Strategic Management of an Invasive Ant‐scale Mutualism Enables Recovery of a Threatened Tropical Tree Species

Mutualisms between invasive ants and honeydew‐producing insects can have widespread negative effects on natural ecosystems. This is becoming an increasingly serious problem worldwide, causing certain ecosystems to change radically. Management of these abundant and influential mutualistic species is essential if the host ecosystem is to recover to its former non‐invaded status. This negative effect is particularly prevalent on some tropical islands, including Cousine Island, Seychelles. On this island, the invasive ant Pheidole megacephala has caused serious indirect damage to the threatened native Pisonia grandis trees via a mutualism with an invasive scale insect, Pulvinaria urbicola. We aimed to suppress the ant, thereby decoupling the mutualism and enabling recovery of the Pisonia trees. We treated all areas where ant pressure was high with a selective formicidal bait, which was deployed in custom‐made bait stations designed to avoid risk of treatment to endemic fauna. In the treated area, ant foraging activity was reduced by 93 percent and was followed by a 100 percent reduction in scale insect density. Abundance of endemic herbivorous insects and herbivorous activity increased significantly, however, after the decline in mutualistic species densities. Despite the native herbivore increase, there was considerable overall improvement in Pisonia shoot condition and an observed increase in foliage density. Our results demonstrate the benefit of strategic management of highly mutualistic alien species to the native Pisonia trees. It also supports the idea that area‐wide suppression is a feasible alternative to eradication for achieving positive conservation management at the level of the forest ecosystem.     

Effects of Phenology at Burn Time on Post‐Fire Recovery in an Invasive C4 Grass

The spread of non‐indigenous, C₄ grasses threatens global conservation of savannas and subtropical grasslands. Identifying control methods to selectively target these invasives has proven difficult. Here, we tested the hypothesis that the effectiveness of prescribed burns for control is determined, in part, by the phenology of the target species at burn time. We conducted two experiments in a subhumid, C₄ grassland in central Texas. The focal invasive was the C₄, perennial bunchgrass Bothriochloa ischaemum (L.) Keng (KR bluestem). Burns were conducted in early and late fall when plants were in different phenological states. In addition, we attempted to manipulate phenological state through temporary rainout shelters to expedite maturation. The two experiments differed in the timing of the rainout shelter application (experiment 1: May to July, experiment 2: August and September), but otherwise had the same complete factorial design (burn time × shelter). Across experiments, when at least 50% of all tillers were pre‐reproductive at burn time, either due to shelter treatment or time of year, spring tiller densities were significantly lower than when plants were burned in a more advanced reproductive state. Trends in fall biomass generally followed trends in spring tiller densities, with one exception where plants in no‐shelter plots burned in October had lower biomass than expected based on tiller densities. Treatment responses for the native C₄ grass B. laguroides were consistent with those of B. ischaemum. These findings suggest that strategic burns can be used to reduce the subsequent recovery of invasive C₄ grasses while not disadvantaging native grasses.     

Relationships between Methylobacteria and Glyphosate with Native and Invasive Plant Species: Implications for Restoration

After removing invasive plants, whether by herbicides or other means, typical restoration design focuses on rebuilding native plant communities while disregarding soil microbial communities. However, microbial–plant interactions are known to influence the relative success of native versus invasive plants. Therefore, the abundance and composition of soil microorganisms may affect restoration efforts. We assessed the effect of herbicide treatment on phytosymbiotic pink‐pigmented facultative methylotrophic (PPFM) bacteria and the potential consequences of native and invasive species establishment post‐herbicide treatment in the lab and in a coastal sage scrub (CSS)/grassland restoration site. Lab tests showed that 4% glyphosate reduced PPFM abundance. PPFM addition to seeds increased seedling length of a native plant (Artemisia californica) but not an invasive plant (Hirschfeldia incana). At the restoration site, methanol addition (a PPFM substrate) improved native bunchgrass (Nassella pulchra) germination and size by 35% over controls. In a separate multispecies field experiment, PPFM addition stimulated the germination of N. pulchra, but not that of three invasive species. Neither PPFM nor methanol addition strongly affected the growth of any plant species. Overall, these results are consistent with the hypothesis that PPFMs have a greater benefit to native than invasive species. Together, these experiments suggest that methanol or PPFM addition could be useful in improving CSS/grassland restorations. Future work should test PPFM effects on additional species and determine how these results vary under different environmental conditions.     

Terpenes as Useful Markers in Differentiation of Natural Populations of Relict Pines Pinus heldreichii,P. nigra,and P. peuce

Comparative analysis of terpene diversity and differentiation of relict pines Pinus heldreichii, P. nigra, and P. peuce from the central Balkans was performed at the population level. Multivariate statistical analyses showed that the composition of needle terpenes reflects clear divergence among the pine species from different subgenera: P. peuce (subgenus Strobus) vs. P. nigra and P. heldreichii (subgenus Pinus). In addition, despite the described morphological similarities and the fact that P. nigra and P. heldreichii may spontaneously hybridize, our results indicated differentiation of their populations naturally growing in the same area. In accordance with recently proposed concept of ‘flavonic evolution’ in the genus Pinus, we assumed that the terpene profile of soft pine P. peuce, defined by high amounts of six monoterpenes, is more basal than those of hard pines P. nigra and P. heldreichii, which were characterized by high content levels of mainly sesquiterpenes. In order to establish precise positions of P. heldreichii, P. nigra and P. peuce within the taxonomic and phylogenetic tree, as well as develop suitable conservation strategies and future breeding efforts, it is necessary to perform additional morphological, biochemical, and genetic studies.     

Field heritability of a plant adaptation to fire in heterogeneous landscapes

The strong association observed between fire regimes and variation in plant adaptations to fire suggests a rapid response to fire as an agent of selection. It also suggests that fire‐related traits are heritable, a precondition for evolutionary change. One example is serotiny, the accumulation of seeds in unopened fruits or cones until the next fire, an important strategy for plant population persistence in fire‐prone ecosystems. Here, we evaluate the potential of this trait to respond to natural selection in its natural setting. For this, we use a SNP marker approach to estimate genetic variance and heritability of serotiny directly in the field for two Mediterranean pine species. Study populations were large and heterogeneous in climatic conditions and fire regime. We first estimated the realized relatedness among trees from genotypes, and then partitioned the phenotypic variance in serotiny using Bayesian animal models that incorporated environmental predictors. As expected, field heritability was smaller (around 0.10 for both species) than previous estimates under common garden conditions (0.20). An estimate on a subset of stands with more homogeneous environmental conditions was not different from that in the complete set of stands, suggesting that our models correctly captured the environmental variation at the spatial scale of the study. Our results highlight the importance of measuring quantitative genetic parameters in natural populations, where environmental heterogeneity is a critical aspect. The heritability of serotiny, although not high, combined with high phenotypic variance within populations, confirms the potential of this fire‐related trait for evolutionary change in the wild.     

Composition and Chemical Variability of the Needle Oil from Pinus halepensis growing in Corsica

The composition of oil samples isolated from needles of Pinus halepensis growing in three locations in Corsica (Saleccia, Capo di Feno, and Tre Padule) has been investigated by combination of chromatographic (GC with retention indices) and spectroscopic (MS and ¹³C‐NMR) techniques. In total, 35 compounds that accounted for 77 – 100% of the whole composition have been identified. α‐Pinene, myrcene, and (E)‐β‐caryophyllene were the major component followed by α‐humulene and 2‐phenylethyl isovalerate. Various diterpenes have been identified as minor components. 47 Oil samples isolated from pine needles have been analyzed and were differentiated in two groups. Oil samples of the first group (15 samples) contained myrcene (M = 28.1 g/100 g; SD = 10.6) and (E)‐β‐caryophyllene (M = 19.0 g/100 g; SD = 2.2) as major components and diterpenes were absent. All these oil samples were isolated from pine needles harvested in Saleccia. Oil samples of the second group (32 samples) contained mostly (E)‐β‐caryophyllene (M = 28.7 g/100 g; SD = 7.9), α‐pinene (M = 12.3 g/100 g; SD = 3.6), and myrcene (M = 11.7 g/100 g; SD = 7.3). All these oil samples were isolated from pine needles harvested in Capo di Feno and Tre Padule.     

Vegetation Recovery 16 Years after Feral Pig Removal from a Wet Hawaiian Forest

Nonnative ungulates can alter the structure and function of forest ecosystems. Feral pigs in particular pose a substantial threat to native plant communities throughout their global range. Hawaiian forests are exceptionally vulnerable to feral pig activity because native vegetation evolved in the absence of large mammalian herbivores. A common approach for conserving and restoring forests in Hawaii is fencing and removal of feral pigs. The extent of native plant community recovery and nonnative plant invasion following pig removal, however, is largely unknown. Our objective was to quantify changes in native and nonnative understory vegetation over a 16 yr period in adjacent fenced (pig‐free) vs. unfenced (pig‐present) Hawaiian montane wet forest. Native and nonnative understory vegetation responded strongly to feral pig removal. Density of native woody plants rooted in mineral soil increased sixfold in pig‐free sites over 16 yr, whereas establishment was almost exclusively restricted to epiphytes in pig‐present sites. Stem density of young tree ferns increased significantly (51.2%) in pig‐free, but not pig‐present sites. Herbaceous cover decreased over time in pig‐present sites (67.9%). In both treatments, number of species remained constant and native woody plant establishment was limited to commonly occurring species. The nonnative invasive shrub, Psidium cattleianum, responded positively to release from pig disturbance with a fivefold increase in density in pig‐free sites. These results suggest that while common native understory plants recover within 16 yr of pig removal, control of nonnative plants and outplanting of rarer native species are necessary components of sustainable conservation and restoration efforts in these forests.     

维护我国生态安全,防范外来物种入侵的几点思考

随着全球经济一体化,国际贸易和旅游业的快速发展,外来物种入侵现象日益加剧,对我国生态安全和生物多样性保护构成了极大的威胁,加强外来入侵物种的防范和管理已迫在眉睫。本文分析了我国外来物种入侵的途径、入侵特征以及外来入侵物种对我国造成的危害,探讨了防范外来入侵物种的对策。     

Impacts of Herbicide Application and Mechanical Cleanings on Growth and Mortality of Two Timber Species in Saccharum spontaneum Grasslands of the Panama Canal Watershed

Reforestation has been suggested as a strategy to control Saccharum spontaneum, an invasive grass that impedes regeneration in disturbed areas of the Panama Canal Watershed (PCW). In this study, the effects of different intensities of herbicide application and mechanical cleanings on the growth and mortality of Terminalia amazonia and Tectona grandis saplings were evaluated in S. spontaneum grasslands within the PCW. Both species exhibited greater height, basal diameter, wood volume index, wider crown diameters, deeper live crowns, and lower mortality with increasing intensity of mechanical cleanings and herbicide application. Height and competition of S. spontaneum correlated negatively with intensity of mechanical cleanings and herbicide application. Grass control costs did not differ between tree species but did increase significantly with intensity of mechanical cleanings and herbicide application. We recommend fire suppression, annual herbicide application, and at least four mechanical cleanings per year in Tec. grandis plantations during the first 3 years of plantation establishment. Given the slower initial growth and mortality patterns of Ter. amazonia, aggressive grass control treatments should be continued until individuals are sufficiently large to effectively shade S. spontaneum. Results from this study suggest that reforestation with commercial timber species can rapidly establish and control S. spontaneum growth in the PCW. Reforestation of areas already invaded or at risk of being invaded by S. spontaneum appears to be a viable strategy to reduce its abundance and subsequent negative ecological effects in the PCW.     

Within‐Year Soil Legacies Contribute to Strong Priority Effects of Exotics on Native California Grassland Communities

Understanding priority effects, in which one species in a habitat decreases the success of later species, may be essential for restoring native communities. Priority effects can operate in two ways: size‐asymmetric competition and creation of “soil legacies,” effects on soil that may last long after the competitive effect. We examined how these two types of priority effects, competition and soil legacies, drive interactions between seedlings of native and exotic California grassland plants. We established native and exotic communities in a mesocosm experiment. After 5 weeks, we removed the plants from half the treatments (soil legacy treatment) and retained the plants in the other half (priority effect treatment, which we interpret to include both competition and soil legacies). We then added native or exotic seed as the colonizing community. After 2 months, we measured the biomass of the colonizing community. When germinating first, both natives and exotics established priority effects, reducing colonist biomass by 86 and 92%, respectively. These priority effects were predominantly due to size‐asymmetric competition. Only exotics created soil legacies, and these legacies only affected native colonizers, reducing biomass by 74%. These results imply that exotic species priority effects can affect native grassland restorations. Although most restorations focus on removing exotic seedlings, amending soil to address soil legacies may also be critical. Additionally, because native species can exclude exotics if given a head start, ensuring that natives germinate first may be a cost‐effective restoration technique.     

Comparison of Invasive Shrub Honeysuckle Eradication Tactics for Amateurs: Stump Treatment versus Regrowth Spraying of Lonicera maackii

Elimination of Asiatic shrub honeysuckles (Lonicera spp.) from preserves and conservation areas in eastern North America is difficult because bird dispersal reintroduces seeds from shrubs in the neighborhood. To reduce this problem, honeysuckle control must be instituted on a broad scale and involve public participation. Many techniques for honeysuckle control are beyond the capabilities and inclinations of volunteers and local landowners. In a replicated study, we evaluated two suitable techniques and applied them in spring, early summer, late summer, fall, and winter 2009. These were stem cutting followed by painting with 18% glyphosate, and stem cutting followed by spraying of regrown shoots with 1% glyphosate about 40 days later. We regarded the spraying of regrown shoots as more practical for neophytes. Overall, cutting followed by stump treatment is more effective, killing 75–85% of individuals in spring and early summer, and >90% later in the year. Cutting and spraying regrowth was most effective in spring (56% killed), and poorer thereafter (20–40% killed). The result for spring was much lower than previously observed. Death rates for the cutting and regrowth spraying treatment were not affected by shrub size, but the amount of regrowth after spraying responded strongly to size. Cutting and regrowth spraying may be suitable in situations where reducing the competitive effects and reproduction of individuals is sufficient, or the resources to treat stumps with concentrated glyphosate are limited.     

Biology and field host range of Ceutorhynchus cardariae,a potential biological control agent for Lepidium draba

Lepidium draba (Brassicaceae) is a clonal herb, originating from Eurasia, which is invasive in North America. A classical biological control project was initiated in 2001, and the gall‐forming weevil Ceutorhynchus cardariae was prioritized as a candidate agent. We studied its biology and field host range between 2003 and 2014 in the laboratory and a common garden in Switzerland and in the field in Romania. Ceutorhynchus cardariae is a univoltine to bivoltine species. In Switzerland, oviposition usually started at the beginning of March and can occur at temperatures as low as 2.5°C. Galls are formed on stems, leaf stalks and midribs of L. draba rosettes and bolting plants. Gall size increased with an increasing number of larvae per gall. The three larval instars feed inside the galls and leave the plant to pupate in the soil once mature. In Switzerland, development from egg to adult took about 12 weeks in spring. Adults emerged from May to July. After a brief feeding period, adults aestivate. From late summer, feeding recommenced and females may oviposit, forming a partial second generation. Eggs and all larval instars can be found in galls throughout winter. The rate of larval ectoparasitism reached 78%, while endoparasitism was low with a maximum of 2.3%. Lepidium draba populations differed in their suitability for development (number of C. cardariae produced), indicating that effectiveness of C. cardariae – in case released – may be variable. In the field, we observed that gall formation by C. cardariae can severely stunt or even kill shoots. Investigations on the field host range of C. cardariae indicated that only the closely related Lepidium campestre may act as an alternative host for the weevil in Europe. Host‐specificity tests are underway to determine its environmental safety before field release in North America is being considered.     

Variability of Pinus halepensis Mill. Essential Oils and Their Antioxidant Activities Depending on the Stage of Growth During Vegetative Cycle

The impact of growth stages during vegetative cycle (B₀ – B₅) on chemical composition and antioxidant activities of Pinus halepensis Mill . needles essential oils was investigated for the first time. GC and GC/MS analyses pointed to a quantitative variability of components; terpene hydrocarbons derivatives, represented by α‐pinene (8.5 – 12.9%), myrcene (17.5 – 21.6%), p‐cymene (7.9 – 11.9%) and (Z)‐β‐caryophyllene (17.3 – 21.2%) as major components, decreased from 88.9% at B₀ growth stage to 66.9% at B₅ growth stage, whereas oxygenated derivatives, represented by caryophyllene oxide (5.4 – 12.6%) and terpinen‐4‐ol (0.4 – 3.3%) as major components, increased from 7% at B₀ growth stage to 28.4% at B₅ growth stage. Furthermore, our findings showed that essential oil of P. halepensis needles collected at B₅ growth stage possess higher antioxidant activities by four different testing systems than those collected at B₀ – B₄ growth stages. This highlighted variability led to conclude that we should select essential oils to be investigated carefully depending on growth stage, in order to have the highest effectiveness of essential oil in terms of biological activities for human health purposes.     

Composting One Invasive Species to Control Another

The need for research and development of effective approaches to weed control continues to increase globally. Adaptive protocols using diverse control methods are often required in ecological restoration as recruitment of native species is highly site‐specific, species‐specific, and experimental. The use of composted weed refuse to control other weeds may be a practical option; yet, the option is not well studied due to the accompanied risk of introducing weed propagules to areas where weed control is desired. Here, we tested the effectiveness of different physical control techniques including the use of mulch made by composting weed refuse on‐site. English ivy (Hedera helix), a non‐native, invasive species in the Pacific northwestern United States, was removed from a heavily invaded site, shredded, and composted. The mulch was compared with other methods of suppressing herb Robert (Geranium robertianum), another invasive species on‐site. Five treatments were tested: flame‐weeding, hand‐pulling, mulching, hand‐pulling followed by mulching, and flame‐weeding followed by mulching. The mulch and pull/mulch treatments were the most effective, reducing G. robertianum cover by 92 and 86% of pre‐treatment levels, respectively, and suppressing G. robertianum 2.9 and 1.6 times more than the control, respectively. The mechanism behind the effectiveness of the mulch is uncertain, but may be related to weed seed burial or the allelopathic potential of the mulch. Composting one invasive species to use as mulch to control another can be effective and merits trial elsewhere.