Larger Trees (larger + tree)

Distribution by Scientific Domains


Selected Abstracts


Mistletoe (Tapinanthus bangwensis Reichenbach) infestation of indigenous and non-indigenous trees at Amani Nature Reserve, Tanzania

AFRICAN JOURNAL OF ECOLOGY, Issue 1 2001
L. M. Lekunze
Abstract A survey of Tapinanthus bangwensis was carried out in a plantation in the botanic garden at Amani Nature Reserve, which forms part of the East Usambara Mountain, located in the north-east of Tanzania. A total of 169 trees were examined on four transects of 100 × 50 m (5000 m2) each, located about 700 m apart. Three treatment transects were established in open woodland with a control transect in the closed canopy. Out of 101 trees (81 non-indigenous and 20 indigenous) examined in the open canopy, T. bangwensis was present on 24; eighteen non-indigenous and six indigenous. Of all the infested trees, a non-indigenous species, silky oak (Grevillea robusta) was the most common (37.4%), followed by an indigenous species, mzindanguruwe (Blighia unijugata) with 16.6%. Chi-squared tests showed that there was no significant difference in frequency of infestation between non-indigenous and indigenous species (,2 = 0.715, P = 0.5826). t -Testing showed that T. bangwensis preferred taller and larger trees (t = , 3.930, P = 0.0002 and t = , 2.416, P = 0.0175, respectively). No T. bangwensis was found on the 68 trees examined in the closed canopy. Résumé On a réalisé une étude sur Tapinanthus bangwensis dans une plantation du jardin botanique de la Réserve Naturelle d'Amani qui fait partie de la East Usambara Mountain, au nord-est de la Tanzanie. On a examiné un total de 169 arbres sur quatre transects de 100 mètres sur 50 (5000 m2) chacun, situés à environ 700 mètres l'un de l'autre. On a créé trois transects de traitement dans la forêt claire et un de contrôle dans la canopée fermée. Sur les 101 arbres (81 non indigènes et 20 indigènes) examinés dans la canopée ouverte, T. bangwensisétait présent sur 24, 18 non indigènes et six indigènes. Parmi les espèces infestées, une espèce non indigène, Grevillea robusta, était la plus commune (37,4%), suivie par une espèce indigène, mzindanguruwe (Blighia unijugata) avec 16,6%. Des tests de ,2 ont montré qu'il n'y avait pas de différence significative dans les fréquences d'infestation des espèces indigènes et non indigènes (,2 = 0,715, P = 0,5826). Les tests de t ont montré que T. bangwensis préférait les arbres plus hauts et plus gros (t = - 3,930, P = 0,0002 et t = - 2,416, P = 0,0175, respectivement). On n'a pas trouvé de T. bangwensis sur les 68 arbres examinés en canopée fermée. [source]


Johansson revisited: the spatial structure of epiphyte assemblages

JOURNAL OF VEGETATION SCIENCE, Issue 1 2007
Gerhard Zotz
Abstract Question: Vertical zonation schemes are widely used in biodiversity studies with vascular epiphytes as a tool to capture spatial distribution patterns, the one most commonly used was proposed by Johansson more than 30 years ago. Does a survey of the epiphytes found on larger trees really yield a representative sample of the local community? Location: Lowland rainforest of the San Lorenzo Crane Plot, Republic of Panama. Methods: A complete census of the vascular epiphytes on all trees > 1 cm DBH in 0.4 ha of undisturbed lowland forest was analysed with both cluster and discriminant analysis to detect groupings of epiphyte species. Results: Six different groups of species were detected, five of them preferring different substrates on larger trees (as defined by (1) the height above ground at the attachment site, (2) the diameter of the substrate and (3) the occurrence on stem vs branches/twigs) and resembling to some extent the original Johansson zones. A sixth group of epiphytes, comprising ca. 10% of all taxa, was almost always found on small diameter stems and branches of trees with small DBH at lower and intermediate heights within the forest. Conclusions: Applying pre-established zonation schemes may lead to misleading results in biodiversity studies with epiphytes. Important aspects of spatial distribution patterns may be missed, and the determination of relative species abundances may carry a strong quantitative and qualitative bias when analyses rely completely on epiphytic plants found on larger trees. [source]


Variation in litter under individual tree crowns: Implications for scattered tree ecosystems

AUSTRAL ECOLOGY, Issue 1 2010
CHRIS MCELHINNY
Abstract In forest ecosystems litter is usually assessed in terms of the average amount produced by the canopy. In scattered tree ecosystems this approach is problematic because the canopy is discontinuous and the spatial arrangement of litter highly variable. We addressed this problem by quantifying the spatial variation in litter load and litter composition associated with individual trees in a Eucalyptus melliodora , Eucalyptus blakelyi woodland. Litter was sampled under crowns and in grassland adjacent to 10 E. blakelyi and 10 E. melliodora trees ranging in diameter at breast height (dbh) from 14 to 129 cm. A total of 302 L samples were collected from these trees, at distances ranging from 0 to 42 m from main stem. The sampled litter loads ranged from 0.02 to 109.3 t ha,1 and were significantly higher under tree crowns than in grassland for litter and each component of litter (leaves, bark, fine twigs, coarse twigs). In particular, the mean litter load under tree crowns (12.5 t ha,1) was an order of magnitude higher than the mean litter load in grassland (1.27 t ha,1). There was a significant (P = 0.0103) positive relationship between mean litter load under the tree crown and dbh, indicating larger trees produced more litter per unit area of ground than smaller trees. Generalized Linear Modelling produced highly significant (P < 0.0001) models predicting the spatial variation in litter load and litter composition in terms of distance from main stem and dbh. Our models demonstrate gradients in litter load and composition under tree crowns. These gradients were most pronounced for the large trees in our study. The disproportionate input of litter and variety of litter components associated with large trees in our study supports their keystone role in scattered tree ecosystems and highlights the need to maintain these structures in agricultural landscapes. [source]


Flowering phenology of myrtaceous trees and their relation to climatic, environmental and disturbance variables in northern New South Wales

AUSTRAL ECOLOGY, Issue 2 2000
B. Law
Abstract Patterns of flowering phenology, which represent a partial description of food availability for nectarivores, are described for 20 species of myrtaceous trees on the mid-north coast of New South Wales (NSW), Australia. Data were recorded monthly between 1982 and 1992 across 23 sites that comprise a variety of local environmental conditions and disturbance histories. Flowering periodicity and intensity were highly variable between species and sites, ranging from annual flowering to no flowering over the 10-year period. Cool temperatures prior to floral budding was a strong predictor of flowering for nine species. Extraordinary climatic events also influenced flowering. The period of greatest flowering for all species combined occurred 9 months after the highest monthly rainfall recorded in the survey (March 1985). An 18-month extreme drought led to poor flowering in Corymbia variegata, Eucalyptus acmenoides, Eucalyptus grandis and Eucalyptus resinifera, but recovery after the drought broke was rapid. In contrast to climate, few site-based environmental variables explained the intersite variation in flowering performance of the tree species. Site disturbance from logging at two sites during the survey did not influence flowering in the remaining canopy over following years. No species showed a negative correlation with a history of recent logging, and direct comparisons, between large- and medium-sized trees, of the percentage of foliage in flower showed no differences for any species. At the scale of a timber production forest, the negligible effect of tree size (if >10 cm diameter at breast height over bark), and high stem density resulting from selective logging, leave about half of the net harvestable area producing flowers at a similar density to unlogged forest. However, larger trees flowered more frequently than medium-sized trees in C. variegata (medium: every 5.9 years; large: every 2.3 years) and there was a trend in this direction for 13 of 17 species. Low-intensity burns and wildfires caused differing amounts of crown scorch, sometimes resulting in bud loss, but most species flowered at prefire levels 1,3 years after the disturbance. Eucalyptus microcorys and Angophora costata flowered poorly at sites that experienced frequent low-intensity burns. Regionally, blossom shortages occur through a combination of spatial and temporal patchiness in flowering and the clearing of those species that occurred on soils preferred for agriculture. On the north coast of NSW, these shortages commonly occur from late winter to spring. Species that flower reliably in this period include Eucalyptus robusta, Eucalyptus tereticornis and Eucalyptus siderophloia in late winter and E. siderophloia and E. acmenoides in spring. [source]


Estimating Canopy Structure in an Amazon Forest from Laser Range Finder and IKONOS Satellite Observations,

BIOTROPICA, Issue 4 2002
Gregory P. Asner
ABSTRACT Canopy structural data can be used for biomass estimation and studies of carbon cycling, disturbance, energy balance, and hydrological processes in tropical forest ecosystems. Scarce information on canopy dimensions reflects the difficulties associated with measuring crown height, width, depth, and area in tall, humid tropical forests. New field and spaceborne observations provide an opportunity to acquire these measurements, but the accuracy and reliability of the methods are unknown. We used a handheld laser range finder to estimate tree crown height, diameter, and depth in a lowland tropical forest in the eastern Amazon, Brazil, for a sampling of 300 trees stratified by diameter at breast height (DBH). We found significant relationships between DBH and both tree height and crown diameter derived from the laser measurements. We also quantified changes in crown shape between tree height classes, finding a significant but weak positive trend between crown depth and width. We then compared the field-based measurements of crown diameter and area to estimates derived manually from panchromatic 0.8 m spatial resolution IKONOS satellite imagery. Median crown diameter derived from satellite observations was 78 percent greater than that derived from field-based laser measurements. The statistical distribution of crown diameters from IKONOS was biased toward larger trees, probably due to merging of smaller tree crowns, underestimation of understory trees, and overestimation of individual crown dimensions. The median crown area derived from IKONOS was 65 percent higher than the value modeled from field-based measurements. We conclude that manual interpretation of IKONOS satellite data did not accurately estimate distributions of tree crown dimensions in a tall tropical forest of eastern Amazonia. Other methods will be needed to more accurately estimate crown dimensions from high spatial resolution satellite imagery. [source]