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Title: Influences of soil nutrients, waterlogging, and disturbance factors on forest processes along a New Zealand soil chronosequence
Author: Bentley, W. A.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2008
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To test how soil nitrogen (N) and phosphorus (P) limit plant growth along a soil fertility gradient, I conducted the first fertilization experiment of its kind in a temperate rain forest, using sixty 20 x 20 m plots that sampled a retrogressive chronosequence. The effects of adding N and P fertilizer, alone and in combination, were established by measuring changes in soil chemistry, foliar N and P concentrations, photosynthetic capacity, and tree diameter and root growth. Adding P increased soil P levels similarly across all forest types, while adding N or P separately increased the soil aerobic N mineralization rate, but there was no synergistic effect. Foliar nutrient content, radial tree growth and photosynthetic capacity responses to fertilizer addition differed between species and varied with respect to surface, while root proliferation responded positively to P addition on two surfaces, but not on the third. I carried out a correlative study to examine the influences of soil waterlogging and soil nutrient levels on tree growth, floristic composition, light, and litter decomposition. Using an established grid of soil sampling points within eight 1.5-ha mapped forest strands situated across the chronosequence, I explored the relationship between soil conditions and neighbourhood processes. My results indicate that on older surfaces, soil waterlogging is an increasingly important factor influencing forest processes. Finally, to investigate the role of disturbance factors on forest age, size, and species composition, I collected tree ring cores from six common tree species in three established 1.5-ha mapped stands. I found that the dominant conifer species was hardly regenerating under present-day conditions, but had recruited en masse about 600 years ago, suggesting a widespread disturbance event or synchronous senescence at that time. Other species of conifer and angiosperm had more continuous regeneration, suggesting that they are capable of regeneration within smaller gaps in the forest.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available