**Abstract**

Oceanic islands are known for their high levels of plant diversity, due to disjunct geographical distribution that leads to speciation. The main factors contributing to genetic speciation includes the creation of a barrier within a previously widely distributed taxon and the limited dispersal of seeds, which favours genetic differentiation and, thus, fosters rapid speciation. Plant survival and population fitness vary according to environmental factors and to human interference. This chapter depicts the importance of oceanic islands as biodiversity hotspots, discusses the threats to which endemic plants on islands are exposed, namely climate change, invasive alien species, urbanisation, touristic activities, fire, changes in agriculture practices and collecting pressure. The best practices worldwide to protect endemic plant species in protected areas are also addressed, namely the implementation of prevention and mitigation actions, the programs executed to protect endemic species, and management plans to avoid future threats.

**Keywords:** small islands, vegetation, invasive alien species, climate change, endemism, conservation

### **1. Introduction**

Oceanic islands are those that never had a connection to continental land masses, being generally composed of volcanic rock, reef limestone or both. Those of volcanic origin are formed over oceanic plates, being a product of volcanism or tectonic uplift. These islands tend to be steep and relatively high for their area and, over time, become highly sheared due to erosion processes. Usually, they lack native mammals and amphibians, but a fair number of birds and insects, as some reptiles are usually present [1]. Not classified as "real" islands, atolls and reef are marine habitats islands, built up by small coelenterate animals (corals) that secrete a calcareous exoskeleton. These form an annular reef rim surrounding a central lagoon, with the rim being more or less occupied by calcareous sand or coral shingle and rubble [2], such as the reef islands of the Maldives, the Solomon Islands, the Bahamas, the Tarawa atoll in Kiribati, and many other islands and atolls in the Pacific Ocean. Coral islands tend to be very low-lying and flat; some only raised a few meters above sea level [1]. As defined by Paulay [3] all these are considered oceanic islands (**Figure 1a** and **b**).

Oceanic island are mainly small islands, which are defined as those which present less than 10,000 km2 [4]. The largest oceanic island on Earth is Iceland, with more than 100 thousand square kilometres, but all the other oceanic island

**Figure 1.**

*Examples of oceanic islands: left: S. Miguel, one of the nine islands of the Azores volcanic archipelago; right: an atoll at the Maldives, one of the 1192 coral islands that are grouped in 26 atolls.*

are much smaller, being New Britain (Papua New Guinea), Grande Terre (New Caledonia), Negros (Philippines), and Hawaii (USA), the other large oceanic islands.

Besides these, there are millions of small islands and islets. **Table 1** states these small oceanic islands and oceanic archipelagos throughout the globe, being referred the main island of the archipelago (if any), the size, and the location. To avoid being over-exhaustive in this analysis, only the main oceanic island of each archipelago is presented, in addition to the isolated islands.

In contrast to oceanic islands, continental islands were joined to continental land in the past, namely during the Quaternary ice ages, and becoming separated owing to sea level rise or to tectonic events, and still sit on the continental shelf. As such such, terrestrial mammals and amphibians are usually present [1, 3]. Most of the larger islands are of continental origin, such as Greenland, New Guinea, Borneo, Madagascar, Baffin Island, Sumatra, Honshu, Victoria Island, or Great Britain.

Oceanic islands are usually smaller, younger, more isolated from the continent, more isolated from the nearest neighbour island and present less plant species than continental islands [5]. Their climate has, evidently, a strong oceanic influence, with the low islands being much drier and the high islands presenting heavy orographic rainfall. Most oceanic islands have freshwater reservoirs, both volcanic and atolls, which depend on rainfall percolating through the island. Small islets, however, may lack such lens, being therefore adverse for plant growth [1].

When a new island emerges, an ecological succession begins with the species that were able to reach the land colonising the island but subjected to island isolation. High dispersal capabilities are more likely to overcome distance, which determines that plants, birds, and insects, for example, are much more common on islands than other taxa with lower dispersal capacity. Of the newly arrived species, only a few will be able to survive and establish new populations. As a result, islands have fewer species than mainland habitats. Island populations are small, exhibit low genetic variability and are isolated from the predators and competitors with which they initially evolved [6]. These small islands are also known to present high levels of endemism, mainly due to disjunct geographical distribution and limited dispersal of seeds. These favour genetic differentiation, which, in turn fosters endemism [7–9]. These endemisms have small population distribution, and present low competitive ability [6].

The isolation and small size of the oceanic islands makes them very vulnerable, highly susceptible to threats such as climate change, natural catastrophes, coastal erosion, seawater intrusion, and overexploitation of natural resources [10]. They are also very vulnerable to invasive alien species, that compete with the native taxa,


#### *Conserving Endemic Plant Species in Oceanic Island's Protected Areas DOI: http://dx.doi.org/10.5772/intechopen.100571*



**Table 1.**

*Main oceanic islands, including the archipelago, the country, the ocean, the island and the archipelago total area, and the coordinates of the main city.*

causing severe ecological and economic problems. Besides, deforestation is frequently a major problem, both for agriculture and for timber, and tourism is causing additional infrastructural and pollution pressure [6]. Biodiversity conservation and sustainability are accordingly major concerns in relation to the oceanic island, to preclude the degradation and destruction of the natural heritage.

The effort of creating protected areas is the first key step to the conservation of threatened natural and cultural heritages. This step should be followed by a successful management of the protected area, which considers both the conservation of ecosystems and the socio-economic development of island inhabitants and considers the specificities of island territories.

This chapter discusses the importance of the oceanic islands, of its endemic plants, the threats they are currently facing, and the conservation measures being implemented to protect these important ecosystems.
