Euan G. Mason

A model of the juvenile growth and survival of Pinus radiata D.Don: Adding the effects of initial seedling diameter and plant handling

Initial ground line diameter (GLD) of Pinus radiata D.Don and the care of treesduring transport to the field growing siteaffect subsequent tree growth and survival. Anexisting model of juvenile growth had notincluded these effects, and so a new model wascreated that represented their effects ongrowth, survival and uniformity. The new modelwas built with cohorts defined by each initialGLD class and with quality of tree stockhandling as an extra independent variable,using data from 17 experiments. Weibulldistributions representing the size classesdeveloping within each cohort enabled the modelto represent interchanges in dominance, andadded to the range of questions that could beanswered using the model. Reducing quality ofhandling and reducing initial GLD decreasedgrowth, survival, and crop uniformity. Changesin small GLDs were more important than changesin large ones. The final model represented theeffects of initial ground line diameter, treestock handling (careful, timely plantingcompared to rough, poorly scheduled planting),site quality, and site preparation on growth ofradiata pine in the central North Island of NewZealand in a way that allows managers toevaluate the impacts of seedling grading.

Wood properties of juvenile Pinus radiata growing in the presence and absence of competing understorey vegetation at a dryland site

Pinus radiata D. Don trees were grown in the presence and absence of the woody weed broom (Cytisus scoparius L.) on a dryland site for 2 years to determine the effects of competition from weeds on wood properties in juvenile trees. Wood property measurements made on cross-sections from the bark to the pith were scaled to convert results from distance to a time basis using sigmoidal equations fitted to monthly measurements of tree diameter. When averaged across the 2 years, the presence of the weeds significantly increased wood density (+11%), wall thickness (+6%) and modulus of elasticity (MOESS, +93%), and significantly reduced microfibril angle (MFA, −21%) and radial diameter (−8%). Radial growth rate was significantly correlated to wood density, and this relationship held across both treatment and age. At the seasonal scale, there was close correspondence between changes in MFA and growth rate. Ring width was significantly related to both MFA and MOESS at the annual scale. Although both of these relationships held across treatments, year significantly influenced the value of coefficients in the relationships. The results highlight the direct effects of the presence of weeds on wood properties and the need to consider silvicultural treatments appropriate for balancing gains in productivity with losses in wood quality for timber production.

A model of the growth of juvenile radiata pine in the Central North Island of New Zealand: links with older models and rotation-length analyses of the effects of site preparation

Abstract Data from 27 site preparation experiments were used to construct a model that predicts growth, survival and size class distributions of radiata pine with respect to altitude, weed control, cultivation, fertilisation, and initial stocking during the first five years after planting. Only stand values, however, are used in this paper. The question of linking the model with existing growth and yield models for older crops is discussed, and a theoretical structure is proposed that clarifies assumptions required if the models are jointly used to evaluate the worth of establishment practices throughout complete crop rotations. It was found that the initial growth model generally predicted similar basal area growth rates to those of the Pumice Plateau Model (PPM88), a growth model for older crops, in age ranges where the two models overlapped, but some of the assumptions required for rotation-length analyses need further testing. Measurements over 8 years in a designed experiment examining alternative site preparation strategies showed that PPM88 was insensitive to the effects of site preparation in predicting growth that occurred after the establishment phase.

The influence of nitrogen and phosphorus supply and genotype on mesophyll conductance limitations to photosynthesis in Pinus radiata

Mesophyll conductance, g(m), may pose significant limitations to photosynthesis and may be differentially affected by nutrition and genotype in Pinus radiata D. Don. Simultaneous measurements of gas exchange and chlorophyll fluorescence were made to determine g(m), using the constant J method (Harley, P.C., F. Loreto, G. Di Marco and T.D. Sharkey. 1992. Theoretical considerations when estimating the mesophyll conductance to CO(2) flux by analysis of the response of photosynthesis to CO(2). Plant Physiol. 98:1429-1436), in a fast- and a slow-growing clone of P. radiata grown in a greenhouse with a factorial combination of nitrogen (N) and phosphorus (P) supply. Values of g(m) increased linearly with the rate of photosynthesis at saturating irradiance and ambient CO(2) concentration, A(sat) (g(m) = 0.020A(sat), r(2) = 0.25, P < 0.001) and with stomatal conductance to CO(2) transfer, g(s) (g(m) = 1.16g(s), r(2) = 0.14, P < 0.001). Values of g(m) were greater than those of stomatal conductance, g(s), and the ratio (g(m)/g(s)) was not influenced by single or combined N and P additions or clone with a mean (+/-SE) value of 1.22 +/- 0.06. Relative limitations to mesophyll conductance, L(m) (16%) to photosynthesis, were generally greater than those imposed by stomata, L(s) (13%). The mean (+/-SE) CO(2) concentration in the intercellular air spaces (C(i)) was 53 +/- 3 mumol mol(-1) lower than that in the atmosphere (C(a)). Mean (+/-SE) CO(2) concentration in the chloroplasts (C(c)) was 48 +/- 2 mumol mol(-1) lower than C(i). Values of L(s), L(m) and CO(2) diffusion gradients posed by g(s) (C(a) - C(i)) and g(m) (C(i) - C(c)) did not significantly differ with nutrient supply or clone. Mean values of V(cmax) and J(max) calculated on a C(c) basis were 15.4% and 3.1% greater than those calculated on a C(i) basis, which translated into different slopes of the J(max)/V(cmax) relationship (C(c) basis: J(max) = 2.11V(cmax), r(2) = 0.88, P < 0.001; C(i) basis: J(max) = 2.43V(cmax), r(2) = 0.86, P < 0.001). These results will be useful for correcting estimates of V(cmax) and J(max) used to characterize the biochemical properties of photosynthesis for P. radiata.

Hydrothermal time germination models for radiata pine (Pinus radiata D. Don)

The objective of this study was to fit a hydrothermal germination model to germination data for a seedlot of radiata pine (Pinus radiata D. Don). Seeds were incubated for 50 d at constant temperatures and water potentials (T ¼ 12.5‐32.58C, C ¼ 0t o21.2 MPa). Most seeds completed germination within 50 d, but for low C and/or non-optimal temperatures (T , 17.58C, T . 258C) many seeds did not complete germination. In general, germination data conformed to the hydrothermal model. Departures from the model were encountered for slow-germinating seeds at suboptimal temperatures (T # 208C). To account for these departures, two alternative hydrothermal models were fitted with an additional term for an upwards shift in seed base water potential with increasing time to germination. The alternative models more correctly predicted germination time than the original model. Similarly, reduced percentage germination at supra-optimal temperatures (T . 208C) was explained by including a term in the hydrothermal model which shifted the base water potential of seeds upwards towards zero, which in turn reduced the predicted rate that hydrothermal time would be accumulated by seeds. The rate of this upwards shift in base water potential was dependent on time to complete germination and ambient water potential as well as supra-optimal temperature.

The influence of N and P supply and genotype on carbon flux and partitioning in potted Pinus radiata plants

Carbon (C) flux and partitioning responses of Pinus radiata (D. Don) clones to a factorial combination of nitrogen (N) and phosphorus (P) supply were estimated in small trees growing in a greenhouse over 44 weeks. Our objective was to use a C budget approach at the plant level to examine how a factorial combination of N and P additions and genotype modify gross primary production (GPP), net primary production (NPP), absolute C fluxes apportioned to aboveground net primary production (ANPP), aboveground plant respiration (APR), total belowground carbon flux (TBCF) and the partitioning of GPP to ANPP, APR and TBCF. Single N or P additions increased plant NPP and GPP similarly, but their combined effects exceeded those of their individual contributions. Nitrogen and to a lesser extent P additions enhanced carbon-use efficiency (CUE, NPP:GPP) and C partitioning to ANPP at the expense of TBCF. The fraction of GPP partitioned to APR was invariant to N or P additions. The ratio of soil respiration (FS) to TBCF was significantly greater in the low-N low-P addition treatment (61%) than in those treatments with single or combined N and P additions (49%). The slowest growing clone partitioned a significantly smaller fraction of GPP to ANPP (29%) than one of the faster-growing genotypes (33%). This research provides insight into how N and P regulate the C fluxes and partitioning in individual plants. Our results contribute to explaining clonal variation in aboveground growth rates and suggest that greater gains in CUE and partitioning to ANPP occur with addition of N rather than P supply.

Early growth and quality of radiata pine in a silvopastoral system in New Zealand

The effect of different understoreys on the early growth and quality of radiata pine (Pinus radiata) in a silvopastoral system was evaluated in Canterbury, New Zealand. Fitted models successfully represented the effect of understorey on the growth (basal area and height) and a quality of trees (diameter over stubs). Basal area, diameter, height and volume growth were affected by understorey competition. Trees growing with no-understorey had 34%and 29% higher volume than trees growing with lucerne (Medicagosativa) and cocksfoot (Dactylis glomerata)understoreys, respectively. However, the height of trees at age 10 grown without understorey competition was only 9% and 15% more than trees grown with grass and lucerne understorey, respectively. Understorey competition effects on growth became more evident during the summer and early autumn months when water deficits occurred. The quality of trees was also affected by understorey competition. While trees grown in bare ground had higher growth than trees grown with understorey competition, they had the poorest stem quality with higher diameters over stubs, branch size, sweep and proportion of stem defects. This will have an impact on the agroforestry system profitability by affecting the net harvest revenue.

Time vs. light: a potentially useable light sum hybrid model to represent the juvenile growth of Douglas-fir subject to varying levels of competition

Substitution of potential useable light sum for time in a commonly used mensurational equation resulted in a better fit to data from a complex vegetation management experiment. The experiment involved Douglas-fir (Pseudotsuga menzeisii (Mirb.) Franco) as a crop species and a variety of competing species. Site occupancy by competing vegetation varied with time because control operations were intermittently either included or excluded from treatments over a period of 4 years. There were four randomized complete blocks of eight competition control treatments. Potentially useable light sum was estimated using measurements of radiation from a meteorological station that were modified by coefficients representing the ability of the crop plants to use light with varying soil water, vapour pressure deficit, and temperature. Light sums were further reduced by estimated competition for light from competing vegetation. Fits of the model to individual plots within the experiment yielded coefficients that did not diff...

A single-tree additive biomass model of Quercus variabilis Blume forests in North China

Key messageFitting and comparing three sets of additive biomass models for prediction of biomass or carbon stocks of natural and plantedQuercus variabilisBlume forests.AbstractTo make the sum of estimated values from biomass models of various components of a tree equal to estimated tree total biomass for Quercus variabilis Blume (cork oak) forests in North China, single-tree additive biomass models were developed. 100 trees from 100 plots in North China were felled to obtain biomass of aboveground components, and roots of 19 of those trees were extracted for measurement of root biomass. After Box–Cox transformations of variables, two sets of independent component biomass models with a dummy variable to define stand origin were separately built using linear mixed effects analyses (one set of models with site as a random factor; the other set without any random factor). Then three methods were compared to force additivity of those models: sums of linear mixed effects models, sums of linear models, and simultaneous equation fits based on linear models. Model parameters were estimated by ordinary least squares (OLS) or seemingly unrelated regression procedures (SUR). Coefficients of determination (R2), root mean square error (RMSE), confidence interval of predictions (CI), residuals plots and histograms of residuals indicated that models fitted with sums of linear mixed effects models were the least biased and most precise at estimating total aboveground biomass. Further testing for the linear mixed effects models with jackknife validation and prediction sum of squares (PRESS) statistics indicated that the additive biomass models can be used to predict biomass or carbon stocks of cork oak forests in North China within specific tree diameter at breast height and height ranges.

Modelling the effects of nursery and site management on the early performance of Picea sitchensis (Bong.) Carr.

This study examined the potential of mathematical modelling, following initial statistical analyses, to describe, summarise, and integrate information from nursery and establishment experiments. It is part of a larger study evaluating this general approach as a means of bringing together information on a wide range of establishment techniques and site factors which is extensive but at present largely inaccessible to managers.Twenty six establishment experiments in NE England were screened. Eight experiments were identified for mathematical modelling on the basis of having at least 3 assessments between planting and canopy closure, replicated designs, and combinations of nursery and site treatments. Nursery spacing, nursery fertilisation, plant height, plant diameter, and handling had insignificant or inconsistent effects on performance and were not modelled.Significant factors in the survival model were cultivation of the planting site, which increased survival; and stock type (transplants had poorer survival than undercut and wrenched seedlings). Significant factors in the height model were the method of cultivation used at the planting site (screefing < no cultivation < ploughing or mounding); stock type (transplants had poorer growth than undercuts); and presence of Calluna vulgaris which was associated with decreased growth.The relationships between plant performance over the first 6 years after outplanting and both nursery and site practices, including their interactions, were adequately described by simple mathematical equations. These mathematical descriptions could in future be incorporated into computer software thereby allowing managers, who are faced with increasingly demanding targets for efficient establishment, to weigh up the resource implications of various establishment techniques against the predicted gain in survival and height.