Ring width,climate and wood density relationships in two long-lived Tasmanian tree species

The great majority of dendroclimatological work in Australia has thus far relied on ring-width chronologies only. We report novel results from a pilot study that show the potential to develop density-based climatically sensitive chronologies from two long-lived conifers endemic to Tasmania: Pencil Pine and Celery Top Pine. Cross-dating of average ring density profiles within each of the two sites examined was comparable with the better replicated ring-width chronologies from the sites. Cross-dating potential for maximum density was also indicated. Correlations between density and climate for both species were stronger and more persistent across a window of several months than correlations between ring width and climate. These stronger correlations suggest that temperature reconstructions based on average density may be possible. The ability to develop high resolution temperature-sensitive chronologies would allow for spatial comparisons across regions such as Tasmania that are affected by multiple broad-scale climate systems. A particularly novel result was the finding that maximum density was significantly related to stream-flow at the end of the growing season. Further work is required to assess the potential to reconstruct temperature, and to reconstruct stream-flow for important Tasmanian catchments over the past 500–800 years.     

Interspecific variation in tree seedling establishment in canopy gaps in relation to tree density

Abstract. We tested whether interspecific variation in tree seedling establishment in canopy gaps was significantly related to interspecific variation in tree density, for seven deciduous forest tree species (Quercus alba, Hamamelis virginiana, Acer rubrum, Sassafras albidum, Quercus rubra, Prunus serotina, Ostrya virginiana). For each species, seedling establishment was calculated as the difference in seedling density before experimental gap creation versus three years after gap creation. In each of the six experimentally-created gap types (33 % or 66 % removal of tree basal area from 0.01-ha, 0.05-ha or 0.20-ha patches), differences in seedling establishment among species were significantly related to differences in their density in the tree canopy. A regression model with log_e tree density as the independent variable accounted for between 93 % and 98 % of interspecific variation in seedling establishment. Our results provide empirical support for models of tree dynamics in gaps that assume seedling establishment depends on canopy tree density.     

Reproductive phenology of two Mimusops species in relation to climate,tree diameter and canopy position in Benin (West Africa)

Assessing species phenology provides useful understanding about their autecology, to contribute to management strategies. We monitored reproductive phenology of Mimusops andongensis and Mimusops kummel, and its relationship with climate, tree diameter and canopy position. We sampled trees in six diameter classes and noted their canopy position. For both species flowering began in the dry season through to the rainy season, but peaked in the dry season, whilst fruiting occurred in the rainy season and peaked during the most humid period. Flowering was positively correlated with temperature. Conversely, fruiting was negatively correlated with temperature and positively with rainfall, only in the Guineo‐Sudanian zone. For M. andongensis, flowering and fruiting prevalences were positively linked to stem diameter, while only flowering was significantly related to canopy position. For M. kummel, the relationship with stem diameter was significant for flowering prevalence only and in the Guineo‐Sudanian zone. Results suggest that phylogenetic membership is an important factor restricting Mimusops species phenology. Flowering and fruiting of both species are influenced by climate, and consequently climate change might shift their phenological patterns. Long‐term investigations, considering flowering and fruiting abortion, will help to better understand the species phenology and perhaps predict demographic dynamics.     

Stomatal and nonstomatal limitations of photosynthesis in relation to the drought and shade tolerance of tree species in open and understory environments

 Light saturated photosynthesis (A) in field saplings of shade tolerant, intermediate, and intolerant tree species was analyzed for stomatal and nonstomatal limitations to test differences between species and sun and shade phenotypes during drought. Throughout the study, photosynthesis was highest and mesophyll limitations of A (L_m) lowest in the intolerant species in both open and understory habitats. The shade tolerant species exhibited the only drought-related decreased A and increased L_m in the open, and the greatest drought-related decreased A and increased L_m in the understory. Few species exhibited significant habitat or drought-related differences in stomatal conductance to CO₂ (g_c), but even slight decreases in g_c during drought were associated with large increases in stomatal limitations to A (L_g). Combined changes in L_m and L_g resulted in increased relative stomatal limitation to A (l _g) in several species during drought. Nevertheless, the overall lack of stomatal closure allowed for nonstomatal limitations to play a major role in reduced A during drought. Higher leaf N was associated with shallower slope of the l _g versus g_c relationship, an indication of greater A capacity. Photosynthetic capacity tended to be greater in the intolerant species than the tolerant species, and it tended to decrease during drought primarily in the shade tolerant species in the understory. Findings in the literature suggest that carbon reduction reactions may be more susceptible to drought than photosynthetic light reactions. If so, reduced carbon reduction capacity of shade tolerant species or shade phenotypes may predispose them to drought conditions, which suggests a mechanism behind the well-recognized tradeoff between drought tolerance and shade tolerance of temperate tree species. Received: 20 October 1995 / Accepted: 20 February 1996     

Ecophysiological responses to simulated canopy gaps of two tree species of contrasting shade tolerance in elevated CO2

1. One-year-old seedlings of shade tolerant Acer rubrum and intolerant Betula papyrifera were grown in ambient and twice ambient (elevated) CO₂, and in full sun and 80% shade for 90 days. The shaded seedlings received 30-min sun patches twice during the course of the day. Gas exchange and tissue–water relations were measured at midday in the sun plants and following 20 min of exposure to full sun in the shade plants to determine the effect of elevated CO₂ on constraints to sun-patch utilization in these species.
2. Elevated CO₂ had the largest stimulation of photosynthesis in B. papyrifera sun plants and A. rubrum shade plants.
3. Higher photosynthesis per unit leaf area in sun plants than in shade plants of B. papyrifera was largely owing to differences in leaf morphology. Acer rubrum exhibited sun/shade differences in photosynthesis per unit leaf mass consistent with biochemical acclimation to shade.
4. Betula papyrifera exhibited CO₂ responses that would facilitate tolerance to leaf water deficits in large sun patches, including osmotic adjustment and higher transpiration and stomatal conductance at a given leaf-water potential, whereas A. rubrum exhibited large increases in photosynthetic nitrogen-use efficiency.
5. Results suggest that species of contrasting successional ranks respond differently to elevated CO₂, in ways that are consistent with the habitats in which they typically occur.     

Effects of climate change on the distribution of Iberian tree species

Question: Will the predicted climate changes affect species distribution in the Iberian Peninsula? Location: Iberian Peninsula (Spain and Portugal). Methods: We modelled current and future tree distributions as a function of climate, using a computational framework that made use of one machine learning technique, the random forest (RF) algorithm. This algorithm provided good predictions of the current distribution of each species, as shown by the area under the corresponding receiver operating characteristics (ROC) curves. Species turnover, richness and the change in distributions over time to 2080 under four Intergovernmental panel on climate change (IPCC) scenarios were calculated using the species map outputs. Results and Conclusions: The results show a notable reduction in the potential distribution of the studied species under all the IPCC scenarios, particularly so for mountain conifer species such as Pinus sylvestris, P. uncinata and Abies alba. Temperate species, especially Fagus sylvatica and Quercus petraea, were also predicted to suffer a reduction in their range; also sub‐mediterranean species, especially Q. pyrenaica, were predicted to undergo notable decline. In contrast, typically Mediterranean species appeared to be generally more capable of migration, and are therefore likely to be less affected.     

Photosynthetic heat tolerance of shade and sun leaves of three tropical tree species

Photosynthesis Research - Previous studies of heat tolerance of tropical trees have focused on canopy leaves exposed to full sunlight and high temperatures. However, in lowland tropical forests...     

Plasticity in seedling morphology,biomass allocation and physiology among ten temperate tree species in response to shade is related to shade tolerance and not leaf habit

• Mechanisms of shade tolerance in tree seedlings, and thus growth in shade, may differ by leaf habit and vary with ontogeny following seed germination. To examine early responses of seedlings to shade in relation to morphological, physiological and biomass allocation traits, we compared seedlings of 10 temperate species, varying in their leaf habit (broadleaved versus needle‐leaved) and observed tolerance to shade, when growing in two contrasting light treatments – open (about 20% of full sunlight) and shade (about 5% of full sunlight).
• We analyzed biomass allocation and its response to shade using allometric relationships. We also measured leaf gas exchange rates and leaf N in the two light treatments.
• Compared to the open treatment, shading significantly increased traits typically associated with high relative growth rate (RGR) – leaf area ratio (LAR), specific leaf area (SLA), and allocation of biomass into leaves, and reduced seedling mass and allocation to roots, and net assimilation rate (NAR). Interestingly, RGR was not affected by light treatment, likely because of morphological and physiological adjustments in shaded plants that offset reductions of in situ net assimilation of carbon in shade. Leaf area‐based rates of light‐saturated leaf gas exchange differed among species groups, but not between light treatments, as leaf N concentration increased in concert with increased SLA in shade.
• We found little evidence to support the hypothesis of a increased plasticity of broadleaved species compared to needle‐leaved conifers in response to shade. However, an expectation of higher plasticity in shade‐intolerant species than in shade‐tolerant ones, and in leaf and plant morphology than in biomass allocation was supported across species of contrasting leaf habit.

     

Exploring wood anatomy,density and chemistry profiles to understand the tree-ring formation in Amazonian tree species

Long-term analysis of tree growth using annual tree rings is increasingly in demand for tropical tree species. The basis of these studies has traditionally been the anatomical identification of the annual ring boundary. However, the structure of these annual rings has been sparsely explored for complementary physical and chemical wood traits. Here, we explore the relationships among wood density features and chemical elements (S, K, Ca, Mn) involved in the annual tree ring formation of 12 tropical tree species from non-flooded forest in the southern Amazon basin. Transverse wood sections were used for each species to determine: 1) macroscopic distinction (radial growth and wood density), 2) microscopic analyse of vessels, axial and ray parenchyma (anatomy) and 3) X-ray densitometry (physical) and X-ray fluorescence (chemical). For some species, the profiles of wood density, and Ca and Mn content showed intra- and inter-annual patterns that allowed to define and characterize the growth boundary of tree rings. Ca, K and S were mainly distributed in axial parenchyma cells, and around vessels, whereas, Mn was mainly distributed in fibres. Our results showed significant species-specific correlations between tree-ring width, density and concentrations of Ca, K and Mn. The anatomical characterization and the complementary information provided by the density and chemical profiles in some Amazonian species can represent a valuable proxy to improve the definition of annual ring-boundaries and improve the understanding of long-term growth and physiological patterns.     

Patterns of tree species richness in Jalisco,Mexico: relation to topography,climate and forest structure

The objective of this study was to identify the major environmental variables and components of forest structure associated with variability in tree species richness on a network of 806 permanent plots in the State of Jalisco, Mexico. Tree data recorded on the sample plots were used to characterize tree species richness by forest type and climatic conditions (temperature and precipitation) in the State. Species composition and other diversity indices were also calculated. Explanatory variables identified in a Poisson regression identified forest cover type, elevation, tree basal area, canopy closure, and winter precipitation as being important to changes in tree species richness. An “extreme quantile curve estimation” approach was then used to approximate the boundary that represented the maximum potential species richness response to the various levels of important variables. Maximum tree species richness decreased with increasing elevation. The relationships between maximum species richness and tree basal area, canopy closure, and winter precipitation followed a hump-back unimodal model, with intermediate values supporting the largest species richness. We believe that results of the current study will contribute to further development of a conservation plan for tree species in the State of Jalisco, Mexico.     

Influence of shade tolerance and development stage on the allometry of ten temperate tree species

Allometry studies the change in scale between two dimensions of an organism. The metabolic theory of ecology predicts invariant allometric scaling exponents, while empirical studies evidenced inter- and intra-specific variations. This work aimed at identifying the sources of variations of the allometric exponents at both inter- and intra-specific levels using stem analysis from 9,363 trees for ten Eastern Canada species with a large shade-tolerance gradient. Specifically, the yearly allometric exponents, α _v,DBH [volume (v) and diameter at breast height (DBH)], β _v,h [v and height (h)], and γ _h,DBH (h and DBH) were modelled as a function of tree age for each species. α _v,DBH, and γ _h,DBH increased with tree age and then reached a plateau ranging from 2.45 to 3.12 for α _v,DBH, and 0.874–1.48 for γ _h,DBH. Pine species presented a local maximum. No effect of tree age on β _v,h was found for conifers, while it increased until a plateau ranging from 3.71 to 5.16 for broadleaves. The influence of shade tolerance on the growth trajectories was then explored. In the juvenile stage, α _v,DBH, and γ _h,DBH increased with shade tolerance while β _v,h was shade-tolerance independent. In the mature stage, β _v,h increased with shade tolerance, whereas γ _h,DBH decreased and α _v,DBH was shade-tolerance independent. The interaction between development stage and shade tolerance for allometric exponents demonstrates the importance of the changing functional requirements of trees for resource allocation at both the inter- and intra-specific level. These results indicate the need to also integrate specific functional traits, growth strategies and allocation, in allometric theoretical frameworks.     

Dispersal mode,shade tolerance,and phytogeographical affinity of tree species during secondary succession in tropical montane cloud forest

Secondary succession following land abandonment, represented by a chronosequence of 15 old fields (0–80 years old) and two old-growth forests, was studied in the tropical montane cloud forest region of Veracruz, Mexico. The objective was to determine successional trajectories in forest structure and species richness of trees ≥5 cm DBH, in terms of differences in seed dispersal mode, shade tolerance, and phytogeographical affinity. Data were analyzed using AIC model selection and logistic regressions. Mean and maximum canopy height reached values similar to old-growth forest at 35 and 80 years, respectively. Species richness and diversity values were reached earlier (15 and 25 years, respectively) while basal area and stem density tended to reach old-growth forest values within 80 years. Along the chronosequence, the proportion of species and individuals of wind-dispersed trees declined, that of bird dispersed small seeded trees remained constant, while that of gravity and animal dispersed large seeded trees increased; shade-intolerant species and individuals declined, while intermediate and shade-tolerant trees increased. Shade-tolerant canopy trees were rare during succession, even in the old-growth forest. Tropical tree species were more frequent than temperate ones throughout the chronosequence, but temperate tree individuals became canopy dominants at intermediate and old-growth forest stages.     

Wood day capacitance is related to water content,wood density,and anatomy across 30 temperate tree species

Water released from wood during transpiration (capacitance) can meaningfully affect daily water use and drought response. To provide context for better understanding of capacitance mechanisms, we investigated links between capacitance and wood anatomy. On twigs of 30 temperate angiosperm tree species, we measured day capacitance (between predawn and midday), water content, wood density, and anatomical traits, that is, vessel dimensions, tissue fractions, and vessel–tissue contact fractions (fraction of vessel circumference in contact with other tissues). Across all species, wood density (WD) and predawn lumen volumetric water content (VWC_L-pd) together were the strongest predictors of day capacitance (r²_adj = .44). Vessel–tissue contact fractions explained an additional ~10% of the variation in day capacitance. Regression models were not improved by including tissue lumen fractions. Among diffuse-porous species, VWC_L-pd and vessel–ray contact fraction together were the best predictors of day capacitance, whereas among semi/ring-porous species, VWC_L-pd, WD and vessel–fibre contact fraction were the best predictors. At predawn, wood was less than fully saturated for all species (lumen relative water content = 0.52 ± 0.17). Our findings imply that day capacitance depends on the amount of stored water, tissue connectivity and the bulk wood properties arising from WD (e.g., elasticity), rather than the fraction of any particular tissue.     

Conspecific density dependence in seedlings varies with species shade tolerance in a wet tropical forest

Density-dependent seedling mortality could increase with a species relative abundance, thereby promoting species coexistence. Differences among species in light-dependent mortality also could enhance coexistence via resource partitioning. These compatible ideas rarely have been considered simultaneously. We developed models of mortality as functions of irradiance and local conspecific density (LCD) for seedlings of 53 tropical woody species. Species varied in mortality responses to these factors, but mortality consistently increased with shading and LCD. Across species, density-dependent mortality on a per-neighbour basis was inversely related to species community abundance, but higher LCD in more common species resulted in a weak relationship between species abundance and density-dependent mortality scaled to species maximum LCD. Species mortality responses to shading and maximum LCD were strongly and positively correlated. Our results suggest that species differences in density-dependent mortality are more strongly related to physiologically based life-history traits than biotic feedbacks related to community abundance.     

Long‐term tree fern dynamics linked to disturbance and shade tolerance

Question: Do New Zealand tree ferns have recognizable shade tolerance niches? Location: Lowland temperate rain forest of New Zealand (41°20′S, 174°58′E). Methods: Growth, death and recruitment of five tree fern species were estimated from a 38‐year record of stem heights, collected within a 2.25‐ha block of forest, and electron transport rates (ETR) of photosystem II of fronds were measured. Results: Two species of Cyathea were comparatively common (603 and 351 stems in total) and two were comparatively rare (155 and 17 stems in total) on the site. The common species had lower rates of growth, recruitment and mortality than the rare species, had skewed age distributions typical of shade‐tolerant species and were probably recruited soon after a catastrophic earthquake in 1855. The two rare species were failing to recruit under closed forests; their age distributions indicated that all had regenerated long after the earthquake. ETR were higher for faster‐growing than for the shade‐tolerant species. A tree fern that regenerates vegetatively from aerial buds, Dicksonia squarrosa, was common on the site (361 stems in total). Its age distribution suggested it was relatively shade tolerant, but its mortality and recruitment rates were much higher than those of the two shade‐tolerating Cyathea species, suggesting that this multi‐stemmed species functions differently from the monopodial Cyathea species. Conclusions: New Zealand Cyathea tree ferns occupy distinct niches along a shade tolerance spectrum and their relative abundances are strongly influenced by disturbance history. The study provides evidence that tree fern species differ strongly in their responses to canopy disturbance and are not ecologically equivalent.     

Decline of photosynthetic capacity with leaf age in relation to leaf longevities for five tropical canopy tree species

The effect of leaf aging on photosynthetic capacities was examined for upper canopy leaves of five tropical tree species in a seasonally dry forest in Panama. These species varied in mean leaf longevity between 174 and 315 d, and in maximum leaf life span between 304 and 679 d. The light-saturated CO2 exchange rates of leaves produced during the primary annual leaf flush measured at 7-8 mo of age were 33-65% of the rates measured at 1-2 mo of age for species with leaf life span of < 1 yr. The negative regression slopes of photosynthetic capacity against leaf age were steeper for species with shorter maximum leaf longevity. In all species, regression slopes were less steep than the slopes predicted by assuming a linear decline toward the maximum leaf age (20-80% of the predicted decline rate). Maximum oxygen evolution rates and leaf nitrogen content declined faster with age for species with shorter leaf life spans. Statistical significance of regression slopes of oxygen evolution rates against leaf age was strongest on a leaf mass basis (r = 0.49-0.87), followed by leaf nitrogen basis (r = 0.48-0.77), and weakest on a leaf area basis (r = 0.35-0.70).