Sugar maple seedling carbon assimilation at the northern limit of its range: the importance of seasonal light

Abstract

Using in situ light curves and understory seasonal light measurements the importance of canopy avoidance was evaluated for a population of sugar maple ( Acer saccharum Marsh.) seedlings living at the boreal ecotone in Lake Superior Provincial Park, Ontario, Canada. At higher latitudes, the time period associated with canopy avoidance is shorter and occurs at cooler temperatures, increasing the risk of frost damage. In 2008, leaf-out began 5 days prior to the last frost of the season. By modeling the potential carbon gain of seedlings, it is clear that the short time period prior to canopy leaf-out still contributes a disproportionate amount of carbon to the overall budget of seedlings. Of the total seasonal carbon gain, 80.6% was assimilated in the initial 15 days following sugar maple seedling leaf-out. Based on our model, by leafing out only 6 days earlier than the average seedling leaf-out date, ∼200% more carbon could be assimilated during the course of the growing season. Vegetation phenology is cued by climatic triggers — as climate changes so too will phenological responses. These mechanisms add to the overall carbon budget of seedlings; recognizing these mechanisms is essential to thoroughly understand the natural history of this species.

Determinants of survival over 7 years for a natural cohort of sugar maple seedlings in a northern hardwood forest

“…Colonization by beneficial AMF, as indicated by the frequency of arbuscules in seedling roots (Table 2), decreased significantly with increasing elevation and was also significantly lower on more northerly slopes, suggesting a soil temperature control. Initiation of AMF early in the growing season may be important as early-season carbon gain is critical to sugar maple seedling performance at its northern range limits where 80% of carbon gains occur within 15 days of leaf emergence (Kwit et al 2010). Moreover, early formation of AMF may help protect against fungal pathogens (Jung et al 2012) such as the Rhizoctonia root rot fungus that is a principal mortality agent in these sites (this study; Cleavitt et al 2011).…”

Extended leaf phenology in deciduous forest invaders: mechanisms of impact on native communities

“…; Augspurger & Bartlett ; Augspurger ; Kwit et al. ). Native tree species Acer saccharum and Aesculus glabra Willd.…”

“…Other 'summer herb' understorey species may also accumulate much of their annual carbon during short windows of time when the canopy is open (Rothstein & Zak 2001). Tree seedlings generally leaf out earlier than adult conspecifics, and accumulate most of their carbon prior to canopy closure in forests (Gill et al 1998;Augspurger & Bartlett 2003;Augspurger 2008;Kwit et al 2010). Native tree species Acer saccharum and Aesculus glabra Willd.…”

The seasonal timing of warming that controls onset of the growing season

“…Onset of the growing season is important in models of productivity and diversity, because plants can respond most to warming before soil moisture depletion in summer (Davi et al, 2006;Delpierre et al, 2009;Richardson et al, 2009;Yang et al, 2012). Early spring accounts for much of annual seedling photosynthesis, potentially controlling future biodiversity through its effects on recruitment (Lopez et al, 2008;Kwit et al, 2010). Warming experiments have been one of the largest research investments for understanding global change impacts on terrestrial productivity (Rustad, 2008;Templer & Reinmann, 2011).…”