The Socotra archipelago is an ancient continental fragment situated in the Western Indian Ocean that has been isolated for at least 18 million years (Ma). Although often described as the ‘Galapagos of the Indian Ocean’, compared to the Galapagos and other island systems, this Arabian Sea archipelago is relatively poorly studied and often overlooked in works on island biology. Nevertheless, the Socotra archipelago is characterised by relatively high floristic diversity and endemism with local adaptations and radiations, making it a good example of a system suitable for the study of island biogeography. We discuss origins, affinities, disjunctions and adaptations in the flora and explore underlying environmental and evolutionary processes that may have helped the Socotra archipelago to its present uniqueness.

The study of plant speciation on oceanic islands has improved enormously with the help of molecular systematics. Studies have targeted groups present on both the mainland and islands with the aim of understanding plant migration and evolution in isolation. In addition, relatively young volcanic islands give the opportunity to place the evolutionary process in a time frame, by dating molecular trees according to the age of the islands or by relying on the fossil record. Molecular phylogenetics can also be valuable in helping to reconstruct character evolution and understand the syndrome of characters diagnosing oceanic species.

Geography

Straddling the Tropic of Capricorn, New Caledonia is situated in the South Pacific Ocean between latitudes 18° 00′ and 23° 50′ S, and longitudes 154° 45′ and 176° 20′ E. It is an archipelago made up of the islands of Grande Terre, Iles Belep, d’Entrecasteaux Récifs, Île des Pins, the Loyalty Islands and several other small islands such as the Chesterfield Islands and Walpole Island (Fig. 9.1). New Caledonia is an isolated archipelago situated some 1500 km east of Australia with the nearest land further to the east at the New Hebrides Islands and Fiji. New Caledonia is one of the extant land masses of an ancient continent known as Zealandia and now almost completely submerged. The island was formerly part of Australasia but separated from it about 60–80 million years ago (Ma) and drifted to its present position by about 50 Ma. It is, therefore, one of the most important and isolated surviving fragments of Gondwanaland. In the process, much or all of the area of New Caledonia appears to have been submerged for up to 20 Ma. During this period, oceanic mantle was deposited over the original schistic rock, eventually forming a thick layer of ultrabasic substrates including peridotite, ferricrete, serpentinite and laterite. These were once widespread over the islands and still cover about 30% of the land surface.

Island plants and their habitats will be affected in the future not just by climate change but by a whole series of factors that make up the ongoing process of global change. While much of the focus in recent years has been on the impacts of climate change, these do not operate, now, nor will they in the future, in isolation but closely interact with human population changes and alterations in disturbance regimes. This inevitably leads to an impoverishment of biodiversity and loss or fragmentation of habitats.

Introduction

The arid shrublands and open woodlands of the North American deserts generally support a sparse vascular plant cover. In these and similar environments, the surfaces unoccupied by taller vascular plant species are often colonized by a unique assemblage of organisms collectively referred to as “biological soil crusts” (Belnap & Lange 2003). This assemblage is extremely diverse phylogenetically, including various species of cyanobacteria, algae, fungi, and lichens as well as bryophytes. These disparate species have been thrown together under one umbrella label due to the specialized niche that they inhabit. Their small size and close association with the soil surface make the term “biological soil crust” particularly appropriate.

Biological soil crusts have received a fair amount of attention and study but bryophytes represent one of the less well understood aspects of this community. In arid landscapes like the Mojave Desert, the bryophyte component in soil crusts is generally made up of mosses in the family Pottiaceae (e.g., species in the genera Syntrichia, Pterygoneurum, Crossidium, Didymodon, and Tortula). In his monographic treatment of the family, Zander (1993) states that the Pottiaceae form a conspicuous part of the vegetation of arid, ruderal, alpine, and Arctic areas. These are also conditions under which biological soil crusts can play a prominent role. As characteristic inhabitants of these extreme environments, bryophytes of biological soil crusts exhibit many morphological and physiological adaptations to stress that remain poorly understood (Zander 1993).

Introduction

If you go hunting for bryophytes in the tropics, you soon learn that streambeds are depauperate and searching is futile. Witness the absence of such aquatic taxa as Fontinalis, Hygroamblystegium, and Rhynchostegium riparioides, so common in temperate mountainous areas. Ruttner (1955) reports that Fontinalis is especially common at 10–15 m depth in alpine lakes, but that in the tropics it is nowhere. And consider the paucity of bryophytes in exposed, warm valley and flatland temperate streams. Ward (1986) described the altitudinal zonation in a Rocky Mountain, USA, stream and noted that bryophytes had the greatest biomass in headwaters, whereas tracheophytes were absent from higher elevations. Suren (1996), in studying 118 streams on South Island, New Zealand, reported that sites with no bryophytes had a lower mean elevation than did sites with bryophytes. Hence rising temperatures are likely to force aquatic bryophytes into higher elevations or more northern locations.

Furthermore, factors that correlate with warmer temperatures may alter bryophyte distributions. Cappelletti and Bowden (2006) suggest that global warming will increase the soluble reactive phosphorus, water temperature, and discharge of Arctic rivers, hence changing other factors that might favor tracheophytes over bryophytes or change the species composition of the aquatic bryophyte communities. Elevated temperatures can be expected to change nutrients, CO2 concentrations, flow rates, flooding depth and frequency, competing primary producers, light penetration, and seasonal coordination.

Introduction

The Antarctic continent occupies about 14.4 million square kilometers, about 99% of which is covered by ice with an average thickness of around 1.8 km. It is the coldest, driest, windiest continent and has the highest mean elevation of all continents. Precipitation, as low as 20 mm on the inland ice plateau and significantly higher in coastal regions (as much as 250 mm annual rainfall equivalent), falls mostly as snow but occasionally as rain, particularly in the climatically milder maritime part of the northern Antarctic Peninsula.

The terrestrial and limnetic plant biota of Antarctica is impoverished and limited to lichens, bryophytes, mostly microscopic algae, cyanobacteria, mostly microscopic fungi, and two small vascular plants found only in the Maritime Antarctic. Invertebrates dominate the terrestrial and limnetic fauna, although large numbers of seabirds breed onshore over the summer months. Despite the severe climate and limited habitat availability, terrestrial plant life flourishes in ice-free areas where moisture is available. The continent of Antarctica with its nearby offshore islands is unique in being the only major land mass with a flora composed almost entirely of cryptogams (Longton 1979; Kappen 1993a; Broady 1996; Green et al. 1999; Vincent 2000; Øvstedal & Lewis Smith 2001; Ochyra et al. 2008).

The strong negative trend of the global thermal budget from the equator towards the poles is regionally altered by the presence of land masses and by general oceanic circulation.

Introduction

As the average shift of isotherms in Central Europe has been some 200 km northeastwards during the past 60 years, we might expect changes in the flora of Hungary, especially among the cryptogams, owing to their superior dispersal ability by spores and gemmae. During the past 50 years of global warming in Central Europe the average temperature rose by 0.8 °C, which alone does not mean as much as the increasing extremes both in temperature and in the annual distribution of precipitation. In Hungary 1990 was probably the hottest year of the millennium, followed by 1997, 1995, 1999, and 2000. At the same time the winters have become milder with shorter very cold periods, and we have had prolonged summer droughts. According to the records of the Hungarian Meteorological Service (Szegő 2005; Takács-Sánta 2005) the number of hot days above 25 and 30 °C increased considerably in Hungary. The amount of precipitation, especially during winter, decreased.

It is highly likely that global warming is anthropogenic, due to the greenhouse effect of increasing CO2 and methane in the atmosphere (Vida 2001). Excessive CO2 emission began with deforestation in the Bronze Age and contributed to the end of the last glacial period. However, its sudden increase by the industrial revolution and especially during the last century (from 270 ppm to 380 ppm CO2 in the atmosphere) resulted in the 160 km NW shift of the annual isotherms in the Pannonian basin in Hungary.

Introduction

Bryophytes and flowering plants are very different in their strategies of adaptation to life on land. These differences are reflected in their responses to climate and their ecological and geographical distribution patterns. The difference is immediately obvious in any region for which both the vascular plant and the bryophyte flora are well known and well mapped. Britain and Ireland are good examples (Hill et al. 1991, 1992, 1994; Preston & Hill 1997; Hill & Preston 1998; Preston et al. 2002). Only around 10% of the vascular plants of Europe occur in the British Isles, and within Britain and Ireland the number of vascular plant species tends to decline from southeast to northwest. With bryophytes the trend is almost reversed. Britain and Ireland have one of the richest bryophyte floras of any comparably sized region of Europe (and a rich bryoflora even by world standards), and bryophyte diversity is heavily concentrated in upland regions and towards the west coast.

Strategies of adaptation to life on land

A planktonic green cell floating near the surface of a lake or the sea has all the necessities of life around it. It is surrounded on all sides by water, from which it can take up nutrients and exchange gases. Light is not a problem either, provided the cell does not sink too far below the surface of the water.

Introduction

Boreal peatlands of Western Canada

Boreal peatland ecosystems occupy less than 3% of the earth's land surface, yet store between 250 and 455 Pg of C, which is roughly 20%–30% of the world's soil carbon (Gorham 1991; Charman 2002; Joosten & Clarke 2002; Vasander & Kettunen 2006). In continental western Canada, peatlands cover 365,157 km2 (Vitt et al. 2000) and dominate the landscape in northern Alberta, Saskatchewan, and Manitoba (Tarnocai 1984, 1998; Vitt et al. 2000; Tarnocai et al. 2005). Overall, these western Canadian peatlands have sequestered about 48 Pg of C during the past 10,000 years, with about half of this peat accumulated in the past 4000 years (Vitt et al. 2000). Peatlands provide a wide diversity of ecosystem services, not the least of which is the conversion of atmospheric CO2 into large accumulations of stored organic carbon (C) – a testament to the long-term function of these ecosystems as net C sinks since their widespread initiation after the most recent glacial retreat (Halsey et al. 2000). Bryophytes typically are dominant components of the vegetation in northern peatlands and play central roles with regard to nutrient cycling and carbon accumulation.

The initiation, development, succession, and rate of peat accumulation in boreal peatlands are dependent on regional factors such as climate, substrate chemistry, landscape position, and hydrological regime.

Introduction

Bryophytes can dominate plant–atmosphere exchange surfaces in mesic to hydric Arctic, boreal, and temperate ecosystems and can contribute up to 50% of gross primary production (Goulden & Crill 1997; Bisbee et al. 2001; O'Connell et al. 2003a), although estimates in more dense forests are lower (Skre & Oechel 1979; Kolari et al. 2006). Soils in these systems store approximately one third of the world's reactive pool of soil carbon (McGuire et al. 1995) with a major contribution coming from bryophytes (Gorham 1991; O'Neill 2000; Turetsky 2003). Within these systems, the bryophyte layer also influences hydrology, nutrient uptake and cycling, and soil temperature.

In the boreal zone, significant research has been undertaken to determine how forest bryophytes affect carbon exchange and sequestration. These studies have focused on the influence of environmental forcing variables (e.g., temperature, light, and water availability) on the productivity and carbon dynamics of feathermoss (Pleurozium) and Sphagnum moss species, the two most dominant groups ecologically. This work has led to a better understanding of temporal variation in bryophyte function and has provided insights into how the performance of individual species varies across gradients of temperature, light intensity, and water availability (Skre & Oechel 1979; Trumbore & Harden 1997; Bisbee et al. 2001; O'Connell et al. 2003a, b; Heijmans et al. 2004; Kolari et al. 2006; Kulmala et al. 2008).

However, these studies have neglected the causes and consequences of intraspecific variation, which can be similar in magnitude to differences among species.