Totara Stands Respond to Thinning

Latest results from a Northland Totara Working Group project show that growth rates of natural stands of totara can be significantly boosted by thinning. Both individual tree diameters and overall stand productivity increased as a response to silvicultural treatments. Analysis of the data has led to the development of a thinning schedule – the first of its kind for naturally regenerating totara stands. This will assist landowners in making practical decisions about thinning intensities within naturally regenerating polestands of totara on farms. Silvicultural trials In 2007, silvicultural trials were established to evaluate the effects of thinning and pruning in natural totara pole stands at 14 sites across three districts in Northland. It was anticipated that silvicultural management would improve growth rates and tree form. The trials were set up in collaboration with Scion and the Diversified Species theme of Future Forests Research, with direct or in-kind contributions from local landowners, the Ministry for Primary Industries’ Sustainable Farming Fund, Northland Regional Council, Far North District Council, and Tane’s Tree Trust. In total 38 Permanent Sample Plots (PSPs) were established within pole-stands of naturally regenerating totara across 10 different farms. The PSPs were established with control plots (that received no silvicultural treatment) at each site as well as one or more plots within each stand that were thinned and pruned, thus allowing a direct comparison of the effects of silviculture to be made. Prior to any silviculture all stems with a Diameter at Breast Height (DBH) of 50 mm and above were measured within each plot. Heights of a sample of canopy trees were also measured. Stands were originally thinned from densities of over 6000 stems per ha to varying levels of stocking ranging from 800-2000 stems per ha. The thinned plots were then remeasured immediately following silviculture and again one and two years later. Five-year measurement All 38 PSPs including the unthinned control plots, were re-measured in 2012, five years after the original thinning was carried out. This involved locating all trees within each plot that had been uniquely identified from the earlier measurements, and remeasuring their DBH. The same sample trees measured for height previously were also remeasured.