What drives retrogressive succession? Plant strategies to tolerate infertile and poorly drained soils

Abstract

1. During retrogressive succession, vegetation shifts from taller forests with higher species richness to shorter woody communities of lower diversity. Studies of soil chronosequences have emphasized the role of phosphorus (P) depletion in driving these changes in community structure and composition, but neglected the possible role of poor drainage which is often associated with the oldest sites. 2. We used a fully factorial pot experiment to investigate the effects of soil water conditions and P availability on seedling relative growth rate and survival of 11 woody species associated with a 290 000-year chronosequence in southern New Zealand. Species were chosen to represent three stages of the chronosequence: young P-rich soils; intermediate-age P-depleted soils; and old P-depleted, waterlogged soils. Plants were grown in soils taken from youngest and oldest sites of the chronosequence; half the pots were freely drained whilst the other half were waterlogged. 3. Species associated with intermediate-age soils were typical 'stress-tolerators'; those of the youngest and oldest sites were faster growing and more responsive to nutrient availability. Only the latter showed tolerance of waterlogging. Specific root length and adventitious-root production were important determinants of species' responses to soil water conditions and nutrient supply. 4. Our study highlights that soil waterlogging and P depletion interact to influence relative growth rate and survival; P depletion is not the sole driver of ecosystem changes in the retrogressive stages of the soil chronosequence. We also show that some species associated with our retrogression did not necessarily conform to conventional views on 'stress-tolerance', but were well adapted to poor drainage. © 2010 The Authors. Journal compilation © 2010 British Ecological Society.