To study the acclimation responses of the leaves of saplings of six tree species when changed to low or high levels of irradiance, we carried out a light exposure experiment. Species representative of contrasting shade tolerance groups were identified across a light gradient in the understorey of a Venezuelan Andean cloud forest. Measured traits included gas exchange, chlorophyll fluorescence, and morphoanatomical, biochemical and optical properties. Saplings were grown for 6 months in a shade-house receiving 20% photosynthetic photon flux (PPF) of full sunlight. Plant samples were then moved to shade-houses receiving low PPF (4%) or high PPF (65%). A factorial model (species × PPF), with repeated measurements (0, 15 and 120 days) was designed. Our results showed that morphological and anatomical traits were more plastic to PPF changes than photosynthetic traits. All species were susceptible to photoinhibition (15 days): shade-intolerant species showed dynamic photoinhibition (120 days), whereas shade-tolerant species presented chronic photoinhibition and the consequent inability to increase C assimilation rates under high PPF. The partially shade-tolerant species showed mixed responses; nonetheless, they exhibited larger adjustments in morphoanatomical and optical properties. Thus the acclimation responses of these species when subject to contrasting light conditions could help to explain their distribution along the light gradient in the understorey.
We developed a forest planning model integrating two operational scales (single-stand and forest levels) for the optimization of timber production and carbon sequestration in forest teak (Tectona grandis L. f.) plantations. At the stand level, growth and yield simulations using a heuristic thinning optimizer provided a set of near-optimal thinning regimes for individual stands differing on initial spacing and site quality, given biological, silvicultural, and financial constraints. The set of near-optimal thinning regimes obtained were then used as input of the forest-level model, which generated optimal harvest plans for the whole plantation by simultaneously maximizing the net present value of merchantable wood and carbon sequestration. The net amount of carbon captured by the biomass and the emissions produced by decomposition of woody debris and timber products after harvest were estimated. The growth and yield model was based on a system of differential equations incorporating heuristics (genetic algorithms) to optimize age and intensity of thinnings. The full model can handle the optimization of harvest schedules for projects up to 10,000 ha and 200 stands and was tested on a validation dataset including teak plantations from Venezuela and other Latin American countries. Results indicated that regimes favoring carbon sequestration reduce the benefits of timber production, and equal profitability of carbon sequestration and timber production was obtained for carbon prices over 40 $US Gg -1 . Sensitivity analysis showed that the proposed model is sensible to variation in growth rates, carbon and timber prices, and production quotas, and barely sensible to harvest and transport costs. The developed model has a modular structure that allows its calibration to incorporate data from a wide range of management regimes for teak and other forest species.
Aim of study: We developed an optimization model for determining thinning schedules in planted teak (Tectona grandis L.f.) stands that maximize the financial output in terms of soil expectation value (SEV) and net present value (NPV) considering a) the simultaneous optimization of timber production and carbon (C) sequestration and b) only for C sequestration.Area of study: Planted teak forests in the western alluvial plains of Venezuela.Material and methods: We integrated a stand growth and yield model with a constrained optimization model based on genetic algorithms (GA) for determining optimal thinning schedules (number, age, and removal intensity) that maximize SEV when simultaneously managing for timber production and C sequestration. The data came from permanent plots established in planted teak stands with remeasurements from 2 to 32 yr.-old. Plots differ in site quality, initial spacing, and thinning schedules. We obtained optimal thinning schedules for several scenarios combining site quality, initial spacing, interest rates, harvest and transport costs, as well as timber and C prices. The stand growth and yield model estimates timber products and C flows (storage and emissions) until most stored C is reemitted to the atmosphere.Main results: When considering simultaneously both, timber production and C sequestration, the scenario with the maximum SEV consisted of initial stand densities = 1,111 trees ha-1, site quality (SQ) I, harvest age 20 years, and four thinnings (ages 6, 10, 14, 17 with removal intensities 26 %, 28 %, 39 %, and 25 % of stand basal area respectively). For maximizing C sequestration only, the best schedule consisted of 1,600 trees ha-1, SQ I, harvest age 25 years, with no-thinning. A sensitivity analysis showed that optimal schedules and SEV were highly sensitive to changes in interest rates, growth rates, and timber prices.Research highlights:The management schedules favoring merchantable timber production are not the same that favor C sequestration.For planted teak, the objectives of maximizing timber production and carbon sequestration are in conflict because the thinning schedules that maximize financial gains from C sequestration reduce economic gains from timber and vice versa.With actual timber teak and market C prices, optimal NPVW is much larger than optimal NPVC.For C prices under 40 $US MgC optimizing simultaneously for timber production and C sequestration is the best option, as additional although sub-optimal revenues can be obtained from C payments.Lengthening the rotation, avoiding thinnings, or reducing their intensity increase carbon storage in planted teak, although, under the analyzed scenarios, after 120 yr. almost all carbon has been re-emitted to the atmosphere.Additional keywords: heuristics, genetic algorithms, operations research, forest management planning, stand level model, carbon stocks.Abbreviations used: C (Carbon); GA (genetic algorithm); NPVW, NPVC, NPVT (net present value from the cash flows of timber (wood), carbon, and total); SEV (Soil (land) expectation value); dbh (diameter at 1.3 m from the ground); G (stand basal area); Gp (potential site carrying capacity in terms of G); SQ (site quality); R (rotation, harvest age); A (age); I (thinning intensity); Vob, Vub (overbark, underbark volume); gr (basal area growth rate); r (interest rate); harvest and transport costs (Hc); Pc (C price).
Cloud forests represent a minor portion of the world forests, though outstanding in terms of biodiversity, endemisms, and environmental services provided. Understanding the factors that drive the regeneration and species composition of these forests, and in particular how light availability affects the patterns of juvenile tree distribution in the understory, is critical for conservation and restoration programs. In this study, we determined the range-size and overlap of the abundance distribution of juveniles for 20 tree species in an Andean tropical cloud forest in Venezuela along a gradient of percentage canopy openness (%CO) used as a surrogate of light availability. The observed distribution of %CO was then compared with a bounded null model of community structure in order to test light partitioning as a driver of tree species' coexistence. We measured %CO using hemispherical photography and the abundance and size of juvenile trees in 280 plots of 1-m radius spread over a 32 ha forest area. The distribution of sites was skewed towards the lower end of the %CO gradient (0.5 to 12.8%), while species abundance sharply diminished at both ends of the gradient. Nevertheless, 15 out of 20 species had a non-random distribution in relation to %CO, with many species concentrated near the lower side of the gradient. The observed pattern of species' overlap was within the 95% confidence limits for the average overlap expected under the bounded null model. These patterns indicate that low canopy openness is the rule in this forest, in spite of the scattered tree-fall gaps, and suggest that light partitioning does not determine the tree community structure at the juvenile stage. High redundancy in light requirements among juveniles of tree species may have a positive effect on species coexistence in cloud forests, thus maintaining a high species diversity. However, other factors such as recruitment limitation and differential growth/carbon-gain among species at the juvenile stage along the light gradient could contribute to the high diversity of these ecosystems.
[Introducción]: Se presenta un nuevo sistema de clasificación de sitios para Tectona grandis L.F. basado en información recolectada durante más de 30 años de investigación, con el fin de contribuir al manejo silvicultural de una de las especies más importantes en Costa Rica. [Objetivo]: Construir curvas actualizadas de índice de sitio para plantaciones de teca. [Metodología]: Los datos provienen del análisis fustal de 55 de árboles dominantes con edades entre 6 y 40 años, a la edad de corte, seleccionados en diferentes localidades de la Vertiente del Pacífico. Estos fueron combinados con mediciones de altura dominante provenientes de 38 parcelas permanentes medidas entre los 10 y 32 años que eran parte de 6 ensayos formales de crecimiento y rendimiento. Se definieron modelos de crecimiento, ajustados por regresión no lineal de efectos mixtos, considerando que se trata de mediciones repetidas anualmente. Se trabajó con seis modelos matemáticos: Richards, Gompertz, Logístico, Korf, Mitscherlich y Weibull. Previo al ajuste, los modelos fueron reparametrizados en función de la altura dominante observada (S), a la edad base de 16 años, asociándola a un efecto aleatorio. El mejor modelo se escogió de acuerdo con criterios de información y estadísticos de bondad de ajuste. [Resultados]: Los criterios de información de Akaike y Bayesiano indican que el modelo de Korf fue superior a los demás, tanto en su variante anamórfica como polimórfica; los estadísticos bondad de ajuste confirmaron esta apreciación. El análisis de los residuos mostró un mejor ajuste para este modelo al proyectar el crecimiento en altura dominante con la edad. Aunque el modelo polimórfico fue superior, la tendencia observada parece descartar la existencia de una asíntota común para las plantaciones de teca creciendo en las diferentes calidades de sitio. [Conclusiones]: Los resultados mostraron que los datos de análisis fustal y de parcelas permanentes presentan patrones similares, los cuales son representados adecuadamente por el modelo de Korf.
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