15 research outputs found
Overview of habitat history in subtropical oceanic island summit ecosystems
Summit ecosystems of oceanic islands constitute one of the most ephemeral and isolated
ecosystems existing, harboring specific features that confer on their biota an outstanding
distinctness. Summits are short-lived entities, being the last ecosystems to be constructed
during the growth of the new oceanic island, and the first to vanish due either to island
subsidence, island erosion, or both. Whereas their geological emergence/disappearance
is controlled by the volcanic/erosion activity, Pleistocene glaciations in the past million
years, by forcing the altitudinal shift of the timberline, have also likely created or destroyed
summit ecosystems, enabling the appearance of alpine ecosystems during glacial
maxima where they were not present in interglacial periods and vice versa.
On the other hand, summit ecosystems constitute islands within islands, being more
isolated from climatically similar ecosystems than the coastlines of the islands containing
them. Thus summit biota, frequently displaying a high endemicity, may originate either
through dispersal from other close summit ecosystems during peak periods, or from the
colonization of the summits and later evolution to the new conditions from mid-altitude
species of the same island. Conversely, if peak periods are absent, the disappearance of
summit ecosystems implies the extinction or extirpation of their constitutive species. Current
summit species have likely occupied a much larger area during glacial periods. Thus
the summits may be classified as climatic refuges. This is especially the case if glacial
periods were associated with much drier conditions on oceanic islands as is the case on
continents
Newly discovered seed dispersal system of Juniperus cedrus questions the pristine nature of the high elevation scrub of El Teide (Tenerife, Canary Islands)
As a working hypothesis, we examined evidence for the former presence of a climacic
woodland of Juniperus cedrus above the pine forest in the high elevation area of Tenerife
(Canary Islands), which would indicate that the current dominant vegetation (endemic
Spartocytisus supranubius scrub) may not be pristine. The main causes of the great regression
of this woodland were caused by human activities (timber harvesting, herbivory
by goats, and fires). The main support for this hypothesis is the survival of a presumably
relict seed dispersal system of the endangered endemic J. cedrus, which relies mainly on
the wintering thrush Turdus torquatus. The fact that genetic factors are directly involved in
the control of bird migration routes strongly supports the idea that this interaction could be
remnant of an older system, probably more widespread in the past. To test this hypothesis,
we propose that a paleoecological approach could reconstruct the vegetation dynamics in
the Teide National Park (Tenerife) and the past presence of this seed disperser migratory
thrush. The analysis of plant microfossils in sediments (e.g., pollen, spores, phytoliths,
coprolites, and charcoal) would allow us to evaluate whether the current vegetation is
the same as that which naturally existed in the past, and assess the impact of the anthropogenic
and natural factors to which it has been subjected during history. The results
of these analyses will be useful for future management policies and practices aimed at
restoring the pristine landscape and biotic interactions of the Teide National Park. To our
knowledge, the case presented in this contribution, based on the high dependence of the
seed dispersal of an endemic tree (J. cedrus) on a migratory bird, is the only reported in
the context of oceanic islands.Ministerio de Ciencia e InnovaciĂłnGobierno de las Islas CanariasOrganismo AutĂłnomo de Parques Nacionale
Future of Water Supply and Demand in the Middle Drâa Valley, Morocco, under Climate and Land Use Change
Regions of scarce fresh water resources, such as the Middle East and North Africa, are facing great challenges already today, and even more in the future, due to climatic and socioeconomic changes. The Middle Drâa valley in Morocco is one of many semi-arid to arid mountainous areas struggling with increasing water scarcity threatening self-sufficient husbandry. In order to maintain people’s livelihoods water management needs to be adapted. The Water Evaluation And Planning System (WEAP) software has been widely used to examine complex water systems in the water resource planning sector all around the world and proved to be a helpful asset to show the various interactions of water supply and demand. This paper presents the application of WEAP on the Middle Draâ valley’s water demand and supply, including several socioeconomic and land use scenarios under one basic climate change scenario. The climate scenario shows a significant decrease in available water resources up to 2029 while all socioeconomic scenarios show an increase in water demand. In years of droughts groundwater is used for irrigation, leading to increasingly depleted aquifers. The aquifers are recharged by percolation losses from irrigation and by river bed infiltration the latter of which is stronger in the northern oases than in the southern oases due to water withdrawal rules. A drastic reduction of irrigated agricultural area is the only solution to guarantee sustainable water use
The effect of fire severity on first-year seedling establishment in a Pinus canariensis forest on Tenerife, Canary Islands
The Canarian pine (Pinus canariensis) exhibits
a striking combination of high adult resistance to fire and
intermediate serotiny. Hence, the study of its post-fire
regeneration can support valuable new insights about
functional adaptations to fire. Here, we analyse the firstyear
seedling establishment after fire in a P. canariensis
forest on the northern slope of Tenerife, Canary Islands.
The effects of fire severity and other explanatory variables
on the seedling density recorded 9 months after fire were
examined. We detected a clear unimodal relationship
between seedling density and fire severity, with maximum
regeneration associated with intermediate fire severity and
no regeneration associated with very high crown damage.
The results suggested that high severity fires may have
caused the partial destruction of the aerial seed bank and/or
the creation of unfavourable seedbed conditions for germination
and seedling emergence. The density of large
pine trees, reflecting seed availability, was the second most
important factor explaining the distribution of seedlings.
Cover of scorched needle litter on the ground correlated
strongly and positively with pine seedling density and
negatively with fire severity. The complete lack of regeneration
at sites most strongly affected by fire does not
represent a major threat for the stand recovery of the
Canarian pine, due to the very high tree resistance to fire
and the tremendous capacity of the Canarian pine to
resprout after fire. The observed very high seedling densities
at sites with intermediate fire impacts can probably be
related to both the complete liberation of the seed bank
(including seeds stored in serotinous cones) and favourable
micro-environmental conditions for seed germination and
seedling establishment