Seedling Germination Marks Ecosystem Boundaries
Source: Cristina Castanha and Dan Hawkes
Seedling germination and survival is a critical control on forest-ecosystem boundaries, Moreover, while it is known that species respond individualistically to the same suite of environmental drivers, the potential additional effect of local adaptation on seedling success has not been evaluated. ESD climate scientist Cristina Castanha recently led a team of investigators (including ESD’s Margaret Torn and Lara Kueppers) in quantifying conifer seedling recruitment across a subalpine forest at Niwot Ridge, Colorado, USA. Their work was an effort to determine whether local adaptation may influence the position and movement of forest-ecosystem boundaries.
Castanha et al. studied Pinus flexilis and Picea engelmannii grown from seed collected locally at high (3400 m a.s.l.) and low (3060 m a.s.l.) elevations. They monitored emergence and survival of seeds sown directly into plots and survival of seedlings germinated indoors and transplanted after snowmelt. They found that emergence and survival through the first growing season was greater for P. flexilis than P. engelmannii and for low compared with high provenances. Yet survival through the second growing season was similar for both species and provenances. Seedling emergence and survival tended to be greatest in the subalpine forest and lowest in the alpine tundra. Survival was greater for transplants than for field-germinated seedlings.
These results suggest that survival through the first few weeks is critical to the establishment of natural germinants. In addition, even small distances between seed sources can have a significant effect on early demographic performance – a factor that has rarely been considered in previous studies of tree recruitment and species range shifts.
To read further, go to: http://www.tandfonline.com/doi/full/10.1080/17550874.2012.716087#tabModule
Castanha, C., M.S. Torn, M J. Germino, B. Weibel, and L.M. Kueppers (2013), Conifer seedling recruitment across a gradient from forest to alpine tundra: effects of species, provenance, and site. Plant Ecol Divers, 6 (3-4), 307-318; DOI:10.1080/17550874.2012.716087.