Defoliation Patterns Research Articles

Pattern and driving factor of intense defoliation of rubber plantations in SW China

The pattern of intense defoliation of rubber trees (Hevea brasiliensis) in Southwest China is assumed to mainly be attributable to drought stress. However,thishas never beenproven, and the pattern remains unclear. Our objectives were to reveal the driving factor and pattern of intense defoliation, and to explore the characteristics of sap flow density (Js) and relate them to climatic factors before, during and after the intense defoliation period. We continuously measured Js and related climatic factors in a rubber plantation in Southwest China from 2013 to 2016 and found that (1) the cold stress (<10 °C) was more relevant to intense defoliation than drought stress, and after encountering cold stress the rubber trees might enter dormancy for approximately 50 days during the defoliation period; (2) Js showed a self-regulating ability to respond to high air temperature (Ta) and water vaporpressuredeficit (VPD) with atime lag of approximately one hour during all periods except during the defoliation period; (3) the sensitivity of Js to Ta weaken (slope = 0.14, r = 0.17, P > 0.05) during the defoliation period, but it rebounded back to a relative high level (slope = 1.44, r = 0.55, P < 0.01) during the refoliation period which was similar to that during the remaining periods; and (4) the relationship between Js and Ta was generally positive, while both SWC5 and SWC100 exerted inhibitory effects on Js, and the interactive effects among Ta, SWC5 and SWC100 on Js were significant during the refoliation period (P < 0.01). Based on these findings, we evaluated Js as a crucial physiological indicator of the processes underlying important phenological transition periods, and the cold stress rather than drought stress was likely the driving factor of the pattern of intense defoliation occurred in Southwest China rubber plantations.

Biomass flows and defoliation pattern of ryegrass grazed by supplemented heifers

To strategically define the best stocking rate management strategy for ryegrass, it is important to know the growth process of forage plants in detail. The study was conducted to analyze the leaf biomass flows and the defoliation intensity and frequency of Italian ryegrass (Lolium multiflorum Lam) grazed by heifers fed exclusively on pasture or on pasture and supplemented with corn or white oat grain. The experimental design was completely randomized following a repeated measures arrangement with three feeding systems and three area replications. Biomass flows (kg DM leaf blades ha1 day1) for leaf growth (40.6), leaf senescence (40.7), and leaf intake (29.7) were similar in the different feeding systems. Leaf blade intake adjusted to body weight was lower in supplemented heifers regardless of grain type. Actual and potential utilization efficiencies and ryegrass biomass net balance were not affected by feeding system. The leaf intake flow was 1.4 times lower than the growth flow, resulting in an actual utilization efficiency less than one (0.7), whereas the senescence flow was higher than the growth flow, resulting in a negative potential utilization efficiency (0.2). Leaf defoliation intensity was similar (54.4%) across feeding systems and defoliation frequency was higher in supplemented heifers. The 29.2% increase in stocking rate of heifers fed corn or oat grain as supplement did not affect the dynamics of ryegrass biomass flows, but reduced leaf blade intake adjusted to heifer body weight leading to alterations in the defoliation frequency of ryegrass pasture.

Detection of the spatiotemporal patterns of beetle-induced tamarisk (Tamarix spp.) defoliation along the Lower Rio Grande using Landsat TM images

The invasive Tamarisk (Tamarix spp.) has long been targeted for removal by land managers in the western United States. Biocontrol of the non-native tamarisk started in 2001 by introducing the tamarisk leaf beetle (Diorhabda spp.) to the riparian ecosystems. Since then, the beetles quickly established and substantial tamarisk defoliation was subsequently observed along river corridors in the western states. The ability to monitor and track the patterns of beetle-induced tamarisk defoliation across space and time is key to understand its impact on ecosystem functioning and processes. In the present study, spatiotemporal patterns of tamarisk defoliation caused by the subtropical tamarisk leaf beetle (D. sublineata) were successfully detected using a classification based method along the Lower Rio Grande in West Texas from 2009 to 2014. Our results indicated that the subtropical beetle species can sustain a dispersal rate of approximately 102kmyr−1 during the first year after release. Tamarisk abundance was the most important factor in directing beetle dispersal. We also found that the beetles preferred to forage within dense, connected tamarisk stands along wide sections of the riparian river corridors. These new findings of our study will help inform the land managers of the possible outcomes of tamarisk biocontrol to make effective management plans.

Timing and frequency are the critical factors affecting the impact of defoliation on long term growth of plantation eucalypts

Insect defoliation of plantation Eucalyptus sp. is a ubiquitous problem, not only in their native Australia but also in many other countries where Australian defoliators have invaded the introduced eucalypt plantations. Although eucalypts are very resilient to defoliation, their growth suffers and reduces the economic benefits of the resource. An artificial defoliation trial investigated the critical factors relating to patterns of insect defoliation that affect the long-term growth of the plantation eucalypt, E. nitens, in Tasmania, Australia. Current season’s adult-phase foliage was removed manually from two- to three-year-old trees to test four factors: severity (50% or 100% of current adult foliage, equivalent to 11% or 25% of total foliage); disbudding following defoliation (with or without disbudding), timing of defoliation (early or late in the summer) and frequency (for one or two consecutive years). Growth parameters of the trees were measured annually for four years after the initial defoliation, and again thirteen years later, before harvest. The most significant factors affecting the growth of the trees were timing and frequency of defoliation; severity of defoliation and disbudding did not have significant effects over the long term. Trees that received either light or heavy defoliation late in the season for two consecutive years were at least 17% smaller in diameter and MAI in diameter was reduced by at least 21% compared to untreated trees over one rotation. This means they would need to be grown for three to four more years to reach the same stand volume as undefoliated trees at harvest. This would have serious cost implications for plantation managers. To prevent these economic losses, an integrated pest management system should focus on protecting eucalypts from defoliation of 50% or more of current season’s adult foliage late in the summer, and in particular, preventing defoliation from occurring in concurrent years. In addition, the continual decline in growth rates of defoliated trees relative to undefoliated trees beyond the initial four years of measurement also suggests that defoliation impacts predicted by models based on short term studies may need to be treated conservatively.

Biomass flow and defoliation pattern in alexandergrass fertilized with nitrogen

The determination of biomass flows can assist on improving pasture fertilization techniques, contributing to identify the best management methods and, in relation the use of fertilizers. Nitrogen deficiency in pastures can reduce forage production. On the other hand, there is an environmental concern on nitrogen (N) losses when this nutrient is used in excess and this concern guides the search for new grazing systems that optimize its use. Leaf biomass flow, intensity and frequency of defoliation were evaluated in Alexandergrass ( Urochloa plantaginea (Link) Hitch) fertilized with Zero, 100, 200 or 300 kg/hanitrogen (N) as urea. The grazing method was put and take stocking in order to keep the forage mass at 3,000 kg/haDM. The experimental animals were Angus heifers with an initial age of 15 months and body weight of 241.5±5 kg. The experimental design was completely randomized following a repeated measure arrangement, with four treatments and variable number of experimental units. The highest growth of leaf blades was achieved with 100 kg/haN. Senescence and intake flows and defoliation intensity were similar among the N levels used. The frequency of return to the same tiller (days) was influenced by N levels and evaluation periods. Our findings recommend the use of 100 kg/ha N in Alexandergrass pasture.

Analysing Atmospheric Processes and Climatic Drivers of Tree Defoliation to Determine Forest Vulnerability to Climate Warming

Crown defoliation is extensively monitored across European forests within the International Co-operative Programme (ICP) as a proxy of forest health. Climate warming and drought are assumed to be the major drivers of tree growth and crown defoliation, particularly in seasonally dry areas such as the Mediterranean Basin. Here we analyse how climate, drought, and atmospheric processes are related to defoliation time series of five oak and five pine species that are dominant across Spanish ICP monitoring forest plots. We found that warmer and drier conditions during April were linked to enhanced defoliation. Warm April conditions were also related to high values of the Atlantic Multi-decadal Oscillation (AMO), thereby indicating large-scale links between atmospheric processes, temperature, and defoliation patterns. The temperature-defoliation association was species-specific since some tree species from wet sites showed a weak association (e.g., Quercus robur L.) whereas others from dry sites (e.g., Quercus ilex L.) presented the strongest associations. The latter tree species could be considered vulnerable to heat stress in terms of leaf shedding. We also explored if defoliation was related to radial growth and found negative associations in relatively dry areas. Warmer and drier conditions linked to increasing AMO values are connected to the post-1990s rise of defoliation in Spanish ICP forest plots. Combined incorporation of defoliation and growth into mortality models can provide insights into assessments of forest vulnerability.

Stand factors influencingPinus halepensisdecline in north‐western Spain

SummaryAlthough decline of Aleppo pine was observed long ago and several climatic and biotic factors have been previously associated with this complex process, site factors involved in this decline remain poorly understood. The objective of the work described here was to identify site factors associated with canopy condition. Canopy condition was estimated both by a visual estimation of defoliation, and by an indirect estimation of leaf area index (LAI) and other stand‐ and light‐related parameters through the analysis of hemispherical photographs. A high percentage of damaged trees (81%) along with high levels of defoliation in plots (up to 53%) and trees (up to 85%) were recorded. Regression models showed that the site factors associated with defoliation were basal area, age, crown depth and elevation, while those associated withLAIwere diameter at breast height, tree density and canopy openness. Analysis of hemispherical photographs proved to be a useful method forLAIestimation, but not for estimation of defoliation due to heterogeneous defoliation patterns caused by fungal pathogens detected in the study area. Soils and climatic conditions were common to all plots, so their influence could not be tested, but poor soil conditions and climatic restraints are known in this area, including low soil productivity, frequent summer droughts and high numbers of frost days. The results obtained suggest that several factors were associated with the decline ofPinus halepensis, including age, basal area, canopy openness, diameter, height and tree density. These factors can influence canopy condition, and thus, they might be acting as predisposing factors for the decline. The modulation of these factors is possible if suitable forest management strategies are applied, which could lead to a decrease of the decline incidence.

Xaraés palisadegrass remains productive after the disappearance of stylo in tropical legume-grass pasture

Gradual reduction of legumes in mixed tropical pastures requires periodic oversowing. Exploiting the carrying capacity of grass for an extra year after the disappearance of legumes can be economically advantageous to the farmer. This study aimed to evaluate the productivity of Xaraes palisadegrass (Brachiaria brizantha) pastures in response to its historical association with stylo (Stylosanthes guianensis) under two canopy heights to determine whether different grazing management conditions affect the defoliation pattern left by grazing animals. The split-plot experimental design was used, with the historical botanical composition (HBC) (24, 34, 45 and 52 % legume composition) corresponding to the main plots and the canopy frequency of defoliation determined at heights of 30 and 45 cm for Xaraes palisadegrass corresponding to the subplots with two replicates (500 m2) grazed by Tabapua cows. Pastures with over 34 % stylo in the botanical composition remained productive for one year after legume disappearance, accumulating more than 8 mg ha−1 of forage per year. Xaraes palisadegrass pastures at a height of 30 cm provided better canopy structure, with 64 % less stem production and 43 % less dead material. The 30-cm pre-grazing canopy height provided a grazing environment conducive to forage intake by animals that resulted in efficient use of the pasture. In response to the improved canopy structure, the cows grazed an average of 60 fewer minutes. A HBC greater than 34 % of legumes in the pastures allows for the postponement of legume oversowing until the next growing season.

Defoliation patterns and their implications for the management of vegetative tropical pastures to control intake and diet quality by cattle

AbstractThis study assessed the use of pasture attributes to control daily intake and diet quality during progressive defoliation on pastures of Axonopus catarinensis. Three consecutive 12‐day grazing treatments of progressive defoliation were conducted with Brahman cross‐steers. Daily forage intake and defoliation dynamics were assessed using a pasture‐based method. The treatments differed in initial sward height (33, 44 and 61 cm) and herbage mass (1030, 1740 and 2240 kg ha−1). The post‐grazing residual sward height, at which forage intake decreased, appeared to increase with the initial sward height (12·3, 14·6 and 15·5 cm). Steers grazed up to four distinctive grazing strata in all treatments. The depth and herbage mass content of the top grazing stratum were at least five times higher than the lower grazing strata in all treatments. This explains why forage intake decreased when the top grazing stratum was removed in approximately 93% of the pasture area in all treatments, equivalent to approximately 7% of the pasture area remaining ungrazed. We conclude that the residual ungrazed area of the pasture, rather than residual sward height, can be used to develop grazing management strategies to control forage intake and diet quality in a wide range of pasture conditions.

Herbage utilisation efficiency of continuously stocked marandu palisade grass subjected to nitrogen fertilisation

Nitrogen fertiliser accelerates plant growth and increases herbage utilisation efficiency in continuously stocked temperate grass swards, indicating greater herbage production and harvest efficiency. There is no similar evidence, however, for tropical pastures. In this study we evaluated the morphogenetic responses, the patterns of defoliation and the efficiency of herbage utilisation of continuously stocked marandu palisade grass (Brachiaria brizantha (Hochst. ex A. Rich.) Stapf. cv. Marandu) maintained at 30 cm by cattle and fertilised with nitrogen. Treatments corresponded to four measures of nitrogen application (0, 150, 300 and 450 kg ha–1), and were assigned to experimental units (1,200 m2 paddocks) according to a randomised complete block design, with four replications. There was a seasonal pattern of variation in the morphogenetic responses and in herbage utilisation efficiency (HUE) characterised by higher herbage growth rates and HUE during late spring and summer. Nitrogen fertilisation increased both leaf appearance and elongation rates (around 60 % between non-fertilised and swards fertilised with 450 kg ha–1, p < 0.05), requiring higher stocking rates (average of 1.6, 2.6, 2.9 and 3.1 Animal Unit (adult animal weighing 450 kg) ha–1 for 0, 150, 300 and 450 kg ha–1, respectively) to maintain the management target. Although the frequency of leaf defoliation increased (with no change in defoliation severity - 56.1 ± 1.88 %), the leaf lifespan decreased, resulting in a similar number of defoliations during the leaf lifespan (average of 0.91 ± 0.069). This resulted in increased HUE only for the 150 kg ha–1 treatment relative to non-fertilisation (37.5, 48.1, 44.0 and 44.5 ± 2.25 % for 0, 150, 300 and 450 kg ha–1 N, respectively), indicating that with nitrogen fertilisation rates above 150 kg ha–1, there are compensatory mechanisms related to morphogenetic responses that buffer changes in utilisation efficiency.

Spatially Heterogeneous Nest-Clearing Behavior Coincides with Rain Event in the Leaf-Cutting Ant Atta cephalotes (L.) (Hymenoptera: Formicidae).

Leaf-cutting ants of the genus Atta construct the probably largest nests among ants and are ecosystem engineers because they alter light and nutrient availability at nest sites. Besides creating canopy gaps in the forest, workers remove all vegetation from atop their nest mounds. Here, we examined the extent and spatial distribution of this nest-clearing behavior by transplanting Licania tomentosa seedlings on Atta cephalotes (Linnaeus) nest mounds in the Atlantic forest in northeast Brazil and documented defoliation patterns by the workers. Within 9 days, workers removed around 53% of the total leaf area planted per colony. All colonies showed a synchronized start of defoliation after a rain event in the fifth night after the seedlings had been transplanted. Defoliation increased with time elapsed since transplanting and with the number of entrances surrounding each seedling. In addition, workers started defoliation on the top of the mound. In contrast, the distance to the next entrance and the size of the seedling did not affect the defoliation pattern. Defoliation was not part of the colony foraging activities but was identified as an element of nest maintenance. Possible cues triggering nest-clearing behavior and the potential link between nest-clearing activities and the control of microclimate of ant nests are discussed.

Nutrient resorption of Castanopsis eyrei varies at the defoliation peaks in spring and autumn in a subtropical forest, Anhui, China

AbstractNutrient resorption from senescing leaves is a key nutrient conservation strategy in many ecosystems. In evergreen broad‐leaved forests, nutrient resorption occurs with concomitant defoliation almost year‐round. However, it is unclear whether nutrient resorption efficiency (NuRE) varies in different defoliation seasons for evergreen broad‐leaved trees and how it may relate to soil nutrient availability. Castanopsis eyrei is a dominant tree species in evergreen broad‐leaved forests in southern China, with distinct bimodal patterns of defoliation in spring and autumn. We investigated seasonal variation of the resorption efficiency of nitrogen (N) and phosphorus (P) of C. eyrei leaf and its relationship with soil mineral N by measuring the concentrations in leaf, leaf litter, and soil for two consecutive years. We hypothesized that leaf NuRE should be higher in seasons with low soil nutrient availability. We found that on average, soil mineral N content was 38.5 % lower during the autumn defoliation peak than in spring, and N and P concentrations in leaf litter at the spring defoliation peak were 10.0 and 26.7 % higher than at the autumn peak. Nitrogen NuRE at the autumnal defoliation peak was 5.1 % higher than that at the spring peak (49.3 vs 44.2 %), and the phosphorus NuRE in autumn was 6.8 % higher than that in spring (77.6 vs 69.8 %). Our findings suggest an inverse relationship between soil nutrient availability and NuRE and that the dynamics in NuRE should be incorporated into modeling of biogeochemical cycling in evergreen forest ecosystems with a bimodal defoliation pattern.

&lt;b&gt;Defoliation patterns and tillering dynamics in Italian ryegrass under different herbage allowances

This work was carried out in order to generate information on the tillering process and to contribute for the understanding of the defoliation process on Italian ryegrass (Lolium multiflorum Lam.) grazed by lambs under different herbage allowances: 6, 8 and12 kg of dry matter per100 kg of animal live weight per day. The grazing method was intermittent. The experimental design was completely randomized following a repeated measure arrangement, with three treatments and two area replications. The intensity of defoliation is greater at 6 and 9% herbage allowances. The defoliation interval is higher at 12% herbage allowance, intermediate at 9% and lower at 6%. The rates of tiller emergence, survival and death, stability index the tiller population are similar for the different herbage allowances and differ according to the phenological stage of ryegrass. Structural changes caused by canopy management with low herbage allowance and/or due to the advance in developmental stage of ryegrass alter defoliation strategies, with more intense and frequent grazing.

Spatial variability of spruce budworm defoliation at different scales

Aerial survey records of defoliation by spruce budworm (Choristoneura fumiferana (Clem.)) in New Brunswick, Canada taken annually from 1965 to 1992, were analyzed at four scales (66×66km, 10×10km, 2×2km, 1×1km) to determine patterns and spatial variability of defoliation. Spruce budworm defoliated 92% of the 7.4 million ha study area in at least one year. Cluster analysis was used to group similar defoliation patterns, and 51% of the variation in the 28-year record was described by 28 representative defoliation patterns, at 1×1km cell size. Individual defoliation patterns were grouped into five spruce budworm outbreak classes (termed A–E), which each covered 12–27% of the area. These differed substantially in defoliation duration and severity: classes A–B had only 1–3years of moderate–severe defoliation and 42–75% cumulative defoliation; class C had 8years and 127% cumulative defoliation; and classes D–E had 13–16years and 170–208% cumulative defoliation. Given the degree of ‘averaging out’ of high defoliation occurrences that cause the largest impacts, larger 10×10km and 66×66km cells were inappropriate for impact analysis. Defoliation variability was highest at 20–60% mean defoliation than at lower or higher defoliation levels. Distributions of area in each class in 1×1km cells for 66×66km areas throughout the province showed that with the exception of several small coastal areas, four or five of the above outbreak classes occurred in all areas. The wide variation in spruce budworm outbreak patterns is important in making management decisions that differentiate insecticide or salvage treatments based on defoliation severity, and emphasizes the importance of accurate annual aerial survey or remote sensing-based defoliation assessment.

Do plant defenses predict damage by an invasive herbivore? A comparative study of the viburnum leaf beetle.

The impact of plant defenses on insect herbivores is widely accepted, but their relative effects on oviposition choice, survival, and larval growth in preventing pest damage, especially for invasive insects, is not fully understood. Here, we examined the potential for plant defenses to reduce the economic and environmental impacts of an invasive herbivore, the viburnum leaf beetle, VLB (Pyrrhalta viburni), on Viburnum species in North America. We used a common garden with 15 host Viburnum species of North American, European, and Asian origin and evaluated oviposition preferences, twig defense against oviposition (a reaction that crushes VLB eggs), larval performance in the lab and field, and foliar damage to mature shrubs in two consecutive years. VLB oviposition preference was the strongest predictor of plant damage, with twig defense and larval performance explaining little of the defoliation patterns. In particular, we showed that VLB females evade key defenses by choosing poorly defended twigs for oviposition; assays on the 15 Viburnum species revealed that adults laid over four times more eggs on dead (undefended) twigs than on living twigs. We additionally tested the hypothesis that shrubs with a higher proportion of dead twigs are preferentially chosen for oviposition, leading to more defoliation by larvae and increased dieback in the following year. We term this the infestation feedback hypothesis. Indeed, we report consistent positive correlations between percentage dieback, oviposition, and percentage defoliation across Viburnum species, and among individuals within two species tested separately (V. dentatum and V. opulus). Our results demonstrate that oviposition preference plays a major role in the susceptibility of Viburnum shrubs to the invasive VLB through adults choosing high-quality species for their larvae (a strong preference-performance correlation) and avoiding well-defended twigs among preferred species. More generally, where invasive insects can avoid plant defenses and when preference and performance are positively correlated, an infestation feedback loop can lead to persistent pest problems. Because dieback weakens Viburnum defenses by providing optimal oviposition sites, we recommend that Viburnum growers mechanically remove dead twigs from susceptible shrubs at the end of the growing season, especially in the early stages of VLB colonization.

Predicting the altitudinal distribution of an introduced phytophagous insect against an invasive alien plant from laboratory controlled experiments: case of Cibdela janthina (Hymenoptera:Argidae) and Rubus alceifolius (Rosaceae) in La Réunion

The sawfly Cibdela janthina (Hymenoptera: Argidae) native to Sumatra was introduced on La Reunion (France, Indian Ocean) in 2007 to control the giant bramble Rubus alceifolius (Rosaceae), one of the most invasive plants on this island. We determined the influence of temperature on the development duration and survival of C. janthina preimaginal stages in controlled conditions in order to parameterize a survival model and to relate the predicted survival with observed patterns of defoliation of the host plant at different altitudes. We adjusted the Regniere model to survival data, combined with the Lactin-2 model on development rate of the three preimaginal stages of C. janthina. This model adequately predicts the observed defoliation and the altitudinal limit of the biological control agent. Our results also show that studies on temperature-related constraints on the biology of an agent introduced for weed control should be emphasized both in the pre-release and the post-release phases of a biological control program to evaluate the potential success of the control programme.

INTERDEPENDÊNCIA ENTRE OS PADRÕES DE DESFOLHAÇÃO E A MORFOGÊNESE DO CAPIM-BRAQUIÁRIA SOB INFLUÊNCIA DAS FEZES DEPOSITADAS POR BOVINOS

The knowledge of interdependence between defoliation patterns and morphogenesis of grasses allows the identification of the effects of feces deposition by cattle on the pasture. Thus, this work was developed to estimate regression equations for morphogenetic characteristics in function of grazing patterns of the same Brachiaria decumbens pasture under influence of feces deposited by cattle. The pasture was managed under continuous stocking with variable stocking rate to maintain the average height of 25 cm. The increases in defoliation frequency (DF) and grazing intensity (GI) reduced linearly the rates of senescence and leaf and stem elongation, but increased linearly the leaf appearance rate. The DF and GI also linearly reduced the number of dead leaves per tiller and the leaf and stem lengths. The forage loss resulted in adverse effects on the morphogenetic and structural characteristics of B. decumbens. The lowest grazing level near the feces increases forage loss on pasture, the size of leafs and stems, senescence and growth of B. decumbens tillers, and reduces leaf appearance.KEYWORDS: Brachiaria decumbens; defoliation frequency; forage loss; grazing intensity; growth.

&lt;b&gt;Biomass flows and defoliation patterns of alexandergrass pasture grazed by beef heifers, receiving or not protein salt

The experiment aimed at evaluating leaf biomass flow, intensity and frequency of defoliation of Alexandergrass (Urochloa plantaginea (Link) Hitch) by beef heifers exclusively on pasture or that grazed and received protein salt. A completely randomized experimental design was used with repeated measures over time, two treatments and two area replications, with three Angus test heifers by paddock. Leaf blade intake flow is 18% superior for heifers exclusively on pasture. Grazing intensity (59.8%) is similar when heifers receive protein salt or not. Heifers receiving protein salt reduce by one day the defoliation frequency of tillers. The supply of protein salt for beef heifers grazing Alexandergrass affects the herbivore-plant relationship, decreasing intake flow and leaf blade defoliation frequency.

Effect of season and interval of prescribed burn on ponderosa pine butterfly defoliation patterns

Current knowledge concerning the interactions between forest disturbances such as fire and insect defoliation is limited. Wildfires and prescribed burns may influence the intensity and severity of insect outbreaks by affecting the vigor of residual trees, altering aspects of stand structure and abundance of preferred hosts, and by changing the physical environment within forest stands. Prescribed burn timing and frequency are particularly important aspects of the fire regime to consider because they can alter numerous aspects of tree vigor, stand structure, and environmental conditions, and can be manipulated by managers. We evaluated ponderosa pine (Pinus ponderosa Douglas ex P. Lawson &amp; C. Lawson) defoliation patterns in relation to season (fall and spring) and interval (5 or 15 years) of prescribed burn in the southern Blue Mountains of Oregon. Beginning in 2008 a pine butterfly (Neophasia menapia C. Felder &amp; R. Felder) (Lepidoptera: Pieridae) outbreak coincided with a long-term experimental study, providing a unique opportunity to address this question. Defoliation patterns were measured in 2012. The 5 year interval plots had burned three times with five growing seasons of recovery and the 15 year interval plots had burned once with 15 growing seasons of recovery. Mean pine butterfly defoliation across the study area was about 71%. We found a significant interaction between season of burn and interval of burn on defoliation. Areas burned in the fall every 5 years had marginally less (about 5%) defoliation compared with areas that were burned in the fall 15 years previous. Regression tree analysis revealed that defoliation patterns varied based on stand location, percent mortality since the start of the experiment, and tree height. Our results show that (i) season of burn and interval of burn did not predispose these stands to increased defoliation during a pine butterfly outbreak and (ii) repeat burning may actually lead to lower defoliation. However, the effect we document is small and only marginally significant.

&lt;b&gt;Defoliation patterns in signal grass tillers with varying heights in the same pasture&lt;/b&gt; - doi: 10.4025/actascianimsci.v35i3.14376

The experiment was carried out to evaluate the patterns of defoliation in plants of various heights in the same pasture of Brachiaria decumbens cv. Basilisk under continuous stocking with cattle. Four plant heights were evaluated (10, 20, 30 and 40 cm) in the same managed sward, with mean height equal to 25 cm. A randomized blocks design was used, with two replications. Defoliation frequency increased linearly along with plant height in the same pasture. Defoliation intensity, number of defoliations in leaf blade and percentage of leaf blade grazed per tiller also increased linearly along with plant height. The defoliation interval decreased linearly according to plant height. The quadratic model was adequately fitted into grazing efficiency data, reaching the highest value (98%) at the sward site with 35 cm plants. The percentage variation in signal grass height showed a negative linear response with initial plant height. The structure of the pasture, characterized by the diversity in plant heights, is simultaneously the cause and consequence of the variability in defoliation patterns in individual tillers, which occur on the horizontal plane of the pasture.