Fertilization of stagnated sitka spruce plantations of northern Vancouver Island
Creators: name: Germain, André Yvon
Publisher: name: University of British Columbia
Year: 2010

description: Extensive areas of Sitka spruce plantations established during the last 15 years on the CH-phase of the salal-moss ecosystem association on northern Vancouver Island are presently exhibiting symptoms of severe chlorosis and growth check. Investigations into the poor performance of these plantations are described in this thesis. Comparisons of the soil nutrient levels between this poorly productive CH-phase and the adjacent highly productive HA-phase were made. In addition, fertilization screening trials were established in order to identify possible limiting nutrients and determine the potential responsiveness of Sitka spruce to fertilization. Soil samples were collected over an age sequence of cutovers from both phases in order to compare differences in the soil nutrient status and to determine the effects of time since harvesting on N mineralization rates. Significantly greater amounts of total and available P and total, KC1 extractable, and mineralizable N (p=.01) were found in the mineral soil and humus of the HA-phase. The mineral soil of the HA-phase also had significantly higher (p=.05) concentrations of exchangeable K. In addition, this phase had a significantly lower (p=.01) C/N ratio. Although significant differences were noted in the mineral nutrient composition of the two phases, in all cases (with the possible exception of mineralizable N), the absolute differences between the two phases did not appear large enough to account for the dramatic differences in productivity. Harvesting plus slashburning appears to have had little effect on the rates of N mineralization in the humus or mineral soil of the HA-phase. However, in the CH-phase harvesting plus slashburning has had a significant influence on the mineralization rates of the humus but not of the mineral soil. Harvesting initially resulted in a significant (p=.05) increase in the mineralization rates, however, within five years they returned to levels comparable to that of the control. Fertilization screening trials were established in five Sitka spruce plantations ranging in age from 8 to 14 years. All plantations were growing on the CH-phase and were exhibiting symptoms of chlorosis and growth check. Changes in the first-year needle dry-weight, needle nutrient composition, and leader growth were monitored. Treatments for these trials consisted of a N, P, K factorial experiment, and one separate treatment of a complete nutrient mixture. Each treatment was replicated seven times in each of the five plantations. N or N plus K fertilization resulted in a 10% increase in needle dry-weight and a 25 to 30% increase in first-year leader growth response over that of the control. P fertilization had a strong synergistic effect and when added in combination with N or N plus K resulted in a needle dry-weight increase of 40 to 41% and a leader growth increase of 78 to 83%. A limited sample of naturally occurring hemlock in some of the plots exhibited similar trends, although leader growth increases were somewhat greater. Fertilization with P and K, alone or together, had no effect on leader growth or needle weight despite the severe deficiencies of these two elements. However, P had a positive influence on the uptake of N, K, Ca and Mg, whereas K positively affected Ca and depressed Mg. After N fertilization, foliar N concentrations increased dramatically, ranging from a mean of 3.2% for the lowest (200 kg N/ha) application rate to 4.1% for the highest (400 kg N/ha) application rate. The high foliar N concentrations had a significant negative influence on foliar K concentrations. This decline in K concentrations could only partially be attributed to a growth dilution effect and occurred whether or not K was added. A similar effect on P, Ca or Mg was not noted. The high N concentrations also appeared to have had a negative influence on both needle weight and leader growth as there was a tendency for the response of both to decline as N concentrations increased. There were significant differences in both leader growth and needle weight responses between some of the plantations, but treatments receiving both N and P fertilizers consistently gave the greatest responses. The individual treatment, however, which gave the greatest and most consistent overall response was that containing all macro- and micro-nutrients. Results from this study indicate that the poor performance of Sitka spruce plantations established on the CH-phase of the salal-moss ecosystem is partially due to a severe N and P deficiency. These deficiencies are associated with the complete invasion of these cutovers by salal. It has also been shown that the Sitka spruce in these plantations would be highly responsive to N and P fertilization. Although K does not appear to limit growth and no apparent benefits were gained from K fertilization, a severe N induced K deficiency is likely.