Canopy Level Research Articles

Effects of different pollinators and herbivores on the fruit set height of the mammal-pollinated tree-climbing vine Mucuna macrocarpa

ABSTRACT Although different flower-visiting frequencies and behaviors are known to cause differences in fruit set rates, the effects of different pollinators on the fruit set position are unclear. The climbing vine Mucuna macrocarpa (Fabaceae) needs mammalian pollinators for fruit set. This species is widely distributed in Asia and is pollinated by different mammals in different regions. This study assessed the effects of different pollinators, including their ability to fly, and of herbivores on the fruit set height of M. macrocarpa. The heights of inflorescences and fruits were measured in Kyushu, Okinawa-jima Island (Okinawa), Taiwan, and Thailand. Flying mammalian pollinator (bat) activity was recorded in Okinawa, and non-flying mammalian pollinator activity was recorded in the other three regions. The flowers were observed from the ground to canopy levels in all regions; no fruits were observed at the ground level on Okinawa, whereas fruits were observed from the ground to the canopy levels in Kyushu, Taiwan, and Thailand. In Kyushu, however, fruits were less frequently observed at the ground level. Although pollinators visited flowers located near the ground level, camera traps frequently recorded sika deer (Cervus nippon) feeding on the flowers and fruits near the ground level. Our data show that both the flying ability of pollinators and the density of large-sized herbivores affect the fruit set position.

Upscaling seasonal phenological course of leaf dorsiventral reflectance in radiative transfer model

Forest top-of-canopy (TOC) reflectance observed by remote sensing instruments is driven by a wide range of parameters, including optical properties of leaves being the major driver, understory and bark together with structural properties of the forest - spatial distribution of leaves and branches in the canopy contributing also to variable extent. In addition, the instantaneous observation geometry (e.g. the sun and sensor zenith and azimuth angles) largely influences the observed TOC reflectance due to the changes in shadow fraction in the canopies. As a result, forest TOC reflectance is highly dynamic, following the seasonal patterns of optical and structural properties of vegetation.From the above-mentioned factors, the leaf optical properties are the most important. They hold an information on leaf biochemical (e.g. chlorophyll and carotenoid contents), water content and structural (e.g., leaf thickness, distribution of pigments within a leaf) properties at the leaf-level. Whereas biochemical effects on leaf reflectance are well understood, the role of dorsiventral asymmetry leaf internal structure on two-sided leaf optical properties has not been paid much attention, assuming equal optical properties on both leaf sides. However, the internal structure of a dorsiventral leaf is highly asymmetric often having different surface structure, tissue density and pigment distribution. Moreover, leaf optical properties are rarely measured during phenological development with high time resolution. Typically, studies focus on peak growing season neglecting the dynamic seasonal change of optical properties for broadleaved vegetation of temperate forests.In this study, we measured the seasonal course of leaf-level two-sided optical properties, biochemical and structural traits of five common broadleaved tree species of Central Europe (Betula pendula, Fagus sylvatica, Acer pseudoplatanus, Acer platanoides, and Sorbus aucuparia) with a typical dorsiventral, leaf anatomy without heliotropism. We link their leaf optical properties (e.g. reflectance difference of adaxial and abaxial sides, reflectance to transmittance ratio, fraction of specular component of leaf reflectance) with the laboratory analyses of inner leaf structure for contrasting leaf phenological stages from spring to fall. This allowed us to quantify both, species and seasonal differences of leaf dorsiventral optical properties and the role of inner leaf structure on leaf dorsiventral optical properties. Next, we up-scaled measured leaf-level dorsiventral optical properties to canopy level using Discrete Anisotropic Radiative Transfer model (DART) for three contrasting seasonal phenological stages - early spring (day of the year; DOY 115), summer (DOY 212) and fall (DOY 285). The aim was to quantify the impact of leaf optical properties parametrization (i.e. assuming equal optical properties on both sides, or dorsiventral leaf optical properties asymmetry) for forest of different species composition, vegetation phenological stage and observation geometries. The biggest differences between simulations were observed in VIS and NIR regions, where the neglecting differences in abaxial side leaf reflectance may introduce relative difference up to 20%, causing the underestimation of “one-sided” scenario compared to “two-sided” one, especially for off-nadir backscattering viewing directions. This may lead to increase in uncertainty when interpreting remote sensing observations, namely the chlorophyll content retrievals from back-scattering observation geometries and canopy structural retrievals (e.g. leaf area index) for all viewing geometries. We, thus, suggest to account for leaf reflectance dorsiventral differences in the next generation of radiative transfer models.

Warming Change Nutritional Status and Improve Stylosanthes capitata Vogel Growth Only Under Well-Watered Conditions

Climate change may impact plant nutritional status and productivity. However, few studies evaluate the effects of global change variables on tropical forage species under field conditions. In this study, we evaluated the isolated and combined effects of warming and drought on nutritional status and its relations with net photosynthesis rate and aboveground dry mass production of Stylosanthes capitata, a C3 tropical forage legume under field conditions. We tested two canopy temperature levels, ambient (Ta) and elevated temperatures (2 °C above ambient temperature, Te), and two soil moisture levels, irrigated (plants maintained at 80% of soil field capacity, I) and drought (D). The experiment was conducted in a randomized complete block design with three replicates in a 2 × 2 factorial scheme. Our results showed that warming decreased leaf N and P content, while leaf K content increased, leading to an increase in C:P and C:N ratios and dry mass production. Drought increased leaf K content, and decreased leaf N content, leading to an increased C:N ratio and decreased dry mass. No changes were observed for leaf C, Ca, Mg, and S content due to our treatments. In addition, regression analysis showed that changes in leaf nutrient contents were not associated with changes in the net photosynthesis rate, except for leaf N content in the combined warming and drought treatment. Our short-term experiment indicates that although biomass production will not be modified under a combination of warming and drought, both environmental factors may negatively impact the animal feeding and livestock in the future due to a decreased leaf N and P content.

Re-absorption and scattering of chlorophyll fluorescence in canopies: A revised approach

The measurement of chlorophyll fluorescence in remote way represents a tool that is becoming increasingly important in relation to the diagnosis of plant health and carbon budget on the planet. However, the detection of this emission is severely affected by distortions, due to processes of light re-absorption both in the leaf and in the canopy. Even though some advances have been made to correct the signal in the far-red, the whole spectral range needs to be addressed, in order to accurately assess plant physiological state. In 2018, we introduced a model to obtain fluorescence spectra at leaf level, from what was observed at canopy level. In this present work, we publish a revision of that physical model, with a more rigorous and exact mathematical treatment. In addition, multiple scattering between the soil and the canopy, and the fraction of land covered by vegetation have also been taken into consideration. We validate this model upon experimental measures, in three types of crops of agronomic interest (Pea, Rye grass and Maize) with different architecture. Our model accurately predicts both the shape of fluorescence spectra at leaf level from that measured at canopy level and the fluorescence ratio. Furthermore, not only do we eliminate artifacts affecting the spectral shape, but we are also able to calculate the quantum yield of fluorescence corrected for re-absorption, from the experimental quantum yield at canopy level. This represents an advance in the study of these systems because it offers the opportunity to make corrections for both the fluorescence ratio and the intensity of the observed fluorescence.

Phosphorus allocation to and resorption from leaves regulate the residence time of phosphorus in above‐ground forest biomass on Mount Kinabalu, Borneo

Abstract The residence time of phosphorus (P) in trees is a consequence of plant adaptation to P deficiency, with longer P residence time on soils with low P availability. P residence time has been studied at the leaf or canopy level but seldom at the whole‐tree level. Whereas P residence time at the leaf or canopy level is largely determined by leaf longevity and the resorption of P before leaf abscission, P residence time at the whole‐tree level will also be influenced by differences in P allocation to different plant parts because leaves and woody organs have distinct longevities. We estimated the residence time of P in above‐ground tree biomass (AGB) as the ratio of P mass (i.e. leaves plus wood) to the annual flux of P via litterfall (i.e. fine litter plus coarse woody debris) for seven tropical rain forests with different soil P availabilities on Mount Kinabalu, Borneo. We analysed the effects of P allocation to and resorption from leaves on P residence time along a soil P gradient. P residence time (2.7–9.8 years) was approximately one‐fifth of biomass residence time (AGB/annual litterfall mass; 19.8–48.8 years). This was due to a disproportionately greater relative allocation of P to leaves (P mass in leaves/P mass in AGB; 0.11–0.46), which had a smaller fraction of biomass (leaf biomass/AGB; 0.02–0.05) but a shorter longevity (1.0–1.8 years). The relative allocation of P to leaves was often high on low‐P soils, and P residence time was expected to be short. By contrast, the resorption rate of P from leaves was also high on low‐P soils, which extended P residence time with P deficiency. Consequently, P residence time was nearly constant across the forests. The short residence time of P relative to biomass indicates that P residence time depends largely on relative P allocation among plant organs. Similar P residence times among sites were maintained because greater P allocation to leaves on low‐P soils was effectively offset by higher P‐resorption efficiency. A free Plain Language Summary can be found within the Supporting Information of this article.

Remotely-sensed assessment of the impact of century-old biochar on chicory crop growth using high-resolution UAV-based imagery

In recent years, special attention has been given to the long-term effects of biochar on the performance of agro-ecosystems owing to its potential for improving soil fertility, harvested crop yields, and aboveground biomass production. The present experiment was set up to identify the effects on soil-plant systems of biochar produced more than 150 years ago in charcoal mound kiln sites in Wallonia (Belgium). Although the impacts of biochar on soil-plant systems are being increasingly discussed, a detailed monitoring of the crop dynamics throughout the growing season has not yet been well addressed. At present there is considerable interest in applying remote sensing for crop growth monitoring in order to improve sustainable agricultural practices. However, studies using high-resolution remote sensing data to focus on century-old biochar effects are not yet available. For the first time, the impacts of century-old biochar on crop growth were investigated at canopy level using high-resolution airborne remote sensing data over a cultivated field. High-resolution RGB, multispectral and thermal sensors mounted on unmanned aerial vehicles (UAVs) were used to generate high frequency remote sensing information on the crop dynamics. UAVs were flown over 11 century-old charcoal-enriched soil patches and the adjacent reference soils of a chicory field. We retrieved crucial crop parameters such as canopy cover, vegetation indices and crop water stress from the UAV imageries. In addition, our study also provides in-situ measurements of soil properties and crop traits. Both UAV-based RGB imagery and in-situ measurements demonstrated that the presence of century-old biochar significantly improved chicory canopy cover, with greater leaf lengths in biochar patches. Weighted difference vegetation index imagery showed a negative influence of biochar presence on plant greenness at the end of the growing season. Chicory crop stress was significantly increased by biochar presence, whereas the harvested crop yield was not affected. The main significant variations observed between reference and century-old biochar patches using in situ measurements of crop traits concerned leaf length. Hence, the output from the present study will be of great interest to help developing climate-smart agriculture practices allowing for adaptation and mitigation to climate.

Role of thinning intensity in creating mixed hardwood and conifer forests within a Cryptomeria japonica conifer plantation: A 14-year study

For managers of conifer plantations, conversion to mixed hardwood and conifer forests is an important management goal. However, the extent to which thinning intensity affects stand volume and timber quantity and quality remains unclear. We investigated the growth of conifer and hardwood trees over 14 years (at 5 and 9 years after the first and second thinning operations, respectively) under unthinned (Control), 33% thinned (Weak), and 67% thinned (Intensive) treatments in a Cryptomeria japonica plantation. The diameter growth of both conifers and hardwoods, stand volume of hardwoods, and relative increment of stand volume of conifers increased with greater thinning intensity in the order of Control < Weak < Intensive, whereas the reverse was observed for the stand volume of conifers, dead conifer trees, and total yield of stand volume (i.e., gross production). These results suggest that intensive thinning can create large conifers and hardwoods, but reduces gross production. Mean annual tree ring width (ATRW), consistency of ATRW value, and mean crown ratio increased with increasing thinning intensity in the order of Control < Weak < Intensive, while height-to-diameter ratio (i.e., slenderness) showed the opposite trend. These findings suggest that timber quality (e.g., wood density, stiffness, visual grading) was better under Weak than under Intensive thinning. However, the production of large conifer timbers with homogeneous ATRW may offset reductions in quality. This study suggests that intensive thinning is a reliable method for rapidly creating mixed hardwood–conifer forests at the canopy level and producing large timbers of both conifer and hardwood species, whereas weak thinning is suitable for producing high-quality conifer timbers and maintaining net primary production, although repeated thinning is necessary.

Inconsistent Responses of Transpiration of Different Canopy Layers to Simulated Canopy and Understory N Depositions in a Low‐Subtropical Evergreen Broadleaf Forest

AbstractQuantifying transpiration and its response to meteorological factors at a stand scale and different canopy layers of forest is important for understanding the hydrological impact of nitrogen (N) deposition on local water balance. For this purpose, sap flows were measured in three upper (Schima superba, Castanea henryi, and Machilus chinensis) and three lower (Symplocos ramosissima, Ilex ficoidea, and Schefflera octophylla) canopy species based on a manipulative experimental platform with canopy (CN) and understory (UN) N additions in a low‐subtropical evergreen broadleaf forest. Each application included concentrations of 0, 25, and 50 kg·ha−1·a−1 N. Results showed that N addition obviously influenced the sap flux density and such influence varied among different species and between canopy layers. Upper canopy species contributed the most transpiration for the whole forest, and CN25 greatly affected the transpiration in both upper and lower canopy layers. Daily water use (Qd) increased logarithmically with daytime average photosynthetically active radiation and daily average vapor pressure deficit. An appropriate canopy N addition (CN25) promoted the Qd and its sensitivity to micrometeorological factors, whereas UN had a minimal effect. These results suggest a substantial difference in response of transpiration to the N addition ways. CN had more effective influence on the canopy transpiration. Thus, UN could not fully reflect the effects of increased N deposition on the canopy‐associated transpiration, and the response of forest transpiration to N deposition needs to be analyzed beyond species and upscaled to the canopy level in favor of meaningful assessments of N deposition.

Potato Late Blight Detection at the Leaf and Canopy Levels Based in the Red and Red-Edge Spectral Regions

Potato late blight, caused by Phytophthora infestans, is a major disease worldwide that has a significant economic impact on potato crops, and remote sensing might help to detect the disease in early stages. This study aims to determine changes induced by potato late blight in two parameters of the red and red-edge spectral regions: the red-well point (RWP) and the red-edge point (REP) as a function of the number of days post-inoculation (DPI) at the leaf and canopy levels. The RWP or REP variations were modelled using linear or exponential regression models as a function of the DPI. A Support Vector Machine (SVM) algorithm was used to classify healthy and infected leaves or plants using either the RWP or REP wavelength as well as the reflectances at 668, 705, 717 and 740 nm. Higher variations in the RWP and REP wavelengths were observed for the infected leaves compared to healthy leaves. The linear and exponential models resulted in higher adjusted R2 for the infected case than for the healthy case. The SVM classifier applied to the reflectance of the red and red-edge bands of the Micasense® Dual-X camera was able to sort healthy and infected cases with both the leaf and canopy measurements, reaching an overall classification accuracy of 89.33% at 3 DPI when symptoms were visible for the first time with the leaf measurements and of 89.06% at 5 DPI, i.e., two days after the symptoms became apparent, with the canopy measurements. The study shows that RWP and REP at leaf and canopy levels allow detecting potato late blight, but these parameters are less efficient to sort healthy and infected leaves or plants than the reflectance at 668, 705, 717 and 740 nm. Future research should consider larger samples, other cultivars and the test of unmanned aerial vehicle (UAV) imagery for field-based detection.

Estimation of cotton Car/Chla ratio by hyperspectral vegetation indices and partial least square regression

<p indent=0mm>Estimating the ratio between carotenoid to chlorophyll <italic>a</italic> (Car/Chla) provides an additional avenue for the assessment of physiology and phenology of plant growth and development. With the aim of assessing cotton Car/Chla ratio from hyperspectral reflectance, a wide range of carotenoid (Car) and chlorophyll <italic>a</italic> concentrations, and leaf and canopy reflectance at cotton different growth stages were measured. The performance of a variety of Car/Chla ratio related vegetation indices and partial least square regression (PLSR) for Car/Chla ratio and Car estimation were tested. Among all tested vegetation indices, PRI (Photochemical Reflectance Index) and linear PRI models had the most significant correlations with Car/Chla ratio and Car, and could accurately estimate, Car/Chla ratio (<italic>R</italic>²_{leaf level} = 0.69 and <italic>R</italic>²_{canopy level} = 0.67) and Car concentration (<italic>R</italic>²_{leaf level} = 0.44 and<italic> R</italic>²_{canopy level} = 0.36). The best estimation of the Car/Chla ratio and Car was provided by PLSR models with <italic>R</italic>² > 0.80 between the estimated and measured value for Car/Chla ratio and <italic>R</italic>² <italic>= </italic>0.74 for Car. Both reflectance indices and PLSR method were more successful for the estimation of Car/Chla ratio than for that of Car concentration, indicating the promising potential of Car/Chla ratio as a powerful indicator using for plant status monitoring by remote sensing. Besides, accuracy test of models using validation dataset highlighted the remarkable performance of PLSR for Car/Chla (<italic>R</italic>²_{leaf level} = 0.87 and <italic>R</italic>²_{canopy level} = 0.84) and Car (<italic>R</italic>²_{leaf level} = 0.73 and<italic> R</italic>²_{canopy level} = 0.74) estimated by hyperspectral reflectance at both the leaf and canopy levels. The results further prove the remarkable performance of hyperspectral reflectance for the estimation of Car/Chla ratio, and enrich the parameters for monitoring high temperature stress, water deficit stress, and nutrient stress and pest diseases by remote sensing in cotton.

Total and diffuse light distribution within the canopy of an apple orchard as affected by reflective ground covers

In recent years, anti-hail nets have been increasingly used to protect apple orchards. As they reduce the light intensity at canopy level, reflective ground covers are frequently placed on the soil surface before fruit harvest with the main aim to enhance color development in bicolored apples. It is not clear however, to which extent the light penetration inside the whole canopy is affected by the reflective ground covers. We performed a study in an intensively cultivated apple district of South Tyrol (northern Italy), with and without reflective ground covers. We measured light intensity at different heights from the ground and different distances from the tree trunk, using two instruments: an 80- cm long ceptometer and a point-like sensor capable of measuring the diffuse radiation component in addition to the total visible light. We found that the reflective ground cover significantly increased the quantity of diffuse light reflected from the orchard floor. The largest effect was recorded at 1 m height from the ground, but it was still significant at 2.5 m height. The influence of the reflective ground cover was particularly remarkable when sun and tree lines were aligned. The increase of total PAR inside the canopy due to the reflective material was however relatively small, suggesting a moderate effect on tree photosynthesis and therefore on apple yields.

Assessment of leaf ultrastructure offers insights into mechanisms regulating sugarcane performance under low-phosphorus stress

Detailed studies of plant responses to phosphorus (P) deficiency might reveal opportunities to improve sugarcane performance under nutrient stress, termed as P use efficiency. Then, we aimed through transmission electron microscopy to offer insights into the effects of varying P supply on leaf ultrastructural traits influencing photosynthesis and leaf area formation. Plants of the genotype RB86-7515 were cultivated under varying nutrient supply (0.0125, 0.05, 0.2 and 0.8 mM P) for 4 months. Diagnostic mature leaves were sampled to evaluate ultrastructural organization and P concentration. Leaf area and plant dry mass responded positively to increasing P rates and maximum values were attained at 0.55 mM P. Leaf P concentration increased as a function of nutrient supply, and the greatest area of diagnostic leaf and whole plant growth was associated with 1.80 g kg−1 P. Under severe deficiency (relative growth ≤ 30% and leaf P ≤ 0.90 g kg−1) generated with 0.0125- and 0.05-mM P, transmission electron microscopy revealed pronounced damages to leaf ultrastructure. In mesophyll cells, the changes were more intense under the lowest P rate, and included disintegration of the middle lamella, collapse of plasma membrane and distortion of thylakoids. Bundle sheath chloroplasts of the severely P-deficient plants exhibited, compared with those under 0.2- and 0.8-mM P, disorganization of lamellar membrane system. Collectively, these ultrastructural alterations offer insights into how P deficiency affects whole plant photosynthetic capacity and provide possible target traits at canopy level related to sugarcane P use efficiency.

Windbreaks as part of climate-smart landscapes reduce evapotranspiration in vineyards, Western Cape Province, South Africa

Under the conditions of climate change in South Africa, ecological and technical measures are needed to reduce the water consumption of irrigated crops. Windbreak hedges are long-rated systems in agriculture that significantly reduce wind speed. Their possibilities to reduce evapotranspiration and water demand are being investigated at a vineyard in the Western Cape Province, South Africa. Detailed measurements of meteorological parameters relevant for the computation of reference and crop-specific evapotranspiration following the FAO 56 approaches within a vineyard in the Western Cape Province of South Africa have shown the beneficial effect of an existing hedgerow consisting of 6 m high poplars (Populus simonii (Carrière) Wesm.). With reference to a control station in the open field, the mean wind speed in a position about 18 m from the hedgerow at canopy level (2 m) was reduced by 27.6% over the entire year and by 39.2% over the summer growing season. This effect leads to a parallel reduction of reference evapotranspiration of 15.5% during the whole year and of 18.4% over the growing season. When applying empirical crop-specific K&lt;sub&gt;c&lt;/sub&gt; values for well-irrigated grapes, the reduction of evapotranspiration is 18.8% over the summer growth period. The introduced tree shelterbelts are a suitable eco-engineering approach to reduce water consumption and to enhance water saving in vineyards.

Managing the number of orthotropic stems in Coffea arabica as strategy for cultivation at low-altitude regions

The objective of this study was to better understand the implications of the management of the number of orthotropic stems in Arabica coffee for its cultivation in low-altitude regions (&lt; 500 m), characterizing its effects over the canopy architecture, production and allocation of biomass, photosynthesis and crop yield, as possible strategy for mitigating the stresses of cultivation at low-altitude regions. The experiment was conducted in a region with 124 m of elevation above sea level, studying four treatments with different numbers of orthotropic stems per plant such as one, two, three and four stems. After planting, during the stage of sprout budding, a number of sprouts were established in accordance to the treatments. The experimental design was a randomized block design, with eight repetitions. Parameters of gas exchange, chlorophyll contents, canopy architecture, production and allocation of biomass, and crop yield were evaluated to characterize the plant development. Overall, increasing the number of orthotropic stems per plant promoted leaf density, number of plagiotropic branches per plant, available leaf area per fruit mass, photosynthetic rate, crop yield, proportion of large grains and, possibly, the de-acceleration of the stem aging rate, mainly for the management with four orthotropic stems. It is concluded that the management of the number of orthotropic stems has potential use as a mitigator for the cultivation of Arabica coffee in low-altitude regions, being able to promote higher canopy density and, possibly, enhance microclimate conditions at the canopy level.

Evaluation of Pheromone Traps for the Management of Pod Borer, Helicoverpa armigera (Hubner) in Redgram [Cajanus cajan (L.) Millsp.] Ecosystem

The present study entitled “Evaluation of pheromone traps for the management of pod borer, Helicoverpa armigera (Hubner) in Redgram [Cajanus cajan (L.) Millsp.] ecosystem” was carried out to study the influence of trap height on catches of H. armigera in redgram ecosystem during kharif 2017 at experimental farm of NPRC, Vamban and farmer’s field at Vadakaddu.Funnel traps were more effective compared to delta traps and green funnel traps placed at the level of crop canopy (96.0 moths / 5 traps) and one foot below the crop canopy (94.8 moths / 5 traps) performed well compared to traps placed at two feet below the crop canopy (77.1 moths / 5 traps), one foot above the crop canopy (66.6 moths / 5 traps) and two feet above the crop canopy (58.9 moths / 5 traps).

Factors controlling the vertical zonation of the intertidal seagrass, Zostera japonica in its native range in the northwestern Pacific

The desiccation tolerance of the intertidal seagrass Zostera japonica has been demonstrated in a number of studies; however, the factors limiting expansion of intertidal seagrass species into subtidal zones remain controversial. We transplanted Z. japonica shoots from the intermediate intertidal zone into the plots with and without Z. marina shoots in both the lower intertidal and shallow subtidal zones to investigate the factors controlling Z. japonica growth in these zones. Daily photon flux density at the Z. japonica canopy level was attenuated by both water depth and coexisting Z. marina shoots but more strongly by Z. marina shoots than water depth in the transplant plots. The shoot density and biomass of Z. japonica transplants were significantly lower in transplant plots in the subtidal zone than in the lower intertidal zone. Although the photon flux density was significantly lower in transplant plots containing Z. marina shoots, the growth of Z. japonica transplants did not differ significantly between plots with and those without Z. marina shoots. Z. japonica transplants exhibited photoacclimatory responses such as increased shoot height and chlorophyll content under the lower-light conditions, offsetting the reduced light availability so that no significant differences in transplant growth occurred between plots with and those without Z. marina shoots. As the growth of Z. japonica transplants decreased significantly in the subtidal zone, the interactive effects of environmental stresses associated with tidal inundation and reduced light availability may restrict penetration of the intertidal seagrass Z. japonica into the subtidal zone. The persistence of high photosynthetic performance after air exposure and a regular arrangement of the densely overlapped leaves atop wet sediments may be desiccation tolerance mechanisms for Z. japonica in the intertidal zone.

Efecto de onda y fenómeno de timidez en bosques homogéneos de Alnus acuminata

El efecto de onda y el fenómeno de timidez en Alnus acuminata (Kunth) son parámetros de copa raramente estudiados, pero importantes en la calidad de la madera de árboles en pie, por lo cual, se realizó un modelaje morfométrico de las copas de A. acuminata en bosques homogéneos en la Sierra Norte de Puebla. En 20 sitios rectangulares de 1000 m2, se evaluó: altura total (AT), diámetro normal (DN), diámetro de copa (DC) y cobertura de copa (CC). A los datos que no cumplieron el supuesto de normalidad, se les aplicó la prueba de Kruskal Wallis; para los que sí cumplieron, se empleó el análisis de varianza (ANOVA), con pruebas de comparación de medias por Tukey (α ≤ 0.05). El índice de valor forestal fue de 14.99, por lo que su estructura bidimensional es normal, con base en DN, AT y CC. Su índice de esbeltez promedio fue de 93.52, lo que hace al arbolado poco estable al daño mecánico. El índice de espacio vital fue de 38.92, es alto y evidencia un mejor desarrollo de los árboles con baja competencia intraespecífica. A nivel del dosel se observó un patrón que sigue un efecto de onda ascendente, oscilatorio y constante, en grupos de 10 árboles. El fenómeno de timidez mostró una apertura de grieta promedio de 27.39 cm entre copas, por lo cual, este fenómeno se encuentra bien definido para la especie. Se concluye que en las copas de A. acuminata, se observa el efecto de onda como consecuencia de la desigualdad en la adquisición de recursos, pero una forma de minimizar esta desigualdad es mediante el fenómeno de timidez botánica.

Effects of varying solar-view geometry and canopy structure on solar-induced chlorophyll fluorescence and PRI

The increasing amount of continuous time series of solar-induced fluorescence (SIF) and vegetation indices (e.g. Photochemical Reflectance Index, PRI) acquired with high temporal (sub-minute) frequencies is foreseen to allow tracking of the structural and physiological changes of vegetation in a variety of ecosystems. Coupled with observations of CO2, water, and energy fluxes from eddy covariance flux towers, these measurements can bring new insights into the remote monitoring of ecosystem functioning. However, continuously changing solar-view geometry imposes directional effects on diurnal cycles of the fluorescence radiance in the observation direction (F) and PRI, controlled by structural and biochemical vegetation properties. An improved understanding of these variations can potentially help to disentangle directional responses of vegetation from physiological ones in the continuous long-term optical measurements and, therefore, allow to deconvolve the physiological information relevant to ecosystem functioning. Moreover, this will also be useful for better interpreting and validating F and PRI satellite products (e.g., from the upcoming ESA FLEX mission).Many previous studies focused on the characterization of reflectance directionality, but only a handful of studies investigated directional effects on F and vegetation indices related to plant physiology. The aim of this study is to contribute to the understanding of red (F687) and far-red (F760) fluorescence and PRI anisotropy based on field spectroscopy data and simulations with the Soil-Canopy Observation of Photochemistry and Energy fluxes (SCOPE) model. We present an extensive dataset of multi-angular measurements of F and PRI collected at canopy level with a high-resolution instrument (FloX, JB Hyperspectral Devices UG, Germany) over different ecosystems: Mediterranean grassland, alfalfa, chickpea and rice.We found, that F760 and F687 directional responses of horizontally homogeneous canopies are characterized by higher values in the backscatter direction with a maximum in the hotspot and lower values in the forward scatter direction. The PRI exhibited similar response due to its sensitivity to sunlit-shaded canopy fractions.As confirmed by radiative transfer forward simulations, we show that in the field measurements leaf inclination distribution function controls the shape of F and PRI anisotropic response (bowl-like/dome-like shapes), while leaf area index and the ratio of leaf width to canopy height affect the magnitude and the width of the hotspot. Finally, we discuss the implications of off-nadir viewing geometry for continuous ground measurements. F observations under oblique viewing angles showed up to 67 % difference compared to nadir observations, therefore, we suggest maintaining nadir viewing geometry for continuous measurements of F and vegetation indices. Alternatively, a correction scheme should be developed and tested against multi-angular measurements to properly account for anisotropy of canopy F and PRI observations. The quantitative characterization of these effects in varying illumination geometries for different canopies that was performed in this study will also be useful for the validation of remote sensing F and PRI products at different spatial and temporal scales.

Thresholds in woody and herbaceous component co‐existence inform the restoration of a fire‐dependent community

AbstractQuestionsA paradoxical co‐existence challenges woodland and savanna restoration worldwide: How are shade‐intolerant, flammable herbaceous layers promoted while maintaining the shade‐casting, more fire‐sensitive woody regeneration that sustains overstorey structure? Where restoration success consisted of robust, diverse herbaceous layers and vigorous, well‐stocked Pinus echinata regeneration (hereafter, shortleaf‐bluestem response), we asked: are there targetable conditions of overstorey, understorey, topography, and proximity to mature Pinus echinata that simultaneously maximize desired woody and herbaceous understorey components? Do these conditions and dependent responses differ across canopy disturbance level and fire season?LocationCumberland Plateau, Tennessee, USA (36°04′8.11″ N, 84°50′38.36″ W).MethodsWe measured 12 shortleaf‐bluestem response and 17 explanatory condition variables at 345 plots spanning an experimental restoration gradient (canopy disturbance level and fire season combinations). We ordinated variation and identified response thresholds using a multivariate regression tree. Differences across tree groupings and splits associated response thresholds with specific explanatory conditions.ResultsPockets of substantial Pinus echinata regeneration (&gt;3,000 stems/ha), C4 grass density (&gt;40,000 ramets/ha), and herbaceous diversity (increase from 22 to 205 species) occurred 7–14 years after canopy disturbance and 3–8 fires. Such shortleaf‐bluestem response was maximized at 3 m2/ha residual tree basal area, 11% canopy closure, reduced midstorey density (5,000 small‐sapling stems/ha), and southwesterly aspects within 70 m of mature Pinus echinata. In contrast, shortleaf‐bluestem response was negligible at 11.3 m2/ha basal area and 68% canopy closure. Fire season, snag basal area, slope, and slope position effects were minimal.ConclusionsWe identified specific conditions fostering the co‐existence of desired herbaceous and woody understorey components, addressing a major woodland and savanna restoration challenge and expanding on previous threshold concept applications by simultaneously considering multiple desired responses. Results can direct the restoration of imperiled shortleaf‐bluestem communities east of the Mississippi River, USA, where work has been scarce or ineffective, and similar approaches could inform fire‐dependent woodland and savanna restoration worldwide.

Spectral behavior of Persian oak under compound stress of water deficit and dust storm

Persian oak (Quercus Brantii Lindl.) which is the most widely distributed tree in the Zagros Mountain forests is affected by western dust storms, mostly originating in Iraq, and harsh water stress as well. The objective of this research is to analyze the spectral behavior of Persian oak under water and dust stress scenarios, aiming to pave the way for modeling the stresses of drought and dust storms on oak trees using remote sensing images. Experiments were carried out on 54 two-year old oak tree seedlings, using a portable wind tunnel in greenhouse conditions. Water stress was induced on seedlings by means of changes in irrigation practices, i.e. well-watered (100 % field capacity), medium water deficit condition (40 % field capacity), and severe water deficit condition (20 % field capacity) treatments. Dust stress is also investigated by using three different dust particle concentrations, i.e. 350, 750 and 1500 (μg/m³). The spectrometry experiments were carried out at leaf and canopy levels in dark room by Fieldspec-3-ASD spectrometer. Spectral analysis was conducted using four procedures: (i) narrow-band spectral indices analysis, (ii) geometric indicators extraction from absorption features, (iii) Partial Least Squares Regression (PLSR), and SVM classifier. Results show that water stress could be modeled much better using PLSR statistic (R2 = 0.87, RMSE = 0.12), narrow-band indices analysis (R2cv = 0.75, RMSEcv = 0.17), and continuum removal (R2 = 0.71, RMSE = 0.20), respectively. For dust stress, PLSR (R2 = 0.83, RMSE = 0.14) and narrow-band indices (R2cv = 0.7, RMSE cv = 0.30) showed the best results, respectively. SVM could successfully separate stressed and not-stressed samples and also the stress types at both leaf and canopy levels, but it could not distinguish the different levels of stresses.