Olive Canopy Research Articles

Olive Growing Farming System and Damage by Cicadas

Although cicadas have traditionally been considered pests of little or no importance, in recent decades, an increase in damages is being recorded in olive groves of southern Spain. New agricultural practices that affect soil management are behind it. During 2024, intensive sampling has been carried out in an organic grove with herbaceous cover (VC2), and in a second one with mixed vegetation cover (VC1, in which the crushed remains of the annual pruning are added). In both ecological groves, inventories of the vegetation have been carried out, as well as intensive sampling in the olive canopy, with the densities of oviposition injuries being recorded and compared with respect to conventional management (CONV). The objectives of this study are to compare the three managements based on the density of oviposition injuries, to determine the priority areas for cicadas’ oviposition within the trees; and to develop a sampling method to assess damage over large areas. The results show significant increases in the density of injuries in organic groves, with maximum values recorded in the olive grove with mixed cover. Oviposition injuries show an altitudinal gradient distribution, with maximum values in the lower zone of the trees. The factors involved are discussed.

Ants and predators cope with pest pressures by interacting with the surrounding vegetation at low spatial scales

AbstractBiological control of pests can be enhanced by the presence of semi‐natural habitats within agricultural landscapes. However, this assumption remains controversial due to inconsistencies related to the type of agroecosystems and the natural enemies studied. Within olive orchards, there is a lack of information regarding the interaction among natural enemies and their relation with habitat structure to control pests at the landscape scale. Here, we investigate the effects of the natural habitat on the pest, pest damage and the interaction of pests and natural enemies – using a trophic guild approach, in organic olive orchards. For this, we decomposed the natural habitats into vegetation structures and analysed their effects with a multi‐scale perspective. Our results show that (1) greater proportions of natural habitats increase the abundance of ants (omnivores) and predators and diminish pest pressures – reducing the impact of Prays oleae on olive fruits. (2) Vegetation structures within natural habitats were grouped, based on their effects, into three main vegetation groups: grassland and forest, scrublands and olive trees. However, the dense scrubland and the dense forest improve the abundance of natural enemies that are linked to pest damage the most. (3) Prays oleae increases in landscapes dominated by low numbers of patches that are highly aggregated. Conversely, ants and predators increased in landscapes dominated by high numbers of patches that have a less edge‐resembling shape. (4) Within the olive canopy, the abundance of lacewing larvae and salticid spiders is related to lower pest damage and a reduction in P. oleae adults respectively. However, when ants and predators interact with the natural habitat, they can cope with pest pressures without the need for high abundances, supporting ‘the more‐effective natural enemy hypothesis’ in agroecosystems.

Halyomorpha halys (Hemiptera: Pentatomidae) as the major contributor to early olive drop in northern Italy.

In recent years, a new phenomenon of early olive drop is causing production losses in olive groves throughout northern Italy. To analyze the possible causes, field and laboratory trials were performed to assess the involvement of fungal pathogens and insect pests in this disease. External and internal symptoms of fungal infections or insect-feeding activities were researched. Fungi present in healthy and dislodged olives were investigated. The relationship between olives that fell and Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) infestation was assessed in a controlled infestation trial, and the effectiveness of an insecticidal strategy in reducing early olive drop was tested in open field conditions. A comparable number of fungi, mostly endophytes, were isolated and identified from both healthy and dislodged olives. The damage observed on dislodged olives was primarily ascribed to pentatomids feeding activity. Six stink bugs species were found in olive canopies, that is, the invasive H. halys, which was by far the most abundant, and Acrosternum heegeri Fieber, Nezara viridula (Linnaeus), Palomena prasina (Linnaeus), Piezodorus lituratus (Fabricious), and Rhaphigaster nebulosa (Poda). Halyomorpha halys caused intense fruit drop in the controlled infestation trial, and its infestation level significantly correlated with the number of olives that fell. Native stink bugs, present in much lower population compared to H. halys, could also partially contribute to early drop of olives. Insect proof net significantly reduced the early olive drop disease, while insecticide applications only partially reduced the stink bugs population density and, proportionally, early olive drop.

Relationship between Height and Exposure in Multispectral Vegetation Index Response and Product Characteristics in a Traditional Olive Orchard.

The present research had two aims. The first was to evaluate the effect of height and exposure on the vegetative response of olive canopies' vertical axis studied through a multispectral sensor and on the qualitative and quantitative product characteristics. The second was to examine the relationship between multispectral data and productive characteristics. Six olive plants were sampled, and their canopy's vertical axis was subdivided into four sectors based on two heights (Top and Low) and two exposures (West and East). A ground-vehicle-mounted multispectral proximal sensor (OptRx from AgLeader®) was used to investigate the different behaviours of the olive canopy vegetation index (VI) responses in each sector. A selective harvest was performed, in which each plant and sector were harvested separately. Product characterisation was conducted to investigate the response of the products (both olives and oils) in each sector. The results of Tukey's test (p > 0.05) showed a significant effect of height for the VI responses, with the Low sector obtaining higher values than the Top sector. The olive product showed some height and exposure effect, particularly for the olives' dimension and resistance to detachment, which was statistically higher in the upper part of the canopies. The regression studies highlighted some relationships between the VIs and product characteristics, particularly for resistance to detachments (R2 = 0.44-0.63), which can affect harvest management. In conclusion, the results showed the complexity of the olive canopies' response to multispectral data collection, highlighting the need to study the vertical axis to assess the variability of the canopy itself. The relationship between multispectral data and product characteristics must be further investigated.

Quality of cold stored lemon fruit from orchards consociated to ancient olive trees

In the hilly area of Gioia Tauro (Calabria, Southern Italy), lemon orchards are grown in consociation with centuries-old olive trees. Lemons are partially shaded by olive canopies and the microclimate at the level of their canopies is suitable for plants growth and quality productions. Under these conditions, lemon trees are grown even without irrigation, providing, despite this limitation, a quality product. This study aimed to i) investigate the qualitative characterisation of two clonal selections of the lemon cultivar Femminello, F. Siracusano (S) and F. Zagara bianca (ZB), from the described intercropping, on irrigated (I) and non-irrigated (NI) crops; ii) assess the quality preservation during cold storage, in order to evaluate the availability of lemons for marketing in a period of shortage such as the summer season. Fruits were harvested at commercial maturity, and cold stored at 10±1°C and RH 85-90%, for 60 days. Decay incidence, physiological disorders, weight loss, and the main physical-chemical parameters were assessed at harvest (T0) and every 15 days (T15, T30, T45, T60). The absence of decay and physiological disorders was observed throughout the 60-day storage period, in both clonal selections under the two management conditions. The weight loss was greater in fruits from irrigated lemon groves of both S and ZB. S_I showed significantly lower fruits weight and higher titratable acidity than S_NI. Total soluble solids and titratable acidity were statistically lower for ZB_I than for NI fruits.

GEOBIA and Vegetation Indices in Extracting Olive Tree Canopies Based on Very High-Resolution UAV Multispectral Imagery

In recent decades, precision agriculture and geospatial technologies have made it possible to ensure sustainability in an olive-growing sector. The main goal of this study is the extraction of olive tree canopies by comparing two approaches, the first of which is related to geographic object-based analysis (GEOBIA), while the second one is based on the use of vegetation indices (VIs). The research area is a micro-location within the Lun olives garden, on the island of Pag. The unmanned aerial vehicle (UAV) with a multispectral (MS) sensor was used for generating a very high-resolution (VHR) UAVMS model, while another mission was performed to create a VHR digital orthophoto (DOP). When implementing the GEOBIA approach in the extraction of the olive canopy, user-defined parameters and classification algorithms support vector machine (SVM), maximum likelihood classifier (MLC), and random trees classifier (RTC) were evaluated. The RTC algorithm achieved the highest overall accuracy (OA) of 0.7565 and kappa coefficient (KC) of 0.4615. The second approach included five different VIs models (NDVI, NDRE, GNDVI, MCARI2, and RDVI2) which are optimized using the proposed VITO (VI Threshold Optimizer) tool. The NDRE index model was selected as the most accurate one, according to the ROC accuracy measure with a result of 0.888 for the area under curve (AUC).

Effect of micro climatic indices on the accuracy of thermographic plant water status monitoring, case study of a semi-arid area

ABSTRACT Plant water stress can be remotely monitored by means of thermography due to its increasing effect on plant temperature. For a more accurate estimation of plant water status, its temperature should be normalised against environmental conditions. In this paper, the aim was to investigate a recently proposed method of normalisation using artificial reference surfaces, different measurement times in a day and different capturing directions regarding to solar trail. At three different times of the day, frontal images were captured from the sunlit side of the olive canopies in two azimuth directions. Two different stress indices of crop water stress index (CWSI) and stomatal conductance index (IG) were calculated using Tc and the temperatures of wet and dry reference surfaces. Trees in different stress levels discriminated better via mean canopy temperature (Tc) of morning measurements. At this time, Tc also provided higher correlated indices with stomatal conductance (SC) rather than those indices calculated based on Tc measured at noon and afternoon. Comparing two measurement directions, the first direction provided Tc with higher correlated indices at morning but the second direction at afternoon. In the most of the measurement conditions, stress indices calculated with air temperature plus five degrees as dry reference temperature had higher correlation with SC.

Yellow or transparent? Comparison of sticky traps for monitoring functional arthropod diversity in an olive agroecosystem

Yellow or transparent? Comparison of sticky traps for monitoring functional arthropod diversity in an olive agroecosystem. A diverse and balanced arthropod community is known to play an important role in the olive canopy but monitoring methods are not always well defined. We monitored canopy arthropods in an olive orchard over two years, comparing the performance of yellow sticky traps and transparent sticky traps. Data used to compare the two types of traps were arthropod abundance, richness, diversity indices, species abundance distribution and aggregation of taxa in functional groups based on prioritized agroecosystem services. The total abundance of arthropods caught in the yellow traps was higher than that in the transparent traps but diversity in both traps was similar. Transparent traps may therefore be a valid option to assess biodiversity in an olive agrosystem as besides being less labor demanding than yellow traps, they are low cost and replicable, and do not damage the overall arthropod.

Spittlebugs of Mediterranean Olive Groves: Host-Plant Exploitation throughout the Year.

Spittlebugs are the vectors of the bacterium Xylella fastidiosa Wells in Europe, the causal agent of olive dieback epidemic in Apulia, Italy. Selection and distribution of different spittlebug species on host-plants were investigated during field surveys in 2016–2018 in four olive orchards of Apulia and Liguria Regions of Italy. The nymphal population in the herbaceous cover was estimated using quadrat samplings. Adults were collected by sweeping net on three different vegetational components: herbaceous cover, olive canopy, and wild woody plants. Three species of spittlebugs were collected: Philaenus spumarius L., Neophilaenus campestris (Fallén), and Aphrophora alni (L.) (Hemiptera: Aphrophoridae). Philaenus spumarius was the predominant species both in Apulia and Liguria olive groves. Nymphal stages are highly polyphagous, selecting preferentially Asteraceae Fabaceae plant families, in particular some genera, e.g., Picris, Crepis, Sonchus, Bellis, Cichorium, and Medicago. Host-plant preference of nymphs varies according to the Region and through time and nymphal instar. In the monitored sites, adults peak on olive trees earlier in Apulia (i.e., during inflorescence emergence) than in Liguria (i.e., during flowering and beginning of fruit development). Principal alternative woody hosts are Quercus spp. and Pistacia spp. Knowledge concerning plant selection and ecological traits of spittlebugs in different Mediterranean olive production areas is needed to design effective and precise control strategies against X. fastidiosa vectors in olive groves, such as ground cover modifications to reduce populations of spittlebug vectors.

Evaluation of Olive Pruning Effect on the Performance of the Row-Side Continuous Canopy Shaking Harvester in a High Density Olive Orchard.

In 2009, the Side-Row Continuous Canopy Shaking Harvester project was set to develop such technology. The prototype comprises two symmetrical harvesters trailed by a farm tractor. Each harvester has a vibratory rotor with flexible rods, a catching platform with conveyors belts delivering fruits to a temporary storage bag. The removal efficiency of canopy shakers are influenced by factors like shaking frequency, ground speed as well as the dimension and shape of olive canopy. In 2014 authors started a trial to evaluate the influence of pruning in olive yield and in the performance of the Side-Row Continuous Canopy Shaking Harvester. The trial was established in an irrigated olive orchard of Picual cultivar planted in 1996 with the array 7 m x 3.5 m. In a randomised complete block design with three replications, four treatments are being compared leading to 12 plots with 30 trees/plot. The treatments under study are: T1—manual pruning using chain saws, in 2014 and 2017; T2—mechanical pruning: topping and hedging the two sides of the canopy, followed by manual pruning complement to remove wood suckers inside the canopy, in 2014 and 2017; T3—mechanical pruning: topping the canopy parallel to the ground and hedging southeast side of the canopy in 2014 and 2017; topping the canopy in July 2015 (summer pruning); hedging northwest side in winter 2016; T4—mechanical pruning: topping and hedging the two sides of the canopy in 2014 and 2017; topping the canopy in July 2015 (summer pruning). Regarding to olive yield per tree, significant differences were found among treatments on different years. However, no significant differences were found regarding the average olive yield per tree, over the period of 2014–2017. Regarding to the olive removal efficiency, only in 2016, significant differences were found among treatments on different years. No significant differences were found regarding the average of the olive removal efficiency, over the period of 2014–2017.

La madurez de las cubiertas vegetales aumenta la presencia de enemigos naturales y la resiliencia de la red trófica de la copa del olivo

Álvarez, H.A., Morente, M., Campos, M., Ruano, F. 2019. Maturity of ground covers increases the resilience and presence of natural enemies in the trophic network of olive canopy. Ecosistemas 28(3):92-106. Doi.: 10.7818/ECOS.1779 The quality of a habitat is related to its lifetime (age) and the disturbances to which it has been exposed. Natural enemies and their interactions in trophic networks can be affected by the maturity of the systems they inhabit. The positive effects of ground covers and adjacent vegetation on natural enemies have been demonstrated in olive groves; however, the effect of the quality of such habitats has been largely neglected. In the present study, we assessed the effects of matureness of ground covers on the arthropod community of the olive canopy, specially the natural enemies. Sampling was made in an organic olive orchard at two periods of time separated by more than 10 years. We analyzed the differences in abundance and richness of arthropods in the olive canopy and their interactions with ground cover and adjacent vegetation using trophic networks. Our results suggest that the establishment and maturity of the ground cover inside the olive orchard affected the structure and complexity of the trophic network. The taxa of herbivores, omnivores, and parasitoids did not change drastically while there was an increase in predator taxa between both periods, which subsequently produced an increase in the vulnerability of herbivores. In essence, the taxa of predators increased twice their number maintaining the same proportion of preys per taxon. According to our analysis, a mature ground cover could provide the trophic network of the olive trees with new efficient taxa to enhance the biological control of pests.

Phenology, seasonal abundance and stage-structure of spittlebug (Hemiptera: Aphrophoridae) populations in olive groves in Italy

Spittlebugs (Hemiptera: Aphrophoridae) are the dominant xylem-sap feeders in the Mediterranean area and the only proven vectors of Xylella fastidiosa ST53, the causal agent of the olive dieback epidemic in Apulia, Italy. We have investigated the structured population phenology, abundance and seasonal movement between crops and wild plant species of both the nymphal and adult stages of different spittlebug species in olive groves. Field surveys were conducted during the 2016–2018 period in four olive orchards located in coastal and inland areas in the Apulia and Liguria regions in Italy. The nymphal population in the herbaceous cover was estimated using quadrat samplings. Adults were collected through sweep nets on three different vegetational components: herbaceous cover, olive canopy and wild woody plants. Philaenus spumarius was the most abundant species; its nymphs were collected from early March and reached a peak around mid-April, when the 4th instar was prevalent. Spittlebug adults were collected from late April until late autumn. P. spumarius adults were abundant on the herbaceous cover and olive trees in late spring, and they then dispersed to wild woody hosts during the summer and returned to the olive groves in autumn when searching for oviposition sites in the herbaceous cover. A relatively high abundance of P. spumarius was observed on olive trees during summer in the Liguria Region. The present work provides a large amount of data on the life cycle of spittlebugs within an olive agroecosystem that can be used to design effective control programmes against these vectors in infected areas and to assess the risk of the establishment and spread of X. fastidiosa to Xylella-free areas.

Assessment of the Accuracy of a Multi-Beam LED Scanner Sensor for Measuring Olive Canopies.

Canopy characterization has become important when trying to optimize any kind of agricultural operation in high-growing crops, such as olive. Many sensors and techniques have reported satisfactory results in these approaches and in this work a 2D laser scanner was explored for measuring canopy trees in real-time conditions. The sensor was tested in both laboratory and field conditions to check its accuracy, its cone width, and its ability to characterize olive canopies in situ. The sensor was mounted on a mast and tested in laboratory conditions to check: (i) its accuracy at different measurement distances; (ii) its measurement cone width with different reflectivity targets; and (iii) the influence of the target’s density on its accuracy. The field tests involved both isolated and hedgerow orchards, in which the measurements were taken manually and with the sensor. The canopy volume was estimated with a methodology consisting of revolving or extruding the canopy contour. The sensor showed high accuracy in the laboratory test, except for the measurements performed at 1.0 m distance, with 60 mm error (6%). Otherwise, error remained below 20 mm (1% relative error). The cone width depended on the target reflectivity. The accuracy decreased with the target density.

Distribution and Relative Abundance of Insect Vectors of Xylella fastidiosa in Olive Groves of the Iberian Peninsula.

The phytosanitary emergency caused by the spread of Xylella fastidiosa in the Mediterranean has raised demands for a better understanding of the ecology of its presumed and candidate insect vectors. Here, we present the results of a two-year survey carried out in olive groves across southern, eastern and Central Spain and northeastern Portugal. Several sampling methods were tested and compared to select the most appropriate to estimate population levels of potential vectors of X. fastidiosa. The spittlebugs Philaenus spumarius and Neophilaenus campestris (Hemiptera: Aphrophoridae) were the main species associated with olive groves. Both species were widely present on herbaceous ground vegetation within the olive groves; P. spumarius mainly associated with Asteraceae and N. campestris with Poaceae. Due to the patchy distribution of spittlebugs within the olive groves, sweep nets were the most effective and least time-consuming sampling method for the estimation of population size both in the ground cover and tree canopies. Trends in population density showed that spittlebugs can be abundant on ground vegetation but very rare on olive canopies. Spittlebugs disperse in late spring to non-cultivated hosts that act as natural reservoirs. In late fall, adults return to the olive groves for oviposition. However, olive trees may act as transient hosts for spittlebugs and high population densities of these insect vectors should be avoided in areas where X. fastidiosa is present.

Soil ecosystem functions in a high-density olive orchard managed by different soil conservation practices

The long-term effects of two different soil management practices, natural grass cover (NC) and conservation tillage (CT), on soil functions (carbon sequestration, habitat for organisms, and water movement and retention) were determined in a high-density, mature olive orchard (Olea europaea L. cv. Frantoio) growing in a sandy loam soil (Typic Haploxeralf) in a Mediterranean environment. Ten years after the beginning of the different soil management, soil samples were collected at 0–10 and 10–20 cm depth and at two distances from the trunk, underneath the olive canopy (UC) and in the inter-row (IR). There were no differences in fruit yield, oil yield, and yield efficiency between the two soil management systems during the 2011–2013 period. CT negatively affected soil organic carbon pools (total and humified), but only at the IR position. The distance from the plant did not significantly influence soil structure and hydrological properties, while NC treatment increased water movement and retention. Tillage reduced the microarthropod abundance, in particular Collembola and eu-edaphic forms, which were the most sensitive groups to soil perturbation. We conclude that natural grass cover was more effective than conservation tillage in maintaining or improving elements of soil functionality.

Prolonged artificial shade affects morphological, anatomical, biochemical and ecophysiological behavior of young olive trees (cv. Arbosana)

Abstract Light requirement in olive trees is the most important factor to ensure both olive production and oil quality. However, in the intensive and hyper intensive olive cultivation, problems of shading frequently appear. The objective of this work was to study the effects of reduced irradiance on growth, morphology, anatomy, physiology and some biochemical traits of young olive plants. Thus, an artificial shade (ca. 60%) was performed in young olive plants cv. Arbosana. Plant responses occurred to shade application may be classified as short- and long-term ones. Shoot growth was started to be affected 18 months after shading application, and after that date a total suppression of growth was observed. However, both leaf surface and leaf angle insertion were affected from the beginning of the experiment (3 months).Shaded leaves had higher area and lower thickness. Palisade and spongy parenchyma thickness were reduced in shaded plants. Stomatal density, net photosynthetic rate, stomatal conductance and transpiration rate were also reduced by shade. Shading induced a significant decrease in the concentration of chlorophyll a, β-carotene, lutein and pigments within the xanthophyll cycle (VAZ). A significant decrease of fruits number was observed in shaded plants after one year of shading application, while with prolonged shade, a total absence of fruits were observed. In conclusion, the limitation of the amount of light intercepted by the olive canopy affects negatively most of studied parameters. Therefore, an adequate management of the olive canopy by applying adequate training and pruning programs or by the application of growth regulators will avoid shading problems with negative effects on vegetative growth and yield.

Arthropod communities within the olive canopy as bioindicators of different management systems

Arthropods, within the olive tree canopy, which can act as bioindicators of different management systems (conventional, integrated and organic), were collected in costal Croatia during 2007-2009. The aim of the research was to determine the arthropod orders present in each of the observed olive groves, to identify the number of individuals in each order, and to set potential bioindicators of different management systems. In order to do that, arthropods were collected from the olive canopies at three locations (Supetar, Kaštel Stari and Duilovo). After the samples were sorted according to orders, and determined according to arthropods determination keys. Olive groves were characterised by the same growth conditions and environment, with differences in agricultural management systems. In this investigation, 7882 arthropods were collected, belonging to 17 orders. It was found that Diptera, Heteroptera and other Hemiptera individuals, excluded Cicadidae and Psyllidae family individuals, could be defined as potential bioindicators of olive groves under different management systems. The number of Araneae and Coleoptera individuals significantly differed in all researched olive groves. So, these orders can be considered as bioindicators of different management systems. The knowledge obtained in this research can potentially be exploited in olive production in the future. Obtained results represent an important contribution to the inventory of arthropods in olive canopy. Also, this research significantly improves understanding of both harmful and beneficial entomofauna in olive groves and consequently contributes to better understanding of the total entomofauna in Croatia.

Olive canopy arthropods under organic, integrated, and conventional management. The effect of farming practices, climate and landscape

ABSTRACTSeveral beneficial components of biodiversity are hosted in the olive tree canopy, providing significant agroecosystem services. Olive canopy arthropods were studied under different management systems and in regard to variables related to farming practices, climate, and landscape. Arthropods were monitored weekly in 24 olive orchards for 2 years using transparent sticky traps. Farm management parameters, as well as climate conditions and landscape complexity, were recorded. Canopy arthropods and main olive pests were classified and aggregated upon functionality. Comparison between management systems was performed. Multivariate analysis was conducted with farming practices, climate conditions and landscape complexity as explanatory variables. Significant differences were not found between management systems, due to high variability of farming practices applied within the same management system. Factors linked to farm management, climate, and landscape explained arthropod variability better than management systems. The functional group approach appeared to be a meaningful, complementary biodiversity measure. Findings suggest that specific farm management, environmental, and landscape factors should be taken into account in agroecological research.

Organic carbon fluxes by precipitation, throughfall and stemflow in an olive orchard in Southern Spain

In forests and grasslands, canopy-derived carbon fluxes have been shown to be an important part of the carbon cycle, yet very few data are available for permanent agricultural crops. Concentration of total (TOC), dissolved (DOC) and particulate organic carbon (POC) was measured during an entire hydrological year in direct rainfall throughfall and stemflow in a mature olive orchard. Throughfall accounted for 68% of incoming rainfall, but TOC concentration was on average 14 times higher than in rainfall (7.63 vs. 106.12 mg/L). Stemflow on the other hand represented only a small fraction of gross precipitation, on average less than 1%, while its TOC concentration was on average 10-fold higher than in rainfall (74.13 mg/L). Dynamics of OC enrichment were mainly driven by precipitation patterns, as well as plant phenology, whereas a dramatic increase happened during flowering. Stemflow and throughfall were proven to be important sources of organic carbon supplying 13.5 g C/m2/year beneath the canopy of each tree, while 2.41 g C/m2/year reached the soil through gross precipitation. This large fraction of carbon is a mean of recirculating important carbon compounds that may help mobilize soil nutrients and maintain water holding capacity in the circumscribed area below olive canopies.

Local Environmental Context Conditions the Impact of Russian Olive in a Heterogeneous Riparian Ecosystem

Local abiotic and biotic conditions can alter the strength of exotic species impacts. To better understand the effects of exotic species on invaded ecosystems and to prioritize management efforts, it is important that exotic species impacts are put in local environmental context. We studied how differences in plant community composition, photosynthetically active radiation (PAR), and available soil N associated with Russian olive presence are conditioned by local environmental variation within a western U.S. riparian ecosystem. In four sites along the South Fork of the Republican River in Colorado, we established 200 pairs of plots (underneath and apart from Russian olive) to measure the effects of invasion across the ecosystem. We used a series of a priori mixed models to identify environmental variables that altered the effects of Russian olive. For all response variables, models that included the interaction of environmental characteristics, such as presence/absence of an existing cottonwood canopy, with the presence/absence of Russian olive canopy were stronger candidate models than those that just included Russian olive canopy presence as a factor. Compared with reference plots outside of Russian olive canopy, plots underneath Russian olive had higher relative exotic cover (exotic/total cover), lower perennial C4 grass cover, and higher perennial forb cover. These effects were reduced, however, in the presence of a cottonwood canopy. As expected, Russian olive was associated with reduced PAR and increased N, but these effects were reduced under cottonwood canopy. Our results demonstrate that local abiotic and biotic environmental factors condition the effects of Russian olive within a heterogeneous riparian ecosystem and suggest that management efforts should be focused in open areas where Russian olive impacts are strongest.