Assessing mangrove species diversity, zonation and functional indicators in response to natural, regenerated, and rehabilitated succession.

The United Nations Decade on Ecosystem restoration (2021¬-2030) lists mangrove ecosystems as a restoration priority. Interest in their conservation has increased recently due to their widespread degradation. Anthropogenic stressors and rehabilitation practices, specifically, have resulted in a significant decline in their species compositions. We investigated the knowledge gaps in terms of potential spatial diversity, intertidal zonation, and the historic state of mangrove forest species, and tested the role of environmental factors such as topography, as well as rehabilitation practices on diversity. Diversity and complexity indices, surface elevation, and species and structural diversities along three simplified transect lines over a broad geographical area and under various management practices were analyzed in Trat province, Thailand. Quantitative statistical zonation analyses within each transect and at the landscape-scale were performed using randomization tests and hierarchical cluster analysis. A modified "automatic regrowth monitoring algorithm (ARMA)," based on Landsat (1987-2020) and Sentinel-2 MSI (2015-2020) annual median composites was also used. Fifteen species were identified, with Ceriops tagal as the dominant species. Statistical analysis, however, failed to identify any significant zonation patterns at transect or landscape-scales at specific elevations. Rehabilitated and naturally regenerated stands showed gradual increases in their Normalized Difference Infrared Index over time. After 30 years, the rehabilitated stands made up of Rhizophoraceae monocultures were the same height as the adjacent natural stands. Depending on the location and propagule availability, the diversity and structure of regenerated stands exhibited high variation. Effluent from shrimp farms may have contributed to the disturbance of the forest stands and changes in shrimp farming practices could have facilitated their recovery. The results of the present study provide a valuable diversity baseline for the study site and secondary succession in rehabilitated and regenerated mangroves. The ARMA algorithm has also been confirmed as a valuable tool for future investigations of secondary succession and mangrove biodiversity status.

Predators, Prey and Habitat Structure: Can Key Conservation Areas and Early Signs of Population Collapse Be Detected in Neotropical Forests?

Tropical forests with a low human population and absence of large-scale deforestation provide unique opportunities to study successful conservation strategies, which should be based on adequate monitoring tools. This study explored the conservation status of a large predator, the jaguar, considered an indicator of the maintenance of how well ecological processes are maintained. We implemented an original integrative approach, exploring successive ecosystem status proxies, from habitats and responses to threats of predators and their prey, to canopy structure and forest biomass. Niche modeling allowed identification of more suitable habitats, significantly related to canopy height and forest biomass. Capture/recapture methods showed that jaguar density was higher in habitats identified as more suitable by the niche model. Surveys of ungulates, large rodents and birds also showed higher density where jaguars were more abundant. Although jaguar density does not allow early detection of overall vertebrate community collapse, a decrease in the abundance of large terrestrial birds was noted as good first evidence of disturbance. The most promising tool comes from easily acquired LiDAR data and radar images: a decrease in canopy roughness was closely associated with the disturbance of forests and associated decreasing vertebrate biomass. This mixed approach, focusing on an apex predator, ecological modeling and remote-sensing information, not only helps detect early population declines in large mammals, but is also useful to discuss the relevance of large predators as indicators and the efficiency of conservation measures. It can also be easily extrapolated and adapted in a timely manner, since important open-source data are increasingly available and relevant for large-scale and real-time monitoring of biodiversity.

Vegetation structure and greenness in Central Africa from Modis multi-temporal data.

African forests within the Congo Basin are generally mapped at a regional scale as broad-leaved evergreen forests, with the main distinction being between terra-firme and swamp forest types. At the same time, commercial forest inventories, as well as national maps, have highlighted a strong spatial heterogeneity of forest types. A detailed vegetation map generated using consistent methods is needed to inform decision makers about spatial forest organization and their relationships with environmental drivers in the context of global change. We propose a multi-temporal remotely sensed data approach to characterize vegetation types using vegetation index annual profiles. The classifications identified 22 vegetation types (six savannas, two swamp forests, 14 forest types) improving existing vegetation maps. Among forest types, we showed strong variations in stand structure and deciduousness, identifying (i) two blocks of dense evergreen forests located in the western part of the study area and in the central part on sandy soils; (ii) semi-deciduous forests are located in the Sangha River interval which has experienced past fragmentation and human activities. For all vegetation types enhanced vegetation index profiles were highly seasonal and strongly correlated to rainfall and to a lesser extent, to light regimes. These results are of importance to predict spatial variations of carbon stocks and fluxes, because evergreen/deciduous forests (i) have contrasted annual dynamics of photosynthetic activity and foliar water content and (ii) differ in community dynamics and ecosystem processes.

Causes and consequences of a tropical forest gold rush in the Guiana Shield, South America.

Statistical and spatial analyses of both historical time series and remotely sensed data show a link between the spatial distribution and growth of gold production across the Guiana Shield in northeast Amazonia. Results indicate that an exponential rise in production across an expanding area is primarily a delayed response to the 1971-1978 market flotation of international gold prices. The subsequent 10-fold (2-fold) average nominal (real) price increase has provided a compelling economic incentive to mass exploitation of lower-grade gold deposits. The ground-based and remotely sensed distributions of mining activity are strongly attached to these deposits that dominate the region's gold geology. The presence of these gold-bearing formations in conservation and sustainable timber zones has sparked social conflict and environmental degradation across the region. Left unmanaged, more than a quarter-million square-kilometer area of tropical forest zoned for protection and sustainable management could ultimately be compromised by the price-driven boom in gold mining through poorly integrated resource use planning, lack of reclamation effort, and control of illegal operations. Serious public health issues propagated through the unregulated mining environment further erode the financial benefits achieved through gold extraction. This study demonstrates in part how international economic policies successfully stabilizing more conspicuous centers of the global economy can have unintended but profound environmental and social impacts on remote commodity frontiers.

Seasonal variations in leaf area index, leaf chlorophyll, and water content; scaling-up to estimate fAPAR and carbon balance in a multilayer, multispecies temperate forest.

Seasonal differences in phenology between coniferous and deciduous tree species need to be considered when developing models to estimate CO(2) exchange in temperate forest ecosystems. Because seasonal variations in CO(2) flux in temperate forests are closely correlated with plant phenology, we quantified the phenology of forest species in a multilayered forest with patches of Scots pine (Pinus sylvestris L.) and oak (Quercus robur L.) in Brasschaat, Belgium. A scaling-up modeling approach was developed to simulate reflectance at the leaf and canopy scales over a one-year cycle. Chlorophyll concentration, water content, specific leaf area and leaf area index of the forest species were measured throughout an entire year (1997). Scaling-up from the leaf to canopy was achieved by linking the PROSPECT and SAIL models. The result is the annual progression of the fraction of absorbed photosynthetically active radiation (fAPAR) in a 1 km(2) forest area, which can be directly related to high-resolution, remotely sensed data.