Artificial Canopy Research Articles

Seasonal variation of dry and wet islands in Beijing considering urban artificial water dissipation

Urbanization has resulted in dry/wet island effects in built-up areas. Compared to the limited number of observational datasets, simulations can provide data with richer spatial distribution, thereby proving to be more helpful for revealing the spatial distribution of dry/wet islands. This study simulated dry/wet island effects during typical summer and winter conditions in Beijing by coupling the Artificial Water Dissipation Urban Canopy Model with the Weather Research and Forecasting model. Observations of relative humidity, absolute humidity, and temperature from weather stations in Beijing were used to verify the model. The results showed that in 2020, Beijing was prone to be a dry island during summer, with the relative humidity approximately 5–10% lower than the surrounding suburbs. The dry island effect was not obvious in winter, and Beijing tended to be a wet island. The influence of artificial water dissipation on dry/wet islands is higher in winter than in summer. By considering the water vapor from artificial water dissipation, humidity in urban areas can be simulated more accurately.

Influence of Simulated Nitrogen Deposition on the Soil Seed Bank of a Subtropical Evergreen Broadleaved Forest

Increased nitrogen (N) deposition may have profound effects on forest ecosystems. However, information on the impacts of elevated N deposition on belowground soil seed bank in forests is lacking. In a field experiment, we added N at 50 and 25 kg N ha−1 year−1 to the canopy (CAN50 and CAN25) and to the understory (UAN50 and UAN25), to determine the effects of N deposition on soil seed bank structure and composition in a subtropical evergreen broadleaved forest. A total of 1545 seedlings belonging to 37 species emerged from the 10 cm-depth soil samples. After 6 years of N addition, soil seed bank density significantly increased at the depth of 0–10 cm under CAN50 treatment relative to the control. N addition did not significantly affect species richness, the Simpson index, Shannon–Wiener index, or Pielou index of the soil seed banks. Seed bank density and species richness were positively correlated with soil organic matter content. For the whole 0–10 cm soil layer, the percentage of total seed abundance and total species richness represented by tree species among the N-addition treatments was ≤9.3% and ≤16.1%, respectively. Soil seed bank composition was similar among UAN25, UAN50, and the control, but canopy N addition and especially CAN50 altered the species composition of the seed bank. Overall, our results indicate that artificial canopy N deposition at 50 kg N ha−1 year−1 but not understory N addition tends to promote seed storage and to change species composition in the soil seed bank. Because of the dominance of shrubs and herbs in the soil seed bank, the potential to regenerate tree species from the soil seed bank is limited in the subtropical evergreen broadleaved forest.

Impact of weather conditions, seasonality and moonlight on the use of artificial canopy bridges by nocturnal arboreal mammals

Natural and artificial canopy bridges can be used to mitigate the effects of habitat fragmentation. Understanding the ecological factors that influence bridge use is imperative to the effective design and placement of this potential conservation intervention. Moonlight, seasonality and weather may influence the cost and risk of using bridges, potentially reducing their effectiveness. We installed five artificial waterline bridges and, between 2017 and 2019, monitored via camera trapping their use by Javan palm civets Paradoxurus musanga javanicus and Javan slow lorises Nycticebus javanicus. We used a weather station to record microclimate data (temperature and relative humidity) and calculated the illumination percentage of the moon. We tested the influence of moon luminosity, relative humidity, seasonality (Julian day) and temperature on the frequency of bridge use via Generalised Additive Models. Camera traps captured 938 instances of bridge use by civets, which was significantly lower than the reference value at moon luminosity > 90%, temperatures > 20 °C, humidity > 90%, and during the drier period (May–July). Camera traps captured 1036 instances of bridge use by lorises, which was significantly lower than the reference value during the drier period and higher than the reference value at temperatures > 20 °C. Lorises showed peaks in bridge use close to sunset and sunrise whereas civets showed peaks around 2 h after sunset and 2 h before sunrise. Our study illustrates the utility of simple-to-construct bridges by two sympatric nocturnal mammals facing severe habitat loss, with bridge use differing between those species according to abiotic factors. In particular, less use by both taxa during the drier season could suggest modifying placement of bridges or providing another intervention during that time. Camera traps were an excellent mechanism to record these differences and to validate the importance of the bridges, including during inclement weather and dark nights, when observations would be more difficult for human observers. By understanding the influence that abiotic factors have on the use of artificial bridges, we can improve bridge placement and construction to encourage use by a variety of species, particularly those threatened by habitat fragmentation.

Dorsal landmark navigation in a Neotropical nocturnal bee

Bees, ants, and wasps are well known to visually navigate when traveling between their nests and foraging sites. When leaving their nest, landmarks in the vicinity are memorized and used upon return to locate the nest entrance.1,2 The Neotropical nocturnal sweat bee Megalopta genalis navigates under the forest canopy at light intensities ten times dimmer than starlight.3 Despite these dim conditions, Megalopta is able to memorize visual landmarks around the nest entrance in the frontal visual field.4 Even though frontal landmarks can clearly be discerned by Megalopta, the visual feature of greatest contrast in the rainforest at night is actually the dark dorsal silhouette of the distant canopy against the brighter night sky. Several species of ants,5-10 as well as a subsocial shield bug,11 use bright open gaps in the canopy as dorsal landmarks to navigate home while walking. Here we show that Megalopta is also able to distinguish dorsal landmarks during homing, the first flying insect known with this capacity. Megalopta is able to discriminate between differently oriented dorsal black striped patterns, or an "artificial canopy" of black circles, and to use this information to locate its nest entrance. These results suggest that the local foliage patterns created by the canopy against the brighter sky could potentially provide the bee with reliable landmark information for navigation during foraging and homing at night. VIDEO ABSTRACT.

Dorsal Landmark Navigation in a Neotropical Nocturnal Bee

Bees, ants and wasps are well known to visually navigate when traveling between their nests and foraging sites. When leaving their nest, landmarks in the vicinity are memorised and used upon return to locate the nest entrance 1-3 . The Neotropical nocturnal sweat bee Megalopta genalis navigates under the forest canopy at light intensities ten times dimmer than starlight. Despite these dim conditions, Megalopta is able to memorise visual landmarks around the nest entrance in the frontal visual field. Even though frontal landmarks can clearly be discerned by Megalopta, the visual feature of greatest contrast in the rainforest at night is actually the dark dorsal silhouette of the distant canopy against the brighter night sky. Several species of day-active ants, as well as a subsocial shield bug, use bright open gaps in the canopy as dorsal landmarks for short-range navigation while walking. Here we show that Megalopta is also able to distinguish dorsal landmarks, the first flying insect known with this capacity. Megalopta is able to discriminate between differently oriented dorsal black striped patterns, or an “artificial canopy” of black circles, and to use this information to locate its nest entrance. These results suggest that the local foliage patterns created by the canopy against the brighter sky could potentially provide the bee with reliable landmark information for navigation during foraging and homing at night.

First use of artificial canopy bridge by the world\u2019s most critically endangered primate the Hainan gibbon Nomascus hainanus

All gibbon species (Primates: Hylobatidae) are facing high extinction risk due to habitat loss and hunting. The Hainan gibbon Nomascus hainanus is the world’s most critically endangered primate, and one of the priority conservation actions identified is to establish artificial canopy corridors to reconnect fragmented forests. The effectiveness of artificial canopy bridge as a conservation tool for wild gibbons has not been widely tested, and the results are rarely published. We constructed the first canopy bridge for Hainan gibbon in 2015 to facilitate passage at a natural landslide; mountaineering-grade ropes were tied to sturdy trees with the help of professional tree climbers and a camera trap was installed to monitor wildlife usage. Hainan gibbon started using the rope bridge after 176 days, and usage frequency increased with time. All members in the gibbon group crossed the 15.8 m rope bridge except adult male. Climbing was the predominant locomotor mode followed by brachiation. This study highlights the use and value of rope bridges to connect forest gaps for wild gibbons living in fragmented forests. While restoring natural forest corridors should be a priority conservation intervention, artificial canopy bridges may be a useful short-term solution.

Implementing and Monitoring the Use of Artificial Canopy Bridges by Mammals and Birds in an Indonesian Agroforestry Environment

Deforestation is a major threat to biodiversity, particularly within tropical forest habitats. Some of the fastest diminishing tropical forest habitats in the world occur in Indonesia, where fragmentation is severely impacting biodiversity, including on the island of Java, which holds many endemic species. Extreme fragmentation on the western part of the island, especially due to small-scale agriculture, impacts animal movement and increases mortality risk for mainly arboreal taxa. To mitigate this risk in an agroforest environment in Garut District, West Java, we installed 10 canopy bridges and monitored them through camera trapping between 2017 and 2019. Five of the monitored bridges were made of waterlines and five of rubber hose. We recorded Javan palm civets using the waterline bridges 938 times, while Javan slow lorises used the waterlines 1079 times and the rubber bridges 358 times. At least 19 other species used the bridges for crossing or perching. Our results demonstrate that relatively simple and cost-effective materials can be used to mitigate the effects of habitat fragmentation. We also recommend the use of camera traps to monitor the effectiveness of these interventions.

Application of LiDAR Data for the Modeling of Solar Radiation in Forest Artificial Gaps—A Case Study

Artificial canopy gaps (forest openings) are frequently used as an element of regeneration cutting. The development of regeneration in gaps can be controlled by selecting a relevant size and shape for the gap, which will regulate the radiation microclimate inside it. Based on the size and shape of a gap computer models can assess where solar radiation is decreased or eliminated by the surrounding canopy. The accuracy of such models to a large extent depends on how the modeled shape of a gap matches the actual shape of the gap. The aim of this study was to compare the results of modeling solar radiation availability by applying Solar Radiation Tools (SRT) that use a different digital surface model (DSM) for a description of the shape of a studied gap, with the results of the analysis of 27 hemispherical photographs. The three-dimensional gap shape was approximated with the use of simple geometrical prisms or airborne laser scanning (LiDAR) data. The impact of two variations of exposure (automatic and manual underexposure) and two variations of automatic thresholding on the congruence of SRT and Gap Light Analyzer (GLA) results were studied. Taking into account information on differences in height between trees surrounding the gap enhanced the results of modeling. The best results were obtained when the boundary of the gap base estimated from LiDAR was expanded in all directions by a value close to a mean radius of the crowns of surrounding trees. Modeling of radiation conditions on the gap floor based on LiDAR data by an SRT program is efficient and more time effective than taking hemispherical photographs. The proposed solution can be successfully applied as a trustworthy source of information about light conditions in gaps, which is needed for management decision-making in silviculture.

Seedling development and regeneration success after 10 years following group selection harvesting in a sessile oak (Quercus petraea [Mattuschka] Liebl.) stand

This study showed that regeneration success (presence of oaks ≥ 150 cm in total height) in artificial canopy openings of a mature mixed sessile oak stand was mainly driven by initial oak seedling density. Small-scale harvesting methods as practiced in close-to-nature forestry may disadvantage the regeneration of more light-demanding tree species including sessile oak (Quercus petraea [Mattuschka] Liebl.) and thus cause regeneration failure. However, owing to the short-term nature of many previous studies, regeneration success of sessile oak could not be properly ascertained. This study examined oak seedling development over a time period of ten growing seasons in canopy openings of 0.05 to 0.2 ha in size created through group selection harvesting in a mature mixed sessile oak forest in southwestern Germany. We tried to answer the following research questions: (i) how do initial stand conditions relate to and interact with oak seedling density and seedling height growth, and (ii) what are the driving factors of regeneration success under the encountered site conditions. We evaluated the influence of solar radiation, Rubus spp. cover, initial oak seedling density, and competition from other tree species on change in density and height of oak seedlings, as well as overall regeneration success (oak seedlings ≥ 150 cm in height). Regeneration success increased with initial oak seedling density and solar radiation levels and decreased with early Rubus spp. cover. Density and maximum height of oak seedlings was negatively related with competition of other woody species. Results of our longer-term study demonstrate that forest management activities to regenerate sessile oak naturally are only successful in stands (i) without advance regeneration of other woody species and without established, recalcitrant ground vegetation, (ii) with a sufficiently high initial oak seedling density in larger patches following mast years, and (iii) where periodic monitoring and control of competing woody individuals can be ensured. Our findings further corroborate the view that natural regeneration of sessile oak in small-scale canopy openings is possible in principle.

Artificial canopy bridges improve connectivity in fragmented landscapes: The case of Javan slow lorises in an agroforest environment.

Canopy bridges are increasingly used to reduce fragmentation in tropical habitats yet monitoring of their impact on the behavior of primates remains limited. The Javan slow loris (Nycticebus javanicus) is endemic to Java, Indonesia, where the species most often occurs in human-dominated, highly patchy landscapes. Slow lorises cannot leap, are highly arboreally adapted, and are vulnerable on the ground. To increase arboreal connectivity, as part of a long-term conservation project in Cipaganti, West Java, we built and monitored seven slow lorises bridges of two types-waterline or rubber-and monitored their use by seven adult individuals from 2016 to 2017. Motion triggered camera traps collected data for 195 ± standard deviation (SD) 85 days on each bridge. We collected 341.76 hr (179.67 hr before and 162.09 hr after the installation of bridges) of behavioral and home range data via instantaneous sampling every 5 min, and terrestrial behavior (distance and duration of time spent on the ground) via all occurrences sampling. We found that slow lorises used bridges on average 12.9 ± SD 9.7 days after their installment mainly for traveling. Slow lorises showed a trend toward an increase in their home range size (2.57 ha before, 4.11 ha after; p = 0.063) and reduced ground use (5.98 s/hr before, 0.43 s/hr; p = 0.063) after implementation of bridges. Although the number of feeding trees did not change, new feeding trees were included in the home range, and the proportion of data points spent traveling and exploring significantly decreased (p = 0.018). Waterline bridges serve a purpose to irrigate the crops of local farmers who thus help to maintain the bridges, and also ascribe value to the presence of slow lorises. Other endemic mammal species also used the bridges. We advocate the use and monitoring of artificial canopy bridges as an important supplement for habitat connectivity in conservation interventions.

Mortality of primates due to roads and power lines in two forest patches in Bangladesh

Primates are in imminent risk of extinction due to different types of anthropogenic activities. Mortality due to road accidents and electrocution from power lines are among the major direct anthropogenic threats to the survival of primates. We collected primate mortality data from 2015 to 2017 at Lawachara National Park and Satchari National Park in northeastern Bangladesh. We recorded 27 fatalities in five species of primates caused by road accidents (n = 15) and electrocution (n = 12). Most mortality records were for Trachypithecus phayrei (Blyth, 1847) (n = 8) while the lowest recorded mortality was for Macaca mulatta (Zimmermann, 1780) (n = 3). Ninety percent of primates in Bangladesh are threatened and populations are gradually declining. Our results suggest that roads and power supply lines are major sources of primate mortality that should be managed in these two forests. We strongly suggest avoiding construction of roads and power supply lines inside forests. Furthermore, control of the speed limit of vehicles inside the forests, use of insulated power lines, maintenance of natural canopy bridges and preparation of artificial canopy bridges are strongly recommended.

Dynamic evaluation of airflow stream generated by a reverse system of an axial fan sprayer using 3D-ultrasonic anemometers. Effect of canopy structure

Air assisted sprayers are currently used for the applications of plant protection products in fruit trees and vineyards. However, the use of these equipment carries a high environmental risk, mainly owing to the generation of airborne spray drift in the lower boundary layer above crop canopy. Hence, many tests are currently focused on investigating several factors that affect the efficiency of the spray process, in which air assistance and air behaviour are two of the most difficult parameters to evaluate. This present work proposes a first approach on the characterization of the airflow generated by an orchard sprayer equipped with an axial fan and an air reverse system in the outlet plane of the air, while circulated through two artificial rows of canopy representing vineyard trellis, using 3D-ultrasonic anemometers to measure the experimental data. A first series of static field tests measured the air velocity at different heights on both sides of the sprayer and at both sides of every row of artificial canopy and evaluated the effect of the canopy on the sprayer airflow passing through. A second set of experiments were carried out with the sprayer moving at 4.1 km h−1 between canopy rows to simulate the normal spray process. Finally, velocity vectors and turbulent intensities were calculated. The resistance of the vegetation was also characterized by using a drag coefficient, both when the sprayer was stationary and moving. The results between the static and dynamic tests were compared. Although there were similarities between the two tests, the results indicated that when the equipment moves along the canopy rows, the axial fan asymmetry on air velocities is more noticeable and turbulence intensity increased. In addition, the vegetation received direct airflow at different times. This could affect the trajectory of the droplets. On the other hand, the resistance of the vegetation on each side was similar. The air reverse system could be affecting the airflow direction to the driving direction. Ultrasonic anemometers were successful in characterizing sprayer fan airflows but it is necessary to continue working on the descriptive analysis of the airflow in other planes different from the air outlet only and with other vineyard systems.

Quantifying the Accuracy of Digital Hemispherical Photography for Leaf Area Index Estimates on Broad-Leaved Tree Species.

Digital hemispherical photography (DHP) has been widely used to estimate leaf area index (LAI) in forestry. Despite the advancement in the processing of hemispherical images with dedicated tools, several steps are still manual and thus easily affected by user’s experience and sensibility. The purpose of this study was to quantify the impact of user’s subjectivity on DHP LAI estimates for broad-leaved woody canopies using the software Can-Eye. Following the ISO 5725 protocol, we quantified the repeatability and reproducibility of the method, thus defining its precision for a wide range of broad-leaved canopies markedly differing for their structure. To get a complete evaluation of the method accuracy, we also quantified its trueness using artificial canopy images with known canopy cover. Moreover, the effect of the segmentation method was analysed. The best results for precision (restrained limits of repeatability and reproducibility) were obtained for high LAI values (>5) with limits corresponding to a variation of 22% in the estimated LAI values. Poorer results were obtained for medium and low LAI values, with a variation of the estimated LAI values that exceeded the 40%. Regardless of the LAI range explored, satisfactory results were achieved for trees in row-structured plantations (limits almost equal to the 30% of the estimated LAI). Satisfactory results were achieved for trueness, regardless of the canopy structure. The paired t-test revealed that the effect of the segmentation method on LAI estimates was significant. Despite a non-negligible user effect, the accuracy metrics for DHP are consistent with those determined for other indirect methods for LAI estimates, confirming the overall reliability of DHP in broad-leaved woody canopies.

Use of canopy gap openings to restore coniferous stands in Mediterranean environment

In Mediterranean regions, climate change increasingly affect tree species distributions. Conifer forests under continuing disturbance show a more rapid shift to dominance by beech and other temperate broadleaves. Thus, there is an urgent need to conserve coniferous vegetation to avoid local extinction. Gap opening has profound effects on the structure and dynamics of most forests and may represent a sustainable way to restore coniferous ecosystems in Mediterranean habitats. What kind of artificial canopy opening is the most sustainable and effective means for restoring coniferous ecosystem functions? We explored the efficacy of artificial gaps in regeneration and dynamics of coniferous in Mediterranean environment. We examined how regeneration of different tree species is associated with soil environmental conditions and how gaps of different sizes influence the ecology and management of Mediterranean forest. Specifically, we analyzed gap disturbance in silver fir and black pine stands, as they dominate central and southern Italian forests. We demonstrated a specificity between gap size and coniferous species regeneration, indicating that small gaps (about 200 m2) favor silver fir regeneration, while black pine, depending on its subspecies, regenerates both in small and medium gaps (about 500 m2). Further, we found that gap characteristics (age and shape) and suitable substrate availability are the primary factors affecting seedling establishment. Our results provide functional information to design a silvicultural system useful to manage the natural regeneration of Mediterranean forest minimizing the environmental and visual impact.

Artificial canopy gaps in the restoration of boreal conservation areas: long-term effects on tree seedling establishment in pine-dominated forests

Creation of canopy gaps can be used as a restoration measure to aid in the diversification of structural variability and tree species composition in forests. However, it is not generally known how the specific properties of gaps influence restoration success. In this study, we examined tree seedling regeneration in 94 small canopy gaps that were established for restoration purposes in two protected Pinus sylvestris (Scots pine)-dominated forests in eastern Finland 10 years earlier. In particular, we assessed the effect of gap size, within-gap position, and soil preparation (exposure of the mineral soil) within the gaps (soil disturbance) on seedling establishment. We found that tree species composition in the sample plots consisted mainly of P. sylvestris (73 %) and Betula spp. (16 %) seedlings. Most Pinus and Betula seedlings were found in the disturbed plots, and only 6 % of the seedlings were found in the undisturbed plots (no soil preparation applied). The mean number of pooled Pinus and Betula seedlings per disturbed plot (40 × 60 cm) was 0.5 and 0.1, respectively. Mean height of the Pinus and Betula seedlings was 9.2 cm and 51.5 cm, respectively, which suggests that seedling development in the disturbed plots was very slow and is probably hindered by an insufficient amount of solar radiation reaching the forest floor, as well as by root competition with the trees that surround the gap. Both factors are affected by gap size, which was probably not large enough (mean diameter ≤23 m) in our study forests to reach a threshold value that meets the requirements of Pinus and Betula seedlings. We conclude that the creation of small canopy gaps does not appear to be an effective method to restore the age class structure and tree species composition in boreal pine-dominated forests. Further studies that manipulate the gap size more widely than this current study are needed.

Artificial canopy gaps accelerate restoration within an exoticPinus radiataplantation

We created small‐scale artificial canopy gaps to accelerate the growth of mature indigenous forest canopy species for restoration of an 18‐year‐old exoticPinus radiataplantation forest, in the Marlborough Sounds, New Zealand. Small and large circular gaps were formed by felling. Seedlings of two indigenous forest canopy species,Podocarpus totara(Podocarpaceae) andBeilschmiedia tawa(Lauraceae), were planted within artificial gaps and undisturbed plantation canopy. Seedling height growth, mortality, and occurrence of animal browse were monitored at approximately 6‐month intervals over 17 months. BothP. totaraandB. tawadiffered significantly in height growth and in animal browse occurrence among artificial gap treatments. Growth of the light‐demandingP. totarawas better under large canopy gaps, whereas growth of the shade‐tolerantB. tawaincreased under gaps of any size but was most consistent under small gaps. ForP. totara, any significant restoration benefit of gap formation on height growth was lost when browsed seedlings were taken into account. Animal browse significantly limitedB. tawaheight growth in large but not in small gaps. Small‐scale canopy gap creation is an effective method of modifying light transmission to the plantation understorey and accelerating seedling growth rates. Canopy gap size can be used to optimize understorey illumination according to species‐specific light requirements. The increased occurrence of animal browse in gaps requires consideration. Artificial canopy gaps within planted monocultures create structural heterogeneity that would otherwise take an extended period of time to develop. These results further support the role of plantations as indigenous forest restoration sites.

Rock‐protecting seaweed? Experimental evidence of bioprotection in the intertidal zone

AbstractBiogeomorphological processes are an important component of dynamic intertidal systems. On rocky shores, the direct contribution of microorganisms, plants and animals to weathering and erosion is well known. There is also increasing evidence that organisms can alter rock breakdown indirectly, by moderating temperature and moisture regimes at the rock–air interface. These influences have been purported to represent mechanisms of bioprotection, by buffering microclimatic fluctuations associated with weathering processes such as wetting and drying and salt crystallization. However, virtually nothing has been done to test whether microclimatic buffering translates to differences in actual rock breakdown rates.Here we report a preliminary laboratory experiment to assess how an artificial canopy (chosen to represent seaweed) affects mechanical rock breakdown. Using a simplified and accelerated thermal regime based on field data from a rocky shore platform in southern England, UK, we find that breakdown (mineral debris release) of mudstone covered with a canopy is reduced by as much as 79% relative to bare rock after around 100 thermal cycles. Reduction in rock surface hardness (measured using an Equotip device) was also greater for bare rock (17%) compared to covered rock (10%) over this period. Measurements of salt crystal formation indicate that the mechanism driving these differences was a reduction in the frequency of crystallization events, via moisture retention and shading of the rock surface. Copyright © 2015 John Wiley & Sons, Ltd.

Air Assisted Sprayer for Improved Spray Penetration in Greenhouse Floriculture Crops

Air assisted spraying is considered as one of the better pesticide application technique. Incorporation of air assistance in the spraying system improves the deposition uniformity in the entire plant canopy structure and spray deposition on the lower part of the plant leaves. In the view of this, an air assisted sleeve boom sprayer was developed for greenhouse floricultural crops. The developed sprayer consisted of air delivery system and spray delivery system. Air delivery system consisted of blower, lance assembly and a tapered air sleeve. Spray delivery system consisted of a pesticide tank, horizontal triplex pump, pressure hose and nozzles. Blower and pump were operated by 5 HP electric motor. Air sleeve and nozzles were supported on horizontal boom. The whole assembly of the sprayer was mounted on the trolley. The developed sprayer was tested in the laboratory to study the effect of different air velocity (9, 12, 16 and 20 m/s) and pump discharge (2.5, 4.5, 7 and 9 L/min) levels on droplet size (VMD), droplet density and uniformity coefficient at six different positions of the artificial plant canopy. Test results revealed that an increase in air velocity resulted in better spray penetration and uniform spray coverage. The optimum results of droplet size (100–150 µm), droplet density (25–35 droplets per cm2) and uniformity coefficient at all plant positions were observed for air velocity of 20 m/s and pump discharge of 2.5 L/min.

Does Ungulate Foraging Behavior in Forest Canopy Gaps Produce a Spatial Subsidy with Cascading Effects on Vegetation?

Concentrated foraging in forest canopy gaps by large ungulates may produce a pulsed spatial resource subsidy with cascading effects on the composition and developmental trajectory of gap vegetation. To test this hypothesis, we investigated the influence of white-tailed deer (Odocoileus virginianus) use of 12 artificial canopy gaps in a hemlock-northern hardwood forest. Ground-layer vegetation was monitored and available reactive nitrogen was assayed using resin beads deployed under the snowpack (March‐April) and soon after snowmelt (May). Deer use of openings was consistent with the forage maturation hypothesis, with the greatest levels of use occurring in small gaps. Allometric relationships suggest that mean localized winter pulses of deer-excreted N may be on par and/or in excess of annual atmospheric N deposition in the region. Correspondingly, deer access plots contained significantly more reactive N than exclosure plots soon after snowmelt (P 0.036) in April. While the pulse was indistinguishable by May, our nonmetric multidimensional scaling ordination results suggest that plant community composition in exclosure and control plots reflects this pulsed gradient in N availability. Given the importance of canopy disturbances and gaps to the perpetuation of forest ecosystems, localized and/or heterogeneous impacts may be magnified as forests turn over.

Visual navigation in the Neotropical ant Odontomachus hastatus (Formicidae, Ponerinae), a predominantly nocturnal, canopy-dwelling predator of the Atlantic rainforest

The arboreal ant Odontomachus hastatus nests among roots of epiphytic bromeliads in the sandy forest at Cardoso Island (Brazil). Crepuscular and nocturnal foragers travel up to 8m to search for arthropod prey in the canopy, where silhouettes of leaves and branches potentially provide directional information. We investigated the relevance of visual cues (canopy, horizon patterns) during navigation in O. hastatus. Laboratory experiments using a captive ant colony and a round foraging arena revealed that an artificial canopy pattern above the ants and horizon visual marks are effective orientation cues for homing O. hastatus. On the other hand, foragers that were only given a tridimensional landmark (cylinder) or chemical marks were unable to home correctly. Navigation by visual cues in O. hastatus is in accordance with other diurnal arboreal ants. Nocturnal luminosity (moon, stars) is apparently sufficient to produce contrasting silhouettes from the canopy and surrounding vegetation, thus providing orientation cues. Contrary to the plain floor of the round arena, chemical cues may be important for marking bifurcated arboreal routes. This experimental demonstration of the use of visual cues by a predominantly nocturnal arboreal ant provides important information for comparative studies on the evolution of spatial orientation behavior in ants.“This article is part of a Special Issue entitled: Neotropical Behaviour”.