A simple and cost-effective method for cable root detection and extension measurement in estuary wetland forests

This work presents the development of a low-cost method to measure the length cable roots of black mangrove (Avicennia germinans) trees to define the boundaries of central part of the anchoring root system (CPRS) without the need to fully expose root systems. The method was tested to locate and measure the length shallow woody root systems. An ultrasonic Doppler fetal monitor (UD) and a stock of steel rods (SR) were used to probe root locations without removing sediments from the surface, measure their length and estimate root-soil plate dimensions. The method was validated by comparing measurements with root lengths taken through direct measurement of excavated cable roots and from root-soil plate radii (exposed root-soil material when a tree tips over) of five up-rooted trees with stem diameters (D130) ranging between 10 and 50 cm. The mean CPRS radius estimated with the use of the Doppler was directly correlated with tree stem diameter and was not significantly different from the root-soil plate mean radius measured from up-rooted trees or from CPRS approximated by digging trenches. Our method proved to be effective and reliable in following cable roots for large amounts of trees of both black and white mangrove trees. In a period of 40 days of work, three people were capable of measuring 648 roots belonging to 81 trees, out of which 37% were found grafted to other tree roots. This simple method can be helpful in following shallow root systems with minimal impact and help map root connection networks of grafted trees

The coastal conservation narrative is shifting from crisis to ecosystem services

Conservation biology emerged as a crisis discipline in the twentieth century amongst an increasing awareness of pollution and habitat loss. Since the early 2000s, societal and monetary benefits of nature were added to the narrative for biodiversity conservation. Using text mining, we show that authors now favour ecosystem-services over a crisis framing in scientific publications on coastal habitats. This may signal a shift in conservation science from a crisis to a services discipline despite continuing habitat loss. We discuss whether authors should more critically assess what conservation narrative they deploy and what consequences this may have for conservation action

Change in drivers of mangrove crown displacement along a salinity stress gradient

1. Crown displacement in trees is an adaptive response driven by neighbours that optimizes space use and reduces competition. But it can also be the result of wind force. Although morphological responses to neighbours have been well studied, the interplay between neighbours and wind in driving crown shape, and the implications for plant interactions remain poorly understood. However, it is crucial to predict such changes in vegetation structure and function under the scope of global change. We test the hypothesis that aboveground interactions are reduced with increasing soil stress and that wind becomes the main driver of crown shape in mangrove forests. 2. We investigated the effect of neighbours and wind intensity and direction on crown displacement of mangrove canopy and below canopy trees along a salinity gradient, and assessed crown asymmetry for three mangrove tree species, as well as the contribution of crown displacement on reducing crown‐projected area overlap and thus neighbourhood competition. 3. Results show that crown displacement of canopy trees is strongly influenced by winds at all salinities. At low salinities, competition for space accounted for 48% of crown displacement away from neighbours, compared to 49% found for the synthetized effects of wind and neighbours. While trees below the canopy displace their crowns away from their neighbours, no response to wind could be detected. This can be due to the wind protection conferred by a dense canopy stand related to bigger crowns that effectively reduce wind drag. At higher salinities, there was a reduction in canopy overlap due to crown displacement, which suggests reduced aboveground plant interactions with increasing soil stress. 4. While neighbourhood avoidance is a fundamental strategy for optimal light foraging, this study shows that wind strength and directionality are main drivers of crown shape with increasing stress and highlights their potential influence in plant interactions and forest structure, pointing to an increased susceptibility of trees to disturbances that should be further studied

Pantropical variability in tree crown allometry

Aim Tree crowns determine light interception, carbon and water exchange. Thus, understanding the factors causing tree crown allometry to vary at the tree and stand level matters greatly for the development of future vegetation modelling and for the calibration of remote sensing products. Nevertheless, we know little about large‐scale variation and determinants in tropical tree crown allometry. In this study, we explored the continental variation in scaling exponents of site‐specific crown allometry and assessed their relationships with environmental and stand‐level variables in the tropics. Location Global tropics. Time period Early 21st century. Major taxa studied Woody plants. Methods Using a dataset of 87,737 trees distributed among 245 forest and savanna sites across the tropics, we fitted site‐specific allometric relationships between crown dimensions (crown depth, diameter and volume) and stem diameter using power‐law models. Stand‐level and environmental drivers of crown allometric relationships were assessed at pantropical and continental scales. Results The scaling exponents of allometric relationships between stem diameter and crown dimensions were higher in savannas than in forests. We identified that continental crown models were better than pantropical crown models and that continental differences in crown allometric relationships were driven by both stand‐level (wood density) and environmental (precipitation, cation exchange capacity and soil texture) variables for both tropical biomes. For a given diameter, forest trees from Asia and savanna trees from Australia had smaller crown dimensions than trees in Africa and America, with crown volumes for some Asian forest trees being smaller than those of trees in African forests. Main conclusions Our results provide new insight into geographical variability, with large continental differences in tropical tree crown allometry that were driven by stand‐level and environmental variables. They have implications for the assessment of ecosystem function and for the monitoring of woody biomass by remote sensing techniques in the global tropics

N2-fixation along a gradient of long-term disturbance in tropical mangroves bordering the gulf of Mexico

Microbial processes are key elements in determining the productivity of mangroves, and reductions in these processes reflect the loss of microbial biodiversity and function due to fabricated disturbances. Because nitrogen is a major limiting nutrient for the productivity of these ecosystems, the goal of this study was to determine profiles of inorganic nitrogen combined with several environmental parameters, all in relation to the degree of long-term hydraulic impairment of a tropical, monospecific black mangrove (Avicennia germinans) forest that showed degradation ranging from total loss of mangrove cover to no disturbance. N2-fixation, oxygen levels, and nitrite contents decreased significantly with the severity of the disturbance, and almost null levels were reached in the completely degraded zone, whereas salinity achieved very high values. Concomitantly, total N, ammonium, and P contents and ammonia volatilization increased significantly. Pore-water temperature and pH increased moderately. Other soil physical properties (sand, silt, clay, organic matter, and total C), which varied among the sampling sites, were not correlated with the level of disturbance. Principal component analyses, including environmental and biological parameters, suggested that the most significant finding was the considerable loss of N2-fixation with increasing impairment, which was concomitant with significant increases in volatilization of ammonia and salinity. The results show that microbial N-cycling processes are highly sensitive to salinity and to man-made disturbances that modify the water level and flow

Changes in allometric relations of mangrove trees due to resource availability – a new mechanistic modelling approach

Models based on allometric responses to competing neighbours and environmental conditions in mangrove forests are increasingly available. However, the improvement of these models requires a mechanistic understanding of how individual trees allocate biomass. This study introduces a new tree model (BETTINA) focusing on this issue. It is designed to investigate the response of trees in terms of biomass allocation patterns to environmental conditions. Additionally, it is suitable as a component of an individual-based mangrove stand model. BETTINA describes the plasticity of trees in growth patterns depending on their below-ground resource uptake. In contrast to the existing mangrove stand models, BETTINA focusses explicitly on the processes leading to variation in resource availability. Based on the physical principle of osmotic potential of solutions, the direct influence of salinity on plant water availability is considered. Allometric model parameters are not restricted to only the above-ground measures of trees’ traits (such as stem diameter and height), but also characterize below-ground biomass. Within BETTINA these measures are not limited to predefined empirical maximum values, but are the result of and depend on environmental conditions. The model is suitable to explain allometric measures and relations in dependence on total plant size and environmental conditions (for now salinity and light), and has a great potential for a physiologically and physically based improvement of plant component related biomass estimations

The coastal conservation narrative is shifting from crisis to ecosystem services

No abstract available

Macrozoobenthic community assemblage as key indicator for mangrove restoration success in North Sumatra and Aceh, Indonesia

The recognition of the high value of mangrove forests and the wide array of ecosystem services they provide has motivated investment in worldwide restoration efforts. However, current metrics of functional restoration (other than seedling survival rates and plant community composition) are often not readily available for local community managers, highlighting an urgency to identify easy-to-measure indicators to assess the functionality of restored mangroves. The macrozoobenthic community, could be such practical indicator, as macrozoobenthic communities are sensitive to changes in their environment, and can be easily surveyed within local managing programs. Focusing on three main mangrove management conditions (natural, planted and naturally regenerated) in North Sumatra and the province of Aceh, Indonesia, we compared vegetation and macrozoobenthic community diversity indices and identified environmental variables that best describe the forest management conditions and their associated macrozoobenthic community assemblage. Results showed that community assemblage, rather than macrozoobenthic diversity index, was associated with management conditions. The highest dissimilarity in macrozoobenthic community assemblages occurred between planted vs. natural mangroves, with non-significant dissimilarity between natural and naturally regenerated mangroves. The Lined Nerite gastropod (Nerita balteata) was identified as an indicator of natural mangroves, and the invasive Giant African snail (Achatina fulica), was abundant in mangrove plantations, but also in natural mangroves bordering harbors, oil palm plantations and aquaculture ponds, suggesting associated anthropogenic pressures. This study showed that the macrozoobenthic community can be used as restoration indicator and, could serve as a baseline to empower monitoring activities and community-based adaptive management practices to improve the outcomes of restoration efforts