Crown Forms and Shoot Elongation of White Spruce at the Treeline, Churchill, Manitoba, Canada

Scott, Peter; Bentley, Catherine V.; Fayle, D. C. F.; Hansell, Roger I. C.

doi:10.2307/1551250

Cited by 65 publications

(39 citation statements)

References 22 publications

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“…In situ root zone temperatures in adult trees also exert immediate, almost linear e ects on stomatal conductance and photosynthesis (once a low threshold between 1 and 4°C is exceeded) with no indication that this response is associated with cold soil induced needle water de®cits Day et al 1989;KoÈ rner et al 1995). Scott et al (1987a) found a linear correlation (r 0.95) between cumulative root zone temperature and shoot elongation in subarctic Picea glauca experiencing atmospheric temperature and moisture conditions quite favourable for photosynthesis, again indicating tight control of shoot activity by a below ground signal. Hellmers et al (1970) were able to block growth in potted P. engelmannii seedlings by exposing them to a daytime temperatures of 15, 19, 23, 27 or 35°C but a night temperature of only 3°C.…”

Section: Growth and Development: A Hypothesis For Treeline Formationmentioning

confidence: 99%

A re-assessment of high elevation treeline positions and their explanation

1998

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In this review I ®rst compile data for the worldwide position of climate-driven alpine treelines. Causes for treeline formation are then discussed with a global perspective. Available evidence suggests a combination of a general thermal boundary for tree growth, with regionally variable``modulatory'' forces, including the presence of certain taxa. Much of the explanatory evidence found in the literature relates to these modulatory aspects at regional scales, whereas no good explanations emerged for the more fundamental global pattern related to temperature per se, on which this review is focused. I hypothesize that the life form``tree'' is limited at treeline altitudes by the potential investment, rather than production, of assimilates (growth as such, rather than photosynthesis or the carbon balance, being limited). In shoots coupled to a cold atmosphere, meristem activity is suggested to be limited for much of the time, especially at night. By reducing soil heat¯ux during the growing season the forest canopy negatively a ects root zone temperature. The lower threshold temperature for tissue growth and development appears to be higher than 3°C and lower than 10°C, possibly in the 5.5±7.5°C range, most commonly associated with seasonal means of air temperature at treeline positions. The physiological and developmental mechanisms responsible have yet to be analyzed. Root zone temperature, though largely unknown, is likely to be most critical.

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Section: Growth and Development: A Hypothesis For Treeline Formationmentioning

confidence: 99%

A re-assessment of high elevation treeline positions and their explanation

1998

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“…The coastal wetland soils become increasingly cool, wet and nutrient-limited with proximity to Hudson Bay, prohibiting extensive seedling establishment (Scott et al 1987). Consequently, only small islands of forest are found near the coast of Hudson Bay, and these tend to be on the drier upland areas.…”

Section: Introductionmentioning

confidence: 99%

The role of individual terrain units in the water balance of wetland tundra

Ld¹,

Wr²

1995

Clim. Res.

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The water balance of a High Subarctic wetland was measured in a newly established research basin near Churchill, Manitoba, Canada. Measurements spanned the growing season from early June through to the end of August 1991. The watershed was instrumented such that the water budget could be monitored over each of the dominant terrain unlts. The study basin has 5 major terrain types consisting of sedge-dominated wetland, upland lichen-heath, tundra lakes and ponds, willowbirch wetland, and open spruce forest, in decreasing order of coverage. These terrain units, and the ecosystem as a whole, are representative of coastal wetlands underlain by permafrost in the Hudson Bay Lowland. Runoff and thus streamflow were closely tied to the moisture status of the peatlands and to the depth of the active layer. During 2 unusually dry periods, the peatlands remained wet, which indicates a lack of water mobility when the water table drops below the surface of the wetland. Streamflow response to rainfall during these periods was small in comparison to early summer when the frost table was near the surface, or to wet periods when the water table rose above the surface. Energy balance measurements showed the lakes and ponds to have about 15 % higher net radiation than wetlands and 29% greater than upland lichen-heath. From 9 to 18% of net radiation was used in thawing and heating the ground whereas the latent heat flux for the various terrain types utilized from 49 to 83 % of net radiation. Even with unusually large rainfalls that occurred in July, evaporation exceeded precipitation over the course of the summer. Despite this, runoff was high and required a large negative change in groundwater storage to account for it. The lichen-heath and ponds exhibited the greatest change in water storage. The drainage of water from the uplands to the lowlands maintained the soil moisture of the peatlands and contributed to streamflow. Each terraln type had a characteristic water balance due to differences in one or more of the hydrologic variables (evapotranspiration, runoff and storage). This has important lrnplications concerning the impact on the water balance of a change in surface cover brought about by a change in climate.

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“…Actually, many A. mariesii trees show the flagged crown form at the timberline on Mount Norikura (Wardle 1977;Nakamoto et al 2013). This crown form is caused by strong wind in winter (Scott et al 1987). By contrast, P. pumila is hardly damaged by strong wind in winter because its creeping trunk is protected by snow accumulation, except for wind-exposed ridges (Nagano et al 2009;Nakamoto et al 2012).…”

Section: Discussionmentioning

confidence: 99%

Effects of wind and thermal conditions on timberline formation in central Japan: a lattice model

Takahashi

2014

Ecological Research

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The upper distribution limit of tall tree species Abies mariesii is the timberline in central Japan, and dwarf pine Pinus pumila dominates above the timberline to near the summit. My previous studies suggested that the main cause of the timberline formation is the increase in mortality due to strong wind in winter rather than low growth due to low summer temperature. This study evaluated how wind velocity affects timberline formation and if the altitude of timberline moves upward due to high thermal conditions, by using a lattice model. Increase in wind velocity throughout the altitude lowered the altitudes of upper distribution limits of the two species. On the contrary, prolonged growth period due to high thermal conditions increased the upper distribution limit of P. pumila, and the upper distribution limit of A. mariesii was hardly affected by the change of growth period. However, the upward shift of the upper distribution limit of P. pumila due to the prolonged growth period in the model would not be realistic because P. pumila had already distributed up to near the summit. This study concludes that A. mariesii is a superior competitor to P. pumila at low altitudes with low wind velocity, but dwarf pine P. pumila can dominate at higher altitudes because A. mariesii suffers severe mechanical damage due to strong wind in winter, and that the altitude of the timberline does not move upward even under high thermal conditions due to global warming.

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Crown Forms and Shoot Elongation of White Spruce at the Treeline, Churchill, Manitoba, Canada

Cited by 65 publications

References 22 publications

A re-assessment of high elevation treeline positions and their explanation

A re-assessment of high elevation treeline positions and their explanation

The role of individual terrain units in the water balance of wetland tundra

Effects of wind and thermal conditions on timberline formation in central Japan: a lattice model

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