Leaf- and plant-level carbon gain in yellow birch, sugar maple, and beech seedlings from contrasting forest litght environments

Leaf-level photosynthetic-light response and plant-level daily carbon gain were estimated for seedlings of moderately shade-tolerant yellow birch (Betula alleghaniensis Britton) and shade-tolerant sugar maple (Acer saccharum Marsh.) and beech (Fagus grandifolia Ehrh.) growing in gaps and under a closed canopy in a sugar maple stand at Duchesnay, Que. All three species had a higher photosynthetic capacity (A(max)) in the gaps than in shade, but yellow birch and beech responded more markedly than sugar maple to the increase in light availability. The high degree of plasticity observed in beech suggests that the prediction that photosynthetic plasticity should decrease with increasing shade tolerance may not hold when comparisons are made among a few late-successional species. Unit-area daily carbon gain (C(A)) was significantly higher in the gaps than in shade for all three species, but no significant difference was observed between light environments for plant-level carbon gain (C(W)). In shade, we found no difference of C(A) and C(W) among species. In gaps, beech had a significantly higher C(A) than sugar maple but similar to that of birch, and birch had a significantly higher C(W) than maple but similar to that of beech. Sugar maple consistently had lower carbon gains than yellow birch and beech but is nevertheless the dominant species at our study site. These results indicate that although plant-level carbon gain is presumably more closely related to growth and survival of a species than leaf-level photosynthesis, it is still many steps removed from the ecological success of a species

Functional ecology of advance regeneration in relation to light in boreal forests

This paper reviews aspects of the functional ecology of naturally established tree seedlings in the boreal forests of North America with an emphasis on the relationship between light availability and the growth and survival of shade tolerant conifers up to pole size. Shade tolerant conifer species such as firs and spruces tend to have a lower specific leaf mass, photosynthetic rate at saturation, live crown ratio, STAR (shoot silhouette area to total needle surface area ratio), and root to shoot ratio than the shade intolerant pines. The inability of intolerant species such as the pines and aspen to survive in shade appears to be mainly the result of characteristics at the shoot, crown, and whole-tree levels and not at the leaf level. Although firs and spruces frequently coexist in shaded understories, they do not have identical growth patterns and crown architectures. We propose a simple framework based on the maximum height that different tree species can sustain in shade, which may help managers determine the timing of partial or complete harvests. Consideration of these functional aspects of regeneration is important to the understanding of boreal forest dynamics and can be useful to forest managers seeking to develop or assess novel silvicultural systems

Modelling fish habitat preference with a genetic algorithm-optimized Takagi-Sugeno model based on pairwise comparisons

Species-environment relationships are used for evaluating the current status of target species and the potential impact of natural or anthropogenic changes of their habitat. Recent researches reported that the results are strongly affected by the quality of a data set used. The present study attempted to apply pairwise comparisons to modelling fish habitat preference with Takagi-Sugeno-type fuzzy habitat preference models (FHPMs) optimized by a genetic algorithm (GA). The model was compared with the result obtained from the FHPM optimized based on mean squared error (MSE). Three independent data sets were used for training and testing of these models. The FHPMs based on pairwise comparison produced variable habitat preference curves from 20 different initial conditions in the GA. This could be partially ascribed to the optimization process and the regulations assigned. This case study demonstrates applicability and limitations of pairwise comparison-based optimization in an FHPM. Future research should focus on a more flexible learning process to make a good use of the advantages of pairwise comparisons

Spatial, temporal, and species -specific patterns of heterogeneity in growth chamber experiments

Despite the sophistication of contemporary growth chambers, growing conditions cannot be uniformly controlled during experiments. Uniformity trials with bean (Phaseolus vulgaris cv. Spartan) and maize (Zea mays cv. Golden Bantam) in the McGill University Phytotron identified three significant sources of variability. First, not even two identically programmed chambers of the same model and from the same manufacturer provide identical growing environments. Second, programmed environmental conditions are not precisely maintained over time even in a single chamber. Third, the growing environment within a chamber has a consistent pattern of spatial variability with poor growth in the chamber corners and best growth in the center. The importance of these effects varies with species and with the parameters measured, but none can be entirely avoided. Good experimental design with replication of treatments across chambers and blocking within chambers can minimize the negative impact of these sources of uncontrolled experimental variability

Contributions of leaf photosynthetic capacity, leaf angle and self-shading to the maximization of net photosynthesis in Acer saccharum: a modelling assessment

BACKGROUND AND AIMS: Plants are expected to maximize their net photosynthetic gains and efficiently use available resources, but the fundamental principles governing trade-offs in suites of traits related to resource-use optimization remain uncertain. This study investigated whether Acer saccharum (sugar maple) saplings could maximize their net photosynthetic gains through a combination of crown structure and foliar characteristics that let all leaves maximize their photosynthetic light-use efficiency (ɛ). METHODS: A functional–structural model, LIGNUM, was used to simulate individuals of different leaf area index (LAI(ind)) together with a genetic algorithm to find distributions of leaf angle (L(A)) and leaf photosynthetic capacity (A(max)) that maximized net carbon gain at the whole-plant level. Saplings grown in either the open or in a forest gap were simulated with A(max) either unconstrained or constrained to an upper value consistent with reported values for A(max) in A. saccharum. KEY RESULTS: It was found that total net photosynthetic gain was highest when whole-plant PPFD absorption and leaf ɛ were simultaneously maximized. Maximization of ɛ required simultaneous adjustments in L(A) and A(max) along gradients of PPFD in the plants. When A(max) was constrained to a maximum, plants growing in the open maximized their PPFD absorption but not ɛ because PPFD incident on leaves was higher than the PPFD at which ɛ(max) was attainable. Average leaf ɛ in constrained plants nonetheless improved with increasing LAI(ind) because of an increase in self-shading. CONCLUSIONS: It is concluded that there are selective pressures for plants to simultaneously maximize both PPFD absorption at the scale of the whole individual and ɛ at the scale of leaves, which requires a highly integrated response between L(A), A(max) and LAI(ind). The results also suggest that to maximize ɛ plants have evolved mechanisms that co-ordinate the L(A) and A(max) of individual leaves with PPFD availability