Foliage Loss Research Articles

Leaf herbivory causes abortion of selfed seeds in Rhododendron kaempferi var. kaempferi

AbstractPlant reproduction is often inhibited by herbivorous leaf damage, which affects the resource pool allocated for reproduction. Rhododendron kaempferi var. kaempferi is a semi‐evergreen shrub widely distributed in Japan, and its leaves are occasionally damaged by sawfly larvae (Arge similis). This species is partially self‐compatible, but its selfed seedlings suffer from inbreeding depression. Our study aimed to clarify (1) the magnitude of herbivorous damage under natural conditions, (2) the effects of foliage damage on seed number and mass, and (3) the possibility of selective abortion of selfed seeds to maintain outcrossed seed production under resource limitation. In the 2022 survey, 2 of the 20 ramets observed were collectively parasitized by sawfly larvae, and the most damaged ramet had a 59.6% foliage loss. In contrast, the herbivorous damage in 2023 was consistently low throughout the growing season, averaging a 3.2% loss. Leaf excision reduced the seed number per fruit (i.e., low seed‐set rate) but did not affect the individual seed mass. The outcrossing rate of the excision treatment (81.7%) was significantly higher than that of the control (72.0%). The values of seed‐set rate × outcrossing rate were 0.172 for the excision treatment and 0.171 for the control, nearly equal. Our results indicated that (1) sawfly larvae damage was concentrated on a few specific plants, (2) intense foliage damage reduced seed number but not seed mass, and (3) R. kaempferi mitigated the decline in outcrossed seed production by the abortion of selfed seeds when leaves were intensively damaged.

Diversity, Stability, and the Forecast Challenge in Forest Lepidopteran Predictive Ecology: Are Multi-Scale Plant–Insect Interactions the Key to Increased Forecast Precision?

I report on long-term patterns of outbreak cycling in four study systems across Canada and illustrate how forecasting in these systems is highly imprecise because of complexity in the cycling and a lack of spatial synchrony amongst sample locations. I describe how a range of bottom-up effects could be generating complexity in these otherwise periodic systems. (1) The spruce budworm in Québec exhibits aperiodic and asynchronous behavior at fast time-scales, and a slow modulation of cycle peak intensity that varies regionally. (2) The forest tent caterpillar across Canada exhibits eruptive spiking behavior that is aperiodic locally, and asynchronous amongst regions, yet aggregates to produce a pattern of periodic outbreaks. In Québec, forest tent caterpillar cycles differ in the aspen-dominated northwest versus the maple-dominated southeast, with opposing patterns of cycle intensity between the two regions. (3) In Alberta, forest tent caterpillar outbreak cycles resist synchronization across a forest landscape gradient, even at very fine spatial scales, resulting in a complex pattern of cycling that defies simple forecasting techniques. (4) In the Border Lakes region of Ontario and Minnesota, where the two insect species coexist in a mixedwood landscape of hardwood and conifers, outbreak cycle intensity in each species varies spatially and temporally in response to host forest landscape structure. Much attention has been given to the effect of top-down agents in driving synchronizable population cycles. However, foliage loss, tree death, and forest succession at stem, stand, and landscape scales affect larval and adult dispersal success, and may serve to override regulatory processes that cause otherwise top-down-driven periodic, synchronized, and predictable population oscillations to become aperiodic, asynchronous, and unpredictable. Incorporating bottom-up effects at multiple spatial and temporal scales may be the key to making significant improvements in forest insect outbreak forecasting.

Propagation Modeling of Unmanned Aerial Vehicle (UAV) 5G Wireless Networks in Rural Mountainous Regions Using Ray Tracing

Deploying 5G networks in mountainous rural regions can be challenging due to its unique and challenging characteristics. Attaching a transmitter to a UAV to enable connectivity requires a selection of suitable propagation models in such conditions. This research paper comprehensively investigates the signal propagation and performance under multiple frequencies, from mid-band to mmWaves range (3.5, 6, 28, and 60 GHz). The study focuses on rural mountainous regions, which were empirically simulated based on the Skardu, Pakistan, region. A complex 3D ray tracing method carefully figures out the propagation paths using the geometry of a 3D environment and looks at the effects in line-of-sight (LOS) and non-line-of-sight (NLOS) conditions. The analysis considers critical parameters such as path loss, received power, weather loss, foliage loss, and the impact of varying UAV heights. Based on the analysis and regression modeling techniques, quadratic polynomials were found to accurately model the signal behavior, enabling signal strength predictions as a function of distances between the user and an elevated drone. Results were analyzed and compared with suburban areas with no mountains but more compact buildings surrounding the Universiti Kebangsaan Malaysia (UKM) campus. The findings highlight the need to identify the optimal height for the UAV as a base station, characterize radio channels accurately, and predict coverage to optimize network design and deployment with UAVs as additional sources. The research offers valuable insights for optimizing signal transmission and network planning and resolving spectrum-management difficulties in mountainous areas to enhance wireless communication system performance. The study emphasizes the significance of visualizations, statistical analysis, and outlier detection for understanding signal behavior in diverse environments.

Exploring the Impact of a Nontoxic Foliar Fungal Endophyte on Regrowth Post‐Defoliation in Tall Fescue (Lolium arundinaceum) Plants

ABSTRACTPlants employ various strategies to mitigate the impact of herbivory and one such strategy involves the associations with fungal endophytes. Some cool‐season forage grasses benefit from protection against herbivores by Epichloë fungal endophytes. However, since the maintenance of symbiosis relies on the plant, costs of hosting endophytes have been also observed. This becomes particularly crucial when forage varieties, inoculated with endophytes that are nontoxic to livestock but still protect host against insect herbivores, experience significant foliage loss (defoliation). We investigated the impact of a nontoxic Epichloë endophyte on the responses of tall fescue plants to defoliation across two morphotype varieties, Continental and Mediterranean, and different seasonal contexts. Under specific defoliation treatments, endophyte‐symbiotic plants showed reduced postdefoliation recovery, indicating the costs of hosting the endophyte for host plants. However, these conditions were not the most severe for plant growth. Regardless of the endophyte's presence, plants from Continental morphotype exhibited superior recovery than those from Mediterranean morphotype, an effect that was more pronounced in summer. Notably, the endophyte promoted plant growth after defoliation in winter for both morphotypes. Our study offers insights into mitigating endophyte‐associated costs on plant recovery postdefoliation by strategically managing cutting intensity and frequency, considering the seasonal variation.

Vegetation Loss Measurements for Single Alley Trees in Millimeter-Wave Bands.

As fixed wireless access (FWA) is still envisioned as a reasonable way to achieve communications links, foliage attenuation becomes an important wireless channel impairment in the millimeter-wave bandwidth. Foliage is modeled in the radiative transfer equation as a medium of random scatterers. However, other phenomena in the wireless channel may also occur. In this work, vegetation attenuation measurements are presented for a single tree alley for 26-32 GHz. The results show that vegetation loss increases significantly after the second tree in the alley. Measurement-based foliage losses are compared with model-based, and new tuning parameters are proposed for models.

Repeat GEDI footprints measure the effects of tropical forest disturbances

More of the Amazon rainforest is disturbed each year than completely deforested, but the impact of these disturbances on the carbon cycle remains poorly understood. Recent algorithmic advances using optical and radar remote sensing have improved detection of disturbances at fine spatiotemporal resolution, but quantifying changes in forest structure and biomass associated with these detected disturbances has proven challenging. The Global Ecosystem Dynamics Investigation (GEDI), a spaceborne lidar mission collecting data from 2019 to 2023, provides an opportunity to address this problem. GEDI captured billions of measurements of forest height, plant area, and understory structure within ∼25-m diameter footprints scattered across the tropics. Though the instrument had no guaranteed repeat cycle, it sometimes sampled nearby locations twice; some of these spatially near-coincident footprints happened to measure forest structure before and after a detected disturbance, providing information on how disturbance affected aboveground biomass. In this study, we developed an efficient general-purpose open-source pipeline for identifying spatially coincident footprints, which is a computationally complex task, and used the pipeline to find over 13,700 footprint pairs with intervening disturbance events across the Amazon biome. We also identified a set of ∼65,000 spatially near-coincident footprint pairs that lacked an intervening disturbance but came from regions with similar disturbance threat; these provided a control dataset to evaluate the effectiveness of estimating forest structure and biomass changes with nearby footprints. Analysis of this Amazon-wide dataset demonstrated that GEDI was able to measure statistically significant canopy height and biomass deficits following non-stand-replacing disturbances as small as 900 m2 (30 m × 30 m). GEDI's unique three-dimensional view of forest structure also reflected the effects of different intensities of fire disturbance, including 20% of burned areas where the upper canopy retained most of its height, but the understory suffered substantial foliage losses. Finally, we modeled the relationship between Landsat and Sentinel-1 disturbance detection parameters and GEDI-estimated percent biomass loss, showing that certain satellite-derived intensity metrics are correlated with increasing biomass loss and identifying temporal trends in biomass loss and recovery following disturbance. This work represents an important step towards the development of a pan-tropical, spatially explicit system for tracking carbon losses and structural changes arising from forest disturbance.

The influence of climate and management on transpiration of residential trees during a bark beetle infestation

AbstractTrees in residential environments are affected by a unique combination of environmental and anthropogenic factors, including occasional insect outbreaks that are increasing in frequency and severity due to climate change. We studied loblolly pine trees infested by bark beetles in a residential backyard in a southeastern US city. We investigated the responses of tree and stand‐level transpiration to environmental factors (solar radiation, atmospheric vapor pressure deficit, and soil moisture), severe weather events (strong winds and heavy storms), bark beetle infestation, and human actions (insecticide treatments and tree removals). We used constant heat dissipation probes to make continuous sap flux measurements (J0) in tree boles. Over 22 months of the study, J0 of trees with confirmed infestation decreased from ~90 to ~60 g cm−2 day−1 and J0 of the rest of the trees increased from ~60 to ~80 g cm−2 day−1. One infested tree died, as its J0 steadily declined from 110 g cm−2 day−1 to zero over the course of 2 months, followed by a loss of foliage and visible signs of severe infestation 6 months later. J0 was sensitive to variations in incoming solar radiation and atmospheric vapor pressure deficit. In most trees, J0 linearly responded to soil water content during drought periods. Yet despite complex dynamics of J0 variations, plot‐level transpiration at the end of the study was the same as at the beginning due to compensatory increases in tree transpiration rates. This study highlights the intrinsic interplay of environmental, biotic, and anthropogenic factors in residential environments where human actions may directly mediate ecosystem responses to climate.

UAV‐derived greenness and within‐crown spatial patterning can detect ash dieback in individual trees

Abstract Ash Dieback (ADB) has been present in the UK since 2012 and is expected to kill up to 80% of UK ash trees. Detecting and quantifying the extent of ADB in individual tree crowns (ITCs), which is crucial to understanding resilience and resistance, currently relies on visual assessments which are impractical over large scales or at high frequency. The improved imaging capabilities and declining cost of consumer UAVs, together with new remote sensing methods such as structure from motion photogrammetry (SfM) offers potential to quantify the fine‐scale structural and spectral metrics of ITCs that are indicative of ADB, rapidly, and at low‐cost. We extract high‐resolution 3D RGB point clouds derived from SfM of canopy ash trees taken monthly throughout the growing season at Marden Park, Surrey, UK, a woodland impacted by ADB. We segment ITCs, extract green chromatic coordinate (gcc), and test the relationship with visual assessments of crown health. Next, we quantify spatial patterning of dieback within ITCs by testing the relationship between internal variation of gcc and path length, a measure of the distance from foliage to trunk, for small clusters of foliage. We find gcc correlates with visual assessments of crown health throughout the growing season, but the strongest relationships are in measurements taken after peak greenness, when the effects of ADB on foliage are likely to be most prevalent. We also find a negative relationship between gcc and path length in infected trees, indicating foliage loss is more severe at crown extremities. We demonstrate a new method for identifying ADB at scale using a consumer‐grade 3D RGB UAV system and suggest this approach could be adopted for widespread rapid monitoring. We recommend the optimum time of year for data acquisition, which we find to be an important factor for detecting ADB. Although here applied to ADB, this framework is applicable to a multitude of drivers of crown dieback, presenting a method for identifying spectral‐structural relationships which may be characteristic of disturbance type.

A multi-criteria drought resistance assessment of temperate Acer, Carpinus, Fraxinus, Quercus, and Tilia species

A rapidly warming climate with growing frequency of hot droughts urges Central Europe’s forestry sector to adapt to increasing climatic stress. One option is to choose native minor timber species with assumed higher stress tolerance; yet, information on the drought resistance of many species is scarce. We examined the drought resistance of adult trees of Norway maple (Acer platanoides), European hornbeam (Carpinus betulus), Common ash (Fraxinus excelsior) and Little-leaved lime (Tilia cordata) at leaf, branch, stem and root levels, combining studies on leaf water status, branch xylem hydraulics, fine root vitality and radial stem growth, for deriving an evidence-based drought resistance ranking of the species. Results were compared to Sessile oak (Quercus petraea), a fairly drought-resistant major timber species. All species showed constant growth rates despite increasing climatic aridity, indicating low climate vulnerability. Foliage loss after the severe 2018/19 drought increased in the sequence Quercus < Fraxinus < Acer < Tilia < Carpinus. The water potential at leaf turgor loss (PTLP) was no suitable indicator of the species’ climate-sensitivity of growth or drought-induced foliage loss. The growth performance of Tilia demonstrates that some angiosperm trees can achieve a fairly high degree of drought resistance through plant-internal water storage and high leaf tissue elasticity, despite a small hydraulic safety margin and high PTLP. Drought resistance as deduced from growth performance and defoliation after severe drought decreased in the sequence Quercus > Fraxinus & Acer > Tilia > Carpinus. We conclude that Acer, Carpinus, and Tilia (and Fraxinus, despite being often Hymenoscyphus-infected) are suitable timber species for Central Europe’s forestry sector in a drier and warmer climate.

Studies on Potential Pests of Japanese Quince (Chaenomeles japonica (Thunb.) Lindl. ex Spach) in Latvia

Abstract The objective of this research was to study potential pests of Japanese quince (Chaenomeles japonica) plantations in Latvia. Studies were carried out in eight plantations during 2017–2019. Major pests that would regularly cause significant yield losses for this plant were not observed. Black-veined white (Aporia crataegi) was considered a local pest, mass outbreaks of which can occur in individual plantations and cause significant losses of plant foliage. Four species were considered minor pests: garden chafer (Phyllopertha horticola), yellow-banded weevil (Chlorophanus viridis), silver-green weevil (Phyllobius argentatus) and copse snail (Arianta arbustorum); they are also pests of plant foliage. The European red spider mite (Panonychus ulmi) was not considered as a pest of Japanese quince. A small population was observed in summers only in one plantation, which was located next to a heavily infested orchard. Overwintering eggs were not found on the plants in any year, and we concluded that the species was an accidental immigrant in this plantation. No aphid (Aphididae) colonies were observed on the quince plants. Monitoring and evaluation of potential harmfulness of four tortrix moths – large fruit-tree tortrix (Archips podana), rose tortrix (Archips rosana), codling moth (Cydia pomonella) and holly tortrix (Rhopobota naevana) – was done. It was concluded that rose tortrix is a minor fruit pest, but the other three species were not yet considered pests of Japanese quince. Significant pests of quince flowers and fruits were not detected in our study.

Are high-severity burns in Alpine beech forests related to eruptive fire behavior?

Abstract In the complex Alpine topography, canyon-like terrain morphology combined with steep slopes may cause sudden changes in fire behavior, for instance, turning fast-spreading surface fires into eruptive fires. This phenomenon was observed during the vegetation dormancy in mountain beech (Fagus sylvatica L.) stands, a forest type usually spared from wildfires. The aim of this study is to understand the impact of eruptive fire behavior on the post-fire trajectories of beech trees. To this end, over the course of 3 years, we monitored the post-fire dynamics of 100 beech trees subjected to different fire intensities in February 2020, including a small-scale eruptive fire behavior associated with a steep slope (~41.4° on average) and canyon-like terrain features. Dendrometric and sylvicultural parameters and fire-related damages such as the presence of bark blackening, scars, foliage loss, crashes of branches or whole trees, and parasitic attacks were assessed. The observed medium to high fire severity was highly dependent on the position of the tree within the eruptive fire sector, whereas the relationship with dendrometric and sylvicultural tree characteristics, such as the crown position or the stem diameter, was less clear. Due to the lethal temperatures generated by the heat convection within the eruptive fire sector, the exposed bud and cambium tissues of the beech trees partially or totally failed to develop in the first post-fire season. Beech crown and stem tissue killed by exposure to convective heat fluxes rapidly dries out, loses its elasticity, and becomes brittle. Starting from the second post-fire season, this greatly increases the risk of the crashing of these crown parts and/or entire trees. A detailed understanding of the factors leading to an eruptive fire behavior would highly benefit the fire risk assessment and the detailed planning of the firefighting tactics in mountain areas, eventually increasing the safety of firefighters and preventing post-fire natural hazards, such as rockfall, erosion, surface runoff, and debris flow.

Site-level estimates of Douglas-fir foliage retention from climate, soil, and topographic variables

Cohort-based live foliage retention of Douglas-fir (Pseudotsuga menziesii), repeatedly shown to be directly related to tree growth, was estimated for areas in western Oregon and Washington by correlating nearly 1000 plot-level estimates of foliage retention with variables of climate, soils, and topography. Sampling of Douglas-fir foliage retention, motivated by the Swiss needle cast-induced loss of foliage (causal agent Nothophaeocryptopus gaeumanii) in western Oregon and Washington, covered the period from 1998 to 2021, with estimates collected from the Oregon Coast Range near the California border to the Olympic Peninsula and the foothills of the northern Oregon Cascades and the foothills near the border of Washington and Canada. Douglas-fir foliage retention was found to be correlated with average June/July relative humidity, December maximum temperature, and May precipitation averaged for the periods of budbreak for the 2–4 yr old needle cohorts, a transformation of slope and aspect, the number of meters above 400 m elevation, topographic position index, and soil cation exchange capacity. Using the constructed equation, foliage retention was estimated across a systematic grid of points in western Oregon and Washington and combined with a regional growth model to estimate potential volume growth loss across the region. The greatest implied average growth losses (∼23%) were in the zones closest to the Pacific Ocean between 46° and 48°N. Premature loss of Douglas-fir foliage in the Pacific Northwest has been primarily associated with Swiss needle cast, and this work may help explain conditions that favor Swiss needle cast or describe additional foliage retention drivers.

Potential of Sentinel-1 SAR to Assess Damage in Drought-Affected Temperate Deciduous Broadleaf Forests

Understanding forest decline under drought pressure is receiving research attention due to the increasing frequency of large-scale heat waves and massive tree mortality events. However, since assessing mortality on the ground is challenging and costly, this study explores the capability of satellite-borne Copernicus Sentinel-1 (S-1) C-band radar data for monitoring drought-induced tree canopy damage. As droughts cause water deficits in trees and eventually lead to early foliage loss, the S-1 radiometric signal and polarimetric indices are tested regarding their sensitivities to these effects, exemplified in a deciduous broadleaf forest. Due to the scattered nature of mortality in the study site, we employed a temporal-only time series filtering scheme that provides very high spatial resolution (10 m ×10 m) for measuring at the scale of single trees. Finally, the anomaly between heavily damaged and non-damaged tree canopy samples (n = 146 per class) was used to quantify the level of damage. With a maximum anomaly of −0.50 dB ± 1.38 for S-1 Span (VV+VH), a significant decline in hydrostructural scattering (moisture and geometry of scatterers as seen by SAR) was found in the second year after drought onset. By contrast, S-1 polarimetric indices (cross-ratio, RVI, Hα) showed limited capability in detecting drought effects. From our time series evaluation, we infer that damaged canopies exhibit both lower leaf-on and leaf-off backscatters compared to unaffected canopies. We further introduce an NDVI/Span hysteresis showing a lagged signal anomaly of Span behind NDVI (by ca. one year). This time-lagged correlation implies that SAR is able to add complementary information to optical remote sensing data for detecting drought damage due to its sensitivity to physiological and hydraulic tree canopy damage. Our study lays out the promising potential of SAR remote sensing information for drought impact assessment in deciduous broadleaf forests.

Prediction of the severity of Dothistroma needle blight in radiata pine using plant based traits and narrow band indices derived from UAV hyperspectral imagery

Dothistroma needle blight, caused by the fungi Dothistroma septosporum and D. pini is globally one of the most damaging diseases of pine species. Infection from the pathogen, which is initiated in the lower crown, causes needle chlorosis, loss of cellular integrity, necrosis and premature needle loss with this developmental sequence impacting key plant functional traits such as chlorophyll content and leaf area index. This study uses data collected from four year old field grown radiata pine (Pinus radiata D. Don) exhibiting a wide range in disease severity (0 – 58%). Hyperspectral data collected from a UAV was used to determine how plant functional traits inverted from a 3D radiative transfer model (PRO4SAIL), can be used by random forests to improve predictions of disease severity, relative to a model with only narrowband hyperspectral indices. Model precision was assessed on a test dataset that was not used for model fitting and this cross validation process was repeated 50 times to ensure reported results were robust, with the mean precision reported from these repeats.The model of disease severity using narrow band hyperspectral indices was moderately precise (R2 = 0.52). Addition of the inverted plant functional traits markedly improved model precision and this final model strongly predicted disease severity with R2 of 0.85. Analyses of variable importance in the final model showed significant interchange in variable importance as the disease progressed. Early stages of the disease were most readily distinguished from asymptomatic trees (severity = 0%) using variables that predominantly describe changes in photosynthesis (Photochemical Reflectance Index), chlorophyll degradation (Normalized Phaeophytinization Index) and chlorophyll content. In contrast, the more severe impacts of the disease were most well characterised by traits associated with an extreme reduction in transpiration (carotenoid content) and loss of foliage.

Linking frass and insect phenology to optimize annual forest defoliation estimation

It is often logistically impractical to measure forest defoliation events in the field due to seasonal variability in larval feeding phenology (e.g., start, peak, and end) in any given year. As such, field data collections are either incomplete or at coarse temporal resolutions, both of which result in inaccurate estimation of annual defoliation (frass or foliage loss). Using Choristoneura pinus F. and Lymantria dispar dispar L., we present a novel approach that leverages a weather-driven insect simulation model (BioSIM) and defoliation field data. Our approach includes optimization of a weighting parameter (w) for each instar and imputation of defoliation. Results show a negative skew in this weighting parameter, where the second to last instar in a season exhibits the maximum consumption and provides better estimates of annual frass and foliage biomass loss where sampling data gaps exist. Respective cross-validation RMSE (and normalized RMSE) results for C. pinus and L. dispar dispar are 77.53 kg·ha−1 (0.16) and 38.24 kg·ha−1 (0.02) for frass and 74.85 kg·ha−1 (0.10) and 47.77 kg·ha−1 (0.02) for foliage biomass loss imputation. Our method provides better estimates for ecosystem studies that leverage remote sensing data to scale defoliation rates from the field to broader landscapes and regions.•Utilize fine temporal resolution insect life cycle data derived from weather-driven insect simulation model (BioSIM) to bridge critical gaps in coarse temporal resolution defoliation field data.•Fitting distributions to optimize the instar weighting parameter (w) and impute frass and foliage biomass loss based on a cumulative density function (CDF).•Enables accurate estimation of annual defoliation impacts on ecosystems across multiple insect taxa that exhibit distinct but seasonally variable feeding phenology.

Ecology, Impacts, and Management of Common Late-season Defoliators of Southern Hardwoods

Abstract Late-season lepidopteran defoliators in the genera Anisota, Dryocampa, Datana, and Lochmaeus are usually considered minor pests which primarily cause aesthetic damage on hardwood trees in managed and natural areas. While foliage loss late in the season does not typically impact tree health, severe defoliation can occur on individual branches or entire trees, causing great concern to homeowners and land managers. We review the distribution, biology, damage, and management of several native late-season hardwood defoliators in the southeastern United States, including oakworms, mapleworms, yellownecked caterpillars, and variable oakleaf caterpillars. Affected hardwood trees typically leaf out the following spring even after severe defoliation. While management is seldom recommended due to timing or amount of damage, it may be warranted in certain situations. We provide management recommendations for these late-season defoliators, including chemical and nonchemical options for homeowners and land managers.

Artificial light at night affects plant–herbivore interactions

Abstract Artificial light at night (ALAN) affects species' physiology and behaviour, and the interactions between species. Despite the importance of plants as primary producers, it remains poorly understood whether and how effects of ALAN on plants cascade through the food web. We assess the extent to which ALAN of different spectra result in plant‐mediated insect herbivory damage. In a 6‐month field experiment, we exposed plants of differing palatability to three colours of ALAN and a dark control, and assessed plant traits (growth rate, leaf size, foliar density and thickness) and insect herbivory (represented by insect damage as loss of foliage to leaf‐chewing insects, and gall abundance by phloem‐feeding herbivory). We found evidence for plant trait‐mediated ALAN effects on herbivory for oak, but not for blueberry. In oak, ALAN of different colours changed the direction of relationships of insect damage with relative growth rate and with leaf thickness. Moreover, we found that the effects of ALAN on herbivory damage differed markedly between forest types within the same locale, particularly in the red light treatment. Synthesis and applications. Our results provide evidence that continuous night‐time light, as provided by street lighting around the world, affects food web interactions. The nature of these effects differed by species and appeared to depend on forest type and the light spectrum employed, thus underlining the context dependency of ALAN in different ecosystems and environmental settings. These findings highlight the complexity of using spectral manipulation as a mitigation measure, and the need for further consideration of ALAN in environmental management and planning, to limit the exposure and impact of cascading effects of artificial light at night on food webs and communities.

Linking remote sensing and insect defoliation biology – A cross-system comparison

The success of space-based forest defoliation monitoring beyond thematic classification hinges on the ability to link units of continuous foliar change with associated units of spectral or vegetation index change across different systems. To explore this, we used multi-temporal Landsat sensor data with respect to three defoliation metrics (shoot-based estimates (%), frass biomass (kg·ha−1), and proportion of foliar loss) across three different forest systems in the United States. While shoot-based defoliation was measured in the field, the later two defoliation metrics were estimated based on the insect phenology model, BioSIM. The systems include spruce budworm (SBW, Choristoneura fumiferana C). in heterogenous mixed forests, Minnesota, jack pine budworm (JPBW, Choristoneura pinus F). in homogenous pine forests, Wisconsin, and spongy moth (SGM, Lymantria dispar dispar L). in mixed broad-leaved forests, Maryland. Our generalized annual defoliation model for budworm was poor (R2adj = 0.35, RMSE = 23.70%) due to difficulty in detecting SBW defoliation in Minnesota. Thus, individual annual JPBW shoot-based defoliation models (R2adj = 0.27 to 0.75 and RMSE = 19.16% to 11.32%) outperformed the SBW models (R2adj = 0.08 to 0.27, RMSE = 23.18% to 34.13%). Cross-system differences between rates of change in ground-based metrics of defoliation with respect to observed change in spectral index values (dVI) were significant for shoot-based estimates of percent annual defoliation for SGM vs. JPBW (p-values <1.00 × 10−4) and SGM vs. SBW (p-values < 4.60 × 10−3). However, such comparison between SGM and JPBW were not significant when either frass biomass (kg·ha−1, p-value = 0.46) or proportion of foliage loss was used (p-value = 0.67). For a given unit of defoliation, the magnitude of vegetation index change, dVI, was significantly different between SGM and JPBW for each defoliation metric used (p-values <1.00 × 10−4), but not between SGM and SBW (p-value = 0.47) or between JPBW and SBW (p-value = 0.06) when shoot-based annual defoliation metrics were used. This study is first to report that, for a given quantity of defoliation, substantial differences in both the magnitude and direction of vegetation index change exists for different defoliator systems, which currently precludes the development of a viable, unified defoliation model. However, outcomes of this research provide an important step in our understanding of these defoliator systems that may enable specific scaling of continuous defoliation at landscape levels and across defoliator systems in the future.

A Multiwall Path-Loss Prediction Model Using 433 MHz LoRa-WAN Frequency to Characterize Foliage’s Influence in a Malaysian Palm Oil Plantation Environment

Palm oil is the main cash crop of tropical Asia, and the implementation of LPWAN (low-power wide-area network) technologies for smart agriculture applications in palm oil plantations will benefit the palm oil industry in terms of making more revenue. This research attempts to characterize the LoRa 433 MHz frequency channels for the available spreading factors (SF7-SF12) and bandwidths (125 kHz, 250 kHz, and 500 kHz) for wireless sensor networks. The LoRa channel modeling in terms of path-loss calculation uses empirical measurements of RSS (received signal strength) in a palm oil plantation located in Selangor, Malaysia. In this research, about 1500 LoS (line-of-sight) and 300 NLoS (non-line-of-sight) propagation measurement data are collected for path-loss prediction modeling. Using the empirical data, a prediction model is constructed. The path-loss exponent for LoS propagation of the proposed prediction model is found to be 2.34 and 2.9 for 125–250 kHz bandwidth and 500 kHz bandwidth, respectively. Again, for the NLoS propagation links, the attenuation per trunk is found to be 7.58 dB, 7.04 dB, 5.35 dB, 5.02 dB, 5.01 dB, and 5 dB for SF7-SF12, and the attenuation per canopy is found to be 9.32 dB, 7.96 dB, 6.2 dB, 5.89 dB, 5.79 dB, and 5.45 dB for SF7-SF12. Moreover, the prediction model is found to be the better choice (mean RMSE 2.74 dB) in comparison to the empirical foliage loss models (Weissberger’s and ITU-R) to predict the path loss in palm oil plantations.

Management strategies and distribution of Aphanomyces root rot of alfalfa (Medicago sativa), a continuing threat to forage production in the United States

AbstractAlfalfa (Medicago sativa) is one of several legumes that is affected by Aphanomyces root rot (ARR) caused by Aphanomyces euteiches. Symptoms of ARR on alfalfa seedlings include a yellow‐grey discolouration of roots, rotting and loss of lateral roots, stunted growth, chlorotic foliage and reduction of nitrogen‐producing nodules on roots. Infection can also occur on adult plants leading to loss of lateral roots and nodules. At the seedling stage, ARR decreases alfalfa stand establishment, and field longevity is reduced when adult plants are infected. A. euteiches is an oomycete pathogen that has motile zoospores and thick‐walled oospores that can survive for many years in soil. Two races are currently recognized by pathogenicity on differential alfalfa check cultivars. Most alfalfa cultivars contain race 1 resistance, but there is an increasing development of cultivars with resistance to race 2. Management strategies include planting resistant cultivars, avoiding planting in fields with poor drainage and rotating crops with nonhost plants.