Barbara L. Gartner

Identification, measurement and interpretation of tree rings in woody species from mediterranean climates

We review the literature dealing with mediterranean climate, vegetation, phenology and ecophysiology relevant to the understanding of tree‐ring formation in mediterranean regions. Tree rings have been used extensively in temperate regions to reconstruct responses of forests to past environmental changes. In mediterranean regions, studies of tree rings are scarce, despite their potential for understanding and predicting the effects of global change on important ecological processes such as desertification. In mediterranean regions, due to the great spatio‐temporal variability of mediterranean environmental conditions, tree rings are sometimes not formed. Often, clear seasonality is lacking, and vegetation activity is not always associated with regular dormancy periods. We present examples of tree‐ring morphology of five species (Arbutus unedo, Fraxinus ornus, Quercus cerris, Q. ilex, Q. pubescens) sampled in Tuscany, Italy, focusing on the difficulties we encountered during the dating. We present an interpretation of anomalies found in the wood structure and, more generally, of cambial activity in such environments. Furthermore, we propose a classification of tree‐ring formation in mediterranean environments. Mediterranean tree rings can be dated and used for dendrochronological purposes, but great care should be taken in selecting sampling sites, species and sample trees.

Patterns of xylem variation within a tree and their hydraulic and mechanical consequences

Publisher Summary This chapter discusses the patterns of variation in xylem structure found within a woody plant, and emphasizes what is known and what is not known about the functional consequences of this variation for shoot water movement and mechanics. The first section reviews the typical structure of xylem within a tree. There is more information on softwood (gymnosperm) than hardwood (woody angiosperm) anatomy, and therefore many of the paradigms of wood anatomy are based on softwoods. The anatomical variation described here results in systematic variation in efficiency of water transport through the stem. The hydraulic properties discussed here are hydraulic conductivity (kh) and specific conductivity (ks) in the axial direction. Stems experience short- and long-term stress (force per unit area) from a variety of causes, such as gravity, wind, weight of snow or a maturing fruit, removal of a branch, partial failure of the anchorage system, or growth and development. This chapter has emphasized optima for mechanics and hydraulics separately, but the trade-offs between the two must be considered more fully. In the ranges of wood densities and water demands that plants have, we do not even know whether there are trade-offs between mechanics and hydraulics, partly because one must define the hydraulic and mechanical criteria in order to try such analysis.

Stem hydraulic properties of vines vs. shrubs of western poison oak, Toxicodendron diversilobum

SummaryThis study investigated the effect of mechanical support on water transport properties and wood anatomy of stems of western poison oak, Toxicodendron diversilobum (T. & G.) Greene. This plant grows as a vine when support is present but as a shrub when support is absent. I compared vines and shrubs growing naturally in the field and those produced from cuttings of 11 source plants in a common garden. Huber value (xylem transverse area/distal leaf area) was lower but specific conductivity (water volume · time-1 · xylem transverse area-1 · pressure gradient-1) was higher in supported than unsupported plants both in the field and the common garden. The opposing effects of Huber value and mon garden. The opposing effects of Huber value and specific conductivity resulted in the same values of leafspecific conductivity (LSC, water volume · time-1 · distal leaf area-1 · pressure gradient-1) for supported and unsupported shoots at a given site. Therefore, for the same rates of evapotranspiration, supported and unsupported shoots will have the same pressure gradients in their stems. Vessel lumen composed a higher proportion of stem cross-section in supported than unsupported plants (due to slightly wider vessels and not to greater vessel density). These results suggest that the narrow stems of supported plants are compensated hydraulically by the production of wider vessels: at a given site, poison oak plants co-ordinate their leaf and xylem development such that their stems achieve the same overall conductive efficiencies (LSCs), regardless of support conditions.

Structural Stability and Architecture of Vines vs. Shrubs of Poison Oak, Toxicodendron Diversilobum

To learn whether vine stems are less structurally stable than shrub stems, I studied the architecture, anatomy, and mechanics of western poison oak (Toxicodendron diversilobum), a plant that grows as a vine when provided with external support but otherwise as a shrub. I assessed the relative structural stabilities of vines and shrubs, and the relative importance of stem morphological vs. material properties for this structural stability using the following types of information: abovegound architecture and biomass distribution, and geometric, anatomical, and material properties of the stems. Shoots that were supported by a fence (vines) had a lower proportion of their dry mass in primary stem and had more aboveground dry mass, more leaves, and a greater total length of stem than did unsupported shoots (shrubs). Both growth forms had about the same proportion of their biomass at a given relative height above the ground. Supported shoots were taller and had lower stem taper (change in radius per unit length ...

Breakage and Regrowth of Piper Species in Rain Forest Understory

Species of Piper in the lowland tropical forest of La Selva, Costa Rica, appear to have many adaptations to avoid death resulting from branches being broken or pinned to the ground. Analysis of breakage scars along the branches shows that the majority of the individuals have at least one broken branch, and some have many more

Demographic patterns of seedling establishment and growth of native graminoids in an Alaskan tundra disturbance

SUMMARY (1) Presence or absence of buried seed was the major factor governing natural revegetation of a bulldozed disturbance in Alaskan tussock tundra. The viable buried seed pool contained 97% Eriophorum vaginatum and Carex bigelowii seed and was restricted to organic soil horizons. Consequently, disturbed organic soils reached a final seedling density of 250 seedlings m-2 (primarily Carex and Eriophorum) 4 years after disturbance, whereas mineral soils which were colonized by current seed deposition had only 30 seedlings m-2, including many grasses. (2) Fertilization enhanced the growth of grass and 2-4-year-old Carex seedlings fourto ten-fold but had no significant effect upon Eriophorum seedling growth. Growth was not significantly affected by presence of already established seedlings and did not differ between substrates, except for grasses which grew more rapidly on mineral than organic soils. (3) Seedling mortality during the first 2 years after germination was low (43% in Eriophorum, 27% in grass, and 13% in Carex) and did not differ between organic and mineral substrates. Mortality of 1- and 2-year-old seedlings was concentrated during the growing season, but mortality of larger seedlings was primarily a consequence of winter grazing. Mortality was increased by fertilization. (4) The greater vascular plant biomass and cover on organic than mineral soils was due primarily to recruitment from the buried seed pool. The increase in biomass and cover with fertilization was a consequence of a stimulation of growth by grass and Carex. (5) We recommend stockpiling and re-utilizing soil organic matter, supplemented under certain conditions by fertilization and sowing of seeds, as a mechanism of enhancing natural community restoration of arctic tussock tundra following man-made disturbances.

Effects of heartwood extractive fractions of Thuja plicata and Chamaecyparis nootkatensis on wood degradation by termites or fungi

The effect of selective removal of extractives on termite or decay resistance was assessed with matched samples of Thuja plicata Donn ex D. Don and Chamaecyparis nootkatensis (D.Don) Spach heartwood. Samples were extracted using a variety of solvents and then exposed to the subterranean termite Coptotermes formosanus Shiraki in a no-choice feeding test or to the brown-rot fungus Postia placenta (Fr.) M. Larsen & Lombard in a soil bottle test. At the same time, the effect of naturally occurring variations in heartwood extractives on termite or decay resistance was evaluated by testing samples from the inner and outer heartwood of five trees of each species against C. formosanus and P. placenta and analyzing matched wood samples for their extractive content. The results suggest that the methanol-soluble extractives in T. plicata and C. nootkatensis play an important role in heartwood resistance to attack by C. formosanus and P. placenta. Total methanol-soluble extractive content of the heartwood was positively correlated with both termite and decay resistance; however, there was much unexplained variation and levels of individual extractive components were only weakly correlated with one another. Further studies are under way to develop a better understanding of the relationships between individual extractive levels and performance.

Between- and within-tree variation in the anatomy and specific gravity of wood in Oregon white oak (Quercus garryana Dougl.)

In order to analyze the variation in wood properties within and between trees of an underutilized tree species, we sampled six Oregon white oak (Quercus garryana Dougl.) trees from an 80-year old mixed stand of Q. garryana and Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) in the Coast Range of Western Oregon, USA. Fibre length, earlywood vessel diameter, tissue proportions, and specific gravity were measured on samples across the diameter at two heights. Trees had a slight lean (2-12°), so we sampled separately both radii of a diametric strip that ran from the lower to upper side of lean.

Structure-function relationships in sapwood water transport and storage

Publisher Summary Primary production by plants requires the loss of substantial quantities of water when the stomata are open for carbon assimilation. The delivery of that water to the leaves occurs through the xylem. The structure, condition, and quantity of the xylem control not only the transport efficiency but also the release of water from storage. For example, if there is high resistance to water flow in the stem, then less water is available to the leaves, so less primary production can occur. High resistance can result from wood material with low conductivity, from having only a small amount of conductive wood, or from having very slow release of stored water to the transpiration stream. This chapter focuses on the efficiency with which different parts of the sapwood transport, store, and release water, and how the structure of the wood affects these processes. Particularly, it describes the radial patterns of axial water transport, their anatomical and physiological causes, the effect that sapwood width and wood structure, especially density, have on water transport, and determinants of sapwood water storage properties.

Genetic variation in basic density and modulus of elasticity of coastal Douglas-fir

Douglas-fir trees from 39 open-pollinated families at four test locations were assessed to estimate heritability of modulus of elasticity (MOE) and basic density. After trees were felled, sound velocity was measured on 4-m logs with the Director HM200. Disks were taken to estimate dry and green wood density; dynamic MOE was estimated as green density × (sound velocity)2. Heritability estimates of MOE (across-site h2=0.55) were larger than those for total height (0.15) and diameter at breast height (DBH; 0.29), and similar to those for density (0.59). Negative genetic correlations were found for MOE with height (rA=−0.30) and DBH (rA=−0.51), and were similar to those found for density with height (rA=−0.52) and DBH (rA=−0.57). The partial correlations of height with MOE and density, while holding DBH constant, were positive, implying that the observed negative correlations between height and the wood properties were a function of the high positive correlation between height and DBH and the strong negative correlations between DBH and the wood properties. Taper [DBH/(height−1.4)] was found to be negatively associated with MOE. Selection for MOE may produce greater gains than selection for density because MOE had a larger coefficient of additive variation (9.6%) than density (5.1%). Conversely, selection for growth may have a more negative impact on MOE than density because of the greater genetic variation associated with MOE. Family mean correlations of the wood quality traits with stem form and crown health were mostly nonsignificant.