1.3.3 Conserving distinct and unique tree lineages
It is logical that national conservation efforts will focus on maintaining the genetic diversity and evolutionary potential of high priority tree species at national level, and that international efforts will focus on those priority species whose distributions overlap the national boundaries and have wider socioeconomic importance or have much more economic importance as planted exotics than in their country of origin. There is also a case to made, from both an international and scientific viewpoint, for conserving those tree species (families and genera) which are genetically most distinctive, e.g. monotypic families and genera, and representing the most evolutionarily divergent lineages. These genetically distinctive lineages and assemblages, may later be found to hold genes or combinations of genes which turn out to be incredibly useful to future generations, and are briefly discussed below and need to be considered in the context of SP11 (when prioritizing genera/species of scientific importance).
The gymnosperms (cone bearing plants) are replete with ancient, separate evolutionary lineages many of which are vital FGR. The order Ginkophytes comprises one family Ginkgoaceae and a single living tree species viz. Ginkgo biloba, a living fossil apparently almost unchanged in form for nearly 175 million years and an important source of herbal medicine. Cunninghamia lanceolata in its own subfamily Subfamily Cunninghamhioideae, while Taiwanioideae consists solely of Taiwania cryptomerioides and the subfamily Sequoioideae includes three renowned monotypic tree genera/species, viz. Metasequoia, Sequoia and Sequoiadendron. Many other coniferous genera comprise a single tree species which is highly valued for its timber, NWFP, cultural and/or environmental purposes, e.g. Cathaya, Fitzroya, Fokienia, Lagarostrobos, Manoao, Nothotsuga, Papuacedrus, Platycladus, Pilgerodendron, Pseudolarix, Sundacarpus, Taxodium, Tetraclinis and Thujopsis. Several of these monotypic conifer genera are at high risk of loss of intraspecific diversity, some threatened with extinction in the wild, including Neocallitropis pancheri in New Caledonia (which has yet to be assessed by IUCN). Many of the endangered and evolutionary unique lines of conifer subfamilies, genera and species are endemic to China and Vietnam; New Caledonia (France) and other Gondwanaland flora, and a continuing strong conservation effort for these taxa is needed in these countries.
The most primitive angiosperm or flowering plant is considered to be Amborella tricopoda: this species has been placed in its own order Amborellales and is of major scientific importance. Whilst its conservation status has yet to be assessed, it is likely to be at risk from climate change and fire entering previously unburnt, wet forest ecosystems in New Caledonia. The monotypic Arillastrum gummiferum from New Caledonia is important for forest science as an ancestral genus/species for eucalypts. Many angiosperm genera comprising a single tree species which may be highly valued for its timber, NWFP, cultural or environmental purposes and/or endangered including: Antiaris, Aralidium, Argania, Aphloia, Aucomea , Bagassa, Baillonella, Bertholletia , Bosqueiopsis, Cantleya, Chloroxylon, Crossopteryx, Cyclocarya, Deckenia, Delavaya, Elingamita, Eusideroxylon, Faidherbia, Falcataria, Franklinia, Gomortega, Gymnostemon, Haldinia, Hartogiella, Itaya, Ixerba, Jablonskia, Jubaea, Kigelia, Kleinhovia, Koordersiodendron, Kostermansia, Krugiodendron, Laguncularia, Limonia , Litchi, Maesopsis, Muntungia, Neobalanocarpus, Noltea, Ochroma, Olneya, Oroxylum, Platycarya, Pleiogynium, Rhoiptelea, Spathodea, Ticodendron, Triplochiton, Umbellularia, Umtiza, Veillonia, Vitellaria, Xanthoceras, Veillonia and Zombia. Monotypic wild fruit tree ancestors, such as Clymenia polyandra from Melanesia, may hold importance for future citrus breeding. Several angiosperm orders and whole families of woody tree species are represented by one or very few taxa. Barbeyaceae comprises the monotypic Barbeya oleoides; a small tree with medicinal uses present in north-east Africa and the Arabian Peninsula. Degeneriaceae includes two Fijian timber tree species, ancestral angiosperms in the genus Degeneria. Sladeniaceae includes three tree species in two genera, viz. Ficalhoa laurifolia a timber tree from montane forests in east Africa, and two Chinese tree species of Sladenia that have potential as sources of novel biochemicals, including for use in insecticides. The order Trochodendrales and family Trochodendraceae includes two East Asian tree species both in monotypic genera, viz. Trochodendron araloides and Tetracentron sinense. These two tree species are notable in angiosperms for their absence of vessel elements in the wood, which unlike Amborella, is thought to have been a secondarily evolved character and of scientific interest. The monotypic Cordeauxia edulis is an important multipurpose woody shrub in Ethiopia and Somalia is classified as vulnerable (IUCN) while the monotypic Canacomyrica monitcola is an endangered tree species (IUCN red list) endemic to New Caledonia. The 194 palm species in Madagascar are almost all endemic at both generic and specific levels (p 16) and together with several monotypic palm genera in Seychelles include unique and endangered genetic lineages.
The unprecedented threats to FGR in recent times are almost exclusively of human origin. With the exception of geological events the categories of threat to species identified by the IUCN are residential and commercial development; agriculture and aquaculture; energy production and mining; transportation and service corridors; biological resource use; human intrusions and disturbance; natural system modifications; invasive and other problematic species; pollution; geological events; and climate change/severe weather. Major modern-day human impacts on the environment involve massive changes in land use systems, destruction and fragmentation of natural habitats, air and soil pollution, salinization and soil acificication, climate change, overexploitation of biological resources, homogenization of biota and biodiversity loss; these impacts interact with one another in complex ways and may result in non-additive cumulative effects (Yachi and Loreau 1999). In recent times and in the future, greatly increased threats to FGR are likely to come from forest cover reduction, degradation and fragmentation; climate change; forest ecosystem modification especially from invasive, ecosystem transforming species and interactions of different threat factors and these factors are discussed below in more detail.
Figure 4: Number of species mentioned as threatened (at various levels) in Country Reports, by region
1.4.1 Causes of genetic erosion, threats and risk status
220.127.116.11 Forest cover reduction, degradation and fragmentation
Over the past few hundred years, the main negative impacts on forest genetic resources, including loss of tree species, have been attributable to human-mediated forest cover reduction, forest degradation and fragmentation. This will almost certainly continue to be the case while the world’s population continues to rise. India lists 261 tree and woody species whose genetic diversity is threatened, including 94 species in highest threat category: the identified threat types are almost entirely related to forest cover loss, degradation and fragmentation, including combinations and interactions of these threats. The major threats identified for 22 priority tree species in Chile come from deforestation and land use change (72%), with a high proportion also threatened by overexploitation (28%) (Hechenleitner et al. 2005). It is estimated that 20-33% of the Brazilian Amazon’s more than 11,000 tree species, especially rare and narrowly distributed endemics, will go extinct due to habitat loss (Hubbell et al. 2008), and a broadly similar situation can be expected for much of the tropics/ The main needs of the world’s growing human population that impact on FGR found in native forests are additional land for agriculture, infrastructure and housing, mining, and to grow wood in plantation for building, paper and fuel.
In sub-Saharan Africa various human activities were noted as threats to FGR. Mining may cause the loss of entire local tree populations and Burundi noted mining and quarrying as threats to FGR. Tanzania noted cutting of firewood and charcoal production as contributing to deforestation. Ethiopia is a prime example of major loss of forested landscapes with forest cover diminishing from more than 50% in the middle of last century to currently around 3-11% cover (depending on forest cover definition). Ethiopia is rich in FGR, including more than 1000 woody plant species and two biodiversity hotspots, Eastern Afromontane and the Horn of Africa, but the viability of populations of important woody species is threatened by fragmentation (reduced gene flows), coupled with utilization pressures, fire and invasive species which increase the risk of local extinctions.
Whilst globally the rate of forest loss is slowing, as indicated in FRA 2010, the impacts of further forest loss on FGR are proportionally increasing because the losses of forests are affecting a smaller residual base of native forest, are concentrated in more biodiverse rich forests, and leading to greater fragmentation with long-term impacts on associated animal species and gene flow and viability of more fragmented species and populations.
18.104.22.168 Atmospheric pollution, rising CO2 levels and climate change
Since the Industrial Revolution atmospheric pollution has caused damage to Europe’s forests, but is a
diminishing direct threatening factor to FGR, with most damage likely to result from stressed trees being more susceptible to insect pests and diseases. Of greater global concern for FGR are the increasing and accelerating CO2 levels. These result from human activities (burning of fossil fuels, forest destruction etc) over the past half-century and are are already, as predicted by IPCC, contributing to more extreme climatic events. Worsening and changed climate, including prolonged drought is mentioned as a threat to FGR in many of the Country Reports to this SoW-FGR, including Burkina Faso, Chad, Niger and Tanzania and the same applies for many other Sahelian zone countries in West Africa. Temperature and precipitation are the two main climate drivers for forest ecosystems such that any significant changes will impact on species composition and forest cover. Impacts can range from extreme disturbances such as forest fires or pest outbreaks to more subtle changes in temperature affecting physiological processes. The ability of tree species to survive the current rapid climate changes will depend on the capacity to quickly adapt to the new conditions at the existing site, manage the changing conditions through a high degree of phenotypic plasticity without any genetic change, and/or migrate to an environment with the desired conditions for that species. Some forest types are more vulnerable than others to climate change. For example, with tropical forests, small changes in climate are likely to affect the timing and intensity of flowering and seeding events, which would in turn have negative impacts on forest biodiversity and ecosystem services. Increased frequency and intensity of extreme events, such as cyclones may result in shifts in species composition. Mangroves are especially vulnerable with projected sea level rises posing the greatest threat to mangrove ecosystems. Mangroves potentially could move inland to cope with sea-level rise, but such expansion can be blocked either by infrastructure, or by the lack of necessary sediment, such as in the reef-based island archipelagos in Melanesia. Temperature stress will also affect the photosynthetic and growth rates of mangroves (McLeod and Salm 2006).
The area covered by forests will alter under climate change, with the ranges of some species being able to expand, whereas others will diminish; shifts will also occur between forest types due to changing temperature and precipitation regimes. For example, boreal forests would shift polewards with grassland moving into areas formerly occupied by boreal species. There is evidence of the migration of keystone ecosystems in the upland and lowland treeline of mountainous regions across southern Siberia (Soja et al., 2007). For temperate forests range reduction is expected to be more rapid at low elevation and low latitude, but at high elevation and high latitude their range is expected to increase to a greater extent than the boreal forests, thus reducing the total area of boreal forests. Thuiller et al., (2006) have shown that at low latitudes in Europe there will be a greater impact on species richness and functional diversity.
In the sub-tropical forests of the Asia-Pacific region, where key biodiversity hotspots are found, endemic species are predicted to decline, resulting in changes in ecosystem structure and function (FAO, 2010). Changes in precipitation rather than temperature may be more critical for these species and systems (Dawson et al., 2011)
Changes in water availability will be a key factor for the survival and growth of forest species, although the response to prolonged droughts will vary among tree species and also among different varieties of the same species (Lucier et al., 2009). In arid and semi-arid lands, increased duration and severity of drought has increased tree mortality and resulted in degradation and reduced distribution of forest ecosystems, including pinyon pine-juniper woodlands in south-western USA (Shaw et al. 2005) and Atlas cedar (Cedrus atlantica) forests in Algeria and Morocco (Bernier and Schoene, 2009). Indirect impacts must also be considered, for example, in Africa where drought is limiting the output from adjoining agricultural land, many communities with limited economic alternatives are likely to use the forests for crop cultivation, grazing and illicit harvesting of wood and other forest products, aggravating the local loss of forest cover (Bernier and Schoene, 2009).
Choat et al. (2012) have found that 70% of 226 forest tree species from 81 sites worldwide operate with narrow hydraulic safety margins against injurious levels of drought stress and therefore potentially face long-term reductions in productivity and survival if temperature and aridity increase as predicted. While gymnosperms were found more tolerant of lower conductivities than angiosperm trees, safety margins are largely independent of mean annual precipitation with all forest biomes equally vulnerable to hydraulic failure and drought-induced forest decline. These finding help to explain why climate-induced drought and heat can result in forest dieback across a broad range of forest and woodland types across the world. Examples can be found from southerly parts of Europe, and in temperate and boreal forests of western North America where background mortality rates have increased rapidly in recent years (Allen 2009). These dieback problems have occurred at a time when increases in temperature have been relatively modest, which does not bode well for future temperature predictions. Greater mortality rates can be expected with the more likely increase of 4oC of warming, and significant long-term regional drying in some areas. Some climate change models predict a very significant dieback in parts of the Amazon and other moist tropical forests which would exacerbate global warming (Bernier and Schoene, 2009).
Changes in temperature and water availability will also influence the incidence and spread of pests and diseases. For example, the absence of consistently low temperatures over a long period of time (unusually warm winters) supported the spread of the mountain pine beetle, Dendroctonus ponderosae, in boreal forests and allowed an existing outbreak to spread across montane areas and into the colder boreal forests with a total of more than 13 million hectares of forest being under attack. Finland is expecting an increase in infestation of root and bud rots in their coniferous forests, due to the spread of a virulent fungus, Heterobasidion parviporum, favoured by longer harvesting periods, increased storm damage and longer spore production season (Burton et al., 2010).
Severe water stress will directly weaken and kill trees, or indirectly through supporting insect attack, for example, bark beetles, which can destroy trees already weak due to stress induced by climatic extremes (McDowell et al., 2008). A thorough analysis of historical records and adequate knowledge of insect population dynamics is needed before outbreak frequencies can be linked to climate change. The availability of such information has enabled researchers to link drought stress due to climate change to the extensive damage caused by insects to pinyon pine (Pinus edulis) in south-western USA (Trotter et al., 2008)
The global spread of harmful forest pest species is a possible outcome of climate change (Regeniere and St-Amant, 2008) with global trade facilitating the movement of mobile insect species to find hospitable habitats which are being increasingly provided by changes in the climate. There is significant evidence accumulating regarding insect distributions, however, the complexity of insect responses to climate factors makes predictions difficult. Generic modelling tools, such as BioSIM, attempt to predict the geographic range and performance of insects based on their responses to key climate factors. The basic premise is the ability of the insect to complete its life cycle under a specific climate with all requirements to sustain that cycle available. Using these models, distributions can be predicted by mapping climates that provide viable seasonality and overlaying the distribution of resources essential for (or most at risk from) that species. Further refinements can be achieved by also considering survival of that species under extreme climatic conditions. This approach has been applied to three species of importance to North American forests within a climate change scenario where there is a 1 percent rise per year in atmospheric CO2. One of these species, the gypsy moth (Lymantria dispar) is prevalent in the USA and some parts of Canada however its northern limit in Canada is set by adverse climatic conditions. The model established for this species shows that it will be a considerable threat to hardwood forest resources as climate change allows for its expansion further north and west into Canada. It has been estimated that the proportion of forest at risk from this pest will grow from the current 15 percent to more than 75 percent by 2050 (Logan et al., 2003)
In the regions where temperate and boreal forests are found reduced snow cover, timing of snowmelt, shorter frost periods are contributing to the extent and severity of different climate conditions, such as drought and heatwaves. Reduced snow cover has been shown to be responsible for the yellow cypress (Xanthocyparis nootkatensis) decline which is affecting about 60 to 70 percent of the 240,000 hectares of yellow cypress, a culturally and economically important tree found in south-eastern Alaska, USA and adjacent areas of British Columbia, Canada. The snow normally protects the vulnerable shallow roots from freezing damage. Coastal Alaska is predicted to experience less snow, but persistent periodic cold weather events in the future, which will support the spread of dieback (http://www.fs.fed.us/pnw/news/2012/02/yellow-cedar.shtml).
Sensitivity to spring temperatures will affect fecundity. In central Spain a decline in cone production in stone pine (Pinus pinea) over the last 40 years has been linked to warming, in particular the hotter summers (Mutke et al., 2005).
A changing climate provides the opportunity for some species more suited to a wide range of climate conditions to invade new areas (Dukes 2003), resulting in the spread of invasive species, such as Leucaena spp. and Eupatorium spp., already known to have adverse impacts on biodiversity in subtropical forests in South Asia. Invasions of new genes via pollen and seed dispersal may have a negative impact on local evolutionary processes but there could be opportunities for finding sources of new adaptive traits (Hoffmann and Sgro, 2011)
Changes in the climate could impact on seed production due to asynchronous timing between flower development and the availability of pollinators, resulting in low seed production for outbreeding species dependent on animal vectors. Pollinators worldwide are being affected by climate change, and this will likely have a major impact on breeding systems and seed production with detrimental impacts on forest health and regeneration.
A greater incidence of intense cyclones, extreme drought, fires, flooding and landslides have been observed in tropical forest ecosystems which have experienced increased temperatures and more frequent and extreme El Niño–Southern Oscillation (ENSO) events. Some climate change models predict a catastrophic dieback of parts of the Amazon and other moist tropical forests which would exacerbate global warming. It is clear from the evidence to date that the changes in the climate are already having an impact on forests throughout the world. Current and future climate change impacts on forests will vary from abrupt negative impacts to more subtle negative and positive impacts that arise in some regions or at particular sites, often only for certain tree species. There is an urgent need for countries to be assisted to cope and deal with impacts of climate change on FGR and to promote and utilise FGR to help with climate change adaptation and mitigation.
22.214.171.124 Changed fire regimes, including expansion of grasslands, and altered hydrological conditions
Climate change could alter the frequency and intensity of forest disturbances such as insect outbreaks, invasive species, wildfires, and storms. In recent years, wildfires consumed more than 2.5 million hectares of forest in Alaska; warm temperatures and drought conditions during the early summer contributed to this event (CCSP, 2008). Forest fires can be the greatest threat to biodiversity. In 2006 fires in New Caledonia engulfed more than 4,000ha near Noumea, destroying rare fauna/ New _aledonia’s tropical forest ecosystems are unique, of the 44 species of gymnosperms that exist, 43 are endemic. In Siberia, Alaska and Canada extreme fire years have been more frequent (Soja et al., 2007). Interactions between disturbances can have an accumulative impact. For example, drought often reduces tree vigour, leading to insect infestations, disease or fire. Insect infestations and disease will add to the fuel available and therefore increase the opportunity of forest fires, which in turn can support future infestations by weakening tree defence systems (Dale et al., 2001). Increased fire frequency could result in the erosion of fire-sensitive species from woodlands and forest. In regions where fires are not normally experienced, a rapid transition could occur from fire-sensitive to fire-resistant species. Countries reporting forest fires as a threat to FGR included Algeria, Burundi and Ethiopia.
Altered hydrological conditions are a major emerging threat to FGR. This includes increases in severity and duration of flooding, associated with climate change which can kill whole stands of trees. Even inundation-tolerant species, such as river red gum (Eucalyptus camaldulensis) and coconut (Cocos nucifera), are killed by waterlogging if the trees have not been regularly exposed to waterlogging and inundation through their development. Coastal inundation due to sea level rise beginning to kill coastal vegetation, in Kiribati a single king tide can kill established breadfruit (Artocarpus altilis) trees which major impacts on food security and livelihoods (as these trees harbour seabirds such as terns which are used by local fisherman to locate schools of fish). Studies with salt-tolerant non-halophyte trees (Thomson et al. 1987; references in Marcar et al 1999), have frequently demonstrated considerable genetically-based resistance to salinity. Given the substantial genetic diversity in breadfruit, including putative salt tolerance in particular varieties and natural hybrids between A. altilis and dugdug (A. mariannensis) (Morton, 1987; Ragone 1997), it is almost certain that salt-tolerant breadfruit can be selected and further developed – this is an urgent task given the impacts of sea level rise on Kiribati, Tuvalu and other atoll island nations in the Pacific Islands and elsewhere, and yet another example of the need to conserve and make use of genetic diversity in multipurpose tree species.