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Tall Trees (tall + tree)
Selected AbstractsVariability in survival and mortality of Acacia drepanolobium Sjøstedt following prescribed burning at Olpejeta Conservancy, KenyaAFRICAN JOURNAL OF ECOLOGY, Issue 3 2010Geoffrey M. Wahungu Abstract Mortalities to Acacia drepanolobium, a main item in the diet of the eastern black rhino (Diceros bicornis Michaeli) in Olpejeta conservancy, Kenya, are caused by three main factors: drought, browsers and fire. The effect of controlled fires on A. drepanolobium was examined by monitoring survival and growth in experimental plots before and after fire episodes between 2003 and 2007. Density, survival and growth in A. drepanolobium trees were compared eighteen months before and after burning. Tall trees were more likely to die from fire compared to short trees (R2 = 0.575; df = 6; P = 0.048), while seedling densities increased after fire (,2 = 36.57; df = 1; P = 0.001). Even with increased seedling densities, burned areas attracted large numbers of seedling predators, lowering the possibility of seedling recruitment into adult, as mean seedling heights reduced significantly (ANOVA, F = 204.42; df = 1; P = 0.036). Fires also significantly lowered flowering (F = 346; df = 1; P < 0.05) in A. drepanolobium, thereby affecting fruit production. Although fires caused mortalities to adult A. drepanolobium, the most significant effect was tree reversals into seedling height class as trees resprouted. Although fire may increase browse biomass of A. drepanolobium available for black rhino, it is not an appropriate black rhino habitat management tool because burnt areas attract many seedling predators that lower seedling recruitment into adult trees. Résumé La mortalité d'Acacia drepanolobium dans l'aire de conservation d'Olpejeta, au Kenya, est causée par trois facteurs principaux, la sécheresse, les herbivores et les feux. On a examiné l'effet des feux contrôlés sur A. drepanolobium en suivant la survie et la croissance dans des parcelles expérimentales 18 mois avant et après les feux, entre 2003 et 2007. On a comparé la densité, la survie et la croissance d'A. drepanolobium 18 mois avant et après les feux. Les grands arbres étaient plus susceptibles de mourir à cause des feux que les petits (R² = 0,575; ddl = 6; P = 0,048) alors que la densité des jeunes plants augmentait après les feux (,² = 36,57; ddl = 1; P = 0,001). Même si la densité de jeunes plants était accrue, les zones brûlées attiraient de grands nombres de prédateurs de ces plants, diminuant ainsi la possibilité de recrutement vers l'âge adulte, parce que la hauteur moyenne des jeunes plants était significativement réduite (Anova, F = 204,42; ddl = 1; P =0,036). Les feux réduisaient aussi significativement la floraison (F = 346; ddl = 1; P < 0,05) chez A. drepanolobium, affectant dès lors la production de fruits. Même si les feux causaient une certaine mortalité chez les A. drepanolobium adultes, l'effet le plus significatif était le retour des arbres dans des classes de hauteur des jeunes plants lorsque les arbres rejetaient. Même si les feux peuvent augmenter la biomasse de brout d'A. drepanolobium disponible pour les rhinos noirs, ils ne sont pas un outil de gestion approprié pour l'habitat des rhinos parce que les zones brûlées peuvent attirer des nombreux prédateurs des jeunes plants qui réduisent le recrutement de ceux-ci vers l'âge adulte. [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] Common use of sleeping sites by two primate species in Tana River, KenyaAFRICAN JOURNAL OF ECOLOGY, Issue 1 2001Geoffrey M. Wahungu Abstract Choice of sleeping sites by two species of primates sharing two adjacent patches of gallery forest in Tana River, Kenya, was studied between August 1992 and February 1993. One group each of the Tana crested mangabey, Cercocebus galeritus galeritus Peters, and yellow baboon, Papio cynocephalus cynocephalus L., interchangeably shared nine sleeping sites distributed among four tree species, Acacia robusta Burch., Ficus sycomorus L., Abizzia gummifera (J. F. Gmel.) E. A. Sm. and Pachystela msolo (Engl.) Engl. The trees used by both species as sleeping sites were mainly tall trees with canopy level or emergent crowns. The trees had relatively larger crowns and lower percentage canopy cover compared to other trees at the site and were characterized by poor to moderate accessibility. Overlap in use of sleeping sites was never simultaneous and baboons occasionally supplanted mangabeys. Site choice by these two primates appeared to be influenced by predation risk, the feeding area used in the late afternoon, daily range and the availability of trees with the preferred structural characteristics. Sleeping sites appeared to be limited during and immediately after the wet season, when the frequency of supplantings increased. This observation is attributed to an increase in percentage canopy cover. Résumé Entre août 92 et février 93, on a étudié le choix des lieux de sommeil par des primates qui partageaient deux portions adjacentes de la galerie forestière de la rivière Tana, au Kenya. Un groupe de cercocèbes à crête, Cercocebus galeritus galeritus Peters, et un de babouins olive, Papio cynocephalus cynocephalus L., partageaient pour y dormir, de façon interchangeable, neuf emplacements répartis parmi quatre espèces d'arbres, Acacia robusta Burch., Ficus sycomorus L., Abizzia gummifera (J.F. Gmel) E.A. Sm. Et Pachystela msolo (Engl) Engl. Les arbres qui servent aux deux espèces comme sites de sommeil étaient principalement des arbres élevés, avec une canopée ou une couronne émergentes. Les arbres avaient une couronne relativement plus large et une couverture de la canopée dont le pourcentage était relativement plus bas que celui des autres arbres de l'endroit, et ils se caractérisaient par une accessibilité médiocre à modérée. Le recouvrement entre les sites de sommeil n'étaient jamais simultanés, et à l'occasion, les babouins supplantaient les cercocèbes. Le choix des sites par ces deux primates semblait influencé par les risques de prédation, par l'aire de nourrissage fréquentée en fin d'après midi, par le déplacement de la journée et par la disponibilité d'arbres qui présentaient les caractéristiques structurelles souhaitées. Les sites de sommeil semblent être limités à la saison des pluies et juste après, lorsque la fréquence d'évictions augmentait. Cette observation a été attribuée à une augmentation du pourcentage du couvert de la canopée. [source] Height-related growth declines in ponderosa pine are not due to carbon limitationPLANT CELL & ENVIRONMENT, Issue 1 2009ANNA SALA ABSTRACT Decreased gas exchange as trees grow tall has been proposed to explain age-related growth declines in trees. We examined changes of mobile carbon stores (starch, sugars and lipids) with tree height in ponderosa pine (Pinus ponderosa) at two sites differing in water availability, and tested the following hypotheses: (1) carbon supply does not become increasingly limited as trees grow tall; rather, the concentration of mobile carbon compounds increases with tree height reflecting greater reductions of carbon sink activities relative to carbon assimilation; and (2) increases of stored mobile carbon compounds with tree height are greater in drier sites. Height-related growth reductions were associated with significant increases of non-structural carbohydrates (NSC) and lipid concentrations in all tissues in the upper canopy and of NSC in the bole. Lipid concentrations in the bole decreased with tree height, but such decrease is not necessarily inconsistent with non-limiting carbon supply in tall trees. Furthermore, we found stronger increases of mobile carbon stores with tree height at the dry site relative to the moist site. Our results provide first direct evidence that carbon supply does not limit growth in tall trees and that decreases of water availability might negatively impact growth processes more than net-photosynthesis. [source] Vegetation correlates of gibbon density in the peat-swamp forest of the Sabangau catchment, Central Kalimantan, IndonesiaAMERICAN JOURNAL OF PRIMATOLOGY, Issue 7 2010Marie Hamard Abstract Understanding the complex relationship between primates and their habitats is essential for effective conservation plans. Peat-swamp forest has recently been recognized as an important habitat for the Southern Bornean gibbon (Hylobates albibarbis), but information is scarce on the factors that link gibbon density to characteristics of this unique ecosystem. Our aims in this study were firstly to estimate gibbon density in different forest subtypes in a newly protected, secondary peat-swamp forest in the Sabangau Catchment, Indonesia, and secondly to identify which vegetation characteristics correlate with gibbon density. Data collection was conducted in a 37.1,km2 area, using auditory sampling methods and vegetation "speed plotting". Gibbon densities varied between survey sites from 1.39 to 3.92,groups/km2. Canopy cover, tree height, density of large trees and food availability were significantly correlated with gibbon density, identifying the preservation of tall trees and good canopy cover as a conservation priority for the gibbon population in the Sabangau forest. This survey indicates that selective logging, which specifically targets large trees and disrupts canopy cover, is likely to have adverse effects on gibbon populations in peat-swamp forests, and calls for greater protection of these little studied ecosystems. Am. J. Primatol. 72:607,616, 2010. © 2010 Wiley-Liss, Inc. [source] After the fire: benefits of reduced ground cover for vervet monkeys (Cercopithecus aethiops)AMERICAN JOURNAL OF PRIMATOLOGY, Issue 3 2009Karin Enstam Jaffe Abstract Here we describe changes in ranging behavior and other activities of vervet monkeys (Cercopithecus aethiops) after a wildfire eliminated grass cover in a large area near the study group's home range. Soon after the fire, the vervets ranged farther away from tall trees that provide refuge from mammalian predators, and moved into the burned area where they had never been observed to go before the fire occurred. Visibility at vervet eye-level was 10 times farther in the burned area than in unburned areas. They traveled faster, and adult females spent more time feeding and less time scanning bipedally in the burned area than in the unburned area. The burned area's greater visibility may have lowered the animals' perceived risk of predation there, and may have provided them with an unusual opportunity to eat acacia ants. Am. J. Primatol. 71:252,260, 2009. © 2008 Wiley-Liss, Inc. [source] Near-ground solar radiation along the grassland,forest continuum: Tall-tree canopy architecture imposes only muted trends and heterogeneityAUSTRAL ECOLOGY, Issue 1 2010DAVID D. BRESHEARS Abstract Solar radiation directly and indirectly drives a variety of ecosystem processes. Our aim was to evaluate how tree canopy architecture affects near-ground, incoming solar radiation along gradients of increasing tree cover, referred to as the grassland,forest continuum. We evaluated a common type of canopy architecture: tall trees that generally have their lowest level of foliage high above, rather than close to the ground as is often the case for shorter trees. We used hemispherical photographs to estimate near-ground solar radiation using the metric of Direct Site Factor (DSF) on four sites in north Queensland, Australia that formed a grassland,forest continuum with tree canopy cover ranging from 0% to 71%. Three of the four sites had tall Eucalyptus trees with foliage several metres above the ground. We found that: (i) mean DSF exceeded >70% of the potential maximum for all sites, including the site with highest canopy cover; (ii) DSF variance was not highly sensitive to canopy coverage; and (iii) mean DSF for canopy locations beneath trees was not significantly lower than for adjacent intercanopy locations. Simulations that hypothetically placed Australian sites with tall tree canopies at other latitude,longitude locations demonstrated that differences in DSF were mostly due to canopy architecture, not specific site location effects. Our findings suggest that tall trees that have their lowest foliage many metres above the ground and have lower foliar density only weakly affect patterns of near-ground solar radiation along the grassland,forest continuum. This markedly contrasts with the strong effect that shorter trees with foliage near the ground have on near-ground solar radiation patterns along the continuum. This consequence of differential tree canopy architecture will fundamentally affect other ecosystem properties and may explain differential emphases that have been placed on canopy,intercanopy heterogeneity in diverse global ecosystem types that lie within the grassland,forest continuum. [source] The role of wood anatomy in phylogeny reconstruction of EricalesCLADISTICS, Issue 3 2007Frederic Lens The systematic significance of wood anatomical characters within Ericales is evaluated using separate and combined parsimony analyses including 23 wood characters and 3945 informative molecular characters. Analyses of wood features alone result in poorly resolved and conflicting topologies. However, when pedomorphic character states are coded as inapplicable, the combined bootstrap topology results in an increase of resolution and support at most deeper nodes compared with the molecular analyses. This suggests that phylogenetic information from the limited number of morphological characters is not completely swamped by an overwhelming amount of molecular data. Based on the morphology of vessels and fibers, and the distribution of axial parenchyma, two major wood types can be distinguished within Ericales: (i) a "primitive" type, nearly identical to the wood structure in the more basal outgroup Cornales, which is likely to have persisted in one major clade, and (ii) a "derived" type that must have evolved in at least two separate evolutionary lines. The occurrence of the first type is strongly correlated with shrubs to small trees growing in cold temperate or tropical montane regions, while the second type is common in tall trees of tropical lowlands. This favors the inclusion of ecologically adaptive features in phylogeny reconstruction. © The Willi Hennig Society 2006. [source] | ||||||||||