Coordination of morphological and physiological traits in naturally recruited <Emphasis Type="Italic">Abies alba</Emphasis> Mill. saplings: insights from a structural equation modeling approach

Key message

Apical dominance ratio (ADR), reported as a suitable indicator for the growth and development of Abies alba , is concurrently determined by morphological and functional plant traits. Structural equation modeling (SEM) proved here to be an effective multivariate technique to represent the contribution of different variables in explaining ADR variability.

Context

During the natural recruitment of understory tree saplings, the light environment and competition among individuals may change drastically as well as their growth patterns. To cope with this, saplings have a remarkable ability to accordingly modify their physiology and morphology. Therefore, understanding the ecological significance of plant structural patterns requires an integrated view of morphological, architectural, and physiological attributes of plants.

Aims

Here, we applied a SEM approach to understand the mechanisms influencing the ADR, recently reported as suitable indicator of the growth conditions favoring silver fir (Abies alba Mill.) natural regeneration in Mediterranean areas.

Methods

A series of plant traits (e.g., root-collar diameter, leaf mass per area, and isotope composition) were combined into two main latent variables, namely Morphology and Physiology, to account for their relative contribution in explaining the ADR variability.

? Results

Our results underline the importance of variables accounting for the photosynthetic capacity and leaf economics in determining ADR; among them, leaf mass per area (LMA) emerged as an important driving variable.

? Conclusion

SEM proved to be an effective multivariate technique to represent the coordination of different morphological and functional variables in explaining ADR variability in silver fir.

     

Spatial pattern of beech (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.) and oak (<Emphasis Type="Italic">Quercus pubescens</Emphasis> Mill.) seedlings in natural pine (<Emphasis Type="Italic">Pinus sylvestris</Emphasis> L.) woodlands

Spatial pattern of recruitment is an important factor influencing population dynamics of plant communities. The spatial pattern is determined by seed dispersal and by the spatial variability of germination and initial survival. In the process of forest expansion following farmland abandonment, mid- and late-successional species are often dispersed in pioneer forests by birds. This could result in an aggregated spatial pattern of seeds that could influence the dynamics of these species in mixed pioneer forests. In the sub-Mediterranean area, mid- and late-successional species such as Quercus pubescens (downy oak) and Fagus sylvatica (European beech) are expected to replace pioneer Pinus species. Using a point sampling method we demonstrated that beech and oak seedlings (height <2 m) have a clumped distribution in the understorey of pine. This could result from an aggregated dispersal by jays (dispersal effect) or from preferential recruitment in particular habitats (habitat effect). To test these hypotheses we proposed a statistical analysis of spatial patterns of regeneration of beech and oak. Ground cover variables (i.e. cover by rock outcrops, herbs, box shrubs, mosses or pine) did not differ significantly around seedlings as compared with random sample plots. Likewise, clumped seedlings had growth similar to isolated seedlings, thus refuting the hypothesis of preferential location in the most favourable microsites. Aggregated dispersal seems to be involved in the process of regeneration. Since beech and oak seedlings have contrasting ecological demands, we discuss the implication of this pattern for the replacement dynamics of pine by these species.     

Composition and partition of biomass in a smith fir (<Emphasis Type="Italic">Abies georgei</Emphasis> var. <Emphasis Type="Italic">smithii</Emphasis>) timberline forest on the Sergyemla Mountain,southeastern Tibetan Plateau

The southeastern Tibetan Plateau has the highest timberlines in the world and climate change affects this area to a considerable extent.Quantification of vegetation biomass in the forests at the timberline is essential for understanding carbon balance,forest structure and functional changes in the forests at timberlines.We describe biomass and its constituent components of a smith fir timberline forest occurring at an elevation of 4320 m on the Sergyemla Mountain in the southeastern Tibetan Plateau.The results show that,in the tree layer,the average diameter at breast height(DBH) was 35.6 cm,the density 251 trees per hectare with a total biomass of 309.9 t.ha-1.Of the total biomass,the trunks accounted for 70.49%,branches for 9.09%,leaves for 5.57% and roots for 14.85%.The total biomass in the shrub layer was 77.9 t.ha-1 of which the biomass of trunks,branches,leaves and roots accounted for 42.8,14.9,4.6 and 15.6 t.ha-1,respectively.The total biomass in the herb layer was 3.0 t.ha-1.The total vegetation biomass in the smith fir timberline forest was 390.9 t.ha-1,to which the tree layer contributed the most(79.3%),followed by shrubs(19.9%) and herbs(0.8%).We estimate that the smith fir forest stand at the timberline had a higher total biomass than other fir or spruce forest stands in the surrounding area.     

Interactions between<Emphasis Type="Italic"> Orthotomicus erosus</Emphasis> (Woll.) (Col., Scolytidae) and the Argentine ant<Emphasis Type="Italic"> Linepithema humile</Emphasis> (Mayr) (Hym., Formicidae)

Interactions occurring between Orthotomicus erosus, an economically important pine bark beetle in Portugal, and the aggressive Argentine ant Linepithema humile were investigated. Tri-trophic experimental enclosures consisting of Pinus pinaster logs, O. erosus adults and L. humile workers were set up in the field and in the laboratory. Interactions between ants and scolytids were observed and quantified in terms of the bark beetles success in colonizing the logs. The presence of L. humile did not influence the ability of O. erosus to colonize the logs, apparently due to the difficulties met by the ants in handling the bark beetles and to their inability to injure them. Thus, although abundant in many pine stands in Portugal and in spite of its aggressiveness, L. humile does not seem to affect populations of O. erosus.     

Ten-year results from red alder (<Emphasis Type="Italic">Alnus rubra</Emphasis> Bong.) provenance-progeny testing and their implications for genetic improvement

Ten-year data on growth and survival of two red alder provenance-progeny test trials located in the southern and northern coastal regions in British Columbia, Canada, were analysed and their implications for the genetic improvement of this species were discussed. A total of 42 and 41 provenances, each represented by two to five open-pollinated families were evaluated at each site, respectively. Results indicate that red alder provenances responded differently to the environmental conditions of the two sites. At age 10, red alder provenances tended to perform better at sites near their origin. The results support earlier work that two breeding zones should be delineated with the boundary at approximately 52° N. One may expect an average of about 5% decrease in stem volume and 6% increase in mortality, respectively, for each degree of southward and northward transfer of seed sources from their origins. Individual, family, and within-family heritabilities for height, diameter, stem volume were moderately high (0.22–0.42), for the southern zone, implying good potential for genetic improvement. Heritabilities were somewhat lower (0.12–0.39) for the northern zone because of greater environmental heterogeneity of the test site. Selecting the top 20 unrelated individuals for seed orchard establishment would result in 29% and 23% gain in stem volume at a rotation age of 40 years in the southern and northern zones, respectively. Correlation between ranks of the predicted breeding values for height at different ages and stem volume at age 10 increased rapidly when plantation was young and became relatively stable after 6 years of out-planting. Stem volume had much stronger correlation with diameter (≥0.84) than with height (≤0.67). Early selection at age 6 based on stem volume is therefore recommended.     

Stand density and growth of Norway spruce (<Emphasis Type="Italic">Picea abies</Emphasis> (L.) Karst.) and European beech (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.): evidence from long-term experimental plots

On the basis of nine Norway spruce (Picea abies (L.) Karst.) and ten European beech (Fagus sylvatica L.) thinning experiments in Germany, for which both residual and removed stock had been registered first during 1870, I scrutinize how moderate and heavy thinning from below (B-, C-grade) affects the production of merchantable volume compared with light thinning (A-grade). In relation to A-grade, cumulative merchantable volume (CV) of B- and C-grade amounts in average to 103–107% in juvenile and to 97–102% in mature Norway spruce stands. The corresponding findings for European beech are 101–106% and 94–102%. CV of individual stands varies between 89% and 130% for Norway spruce and 73% and 155% for European beech (CV of A-grade = 100%). These findings are substantiated by the relation between stand density (SDI) and periodic annual increment (PAI). On the B- and C-grade plots of spruce and beech, respectively, SDI was reduced down to 41–91% and 31–83% of the A-grade. When SDI is reduced in young stands, PAI follows a unimodal curve. Norway spruce’s PAI culminates in 109% if SDI is reduced to 59%; European beech’s PAI culminates in 123% when density is reduced to 50%. Whereas Norway spruce’s growth reacts most positively on thinning under poor site conditions and with increment reduction on favourable sites, European beech behaves oppositely. With stand development the culmination point of the unimodal relation moves towards maximum density, so that in older stands PAI follows the increasing pattern, which is the left portion of a unimodal curve. A model is presented which apparently unifies contradictory patterns of stand density–growth reactions by integrating relative stand density, average tree size and site fertility effects, and makes the findings operable for forest management.     

Insects reared from stems and branches of goat willow (<Emphasis Type="Italic">Salix caprea</Emphasis> L.) in Bulgaria

Seven xylophagous insect species were established in stems and branches of Salix caprea L. during the period 1998–2003 in Bulgaria: Agrilus lineola lineola Redtenbacher (Coleoptera: Buprestidae), Aromia moschata (Linnaeus), Oberea oculata (Linnaeus), Saperda populnea (Linnaeus), Saperda similis Laicharting (Coleoptera: Cerambycidae), Synanthedon formicaeformis (Esper) (Lepidoptera: Sesiidae) and Rhabdophaga clavifex (Kieffer) (Diptera: Cecidomyiidae). From them, six parasitoid species were reared: Dolichomitus mesocentrus (Gravenhorst), Dolichomitus populneus (Ratzeburg) (Hymenoptera: Ichneumonidae), Stephanus serrator (Fabricius) (Hymenoptera: Stephanidae), Aprostocetus metra (Walker), Euderus caudatus (Thomson) (Hymenoptera: Eulophidae) and Billaea irrorata (Meigen) (Diptera: Tachinidae). D. populneus, E. caudatus and B. irrorata were connected with S. populnea; D. mesocentrus and S. serrator with S. similis; and A. metra with R. clavifex. Two parasitoids (A. metra and E. caudatus) had not previously been reported for the fauna of Bulgaria. The parasitoid–host relationships D. mesocentrus–S. similis and S. serrator –S. similis were established for the first time in this study.     

Genetic variability of Italian southern Scots pine (<Emphasis Type="Italic">Pinus sylvestris</Emphasis> L.) populations: the rear edge of the range

Understanding the genetic structure and diversity of edge populations can shed light on the role of peripheral populations and their relevance for conservation strategies. In this study, three fragmented and isolated Apennine populations of Scots pine (Pinus sylvestris L.) belonging to the rear edge of the species’ distribution were analyzed using both nuclear (nSSR) and chloroplast (cpSSR) microsatellites and were compared with an Alpine population belonging to the species’ main range. Although small population size and considerable isolation have probably reduced the genetic variability of Apennine populations, these fragmented populations maintain a high level of within-population genetic diversity. A significant among-population differentiation was found using both nSSR (F _ST = 0.08) and cpSSR markers (ρ = 0.14). Analysis of molecular variance (AMOVA) on the nSSRs attributed all variabilities to the among Apennine populations component supporting the theoretical predictions regarding fragmentation effects on genetic structure. On the other hand, AMOVA on the cpSSRs attributed all variances to the between-region component and no differentiation was found within region, among the Apennine populations. This result suggests the importance of pollen gene flow in homogenizing populations on this geographical scale. Our results confirm the genetic distinctiveness of Apennine populations and their possible derivation from different glacial refugia than those of the Alps. Considering their peculiarity and the high level of intrapopulation genetic diversity that they still retain, fragmented Apennine populations should be considered of high priority for conservation.     

Effect of moisture on physical parameters of timber from Turkey oak (<Emphasis Type="Italic">Quercus cerris</Emphasis> L.) coppice in Central Italy

This study aims to investigate wood density at different levels of moisture, basic density and shrinkage of timber from Turkey oak (Quercus cerris L.) coppice forests growing in Central Italy. We also studied the variability in density in the trees within and among sites. Density shows no significant statistical differences in the tested population. A higher variability in the shrinkage than in the density was found. Wood moisture is referred to as dry mass and fresh mass, which is related to many performance characteristics of wood, i.e., energy production. Trends in moisture and water content were studied because these physical parameters play an important role in the specific area of firewood which requires an accurate estimation of mass, volume and energy content. This work is a contribution to improve xylo-energy estimates of small and medium forestry issues.     

Experimental determination and modeling of equilibrium moisture content from the sapwood of Mexican pine (<Emphasis Type="Italic">Pinus pseudostrobus</Emphasis> Lindl.)

A desorption isotherm is a very important basis in the understanding of drying process. In this study, the desorption isotherms from the sapwood of Mexican pine (Pinus pseudostrobus Lindl.) were determined by the gravimetric method (discontinuous control of sample weight) at 30℃ and 50℃. The salt method was used in the range of water activities from 0.11 to 0.89. The results show that the desorption ability of Mexican pine sapwood increased with temperature at a given relative humidity. The experimental data was further simulated with the models, i.e., BET, GAB, Oswin and Henderson models. The GAB, Oswin and Henderson models allow the representation of the entire desorption isotherms. The BET model showed a better fit for water activity lower than 0.35, with a mean relative deviation of 0.0286 at 30℃ and 0.0167 at 50℃. Simultaneously, the BET model gave a better representation of moisture content in the monolayer saturation region. Overall, the GAB model ensured the best simulation of the entire isotherm, while the Henderson model displayed the worst simulation.