Variation in specific needle area of old-growth Douglas-fir in relation to needle age, within-crown position and epicormic shoot production

Abstract

Variation in specific needle area (SNA; cm2 projected fresh needle area g-1 oven-dried needle weight) was investigated in relation to needle age, within-crown position and epicormic shoot production in 450-year-old Douglas-fir (Pseudotsuga menziesii Mirb. (Franco) var. menziesii) trees. Specific needle area decreased with increasing needle age. The magnitude and rate of change in SNA with needle age were greatest for lower-crown branches, and decreased toward the middle- and upper-crown branches. For all branches, there was no difference between regular and epicormic shoots in the relationship between SNA and needle age. Specific needle area decreased with increasing distance from branch base, and this relationship was significant for the majority of needle age classes of the upper- and middle-crown branches. In the lowercrown branches, SNA did not vary with distance from branch base for the majority of needle age classes. For all branches, there was no difference between regular and epicormic shoots in the relationship between SNA and distance from branch base for the majority of needle age classes. These results indicate that renewal of foliage by epicormic shoot production maintains needle quality. Branch SNA increased linearly with decreasing height in the crown at a mean rate of 0.951 +/- 0.110 cm2 g-1 per vertical meter. Total needle area of branches was estimated from total needle dry weight taking into account within-branch variation in SNA. Analyses of allometric relationships between branch size and foliage amount (needle area and needle dry weight) showed that branch length was a better predictor of foliage amount than branch diameter for old Douglas-fir trees. Total needle dry weight and needle area of the sample trees, estimated from branch length and branch height and taking into account vertical within-crown variation in branch SNA, ranged from 42.4 to 154.2 kg and from 246.2 to 816.0 m2 per tree, respectively.

Sources of within- and between-stand variability in specific leaf area of three ecologically distinct conifer species

“…In this case, SLA of a given foliage age class declined with increasing distance from bole. Although we could not test this trend for Douglas-fir in our study, Ishii et al [17] found a similar decline in SLA with increasing distance from bole in Douglas-fir old growth, particularly in the upper portion of the crown. The greater SLA of foliage close to the bole most likely is a direct result of the light environment at the time of needle development, and perhaps secondarily a response to gradients in water potential from branch base to tip.…”

“…Other tree-and stand-level factors, including leaf area index, had little influence on SLA after accounting for these covariates. In other studies, foliage age class [2,7,13,17] and branch location [21,30] have consistently been key factors controlling SLA. The data collected from hybrid spruce provided a unique opportunity to test the effect of distance from bole on SLA within a branch.…”

“…The rate of decline, however, would depend on not only the amount of leaf area accumulated per m depth into crown, but also on the relative shade tolerance of the species. Ishii et al [17] found that rates of accumulation of secondary substances are greater in lower-crown branches than in upper-crown branches in mature Douglas-fir, but needles with greater SLA are also shed more rapidly. This supports the idea that rate at which SLA decreases through the canopy is dependent on foliage age class, which was found in this study.…”

“…Light conditions at the time of foliage formation have generally been regarded as the primary factor influencing SLA in both hardwoods [8,29] and conifers [5,26]. Hence, SLA within a stand generally decreases with increasing foliage age [7,13,17] and with increasing height from the ground [21]. Differences in SLA from the interior to the periphery of the crown have rarely been examined; however, SLA decreased with distance from bole in both silver birch (Betula pendula Roth) [36] and old-growth Douglas-fir (Pseudotsuga menziesii var.…”

Low stomatal and internal conductance to CO2 versus Rubisco deactivation as determinants of the photosynthetic decline of ageing evergreen leaves

“…In Douglas-fir, LMA increases with irradiance during the first growing season (Aussenac 1973;Warren et al 2003b), and then increases with needle age regardless of light in subsequent years (Ishii et al 2002;this study) In both cases, the increase in LMA is modulated through changes in both needle thickness and tissue density, although in developing needles the changes mostly take place in the palisade mesophyll layer (Aussenac 1973), whereas in ageing needles, they are more likely to occur in the hypodermal layer and other lignified tissues (Apple et al 2002). According to Niinemets et al (2005Niinemets et al ( , 2006 who discussed the possible effect of light acclimation versus leaf ageing on LMA and g i in Mediterranean broadleaf evergreens, the initial positive effect of light on LMA and g i (area basis) is a consequence of the greater chloroplast to total leaf surface area ratio of the 'sun leaf type' palisade tissue (see references given therein), whereas the subsequent negative effect of LMA on g i (mass or area basis) reflects the accumulation of cell wall compounds which would impede the diffusion of CO 2 in the liquid phase.…”