Canopy Exposure Research Articles

Leaf trait networks shift toward high modularity during the succession of a subtropical forest, in southwest China

During the process of forest succession, coexisting plant species fulfill diverse functions by modifying the interrelationships among functional traits. Examining the interrelationships of functional traits across multiple dimensions would enable a comprehensive understanding of the plants’ adaptive strategies during forest succession. Plant trait networks (PTNs) comprehensively capture and visualize these intricate relationships among functional traits. Nonetheless, the changes in PTNs during forest secondary succession remain unclear. In this study, we measured 24 functional traits related to leaf resource acquisition, photosynthesis, hydraulics, and physical defense across tree species at three successional stages: young forest (YF), intermediate forest (IF), and old-growth forest (OF) in the Ailao Mountains, Southwest China. We established leaf trait networks (LTNs) to investigate the interrelationships among functional traits during forest succession. Our results revealed a decrease in the Edge Density decreased and an increase in the Modularity as succession advanced. In the YF stage, leaf nitrogen, photosynthetic rate, and force to punch were the hub traits; whereas, canopy exposure and leaf dry mass were highly connected traits in the IF and OF stages, respectively. The connectivity of highly connected traits was related to the plant’s life-history strategies and environmental adaptations at different successional stages. In terms of the importance of the four trait dimensions, resource acquisition and photosynthetic traits consistently demonstrated strong connectivity within LTNs throughout the succession. We concluded that co-occurring tree species adapted to the changing environmental conditions by adjusting trait modules through alternative strategies during secondary succession. Specifically, resource acquisition and trait coordination were more advantageous in the YF stage, while higher modularity offered greater opportunities for niche differentiation in the OF stage. This study provides new insights into exploring the mechanisms of forest succession through the analysis of trait correlation networks.

Early Life Exposure to Greenspace and Autism Spectrum Disorder and the Mediating Effects of Air Pollution in Ontario, Canada

BACKGROUND AND AIM Early life exposure to greenspace is associated with health benefits on childhood development, but the pathways of this relationship are not completely understood. This study aimed to evaluate early life exposure to different greenspace metrics on the development on autism spectrum disorder (ASD) and whether these associations are mediated by reductions in ambient air pollution. METHODS This case-control study included 1,801 ASD cases and 9002 controls less than 5 years of age identified from 2012 to 2017 using health administrative databases in the province of Ontario, Canada. Greenspace metrics were estimated using the Normalized Difference Vegetation Index (NDVI), Green View Index (GVI) and percent tree canopy coverage using values within 250 m of participants’ residential postal codes at birth. Conditional logistic regression was used to investigate associations between greenspace exposure and ASD while adjusting for maternal age, parity, maternal comorbidities, substance use (i.e. smoking and alcohol), socioeconomic status and urbanicity. We estimated the mediation effects of nitrogen dioxide (NO2), fine particulate matter (PM2.5), and ozone (O3) using causal mediation analyses. RESULTS In the adjusted model, we found that one interquartile range (IQR) increase in percentage tree canopy was associated with a 6% reduction in the odds of ASD (Odds ratio = 0.94; 95% CI: 0.90, 0.98). No associations were found for NDVI and GVI in relation to ASD. We found that 81.8% (77.6 – 85.9), 20.1% (16.6 – 23.6) and 13.6% (11.1 – 16.0) of the association between tree canopy exposure and ASD was mediated through reductions in NO2, PM2.5, and O3, respectively. CONCLUSIONS Early life exposure to greenspace might reduce the risk of ASD through reductions in ambient air pollution, in particular traffic pollution from NO2. Our findings may provide support to communities on the potential health benefits of greenspaces.

COVID-19, green space exposure, and mask mandates

IntroductionMask-wearing and social distancing are critical prevention measures that have been implemented to stem the spread of COVID-19. The degree to which these measures are adhered to in the US, however, may be influenced by access to outdoor resources such as green space, as well as mask mandates that may vary by state. PurposeTo examine the association between the presence or absence of statewide mask mandates and green space exposure with COVID-19 cumulative incidence in the US. MethodsIn October 2020, COVID-19 case data for each US county was downloaded from USA Facts, in addition to statewide mask mandates from a database maintained by the American Association of Retired Persons. The Normalized Difference Vegetation Index from the US Geological Survey (USGS), was used as a measure of greenspace, while the 2016 National Land Cover Database was used to assess tree canopy exposure as an alternative measure of greenspace. We performed generalized linear regression to evaluate associations with COVID-19 incidence, adjusting for potential confounders such as other environmental factors (i.e., air pollution and climate) and socio-economic factors derived from the CDC social vulnerability index. In addition, we also performed spatial regression analyses to account for spatial autocorrelation across counties. ResultsCounties with mandatory mask-wearing policies had a lower cumulative incidence of COVID-19 (B = −0.299, SE = 0.038). Among environmental factors, precipitation (B = 0.005, SE = 0.001) and PM 2.5 (B = 0.072, SE = 0.012) were associated with a higher incidence of COVID-19, while tree canopy (B = −0.501, SE = 0.129) was associated with a lower risk of COVID-19. COVID-19 incidence was higher in counties with socially vulnerable populations regarding socioeconomic status, minority status, and housing and transportation. ConclusionMandatory mask regulation, exposure to green space, and reduced exposure to air pollution may reduce COVID-19 incidence in the US. Additional public health policies should consider ways to mitigate environmental conditions that may contribute to the risk of COVID-19, especially for vulnerable populations.

A Comprehensive Thrips Species Assessment for Eco-Consistent Management of Infestations in Mediterranean Citrus Crops

Insects belonging to the Thysanoptera order are an important group of insect pests that require phytosanitary interventions for the protection of citrus crops. This study provides a general and complete overview on the thrips pest species present in citrus orchards in the main countries of the Mediterranean basin. For most species, the distribution areas, host plants, and IPM control methods are provided. The study also presents new data on the status of thrips infestations in three main crops in southern Italy (Calabria), including lemon, bergamot, and orange. The results concern the abundance and the co-occurrence of thrips species in the investigated area. Statistical analysis showed that there were differences between citrus species, canopy exposure, and monitoring period in thrips abundance. In particular, orange species showed the lowest density of thrips present on the plant. Three species, namely Pezothrips kellyanus, Frankliniella occidentalis, and Thrips major, were the most abundant in the monitored area with a marked seasonal increase, especially for the highest density species, P. kellyanus, between March and June. Moreover, for F. occidentalis, the close relationship between its presence on herbaceous flora inside crops and in citrus flowers confirms a thrips interaction with no crops and herbaceous plants and the numerical response of the thrips species. These latest results suggest that wild plants constantly host thrips and therefore an alternative ground cover could be an ecological tool to limit or mitigate the density and damaging activity of thrips populations in citrus crops.

1006 Residential proximity to green space and preterm birth in Black women

There are significant racial disparities in obstetric outcomes with the incidence of preterm birth (PTB) being the highest in non-Hispanic black (NHB) women. The presence of green space, such as forests and parks, is now widely viewed as a health-promoting characteristic of residential environments; however, obstetric research involving green space is limited. The objective of this study was to examine the association between proximity of green space (measured as percent of tree canopy) to a prenatal residential address and the rates of PTB in NHB women. A retrospective case-control study utilizing hospital pregnancy records of self-identified NHB women. Addresses of women delivered between 2011 and 2019 were geocoded to characterize the percentage of tree canopy surrounding prenatal address using National Land Cover Database. The value of each pixel in the data represented 30-square meter resolution (Fig). The 100-, 150-, 250- and 500-meter buffers were used to assess exposure of tree canopy in proximity to a prenatal address. Univariable and multivariable analyses were conducted to determine whether tree canopy percent at 4 different proximity buffers (examined both in means and quartiles) was associated with PTB (<37wks). Of 2,771 NHB women included in the study, 333 (12.0%) had PTB. Less tree canopy coverage was significantly associated with PTB, whether that coverage was quantified as a mean or by quartile percent. In unadjusted and adjusted models, controlling for sociodemographic and clinical risk factors for PTB, each 10% increase in tree canopy was associated with lower odds of PTB at all 4 buffers (Table). When examining the green space by quartile of tree canopy percent, higher quartiles were associated with even lower odds of preterm birth at 100-,150-, and 250-meter buffers, but not at 500 meters (Table). Higher percent of tree canopy in proximity to prenatal residential address is associated with lower odds of PTB in NHB women. These findings suggest that increasing neighborhood access to green space could be a new strategy to reduce PTB in NHB women.View Large Image Figure ViewerDownload Hi-res image Download (PPT)

Remotely sensed phenological heterogeneity of restored wetlands: linking vegetation structure and function

Seasonal phenological dynamics of vegetation hold important clues on ecosystem performance towards management goals, such as carbon uptake, and thus should be considered in projections of their targeted services. However, in wetlands spatio-temporal heterogeneity due to mixing of open water, soil, green and dead vegetation makes it difficult to generalize ecosystem functioning across different regions. Remote sensing observations can provide spatially-explicit, cost-effective phenology indicators; however, little is known about their capacity to indicate the links between wetland ecosystem structure and function. Here we assessed this potential by comparing one-year Enhanced Vegetation Index (EVI) from satellite products at high (5m; RapidEye) and low (30m; Landsat) spatial resolutions with eddy covariance time series of net carbon exchange, field digital camera (phenocam) greenness and water temperature among three floristically similar restored wetlands in California, USA. Phenological timing differed by wetland site: depending on satellite, the range in site-median start of greening was up to 28 days, end of greening – up to 73 days, start of senescence – up to 79 days, and end of senescence – up to 10 days. Key transition dates from satellite inputs agreed with seasonal changes in net carbon exchange, phenocam greenness and water temperatures, suggesting that phenological contrasts could result in part from site differences in vegetation configuration and litter affecting the exposure of canopy, soil and water to sunlight and thus sub-canopy microclimate and ecosystem functioning. Yet, the agreement between satellite inputs was non-systematic, with the greatest disparities at the more heterogeneous, less vegetated site. Phenological model fitting uncertainty increased with greater spatial resolution, highlighting the tradeoff between the accuracy of representing vegetation and the complexity of local seasonal variation. These findings highlight the sensitivity of satellite-derived phenology to structural and functional heterogeneity of ecosystems and call for more rigorous spatially-explicit analyses to inform assessments of restoration and management outcomes.

Effect of Grapevine Canopy Side on Selected Sensory Attributes of Pinotage and Cabernet Sauvignon Wines

Grapevine row direction, canopy exposure and grape maturity can define the sensory attributes of wine. From this perspective, canopy exposure that favours colour intensity, astringency, aroma intensity and balanced acidity could result in improved wine quality. The aim of this study was to examine the effect of canopy exposure on selected sensory attributes of Pinotage and Cabernet Sauvignon wines from Paarl, Durbanville and Darling in South Africa. Pinotage and Cabernet Sauvignon grapes were harvested from both sides of the canopy of vines planted to E-W and N-S directions. Wines were made from the harvested grapes. Grapes and wines underwent physicochemical and sensory analysis. Durbanville Cabernet Sauvignon from the south side had decreased alcohol content. Total acidity, residual sugar (RS) and pH were not different between sides. Wines from the east side had increased colour, aroma, mouthfeel and overall quality. Paarl Cabernet Sauvignon was not different between sides for any physicochemical characteristics, except TA. Wines from the south side had increased colour, aroma, mouthfeel and overall quality. Darling Pinotage was not different between sides for any physicochemical characteristics. Wines from the west side had increased intensity of aroma and acidity, whereas Durbanville Pinotage from the east side had increased alcohol, pH, TA, colour and aroma intensity, as well as overall quality. The results confirm that canopy exposure has an effect on the wine sensory attributes. This investigation illustrates the variation in sensory attribute scores of Pinotage and Cabernet Sauvignon wines from different canopy sides. Canopy exposure in a vineyard of a specific region, orientated to an E-W or N-S direction, which favours colour intensity, aroma intensity and/or mouthfeel, could result in improved wine quality. Future investigations should focus on samples collected over at least three consecutive vintages, as well as the monitoring of temperature and photosynthetic active radiation.

Urban green space, tree canopy and prevention of cardiometabolic diseases: a multilevel longitudinal study of 46786 Australians.

BackgroundCross-sectional studies suggest that more green space may lower the odds of prevalent diabetes, hypertension and cardiovascular diseases (CVD) in cities. We assess if these results are replicable for tree canopy exposure and then extend the study longitudinally to examine incident cardiometabolic outcomes. MethodsThe study was set in the Australian cities of Sydney, Wollongong and Newcastle. Total green space and tree canopy as percentages of landcover within 1.6 km (1 mile) from home were linked to a residentially stable sample of 46 786 participants in the Sax Institute’s 45 and Up Study (baseline 2006–09; follow-up 2012–15). Separate multilevel models were used to investigate whether the odds of prevalent and incident doctor-diagnosed diabetes, hypertension and CVD were associated with total green space and tree canopy provision, adjusting for age, sex, income, education, employment and couple status. ResultsLower odds of prevalent diabetes were observed with 1% increases in total green space [odds ratio (OR) 0.993, 95% confidence interval (CI) 0.988 to 0.998] and tree canopy (0.984, 0.978 to 0.989). Lower odds of prevalent CVD were found with a 1% increase in tree canopy only (0.996, 0.993 to 0.999). Lower odds of incident diabetes (0.988, 0.981 to 0.994), hypertension (0.993, 0.989 to 0.997) and CVD (0.993, 0.988 to 0.998) were associated with a 1% increase in tree canopy, but not total green space. At ≥30% compared with 0–9% tree canopy, there were lower odds of incident diabetes (0.687, 0.547 to 0.855), hypertension (0.828, 0.719 to 0.952) and CVD (0.782, 0.652 to 0.935). However, ≥30% compared with 0–4% total green space was associated with lower odds of prevalent diabetes only (0.695, 0.512 to 0.962). ConclusionsRestoring local tree canopy in neighbourhoods may help to prevent the incidence of cardiometabolic diseases.

Spatiotemporal effects of Hurricane Ivan on an endemic epiphytic orchid: 10 years of follow-up

ABSTRACTBackground: Hurricanes have a strong influence on the ecological dynamics and structure of tropical forests. Orchid populations are especially vulnerable to these perturbations due to their canopy exposure and lack of underground storage organs and seed banks.Aims: We evaluated the effects of Hurricane Ivan on the population of the endemic epiphytic orchid Encyclia bocourtii to propose a management strategy.Methods: Using a pre- and post-hurricane dataset (2003–2013), we assessed the population asymptotic and transient dynamics. We also identified the individual size-stages that maximise population inertia and E. bocourtii’s spatial arrangement relative to phorophytes and other epiphytes.Results: Hurricane Ivan severely affected the survival and growth of individuals of E. bocourtii, and caused an immediate decline of the population growth rate from λ = 1.05 to λ = 0.32, which was buffered by a population reactivity of ρ1 = 1.42. Our stochastic model predicted an annual population decrease of 14%. We found an aggregated spatial pattern between E. bocourtii and its host trees, and a random pattern relative to other epiphytes.Conclusion: Our findings suggest that E. bocourtii is not safe from local extinction. We propose the propagation and reintroduction of reproductive specimens, the relocation of surviving individuals, and the establishment of new plantations of phorophytes.

EFFECTS OF SHADE TREE SPATIAL DISTRIBUTION AND SPECIES ON PHOTOSYNTHETIC RATE OF COFFEE TREES

The use of shade trees in coffee fields have been motivated by climatic changes. However, microclimatic conditions in shaded coffee fields differ due to shade tree spatial distribution and species, altering physiological responses of coffee trees. This study aimed to evaluate the effects of shade tree spatial distribution and species on coffee trees photosynthetic rate in two growth seasons, of high (HSD) and low (LSD) sink demand. The experimental design consisted of randomized blocks with three replicates in split-split-plots. Plots were the shade tree species: &lt;em&gt;Anadenanthera falcata&lt;/em&gt;, &lt;em&gt;Cassia grandis&lt;/em&gt; and &lt;em&gt;Peltophorum dubium&lt;/em&gt;. Split plot was formed by five distances between coffee trees and shade tree trunks: coffee trees on planting row of shade trees, distancing one (D1L) and five (D5L) meters from shade trees trunk; coffee trees on inter-rows of shade trees, parallel to D1L and D5L (D1E and D5E); coffee trees distancing 77 meters from shade tree trunks, in a full-sun field (PS). The split-split-plots correspond to coffee tree canopy exposure to the sun: branches facing North or South. Shade trees canopy density and occupation was evaluated with a convex densiometer. Photosynthetic rate (Pn)and photosynthetic active radiation (PAR) were measured with an Infrared Gas Analyzer (IRGA) on two time-frames, between 7.00 and 9.00 solar hours and between 11.00 and 13.00. Shade tree canopy density and occupation was not homogenous during the change of seasons and shift due to spatial distribution, which also changes PAR levels. Shade trees reduce PAR to more suitable values for coffee tree exploitation, especially on D1L and D5L. During HSD, shading did not affect P&lt;sub&gt;n&lt;/sub&gt;, which was greater in branches facing North. Yet, in LSD, between 11.00 and 13.00, coffee trees shaded with &lt;em&gt;A. falcata&lt;/em&gt; showed greater P&lt;sub&gt;n&lt;/sub&gt; than at PS. Coffee trees shaded with &lt;em&gt;C. grandis&lt;/em&gt; at D5L and D1E had greater values of P&lt;sub&gt;n&lt;/sub&gt; than PS.

KETERBUKAAN TAJUK AKIBAT KEGIATAN PEMANENAN DENGAN TEKNIK REDUCED IMPACT LOGGING DALAM PENGELOLAAN HUTAN ALAM (Studi Kasus Pada Petak Tebangan L37 RKT 2015 IUPHHK–HA PT. Batasan Camp Tontang)

Tropical rainforests have very important functions such as hydrological functions, ecology, economic and social. However, the existence of forest harvesting activities potentially decrease the function. Implementation of poor forest management, causing damages resulting from harvesting processes such as canopy exposure, areal exposure and damage to residual stands. Based on the description it is necessary to do research on the analysis of canopy exposure in natural rain forest area IUPHHK-HA PT. Batasan Camp Tontang. This study aims to determine the extent of canopy exposure due to harvesting activities and to know the relationship between the width of the basic fields of cut down trees per hectare to the exposure of the canopy. This research was conducted on the 2015 RKT and in IUPHHK-HA area of PT.Batasan Camp Tontang,Nanga Serawai Sub-district, Sintang District, West Kalimantan Province. Canopy exposure as a result of harvesting activities is obtained by measuring its openness using a spiracle densiometer tool. The percentage of openness is then analyzed by the equation Y = a + bX, where Y is the percentage of canopy exposure whereas X is the base area of the harvested trees per hectare. To find out the real relationship between the width of the tree base area felled by the openness of the canopy, it is done with the F test and to know the close relationship between variables X with variable Y by closeness relationship test or r test. Timber potential before harvesting in 9 research plots with the tree level average value is 35.78 stems / ha. After harvesting activities, timber potential has decreased due to timber harvesting activities to be 9.33 stems / ha. The percentage of canopy exposure after harvesting activity was 49.35% and included in medium level of exposure. From the calculation results, the equation which is obtained by regression line of the relationship between the width of the base area of the trees cut down per hectare with the value of the canopy expose, shows that the greater tree cutting base area, the greater canopy exposure that occurs.Keyword: Canopy exposure, Degradation, Spiracle Densitometer.

Predominance of abiotic drivers in the relationship between species diversity and litterfall production in a tropical karst seasonal rainforest

Litterfall production is a major contributor to ecosystem net primary productivity and biogeochemical cycles. However, how various abiotic and biotic drivers influence litterfall production in heterogeneous natural forests is still debated. We used structural equation models (SEM) to test the direct and indirect effects of tree species diversity, tree diameter variation, stand basal area, and abiotic drivers (canopy exposure, elevation, slope, convexity, aspect, topographic wetness index and altitude above channel) on annual litterfall production in a heterogeneous tropical karst seasonal rainforest in Southern China. The SEM with tree species diversity, tree diameter variation, stand basal area, and abiotic drivers accounted for 43.4% of the variation in annual litterfall production. Tree species diversity and stand basal area had positive direct effects, while tree diameter variation had a negative direct effect on annual litterfall production. Tree species diversity had no significant effect on tree diameter variation nor stand basal area. Both annual litterfall production and tree species diversity decreased directly with water availability, while canopy exposure positively affected annual litterfall production but not tree species diversity. Our results indicate that the positive relationship between tree species diversity and litterfall production did not result from the effects of species diversity on canopy packing; instead, it appears that increasing soil water availability simultaneously reduce tree species diversity and annual litterfall production in the tropical karst seasonal rainforest.

Shoot Heterogeneity Effects on Shiraz/Richter 99 Grapevines. II. Physiological Activity

In this study, the physiology of normally developed and underdeveloped shoots is compared in an attempt to quantify the effect of shoot heterogeneity in a Shiraz/Richter 99 vineyard, located in the Stellenbosch area of the Western Cape, South Africa. Comparisons are made between normally developed and underdeveloped shoots from shaded and well-exposed canopies. In the first five weeks after veraison, photosynthetic and transpiration rates, stomatal conductance and water-use efficiency (WUE) decreased as berry ripening progressed, while the internal CO2 levels of the leaves increased. Since differences in activity between individual leaves from normally developed and underdeveloped shoots only became apparent in the third week after veraison, it seemed as if the leaf area per shoot played a more important role than the photosynthetic output per unit leaf area in determining photosynthetate supply to the rest of the vine up to this stage. From the third week after veraison, higher levels of photosynthetates were produced by normally developed shoots than by underdeveloped shoots, due to the larger effective leaf area per shoot as well as the higher photosynthetic activity per unit leaf area. This points to premature senescence of the leaves on underdeveloped shoots. The quantity and quality of the yield from normally developed shoots are expected to benefit from the higher physiological output of the leaves. The enhancing effect on leaf functioning induced by canopy exposure became apparent from the third week after veraison.

Predator avoidance and dietary fibre predict diurnality in the cathemeral folivore Hapalemur meridionalis

Though numerous mammalian taxa exhibit cathemerality (i.e. activity distributed across the 24-h cycle), this includes very few primates, exceptions being species from Aotinae and Lemuridae. Four non-mutually exclusive hypotheses have been proposed to explain the ultimate determinants for cathemeral activity in lemurs: thermoregulatory benefits, anti-predator strategy, competition avoidance and metabolic dietary-related needs. However, these have only been explored in the frugivorous genus Eulemur, with some species increasing nocturnality as a possible response to avoid diurnal raptors and to increase their ability to digest fibre during resource-scarce periods. Since Eulemur lack specializations for digesting bulk food, this strategy would allow for processing fibres over the full 24-h. The folivorous lemurids, i.e. genus Hapalemur, provide a divergent model to explore these hypotheses due to gastrointestinal adaptations for digesting dietary fibre and small body size compared to Eulemur. We linked continuous activity data collected from archival tags with observational behaviour and feeding data from three groups of adult Hapalemur meridionalis from January to December 2013. We tested the effects of thermoregulation, predator avoidance and the weighted proportion of digestible dietary fibre on the daily diurnal/nocturnal activity ratio using a Linear Mixed-Model. Our best-fit model revealed that increased canopy exposure and dietary fibre predicted greater diurnality. Our findings partly contrast with previous predictions for frugivorous lemurids. We propose a divergent adaptive explanation for folivorous lemurids. We suggest that the need to avoid terrestrial predators, as well as longer digestive bouts during bulk food periods, may override cathemerality in favour of diurnality in these bamboo lemurs. Southern bamboo lemurs are active throughout the 24-h day, with high proportions of dietary fibre increasing diurnality, in contrast to other cathemeral primates. They also increase diurnality on days when using areas with greater canopy exposure, potentially avoiding nocturnal predators in risky foraging areas. We suggest that folivorous lemurids may require long periods of inactivity to conserve energy and digest dietary fibre, thus limiting activity to periods of optimal foraging efficiency over the 24-h cycle.

Divergent reproductive allocation trade‐offs with canopy exposure across tree species in temperate forests

AbstractVariation in tree reproduction can alter forest community dynamics, especially if reproductive output is costly for other functions like growth. However, empirical studies reach conflicting conclusions about the constraints on reproductive allocation relative to growth and how they vary through time, across species, and between environments. Here, we test the hypothesis that a critical resource, canopy exposure to light availability, limits reproductive allocation by comparing long‐term relationships between reproduction and growth for trees from 21 species in forests throughout the Southeastern United States. We found that species have divergent responses to light availability, with shade‐intolerant species experiencing an alleviation of trade‐offs at high light‐ and shade‐tolerant species showing no changes in reproductive output across light environments. Correlations between temporal variation in individual growth and reproduction were weak and generally insensitive to canopy exposure, but changed when considering time lags. The diversity of responses across species indicates that reproductive allocation for trees in these forests is strongly influenced by both species’ life history and environmental heterogeneity in space and time.

Nanoparticle-based measurements of pH and O2 dynamics in the rhizosphere of Zostera marina L.: effects of temperature elevation and light-dark transitions.

Seagrasses can modulate the geochemical conditions in their immediate rhizosphere through the release of chemical compounds from their below-ground tissue. This is a vital chemical defence mechanism, whereby the plants detoxify the surrounding sediment. Using novel nanoparticle-based optical O2 and pH sensors incorporated in reduced and transparent artificial sediment, we investigated the spatio-temporal dynamics of pH and O2 within the entire rhizosphere of Zostera marina L. during experimental manipulations of light and temperature. We combined such measurements with O2 microsensor measurements of the photosynthetic productivity and respiration of seagrass leaves. We found pronounced pH and O2 microheterogeneity within the immediate rhizosphere of Z. marina, with higher below-ground tissue oxidation capability and rhizoplane pH levels during both light exposure of the leaf canopy and elevated temperature, where the temperature-mediated stimuli of biogeochemical processes seemed to predominate. Low rhizosphere pH microenvironments appeared to correlate with plant-derived oxic microzones stimulating local sulphide oxidation and thus driving local proton generation, although the rhizoplane pH levels generally where much higher than the bulk sediment pH. Our data show that Z. marina can actively alter its rhizosphere pH microenvironment alleviating the local H2 S toxicity and enhancing nutrient availability in the adjacent sediment via geochemical speciation shift.

Hemiparasite--host plant interactions in a fragmented landscape assessed via imaging spectroscopy and LiDAR.

Species interactions are susceptible to anthropogenic changes in ecosystems, but this has been poorly investigated in a spatially explicit manner in the case of plant parasitism, such as the omnipresent hemiparasitic mistletoe-host plant interactions. Analyzing such interactions at a large spatial scale may advance our understanding of parasitism patterns over complex landscapes. Combining high-resolution airborne imaging spectroscopy and LiDAR, we studied hemiparasite incidence within and among tree host stands to examine the prevalence and spatial distribution of hemiparasite load in ecosystems. Specifically, we aimed to assess: (1) detection accuracy of mistletoes on their oak hosts; (2) hemiparasitism prevalence within host tree canopies depending on tree height, and (3) spatial variation in hemiparasitism across fragmented woodlands, in a low-diversity mediterranean oak woodland in California, USA. We identified mistletoe infestations with 55-96% accuracy, and detected significant differences in remote-sensed spectra between oak trees with and without mistletoe infestation. We also found that host canopy height had little influence on infestation degree, whereas landscape-level variation showed consistent; non-random patterns: isolated host trees had twice the infestation load than did trees located at the core of forest fragments. Overall, we found that canopy exposure (i.e., lower canopy density or proximity to forest edge) is more important than canopy height for mistletoe infestation, and that by changing landscape structure, parasitic prevalence increased with woodland fragmentation. We conclude that reducing fragmentation in oak woodlands will minimize anthropogenic impact on mistletoe infestation at the landscape level. We argue that advanced remote sensing technology can provide baselines to quantitatively analyze and monitor parasite-host trajectories in light of global environmental change, and that this is a promising approach to be further tested in other temperate and tropical forests.

Assessing the influence of topography and canopy structure on Douglas fir throughfall with LiDAR and empirical data in the Santa Cruz mountains, USA.

Atmospheric inputs to forest ecosystems vary considerably over small spatial scales due to subtle changes in relief and vegetation structure. Relationships between throughfall fluxes (ions that pass through the canopy in water), topographic and canopy characteristics derived from sub-meter resolution light detection and ranging (LiDAR), and field measurements were compared to test the potential utility of LiDAR in empirical models of atmospheric deposition. From October 2012 to May 2013, we measured bulk (primarily wet) deposition and sulfate-S, chloride (Cl(-)), and nitrate-N fluxes beneath eight clusters of Douglas fir trees differing in size and canopy exposure in the Santa Cruz Mountains, California. For all trees sampled, LiDAR data were used to derive canopy surface height, tree height, slope, and canopy curvature, while tree height, diameter (DBH), and leaf area index were measured in the field. Wet season throughfall fluxes to Douglas fir clusters ranged from 1.4 to 3.8kg Sha(-1), 17-54kg Cl(-)ha(-1), and 0.2-4kg Nha(-1). Throughfall S and Cl(-) fluxes were highest under clusters with large trees at topographically exposed sites; net fluxes were 2-18-fold greater underneath exposed/large clusters than all other clusters. LiDAR indices of canopy curvature and height were positively correlated with net sulfate-S fluxes, indicating that small-scale canopy surface features captured by LiDAR influence fog and dry deposition. Although tree diameter was more strongly correlated with net sulfate-S throughfall flux, our data suggest that LiDAR data can be related to empirical measurements of throughfall fluxes to generate robust high-resolution models of atmospheric deposition.

Unusual canopy architecture in the umbrella thorn acacia, Vachellia tortilis (= Acacia tortilis), in the United Arab Emirates

Populations of the umbrella thorn acacia, Vechellia tortilis (formerly Acacia tortilis), in the United Arab Emirates (UAE) have an unusual tilted canopy architecture compared with the flat or dome-shaped morphology typical throughout its pan-tropical range. UAE populations were shown to have a distinctive tilt as a result of consistent height and canopy angle differences between opposing sides of canopies. These tilted canopies were found to be highly directional in their orientation, facing almost due south. The wind environment and latitude were excluded as potential causes for this morphology. Canopies of V. tortilis were shown to have a mean compass orientation and slope which maximized canopy exposure to the midday sun, specifically during peak summer when climactic conditions are extreme relative to populations elsewhere in the pan-tropical range of this species. It is suggested that the unique canopy architecture characteristic of the UAE population is a plastic response which maximizes soil shading and reduces soil temperature around the base of the tree. Such shading would reduce evaporative loss of soil moisture that had been deposited in the surface layers by hydraulic lift from the taproots, enhancing total water availability and water transport efficiency in this hot, hyper-arid climate.

Geomorphic changes of headwater systems 3–23 years after forest harvesting by clearcutting

Forest harvesting directly affects headwater systems, causing changes in catchment hydrology and riparian habitats. We investigated geomorphological impacts of clearcut harvesting on headwater systems and their recovery in the boreal mixedwood forests of northwestern Ontario, Canada. We studied 30 headwater streams (width <3 m), 24 in previously clearcut sites and six in undisturbed mature forests as reference. Each sampled stream had two segments, i) in clearcut 10 m away from the cut edge and ii) in riparian buffer of the larger stream to which it flows. Using MANOVA and discriminant function analysis, we examined harvesting impacts on stream width, depth, number of stream channels, riparian width, ground exposure, canopy exposure and organic matter depths as disturbance index in clearcut chronosequence and reference forest. Among all these factors we found canopy exposure contributed most to the observed harvesting impacts, which remained significantly high up to 15 years after clearcutting compared to the reference forest. Stream width and number of stream channels were also significantly high in clearcut sites for up to three years after harvesting but the differences tapered within 10 years. Streams were shallower in recently harvested sites, a difference that remained detectable even 23 years after clearcutting. General impacts of harvesting adjacent to headwater streams and their riparian zones were detectable at least until 15 years after harvesting. Although it is likely that harvest related biophysical damage in the headwater systems have negative effects on the aquatic ecosystems of the larger streams no study in the boreal forests has yet evaluated this direct link. We argue that although protecting all small streams and their headwater system by buffers is not possible, biophysical damage during harvesting can be avoided by complying with guidelines that forbid harvesting equipments near waters edge and retaining residual vegetation along small streams.