Remote Sensing of Vegetation: Potentials, Limitations, Developments and Applications

Assessing the fragility of forest remnants by using landscape metrics. Comparison between river basins in Brazil and Portugal

The environmental vulnerability of a landscape is directly associated with any physical, geomorphological, and spatial factors which directly interfere with the ecological functionality of natural areas. Therefore, the composition, diversity, and structure of fragmented forest areas are essential to identify the patterns in the landscape and propose the most appropriate management measures for its conservation. The present study set out to analyse the applicability of landscape metrics for assessing the environmental fragility of forest remnants of different geographical conditions and phyto-physiognomies. This would contribute to landscape assessment and the diagnosis of remnants, and support decision making for strategic and effective environmental planning. The study areas selected were two river basins, the Atibaia river basin in Brazil, and the Cértima river basin in Portugal. The maps used as a basis for the selection of the forest remnants analysed were made available by public managers and date from 2015 for both basins. The analyses were performed with GIS software, and two groups of landscape metrics were considered: the first applied to the general landscape of the basin and the second applied to each remaining forest patch as a landscape unit. At the remaining forest level, the metrics analysed were the area, central area index, circularity index, shape index, distance from the nearest neighbour, proximity of the remnant to the road network, and proximity to the watercourse. The results showed that there are many remnants in both basins with predominantly small size and located close to each other. However, their fragilities vary in each basin, indicating that the applied metrics are effective tool for the preliminary diagnosis of natural vegetation remnants in areas with different geospatial and phyto-physiognomic conditions. Therefore, the results obtained are of great importance as a basis for formulating landscape development policies, by integrating appropriate land management strategies.

Canopy leaf area index at its higher end: dissection of structural controls from leaf to canopy scales in bryophytes

There is evidence that mosses with miniature foliage elements have extremely large leaf area index (LAI) values, but it is unclear what canopy traits are responsible for these high LAI values in architecturally divergent mosses, and how the inherent trade-offs limiting maximum LAI in vascular plants can be overcome in mosses. To determine the quantitative significance of different traits in determining LAI, we developed a method to dissect LAI into underlying functionally dependent constituent traits at leaf, shoot and canopy scales. The suites of structural traits were studied altogether for 43 moss canopies from 11 species with contrasting light and water requirements along gap-understory gradients to obtain as large a range of variation in moss architecture as possible and evaluate the differentiation in moss LAI in relation to species ecology. Extensive variation in moss structural traits, 11- (shoot length) to 77-fold (shoot number per area, NS¯ ), was observed at all structural scales from leaf to canopy. However, LAI only varied nine-fold, as the result of two key trade-offs: leaf size vs number trade-off and shoot leaf area vs shoot density trade-off. Owing to these negative relationships, and greater variability in NS¯ , LAI primarily scaled with NS¯ . NS¯ and LAI increased with site light availability, and LAI was greater in open and dry habitat species. This study highlights a huge structural diversity among moss canopies, but indicates that canopies converge to a much narrower range of LAI due to trait trade-offs such that, counterintuitively, minute leaf size and densely leafed stems are not necessarily responsible for high LAI in mosses.

Weighing trees with lasers: advances, challenges and opportunities

Terrestrial laser scanning (TLS) is providing exciting new ways to quantify tree and forest structure, particularly above-ground biomass (AGB). We show how TLS can address some of the key uncertainties and limitations of current approaches to estimating AGB based on empirical allometric scaling equations (ASEs) that underpin all large-scale estimates of AGB. TLS provides extremely detailed non-destructive measurements of tree form independent of tree size and shape. We show examples of three-dimensional (3D) TLS measurements from various tropical and temperate forests and describe how the resulting TLS point clouds can be used to produce quantitative 3D models of branch and trunk size, shape and distribution. These models can drastically improve estimates of AGB, provide new, improved large-scale ASEs, and deliver insights into a range of fundamental tree properties related to structure. Large quantities of detailed measurements of individual 3D tree structure also have the potential to open new and exciting avenues of research in areas where difficulties of measurement have until now prevented statistical approaches to detecting and understanding underlying patterns of scaling, form and function. We discuss these opportunities and some of the challenges that remain to be overcome to enable wider adoption of TLS methods.