Applying LiDAR to Quantify the Plant Area Index Along a Successional Gradient in a Tropical Forest of Thailand

Long-term monitoring of vegetation is critical for understanding the dynamics of forest ecosystems, especially in Southeast Asia’s tropical forests, which play a significant role in the global carbon cycle and have continually been converted into various stages of secondary forests. In Thailand, long-term monitoring of forest dynamics during the successional process is limited to plot scales assuming from the distinct structure of successional stages. Our study highlights the potential of coupling airborne light detection and ranging (LiDAR) technology and stand age data derived from Landsat time-series to track back forest succession, and infer patterns in the plant area index (PAI) recovery. Here, using LIDAR data, we estimated the PAI of the 510 sample plots of a seasonal evergreen forest dispersed over the study area in Khao Yai National Park, Thailand, capturing a successional gradient of tropical secondary forests. The sample plots age was derived from the available Landsat time-series dataset (1972–2017). We developed a PAI recovery model during the first 42 years of the succession process. We investigated the relationship between the model residuals and PAI values with topographic factors, such as elevation, slope, and topographic wetness index. The results show that the PAI increased non-linearly (pseudo-R2 of 0.56) during the first 42 years of forest succession, and all three topographic factors have less influence on PAI variability. These results provide valuable information of the spatio-temporal PAI patterns during the successional process and help understand the dynamics of tropical secondary forests in Khao Yai National Park, Thailand. Such information is essential for forest management and local, regional, and global PAI synthesis. Moreover, our results provide significant information for ground-based spatial sampling strategies to enable more accurate PAI measurements.

Functional morphology of subtropical tree seedlings in southern Brazil

The objective of this study was to analyze the morphofunctional attributes of Mixed Ombrophyllous Forest species of different successional categories. Fruits were collected from forest remnants in Curitiba, Paraná. It was analyzed the biometrics of seeds and seedlings of all species and the following ratios were estimated: shoot/seedling length, shoot/seedling mass, cotyledons/seedling mass, eophyll/seedling mass and seedling/ seed mass. Statistical differences among sucessional groups were observed in many of the evaluated traits. The variability among species is mainly explained by seedling size, tissue investment for light interception and shoot resource allocation. Late secondary species have larger seedlings with characteristics that indicate slower initial development, dependent on seed reserves. The pioneers species have smaller seedlings but faster development and earlier dependence on photosynthesis. These morphological and functional differences can result in different strategies for the establishment of seedlings in the successional process. The cluster analysis results on formation of two major groups. The first group is comprised of the late secondary species. The second group includes two distinct subgroups that separate the pioneers, and most of the early secondary species. These results indicate that the number and quality of available data should be considered in the definition of successional categories adopted in ecological studies.

Paleofire severity and vegetation change in the Cascade Range, Oregon, USA

Paleoecological research has expanded our knowledge of the relationships between climate, fire and vegetation. Fire can be a significant driver of forest composition and structure change, but identifying and quantifying fire regimes has been elusive. Using high-resolution charcoal analysis and pollen analysis we reconstructed a 13,200-year-old fire and vegetation history from Breitenbush Lake, Oregon, located in the central Cascade Range, USA. Our objective was to examine if fire occurrence and severity may have been a driver of Holocene forest-composition change. The data from this study suggests that while fire can create opportunities for successional process to occur, fire events were not significant catalysts for forest change. Instead, most major transitions at Breitenbush Lake occurred during prolonged fire-free intervals. Our results reinforce the view that climate is the major control of vegetation composition change in the Cascade Range.

Functional diversity and functional traits of periphytic algae during a short-term successional process in a Neotropical floodplain lake

Due to the lack of knowledge in periphytic algae functional diversity patterns during successional processes in floodplains, the present study aimed to analyze the dynamics of the functional traits and functional diversity of periphytic species during a short-term successional process in a floodplain lake. The functional traits analyzed were size class, growth form, strength of attachment to the substratum, and functional strategies. We evaluated the dynamics of these traits, considering richness, density and biovolume during an 18-day colonization in two hydrological periods. The functional diversity was assessed using the mean pairwise distance index (MPD). Dominant functional traits during the colonization changed in association with the flood pulse. Under the pulse effect, higher development of C-S strategist, loosely attached, filamentous and nanoperiphytic species occurred. The highest values of functional diversity were associated with the algal biomass peak during the colonization and the high water hydrological period, possibly indicating greater efficiency in the ecosystem functioning. These findings show the importance of the functional traits approach in periphyton studies and that the selection of functional traits must be performed taking into account traits that represent the species niche.

Successional trajectory of the fouling community on a tropical upwelling ecosystem in southeast Rio de Janeiro, Brazil

The present study describes the successional trajectory of the fouling community in the upwelling region of Cabo Frio in southeastern Rio de Janeiro, Brazil. For 12 months, five PVC panels were sampled monthly by underwater photography to record the percent cover of fouling organisms, which allowed for the evaluation of the successional process through functional groups. The variability in the composition of the fouling community increased throughout the successional trajectory, creating a mosaic pattern. The identification of two associations after a year of observation, with one characterized by filamentous algae, Hydrozoa and Cirripedia and another mainly by articulated calcareous algae, shows that divergent trajectories can be observed even under the same environmental conditions. As an important seasonal factor of the local oceanographic characteristics, the upwelling events allowed for an environmental heterogeneity, and rejecting the classic orderly and directional succession model.

SUCESIÓN DE MICROALGAS PERIFÍTICAS EN TRIBUTARIOS DEL RÍO GAIRA SIERRA NEVADA DE SANTA MARTA-COLOMBIA

<p class="Body">En ecosistemas acuáticos tropicales con altos niveles de intervención antrópica como algunos ríos de la Sierra Nevada de Santa Marta (SNSM) es de vital importancia la determinación del tipo de variables que permiten ponderar el buen estado o por el contrario, el nivel de impacto sufrido en estos ambientes con importancia ecológica y con vocación para ofrecer servicios de abastecimiento. Para este estudio se seleccionaron tributarios de la cuenca media del río Gaira (SNSM), se evaluó el proceso sucesional de microalgas perifíticas, desde enero hasta abril de 2012, mediante el análisis de la comunidad asociada a sustratos artificiales. El propósito del estudio fue analizar la variación en la estructura de la comunidad de microalgas perifíticas durante el proceso de sucesión y evaluar los factores ambientales que determinan esta variación en un rio tropical. Los resultados destacan el caudal, la luz y el oxígeno disuelto los cuales presentaron los valores más altos para el tributario C (Jabalí); el pH fue ligeramente básico para todos los sitios, la temperatura y conductividad presentaron valores más altos en el tributario A (Honduras). El análisis biológico mostró que durante las primeras semanas de exposición del sustrato <em>Melosira varians</em> y <em>Lyngbya </em>sp. fueron dominantes para los tributarios A y B (La Picúa), mientras que para el tributario C se registró una dominancia de <em>Fragilaria </em>sp, <em>Nitzschia</em> sp y <em>Melosira varians</em>. Semanalmente se evaluó la diversidad y riqueza de especies, los mayores valores se registraron después de la cuarta semana de colecta. En el estudio fueron más notorios los cambios en la densidad que en la composición de especies, a pesar de esto el proceso de sucesión fue completo y se evidenció la presencia de especies pioneras (<em>Lyngbya </em>sp, <em>Nitzschia</em> sp), intermedias (<em>Melosira varians</em>, <em>Cocconeis placentula</em>) y tardías (<em>Surirella </em>sp); al igual que la desaparición de especies como <em>Lyngbya </em>sp., proceso mediado por la consecuente aparición de algas tardías de mayor tamaño (<em>Surirella </em>sp).</p><p class="Body"><strong>ABSTRACT</strong></p><p class="Body">In tropical aquatic ecosystems with high levels of human intervention as some rivers in the Sierra Nevada de Santa Marta (SNSM) is vital to determine the type of variables that weigh the good condition or otherwise, the level of impact suffered these environments ecological importance and vocation to offer catering services. For this study were selected tributaries of the middle basin of Gaira (SNSM) River, the successional process periphytic microalgae was evaluated, from January to April 2012, by analyzing the community associated with artificial substrates. The purpose of the study was to analyze the variation in community structure of periphytic microalgae during the succession process and assess environmental factors that determine this variation in a tropical river. The results showed that the discharge, light and dissolved oxygen showed the highest values for the tax C (Jabalí Stream) the pH was slightly basic for all sites, temperature and conductivity showed the highest values for tax A (Honduras Stream). Biological analysis showed during the first weeks of substrate exposure that <em>Lyngbya</em> sp., and <em>Melosira varians</em> were dominant from A and B streams (Honduras and La Picúa), while for the tax C be a dominance of <em>Fragilaria</em> sp. was recorded, <em>Nitzschia</em> sp and <em>Melosira varians</em>. The highest values of diversity and richness were registered after the fourth week of collection. Changes in density were most noticeable than species composition. The successional process was complete and showed the presence of pioneer species (<em>Lyngbya</em> sp., <em>Nitzschia</em> sp), intermediate (<em>Melosira varians,</em> <em>Cocconeis placentula</em>) and late (<em>Surirella</em> sp.), as well as the disappearance of species Lyngbya sp. a process mediated by the consequent occurrence of late larger mycroalgae (<em>Surirella</em> sp.).</p><p class="Body"> </p>

Plant population processes in the course of forest succession in abandoned meadows. II. Demography of succession promotors

The studies on populations in the course of forest succession in abandoned meadows (15 ha) were conducted for 15 years (1974-1988). It was found that the population size of species which took part in the successional process either changed directionally, i.e. developmental phases of populations conformed to the succession stages, or fluctuated, when no direct relationship between both was determined. Three types of population dynamics were distinguished: 1) developmental cycle (increase, decrease and equilibrium in population size) lasted as long as forest comeback; 2) developmental cycle accompanied one successional phase; 3) species appeared in cycles, as a series of populations in the course of long-term succession. Following species groups were distinguished regarding their role in the vegetation transformation in unmown meadows: 1) long-term promotors, present throughout succession and affecting both, changes in meadow vegetation, and initiation of tall-herb and brushwood communities; 2) short-term promotors, present in the first successional phases, especially at the stage of transformation of meadow phytocoenoses; 3) stenoecious promotors, confined to various depressions, periodically or permanently overlogged. All succession promotors were characterized by: high fecundity, ability to form polycormones and clones, strong and long-lived underground organs, modification of lifecycles, dual reproductive mode.