Analysis of Nutrient Depletion in a Radiata Pine Plantation

This project analysed the effects of accelerated loss of nutrients from a pine plantation site, looking at forest productivity and nutrient status. Over 16 years, at approximately six monthly intervals, all forest litter in some of the experimental plots was raked up and removed. Raked and unraked plots were either left as is, had nutrients completely replaced or had nutrients replaced to adjust for imbalances between nutrients in litter and those in the tree stem. All plots were thinned at 14 years.

Up to the time of thinning, raking reduced basal area increment (BAI) by 25% while raking together with replacement of nutrients reduced BAI by about 12%. Adding nutrient to unraked plots led to BAI increases of up to 14%. The raking treatment reduced foliage nitrogen and this was correlated with reduced growth while other nutrients such as boron and sulphur were reduced but not to a degree to affect growth or health.

The results were used to assess the effects on soil nutrient status and growth of different harvesting regimes (wood only, wood plus bark, total tree). The balance of inputs and outputs of nitrogen was also compared with initial soil nutrient contents and was related to relative growth rates but the changes due to harvesting wood only are probably difficult to detect at an operational level.

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