Anthropogenic climate change has led to a 40% increase in woody cover in just 27 years along the Virginia Coast Reserve, Long-Term Ecological Research site. Normally limited by fatally low temperatures to upland areas where they are more protected, warmer wintertime temperatures and fewer freezing events in recent decades have allowed the dominant shrub, Morella cerifera, to encroach into low-elevation grassland communities. Previous work has documented a correlation between M. cerifera presence in the vegetation community and overwash frequency, leading to the assumption that the shrub is burial-intolerant. Lack of experimental evidence and the recent encroachment into swale communities merits investigation into whether burial limits shrub growth. My objective was to examine morphological response of M. cerifera over a range of burial levels. In a greenhouse experiment, seedlings ~10 cm of height and adult shrubs ~60 cm were buried in sand at four different levels as a percentage of height: 0% (control), 25%, 50% and 75% (n=8). Over the course of the experiment photosynthetic rate, plant height, crown area, and number of shoots were measured.
Results/Conclusions
Morella cerifera showed no significant morphological response at 25% burial. At 50% burial, photosynthetic rate was reduced and growth (i.e. height, crown area) slowed significantly. At 75% burial, several plants did not survive. Seedlings produced more new stems and adventitious roots than their adult counterparts when buried, but mortality rate increased at 75% burial. Overall, M. cerifera did not exhibit a significant capacity to overcome burial stress. Above a certain threshold, the plant is unable to remain physiological function. When buried at 50%, M. cerifera shrubs experience reduced physiological function and at 75% burial, the plant does not survive. Burial as a result of overwash is likely to contribute to controlling range expansion of M. cerifera. If burial occurs during the earliest stages of life, a much less severe overwash event is needed to prevent seedling establishment. Once established, an unusually severe event is needed to cause shrub death.