Renato Benesperi

Forest plant diversity is threatened by Robinia pseudoacacia (black-locust) invasion

The effects of black-locust invasion on plant forest diversity are still poorly investigated. Vascular plants are likely to be influenced by increasing nutrient availability associated with the nitrogen-fixing activity of black-locust, whereas it is not clear if, along with stand aging, black-locust formations regain forest species. The main aim of the present study was to test whether the increase of black-locust stand age promoted a plant variation in mature stands leading to assemblages similar to those of native forests. Therefore, plant richness and composition of stands dominated by native trees were compared with pure black-locust stands of different successional stages. Our study confirmed that the replacement of native forests by pure black-locust stands causes both plant richness loss and shifts in species composition. In black-locust stands plant communities are dominated by nitrophilous species and lack many of the oligothrophic and acidophilus species typical of native forests. Plant communities of native forests are more diverse with respect to pure black-locust stands, suggesting that black-locust invasion also causes a homogenization of the plant forest biota. We did not detect differences across the successional gradient of black-locust stands, and mature stands do not recover the diversity of plant species which are lost by the replacement of the native forests by black-locust. Accordingly some efforts in reducing the negative impacts of black-locust invasion on plant forest biota should be focused at least in those areas where conservation is among management priorities, such in the case of habitats included in the Habitat Directive (92/43 ECE).

Soil and plant changing after invasion: the case of Acacia dealbata in a Mediterranean ecosystem.

Acacia dealbata Link (Fabaceae) is one of the most invasive species in the Mediterranean ecosystems of Europe, Africa and America, where it has been proved to exert strong effects on soil and plant communities. In Italy A. dealbata has been largely used for ornamental and forestry purpose and is nowadays spreading in several areas. The present study was addressed to evaluate the impacts on soil chemical properties, soil microbial communities and understory plant communities and to assess the relationships among these compartments after the invasion of A. dealbata in a typical Mediterranean shrubland. Towards these aims, a soil and vegetation sampling was performed in Elba Island where A. dealbata is invading the sclerophyllous native vegetation. Three levels of invasion status were differentiated according to the gradient from invaded, to transitional and non-invaded vegetation. Quantitative and qualitative alterations of soil chemical properties and microbial communities (i.e. bacterial and fungal communities) and above-ground understory plant communities were found. In particular, the invaded soils had lower pH values than both the non-invaded and transitional ones. High differences were detected for both the total N and the inorganic fraction (NH4(+) and NO3(-)) contents, which showed the ranking: invaded>transitional>non-invaded soils. TOC and C/N ratio showed respectively higher and lower values in invaded than in non-invaded soils. Total plant covers, species richness and diversity in both the non-invaded and transitional subplots were higher than those in the invaded ones. The contribution of the nitrophilous species was significantly different among the three invasion statuses, with a strong increase going from native to transitional and invaded subplots. All these data confirm that A. dealbata modifies several compartments of the invaded ecosystems, from soil chemical properties to soil and plant microbial communities determining strong changes in the local ecosystem processes.

Rapid biodiversity assessment in lichen diversity surveys: implications for quality assurance

Rapid Biodiversity Assessments (RBAs) of lichen communities, obtained by means of simplified sampling lists based on morphospecies, showed good correlations with Lichen Diversity Values (LDVs), based on the complete identification of lichen species only when performed by operators with high levels of taxonomic knowledge. Furthermore, the use of highly simplified sampling lists did not lead to significant advantages in terms of time needed for field operations. This approach proved to be especially unreliable in high diversity ecological contexts where variation of morpho-structural composition within lichen communities is frequent (i.e. co-occurring crustose- and foliose-dominated communities); it may also lead to weak results if applied for conservation purposes. Hence, the use of simplified RBA sampling lists in lichen monitoring has to be carefully evaluated and, in any case, should be based on sound taxonomic knowledge on the part of those in charge of data collection. The proper assessment of descriptors of lichen abundance and/or frequency, however, strictly depends on the skill, taxonomic knowledge, and willingness to learn of the lichenologist-in-training.

Mature non-native black-locust (Robinia pseudoacacia L.) forest does not regain the lichen diversity of the natural forest

The responses of lichens to habitat changes caused by invasive trees are poorly understood. Invasive forest trees may impact epiphytic lichens by altering both substrate and stand conditions. Previous research has demonstrated that black locust invasion, associated with intensive exploitation of native oak forests, led to dramatic shifts in lichen composition. However, it is not clear if, along with stand aging, black locust formations regain forest species. The main aim of this study was to test whether the succession of black locust stands promotes a lichen succession leading to assemblages in mature black locust stands which are similar to those of native forests. To test the influence of macro-environmental conditions, we performed the study in two bioclimatically different areas of Italy. The epiphytic lichen biota of native oak and chestnut stands was compared with that of black locust stands of different successional stages. In both regions we did not find a lichen succession in black locust stands of different age, and mature black-locust stands did not recover the diversity of epiphytic species, which are lost by the replacement of the native forests by black locust. The absence of this pattern may be caused by factors related to the management of black locust stands, and to bark features. The different bioclimatic conditions between the two study areas may explain differences in the lichen biota of native forests, while that of black locust stands tend to be similar between regions, suggesting that forest habitat changes associated with the spread of black locust could decrease lichen diversity among bioclimatically different regions.

Differential land snail damage to selected species of the lichen genus Peltigera

Abstract The intensity of grazing of two land snails, Cantareus aspersa and Limax sp., on three epigaeic species of Peltigera with (P. horizontalis, P. neckeri) and without (P. praetextata) secondary compounds, were studied in the field in three transects of 2×50 m along an altitudinal gradient in the surroundings of Pistoia (Tuscany, Italy). The results were confirmed by laboratory experiments and were carried also out on a further species lacking lichen compounds (P. degenii), showing that land snails definitely prefer thalli lacking lichen secondary compounds. Damage intensity is correlated to the thallus size of the lichens.

Long-term monitoring of an invasion process: the case of an isolated small wetland on a Mediterranean Island

Invasions of Typha (cattail) and/or Phragmites (common reed) in wetland ecosystems result in changes in species richness, diversity and composition of vascular plants. These invasions are particularly harmful in lakes where threatened species and/or communities are found. The spread of two species of Typha (T. angustifolia and T. latifolia) and of Phragmites australis in the Stagnone Lake, on Capraia Island (Tuscan Archipelago — Mediterranean sea) was studied. We report this progressive invasion, documented by means of a series of vegetation maps (1991, 1995, 1998 and 2009). The expansion rate of the three invasive helophytes and the shrinking of the aquatic communities were studied using a GIS system. The impact of the spread of these three species on the floristic characteristics of the plant communities and the lake vegetation in general, was analysed by means of 15 plots of 1 m2 in 2000 and in 2009. Statistical analysis of the two series shows a significant change in the floristic composition of the communities as a result of the invasion process. Many important groups of species, such as many aquatic species, decrease in number and in cover value.

Epiphytic lichen communities in chestnut stands in Central-North Italy

Chestnut forest ecosystems represent an important component of the European Mediterranean basin and the Southern Alps landscape. Despite the good knowledge acquired in the phytosanitary and cultural aspects of chestnut, there is still a lack of data on the relationships between chestnut and epiphytes. We have investigated the changes in frequency of occurrence and species composition of lichen assemblages against the main site characteristics and environmental variables in chestnut woods along a bioclimatic and geographical gradient in Central-North Italy.The study has highlighted a geographic gradient from the Western Alps to the Northern Apennines. We recorded a total of 152 taxa, only 49 of which occurring in all the bioclimatic zones. The distribution of lichen communities in chestnut stands is mainly associated with increasing precipitation and decreasing temperature, thus confirming the prevailing influence of macroclimatic factors on epiphytic lichens. The species composition statistically differs also in stands differently managed (orchards vs. coppices).Chestnut woods host interesting communities, with rare species related to Lobarion, and can represent a good habitat for threatened epiphytic species.

Infraspecific variability in baseline element composition of the epiphytic lichen Pseudevernia furfuracea in remote areas: implications for biomonitoring of air pollution

The epiphytic lichen Pseudevernia furfuracea is widely used as biomonitor of airborne trace elements and other contaminants and consists of two taxonomic varieties (var. furfuracea and var. ceratea). Here, we assessed the occurrence of inter-varietal differences in the elemental composition of paired samples of var. furfuracea and var. ceratea collected in 20 remote sites of Italian mountains. The concentration of 40 elements was measured by inductively coupled plasma mass spectroscopy, after digestion with HNO3 and aqua regia. The magnitude of inter-varietal differences compared to the effect of large-scale site-dependent environmental factors (i.e., lithological substrate, host tree species, and altitude) on overall element content was explored by multivariate analysis techniques and tested by generalized linear mixed modeling (GLMM). Further GLMMs were separately fitted for each element testing taxonomic-related variability against uncertainty associated to the analytical procedure. Inter-varietal differences were statistically significant only for Hg and P, with higher content in var. ceratea at most sites, and for Mg and Zn, showing the opposite pattern. Since the elemental composition of P. furfuracea in remote sites was mostly affected by local lithology and climatic conditions, our results confirm that lichen material for active biomonitoring should be collected in a single ecologically homogeneous remote area. We also indicate sites in the Eastern Alps where P. furfuracea showed the minimum content of most elements, which are suggested as locations to collect lichen material for transplants. Besides the context-dependency at large spatial scale, variations of elemental composition apparently related to taxonomy, could possibly be due to unequal incidence of morphological traits of the collected material. Further research is needed to clarify this issue, and how it affects bioaccumulation phenomena.

Human Disturbance Threats the Red-Listed Macrolichen Seirophora villosa (Ach.) Frödén in Coastal Juniperus Habitats: Evidence From Western Peninsular Italy

In Europe, coastal dune systems with Juniperus spp. (Natura 2000 habitat code 2250) are a priority habitat for conservation according to the Natura 2000 policies. Currently, anthropogenic pressure is threatening the biodiversity of this habitat. While the impact of human pressure on animals and vascular plants is already documented, information is still scanty for other organisms such as epiphytic lichens. The main aim of this study is to test the effect of human disturbance on the occurrence and abundance of the red-listed macrolichen Seirophora villosa. We also tested the effect of human disturbance on the whole community of epiphytic lichens in terms of species richness and composition. The study was performed along the coast of Tuscany by comparing both disturbed and undisturbed Juniperus stands according to a stratified random sampling design. Our results provided evidence that in coastal systems the long-term conservation of the red-listed macrolichen S. villosa and its characteristic community composed by several Mediterranean species of conservation concern depends on the maintenance of undisturbed Juniperus habitats. Results also support the possibility of using S. villosa as an indicator species of habitat conservation importance and habitat integrity since its occurrence is predicted on nestedness in term of species composition, assemblages of species poor disturbed stands being subsets of those of richer undisturbed stands.

Plant species loss and community nestedness after leguminous tree Acacia pycnantha invasion in a Mediterranean ecosystem

Invasions of ecosystems by alien species are one of the major threats to biodiversity. Among alien plant species, members of the family Fabaceae s.l. represent some of the most dangerous and well known global invaders. In Mediterranean ecosystems, many Australian acacias have been found to establish and rapidly spread, often determining severe impacts on understorey vegetation. In the present work, we report a case study of an Acacia pycnantha invasion in a typical Mediterranean matorral (Elba Island, central Mediterranean Sea, Italy). We conducted a survey of understorey plant communities across an invasion gradient from non-invaded to transitional and invaded areas, aiming to quantify the impacts on the understorey assemblage and to investigate the ecological processes involved in the changes in species composition. The understorey plant community was highly affected starting from the intermediate stage of invasion. Species richness, diversity and total cover were all lower in invaded than in non-invaded plots, with a transition generally in the middle. In addition, plant community composition severely changed along the invasion gradient. The species set we recorded showed a nested structure, with the composition of species in the invaded plots representing a subset of the others. According to our findings, A. pycnantha exerted detrimental impacts on the native vegetation, mainly causing a severe species loss in the understorey assemblage and the impoverishment of the invaded ecosystems.