H.M. McKay

The physiological basis for the establishment of bare-root larch seedlings

Abstract Data on physiological attributes and early forest performance of bare-rooted Japanese and hybrid larch in Britain are summarised. Physiological attributes included root growth potential (RGP), root membrane function, bud dormancy, shoot and root frost hardiness, resistance to desiccation, rough-handling and cold-storage, and sensitivity to insecticide. The survival pattern of freshly planted stock followed that of RGP, which was bimodal with peaks in October and March, whereas the survival pattern of cold-stored stock was more closely related to root membrane function at planting. Seasonal trends in bud dormancy and stress resistance are described. The optimum time for handling, as opposed to planting, larch was in December–February when shoots were hardy to about −30°C, roots were hardy to around −13°C, and root electrolyte leakage (REL) had fallen to about 10%. The optimum cold storage time varied from year to year but seemed to be generally best from mid-November to late December. Undercutting and wrenching improved survival. RGP was of major importance in determining establishment with fine root membrane function, root fibrosity and root:shoot ratio of secondary importance. Since the larches’ unique pattern of RGP seems related to their deciduous habit, it is probable that RGP will be an important determinant of survival in other species of larch.

Autumn frost damage: clonal variation in Sitka spruce.

Current-year needles of Sitka spruce (Picea sitchensis) can be injured by frost after hardening of stem and buds in the autumn, and in Scotland trees of southern provenances are most susceptible to damage. In October 1993 a frost of -5°C caused needle damage to clonal plants of Alaskan, Queen Charlotte Islands, and Washington provenances of Sitka spruce that had been selected for variation in the onset of root dormancy. Visual damage assessment revealed significant differences among clones in the severity of damage, and this damage was positively correlated with the lateness of root dormancy. Measurement of electrolyte leakage from shoot samples confirmed the observed differences between clones. The large clonal differences in frost hardiness found in this study demonstrate a potential for selecting frost tolerant trees from within southern provenances of Sitka spruce.

Assessing tree seedling vitality tests using sensitivity analysis of a process-based growth model

A process-based model of tree seedling growth was used to assess the predictive capability of various plant vitality tests. Eight model parameters which could be directly equated with specific plant vitality tests were varied in a sensitivity analysis, using a Monte Carlo approach with Latin hypercube sampling. Probability distributions of these parameters were estimated using data from two research projects in which relevant parameters were measured in a range of experiments across Europe. The sensitivity of predicted growth to these parameters was analysed at four European sites chosen to have contrasting climates, ranging from cool oceanic to Mediterranean (Greece, Portugal, Germany and Scotland). In general, those parameters to which the predictions are most sensitive will correspond to the best vitality tests. The objective was to identify vitality tests which will be useful predictive tools in the context of forest establishment, and to what extent their usefulness varies with climate. The results were related to experimental evaluations of vitality tests reported in the literature. The pattern of sensitivity to the eight parameters was relatively consistent at the four sites. In all cases, initial mass was the most sensitive parameter, followed by maximum relative growth rate of roots. Initial soluble nitrogen content and root fraction generally ranked third and fourth, though the latter was rather variable. The remaining four parameters (maximum electron transport rate, maximum carboxylation rate, initial starch content and initial soluble sugar content) were generally poor indicators of growth. The results suggest that commonly-used assessments such as stem diameter and root growth potential (RGP) should be reliable indicators of field performance. The value of our approach is in quantifying the importance of observed variation in a parameter in relation to variation in other model parameters and inputs. The approach permits seedling vitality tests to be linked to a process-based modelling framework.