeneration standards are poorly linked to growth of spruce in boreal mixedwoods

Lieffers¹,

Stadt²,

Zhang³

2007

The Forestry Chronicle

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“…In turn, willow may influence spruce establishment and seedling growth in the shrubland zone. There is evidence to suggest that these competitive relationships are density dependent and vary significantly with aspect (Green & Hawkins 2005). Identifying the magnitude of these interactions and their influence on tree line dynamics is an important avenue for further work.…”

Section: Discussionmentioning

confidence: 99%

Variability, contingency and rapid change in recent subarctic alpine tree line dynamics

2007

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Summary1 Boundaries between forest and tundra ecosystems, tree lines, are expected to advance in altitude and latitude in response to climate warming. However, varied responses to 20th century warming suggest that in addition to temperature, tree line dynamics are mediated by species-specific traits and environmental conditions at landscape and local scales. 2 We examined recent tree line dynamics at six topographically different, but climatically similar, sites in south-west Yukon, Canada. Dendroecological techniques were used to reconstruct changes in density of the dominant tree species, white spruce ( Picea glauca ), and to construct static age distributions of willow ( Salix spp.), one of two dominant shrub genera. Data were analysed to identify periods and rates of establishment and mortality and to relate these to past climate. 3 Tree line elevation and stand density increased significantly during the early to mid 20th century. However, this change was not uniform across sites. Spruce advanced rapidly on south-facing slopes and tree line rose 65-85 m in elevation. Tree line did not advance on north-facing slopes, but stand density increased 40-65%. Differences observed between aspects were due primarily to the differential presence of permafrost. Additional variability among sites was related to slope and vegetation type. Results were less conclusive for willow, but evidence for an advance was found at two sites. 4 Increases in stand density were strongly correlated with summer temperatures. The period of rapid change coincided with a 30-year period of above average temperatures, beginning in 1920. The highest correlations were obtained using a forward average of 30-50 years, supporting the hypothesis that tree line dynamics are controlled more by conditions influencing recruitment than by establishment alone. 5 The changes observed at several sites are suggestive of a threshold response and challenge the notion that tree lines respond gradually to climate warming. Overall, the results provide further evidence to support the idea that the pattern and timing of change is contingent on local, landscape, and regional-scale factors, as well as species' biology.

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“…Pritchard (2003) and Voicu and Comeau (2006) also found significant site differences in relationships between white spruce growth and transmittance. Green and Hawkins (2005) suggested that competitive interactions may differ between north-facing and south-facing slopes in subboreal mixedwood stands owing to changes in environmental conditions. There are few plant competition studies that examined the influence of environmental factors on competition.…”

Section: Discussionmentioning

confidence: 99%

Aspen competition affects light and white spruce growth across several boreal sites in western Canada

Filipescu

Comeau

2007

Can. J. For. Res.

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The effectiveness of competition indices for predicting light transmittance and white spruce (Picea glauca (Moench) Voss) growth were examined across trembling aspen (Populus tremuloides Michx.) density gradients using sites from a long-term study of mixedwood growth and development in Alberta and Saskatchewan. Competition indices based on density (number of trees, basal area, and spacing factor), distance-dependent and -independent size ratio (Hegyi's and Lorimer's), and crown characteristics (crown volume, surface area, and cross-sectional area) were tested. Transmittance was effectively predicted by crown competition indices followed closely by aspen basal area and size ratio indices. Models of spruce growth indicated better results for stem volume compared with diameter or height. Competition alone accounted for less than 60% of stem growth variation, with basal area and transmittance providing some of the best models. The predictive ability of spruce growth was increased up to 93% by adding initial size as a second explanatory variable. In this respect, initial diameter was superior to initial height, crown volume, and surface area. Relationships between competition, transmittance, and spruce growth were found to differ significantly between geographical locations. These results suggest the need for local development of models relating tree growth to competition.Résumé : L'efficacité d'indices de compétition à prédire la transmittance de la lumière et la croissance de l'épinette blanche (Picea glauca (Moench) Voss) a été étudiée le long de gradients de densité de peuplier faux-tremble (Populus tremuloides Michx.) en utilisant les stations d'une étude à long terme de la croissance et du développement de peuplements mixtes en Alberta et en Saskatchewan. Parmi les indices de compétition testés, certains étaient basés sur la densité (nombre d'arbres, surface terrière et facteur d'espacement), d'autres étaient dépendants de la distance et indépendants de la taille relative (indices de Hegyi et de Lorimer) et d'autres considéraient les caractéristiques de la cime (volume, surface ou surface projetée de la cime). La transmittance était efficacement prédite par les indices de compétition basés sur la cime, suivis étroitement par les indices basés sur la surface terrière en peuplier et la taille relative. Les modèles de croissance de l'épinette donnaient de meilleurs résultats pour le volume de la tige que pour le diamètre ou la hauteur. Moins de 60 % de la variation de la croissance des arbres était expliquée par la compétition et les meilleurs modèles incluaient la surface terrière et la transmittance. L'efficacité à prédire la croissance de l'épinette a pu être augmentée jusqu'à 93 % en ajoutant la taille initiale comme deuxième variable explicative. À cet égard, le diamètre initial était meilleur que la hauteur initiale, le volume de la cime ou la surface de la cime. Les relations entre la compétition, la transmittance et la croissance de l'épinette étaient significativement différentes selon l'endroit. Ces résul...

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Competitive interactions in sub-boreal birch–spruce forests differ on opposing slope aspects

Cited by 15 publications

References 32 publications

Free-to-grow regeneration standards are poorly linked to growth of spruce in boreal mixedwoods

Free-to-grow regeneration standards are poorly linked to growth of spruce in boreal mixedwoods

Variability, contingency and rapid change in recent subarctic alpine tree line dynamics

Aspen competition affects light and white spruce growth across several boreal sites in western Canada

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