Multi-site monitoring of heat stresses and micrometeorological conditions in the rice plants communities under various climates. The micrometeorological measurements system for a common measure of the paddy environments

Rice yield can be reduced substantially when the crop is exposed to excessive hest, which will likely occur more frequently under future climates, but the magnitudes of yield losses under open-field conditions are still difficult to predict, despite many efforts being conducted to detennine temperature response in the closed environments. To better understand the occurrence of heat stress under field conditions. we need thermal conditions of rice canopy under heat conditions, which can be very much different depending on other environmental factors, but taking correct measurements of canopy micrometeorology needs careful considerations. In this study, we will distribute a simple but well-designed system for measuring thermal environments of the canopy to different rice growing regions covering continental and coastal climates in low and mid latitude regions. With them, we attempt to establish a monitoring network of canopy thermal environments in the paddy fields that will help to bridge gaps between chamber and open-field and to better assess potential impacts of climate change on rice production. Keyword.: Canopy heat budget, Climate change, Micrometeorology, Multi-lateral research network, Rice. (Résumé d'auteur

The impact of lianas on tree regeneration in tropical forest canopy gaps: evidence for an alternative pathway of gap‐phase regeneration

1 Regeneration in forest canopy gaps is thought to lead invariably to the rapid recruitment and growth of trees and the redevelopment of the canopy. Our observations, however, suggest that an alternate successional pathway is also likely, whereby gap‐phase regeneration is dominated by lianas and stalled in a low‐canopy state for many years. We investigated gap‐phase regeneration in an old‐growth tropical forest on Barro Colorado Island (BCI) in Panama to test the following two hypotheses: (i) many gaps follow a pathway in which they remain at a low canopy height and are dominated by lianas and (ii) the paucity of trees in this pathway is a function of liana density. 2 We surveyed a total of 428 gaps of varying ages (c. 5, c. 10, and 13+ years old) and identified those which followed the conventional pathway of regeneration and others that remained stalled in a low‐canopy state for many years and were dominated by either lianas or palms. Each of these pathways will likely have different successional trajectories that will favour the growth of a distinct suite of mature species and ultimately result in contrasting species composition. 3 The successional pathway of liana‐dominated, stalled gaps is common throughout the forest. We estimate conservatively that 7.5% of the gaps that form each year will follow this pathway, probably due to the suppression of tree regeneration by lianas, and that many of these stalled gaps will persist for much longer than 13 years. Consequently, a high proportion of gaps in the forest at any given time will be stalled. Furthermore, liana tangles, which persist in the tropical forest understorey for extended periods of time, almost certainly originate in these gaps. 4 Liana abundance was positively correlated with pioneer tree abundance and diversity while negatively correlated with non‐pioneer tree abundance and diversity. Thus, lianas appear to inhibit non‐pioneer tree survival while indirectly enhancing that of pioneer trees. 5 Lianas are abundant in many types of tropical and temperate forests and a successional pathway involving liana‐dominated, stalled gaps may therefore be frequent and widespread

A remote sensing tool for logging-related canopy gap detection : method and applications

Monitoring the logging impacts is essential to ensuring the sustainability of forest management under a certification process. Control tools need to be put in place in order to achieve these objectives. The use of remote sensing to detect canopy gaps in tropical rainforests is an attractive alternative to ground surveys, which are laborious to carry out and lack precision. In French Guiana, detection of logging-related gaps using very high spatial resolution optical satellite images produced by the SPOT 5 sensor is carried out by ONF (French National Forestry Agency). Gaps are detected using an automatic segmentation method. The principle of the automation is to model the forest's signature and calculate a divergence between that theoretical signature and the image histogram in order to detect gaps that constitute a deterioration of forest cover. This tool has been used to assess the quality of logging operations at different scales: forests, blocks, local (onehectare- pixels). Results show that canopy opening is quite independent from logging intensity at the blocks scale but well correlated at the local scale. The relief shows also a significant influence on the canopy degradation. (Résumé d'auteur

Differential Effects of Understory and Overstory Gaps on Tree Regeneration

Gaps in the forest canopy can increase the diversity of tree regeneration. Understory shrubs also compete with tree seedlings for limited resources and may depress tree recruitment. We compared effects of shrub removal and canopy windthrow gaps on seedling recruitment and understory resource levels. Shrub removal, with the canopy left intact, was associated with increased levels of understory light and soil moisture and coincided with increased species richness and diversity of tree regeneration compared to both control plots and canopy gaps. Canopy windthrow gaps, however, resulted in a more than 500 fold increase in soil nitrate concentrations, and seedling growth rates that were twice as high as that observed with shrub removal. Our results suggest that gaps in the understory shrub layer and the overstory canopy may have complementary effects on resource availability with corresponding benefits to seedling establishment and growth

Avoidance of Canopy Gaps by a Common Land Snail

Because canopy gaps are characterized by elevated temperature and decreased humidity relative to closed-canopy forest, terrestrial gastropods may be exposed to greater desiccation stress in gaps than in undisturbed forest. We placed individuals of Caracolus caracolla at the edges of canopy gaps in montane forest in Puerto Rico and observed their movements. Individuals preferentially moved out of gaps except in one gap on the first night of the study, and the proportion of individuals recaptured inside gaps decreased over time. Individuals moved, on average, farther into forest than into gaps. Juveniles and adults responded similarly. These results suggest that C. caracolla actively avoids canopy gaps, and that its activity and ability to disperse are restricted in a post-disturbance environment

Comparison of four different programs for the analysis of hemispherical photographs using parameters of canopy structure and solar radiation transmittance

There have been many studies involving the use of hemispherical photographs to indirectly estimate canopy structures and forest light environments. A variety of commercial and free software packages are available for the analysis of hemispherical photographs. The costs of investment might represent an advantage of the free programmes over the commercial, but as yet little has been documented about the differences in their outputs and in the technical applications from a user (ecologist and forester) perspective. The objective of the study was to compare the canopy structure variables (canopy openness and effective plant area index) and solar radiation transmission estimates (direct, diffuse and global solar radiation transmittances) from digital hemispherical photographs taken under two forest canopy conditions (gap and closed canopy) in three different broadleaf forest regions (Chile, Germany, Venezuela) and calculated using four different programmes. The hemispherical photographs were analysed using one commercial (HemiView) and three free programmes (Gap Light Analyzer, hemIMAGE and Winphot). The results obtained revealed that all of the programmes computed similar estimates of both canopy structures and below-canopy solar radiation. Only the results relating to the effective plant area index with an ellipsoidal leaf angle distribution made with HemiView and Winphot deviated significantly. Other user aspects are also discussed, such as costs, image formats, computer system requirements, etc.In vielen Studien werden Hemisphärenphotos genutzt um indirekt die Kronenstruktur und die Belichtungsverhältnisse zu schätzen. Verschiedene kommerzielle und kostenfreie Softwarepakete sind zu Analyse von Hemisphärenphotos verfügbar. Es gibt bisher keine umfassende Vergleichsstudie zu Ergebnissen oder technischer Handhabung aus Sicht der Nutzer dieser Programme (Ökologen und Forstwissenschaftler). Das Ziel dieser Studie war der Vergleich der Schätzungen von Kronenstrukturvariablen (Kronenöffnung und effektiver Pflanzenflächenindex) Solartransmission (direkte, diffuse und Global-Strahlung) aus digitalen Hemisphärenphotos berechnet mit vier verschiedenen Programmen (kostenpflichtig: Hemi- View und frei: Gap Light Analyzer, hemIMAGE and Winphot). Die verwendeten Photos stammen aus drei verschiedenen Laubwaldregionen (Chile, Deutschland und Venezuela) und repräsentieren jeweils Verhältnisse unter geschlossenem Kronendach und in Lücken. Die ermittelten Schätzungen für die verschiedenen Strukturvariablen und Einstrahlungsverhältnisse zeigten eine sehr hohe Übereinstimmung. Einzig der effektive Pflanzenflächenindex basierend auf ellipsoider Blattwinkelverteilung unterschied sich signifikant zwischen den Programmen. Weitere für Nutzer interessante Aspekte wie Kosten, Bildformate, Systemvoraussetzungen und mehr wurden verglichen und diskutiert

Stand-level drivers of tree-species diversification in Mediterranean pine forests after abandonment of traditional practices

The progressive abandonment of traditional forest management over the last few decades has led to significant densification processes in most Mediterranean pine stands. In parallel, some of these stands have also shown tree-species diversification processes, the occurrence of which is considered essential for future adaptability and resilience to change. Here we aim to gain further understanding of the main factors driving these diversification processes via a case-study approach using the long-term-managed black pine (Pinus nigra Arn. ssp. salzmannii) forests of the Catalan Pre-Pyrenees (NE Spain). For this purpose, we sampled 155 plots distributed in 8 different stands and analyzed the role played by a number of microsite factors and stand attributes (including canopy openness and heterogeneity) on the abundance of seedlings (h 1.3 m; dbh < 7.5 cm) of the main tree-species in the area (i.e. black pine, evergreen oak and marcescent oaks). Results revealed ongoing black pine recruitment limitation processes mainly associated to the high canopy cover of the overstory and the increasing abundance of shrubs, which may compete with pines for light resources. In contrast, we found that current environmental and stand-level conditions favor the progressive advance of the recruitment of evergreen and marcescent oaks, which are able to establish successfully under the dominant pine canopy. However, in the absence of canopy openings, light levels may not allow the established oaks (in particular the evergreen Quercus ilex) to grow and progress to higher developmental stages. Our findings bring deeper insight into the role of stand-level factors regulating species diversification, and can be used by forest managers to adjust their practices (e.g. by modifying the spatial and temporal patterns of silvicultural treatments such as thinnings or selection cuttings) in order to favor this natural process and increase stand resilience.This research was primarily supported by the Spanish Ministry of Science and Innovation via the RESILFOR project (AGL2012-40039-C02-01). It also was part of a cooperation agreement between the Forest Sciences Center of Catalonia and the Institut Cartogràfic i Geològic de Catalunya (ICGC) frameworking wider use of aerial remote-sensing data for forest characterization. The Catalan Agency for Management of University and Research Grants provided S.M.A. with support through a ‘pre-doctoral’ grant (FI-DGR) and the Spanish Ministry of Science and Innovation provided L.C. with support through post-doctoral ‘Ramon y Cajal’ contracts. This work benefited from a short-term scientific mission grant provided by the COST Action EuMIXFOR (FP1206) to SMA, and from the Erasmus Mundus Master Course Mediterranean Forestry and Natural Resources Management (MEDfOR) which provided support to SS

Determination of the best canopy gap area on the basis of soil characteristics using the Analytical Hierarchy Process (AHP)

The assessment of canopy gap areas on the basis of soil characteristics in forest ecosystems could be one of benefit points for management of forests. This research was conducted in 20 ha areas of Experimental Forest Station of Tarbiat Modares University that is located in a temperate forest of Mazandaran province in the north of Iran. Twenty one canopy gaps with different areas were found in studied areas and classified as small (85.12 m2), medium (325.21 m2), large (512.11 m2) and very large (723.85 m 2) gaps. These areas classes of canopy gaps were assessed with respect to nine criteria (soil pH, carbon to nitrogen ratio, cation exchange capacity, phosphorus, potassium, calcium, nitrogen mineralization, microbial respiration and earthworm's biomass). Soil samples (0-45 cm depth from the gap center and edge positions) were measured in the laboratory. The Analytical Hierarchy Process (AHP) was used for assessment of canopy gap areas. This method is widely used the Multiple Criteria Decision Support (MCDS) method and perhaps the most popular in many fields, including natural resource management, especially in forest sciences. Results of AHP indicate that the maximum of local priority belongs to small areas of canopy gaps when considering all soil characteristics. However, medium, large and very large canopy gap areas have priorities, respectively. The calculated overall priority showed that with respect to considered criterias, small and medium gap areas have higher, more ideal condition in comparison to large and very large areas. AHP results emphasise that considering soil characteristics canopy gap areas should be less than 400 m2 in Hyrcanian forests of Iran. Also, AHP can be introduced as an effective instrument in decision-making processes for investment planning and prioritization in compliance with environmental regulations

Solar Radiation Transfer Through a Subarctic Shrub Canopy

Much of the low Arctic is covered with shrubs that are partially buried by snow in winter and become exposed during melt. This study presents measurements and modeling of shortwave radiation reflection and extinction by a deciduous shrub canopy emerging from a melting snowcover in the mountains of the Yukon Territory, Canada. Shrubs shade most of the snow surface at low solar elevation angles, so only a fraction of the incoming radiation reaches the surface, but there is greater direct shortwave transmission to the surface in gaps between shrubs for higher solar elevations. A simple model is developed to incorporate the changing contributions of sun-lit gaps, shaded gaps, and shrubs to the landscape-averaged (areal) transmission and reflection of shortwave radiation. The areal transmissivity and albedo in this model are lower than in a two-stream approximation that neglects gap shading. A simple shadow parameterization is proposed for calculating shrub tundra snowmelt rates and surface energy balances in hydrological and land-surface models

Testing Ecological Theory with Lianas

Lianas constitute a diverse polyphyletic plant group that is advancing our understanding of ecological theory. Specifically, lianas are providing new insights into the mechanisms that control plant distribution and diversity maintenance. For example, there is now evidence that a single, scalable mechanism may explain local, regional, and pan‐tropical distribution of lianas, as well as the maintenance of liana species diversity. The ability to outcompete trees under dry, stressful conditions in seasonal forests provides lianas a growth advantage that, over time, results in relatively high abundance in seasonal forests and low abundance in aseasonal forests. Lianas may also gain a similar growth advantage following disturbance, thus explaining why liana density and diversity peak following disturbance at the local, forest scale. The study of ecology, however, is more than the effect of the environment on organisms; it also includes the effects of organisms on the environment. Considerable empirical evidence now indicates that lianas substantially alter their environment by consuming resources, suppressing tree performance, and influencing emergent properties of forests, such as ecosystem functioning, plant and animal diversity, and community composition. These recent studies using lianas are transcending classical tropical ecology research and are now providing novel insights into fundamental ecological theory