Yellow birch seedlings. Photo: J-B Lambert Some tree species - especially those with small seeds - cannot germinate on leaf litter and need high-porosity seedbeds. This is the case of yellow birch (Betula alleghaniensis), a species that requires mineral soil or deadwood to germinate. However, very little is known about how seedbed affects plant performance along light gradients, and even more, about how the characteristics of the deadwood (species, decay class) can affect its germination.
A study recently published, in which FiDBosc participates, tries to answer these questions. The leading author, Jean-Bastien Lambert (UQAM, Canada) sampled more than 1,000 yellow birch juveniles in hardwood forests of southern Quebec, recorded the substrate in which they were growing, and measured their height, growth, morphology, light availability and several other physiological variables.
A study recently published, in which FiDBosc participates, tries to answer these questions. The leading author, Jean-Bastien Lambert (UQAM, Canada) sampled more than 1,000 yellow birch juveniles in hardwood forests of southern Quebec, recorded the substrate in which they were growing, and measured their height, growth, morphology, light availability and several other physiological variables.
A nurse log, and adequate substrate for yellow birch seedlings The study shows that more than a half of the total seedlings were growing on logs, revealing the importance of deadwood for yellow birch germination. But interestingly, species identity matters, and it turns out that sugar maple logs - the most common species in the area - are not adequate for yellow birch germination, and less than 10% of the birch seedlings were growing on maple logs. Conversely, birch and conifer logs seem to be very adequate, and hosted more than 90% of the birch seedlings found on deadwood. The reason is not clear and will require further research, but the different decay rates between birch, maple and conifer woody debris could be related.
But seedlings growing on deadwood also had different characteristics than those growing in mineral soil. For instance, they had slower height growth, greater number of living branches and a more efficient resource capture, which are all characteristics that promote shade tolerance. And indeed, we found that regeneration cohorts did not follow the same temporal pattern of establishment on different seedbed types, and advanced regeneration were more numerous on deadwood. In fact, we found that yellow birch has the potential to establish almost continuously if adequate deadwood are available, and can persist for more than 20 years in the understory as seedlings or saplings.
But seedlings growing on deadwood also had different characteristics than those growing in mineral soil. For instance, they had slower height growth, greater number of living branches and a more efficient resource capture, which are all characteristics that promote shade tolerance. And indeed, we found that regeneration cohorts did not follow the same temporal pattern of establishment on different seedbed types, and advanced regeneration were more numerous on deadwood. In fact, we found that yellow birch has the potential to establish almost continuously if adequate deadwood are available, and can persist for more than 20 years in the understory as seedlings or saplings.
Yellow birch has a characteristic golden bark These results can have important implications for management. Regeneration of yellow birch in managed stands usually relies on the availability of mineral soil after disturbance of forest floor by skidding machinery. However, an excessive dependence on skid trails for regeneration of yellow birch can have some risks, as recently shown by Beaudet el al. (2014). Therefore we argue that specific guidelines and management plans should incorporate the need to increase the retention of deadwood of species suitable to act as nurse logs in order to maintain an abundant, natural, spatially well-distributed, and multi-storied regeneration of yellow birch.
You can find the study published online at Canadian Journal of Forest Research.
Reference: Lambert J-B, Ameztegui A, Delagrange S, Messier C. (2015) Birch and conifer deadwood favour early establishment and shade tolerance in yellow birch juveniles growing on sugar maple dominated stands. Canadian Journal of Forest Research. In press.
You can find the study published online at Canadian Journal of Forest Research.
Reference: Lambert J-B, Ameztegui A, Delagrange S, Messier C. (2015) Birch and conifer deadwood favour early establishment and shade tolerance in yellow birch juveniles growing on sugar maple dominated stands. Canadian Journal of Forest Research. In press.
Birch seedlings growing on a nurse log. Photo: J-B Lambert
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