Juana M. González-Mancebo

Host Specificity of Epiphytic Bryophyte Communities of a Laurel Forest on Tenerife (Canary Islands, Spain)

Abstract We studied bryophyte species composition on five tree species (Erica scoparia, Laurus azorica, Myrica faya, Ilex canariensis, and I. Perado) of the laurel forest on Tenerife in order to determine the dominant factors influencing bryophyte community structure. Most of the 37 bryophyte species we found (24 liverworts and 11 mosses) are facultative epiphytes; many were found on several tree species, while five occurred on all tree species. DCA and CCA indicated that bryophyte species composition is significantly related to tree species identity. For each tree species, bark characteristics, plot exposure (windward and leeward to the prevailing trade winds), height (50 or 130 cm), tree size, and uprightness have differing relationships to bryophyte species composition. Bryophyte growth forms appeared to relate to the moisture conditions of the tree bark.

Approximate Bayesian Computation Reveals the Crucial Role of Oceanic Islands for the Assembly of Continental Biodiversity.

The perceived low levels of genetic diversity, poor interspecific competitive and defensive ability, and loss of dispersal capacities of insular lineages have driven the view that oceanic islands are evolutionary dead ends. Focusing on the Atlantic bryophyte flora distributed across the archipelagos of the Azores, Madeira, the Canary Islands, Western Europe, and northwestern Africa, we used an integrative approach with species distribution modeling and population genetic analyses based on approximate Bayesian computation to determine whether this view applies to organisms with inherent high dispersal capacities. Genetic diversity was found to be higher in island than in continental populations, contributing to mounting evidence that, contrary to theoretical expectations, island populations are not necessarily genetically depauperate. Patterns of genetic variation among island and continental populations consistently fitted those simulated under a scenario of de novo foundation of continental populations from insular ancestors better than those expected if islands would represent a sink or a refugium of continental biodiversity. We, suggest that the northeastern Atlantic archipelagos have played a key role as a stepping stone for transoceanic migrants. Our results challenge the traditional notion that oceanic islands are the end of the colonization road and illustrate the significant role of oceanic islands as reservoirs of novel biodiversity for the assembly of continental floras.

And if Engler was Not Completely Wrong? Evidence for Multiple Evolutionary Origins in the Moss Flora of Macaronesia

The Macaronesian endemic flora has traditionally been interpreted as a relict of a subtropical element that spanned across Europe in the Tertiary. This hypothesis is revisited in the moss subfamily Helicodontioideae based on molecular divergence estimates derived from two independent calibration techniques either employing fossil evidence or using an Monte Carlo Markov Chain (MCMC) to sample absolute rates of nucleotide substitution from a prior distribution encompassing a wide range of rates documented across land plants. Both analyses suggest that the monotypic Madeiran endemic genus Hedenasiastrum diverged of other Helicodontioideae about 40 million years, that is, well before Macaronesian archipelagos actually emerged, in agreement with the relict hypothesis. Hedenasiastrum is characterized by a plesiomorphic morphology, which is suggestive of a complete morphological stasis over 40 million years. Macaronesian endemic Rhynchostegiella species, whose polyphyletic origin involves multiple colonization events, evolved much more recently, and yet accumulated many more morphological novelties than H. percurrens. The Macaronesian moss flora thus appears as a complex mix of ancient relicts and more recently dispersed, fast-evolving taxa.

Floristic and structural recovery of a laurel forest community after clear-cutting: A 60 years chronosequence on La Palma (Canary Islands)

We analyzed a post-clearcut chronosequence (0.5 to 60 years after harvesting) in the laurel forest of La Palma island (Canarian Archipelago) to determine the recovery of the stands with respect to species composition, richness, life strategies and structural parameters of the canopy. Multivariate analysis showed that exotic species, as well as annual ruderal species were confined to early-successional stages, while native perennials, typical of laurel forests, dominated the late-successional stages. Total species richness decreased significantly with time after clear-cutting. The relative fast recovery of understory native species may be due to low forest floor disturbance during harvesting. Shade-intolerant pioneer, pioneer-remnant and shade-tolerant late-successional species were the main life strategies of native tree species. Most structural parameters showed a continuous and monotonic increase (basal area, biomass) or decrease (density, percentage of photosynthetic biomass) during succession. Once clear-cutting, here performed with an interval of 8 years, is abandoned, the recovery of the laurel forest seems possible due to careful logging that protects the soil and a rapid asexual regeneration of native tree species, revealing this to be a sustainable management practice.RésuméOn a analysé une chronoséquence après coupe rase (0,5 à 60 ans après récolte) dans la forêt de lauracées de l’île de Palma (Archipel des Canaries) pour déterminer la reconstitution des peuplements pour ce qui concerne la composition spécifique, la richesse et les paramètres structuraux de la canopée. Une analyse multivariable a montré que les espèces exotiques aussi bien que les espèces rudérales étaient confinées aux premiers stades de la succession, tandis que les espèces naturelles pérennes typiques de la forêt de lauracées dominaient les derniers stades de la succession. La richesse spécifique totale a diminué significativement avec le temps après la coupe rase. La reconstitution relativement rapide des espèces naturelles du sous-bois peut être due à la faible perturbation de la surface du sol forestier au moment de la coupe rase. Les pionnières intolérantes à l’ombre, les pionnières rémanentes et les tolérantes à l’ombre des stades finaux de la succession constituaient les principales stratégies des espèces naturelles d’arbres. La plus grande partie des paramètres structuraux ont montré un accroissement continu et monotone (surface terrière, biomasse) ou décroissant (densité, pourcentage de la biomasse photosynthétique) pendant la succession. Autrefois réalisée ici avec un intervalle de 8 ans la coupe rase est abandonnée, la reconstitution de la forêt de lauracées semble possible grâce à une exploitation prudente des bois protégeant le sol et une régénération asexuée des espèces naturelles d’arbres, révélant que ceci est une pratique de gestion durable.

Exploring the effect of host tree identity on epiphyte bryophyte communities in different Canarian subtropical cloud forests

This study explores the host tree preferences of epiphyte bryophyte communities in two key types of evergreen cloud forests on La Gomera (Canary Islands, Spain): ericaceous versus broadleaved laurel forest. By comparing two pairs of tree species (Erica arborea and Myrica faya vs. Ilex canariensis and Laurus novocanariensis) that occur in both forest types, we quantitatively examined whether epiphyte-host relationships change with the type of forest. In 51 ancient forest stands, the low-trunk bryophyte composition on the two host tree groups was analysed with both non-parametric procedures and ordination analyses. Our results highlight that the influence of local environmental conditions on the structuring of epiphyte communities may be different depending on the host tree identity. Whilst the epiphyte composition of the host tree group formed by I. canariensis and L. novocanariensis differed significantly between forest types depending on solar exposure, we failed to find variations for the other host tree group, excepting in those localities wherein mist precipitation was extremely high. Our findings highlight the importance of the natural diversity of tree species along environmental gradients, as well as of water availability at different spatial scales for epiphytic bryophytes in montane cloud forests.

The impact of forest disturbance on the genetic diversity and population structure of a late-successional moss

Abstract Human-induced disturbances threaten the genetic variation of wild plant populations. The genetic diversity and spatial population structure of the moss Isothecium myosuroides, a late-successional forest species, was investigated in subtropical cloud forests (La Gomera, Canary Islands) using inter-simple sequence repeat (ISSR) markers. Inter- and intrapopulation genetic variability was assessed in two ancient and four disturbed forest stands, which were classified according to their vegetation, forest age and type of disturbance. ISSR analysis of 144 epiphyte colonies with eight primers resulted in 211 reliably amplified bands. Our findings show that in disturbed forest stands, the population structure is increased, and the genetic diversity decreased compared with the levels observed in ancient forests. Although ancient and disturbed stands were located relatively close to each other, the (re-) established epiphyte populations did not reach their original genetic condition, 40 years following disturbance. Strong differentiation among populations of I. myosuroides at several spatial scales and differences in genetic diversity are mainly related to the local environmental conditions and the availability of suitable microhabitats in anthropogenically disturbed forest stands.

The taxonomic status and the geographical relationships of the Macaronesian endemic moss Fissidens luisieri (Fissidentaceae) based on DNA sequence data

Abstract The taxonomic identity and the geographical relationships of the Macaronesian endemic moss Fissidens luisieri have been studied using the chloroplast trnGUCC intron, the spacer between trnM and trnV, together with the trnV intron and ITS1 and ITS2 sequences. A comparison of F. luisieri with the most closely related species, F. serrulatus, from the same geographical areas reveals that the distribution pattern of F. serrulatus and F. luisieri, rather than their morphological differences, explains the observed differences. Therefore, we conclude that both names correspond to the same species. One of the primers for the chloroplast trnGUCC intron and both primers for the trnM–trnV region were designed for this study; they can all be widely used within bryophytes because they provide similar degrees of variability as other regions of the chloroplast genome such as the atpB–rbcL intergenic spacer.

Short-term effects of clear-cutting on the biomass and richness of epiphytic bryophytes in managed subtropical cloud forests.

Abstract• Managed laurel forests in the Canary Islands have undergone clear-cutting with rotation periods of less than 30 y. Forest owners have recently requested a drastic reduction in the cutting interval. The effects of this new harvesting cycle on organisms like epiphytic bryophytes are not well known.• This study investigates how time since last clear-cut, host species and characteristics of tree zones influence the biomass, cover and richness of epiphyte bryophytes in managed laurel forests in La Palma, Canary Islands. Four forest ages (8, 15, 25 and 60 y) and three host tree species (Erica arborea, Laurus novocanariensis and Myricafaya) were studied.• Biomass, cover and richness of bryophytes increased through the chronosequence, both at the level of each plot and overall for L. novocanariensis. Most of the biomass (53%) and richness (81%) was concentrated in one of the tree species (L. novocanariensis), in plots for which 60 y had elapsed since the last clear-cutting. Trunks supported greater bryophyte biomass and richness than canopies, even in the oldest plots.• Our results suggest that the current rotation periods used to manage laurel forests are insufficiently long to allow for complete reestablishment of epiphytic bryophyte assemblages.Résumé• Les forêts de lauriers gérées dans les îles Canaries ont subi la coupe à blanc avec des périodes de rotation de moins de 30 ans. Les propriétaires des forêts ont récemment demandé une réduction drastique de l’intervalle de coupe. Les effets de ce nouveau cycle de récolte sur des organismes épiphytes comme les bryophytes ne sont pas bien connus.• Cette étude examine la façon dont le temps depuis la dernière coupe, les espèces hôtes et les caractéristiques des espèces d’arbres influencent la biomasse, la couverture et la richesse des bryophytes épiphytes dans les forêts gérées de lauriers à La Palma, îles Canaries. Quatre forêts âgées de 8, 15, 25 et 60 ans et trois espèces d’arbres hôtes (Erica arborea, Laurus novocanariensis et Myrica faya) ont été étudiées.• La biomasse, la couverture et la richesse des bryophytes ont augmenté à travers la chronoséquence, au niveau de chaque parcelle et de l’ensemble de L. novocanariensis. La plus grande partie de la biomasse (53 %) et de la richesse (81 %) est concentrée sur l’une des espèces d’arbres (L. novocanariensis), dans les parcelles pour lesquelles 60 ans se sont écoulés depuis la dernière coupe à blanc. Les troncs supportent une plus grande biomasse de bryophytes et une plus grande richesse que les canopées, même dans les parcelles les plus anciennes.• Nos résultats suggèrent que les périodes courantes de rotation utilisées pour gérer les forêts de lauriers ne sont pas suffisamment longues pour permettre le rétablissement complet des assemblages des bryophytes épiphytes.

Climate threat on the Macaronesian endemic bryophyte flora

Oceanic islands are of fundamental importance for the conservation of biodiversity because they exhibit high endemism rates coupled with fast extinction rates. Nowhere in Europe is this pattern more conspicuous than in the Macaronesian biogeographic region. A large network of protected areas within the region has been developed, but the question of whether these areas will still be climatically suitable for the globally threatened endemic element in the coming decades remains open. Here, we make predictions on the fate of the Macaronesian endemic bryophyte flora in the context of ongoing climate change. The potential distribution of 35 Macaronesian endemic bryophyte species was assessed under present and future climate conditions using an ensemble modelling approach. Projections of the models under different climate change scenarios predicted an average decrease of suitable areas of 62–87% per species and a significant elevational increase by 2070, so that even the commonest species were predicted to fit either the Vulnerable or Endangered IUCN categories. Complete extinctions were foreseen for six of the studied Macaronesian endemic species. Given the uncertainty regarding the capacity of endemic species to track areas of suitable climate within and outside the islands, active management associated to an effective monitoring program is suggested.

Effect of forest clear-cutting on subtropical bryophyte communities in waterfalls, on dripping walls, and along streams

Forested freshwater ecosystems worldwide are threatened by a number of anthropogenic disturbances, such as water pollution and canalization. Transient or permanent deforestation can also be a serious threat to organisms in forested watersheds, but its effects on different types of freshwater systems has been little studied. We investigated lotic bryophyte communities on rock and soil in subtropical cloud laurel forests on La Gomera Island in the Canary Islands, Spain, and asked whether the response to forest clear-cutting varied among the communities associated with dripping walls, streams, and waterfalls. We compared three successional forest stages: ancient forests (> 250 years), young forests (20-50 years after clear-cutting), and open stands (5-15 years after clear-cutting). In each of 56 study sites we sampled general vegetation and substrate data in a 0.01-ha plot and took composition data of bryophyte species in 3 + 3 subplots of 1 x 1 m. The general pattern of decline in species richness and change in species composition after forest clear-cutting was stronger for streamside assemblages compared to assemblages on dripping walls and in waterfalls. The change in species numbers on rocks was larger than that on soils, because a guild of species growing on soil (but not on rocks) were favored by disturbance and thus increased in the disturbed sites. Most of the sensitive species could be classified as typical laurel forest species. Mosses were generally more tolerant to forest clear-cutting than were liverworts. We suggest that streamsides are more sensitive to disturbance than waterfalls and dripping walls because of a larger variation in microclimate before than after clear-cutting and because they are more easily invaded by early-successional species (both bryophytes and highly competitive vascular plants). We propose that special care should be taken along small streams within disturbed watersheds if bryophyte assemblages and threatened species should be protected. The susceptibility to anthropogenic pressures is probably rather high in ecosystems that do not regularly experience large-scale stand-replacing disturbances, especially on oceanic islands because of isolation and a small total habitat area for focal organisms.