THE CROWN OF PINE (ILLUSTRATED)
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In late July the larvae pupate in cocoons on the underside of foliage and emerge two weeks later as adults to begin the cycle again. Damage symptoms : The upper part of the crown and the branch tips are defoliated first. The remainder of the foliage is destroyed as the larvae migrate down the crown.
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By July, defoliated trees appear scorched. Trees may die after one or more years of severe defoliation. Frequently, the top third of the crown is completely defoliated, which leads to damage in the form of top-kill and branch dieback. Douglas-fir trees that have been weakened by tussock moth defoliation may also be susceptible to attack by other insect pests, such as the Douglas-fir beetle.
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Pine - Wikipedia
All B. The pipe model theory views trees as an assembly of pipes that connect the leaves to the roots Shinozaki et al. Through empirical evidence, the authors demonstrate that the relationship between the foliage biomass above a given point in the stem and the used pipe area at that point is linear without an intercept. The linearity of the pipe model has been questioned by several authors by considering that the sapwood area is equivalent to the used pipe area.
Moreover, results using either foliage biomass or leaf area lead to the same results Kershaw , although some authors have argued the contrary Valentine Kershaw and Maguire found that the relationship between the cumulative foliage area above a given point and the sapwood area of the stem at that point was non-linear. Similar results were presented by Long and Smith that related sapwood area at breast height to projected leaf area.
The authors conclude that the leaf area to sapwood area ratio is directly related to tree size and stand conditions and is non-linear in form. Several studies have also shown that the pipe model ratio i. Berninger and Nikinmaa postulated that the pipe model relationship might have an intercept. Modelling approaches have demonstrated that constant pipe model ratios are not necessarily ecologically meaningful Magnani et al. Lastly, the ratio varies with the height at which sapwood area is measured.
For example, the foliage area to sapwood area ratio will decrease from crown base to breast height, since the relationship between the sapwood area at crown base and that at breast height is proportional to the crown ratio Long and Smith Moreover, biomechanics have also questioned the validity of the pipe model theory.
Farnsworth and van Gardingen demonstrated from empirical evidence that mechanical design principles were better suited to predict branch diameter. They also stated that branches constructed following the pipe model principle would use structural resources inefficiently. Further work by Taneda and Tateno also illustrated that mechanical design principles better predict biomass partitioning between shoot and foliage. Using knowledge of the vertical foliage biomass distribution, coupled with the pipe model theory, the model is able to simulate stem taper and branchiness.
Due to the importance of the pipe model theory in process-based models, in particular, and the fact that it forms the basis of a lot of research in eco-physiology, in general, we want to see to what extent the pipe model theory holds for jack pine Pinus banksiana Lamb. Statistical work based on linear and non-linear mixed-effect nlme models is used to verify whether the relationship between foliage biomass and sapwood area is linear. In the present analysis, the proposed models relate whorl foliage biomass to sapwood area increment between two consecutive whorls.
If the pipe model theory is valid, the models ought to be linear. The tested non-linear forms, however, present the best fit statistics. The non-linear models are able to capture more of the observed variability in the foliage biomass to sapwood area ratios. The model with the best fit statistics is influenced by foliage biomass distribution: the foliage biomass to sapwood area at crown base ratio increases as foliage biomass distribution is pushed towards the crown base.
The data used for the analysis come from three jack pine sites in Eastern Canada: Petawawa Research Forest eastern Ontario, 16 trees , Smurfit-Stone freehold central Quebec, 47 trees and Eel River precommercial thinning trial eastern New Brunswick, 18 trees. Details of the measurements carried out on the stems and the stands as well as site characteristics have previously been published Schneider et al. A subsample of five branches per tree was used to parameterize a branch foliage biomass to branch diameter model, which was applied with the site, plot and tree random effects to all of the branches to estimate whorl foliage biomass.
The stem diameter below each nodal whorl was also noted. Stem analysis discs were taken at regular intervals within the crown, with spacing not exceeding 1. Linear interpolation of the sapwood and heartwood areas from the discs to the stem measurements was then carried out to estimate the sapwood area at the base of each whorl.
One could suppose that the bias would be even smaller if the span is reduced. Model 2 predicts foliage biomass from the sapwood area increment and relative position of the whorl within the crown. The insertion of an exponent on the sapwood area increment also contributes to improving the fit Model 3 , where foliage biomass is predicted using sapwood area increment, relative position within the crown and crown length.
More importantly, the exponent is statistically different from 1. Fit statistics, parameter estimates and variance—covariance estimates of the best models all parameter estimates are highly significant, i. It either increases or decreases asymptotically from stem apex to crown base. When the predicted pipe model ratio for each model is observed, calculated by summing from stem apex the increase in sapwood area of each whorl, the non-linear form is the only one that is able to capture the observed trends.
The original pipe model predicts a constant ratio throughout the crown. The model, which includes whorl location but is linear with respect to foliage biomass, indicates a constant decrease within the crown. Observed and predicted pipe model ratios versus distance from stem apex per site. Predicted values are obtained by inverting the models i. In other words, according to the model, trees that have the majority of their foliage near the crown base will have less sapwood area when compared with trees that have their foliage biomass near the top of the tree.
Influence of foliage biomass distribution on the pipe model ratio at the crown base ratio. Foliage biomass is estimated through a beta distribution shown on the left and used with the summation to crown base of the inverted Model 3.
At first glance, the pipe model seems to adequately describe the changes in foliage biomass for a given sapwood increment in jack pine crowns. Upon more detailed inspection, important deviations from the pipe model appear. Other factors such as whorl position within the crown improve the predictions of the pipe model. The different models give similar fit statistics because several of the explanatory variables are closely related.
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By using different foliage biomass distributions which represent tree social status and stand conditions Schneider et al. Moreover, such changes are also observed for Scots pine Berninger et al. We first thought that differences in leaf-specific transpiration rates were responsible for the reduction in foliage biomass to sapwood area ratios with distance from stem apex.
Crowns are subject to large gradients of shading. Foliage at the top of the tree will have higher photosynthetic output per leaf area than that at crown base and have, therefore, higher requirements in terms of water to be transpired. This is particularly true since pine canopies are well coupled to the atmosphere.
Also, gradients in water vapour pressure deficit will be small compared with gradients in light Stewart This does not, however, explain that foliage mass per change of stem sapwood area increases in the lower parts of the crown, but would lead to the opposite prediction. Moreover, potential changes in specific conductivity of the sapwood along the stem might explain the presented results Spicer and Gartner : specific conductivity usually increases from pith to bark and reaches a maximum at crown base. Hydraulic conductivity of branches is much lower than that of the stem, where hydraulic segmentation may lead to lower water potentials in the branches of the lower crown e.
Altogether, it seems that changes in leaf-specific transpiration rates cannot be used solely to explain the observed deviations from the pipe model theory. We hypothesize that our results may be explained by differences between the turnover rates of sapwood and foliage. The non-linear relationship and the lower foliage mass-to-sapwood area ratios in the lower crown could indicate that heartwood is produced in the larger and older branches.
Branch junctions are usually less efficient than they should be according to hydraulic theories Schulte and Brooks Experimentally, sapwood turnover is very hard to measure and few theories can explain it. Both are of Mesozoic origin and the former is a vigorous resprouter adapted to infrequent crown fires, and the latter is a non-resprouter but tolerates frequent fires due its extremely thick bark and self-pruning Keeley et al. Although climates of the Cretaceous are often characterized as lacking seasonal droughts, decadal scale droughts would have made landscapes fire-prone as is true of many aseasonal climatic regions today.
Although these distant Cretaceous landscapes are often discussed as though they were homogenous, landscapes did exhibit topographic heterogeneity and coastal and interior climates added to this heterogeneity Mix et al. Indeed, at higher latitudes, freezing temperatures would have selected for evergreen sclerophylls Spicer et al.
Semi-arid fire-prone landscapes were not lacking at middle and lower latitudes Spicer et al. As is the case today, small changes in climate would have affected site productivity in ways that could profoundly alter fire regimes Rehfeldt et al. Today most species in the subgenus Pinus exhibit life histories very closely tied to fire, and there is little reason to not accept that Cretaceous radiation of pines was driven in large part by fire.
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Allen interpreted many charred fossil remains from these sites as fire adaptations, including serotinous cones, fire-stimulated hard seeds, and highly sclerotic fern indusia dropped when heated by fire. The warm, aseasonal climates of the Eocene led to tropical angiosperm dominance that displaced pines from middle to high latitudes where they previously had dominated Millar The widespread extirpation of middle latitude pines at the beginning of the Cenozoic is hypothesized to have led to extinction of many species and depleted genetic diversity.
Many Cretaceous fossil pines with combinations of traits not known in extant species went extinct Millar Based on the fossil record, this was a period of fragmentation in pine populations and apparently limited pine diversification Millar The rise in highly productive angiosperm forests is thought to have greatly diminished fire activity during the Eocene Bond and Scott However, this conclusion is based on temporal changes in the distribution of the charcoal inertinite laid down in moist mire habitats.
In the Cretaceous, these mires were highly fire-prone habitats, but the inertinite signal declines with the Eocene dominance of such sites by tropical angiosperm forests, suggesting to these authors that early Cenozoic fires were relatively rare. However, this inertinite signal need not be interpreted as evidence for lack of Eocene fire. I hypothesize that fire-prone habitats shifted to more drought-prone upland sites, promoted in large part by the rapid diversification of fast growing drought-adapted angiosperms that provided fuel to carry fires far beyond the apparently limited fire-prone landscape of the Mesozoic.
Indeed, on contemporary landscapes, mires, and the inertinite fire signal, comprise only a few percent of the land surface compared to contemporary fire-prone environments that occupy over half of the land surface Krawchuk et al. Fossil evidence for such fire-prone Eocene sites is not very plentiful, but then fossil records throughout both the Tertiary and Quaternary are highly biased against recording upland fire-prone vegetation Keeley et al.
Although the equable climates of the Eocene make it appear as though this world was not highly conducive to fires, this is something of an artifact since climatic oscillations on multiple time scales are permanent features of earth history Bennett In addition to temporal variation, there was spatial variation as evident by precipitation gradients that generated dry seasons in parts of southwestern North America Frederiksen with a clear potential for a predictable wildfire season Keeley et al.
Dry zones at this time along the European and North African Tethys Parrish may have favored fire-prone pines. Much of the Eocene world may not have been conducive to fire-dependent pine evolution, but it is unknown what was transpiring along the more arid fringes and as a consequence of anomalous climatic events. That pine evolution continued is supported by molecular phylogenies, which show, in contrast to the apparent contraction and limited evolution of pines implied by the fossil record, that there was very little change in diversification rates during the Eocene Epoch Eckert and Hall These changes would have had an immediate impact on the radiation of those pines adapted to abiotically extreme cold and aridity.
In addition, with a change to more seasonal conditions, changes in fire regimes would have followed. Although it is hypothesized that Eocene fires were spatially limited to arid margins and drought-prone substrates, or temporally limited to anomalously dry years, the Oligocene expanded both the spatial and temporal distribution of fire-prone landscapes. Thus, patches of fire-prone landscape once isolated by more mesic vegetation were now connected with greater fuel continuity and thus greater predictability of fires.
Increased seasonality characterized the Miocene thus creating greater opportunities for exploiting new fire regimes, and this was likely an important driver of the high pine speciation rates observed during this epoch Willyard et al. This model is supported by phylogenetic data indicating that taxa typical of surface fire regimes gave rise to new lineages of crown fire-adapted pines and vice versa.
Another example would be the apparent derivation of the fire-tolerater Pinus lambertiana from the fire-avoider P. Axelrod contended that by late Miocene, many closed-cone pines dominated large portions of semi-arid landscape but with the Quaternary intensification of summer drought were restricted to islands of more mesic habitat. Alternatively, Millar has hypothesized that contemporary disjunct populations are not the result of contraction of a broader distribution but a metapopulation pattern that persisted through the Quaternary and was the result of anomalous climate fluctuations that caused populations to expand and shrink.
With these fire-adapted species, subtle spatial and temporal variations would have produced a mosaic of fire regimes and selected for different suites of species in a fine-grained distribution pattern, generating a patchy distribution of pine species.
Pine evolution has always been interpreted in terms of climate and geology. I propose that one must understand the role of fire to adequately interpret the patterns of diversification in this genus. Contemporary pines have diverged into species that favor abiotically stressful sites or ones that favor more productive sites subject to regular and predictable fires. Associated with these different environmental stresses are a suite of plant traits that are interpreted as character syndromes in response to different environments.
The majority of species are fire-adapted, but it is useful to keep in mind that species do not adapt to fire per se, but rather to a particular fire regime. Several syndromes are described that are associated with different fire regimes. The presence of high fire activity in the Mesozoic and the phylogenetic analyses that show fire-adaptive traits can be traced to this era support the conclusion that the evolution of pines is best understood in terms of fire and abiotic stresses as driving trajectories of life history adaptation in pine evolution.
This work was funded by the U. This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author s and the source are credited. Skip to main content Skip to sections.
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Advertisement Hide. Download PDF. Ecology and evolution of pine life histories. Open Access. First Online: 09 May Introduction Pinus is a diverse genus of trees widely distributed throughout the Northern Hemisphere. Objectives Here I lay out the different pathways of pine life history adaptation and a brief overview of pine evolution and the very significant role that fire has played. Conclusion Understanding the current pattern of pine distribution requires interpreting their evolution in terms of climate, geology, and fire.
It is a diverse genus of more than species of evergreen sclerophyllous-leaved trees largely restricted to temperate latitudes, or to high elevation temperate conditions at lower latitudes, characteristics shared only by Quercus in the northern hemisphere and Eucalyptus in the southern hemisphere. Unlike the latter two angiosperm genera, which are largely of Cenozoic origin, Pinus is a gymnosperm that originated in the Mesozoic Era Fig.
Open image in new window. Life history evolution in pines has taken two pathways that have reduced close competition with fast growing angiosperms. One is an adaptive shift toward abiotically stressful environments, and another is toward fire disturbed environments Keeley and Zedler These adaptive modes largely follow the subgeneric split between Strobus and Pinus although there are exceptions Fig.
Fire scar dendrochronology studies shows that historically these trees were exposed to repeated fires, providing information on past fire frequencies as well as demonstrating that these fires were of sufficiently low intensity that trees survived repeated fires Fig. Examples of such pines would include Pinus pinea and Pinus pinaster in Europe, Pinus sylvestris throughout many parts of Euro-Asia, and Pinus ponderosa in North America and closely related taxa in Central America. Survival of these low intensity surface fires is enhanced by several traits. Height is an important attribute and when coupled with self-pruning of dead branches maintains a significant gap between surface fuels and potential canopy fuels Fig.
Thick bark enhances tree survival by protecting sensitive cambial tissue from heat shock van Mantgem and Schwartz ; Bova and Dickinson Phylogenetic studies indicate a strong correlation between height, self-pruning, and bark thickness in these pines Schwilk and Ackerly These fire-tolerater pines have long needles, which leads to litter with minimal compaction and contributes to high fire intensity, relative to shorter needle species Fonda et al.
In mixed forests, those sites with higher basal area of pines have significantly greater scorch height due to the greater flame lengths generated from these needles Knapp and Keeley