Pollen grains represent the male gametes of seed plants and their viability is critical for sexual reproduction in the plant life cycle. Palynology and viability studies have traditionally been used to address a range of botanical, ecological and geological questions, but recent work has revealed the importance of pollen viability in invasion biology as well. Here, we report an efficient visual method for assessing the viability of pollen using digital holographic microscopy (DHM). Imaging data reveal that quantitative phase information provided by the technique can be correlated with viability as indicated by the outcome of the colorimetric test. We successfully test this method on pollen grains of Lantana camara, a well-known alien invasive plant in the tropical world. Our results show that pollen viability may be assessed accurately without the usual staining procedure and suggest potential applications of the DHM methodology to a number of emerging areas in plant science.

Invasive alien plant species (IAPS) are spreading into protected areas worldwide; however, knowledge of these invasions and their impacts in Nepal’s protected areas is poor. Here, the spatial distribution pattern of IAPS in Bardia National Park (BNP), Nepal, was analysed using roadside surveys and grid sampling. The impacts of the most abundant IAPS, Lantana camara, on plant communities were analysed by comparing 60 pairs of non-invaded and invaded quadrats. Twelve IAPS, including two of the most prolific species globally, L. camara and Chromolaena odorata, were recorded from BNP. The Karnali floodplain in the south-western region of the park, a prime habitat of one-horned rhinoceros, was highly invaded by the IAPS. Tree canopy and distance to road, river and settlement were the major factors affecting IAPS occurrence. Lantana camara modified plant community structure and significantly reduced plant species richness and diversity; species richness of native plants was reduced to less than half in invaded plots. Plant invasions and impacts on native plant diversity have been increasing in BNP. We recommend management interventions involving immediate eradication of C. odorata and other species with single satellite populations and control measures for other widespread species such as L. camara and Ageratum houstonianum.

Non-native species impact tropical ecosystems, but the role of different anthropogenic disturbances on the success of non-natives remains unclear, especially in island tropical forests. We sought to understand the influence of anthropogenic habitat degradation and disturbance on non-native plant species in Madagascar. Specifically, we evaluated how densities of non-native species of woody shrub (Lantana camara), climber (Mucuna pruriens) and tree (Mangifera indica, Albizia lebbeck, Tamarindus indica) varied with forest habitat degradation and by disturbance type. We surveyed 60400 m2, recording 482 instances of disturbance and 903 non-native plants in and around the Ankarana National Park. Non-native plant densities were higher in degraded than primary forest. Within degraded forest, densities of non-native trees increased with disturbance. Tree densities correlated with extent of tree damage only in Tamarindus indica, never correlated with extent of tree removal, and always correlated with proximity to roads and trails. Our results suggest roads and trails have relatively greater importance in facilitating the success of non-native tree species than structural changes to habitat. In contrast, densities of Lantana camara and Tamarindus indica did not correlate with any measured type of disturbance; other unmeasured or historical factors may be more important drivers of these smaller, faster-reproducing species.

We examined changes in a community of seedlings/saplings 10–150 cm tall associated with the presence of a widely invasive plant, Lantana camara and environmental covariates along 67 randomly located transects, in Mudumalai, India. We compared plant species assemblage and grass cover in L. camara-invaded and uninvaded plots in three habitats. Multivariate analyses revealed a significant association of all environmental covariates with plant species assemblage. Pairwise tests indicated that L. camara was significantly associated with changes in plant species assemblage and grass cover within the moist and dry deciduous forest, but not in the thorn forest. The relationship between L. camara and that of elephant browse plants varied with species. A linear regression analysis indicated that L. camara invasion was the only significant predictor of grass occupancy. Our results indicate that in addition to other factors, L. camara was associated with altering plant species assemblage, some elephant browse plants and grass cover in the moist and dry deciduous forest. It appears that L. camara can have a major effect on diversity within this reserve, but whether this effect is by L. camara driving the change or being associated with other habitat change requires further experimental evidence.

Invasive weeds like Lantana camara have a range of effects on animals such as elephant. These plants are not edible by the Asian elephant (Elephas maximus). They also compete for space with elephant food plants and take over large areas of elephant habitat. We tested whether the addition of L. camara to a model consisting of measured environmental variables improved predictions of habitat use by elephant in Mudumalai Tiger Reserve, India. Elephant dung density was used to assess elephant habitat use from 62 line transects 1-km in length. Results indicated that habitat and impact of human settlements significantly influenced elephant habitat use at a landscape scale. However, we found no evidence for the hypothesis that the addition of L. camara significantly predicted elephant habitat use at the landscape level. We then tested the association of L. camara on elephant habitat use in the dry deciduous forest (DDF) where there was a significant interaction between DDF and L. camara. In the DDF, L. camara significantly predicted elephant habitat use. We conclude that while no significant effects of L. camara were seen at the level of an entire reserve, at a finer scale and in specific habitats negative effects of this invasive plant on elephant habitat use were observed.

Among the most endangered tropical ecosystems, tropical dry forests are threatened by degradation that includes edge effects arising from perturbations such as the creation and maintenance of roads and other clearings. While much is known about these adverse effects on tree communities in tropical moist forests, similar effects in tropical dry forests are little understood. This paper examines the relationship between roads, road-related exotic plant invasion and tree community change in a tropical dry forest in southern India. Forty pairs of roadside and interior plots across four factorial combinations of road width (wide and narrow) and understorey type (native and exotic) were sampled. Tree death and extant tree community composition were compared using generalized linear models and similarity analyses. Tree death near roads was more than double that away from them, suggesting that roads may increase tree death in these forests. The interactive effect of understorey type (exotic or native) and road width on tree death was significant, with highest tree death near wide roads bordered by exotic understorey. Conversely, tree community composition was influenced by road width and understorey type, but not by proximity to roads. Creation and maintenance of roads for forest management may have serious implications for tree communities in tropical dry forests and should thus be minimized. Exotic plants may also be important contributors to increasing tree death, and further research on their impacts, particularly into underlying mechanisms, is critical to the long-term conservation of tropical dry forest communities.

The root-feeding flea beetle Longitarsus bethae Savini & Escalona, was introduced into South Africa as a candidate biological control agent for the noxious and invasive weed, Lantana camara L. As part of the study to predict the beetles' survival in its new range, the influence of climatic conditions on its egg development and reproductive performance were investigated in the laboratory. The threshold temperature (T°) and degree-days (DD) required for egg hatch were determined after exposing the eggs to various constant temperatures (12, 17, 22, 27 and 32°C) in separate growth chambers. The DD required for egg hatch was 178.6, and the temperature threshold required for egg hatch was 11.3°C. Survival of eggs varied from 27 to 56% at 32 and 17°C, respectively, and was optimum between 17 and 25°C. Oviposition was examined under high and low relative humidity (RH) regimes while egg hatch was determined at six RH levels, each maintained in a separate controlled growth chamber set at a constant temperature (25°C). Whilst RH had no influence on oviposition, eggs were highly susceptible to aridity, and continuous exposure to relative humidity below 63% for more than three days was wholly lethal at 25°C. Optimum egg hatch occurred at RH between 85 and 95% for up to 12 days. The effect of day length on oviposition and subsequent egg hatch was investigated under two photoperiod regimes. Neither oviposition nor subsequent egg hatch was influenced by photoperiod. The knowledge obtained will be useful for mass rearing as well as field release programmes for L. bethae.

Resource-poor farmers often have diverse but small quantities of materials available that might be used to manage soil fertility. Opportunity costs of money are very high and farmers often opt to invest their scarce financial resources elsewhere rather than in fertilizer. This paper presents an approach to adaptive research and technology dissemination that was applied in Uganda and is applicable for improvement of integrated nutrient management (INM) in resource-poor farming systems. While little information may be available from research conducted in a particular agroecological zone (AEZ), information on INM components from diverse sources may be applicable for major crops in that AEZ. This information must be compiled and subjected to agronomic and economic analysis. A conceptual framework, e.g., in the form of a tentative decision guide, is then constructed, with consideration of interactions among nutrient sources, given the farmers' situations. Researchers estimate the most likely rates of application and substitution ratios, and then judge their confidence in the estimates. Priority actions are then identified for research and extension. When confident of their estimates, researchers formulate recommendations for promotion through extension means. If confidence is lacking, on-farm verification trials or other research may be needed. The approach is illustrated by work done for one AEZ in Uganda for maize and dry bean production, but is intended for application to other resource-poor farming systems in eastern Africa.