Invasive plant species

Black locust (Robinia pseudoacacia L.) is a fast growing tree species native to temperate North America, and widely diffused and naturalized in Europe. It is one of the candidate species for establishing bioenergy plantations on marginal lands in temperate and sub-Mediterranean regions. This potential is in contrast to its well-known invasive habit, leading to a potential damage to plant biodiversity in many European countries. Advise against black locust plantation in regions where it is already invasive has been issued by several international reports, as well as the adoption of mitigation measures (e.g., " containment " buffer zones) to prevent the spread of the species into natural and semi-natural habitats. In the Mediterranean basin, however, no studies have been carried out aimed at quantifying the escape rate of black locust saplings from plantation stands and its recruitment into natural habitats, together with the effectiveness of a buffer zone in reducing the spread. In this study we investigated the spread of black locust along 35 transects surrounding three 20-year-old plantations and including three different land cover types: abandoned arable land, semi-natural woodland and a buffer zone (orchards) with a low degree of farming input. In addition, the effect of soil disturbance on seed propagation was investigated. Our results demonstrate that the density of black locust regeneration is strongly affected by the land cover, abandoned agricultural land being the most prone to black locust colo-nization. Contrastingly, the spread was minimal in the buffer zone and negligible in semi-natural woodland. During the investigated year, seed generative propagation was also negligible. The semi-natural woodland seems to resist well to black locust invasion, though further observations are needed to assess the consequences of stand harvesting disturbance as well, according to local standard forest management. Buffer zones seem to be very effective in controlling black locust invasion. Best management practices, with active farming inputs, are also discussed.

The main focus of this study was to examine the morphology of Mimosa pigra, an invasive weed in response to artificial biotic and abiotic stressors. Seedlings of M. pigra were subjected to stressors such as seed sowing density, leaf defoliation and water regime. Comparatively, morphological performance related to different sowing practices differed significantly (p<0.05), as seedlings that grew from high density populations had lean and outstanding apical growth. A comparison between the four different levels of defoliation on the morphological changes revealed that the increase in leaf defoliation significantly decreased the plant morphological traits (i.e. height, stem diameter and flower bud productivity) and biomass allocation. Relatively low growth performance was found in plants subjected to 100% defoliation, with markedly lower flower bud productivity in comparison with 0%, 25% and 50% (no flower buds compared to 27, 13 and 6 flower buds, respectively). For water stress treatment, M. pigra showed no significant difference (p>0.05) in morphological performance under different levels of water regime. However, seedlings that received low water (LW) treatment showed better growth performance than seedlings that received high water (HW) treatment, which had the lowest morphological traits and biomass allocation. ABSTRAK Fokus utama penyelidikan ini adalah mengkaji tindak balas Mimosa pigra terhadap tekanan biotik dan abiotik tiruan. Anak benih M. pigra telah dikenakan tekanan kepadatan penyemaian benih, pemotongan daun dan rejim air. Secara perbandingan, prestasi morfologi bagi kesemua kepadatan yang berlainan menunjukkan perbezaan yang ketara (p<0.05) disebabkan anak benih yang tumbuh daripada kepadatan penyemaian benih tinggi mempunyai pertumbuhan atas yang kurus dan tinggi berbanding dengan anak benih daripada kepadatan yang lain. Perbandingan antara empat tahap pemotongan daun yang berbeza terhadap perubahan morfologi M. pigra menunjukkan bahawa peningkatan pemotongan daun secara ketara mengurangkan ciri morfologi (tinggi, diameter batang dan penghasilan kudup bunga) dan pengagihan biojisim. Prestasi pertumbuhan relatif yang rendah telah ditunjukkan oleh pokok yang dikenakan 100% pemotongan dengan penghasilan kudup bunga yang sangat rendah berbanding dengan 0%, 25% dan 50% pemotongan (tiada kudup bunga berbanding 27, 13 dan 6 kudup bunga). Bagi perlakuan tekanan air, tiada perbezaan morfologi yang ketara (p>0.05) ditunjukkan oleh M. pigra yang telah dikenakan dengan pelbagai tahap tekanan air yang berbeza. Walau bagaimanapun, anak benih yang telah menerima perlakuan air rendah (LW) menunjukkan prestasi pertumbuhan yang lebih baik berbanding anak benih yang menerima perlakuan air tinggi (HW) kerana mempunyai ciri morfologi dan pengagihan biojisim terendah.

The introduced black locust (Robinia pseudoacacia) has become an invasive plant species in Europe. The introduction of alien plants such as the black locust may modify ecosystem composition and functioning. In response to the presence of a potential host plant, herbivores can adapt and shift to the consumption of the new host plant. In Eastern-Central Europe, the seed predator Bruchophagus robiniae (Hymenop-tera: Eurytomidae) is an important consumer of black locust seeds which presumably shifted from its formerly host species to black locust. We tested the influence of host plant abundance on a seed predator e parasitoid community. We found that the seed predator B. robiniae was present in higher numbers in woodlots than in small patches of black locust. The density of the specialist parasitoid Mesopolobus sp. was lower in woodlots than in small patches, while the generalist parasitoid Eupelmus urozonos was evenly distributed between woodlots and small patches of black locust. We found that parasitoid species are influenced by the patch size of host plants, thus characteristics of introduced host plants can also manifest in higher trophic levels.