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The development of stem heartwood and the factors that control it play an important role in tree physiology, thereby impacting demographic and ecological processes of woody species. We investigated the relationships of stem heartwood with site- and tree-level variables in Pinus canariensis plantations. A total of 30 plots were sampled in the island of Gran Canaria, Spain, over a large elevation range (995–1875 m) and on terrain with different slopes (4%–70%) and exposures. The 15 pines closest to each plot center were measured and cored to quantify growth rates and the size of heartwood, also known as "tea". We used generalized linear mixed models (GLMMs) to account for both fixed and random effects while evaluating the best predictors of heartwood presence. Stem diameter was the variable most correlated with heartwood radius, and allowing for a random slope and intercept of this relationship accounted for spatially related variability. Furthermore, the GLMM model became more effective when the relationship between stem diameter and heartwood was modeled using the presence/absence of the "tea" rather than its measured size. Other site- and tree-level variables either were not statistically significant or improved the model relatively little. Because stem heartwood affects both wood quality and the amount of carbon that trees can store, our findings have implications for forest management and carbon-conscious policies. [ABSTRACT FROM AUTHOR]

The development of stem heartwood and the factors that control it play an important role in tree physiology, thereby impacting demographic and ecological processes of woody species. We investigated the relationships of stem heartwood with site- and tree-level variables in Pinus canariensis plantations. A total of 30 plots were sampled in the island of Gran Canaria, Spain, over a large elevation range (995–1875 m) and on terrain with different slopes (4%–70%) and exposures. The 15 pines closest to each plot center were measured and cored to quantify growth rates and the size of heartwood, also known as “tea”. We used generalized linear mixed models (GLMMs) to account for both fixed and random effects while evaluating the best predictors of heartwood presence. Stem diameter was the variable most correlated with heartwood radius, and allowing for a random slope and intercept of this relationship accounted for spatially related variability. Furthermore, the GLMM model became more effective when the relationship between stem diameter and heartwood was modeled using the presence/absence of the “tea” rather than its measured size. Other site- and tree-level variables either were not statistically significant or improved the model relatively little. Because stem heartwood affects both wood quality and the amount of carbon that trees can store, our findings have implications for forest management and carbon-conscious policies.

Resprouting woody species adapted to perturbations store large amounts of carbon reserves to sustain plant metabolism during and resprout following perturbations. However, it is not known how carbon sources and sinks re-adjust in response to perturbations. Here, we studied when and where different reserve pools were mobilized after an aboveground perturbation, and how were new assimilates used after resprouting. Leaf gas exchange, plant organ carbon isotopic composition (δ13C) and nonstructural carbohydrate concentrations [NSC] were measured over one year in Pinus canariensis saplings subjected to complete defoliation (D) or complete defoliation plus stem damage (DD). Growth stopped completely in D and DD trees by the second month after the treatment application and during subsequent crown development. Growth resumed in most trees (60%) by the end of the growing season. Relative to control (C) trees, stem xylem [starch] decreased in D and DD during resprouting of new buds. Stem and root [starch] were also lower during growth resumption in these trees. One year after aboveground damages, leaf and root δ13C were significantly lower in D and DD, whereas [starch] recovered to values of C trees, except in roots of DD trees. Mobilization of carbon reserves from woody organs allows for resprouting and contributes to crown regeneration, stem growth resumption and wound healing in DD trees. New 13C-depleted photoassimilates contribute to these processes, and to refilling carbohydrates reserves. High [starch], plasticity in growth during and recovery of [starch] after severe aboveground disturbance, highlights high resilience of P. canariensis to perturbation. [ABSTRACT FROM AUTHOR]

Many studies report the history of fire in pine dominated forests but almost none have occurred on islands. The endemic Canary Islands pine ( Pinuscanariensis C.Sm.), the main forest species of the island chain, possesses several fire resistant traits, but its historical fire patterns have not been studied. To understand the historical fire regimes we examined partial cross sections collected from fire-scarred Pinuscanariensis stands on three western islands. Using dendrochronological methods, the fire return interval (ca. 1850–2007) and fire seasonality were summarized. Fire-climate relationships, comparing years with high fire occurrence with tree-ring reconstructed indices of regional climate were also explored. Fire was once very frequent early in the tree-ring record, ranging from 2.5 to 4 years between fires, and because of the low incidence of lightning, this pattern was associated with human land use. After ca. 1960, the fire regime changed to a more widespread pattern at a lower frequency. Climate variability was not associated with widespread fires early in the fire record. After 1960, widespread fire years were significantly drier than normal while antecedent conditions were wetter. Over the last several decades fire suppression has essentially eliminated all but the largest, higher intensity wildfires, establishing a new fire regime. We suggest strategies that promote fire as a forest management tool to restore a fire regime consistent with historical patterns. Canary Island pine could be useful in management programs in fire prone environments of the world because of its fire trails (fire tolerance and sprouting ability). [ABSTRACT FROM AUTHOR]

Key message : Intrinsic water use efficiency of Pinus canariensis (Sweet ex Spreng.) growing at a semi-arid treeline has increased during the past 37 years. Tree ring width by contrast has declined, likely caused by reduced stomatal conductance due to increasing aridity. Context : Rising atmospheric CO concentration ( C ) has been related to tree growth enhancement accompanied by increasing intrinsic water use efficiency (iWUE). Nevertheless, the extent of rising C on long-term changes in iWUE and growth has remained poorly understood to date in Mediterranean treeline ecosystems. Aims : This study aimed to examine radial growth and physiological responses of P. canariensis in relation to rising C and increasing aridity at treeline in Tenerife, Canary Islands, Spain. Methods : We evaluated temporal changes in secondary growth (tree ring width; TRW) and tree ring stable C isotope signature for assessing iWUE from 1975 through 2011. Results : Precipitation was the main factor controlling secondary growth. Over the last 36 years P. canariensis showed a decline in TRW at enhanced iWUE, likely caused by reduced stomatal conductance due to increasing aridity. Conclusion : Our results indicate that increasing aridity has overridden the potential CO fertilization on tree growth of P. canariensis at its upper distribution limit. [ABSTRACT FROM AUTHOR]

We tested the hypothesis that fertilized containerized Pinus canariensis seedlings increases survival when planted in semiarid sites through the improvement of their physiological status during the establishment phase by an increment in root growth. Seedlings were cultured under two different regimes: traditional (in non-fertilized natural soil) and alternative (in fertilized peat). Morphological attributes and nitrogen content were measured before planting. Measurements of survival and growth in the plantation were made periodically for 2 years and physiological plant responses (leaf water potential, gas exchange and chlorophyll fluorescence) during the third summer after planting were tested and finally a set of plants were excavated to measure the same parameters as before planting. Seedlings cultivated using fertilized peat achieved the highest values for all of evaluated parameters. During the third dry season, big seedlings exhibited better physiological status. Therefore, enhanced root growth can result in better water uptake during the dry period thereby increasing survival and growth in the next few years after planting. A feed-back physiological model is proposed to explain P. canariensis establishment in a semiarid environment. [ABSTRACT FROM AUTHOR]

Abstract: High O3 levels, driving uptake and challenging defense, prevail on the Canary Islands, being associated with the hot and dry summers of the Mediterranean-type climate. Pinus canariensis is an endemic conifer species that forms forests across these islands. We investigated the effects of ozone on photosynthesis and biochemical parameters of P. canariensis seedlings exposed to free-air O3 fumigation at Kranzberg Forest, Germany, where ambient O3 levels were similar to those at forest sites in the Canary Islands. The twice-ambient O3 regime (2xO3) neither caused visible injury-like chlorotic or necrotic spots in the needles nor significantly affected violaxanthin, antheraxanthin and zeaxanthin levels and the de-epoxidation state of the xanthophyll cycle. In parallel, stomatal conductance for water vapour, net photosynthesis, intercellular CO2 concentration, chlorophyll fluorescence parameters, as well as antioxidant levels were hardly affected. It is concluded that presently prevailing O3 levels do not impose severe stress on P. canariensis seedlings. [Copyright &y& Elsevier]

We investigated the seasonal variation in the gas exchange of current and 1-year-old needles in the upper sun and lower shade crown of adult Pinus canariensis trees. In general, current year needles displayed lower gas exchange rates than the 1-year-old needles. In both needle age classes, gas exchange was significantly lower in the shade than in the sun crown. However irrespective of crown position and needle age, maximum daily net photosynthesis, transpiration, and stomatal conductance for water vapour were generally higher during the wet and cold winter as compared to the dry and hot summer. These higher gas exchange values obtained during the cold and wet season can mainly be explained by higher soil-water availability and lower evaporative demand as compared to the warm and dry seaon. In addition, we also observed a displacement in the temperature optimum of net photosynthesis towards lower temperatures during the cold and wet season as compared to the warm and dry season. The observed gas exchange characteristics indicate a conservative water saving strategy and thus allowing P. canariensis needles to maintain a positive carbon gain even at periods of high evaporative demand and low soil-water availability. [ABSTRACT FROM AUTHOR]