Key points

1. 1. Extant ferns and lycophytes are ecologically important and contribute 4% of the vascular plant diversity on Earth but currently face an unprecedented threat caused mainly by human disturbances such as fire or land use change. Few fern species benefit from these disturbances, and most become less abundant or locally extinct.

2. 2. Current risk assessments for ferns are mainly based on abundance and geographic range. Risk assessments improve when additional ecological characteristics (e.g., habitat specificity, intrinsic biological factors, population dynamics and environmental disturbances) are considered.

3. 3. By 2008 a global risk assessment had been completed for only 2% of the 11 000 species of ferns and lycophytes; 89% of these ferns were considered to be at risk. Global risk assessment of ferns is geographically biased toward Ecuador and China and taxonomically biased toward nine of c. 300 extant genera.

4. 4. A mixed approach of habitat protection for hot spots of fern diversity and in situ protection of endangered fern species outside such hot spots is recommended as a management strategy for fern conservation. Ex situ cultivation of endangered fern species may supplement in situ protection efforts but should not replace them.

Introduction

Extant plants and animals likely represent only 1–2% of all organisms that have ever existed on our planet during the last 450 million years (May et al., 1995) because extinction is common.

Key points

1. 1. Ferns and lycophytes have developed a wide spectrum of antagonistic and mutualistic relationships with fungi and animals. While some of these interactions, such as endomycorrhizae, are old and may have coexisted with their host plants for a long time, other interactions may have originated more recently, such as some herbivorous insects that have switched from seed plants to ferns.

2. 2. More than 80% of sporophytes possess endomycorrhizae, while for a few species fern–ericoid mycorrhizae and ectendomycorrhizae have been reported. In the gametophytic stage, mycorrhizae are obligate in older fern and lycophyte lineages but are facultative or can be absent in more modern lineages.

3. 3. Interactions with parasitic, symbiotic and neutral endophytic fungi that infect aerial parts of the ferns seem to be as common as in seed plants, while the proportion of interactions with insects seems to be 3–7 times lower than in seed plants.

4. 4. Fern herbivores are most often members of the insect orders Coleoptera, Hemiptera and Lepidoptera and can be either generalists or insect species that have specialized on ferns. Two fern genera have strong mutualistic relationships with ants: Microgramma subgenus Solanopteris in the New World and Lecanopteris in the Old World tropics; a third, more facultative relationship has recently been described for Antrophyum in Costa Rica.

5. 5. Most ferns have few specific biochemical defense mechanisms in comparison with seed plants, yet ferns and seed plants sustain similar levels of herbivore damage.

Key points

1. 1. Ferns often colonize habitats disturbed by tectonic activity, wind, water, fire and humans.

2. 2. Fern dispersal into disturbed habitats can result from long distance movement of spores but is usually by short distance spore dispersal or vegetative expansion of nearby plants.

3. 3. Rapid establishment and dense growth can make ferns competitive with other vascular plants through light reduction and nutrient uptake or immobilization. Fern thickets can delay successional transitions but ferns also provide regeneration sites for other species and stabilize slopes. Fern influences may vary across environmental resource (e.g., light, water, nutrients) and topographic gradients.

4. 4. Ferns can have important roles in the restoration of disturbed ecosystems.

Introduction

A typical image of fern habitat is a wet, shady forest untouched by disturbance. In fact, many ferns colonize recently disturbed and exposed areas such as scoured riverbanks (Reudink et al.,2005) or the uprooted pits, mounds and trunks of fallen trees (Peterson et al., 1990; Nadkarni and Wheelwright, 2000). Ferns tolerate a wide range of environmental conditions (Hemp, 2001), and some species can colonize such highly disturbed habitats as lava flows, dunes, landslides or floodplains as well as areas of forests that have been damaged by burning, ice storms, hurricanes or logging (Walker et al., 1996b; Barson, 1997; Russell et al., 1998; Arens and Sánchez Baracaldo, 1998, 2000; Woods, 2002). One reason some ferns readily colonize recent disturbances is that they have widely dispersed spores that reach even the most remote islands (see Chapter 2; Carlquist, 1980).

Introduction

Ferns immediately capture the imagination of all who are fortunate enough to notice them. With their large, highly dissected and shiny green leaves, ferns are so visually appealing that many are sold as ornamentals. Most moist woodlands will have a number of fern species blanketing the understory with their pungent foliage. In tropical woodlands, ferns are often at eye level or above, providing an aesthetic and delicate subcanopy. Even in arid lands or on newly exposed surfaces such as burns, clear-cuts or landslides, ferns can be present and sometimes dominant, catching your full attention as you push through fern thickets or get snagged by their spines. Beyond their immediate visual appeal, ferns are curious objects. How do plants of such ancient origin persist in the modern world? How can something so fragile survive trampling, burning, logging or grazing? Ferns and lycophytes were long considered as mystical plants, because people did not understand how they could reproduce without ever producing a flower, a fruit or a seed (Moran, 2004). In this book, we address the mystique that surrounds ferns by exploring fern ecology, or how ferns relate to their environment. Throughout the world, whenever ferns are the focus of ecological research, important and often surprising findings emerge.

We present four approaches to fern ecology. First, we provide a conceptual synthesis of the rapidly expanding field of fern ecology in order to establish a framework for future research and to encourage interdisciplinary approaches to studies of ferns.

There are many ways to appreciate ferns and lycophytes. We admire their shapes, from tiny, filmy ferns on tree trunks, to lacy maidenhair ferns in rock crevices, to sturdy tree ferns with their huge, dissected leaves. We wonder at the beauty of their leaves that vary from subtle shades of green to gray, pale yellow, reddish or even iridescent blue. As we become more acquainted with ferns, the fascination deepens and the questions begin. Some of the first questions are about fern habitats. How do they survive in the deep shade of forest understories? On flooded banks of streams? On wind-swept mountain tops? On hot, vertical rock faces? Why are they so abundant on tropical mountains and oceanic islands? Questions then arise about fern growth. How do they survive drought or freezing temperatures? How do they reproduce? How old are they? What is a spore and that always elusive little “gametophyte”? We also ponder how the presence of ferns impacts other organisms. Do ferns compete with seed plants? Do they get eaten by herbivores? Finally, how do humans interact with ferns? Which species are edible or have medicinal qualities? Why are some ferns a nuisance to us? What makes them weedy ferns? We, the editors of this book, have each pondered these questions, both as people who are fascinated by the beauty and variety of ferns and as scientists whose job it is to question how the natural world is assembled, collate information about it and synthesize what is known.

Index to genera of ferns and lycophytes and their family placement. Families listed below are those accepted by Smith et al. (2006, 2008). Numbers in parentheses correspond to family numbers assigned by Smith et al. (2006), and are indicated for each accepted genus. All accepted genera (but not all synonyms) in Pichi Sermolli (1977), Ching (1978), and Kramer (1990) are accounted for. Newly described or recircumscribed genera since 1990 are also included. Accepted names are in roman, synonyms are in italics; for both accepted names and synonyms, the number of species (sometimes approximate) is given, except for synonyms whose circumscription varies sufficiently (or is unclear) such that this number would be relatively meaningless. An asterisk (*) indicates genera likely or soon to undergo redefinition or inclusion in another accepted genus, based on existing morphological and molecular data. Superscript 1 (1) indicates genera in which species circumscription requires more study before limits are clear. Sources for numbers of species include Copeland (1947), Kramer (1990), and several recent publications, e.g., Ebihara et al. (2006), as well as some unpublished information by Smith. IPNI (The International Plant Names Index: http://www.ipni.org/) has also been consulted for many genera, in order to incorporate recently described species in the totals.

For more complete references documenting the family level classification, see Smith et al. (2006, 2008). A few accepted names given herein are not validly published, as, for example, some in Thelypteridaceae (see Smith, in Kramer, 1990) and are indicated by superscript 2 (2).

Key points

1. 1. Ferns are most prominent in shady and humid environments, but many species are also found in drought-prone habitats, either (semi) arid ecosystems or locations with discontinuous water supply within otherwise humid ecosystems. These locations include tree branches and rocks, both substrates with little water storage capacity.

2. 2. Drought tolerance is gained through adaptations in water uptake, water loss, water storage and, in many ferns, desiccation tolerance, a feature that ferns share with other cryptogams. The little information available on the cuticle's efficiency to limit water loss suggests that it may be similar to other vascular plants. Thus many xerophytic ferns, while tolerating desiccation, normally avoid it through low cuticular and stomatal water loss and may not be considered truly poikilohydric. Exceptions are filmy ferns with very little control of water loss and whose water relations are akin to mosses rather than vascular plants.

3. 3. Other adaptations found in xerophytic ferns include photoprotection with pigments, antioxidants, dense indument, leaf curling and drought avoidance by shedding leaves in the dry season. Crassulacean acid metabolism (CAM) is a common adaptation of xerophytic angiosperms, but is very rare in ferns. Succulence is not strongly developed in xerophytic ferns.

4. 4. Drought adaptations of ferns are analyzed in light of their phylogenetic positions and compared with those of angiosperms. This chapter discusses the potentially underlying causes of drought tolerance in ferns and points to gaps in our understanding as well as possible future research.

Key points

1. 1. Despite the popular image of ferns as decorative, innocuous plants, certain fern species can become substantial problems where human activities disturb the natural equilibrium. Making the distinction between native and alien species helps us to understand how some ferns become problematic in the first place and how such problems can be managed.

2. 2. About 60 species of ferns create problems for ecology and conservation in terrestrial and aquatic environments. Some of these ferns have significant negative impacts on human and animal health, food production and management of both land and water.

3. 3. Where legislative or other preemptive controls fail, problem ferns need to be managed by timely and effective combinations of physical, chemical and biological methods. Researchers continue to improve methods of managing problem fern species in order to enhance efficacy and to minimize damage to nontarget vegetation and the local environment.

4. 4. The full human, economic and environmental costs of problem ferns have not been investigated on a global basis. Continued international development of effective legislation and chemical and biological management of problem ferns will be required in order to contain their further spread which, in some cases, may be extensive and catastrophic.

Introduction

At least 60 fern species (see Table 8.1) have the proven or potential ability to occupy areas where they may create a variety of problems. The terrestrial ferns in this group can disrupt local ecosystems, conservation efforts, wildlife management and the productivity of land (including grazing lands, certain crops and forestry).