The role of total belowground carbohydrates in resprout survival of chaparral shrubs
Resprouting is an important trait that allows an individual plant to persist after disturbance. Species widely differ in resprouting ability and understanding the mechanistic causes of these differences is important for modeling vegetation response to disturbance. We examined resprout success (survival) of shrubs in chaparral shrublands of southern California and factors that we predicted would be linked with success. We hypothesized that resprout success in these crown fire systems would be controlled by physiological traits related to carbon balance and drought resistance, and life history traits. We were particularly interested in the role of belowground carbohydrate stores. To examine this, we established a field site at a recently burned site in 2008. Resprouting plants of 6 species were targeted and were shaded (~1% of ambient light). Biomass from these plants was harvested for six years, in some cases, and used to estimate the available belowground carbon for growth. Tissue samples from below ground storage organs (lignotubers) were also analyzed for starch levels at the start of the experiment and at the point of plant death.
We found that shrubs with an obligate resprouting life history type, i.e. shrubs that resprout after fire and do not recruit seedlings immediately post-fire, had greater post-fire resprout success than facultative seeder life history types, i.e. those that both resprout and recruit seedlings post-fire from a fire-cued seed bank. Resprout success was positively associated with traits related to carbon balance such as early resprouting, growth rate, and pre-fire vigor and was negatively affected by drought. Total belowground stores of carbohydrates, measured as repeatedly harvested dry biomass of shaded plants was correlated with both resprout success and starch storage of lignotubers when compared interspecifically. The concentration of lignotuber starch before the onset of resprouting was correlated with resprout success, but net starch removed was more strongly correlated.
We conclude that resprouters are not a homogenous group and that facultative and obligate resprouters differ in resprout success and key traits that are adaptive in the context of resprouting. The different life history types found in mediterranean-type environments represent a continuum from short-lived (obligate seeders) to long-lived (obligate resprouters), with facultative seeders as intermediate. Traits that contribute to successful seedling recruitment are hypothesized to be at odds with those associated with persistence, thus giving rise to tradeoffs.