Browsing by Autor "Frank J. Sterck"

Now showing 1 - 7 of 7

Functional traits determine trade-offs and niches in a tropical forest community
(National Academy of Sciences, 2011) Frank J. Sterck; Lars Markesteijn; F. Schieving; Lourens Poorter
How numerous tree species can coexist in diverse forest communities is a key question in community ecology. Whereas neutral theory assumes that species are adapted to common field conditions and coexist by chance, niche theory predicts that species are functionally different and coexist because they are specialized for different niches. We integrated biophysical principles into a mathematical plant model to determine whether and how functional plant traits and trade-offs may cause functional divergence and niche separation of tree species. We used this model to compare the carbon budget of saplings across 13 co-occurring dry-forest tree species along gradients of light and water availability. We found that species ranged in strategy, from acquisitive species with high carbon budgets at highest resource levels to more conservative species with high tolerances for both shade and drought. The crown leaf area index and nitrogen mass per leaf area drove the functional divergence along the simulated light gradient, which was consistent with observed species distributions along light gradients in the forest. Stomatal coordination to avoid low water potentials or hydraulic failure caused functional divergence along the simulated water gradient, but was not correlated to observed species distributions along the water gradient in the forest. The trait-based biophysical model thus explains how functional traits cause functional divergence across species and whether such divergence contributes to niche separation along resource gradients.
Long-term growth patterns of juvenile trees from a Bolivian tropical moist forest: shifting investments in diameter growth and height growth
(Cambridge University Press, 2015) Danaë M. A. Rozendaal; Heinjo J. During; Frank J. Sterck; Daan Asscheman; Jeroen Wiegeraad; Pieter A. Zuidema
Abstract: Juvenile tropical trees grow from the shaded understorey to the high-light conditions of the canopy, but actual height growth trajectories towards the canopy remain unknown. Although height growth is the determining factor for reaching the canopy, investment in diameter growth is needed to sustain mechanical stability. We quantified variation in long-term juvenile tree growth patterns in diameter and height within three Bolivian moist forest species, and evaluated whether diameter growth and height growth were related. We reconstructed lifetime growth in diameter and height for 21–27 juvenile trees per species by measuring tree rings at various heights in the stem. Growth in diameter and height strongly varied among and within tree species. The light-demanding species Cedrelinga cateniformis needed just 6–19 y to reach a height of 3 m, while the more shade-tolerant species Clarisia racemosa and Peltogyne cf. heterophylla needed 8–39 y and 13–43 y, respectively. Diameter growth and height growth were not, or just weakly, positively related, and trees of the same height displayed a wide range in stem diameter. Our results indicate that trees of all three species shifted investment in diameter growth and height growth over time, most likely in response to variation in light levels.
Mechanical branch constraints contribute to life‐history variation across tree species in a Bolivian forest
(Wiley, 2006) Frank J. Sterck; H. ARNOLD VAN GELDER; Lourens Poorter
Summary Trade‐offs among plant traits may contribute to specialization for different environments and coexistence of plant species. This may be the first study that shows how trade‐offs among branch traits contribute to variation in crown size, light requirements and maximum height across multiple sympatric tree species in a tropical rain forest. Ten saplings were selected for each of 30 tree species in a Bolivian rain forest. Sapling height and crown dimensions were measured and branch and stem samples were harvested. Fresh density, dry density, modulus of rupture, centre of mass, biomass and diameters were determined for those samples. For each species, cantilever theory predicted the mass needed to produce a stable 1‐m long horizontal branch. Generally, shade‐tolerant species had denser and stronger branches, and produced a stable horizontal branch at lower resource costs. These species had branches with a higher resistance against mechanical failure, and a wide crown that favours effective light acquisition. Less shade‐tolerant species had low density and weak branches, short branches, high resource costs per unit branch length, and low resource costs per unit stem length. These traits seem advantageous under conditions of prolonged exposure to direct sunlight, where such species grow rapidly to reproductive size, while mechanical risks are low and light levels are favourable. Branch (wood and bark) traits are good predictors for performance differences across tree species in heterogeneous forest light environments. Physical trade‐offs among branch traits contribute to the specialization of tree species for different light habitats and to tree species coexistence in tropical rain forests, even within classical functional groups such as pioneers and shade tolerants.
Sapling performance along resource gradients drives tree species distributions within and across tropical forests
(Wiley, 2014) Frank J. Sterck; Lars Markesteijn; Marisol Toledo; F. Schieving; Lourens Poorter
Niche differentiation is a major hypothesized determinant of species distributions, but its practical importance is heavily debated and its underlying mechanisms are poorly understood. Trait‐based approaches have been used to infer niche differentiation and predict species distributions. For understanding underlying mechanisms, individual traits should be scaled up to whole‐plant performance, which has rarely been done. We measured seven key traits that are important for carbon and water balance for 37 tropical tree species. We used a process‐based plant physiological model to simulate the carbon budget of saplings along gradients of light and water availability, and quantified the performance of the species in terms of their light compensation points (a proxy for shade tolerance), water compensation points (proxy for drought tolerance), and maximum carbon gain rates (proxy for potential growth rate). We linked species performances to their observed distributions (the realized niches) at two spatial scales in Bolivian lowland forests: along a canopy openness gradient at local scale (∼1 km 2 ) and along a rainfall gradient (1100–2200 mm/yr) at regional (∼1000 km) scale. We show that the water compensation point was the best predictor of species distributions along water and light resource gradients within and across tropical forests. A sensitivity analysis suggests that the stomatal regulation of minimum leaf water potentials, rather than stem hydraulic traits (sapwood area and specific conductivity), contributed to the species differences in the water compensation point of saplings. The light compensation point and maximum carbon gain, both driven by leaf area index and leaf nitrogen concentration, also contributed to differential species distributions at the local scale, but not or only marginally at the regional scale. Trait‐and‐physiology‐based simulations of whole‐plant performance thus help to evaluate the possible roles of individual traits in physiological processes underlying species performance along environmental gradients. The development of such whole‐plant concepts will improve our ability to understand responses of plant communities to shifts in resource availability and stress under global change.
Silviculture enhances the recovery of overexploited mahogany <i>Swietenia macrophylla</i>
(Wiley, 2008) C.C. Verwer; Marielos Peña‐Claros; Daniël Van Der Staak; Kristen Ohlson‐Kiehn; Frank J. Sterck
Summary Big leaf mahogany Swietenia macrophylla is the most valuable timber species in the tropics but its future as a commercial timber species is at risk. This study evaluates whether recovery of overexploited mahogany populations is enhanced by actively managing the species and its surrounding forest. We assessed the effect of four different management interventions that varied in their intensities of harvesting and silvicultural treatments. We tested the hypothesis that intensive forest management stimulates population growth rates. Data were gathered over a 4‐year period in the plots (326 ha) of the Long Term Silvicultural Research Program in Bolivia. Plants > 1·3 m tall were identified and monitored in the plots, while seedlings and saplings (< 1·3 m tall) were recorded and measured around 58 adult mahogany trees. Population growth rate was simulated using population matrices based on observed vital rates. The application of silvicultural treatments only had an effect on seedling and sapling survival; survival being lowest in the unlogged forest and highest at intermediate levels of treatment application. Growth of larger trees tended to increase with management intensity, and was dependent on crown position and liana infestation. Removal of lianas and other competing trees had a positive effect on growth rates. Model simulations suggested that the recovery of overexploited mahogany population is enhanced by the application of intermediate levels of silvicultural treatments. Recovery is dependent on the retention of large seed trees (> 70 cm diameter at 1·3 m height) that produce large numbers of seedlings. Harvesting simulations indicate that mahogany populations can only be sustainably harvested by increasing the cutting cycle length, reducing harvesting intensity and by maintaining optimal growing conditions. Synthesis and applications. Mahogany is the most valuable timber species in the tropics, and its range has dramatically decreased mostly due to commercial harvesting. The results of simulation modelling based on field and experimental data suggest that overexploited populations are recovering and that sustainable harvesting will be possible in the future when cutting cycle length is increased, harvesting intensity is reduced and silvicultural treatments are applied regularly throughout the cutting cycle.
The importance of wood traits and hydraulic conductance for the performance and life history strategies of 42 rainforest tree species
(Wiley, 2009) Lourens Poorter; Imole McDonald; Alfredo Alarcón; Esther Fichtler; Juan‐Carlos Licona; Marielos Peña‐Claros; Frank J. Sterck; Z. Villegas; Ute Sass‐Klaassen
*In a comparative study of 42 rainforest tree species we examined relationships amongst wood traits, diameter growth and survival of large trees in the field, and shade tolerance and adult stature of the species. *The species show two orthogonal axes of trait variation: a primary axis related to the vessel size-number trade-off (reflecting investment in hydraulic conductance vs hydraulic safety) and a secondary axis related to investment in parenchyma vs fibres (storage vs strength). Across species, growth rate was positively related to vessel diameter and potential specific hydraulic conductance (K(p)), and negatively related to wood density. Survival rate was only positively related to wood density. *Light-demanding species were characterized by low wood and vessel density and wide vessels. Tall species were characterized by wide vessels with low density and large K(p). Hydraulic traits were more closely associated with adult stature than with light demand, possibly because tall canopy species experience more drought stress and face a higher cavitation risk. *Vessel traits affect growth and wood density affects growth and survival of large trees in the field. Vessel traits and wood density are therefore important components of the performance and life history strategies of tropical tree species.
Wood mechanics, allometry, and life‐history variation in a tropical rain forest tree community
(Wiley, 2006) H. ARNOLD VAN GELDER; Lourens Poorter; Frank J. Sterck
Wood density plays a central role in the life-history variation of trees, and has important consequences for mechanical properties of wood, stem and branches, and tree architecture. Wood density, modulus of rupture, modulus of elasticity, and safety factors for buckling and bending were determined for saplings of 30 Bolivian rain forest tree species, and related to two important life-history axes: juvenile light demand and maximum adult stature. Wood density was strongly positively related to wood strength and stiffness. Species safety factor for buckling was positively related to wood density and stiffness, but tree architecture (height : diameter ratio) was the strongest determinant of mechanical safety. Shade-tolerant species had dense and tough wood to enhance survival in the understorey, whereas pioneer species had low-density wood and low safety margins to enhance growth in gaps. Pioneer and shade-tolerant species showed opposite relationships between species traits and adult stature. Light demand and adult stature affect wood properties, tree architecture and plant performance in different ways, contributing to the coexistence of rain forest species.