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Individual Trees (individual + tree)

Distribution by Scientific Domains
Life Sciences76%
Earth and Environmental Science19%
Distribution within Life Sciences
Ecology & Organismal Biology43%
Plant Science18%

Selected Abstracts

Local-scale synchrony and variability in mast seed production patterns of Picea glauca

JOURNAL OF ECOLOGY, Issue 5 2007
JALENE M. LAMONTAGNE
Summary 1Mast seeding is the synchronous and highly variable production of seed by a population of plants. Mast seeding results from the behaviour of individuals; however, little is known about the synchrony of individuals at local scales. 2We address two primary questions at a within-population (17,36 ha study plots) and individual level: (i) How variable is seed production between and within years? (ii) How synchronized is seed production between individuals? 3We monitored annual cone production of 356 Picea glauca (white spruce) from 1990 to 2005 within four plots spanning a total distance of 5.3 km in the Yukon Territory, Canada. 4Spearman correlations (rs) were conducted to test for synchrony. Overall, the trees were moderately synchronous (mean rs (± SE) of 0.52 ± 0.14), and synchrony was statistically detectable (rs > 0) over all distances. Individuals < 75 m apart were highly synchronous (0.64 ± 0.18), and correlations dropped to 0.33 ± 0.07 for trees > 3 km apart. There was considerable variation in cone production patterns among pairs of individuals. 5The number of mast years per plot varied from one to three. During a mast year, many individuals within plots produced large cone crops, with more variability between individuals in low mean cone years. Individual trees had dominant endogenous cycles varying from none to 1,5 years. Forty-four per cent of trees had no significant lag, 23% a negative 1-year lag, and 20% a positive 3-year lag. Basal area did not influence lags, but trees with higher mean cone production throughout the study were more likely to have a 3-year lag compared with no lag. 6The scale of highest synchrony coincided with the scale at which the dominant seed predator in the area, the territorial red squirrel (Tamiasciurus hudsonicus), operates. This may be the scale at which selection for synchrony occurs. 7Based on high synchrony locally, high synchrony within a mast year, and multiple lags in cone production by individuals, both available resources and strong weather cues appear to play roles in the observed patterns. [source]

Applying Network Analysis to the Conservation of Habitat Trees in Urban Environments: a Case Study from Brisbane, Australia

CONSERVATION BIOLOGY, Issue 3 2006
MONIKA RHODES
conectividad de perchas; fauna que utiliza oquedades; planificación de la conservación; red sin escala; Tadarida australis Abstract:,In Australia more than 300 vertebrates, including 43 insectivorous bat species, depend on hollows in habitat trees for shelter, with many species using a network of multiple trees as roosts. We used roost-switching data on white-striped freetail bats (Tadarida australis; Microchiroptera: Molossidae) to construct a network representation of day roosts in suburban Brisbane, Australia. Bats were caught from a communal roost tree with a roosting group of several hundred individuals and released with transmitters. Each roost used by the bats represented a node in the network, and the movements of bats between roosts formed the links between nodes. Despite differences in gender and reproductive stages, the bats exhibited the same behavior throughout three radiotelemetry periods and over 500 bat days of radio tracking: each roosted in separate roosts, switched roosts very infrequently, and associated with other bats only at the communal roost. This network resembled a scale-free network in which the distribution of the number of links from each roost followed a power law. Despite being spread over a large geographic area (>200 km2), each roost was connected to others by less than three links. One roost (the hub or communal roost) defined the architecture of the network because it had the most links. That the network showed scale-free properties has profound implications for the management of the habitat trees of this roosting group. Scale-free networks provide high tolerance against stochastic events such as random roost removals but are susceptible to the selective removal of hub nodes. Network analysis is a useful tool for understanding the structural organization of habitat tree usage and allows the informed judgment of the relative importance of individual trees and hence the derivation of appropriate management decisions. Conservation planners and managers should emphasize the differential importance of habitat trees and think of them as being analogous to vital service centers in human societies. Resumen:,En Australia, más de 300 vertebrados, incluyendo 43 especies de murciélagos insectívoros, dependen de oquedades en árboles para refugiarse; muchas de ellas perchan en una red de múltiples árboles. Utilizamos datos de cambio de perchas en Tadarida australis (Microchiroptera: Molossidae) para construir una representación reticular de las perchas diurnas en los suburbios de Brisbane, Australia. Los murciélagos fueron capturados en un árbol con un grupo de varios cientos de individuos y liberados con transmisores. Cada percha utilizada por los murciélagos representó un nodo individual en la red, y los movimientos de murciélagos entre perchas constituyeron los eslabones entre los nodos. A pesar de las diferencias de género y etapas reproductivas, los murciélagos mostraron el mismo comportamiento en tres períodos de radiotelemetría y en más de 500 días de seguimiento de murciélagos: cada uno utilizó perchas separadas, cambiaban de percha poco frecuentemente, y se asociaron con otros murciélagos sólo en las perchas comunales. Esta red fue semejante a una red sin escala en la que la distribución del número de eslabones de cada percha cumplió una ley potencial. A pesar de estar dispersas en un área geográfica extensa (>200 km2), cada percha estaba conectada con otras por menos de tres eslabones. Una percha (el centro o percha comunal) definió la arquitectura de la red porque tenía a la mayoría de los eslabones. El hecho de que la red mostrara propiedades libres de escala tiene implicaciones profundas para la gestión de árboles que funcionan como perchas. Las redes libres de escala proporcionan alta tolerancia a eventos estocásticos como la remoción aleatoria de perchas, pero son susceptibles a la remoción selectiva de nodos centrales. El análisis de redes es una herramienta útil para el entendimiento de la organización estructural del uso de de árboles y permite el juicio informado de la importancia relativa de árboles individuales y por lo tanto la derivación de decisiones administrativas apropiadas Los planificadores y gestores de la conservación deberían enfatizar la importancia diferencial de árboles y considerarlos análogos a los centros de servicio vitales en las sociedades humanas. [source]

Plant functional type classifications in tropical dry forests in Costa Rica: leaf habit versus taxonomic approaches

FUNCTIONAL ECOLOGY, Issue 4 2010
Jennifer S. Powers
Summary 1.,One way to simplify the high taxonomic diversity of plant species in vegetation models is to place species into groups based on shared, dominant traits. Many studies have suggested that morphological and physiological traits of tropical dry forest tree species vary with leaf habit (i.e. leaves from evergreen, deciduous or semi-deciduous species) and thus this characteristic may serve as a useful way to distinguish ecologically meaningful functional types. 2.,In this study we examine whether 10 plant traits vary with leaf habit in replicated leaves and individual trees of 87 species from a tropical dry forest in Costa Rica. We also looked for evidence of phylogenetic conservatism, i.e. closely related species sharing similar trait values compared to more distantly related taxa. 3.,While some of the traits varied within and among individual trees of the same species, interspecific variation accounted for 57,83% of the variance among samples. Four traits in addition to leaf habit showed evidence of phylogenetic conservatism, but these results were strongly dependent on the inclusion of the 18 species of legumes (Fabaceae) in our dataset. Contrary to our predictions, none of the traits we measured differed among leaf habits. However, five traits (wood density, leaf C, leaf N, N/P and C/N) varied significantly between legumes and other functional types. Furthermore, when all high-nitrogen non-legume taxa were compared to the high-nitrogen legumes, six traits excluding leaf N differed significantly, indicating that legumes are functionally different from other tree species beyond high N concentrations. Similarly, the 18 legume taxa (which all have compound leaves) also differed from other compound-leaved species for six traits, thus leaf type does not explain these patterns. 4.,Our main conclusions are that (i) a plant functional type classification based on leaf habit alone has little utility in the tropical dry forest we studied, and (ii) legumes have a different suite of traits including high leaf carbon and wood density in addition to high leaf nitrogen. Whether this result generalizes to other tropical forests is unknown, but merits future research due to the consequences of these traits for carbon storage and ecosystem processes. [source]

Measurements of transpiration in four tropical rainforest types of north Queensland, Australia

HYDROLOGICAL PROCESSES, Issue 26 2007
David McJannet
Abstract Transpiration of four different rainforest types in north Queensland, Australia, was determined using the heat pulse technique for periods ranging between 391 and 657 days. Despite the complexity of the natural rainforest systems being studied, the relationship between sample tree size and daily water use was found to be strong, thus providing a robust means by which to scale transpiration from individual trees to the entire forest stand. Transpiration was shown to be dependent on solar radiation and atmospheric demand for moisture with little evidence of limitation by soil moisture supply. Total stand transpiration was controlled by forest characteristics such as stem density, size distribution and sapwood area. Annual transpiration for each of the four sites ranged between 353 mm for cloud forest and 591 mm for montane rainforest. In comparison with the international literature, transpiration from Australian rainforests is low; the reasons for this could be related to a combination of differences in forest structure, climatic conditions, canopy wetness duration and tree physiology. Copyright © 2007 John Wiley & Sons, Ltd. [source]

High temporal variation in the assemblage of Lepidopteran larvae on a constant resource

AFRICAN JOURNAL OF ECOLOGY, Issue 4 2009
Sini Skippari
Abstract We studied variation in the assemblage of lepidopteran larvae between individual trees, and temporal variation in the diversity and species composition of the assemblage in a medium-altitude rainforest in Kibale National Park, Uganda. Monthly samples of lepidopteran larvae were collected from the leaves of Neoboutonia macrocalyx Pax. between January 1995 and December 1996. During this period, a total of 1961 specimens representing 76 lepidopteran morphospecies were found. The numbers of individuals within species varied enormously, ranging from one to 707 individuals. Assemblages of individual trees were highly similar and dominated by geometrid larvae. Temporal variation in herbivore abundance was high. The number of individuals peaked during the major rainy season in 1995 but not in 1996 and was not correlated significantly with rainfall within these 2 years. In contrast, a negative correlation was found between lepidopteran diversity and rainfall that seems to cause a semi-annual trend in diversity with one or two peaks per year. Furthermore, there was seasonality in the similarity of the assemblage. Consequently, the same species were found in the assemblage during certain times of the year. Our study shows that short-term biodiversity assessments can give a skewed picture of the diversity of tropical forests. Résumé Nous avons étudié la variation de l'assemblage de larves de lépidoptères entre différents arbres, et la variation temporelle de la diversité et de la composition des espèces de l'assemblage dans une forêt pluviale de moyenne altitude du Parc National de Kibale, en Ouganda. Des échantillons de larves de lépidoptères furent récoltés tous les mois sur les feuilles de Neoboutonia macrocalyx Pax entre janvier 1995 et décembre 1996. Pendant cette période, nous avons trouvé un total de 1961 spécimens représentant 76 morphoespèces de Lépidoptères. Le nombre d'individus variait énormément selon les espèces, allant de un à 707 individus. Les assemblages des arbres pris individuellement étaient très comparables et dominés par les larves de géométrides. La variation temporelle de l'abondance des herbivores était importante. Le nombre d'individus a culminé lors de la principale saison des pluies de 1995, mais pas en 1996, et il n'y avait pas de corrélation significative avec les chutes de pluies ces deux années-là. Par contre, nous avons trouvé une corrélation négative entre la diversité des lépidoptères et les chutes de pluies qui semblent causer une tendance semi-annuelle de la diversité, avec un ou deux pics par an. De plus, il y avait une saisonnalité dans la similitude des assemblages. Par conséquent, la même espèce se trouvait dans les assemblages à certaines périodes de l'année. Notre étude montre que les évaluations de courte durée de la biodiversité peuvent donner une image faussée de la diversité des forêts tropicales. [source]

The impact of elephants on the marula tree Sclerocarya birrea

AFRICAN JOURNAL OF ECOLOGY, Issue 4 2002
Michelle E. Gadd
Abstract This study determined the abundance, density and population structure of the marula tree, Sclerocarya birrea, in three game reserves in South Africa, and assessed patterns and amounts of new and cumulative impact of elephants. Elephant feeding was very patchy so several attributes of individual trees, sampled transects and communities that might influence elephant herbivory were investigated. The incidence and type of elephant impact (bark, branch or stem breakage) were significantly related to tree diameter, but not to fruiting nor proximity to roads. At the transect level, elephant impact was influenced by density of marula trees, but was not influenced by proximity to roads, nor proportion of marula trees bearing fruits in the vicinity. At the community level, elephant impact was higher on reserves with higher total marula densities. Fourfold differences in elephant densities (0.08,0.30 elephants km,2) did not explain marula consumption: the percentage of trees with branch damage was similar across reserves and bark damage was inversely proportional to elephant density. Variation across reserves may reflect local and landscape-level marula tree abundance, differences in alternative food plants and individual feeding habits. The recorded levels of impact appeared to be sustainable because mortality rates were low, affected trees often recovered, and small trees were not preferentially preyed upon. Résumé Cette étude détermine l'abondance, la densité et la structure de la population de l'arbre à Marula, Sclerocarya birrea, dans trois réserves de faune sud-africaines et évalue le schéma et la totalité des impacts nouveaux et successifs des éléphants. Les éléphants se nourrissaient çà et là, de sorte que l'on a étudié divers attributs des arbres pris individuellement, des transects échantillons et des communautés, qui pouvaient influencer le caractère herbivore des éléphants. L'incidence et le type d'impact (écorces, branches ou jeunes pousses) étaient significativement liés au diamètre de l'arbre, mais non à la fructification, ni à la proximité des routes. Au niveau du transect, l'impact des éléphants était influencé par la densité des arbres à Marula, mais pas par la proximité des routes, ni par la proportion d'arbres à Marula en fruits dans le voisinage. Au niveau de la communauté, l'impact des éléphants était plus élevé dans les réserves qui comptaient la plus forte densité totale d'arbres à Marula. Une différence de 1 à 4 dans la densité des éléphants (0.08-0.30/km2) n'explique pas la consommation de marula : le pourcentage d'arbres présentant des branches endommagées était similaire dans toutes les réserves, et les dommages causés aux écorces étaient inversement proportionnels à la densité des éléphants. La variation observée entre les réserves pourrait refléter l'abondance des arbres à Marula tant locale que liée au paysage, des différences dans l'abondance de nourriture végétale alternative et les habitudes alimentaires individuelles. L'importance de l'impact relevé semblait être soutenable parce que le taux de mortalitéétait faible, que les arbres touchés récupéraient souvent et que les petits arbres n'avaient pas souvent la préférence des éléphants. [source]

Seed predation during general flowering events of varying magnitude in a Malaysian rain forest

JOURNAL OF ECOLOGY, Issue 4 2007
I-FANG SUN
Summary 1The lowland dipterocarp forests of Southeast Asia exhibit interspecifically synchronized general flowering (GF) and mast fruiting at irregular multi-year intervals of 1 to 11 years. The predator satiation hypothesis (PSH) posits that GF events enhance seed survival by reducing the survival, reproduction and population sizes of seed predators between GF events, and then satiating the reduced seed predator populations during GF events. 2Three GF events of different magnitudes occurred in Pasoh Forest Reserve, Peninsular Malaysia, during 2001, 2002 and 2005. We exploited this natural experiment to test two predictions of the PSH. The first prediction was that seed survival should increase with the magnitude of the GF event. The second prediction was that seed predation should decrease with time since the previous GF event. 3A reproductive survey of all (c. 900) dipterocarp trees 30 cm d.b.h. in a 50 ha plot showed that flowering pervasiveness (the proportion of dipterocarp species participating) was high and similar in all three GF events. However, relative flowering magnitudes (measured by an index of individual tree participation and flowering intensity in Shorea species) were 2, 5 and 8 for the 2001, 2002 and 2005 GF events, respectively. 4The percentage of Shorea seeds surviving pre- and post-dispersal predation increased with the magnitude of GF events, which is consistent with the first prediction. 5Pre-dispersal insect seed predators consumed 12.9%, 11.2% and 3.4% of Shorea seeds in the 2001, 2002 and 2005 GF events, respectively, which is consistent with both predictions. 6Pre-dispersal seed predation by primates (mainly leaf monkeys) increased from 11.9% to 38.6% then fell to 9.3% in the 2001, 2002 and 2005 GF events, respectively. 7Predator satiation occurred only at population and community levels. At the individual tree level there was no relationship between the percentage of seeds surviving pre- and post-dispersal seed predation and variation in seed crop size or seed density beneath the tree. This suggests that attempts to test the PSH on the scale of individual trees may miss key community level effects. 8Our results suggest a more significant role of pre-dispersal seed predation in the evolution of reproductive synchrony than was recognized in the original statement of the PSH. [source]

The invasive alien leaf miner Cameraria ohridella and the native tree Acer pseudoplatanus: a fatal attraction?

AGRICULTURAL AND FOREST ENTOMOLOGY, Issue 2 2010
Christelle Péré
1The horse-chestnut leaf miner Cameraria ohridella is an invasive moth in Europe and a serious pest of horse-chestnut Aesculus hippocastanum. The moth also occasionally attacks sycamore maple Acer pseudoplatanus, when situated beside infested horse-chestnuts. 2The main objective of the present study was to provide an overview of the relationship between C. ohridella and A. pseudoplatanus and to determine whether C. ohridella has the potential to shift to this native tree. 3In the field, females oviposit on different deciduous tree species. Although less frequently attacked than A. hippocastanum, A. pseudoplatanus was clearly preferred for oviposition over 12 other woody species investigated. 4Surveys in Europe demonstrated that the majority of A. pseudoplatanus trees found beside infested A. hippocastanum had mines of C. ohridella, even though more than 70% of the larvae died within the first two instars. Attack rates and development success greatly varied from site to site. Attack levels on A. pseudoplatanus were not always correlated with those on A. hippocastanum, and mines on A. pseudoplatanus were sometimes observed beside weakly-infested A. hippocastanum. 5Field observations, experimental exposure of A. pseudoplatanus saplings and rearing trials in a common garden study showed that individual trees may vary in their susceptibility to C. ohridella, whereas there was no evidence that C. ohridella populations vary in their performance on A. pseudoplatanus. 6To date, there is little evidence that C. ohridella represents a major risk for A. pseudoplatanus. [source]

Consistency of resistance to attack by the green spruce aphid (Elatobium abietinum Walker) in different ontogenetic stages of Sitka spruce

AGRICULTURAL AND FOREST ENTOMOLOGY, Issue 2 2003
S. Harding
Abstract 1,The susceptibility of different genotypes of 29-year-old Sitka spruce to damage by the green spruce aphid, Elatobium abietinum, was investigated in a progeny trial where aphid damage on individual trees had previously been assessed twice in an earlier stage of ontogenetic development. The progeny trial comprised 14 open-pollinated families originating from a clonal seed orchard that had been established using mature spruce trees selected for aphid resistance. 2,Previous investigations had demonstrated that resistance was inherited by the offspring, and that differences in resistance between progenies of the individual orchard clones were highly significant. 3,Susceptibility to aphid attack was recorded as the percentage loss of previous year's needles. Differences in susceptibility recorded between the juvenile trees were found to persist after the trees had developed into the closed-canopy, sexually reproducing stage. Needle loss of the families was significantly less than that of the reference population of Sitka spruce. 4,Hybrids between Sitka spruce and white spruce were defoliated more heavily than pure Sitka spruce, and the difference increased with age. 5,Family heritability of resistance was estimated as 0.60 compared to 0.73 when the trees were assessed in the juvenile stage. The genetic correlation based on family means between damage in the juvenile and sexually reproducing stand was high (0.83), indicating a high consistency of resistance to the aphid over years and ontogenetic stages. 6,A skewed distribution of defoliation indicated that major genes are involved in the expression of resistance, and that the genetics behind resistance has a nonadditive component. [source]

Tree spacing and area of competitive influence do not scale with tree size in an African rain forest

JOURNAL OF VEGETATION SCIENCE, Issue 5 2008
Michael J. Lawes
Abstract Questions: Is the area of influence of individual trees determined by tree size? Does competition, inferred from spatial pattern between neighbouring trees, affect adult tree spacing patterns in an tropical forest? At what size-class or stage is competition between neighbours most likely to affect adult tree spacing patterns? Location: Kibale National Park, western Uganda. Methods: Relationships between focal tree size and nearest neighbour distance, size, density, and species in a 4-ha permanent plot, using point pattern analyses. Results: We found non-random patterns of distribution of nearest tree neighbours (stems > 10 cm DBH). Independent of identity, tree density was highest and neighbours were regularly spaced within 3,5m of an individual. Tree densities were lower and relatively constant at distances >5m and neighbours were typically randomly spaced. In general, conspecific patterns conformed to the latter trends. Thus, individual area of influence was small (within a radius of 3,5 m). Rarer species were more clumped than common species. Weak competitive thinning occurred among more densely packed small trees (<20 cm DBH), and rapidly disappeared with increasing tree size and distance from an individual. The clumping and density of individuals was not significantly affected by tree size. Conclusions: Negative effects of competition among trees are weak, occur within the crown radius of most individuals, and are independent of adult tree size and identity. The density of neighbouring trees (aggregation) did not decline with increasing focal tree size at either the conspecific or the community level and tree diameter (tree size) was not a good estimator of the implied competitive influence of a tree. Mechanisms operating at the recruitment stage may be important determinants of adult tree community diversity and spacing patterns. [source]

Variation in vegetative water use in the savannas of the North Australian Tropical Transect

JOURNAL OF VEGETATION SCIENCE, Issue 3 2002
Garry D. Cook
Abstract. The decline in tree density on sandy soils in savannas is highly correlated with declining mean annual rainfall along the North Australian Tropical Transect (NATT). We reanalyse various data on water use by individual trees and argue that a common relationship can be used to estimate annual water use by tree stands along the NATT from ca. 600 mm mean annual rainfall to at least 1600 mm. Where rainfall is less than 600 mm, trees of a given size use less water than at sites where rainfall is higher. We use these relationships to relate water use at the stand scale with mean annual rainfall along the NATT. From this we show that the empirical data imply that the minimum depth of sandy soil that needs to be exploited by trees declines with increasing aridity along the NATT from more than 5 m to less than 1 m. This finding is consistent with other observations and the pattern that with increasing aridity, an increasing proportion of rainfall coming from isolated storms rather than from periods of extended monsoon activity. [source]

Extensive spatial genetic structure revealed by AFLP but not SSR molecular markers in the wind-pollinated tree, Fagus sylvatica

MOLECULAR ECOLOGY, Issue 5 2007
ALISTAIR S. JUMP
Abstract Studies of fine-scale spatial genetic structure (SGS) in wind-pollinated trees have shown that SGS is generally weak and extends over relatively short distances (less than 30,40 m) from individual trees. However, recent simulations have shown that detection of SGS is heavily dependent on both the choice of molecular markers and the strategy used to sample the studied population. Published studies may not always have used sufficient markers and/or individuals for the accurate estimation of SGS. To assess the extent of SGS within a population of the wind-pollinated tree Fagus sylvatica, we genotyped 200 trees at six microsatellite or simple sequence repeat (SSR) loci and 250 amplified fragment length polymorphisms (AFLP) and conducted spatial analyses of pairwise kinship coefficients. We re-sampled our data set over individuals and over loci to determine the effect of reducing the sample size and number of loci used for SGS estimation. We found that SGS estimated from AFLP markers extended nearly four times further than has been estimated before using other molecular markers in this species, indicating a persistent effect of restricted gene flow at small spatial scales. However, our SSR-based estimate was in agreement with other published studies. Spatial genetic structure in F. sylvatica and similar wind-pollinated trees may therefore be substantially larger than has been estimated previously. Although 100,150 AFLP loci and 150,200 individuals appear sufficient for adequately estimating SGS in our analysis, 150,200 individuals and six SSR loci may still be too few to provide a good estimation of SGS in this species. [source]

Effects of altered water regimes on forest root systems

NEW PHYTOLOGIST, Issue 1 2000
J. D. JOSLIN
How ecosystems adapt to climate changes depends in part on how individual trees allocate resources to their components. A review of research using tree seedlings provides some support for the hypothesis that some tree species respond to exposure to drought with increases in root,shoot ratios but little change in total root biomass. Limited research on mature trees over moderately long time periods (2,10 yr), has given mixed results with some studies also providing evidence for increases in root: shoot ratios. The Throughfall Displacement Experiment (TDE) was designed to simulate both an increase and a decrease of 33% in water inputs to a mature deciduous forest over a number of years. Belowground research on TDE was designed to examine four hypothesized responses to long-term decreases in water availability; (1) increases in fine-root biomass, (2) increases in fine root,foliage ratio, (3) altered rates of fine-root turnover (FRT), and (4) depth of rooting. Minirhizotron root elongation data from 1994 to 1998 were examined to evaluate the first three hypotheses. Differences across treatments in net fine-root production (using minirhizotron root elongation observations as indices of biomass production) were small and not significant. Periods of lower root production in the dry treatment were compensated for by higher growth during favorable periods. Although not statistically significant, both the highest production (20 to 60% higher) and mortality (18 to 34% higher) rates were found in the wet treatment, resulting in the highest index of FRT. After 5 yr, a clear picture of stand fine-root-system response to drought exposure has yet to emerge in this forest ecosystem. Our results provide little support for either an increase in net fine-root production or a shift towards an increasing root,shoot ratio with long-term drought exposure. One possible explanation for higher FRT rates in the wet treatment could be a positive relationship between FRT and nitrogen and other nutrient availability, as treatments have apparently resulted in increased immobilization of nutrients in the forest floor litter under drier conditions. Such hypotheses point to the continued need to study the interactions of water stress, nutrient availability and carbon-fixation efficiency in future long-term studies. [source]

Growth,mortality relationships as indicators of life-history strategies: a comparison of nine tree species in unmanaged European forests

OIKOS, Issue 6 2008
Jan Wunder
Forest succession depends strongly on the life history strategies of individual trees. An important strategic element is the ability to survive unfavourable environmental conditions that result in strongly reduced tree growth. In this study, we investigated whether the relationship between growth and mortality differs among tree species and site conditions. We analysed 10 329 trees of nine tree species (Picea abies, Taxus baccata, Fagus sylvatica, Tilia cordata, Carpinus betulus, Fraxinus excelsior, Quercus robur, Betula spp. and Alnus glutinosa) from unmanaged forests of Europe: the continental Bia,owie,a forest (Poland) and several oceanically influenced Swiss forest reserves. For each species, we calculated a set of flexible logistic regression models with the explanatory variables growth (as measured by relative basal area increment), tree size and site. We selected the species-specific model with the highest goodness-of-fit and calculated its discriminatory power (area under the receiver operating characteristic curve, AUC) and calibration measures. Most models achieved at least a good discriminatory power (AUC>0.7) and the AUC ranged from 0.62 to 0.87; calibration curves did not indicate any overfitting. Almost all growth,mortality relationships differed among species and sites, i.e. there is no universal growth,mortality relationship. Some species such as F. excelsior showed reduced survival probabilities for both unfavourable and very good growth conditions. We conclude that the growth,mortality relationships presented here can contribute to the life-history classification of trees and that they should also help to improve projections of forest succession models. [source]

Effects of site and fruit size on the composition of avian frugivore assemblages in a fragmented Afrotropical forest

OIKOS, Issue 2 2002
M. Githiru
Factors influencing the interaction between fruiting trees and their frugivorous seed dispersers in fragmented Afrotropical landscapes are poorly known. With the use of Mantel statistics we analysed assemblages of frugivorous birds on 58 individual trees belonging to 11 species growing in seven Kenyan cloud forest fragments. Overall, frugivores showed little specialization on particular trees. Fruit size explained a substantial amount of the variation in frugivore assemblages among different tree species at the same site. In addition, frugivore assemblages on conspecific trees were significantly more similar when the trees occurred at the same site. This location effect was attributable to the different sites and forest fragments (of different sizes and disturbance levels) varying in the densities and composition of their avian frugivores, vegetation composition and tree fruiting phenologies. It was consolidated further by the low mobility of most of these avian frugivores, particularly their reluctance to cross between forest fragments. Habitat disturbance and fragmentation may therefore have affected fruit selection, with implications for both seed dispersal and regeneration. [source]

Dynamics of water transport and storage in conifers studied with deuterium and heat tracing techniques

PLANT CELL & ENVIRONMENT, Issue 1 2006
F. C. MEINZER
ABSTRACT The volume and complexity of their vascular systems make the dynamics of long-distance water transport in large trees difficult to study. We used heat and deuterated water (D2O) as tracers to characterize whole-tree water transport and storage properties in individual trees belonging to the coniferous species Pseudotsuga menziesii (Mirb.) Franco and Tsuga heterophylla (Raf.) Sarg. The trees used in this study spanned a broad range of height (13.5,58 m) and diameter (0.14,1.43 m). Sap flow was monitored continuously with heat dissipation probes near the base of the trunk prior to, during and following injection of D2O. The transit time for D2O transport from the base of the trunk to the upper crown and the tracer residence time were determined by measuring hydrogen isotope ratios in water extracted from leaves sampled at regular intervals. Transit times for arrival of D2O in the upper crown ranged from 2.5 to 21 d and residence times ranged from 36 to 79 d. Estimates of maximum sap velocity derived from tracer transit times and path length ranged from 2.4 to 5.4 m d,1. Tracer residence time and half-life increased as tree diameter increased, independent of species. Species-independent scaling of tracer velocity with sapwood-specific conductivity was also observed. When data from this study were combined with similar data from an earlier study of four tropical angiosperm trees, species-independent scaling of tracer velocity and residence time with sapwood hydraulic capacitance was observed. Sapwood capacitance is an intrinsic tissue-level property that appears to govern whole-tree water transport in a similar manner among both tracheid- and vessel-bearing species. [source]

Flowering system of heterodichogamous Juglans ailanthifolia

PLANT SPECIES BIOLOGY, Issue 2-3 2003
MEGUMI KIMURA
Abstract To determine the sex-expression of Juglans ailanthifolia, we monitored its flowering phenology for 3 years in two natural populations and observed the following four mating types: protogyny, protandry, female and male. In each population, the number of protogynous trees was most numerous, followed by protandrous tree. These monoecious types constituted 61,95% of the individuals at each site in each year. Observations of flowering phenology of the monoecious types showed that female and male functions were temporally segregated within individual trees and that the sexual functions of each protogynous and protandrous mating type were synchronous and reciprocal. Such a system may help to reduce selfing and promote outcrossing. Trunk size was smaller in the unisexual types than in the monoecious types. Sixty-seven percent of trunks were oblique due to snow pressure in the unisexual types, whereas only 23% were oblique in the monoecious types. It seemed that unisexuality is a temporary trait because the changes in mating category occurred mainly from unisexual to monoecious types and inverse changes were very few. [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]

Diet selection in the green ringtail possum (Pseudochirops archeri): A specialist folivore in a diverse forest

AUSTRAL ECOLOGY, Issue 7 2006
KATHERINE M. W. JONES
Abstract This study investigated the feeding ecology of the green ringtail possum, Pseudochirops archeri (Pseudocheiridae) in a tropical rainforest with 94 plant species in the canopy. Over 50% of tree use was from only four tree species, Aleurites rockinghamensis, Ficus fraseri, Arytera divaricata and Ficus copiosa. These species were used significantly more frequently than would be expected if tree species were selected randomly in proportion to their relative abundance in the forest. Conversely, 88 other tree species present were used less frequently than expected. Possums also favoured particular individual trees within some of the preferred tree species. In 91% of feeding observations, possums consumed mature leaves only. The availability of young leaves, flowers and fruit varied throughout the year, with a peak in availability of these resources during the early wet season. By primarily selecting mature leaves, green ringtail possums reduce their dependence on seasonally variable resources. We suggest that green ringtail possums should be considered as specialist folivores, focusing on only a few of the tree species available, possibly due to advantages associated with limiting the number of plant secondary metabolites in their diet. Furthermore, they favour certain individual trees within species, perhaps due to intraspecific variation in plant secondary metabolites or nutrient content, behaviour that has been well established in eucalypt folivores. We conclude that green ringtail possums are highly specialized in their feeding ecology, limiting their diet to a small number of continuously available food items. [source]

Age-Dependent Radial Increases in Wood Specific Gravity of Tropical Pioneers in Costa Rica

BIOTROPICA, Issue 5 2010
G. Bruce Williamson
ABSTRACT Wood specific gravity is the single best descriptor of wood functional properties and tree life-history traits, and it is the most important variable in estimating carbon stocks in forests. Tropical pioneer trees produce wood of increasing specific gravity across the trunk radius as they grow in stature. Here, we tested whether radial increases in wood specific gravity were dependent on a tree's diameter or its age by comparing trees of different diameters within cohorts. We cored trunks of four pioneer species in naturally regenerating, even-aged stands in the lowland, wet forests of Costa Rica. For each core, specific gravity was determined for 1-cm radial wood segments, pith to bark. Increases across the radius were evident in all four species studied, and in four different stands for one species. For any given species in a given stand, the rate of radial increase in specific gravity as a function of radial distance from the pith was greater in smaller diameter trees. As the trees in a stand represent a colonizing cohort, these results strongly suggest that the radial increases in specific gravity in lowland pioneers are associated with tree age, not with tree diameter. Furthermore, the specific gravity of the outermost wood was not associated with tree radius, further negating size dependence. One consequence of these results is that species-specific biomass estimates for trees in secondary forests are likely to be confounded by age, as diameter alone may be a poor indicator of specific gravity in individual trees for pioneers of tropical wet forests. Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp [source]

The Role of Cloud Combing and Shading by Isolated Trees in the Succession from Maquis to Rain Forest in New Caledonia1

BIOTROPICA, Issue 2 2002
L. S. Rigg
ABSTRACT This study examined the role of shading and cloud combing of moisture by scattered trees of the emergent conifer Araucaria laubenfelsii (Corbass.) in montane shrubland-maquis at Mont Do, New Caledonia, in facilitating the succession from shrubland to rain forest. Water collection experiments showed that these trees combed significant amounts of water from low clouds on days when no rainfall was recorded and deposited this moisture on the ground beneath the tree canopy. Analysis of photosystem II function in A. laubenfelsii and five other plant species using fluorometry revealed much lower photosystem stress in plants beneath scattered A. laubenfelsii than for individuals exposed to full sunlight in the open maquis. Transition matrix analyses of vegetation change based on "the most likely recruit to succeed" indicated that the transition from maquis to forest was markedly faster when emergent trees of A. laubenfelsii acted as nuclei for forest species invasion of die maquis. On the basis of these lines of evidence, it is argued that increased moisture and shading supplied to the area directly below the crown of isolated A. laubenfelsii trees in the maquis facilitates the establishment of both conifer seedlings and other rain forest tree and shrub species. In the absence of fire, rain forest can reestablish through spread in two ways: first, by expansion from remnant patches, and second, from coalescence of small rain forest patches formed around individual trees of A. laubenfelsii. [source]