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Stem Diameter (stem + diameter)
Selected AbstractsTree growth in an African woodland savanna affected by disturbanceJOURNAL OF VEGETATION SCIENCE, Issue 3 2006R.M. Holdo Abstract: Questions: How does tree growth in a tropical woodland savanna vary as a function of size, and how is it affected by competition from neighbours, site attributes, and damage caused by disturbance? Location: western Zimbabwe. Methods: Trees of common species were tagged, mapped, and measured annually between 2001 and 2003 in a Kalahari sand woodland savanna. Diameter increments were analysed with mixed model regressions for the largest ramet in each genet. Stem diameter and damage, soil texture, and indices of competition at multiple spatial scales were used as covariates. Results: Stem diameter increased initially and then declined as a function of size in undamaged trees, which grew faster than damaged trees. Growth in damaged trees declined with size. No site differences were detected, and there was evidence for between-tree competition on growth only in the fastest-growing species, Brachystegia spiciformis. In several species the growth rate of the largest ramet increased as a function of the basal area of secondary ramets, contrary to expectations. For many species, the growth models showed poor explanatory power. Conclusions: Growth in Kalahari sand savanna trees varies as a function of size and changes in tree architecture caused by disturbance agents such as fire, frost, and elephant browsing. Disturbance may thus play an important role on vegetation dynamics through its effects on growth in the post-disturbance phase. Growth is highly stochastic for some species in this system, and more deterministic in others. It is hypothesized that this dichotomy may be driven by differences in rooting depth among species. [source] Water use characteristics of cacao and Gliricidia trees in an agroforest in Central Sulawesi, IndonesiaECOHYDROLOGY, Issue 4 2009Michael Köhler Abstract Water use characteristics of cacao (Theobroma cacao) and Gliricidia sepium shade trees were studied in an agroforest on Sulawesi, Indonesia. The objectives were: (1) to identify environmental and tree structural factors controlling water use, (2) to analyse the effect of shade tree cover on cacao water use and (3) to estimate stand level transpiration. Sap flux density was measured in up to 18 trees per species and described with a Jarvis-type model. Model parameters suggested a 49% higher maximum sap flux density in cacao than in Gliricidia and species differences in the response to vapour pressure deficit and radiation. Tree water use was positively related to tree diameter in both species, but this relationship tended to differ between species. In cacao trees maximal tree water use increased with decreasing canopy gap fraction above the trees (R2adj = 0·39, p = 0·04). This was paralleled by an increase of cacao stem diameter and leaf area with decreasing gap fraction. Maximum water use rate per unit crown area of cacao was 13% higher than that of Gliricidia. At the stand level the average transpiration rate was estimated at 1·5 mm day,1 per unit ground area, 70% of which was contributed to by cacao. We conclude that, in the given stand, species differed substantially in water use characteristics, while estimated stand transpiration is in line with findings from other studies for cacao stands. Shade trees may enhance stand transpiration through own water use and additionally by increasing water use rates of cacao trees. Copyright © 2009 John Wiley & Sons, Ltd. [source] Separating host-tree and environmental determinants of honeydew production by Ultracoelostoma scale insects in a Nothofagus forestECOLOGICAL ENTOMOLOGY, Issue 4 2007ROGER J. DUNGAN Abstract 1.,Sugar-rich honeydew excreted (,produced') by insects feeding on phloem sap is a key energy flow in a range of temperate and tropical ecosystems. The present study measured honeydew produced by Ultracoelostoma sp. (Homoptera: Coelostomidiidae) scale insects feeding on Nothofagus solandri var. solandri (Hook f.) Oerst. trees in a temperate evergreen forest in New Zealand. Simultaneous measurements of environmental variables and canopy photosynthesis were conducted to allow separation of host-tree and environmental determinants of honeydew production. These relationships were further examined in experiments where canopy photosynthesis was manipulated by shading or plant nitrogen levels increased by foliar spray. 2.,Rates of honeydew production varied nine-fold from a maximum (± 1 SE) of 64.4 ± 15.2 mg dry mass m,2 bark h,1 in early summer (December) to a minimum of 7.4 ± 4.2 mg m,2 h,1 in winter (August). Rates of production measured 1.4 m from the base of the trees' stems varied significantly with stem diameter, and were higher on medium-sized (18 cm diameter) than small or large stems. 3.,Rates of production were significantly related to environmental conditions over the hours preceding measurement (air temperature and air saturation deficit averaged over the preceding 24 and 12 h respectively). There was no evidence that rates of production were directly related to short-term changes in the supply of carbohydrates from the canopy (either when compared with measurements of unmanipulated photosynthetic rate, or after sugar levels were manipulated by shading 80% of host-trees' leaf area), or to changes in phloem nitrogen content. 4.,The results show that there is no clear effect of host-tree carbon supply on honeydew production; if production is related to photosynthesis, the effect of this is much less important that the large and significant direct effect of environmental conditions on honeydew production. [source] Nitrogen fertilization effects on Myzus persicae aphid dynamics on peach: vegetative growth allocation or chemical defence?ENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 2 2010Marie-Hélène Sauge Abstract Plant nitrogen (N) fertilization is a common cropping practice that is expected to serve as a pest management tool. Its effects on the dynamics of the aphid Myzus persicae (Sulzer) (Hemiptera: Aphididae) were examined on young peach [Prunus persica (L.) Batsch (Rosaceae)] trees grown under five N treatments, ranging from N shortage to supra-optimal supply for growth. Aphid population increased over time at the three intermediate N levels. It remained stable at the lowest N level and decreased at the highest N level. Four weeks after the start of infestation, the number of aphids displayed a parabolic response to N level. The relationships between N status and parameters of plant vegetative growth (stem diameter) or biomass allocation (lateral-total leaf area and root-shoot ratio) were consistent with responses proposed by models of adaptive plasticity in resource allocation patterns. However, the variation in plant growth predicted aphid population dynamics only partially. Whereas aphid number was positively correlated with plant N status and vegetative growth up to the intermediate N level, it was negatively correlated with plant N status above this level, but not with vegetative growth. The concentrations of primary and secondary (plant defence-related) metabolites in the plant shoots were modified by N treatments: amino acids (main nutritional resource of aphids) and prunasin increased, whereas chlorogenic acid decreased with increasing N availability. Constitutive changes in plant chemistry in response to N fertilization could not directly explain the reduced aphid performance for the highest N level. Nevertheless, the indirect effect of N on the induction of plant defence compounds by aphid feeding warrants further investigation. The study focuses on the feasibility of handling N fertilization to control M. persicae in orchards, but findings may also be relevant for our understanding of the physiological relationships between the host's nutritional status and the requirements of the insect. [source] Pine mistletoe (Viscum album ssp. austriacum) contributes to Scots pine (Pinus sylvestris) mortality in the Rhone valley of SwitzerlandFOREST PATHOLOGY, Issue 5 2006M. Dobbertin Summary In recent years unusual high mortality of Scots pine (Pinus sylvestris) has been observed in the Swiss Rhone Valley. The exact causes, however, are not known. At a 2-ha monitoring plot, tree mortality and crown condition have been monitored since 1996. Between 1996 and 2004, 59% of the Scots pines died, most of them following the drought periods 1996,1998 and 2003,2004, while only 15% of the deciduous trees died. Crown transparency, needle discolouration, dead branch percentage, mistletoe (Viscum album ssp. austriacum) rating, Tomicus sp. shoot feeding, male flowering effect, tree stem diameter, crown shading and social tree class assessed in 1998 were used in a logistic regression model to predict tree mortality. Crown transparency, mistletoe rating and percentage of dead branches were found significant in the model and the probability of tree mortality increased with increasing rankings of these parameters. Needle discolouration could be used to substitute ,dead branch percentage' as predictor. While crown transparency increased with mistletoe rating, for trees in the same transparency class, trees with medium and heavy mistletoe infection were two to four times more likely to die than trees with no or only low mistletoe infection. For the surviving trees we found that trees with mistletoes showed a significantly higher increase in transparency in the year following a drought than trees without, while in a drought year the opposite was true. At the beginning of the observations no significant differences in transparency had been found between the trees with and without mistletoe. However, by the end of the observation period trees with mistletoe had significantly higher crown transparency. We conclude that mistletoe infection can be considered as both a predisposing factor for tree death, by increasing needle loss following drought and a contributing factor by increasing water stress during drought. Résumé Une forte mortalité des pins sylvestres (Pinus sylvestris) a été observée ces dernières années dans la vallée du Rhône en Suisse. Les causes exactes n'en sont pas connues. La mortalité des arbres et l'état des houppiers ont été suivis depuis 1996 dans une parcelle de 2 ha. Entre 1996 et 2004, 59% des pins sylvestres sont morts, la plupart après les périodes de sécheresse de 1996,98 et 2003,2004, comparéà 15% pour les feuillus. La transparence des houppiers, le jaunissement des aiguilles, le pourcentage de mortalité de branches, une note d'importance du gui (Viscum album ssp. austriacum), les attaques d'alimentation sur pousses par Tomicus sp., la floraison mâle, le diamètre du tronc, l'ombrage du houppier et le statut social des arbres, mesurés en 1998, ont été utilisés dans un modèle de régression logistique pour prédire la mortalité des arbres. La transparence des houppiers, le taux de gui et le pourcentage de branches mortes sont des variables significatives, dont l'augmentation est associée à une augmentation de la probabilité de mortalité des arbres. Le jaunissement des aiguilles pourrait être substituée à la mortalité des branches comme variable prédictrice. Tandis que la transparence des houppiers augmente avec le taux de gui, au sein de la même classe de transparence, les arbres avec une infestation de gui moyenne à forte ont une probabilité de mortalité 2 à 4 fois plus élevée que les arbres à infestation faible ou nulle. Chez les arbres survivants, on observe que les arbres porteurs de gui ont une augmentation plus forte de la transparence du houppier l'année suivant une sécheresse que les arbres sans gui, l'inverse étant vrai pendant une année sèche. La différence de transparence des houppiers entre arbres porteurs de gui et arbres sans gui n'était pas significative au début des observations, alors qu'à la fin de la période, les arbres avec gui ont une transparence plus forte. Nous concluons que l'infestation par le gui peut être considérée à la fois comme un facteur prédisposant à la mortalité, en augmentant la perte d'aiguilles après sécheresse, et un facteur contribuant, en augmentant le stress hydrique pendant la sécheresse. Zusammenfassung Seit einigen Jahren werden im Schweizer Rhonetal hohe Absterberaten der gemeinen Kiefer (Pinus sylvestris L.) beobachtet. Die genauen Ursachen sind bis jetzt unbekannt. Auf der zwei Hektar grossen langfristigen Waldökosystemfläche (LWF) Visp werden seit 1996 jährlich Absterberaten, Kronenverlichtung, Mistelbefall (Viscum album ssp. austriacum) und andere Symptome aufgenommen. Zwischen 1996 und 2004 sind 59% aller Föhren auf der Fläche abgestorben, die meisten nach den Trockenperioden 1996,98 und 2003,2004. Dagegen starben nur 15% der Laubbäume ab. Kronenverlichtung, Nadelverfärbung, Totast- und Totzweiganteil (als Indikatoren der Vitalität des Baumes), Mistelbefallsklasse, Triebabwurf durch Waldgärtner, männliche Blütenbildung, Stammdurchmesser, Kronenkonkurrenz und soziale Stellung, alle im Jahr 1998 erhoben, wurden in einer logistischen Regression zur Bestimmung der Absterbewahrscheinlichkeit auf Signifikanz getestet. Kronenverlichtung, Mistelbefallsklasse und Totastanteil waren in dem Model signifikant. Die Wahrscheinlichkeit des Absterbens stieg dabei mit ansteigender Kronenverlichtung, ansteigendem Mistelbefall und ansteigendem Totastanteil. Der Totastanteil konnte im Model durch die Nadelverfärbung ersetzt werden. Die Kronenverlichtung stieg mit dem Mistelbefall an. Bei gleicher Verlichtung starben jedoch Bäume mit mittlerem und starkem Mistelbefall zwei- bis viermal häufiger ab als Bäume ohne oder mit leichtem Mistelbefall. Von den überlebenden Bäumen zeigten solche mit Mistelbefall einen deutlichen Anstieg der Transparenz im Jahr nach Beginn der Trockenheit im Vergleich zu den Bäumen ohne Misteln, während im Jahr der Trockenheit das Umgekehrte der Fall war. Zu Beginn der Beobachtung ergaben sich keine signifikanten Unterschiede in der Kronentransparenz der überlebenden Bäume mit und ohne Misteln. Am Ende der Beobachtungsperiode wiesen jedoch die Bäume mit Misteln signifikant höhere Kronenverlichtungen auf. Wir schliessen daraus, dass die Misteln auf der einen Seite den Baum langfristig schwächen, indem sie zur Reduzierung der Nadelmasse führen und sie auf der anderen Seite während Trockenheit durch erhöhten Wasserstress zum vorzeitigen Absterben beitragen. [source] Below-ground hydraulic conductance is a function of environmental conditions and tree size in Scots pineFUNCTIONAL ECOLOGY, Issue 6 2007J. MARTÍNEZ-VILALTA Summary 1Variations in water tension in a transpiring tree cause elastic changes in stem diameter. To better understand the dynamics of these variations, stem diameter changes and sap flow rates were monitored simultaneously in trees from two Scots pine chronosequences in Scotland. 2Tree below-ground hydraulic conductance (kbg) was estimated from the relationship between leaf-specific sap flow rates and the difference between stem and soil water potentials estimated from diameter variations in the stem. 3In a given tree, kbg varied both within and among days, with conductance increasing as a function of sap flow and evaporative demand. These patterns could be explained in terms of a composite model of root water transport and possible changes in the gating of aquaporins. 4We interpreted these trends of increasing kbg with evaporative demand as a mechanism to enhance the ability of trees to control leaf water potential and keep it within physiologically acceptable limits, with potential implications for our general understanding of plant water relations, and for the estimation and modelling of ecosystem water fluxes. 5Across trees, kbg declined with increasing tree age/size, but the proportional contribution of below-ground to whole-tree hydraulic resistance also declined. This is consistent with an increase in below-ground carbon allocation in old/tall trees and a partial acclimation of tall trees to hydraulic limitations. It is argued that these trends have to be considered when discussing the importance of tree height for water transport and growth. [source] Comparative fire ecology of tropical savanna and forest treesFUNCTIONAL ECOLOGY, Issue 6 2003William A. Hoffmann Summary 1Fire is important in the dynamics of savanna,forest boundaries, often maintaining a balance between forest advance and retreat. 2We performed a comparative ecological study to understand how savanna and forest species differ in traits related to fire tolerance. We compared bark thickness, root and stem carbohydrates, and height of reproductive individuals within 10 congeneric pairs, each containing one savanna and one forest species. 3Bark thickness of savanna species averaged nearly three times that of forest species, thereby reducing the risk of stem death during fire. The allometric relationship between bark thickness and stem diameter differed between these two tree types, with forest species tending to have a larger allometric coefficient. 4The height of reproductive individuals of forest species averaged twice that of congeneric savanna species. This should increase the time necessary for forest species to reach reproductive size, thereby reducing their capacity to reach maturity in the time between consecutive fires. 5There was no difference in total non-structural carbohydrate content of stems or roots between savanna and forest species, though greater allocation to total root biomass by savanna species probably confers greater capacity to resprout following fire. 6These differences in fire-related traits may largely explain the greater capacity of savanna species to persist in the savanna environment. [source] Structural response of Caribbean dry forests to hurricane winds: a case study from Guánica Forest, Puerto RicoJOURNAL OF BIOGEOGRAPHY, Issue 3 2006Skip J. Van Bloem Abstract Aim, Tropical dry forests in the Caribbean have an uniquely short, shrubby structure with a high proportion of multiple-stemmed trees compared to dry forests elsewhere in the Neotropics. Previous studies have shown that this structure can arise without the loss of main stems from cutting, grazing, or other human intervention. The Caribbean has a high frequency of hurricanes, so wind may also influence forest stature. Furthermore, these forests also tend to grow on soils with low amounts of available phosphorus, which may also influence structure. The objective of this study was to assess the role of high winds in structuring dry forest, and to determine whether soil nutrient pools influence forest response following hurricane disturbance. Location, Guánica Forest, Puerto Rico. Methods, Over 2000 stems in five plots were sampled for hurricane effects within 1 week after Hurricane Georges impacted field sites in 1998. Sprout initiation, growth, and mortality were analysed for 1407 stems for 2 years after the hurricane. Soil nutrient pools were measured at the base of 456 stems to assess association between nutrients and sprout dynamics. Results, Direct effects of the hurricane were minimal, with stem mortality at < 2% and structural damage to stems at 13%, although damage was biased toward stems of larger diameter. Sprouting response was high , over 10 times as many trees had sprouts after the hurricane as before. The number of sprouts on a stem also increased significantly. Sprouting was common on stems that only suffered defoliation or had no visible effects from the hurricane. Sprout survival after 2 years was also high (> 86%). Soil nutrient pools had little effect on forest response as a whole, but phosphorus supply did influence sprout dynamics on four of the more common tree species. Main conclusions, Hurricanes are able to influence Caribbean tropical dry forest structure by reducing average stem diameter and basal area and generating significant sprouting responses. New sprouts, with ongoing survival, will maintain the high frequency of multi-stemmed trees found in this region. Sprouting is not limited to damaged stems, indicating that trees are responding to other aspects of high winds, such as short-term gravitational displacement or sway. Soil nutrients play a secondary role in sprouting dynamics of a subset of species. The short, shrubby forest structure common to the Caribbean can arise naturally as a response to hurricane winds. [source] Effects of natural disturbance and selective logging on Nothofagus forests in south-central ChileJOURNAL OF BIOGEOGRAPHY, Issue 7 2002William Pollmann Aim Changes in stand structure, floristic composition and tree population dynamics during the last four centuries were described in southern temperate rain forests. The impacts of natural and anthropogenic disturbance since the late 1560s were examined for old-growth and logged forests. Location The study was conducted in montane Nothofagus alpina forests in the Andean Range of south-central Chile. Study sites were located at a range of altitudes between 1000 and 1250 m a.s.l. Methods Temporal variation in species recruitment and annual dendroecological data were used to determine the historical development and disturbance history of three old-growth forests, and three stands after selective logging in the late 1880s to early 1900s. Considering the spatial structure of evergreen vs. deciduous elements, the forests are a mixture of deciduous and evergreen tree species. Results Stem density, maximum stem diameter and basal area differed between the old-growth and logged stands, but species composition did not. At lower altitudes, N. alpina was the dominant canopy species in both old-growth and logged stands, but regeneration of N. alpina was significantly different in these stands. At higher altitudes, N. alpina and N. dombeyi were the dominant canopy species in both old-growth and logged stands, and here regeneration patterns of these Nothofagus species were similar. After selective logging, in mixed forests of shade-intolerant Nothofagus and more shade-tolerant trees (such as Laurelia philippiana) there has been a shift in regeneration from more shade-tolerant resprouting species towards Nothofagus. Major and moderate releases in radial growth, indicative of disturbance, occurred in most of the older trees during the last four centuries, and especially during the last 100 years. Growth rates of N. alpina are higher than those of associated shade-tolerant trees, and apparently increase after disturbances. Main conclusions Results suggest that under disturbance regimes dominated by treefall gaps, and additionally canopy openings by selective logging, maintenance of Nothofagus species appears to be associated with complementary differences in growth rate, sprouting capacity, canopy residence time, and longevity. Such small-scale canopy openings may help explain the relative abundance of N. alpina in montane mixed rain forests in the Andean Range, where the maintenance of Nothofagus species in many stands has been attributed to a high frequency of coarse-scale disturbance. My results serve to emphasize that understanding the species coexistence and forest dynamics in Nothofagus forests may require attention to interspecific differences in life-history characteristics. [source] Effects of simulated browsing on growth and leaf chemical properties in Colophospermum mopane saplingsAFRICAN JOURNAL OF ECOLOGY, Issue 1 2010Edward M. Kohi Abstract Browsing intensity influences a plant's response to herbivory. Plants face a trade-off between investment in the production of secondary compounds and investment in growth. To elucidate this trade-off, we simulated four browsing intensities (0%, 50%, 75% and 100%) on mopane saplings, Colophospermum mopane (J. Kirk ex Benth.) J.Léonard, in a greenhouse experiment. This showed that, with increasing defoliation intensity, plants change their investment strategy. At intermediate levels of defoliation (50%), mopane saplings increased the synthesis of condensed tannins, so that tannin concentrations followed a hump-shaped relation with defoliation intensity, with significantly higher tannin concentration at intermediate defoliation levels. When defoliated heavily (75% and 100%), tannin concentrations dropped, and plants were carbon stressed as indicated by a reduced growth rate of the stem diameter, and leaf production and mean individual leaf mass were reduced. This suggests that, at intermediate defoliation intensity, the strategy of the plants is towards induced chemical defences. With increasing defoliation, the relative costs of the secondary metabolite synthesis become too high, and therefore, the plants change their growing strategy. Hence, browsers should be able to benefit from earlier browsing by either adopting a low or a relatively high browsing pressure. Résumé La réponse d'une plante à sa consommation dépend de l'intensité de ce phénomène. Les plantes sont confrontées à un compromis entre un investissement dans la production de composants secondaires et un investissement dans leur croissance. Pour élucider ce compromis, nous avons simulé quatre intensités de consommation (0%, 50%, 75% et 100%) sur des jeunes mopanes, Colophospermum mopane (J. Kirk ex Benth.) J.Leonard, lors d'expériences sous serre. Ceci a montré que, lorsque la défoliation s'intensifie, les plantes changent leur stratégie d'investissement. À des niveaux de défoliation intermédiaires (50%), les jeunes plants de mopanes augmentaient la synthèse de tanins condensés, de sorte que les concentrations en tanins suivaient une courbe en cloche (hump-shaped) selon l'intensité de la défoliation; elles étaient significativement plus élevées aux niveaux de défoliation intermédiaires. Lorsque les plantes sont fortement défoliées (75% et 100%), leurs concentrations en tanins chutent, et elles sont en stress carbone comme le montre le taux de croissance réduit du diamètre du tronc; la production de feuilles et la masse moyenne de feuilles par individu sont aussi réduites. Cela suggère que, quand l'intensité de défoliation est intermédiaire, la stratégie des plants va vers une défense chimique induite. Lorsque la défoliation augmente, le coût relatif de la synthèse du métabolite secondaire devient trop élevé et le plant change de stratégie de croissance. Donc, les herbivores qui les consomment devraient pouvoir bénéficier d'une consommation antérieure en adoptant une pression de consommation faible ou relativement élevée. [source] Browsing impact of large herbivores on Acacia xanthophloea Benth in Lake Nakuru National Park, KenyaAFRICAN JOURNAL OF ECOLOGY, Issue 2 2009N. Dharani Abstract Significant differences (P<0.05) were found in growth of plant height, canopy cover and stem diameter of Acacia xanthophloea trees in fenced plot as compared with unfenced plot both in the wet and in the dry seasons. Finding of this study showed that although heavy browsing reduced the height and canopy of trees, it did not kill any trees and seedling regeneration took place simultaneously. Despite the presence of large herbivores that impact some considerable browsing pressure results indicate that the A. xanthophloea habitat type would continue to remain in balance in the presence of recruitment of seedlings and saplings. The conditions at the time of study indicate that the browsing on A. xanthophloea was not significant and was not serious enough to warrant management intervention at present. Résumé Des différences significatives (P<0,05) ont été relevées dans la croissance en hauteur, le couvert de la canopée et le diamètre des tiges d'Acacia xanthophloea dans des parcelles clôturées, comparées à des parcelles non clôturées, en saison sèche comme en saison des pluies. Les résultats de cette étude ont montré que, même si un pâturage intense réduisait la hauteur et la canopée des arbres, il n'en tuait aucun et que la régénération des jeunes plants se faisait simultanément. Malgré la présence de grands herbivores qui exercent une pression considérable, les résultats indiquent que le type d'habitat àA. xanthophloea resterait équilibré grâce au recrutement de jeunes plants et de repousses. Les conditions prévalant au moment de l'étude indiquaient que la consommation d'A. xanthophloea n'était pas significative et qu'elle n'était pas assez grave pour justifier pour le moment une intervention en matière de gestion. [source] Growth properties of 16 non-pioneer rain forest tree species differing in sapling architectureJOURNAL OF ECOLOGY, Issue 5 2009Masahiro Aiba Summary 1.,Sapling architecture may be an important determinant of performance traits, such as light interception and height growth, but few studies have examined the direct relationship between sapling architecture and growth properties. To study this relationship and the potential for strategic diversification, we analysed the growth properties in saplings of 16 Bornean tree species that differ in architecture. 2.,Annual net production significantly differed amongst species and was positively correlated with total above-ground dry mass, total leaf area and crown area. In contrast, the net assimilation rate was weakly but negatively correlated with these architectural traits. The net assimilation rate was virtually independent of leaf size and specific leaf area. Relationships between sapling architecture and relative growth rate in mass were weak. 3.,The relative growth rate in height did not significantly differ amongst species, although their total dry mass, a proxy for extension cost, varied fourfold across species for a given sapling height. This is because the proportional increase in net production with total dry mass, which is based on a larger total leaf area and larger crown area, cancelled out the higher extension cost. All architectural traits, including leaf size and specific leaf area, failed to predict height growth rate. 4.,Synthesis. Relative growth rates in both mass and height were relatively independent of sapling architecture. Of the architectural traits, leaf size, specific leaf area and stem diameter were poor predictors of growth properties, even though they were considered functionally important. These results clearly reject the classic hypothesis that architectural variation leads to a trade-off between height growth and light interception, at least for the species that are under shaded conditions. However, functional variation ranging from species with high net production and low net assimilation rates (in saplings of equal height) to species with the opposite traits, which was accompanied by architectural variation in total dry mass and related size factors, may be important for the coexistence of these tree species. The possibility that small total dry mass may be advantageous in height growth under well-lit conditions should be examined in future studies. [source] Effects of size, competition and altitude on tree growthJOURNAL OF ECOLOGY, Issue 5 2007DAVID A. COOMES Summary 1,Understanding the factors influencing tree growth is central to forest ecology because of the significance of growth to forest structure and biomass. One of the simplest, yet most controversial growth models, proposed by Enquist and colleagues, predicts that stem-diameter growth scales as the one-third power of stem diameter. Recent analyses of large-scale data sets have challenged the generality of this theory and highlighted the influence of resource competition on the scaling of growth with size. 2Here we explore the factors regulating the diameter growth of 3334 trees of mountain beech (Nothofagus solandri var. cliffortioides) growing in natural single-species forests in New Zealand. Maximum-likelihood modelling was used to quantify the influences of tree size, altitude, the basal area of taller neighbours (BL) and the basal area of all neighbours (BT) on growth. Our interpretation of the models assumed that taller neighbours compete for light whereas all neighbours compete for nutrients. 3The regression analyses indicate that competition for light has a strong influence on the growth of small trees, whereas competition for nutrients affects trees of all sizes. These findings are consistent with experimental manipulation studies showing that competition for light and nutrients inhibits the growth of small mountain beech trees, and fertilizer application studies showing that nitrogen limits the growth of large trees. 4Tree growth declined with altitude. The regression analyses suggest that the intensity of light competition also declines with altitude, when trees with similar BT and BL values were compared along the gradient. These results are consistent with observations that trees become stunted and have more open canopies at high altitudes. 5Our study is the first to build the effects of competition and environment into Enquist's model of tree growth. We show that competitive interactions alter the scaling of mean growth rate with size, whereas altitude does not influence the scaling of potential growth rate with size. [source] Interactions between the stem-mining weevils Ceutorhynchus napi Gyll. and Ceutorhynchus pallidactylus (Marsh.) (Coleoptera: Curculionidae) in oilseed rapeAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 3 2004Georg Dechert Abstract 1,The rape stem weevil Ceutorhynchus napi Gyll. and the cabbage stem weevil Ceutorhynchus pallidactylus (Marsh.) share the same habitat and food resource within the stems of oilseed rape, Brassica napus L. var. oleifera. Interactions occurring between these two sympatric species on this host were studied under both field and laboratory conditions. 2,The oviposition preference of C. pallidactylus and the within-plant distribution of eggs and larvae were examined in field plots of oilseed rape. Female C. pallidactylus tended to lay their eggs in plants already infested by eggs and larvae of C. napi rather than in uninfested plants. The within-plant distribution of the egg batches of C. pallidactylus did not differ significantly between uninfested plants and those preinfested by C. napi. Ovipositing females of C. napi and C. pallidactylus generally showed a significant preference for plants with larger stem diameter. 3,Laboratory choice tests provided further evidence for the oviposition preference of C. pallidactylus. Females laid significantly more eggs in leaves of plants that had been previously infested by C. napi than in leaves of previously uninfested plants. 4,Larvae of C. pallidactylus showed a significant shift of their feeding niche towards the stem base when feeding in individual plants attacked by both species. This possibly indicates ressource partitioning between C. pallidactylus and C. napi. The within-plant distribution of C. napi larvae was not affected by the simultaneous attack of C. pallidactylus. 5,The size of the head capsule of full-grown larvae of C. napi and C. pallidactylus was not significantly correlated with the diameter of the stem of their host plant or with the number of conspecific larvae within individual plants. [source] Growth and Wood/Bark Properties of Abies faxoniana Seedlings as Affected by Elevated CO2JOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 3 2008Yun-Zhou Qiao Abstract Growth and wood and bark properties of Abies faxoniana seedlings after one year's exposure to elevated CO2 concentration (ambient + 350 (± 25) ,mol/mol) under two planting densities (28 or 84 plants/m2) were investigated in closed-top chambers. Tree height, stem diameter and cross-sectional area, and total biomass were enhanced under elevated CO2 concentration, and reduced under high planting density. Most traits of stem bark were improved under elevated CO2 concentration and reduced under high planting density. Stem wood production was significantly increased in volume under elevated CO2 concentration under both densities, and the stem wood density decreased under elevated CO2 concentration and increased under high planting density. These results suggest that the response of stem wood and bark to elevated CO2 concentration is density dependent. This may be of great importance in a future CO2 enriched world in natural forests where plant density varies considerably. The results also show that the bark/wood ratio in diameter, stem cross-sectional area and dry weight are not proportionally affected by elevated CO2 concentration under the two contrasting planting densities. This indicates that the response magnitude of stem bark and stem wood to elevated CO2 concentration are different but their response directions are the same. [source] Species and structural diversity of church forests in a fragmented Ethiopian Highland landscapeJOURNAL OF VEGETATION SCIENCE, Issue 5 2010Alemayehu Wassie Abstract Question: Thousands of small isolated forest fragments remain around churches ("church forests") in the almost completely deforested Ethiopian Highlands. We questioned how the forest structure and composition varied with altitude, forest area and human influence. Location: South Gondar, Amhara National Regional State, Northern Ethiopia. Methods: The structure and species composition was assessed for 810 plots in 28 church forests. All woody plants were inventoried, identified and measured (stem diameter) in seven to 56 10 m x 10-m plots per forest. Results: In total, 168 woody species were recorded, of which 160 were indigeneous. The basal area decreased with tree harvest intensity; understorey and middle-storey density (<5 cm DBH trees) decreased with grazing; overstorey density (>5 cm DBH trees) increased with altitude. The dominance of a small set of species increased with altitude and grazing intensity. Species richness decreased with altitude, mainly due to variation in the richness of the overstorey community. Moreover, species richness in the understorey decreased with grazing intensity. Conclusions: We show how tree harvesting intensity, grazing intensity and altitude contribute to observed variations in forest structure, composition and species richness. Species richness was, however, not related to forest area. Our study emphasizes the significant role played by the remaining church forests for conservation of woody plant species in North Ethiopian Highlands, and the need to protect these forests for plant species conservation purposes. [source] Demographic and life-history correlates for Amazonian treesJOURNAL OF VEGETATION SCIENCE, Issue 6 2005Henrique E.M. Nascimento Abstract Questions: Which demographic and life-history differences are found among 95 sympatric tree species? Are there correlations among demographic parameters within this assemblage? Location: Central Amazonian rain forest. Methods: Using long-term data from 24 1,ha permanent plots, eight characteristics were estimated for each species: wood density, annual mortality rate, annual recruitment rate, mean stem diameter, maximum stem diameter, mean stem-growth rate, maximum stem-growth rate, population density. Results: An ordination analysis revealed that tree characteristics varied along two major axes of variation, the major gradient expressing light requirements and successional status, and the second gradient related to tree size. Along these gradients, four relatively discrete tree guilds could be distinguished: fast-growing pioneer species, shade-tolerant sub-canopy species, canopy trees, and emergent species. Pioneers were uncommon and most trees were canopy or emergent species, which frequently had low mortality and recruitment. Wood density was negatively associated with tree mortality, recruitment, and growth rates when all species were considered. Growth rates varied markedly among and within species, with pioneers exhibiting far faster and less variable growth rates than did the other species. Slow growth in subcanopy species relative to canopy and emergent trees was not a simple consequence of mean tree size, but apparently resulted from physiological constraints imposed by low-light and other conditions in the forest understorey. Conclusions: Trees of Amazonian rain forests could be classified with some success into four relatively distinctive guilds. However, several demographic and life-history traits, such as those that distinguish early and late successional species, probably vary along a continuum, rather than being naturally grouped into relatively discrete categories. [source] Evaluation of mangrove structure and condition in two trans-boundary areas in the Western Indian OceanAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue S1 2009S. O. Bandeira Abstract 1.The structure, forest condition and regeneration status of nine mangrove forests in two trans-boundary areas of Mozambique bordering Tanzania and South Africa were studied. The main objective was to estimate the cutting intensity in the selected sites , Saco and Sangala in southern Mozambique; Mecúfi, Pemba, Ibo, Luchete, Ulo in northern Mozambique, and Mngoji 1 and Mngoji 2 in Tanzania. 2.A total of 135, 10,m×10,m quadrats were set in the outer, middle and lower parts of the mangrove forests at all sampling sites. Measurements included stem diameter at breast height (DBH) and height of adult trees (i.e. all trees with stem diameter more than 2.5,cm). Young trees (with stem diameter of less than 2.5,cm) were classified as juveniles. To assess forest condition, trees within the quadrat were classified into intact, partially cut, coppiced, die back and stump. Pole quality was appraised through the classification of the lead stem into three categories,straight, semi-straight and crooked poles. 3.The results indicate different levels of exploitation with Mngoji 1 and Mngoji 2, the most degraded sites, having stump densities of 959,stumps,ha,1 and 592,stumps,ha,1, respectively. Most sites had mostly poles of inferior quality (crooked poles), but high densities of straight and semi-straight poles were found in Mngoji 1 (742,stems,ha,1) and Saco (636,stems,ha,1). 4.Natural regeneration was observed in most sites but not for all species, with adequate regeneration in Saco (14,766 saplings ha,1) and Mecúfi (14,706 saplings ha,1), while low regeneration was recorded in Mngoji 1 and 2 (2212 saplings ha,1 and 4799saplingsha,1, respectively). 5.These results indicate the need for improved mangrove management and replanting especially in mangrove depleted conservation areas of southern Tanzania. Copyright © 2009 John Wiley & Sons, Ltd. [source] Allometry and biomass distribution in replanted mangrove plantations at Gazi Bay, KenyaAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue S1 2009J. G. Kairo Abstract 1.This study reports above-ground biomass of 5 and 8 years old mangrove plantations in Kenya. Trees with stem diameter greater than 5.0,cm inside 100,m2 sample plots were harvested, and then separated into stems (trunks), branches, leaves and prop roots. 2.Mean above-ground biomass was calculated at 20.25 t dry matter ha,1 for Rhizophora mucronata Lam., 11.7 t dry matter ha,1 for Avicennia marina (Forsk.) Vierh., 6.7 t dry matter ha,1 for Sonneratia alba Sm. and 3.7 t dry matter ha,1 for Ceriops tagal (Perr.) C. B. Robinson. In A. marina and R. mucronata, stems (52.19%) and prop-roots (30.28%), respectively, accounted for the highest proportion of the above-ground dry weight. While in S. alba and C. tagal, branch biomass represented the highest percentage of biomass, 48.20% and 43.62%, respectively. 3.The total above-ground biomass of R. mucronata was best estimated from regression equations using a combination of height and diameter above stilt root as the independent variables. For A. marina, C. tagal and S. alba there was no simple correlation found between the above-ground biomass and tree height or stem diameter. 4.Comparison of the regression models with those developed elsewhere gave different biomass values in these plots, further reinforcing the need for the use of site-specific allometric equations for biomass estimation. Copyright © 2009 John Wiley & Sons, Ltd. [source] Growth responses of African savanna trees implicate atmospheric [CO2] as a driver of past and current changes in savanna tree coverAUSTRAL ECOLOGY, Issue 4 2010BARNEY S. KGOPE Abstract Atmospheric CO2 has more than doubled since the last glacial maximum (LGM) and could double again within this century, largely due to anthropogenic activity. It has been suggested that low [CO2] contributed to reduced tree cover in savanna and grassland biomes at LGM, and that increasing [CO2] over the last century promoted increases in woody plants in these ecosystems over the past few decades. Despite the implications of this idea for understanding global carbon cycle dynamics and key global role of the savanna biome, there are still very few experimental studies quantifying the effects of CO2 on tree growth and demography in savannas and grasslands. In this paper we present photosynthetic, growth and carbon allocation responses of African savanna trees (Acacia karroo and Acacia nilotica) and a C4 grass, Themeda triandra, exposed to a gradient of CO2 concentrations from 180 (typical of LGM) to 1000 µmol mol,1 in open-top chambers in a glasshouse as a first empirical test of this idea. Photosynthesis, total stem length, total stem diameter, shoot dry weight and root dry weight of the acacias increased significantly across the CO2 gradient, saturating at higher CO2 concentrations. After clipping to simulate fire, plants showed an even greater response in total stem length, total stem diameter and shoot dry weight, signalling the importance of re-sprouting following disturbances such as fire or herbivory in savanna systems. Root starch (per unit root mass and total root starch per plant) increased steeply along the CO2 gradient, explaining the re-sprouting response. In contrast to the strong response of tree seedlings to the CO2 gradient, grass productivity showed little variation, even at low CO2 concentrations. These results suggest that CO2 has significant direct effects on tree recruitment in grassy ecosystems, influencing the ability of trees to recover from fire damage and herbivory. Fire and herbivore regimes that were effective in controlling tree increases in grassy ecosystems could thus be much less effective in a CO2 -rich world, but field-based tests are needed to confirm this suggestion. [source] Host infestation patterns of the massive liana Hydrangea serratifolia (Hydrangeaceae) in a Chilean temperate rainforestAUSTRAL ECOLOGY, Issue 7 2009MYLTHON JIMÉNEZ-CASTILLO Abstract As competition from lianas reduces fitness of host trees, lianas could influence community composition and structure if potential host species differ in susceptibility to infestation. We quantified infestation frequencies of Chilean temperate rainforest tree species by the massive liana Hydrangea serratifolia (H. et A.) F. Phil (Hydrangeaceae), which climbs using adhesive adventitious roots, and examined relationships with host light requirements and stem diameter. We recorded presence or absence of H. serratifolia in a random sample of 515 trees ,10 cm diameter. Fifty-four per cent of trees were infested by at least one individual of H. serratifolia. Although there was significant interspecific variation in infestation frequency, this variation was not systematically related to light requirements of host tree species. Probability of infestation increased with diameter for most host tree species, and old trees were found to be infested by a wide range of liana size classes, including some stems <2 cm diameter. This evidence supports the proposal that lianas which attach by adhesive roots can colonize host stems of any size. [source] Sap flow of Artemisia ordosica and the influence of environmental factors in a revegetated desert area: Tengger Desert, ChinaHYDROLOGICAL PROCESSES, Issue 10 2010Huang Lei Abstract Artemisia ordosica is considered as an excellent sand-fixing plant in revegetated desert areas, which plays a pertinent role in stabilizing the mobile dunes and sustaining the desert ecosystems. Stem sap flows of about 10-year-old Artemisia ordosica plants were monitored continuously with heat balance method for the entire growing season in order to understand the water requirement and the effects of environmental factors on its transpiration and growth. Environment factors such as solar radiation, air temperatures, relative humidity, wind speed and precipitation were measured by the eddy covariance. Diurnal and seasonal variations of sap flow rate with different stem diameters and their correlation with meteorological factors and reference evapotranspiration were analysed. At the daily time scale, there was a significantly linear relationship between sap flow rate and reference evapotranspiration with a correlation coefficient of R2 = 0·6368. But at the hourly time scale, the relationship of measured sap flow rate and calculated reference evapotranspiration (ET0) was affected by the precipitation. A small precipitation would increase the sap flow and the ET0; however, when the precipitation is large, the sap flow and ET0 decrease. Leaf area index had a coincident variation with soil water content; both were determined by the precipitation, and meteorological factors were the most significant factors that affected the sap flow of Artemisia ordosica in the following order: solar radiation > vapour pressure deficit > relative humidity > air temperature > wind speed. The close correlation between daily sap flow rate and meteorological factors in the whole growing season would provide us an accurate estimation of the transpiration of Artemisia ordosica and rational water-carrying capacity of sand dunes in the revegetated desert areas. Copyright © 2010 John Wiley & Sons, Ltd. [source] Sowing density and harvest time affect fibre content in hemp (Cannabis sativa) through their effects on stem weightANNALS OF APPLIED BIOLOGY, Issue 2 2009W. Westerhuis Abstract Sowing density and harvest time are considered important crop management factors influencing fibre quantity and quality in hemp (Cannabis sativa). We investigated whether the effects of these factors are essentially different or that both factors affect stem weight and thereby total and long-fibre content. The effects of all combinations of three sowing densities and three harvest times were studied for six different stem parts. Almost 500 samples consisting of stem parts from 50 plants and with a length of 50 cm were tested. Fibres were extracted by a controlled warm-water retting procedure, followed by breaking and scutching. The initial sample weight was fractionated into retting losses, wood, tow and long fibre. In both Italy and the Netherlands, crops were successfully established with different stem densities (99,283 m,2), plant heights (146,211 cm) and stem diameters (4.5,8.4 mm) at harvest. Stem dry matter yields (6.8,11.7 Mg ha,1) increased with a delay in harvest time but were not affected by sowing density. Retting loss percentages were lower in lower stem parts and decreased with later harvest because maturation was associated with increasing amounts of fibre and wood. Within a certain stem part, however, the absolute retting losses were constant with harvest time. Multiple linear regression analyses showed that the amount of fibre in a hemp stem is almost completely determined by the weight and the position of that stem part. When the plant grows, the increase in dry matter is split up into fibres and wood in a fixed way. This total fibre/wood ratio was highest in the middle part of the stem and lower towards both bottom and top. Sowing density and harvest time effects were indirect through stem weight. The long-fibre weight per stem increased with the total fibre weight and hence with stem weight. Stem weight increased with harvest time; as harvest time did not affect plant density, the highest long-fibre yields were obtained at the last harvest time. The long fibre/total fibre ratio was lowest in the bottom 5 cm of the stems but similar for all other parts. Sowing density and harvest time effects again were indirect. Fibre percentages in retted hemp decreased with increasing stem weights towards a level that is presumably a variety characteristic. The dry matter increase between harvests, however, is much more important with respect to total and long-fibre yield. [source] | |||||||||||||||||||||||||