Aim
Understanding the historical and contemporaneous drivers of invasion success in island systems can decisively contribute to identifying sources and pathways that are more likely to give rise to ...new invaders. Based on a floristic‐driven approach, we aimed at determining the origins of the invasive alien flora of the Canary Islands and shedding light in the mechanisms shaping their distribution within the archipelago.
Location
Canary Islands.
Taxon
Vascular plants.
Methods
An updated checklist of the invasive alien flora of the Canary Islands was assembled along with complementary information related to the native biogeographical regions, stage of invasiveness and dates of naturalization. Statistical models were employed to describe differences in the number of species over space and time. We also used multivariate techniques to evaluate competing hypotheses related to the mechanisms driving invasive floristic composition within the archipelago.
Results
We provided a list of 149 alien plant species with a certain degree of invasiveness. The greatest number of invasive species originated from the Neotropics followed by the Cape Region, tropical Africa and the Mediterranean Basin. We observed a slow but steady increase in numbers of invasive species until the 1950s, followed by a stronger rise thereafter. In order to explain composition dissimilarity of the invasive flora among islands, a climatic matching hypothesis was fully supported, with geographic isolation and contemporary human‐mediated connectivity hypotheses receiving less and null support respectively.
Main Conclusions
We showed that the Neotropical region is the main source of plant invasions to the Canary Islands, outnumbering those from other regions with a Mediterranean‐type bioclimate. The assembly of the invasive flora within the archipelago appears to be driven primarily by climate, but with geographic distance also playing a role. This study calls for archipelago‐dependent assessments of the underlying mechanisms that contribute to plant invasion success within insular systems.
•P. halepensis is expanding at short distance and at several kilometres from plantations in La Gomera.•That expansion is especially affecting the potential areas of endemic Juniper ...woodlands.•Legislation and classification system in the Canary Islands must change to start considering this species as invasive.
Aleppo pine (Pinus halepensis Miller) has been one of the most used Pinus species in reforestation in the Mediterranean Basin and in many other regions outside its native range. Its massive use in plantations combined with its low environmental requirements, relatively short juvenile period and adaptability to human disturbance make P. halepensis a great competitor for local species, becoming invasive in many natural and anthropized areas. As little is known about the effects of these plantations on oceanic islands ecosystems, we evaluated in this study the expansion dynamics of a series of P. halepensis plantations carried out on the island of La Gomera (Canary Islands) in the 1960s and 1970s of the past century. At short distance, we counted and measured P. halepensis individuals along transects of 140 m from the inside of the plantation to the outside, assessing also the proportion occupied by other native, endemic and ruderal species in two habitat types: thermo-sclerophyllous woodlands and laurel forests. To examine seed dispersal over longer distances, we selected one of the areas that showed a greater expansion and we analyzed factors influencing regeneration. Our results revealed that expansion is occurring mostly in open or disturbed areas instead of closed-canopy humid forests and we found a clear negative relationship between the presence of the species and the abundance of other trees or the endemic and native flora. Furthermore, we detected potential new foci of regeneration away from the plantations too. Overall, we suggest that the status of P. halepensis as a non-native species and its classification for the purposes of management in the Canary Islands needs to be re-examined.
The monitoring of ecosystems and forests is an urgent requirement in the current framework of global change. It is particularly necessary on oceanic islands where their rich biodiversity is highly ...vulnerable, with many narrow-ranged endemic species. Quantifying and mapping forest health through key ecological variables are essential steps for management, but it will also be challenging and may require a lot of resources. Remote sensing has the potential to be a very useful tool to assess the development and conservation status of forests. We assessed the applicability of the light detection and ranging (LiDAR) on the laurel forests of La Gomera, making allometric equations for various measurements of the forest structure, linking field inventory from 2019 and 2017 LiDAR data through standard linear regressions. Decision trees and logistic regressions were also used to assess the performance of LiDAR in the recognition of young-growth and old-growth laurel forests. The obtained allometric models were a good fit in general and their predictions were in line with already known data. Likewise, decision tree and logistic regression to distinguish young-growth and old-growth forests had a similar performance in both cases, with a high to medium-high degree of accuracy. Therefore, LiDAR was revealed to be a useful tool for the monitoring of the laurel forest by the managers.
The recurrence of fires has increased considerably due to human activity, affecting even forests where traditionally fire is uncommon. In this study, we verify the effects of degradation caused by ...fire in the Canarian laurel forests, which is a subtropical forest formation restricted to the humid montane areas of these Macaronesian islands. We evaluated the effect of fire by comparing a series of burned plots corresponding to fires from 1960, 1984, 1995, to 2012 with geographically proximate and comparable unburned plots in the Garajonay National Park (La Gomera Island, Spain). We focused on three aspects that are immediately altered by fire: forest structure, floristic composition, and microclimate. These aspects have been quantified using (a) tree density, the Pielou index using tree height classes, and DBH for the vertical structure of the forest; (b) DCA, the Bray Curtis dissimilarity index, and a species indicator analysis for the floristic composition; and (c) temperature and relative humidity for microclimate under three canopy cover conditions. Our results reveal that, overall, structural complexity and its composition in the burned areas have barely reached 40% and 35%, respectively, when compared with unburned areas, and recovery mainly depends on time since fire. Additionally, burned plots presented more pioneer species, a higher density of trees, and climatic variables tend to have a wider range throughout the day. These data reveal the long time span that this ecosystem needs for recovery to a prefire state and how it may be more prone to subsequent fire events.
The endemic flora of the Canary Islands is remarkable but highly vulnerable to environmental changes. Several factors, such as fire, could be threatening. The purpose of this study was to analyze ...various treatments in endemic threatened species which could have been growing in the understory of the Canary pine forest. We attempted to improve germination through dormancy breaking, and analyze the influence of fire on these plants. Seven physical and chemical treatments were tested: control, mechanical scarification, boiling water, dry heat (50 and 120 °C), smoke and smoked water. Mechanical scarification showed a positive response in germination percentage in two species characterized by hard seed coat, but out of all of the species tested, only one demonstrated a positive response to any of the treatments related to fire. At the temperatures registered on wildfires, neither the seeds situated on the aerial structure nor seeds in seed bank seem to be able to survive and germinate. The increasing incidence of fires through anthropogenic causes could contribute to the current threat status of these species and poorness of the Canary pine forest understory.
Disruptive effects have been described on the plants and ecosystems of oceanic islands due to the introduction of invasive herbivores. In the Canary Islands the European rabbit (Oryctolagus cuniculus ...L.) was introduced five centuries ago and currently is widespread in all ecosystems, although in the laurel forests it is very scarce. However, on Morello-Ericetum woodland mostly represented by disturbed laurel forest areas, rabbit density is higher. Here we analyzed the impact of rabbits on the Morello-Ericetum woodland using exclusion and control plots located in 11 sites in the Garajonay National Park (La Gomera Island). Rabbit browsing was assessed for 36 endemic species, 15 of them threatened, which were sowed in both control and exclusion plots. After three years of monitoring, our results show a significant negative effect on the establishment and seedling recruitment for 55% of the analyzed species, especially in summer when the rabbit density increases by nearly 30%. Also, plant growth (in 91% of the species) and flowering rate (36% of the species), were disrupted, which could cause a depletion of the seed bank. Among the five tree species included in the experiment, three were also significantly damaged, so rabbits could be even influencing canopy species, delaying forest recovery. The management of Morello-Ericetum woodland should be countered the effects produced by the rabbits on their tree composition, and to allow the development of an understory where endemic species recover their abundance.
•Exclusion and control plots with sowing were used in this experiment.•Seedling recruitment, plant growth and flowering rate were disrupted.•At least 13 of 15 studied endangered species were browsed by the rabbits.•Seedling of some tree species was browsed, delaying the laurel forest recovery.
•Laurel forest recovery does not depend only on initial vegetation conditions.•The early recovery stage was driven by aspect and distance from young-growth forests.•In middle stage, the recovery was ...driven by old-growth forest cover around each site.•The oldest-growth forests showed more endemic, threatened species and β-diversity.
Deforestation and forest fragmentation have serious negative consequences for biodiversity and species distribution, but many studies approach species distributions and speciation processes without taking in account the local history of human disturbances. Nevertheless, the complex recovery process after forest destruction is widely distributed around the world and takes place under a wide mosaic of biotic and abiotic factors that may be influencing the species distribution. In this study aerial pictures from 1951 and 2019 were used to assess forest recovery during about sixty years. We tested if the initial stage (forest completely destroyed or young growth forest in 1951) determines the successional process, evaluating the role of different spatial drivers (distance from remnant forest fragments and unfelled areas around each site) and mesoclimate conditions, by examining 40 disturbed sites and 18 old-growth forest sites distinguished in 1951 aerial photos. The final stage during this successional process was assessed using 2019 aerial photos, covering the same these sites. At each plot, plant species composition and forest structure were studied, which allowed us to obtain a maturity index. Our results reveal that the initial stage is not the only driver explaining forest structure and species composition at the end of the 60-year period analyzed. The role of each forest recovery driver varies depending on each stage. In the early successional stages, the slope aspect (exposure) was the most important factor, which is correlated with mesoclimatic conditions, followed by the distance from young-growth forest in 1951. However, in intermediate successional stages the cover of old-growth forest around each plot in 1951 was the main factor in the recovery. At the end of the study period (2019), the differences in species richness between young-growth and old-growth forest were not significant, although old-growth forests were characterized by high densities of endemics, threatened species and β-diversity, showing the species composition a strong dependence on forest structure. Our results reveal the important need to consider human disturbance history in forest research and how climate conditions and the lack of nearby remnants can negatively affect the forest recovery process, greatly increasing the time needed to return to old-growth laurel forest conditions, which requires specific management recommendations.
The introduction of alien species is one of the main threats to conservation. However, the same species may be threatened and be a threat in nearby areas. This is the case of the Barbary sheep ...(Ammotragus lervia) and mouflon (Ovis orientalis), which greatly hinder the management and conservation of biodiversity outside their native range. To prevent the extinction of many endemic plants, it is necessary to overcome several methodological difficulties.
The name Zygophyllo fontanesii-Sarcocornietum perennis is rejected as it is invalid and the new name Halimiono portulacoidis-Salicornietum perennis is proposed with two subassociations: typicum and ...limonietosum canariensis. The name Salicornietum perennis for Cuban communities is corrected to Salicornietum ambiguae.
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