Technical guidelines for genetic conservation and use Wild service tree Sorbus torminalis B. Demesure-Musch and S. Oddou-Muratorio EUFORGEN INRA, Genetic Conservation of Forest Trees ONF, Olivet, France These Technical Guidelines are intended to assist those who cherish the valuable wild service tree genepool and its inheritance, through conserving valuable seed sources or use in practical forestry. The focus is on conserving the genetic diversity of the species at the European scale. The recommendations provided in this module should be regarded as a commonly agreed basis to be complemented and further developed in local, national or regional conditions. The Guidelines are based on the available knowledge of the species and on widely accepted methods for the conservation of forest genetic resources. Biology and ecology Wild service tree (Sorbus tormi- nalis L. (Crantz)) is a diploid species (2n=34) belonging to the family Rosaceae. It can hybridize with at least two other species of Sorbus: whitebeam (Sorbus aria) and mountain ash (Sorbus aucu- paria). Hybridization with white- beam commonly occurs, especially where the natural ranges of these species over- lap. Most of these hybrids are triploid (3n=51) and a few (mainly Sorbus latifolia) are tetraploid (4n=78). Hybrids reproduce mainly by apomixes. Wild service tree is a fast- growing tree, reaching maximum height at around 80–100 years, when they are typically 20–25 m in height with trunks of 50–70 cm diameter. Exceptional trees can reach up to 30 m in height and 1 m diameter at 200 years old. Wild service tree produces hermaphrodite flowers visited by a wide range of generalist polli- nators (social bees, bumblebees orbusSorbus torminalisWild service treeSorbus torminalistorminalisWild service treeSorbus torminalisWild s and beetles). Flowering and seed Distribution Importance and use production can start in trees <10 cm diameter under optimal condi- tions. The fleshy fruits are dis- Wild service tree is widely dis- Wild service tree is favoured by persed by birds, especially thrush- tributed across Europe, from the hunters, because its fruits are es, and by mammals (foxes, northern extremity of Africa to well appreciated by many bird martens). Seed dormancy is usu- the south of Sweden and from species and a few mammals. ally one winter long. Alternation the east of Great Britain to the The fruits are also used to pro- of warm and cold temperatures north of Iran. It usually occurs at duce liquors, especially in Ger- has been reported to increase low density throughout its range many and Austria. the rate of germination in labora- (0.1–30 individuals/ha). Wood of the wild service tree tory conditions. is fine-grained, very dense and Wild service tree favours has good bending strength. It deep fertile soils, but can tolerate was used in the past to make a wide range of soil conditions, screws for winepresses, billiard from chalky, superficial, dry soils queue sticks, musical instru- to temporarily waterlogged soils. ments and turnery. Today, it is It can adapt to a variety of cli- usually only used for decorative matic conditions, but occurs veneers. Wild service tree is one most often in lowlands. of the most valuable hardwoods Wild service tree is a light- in Europe. In the 1990’s, wild demanding species, often out- service tree has been the highest competed by other hardwood priced timber species in species, in particular beech. Europe. When overtopped by other trees, wild service tree rapidly weakens and wastes away, but even a small opening in the canopy is enough to allow its development. It is described as a nomad, post- pioneer species often found growing as a minor component of oak and beech woodland. It can easily colonize forest clear- ings and low-density forest stands, notably thanks to effi- cient seed dispersers. Vegetative propagation by root suckers can occur, and may increase the tree’s competitive abilities. This is the major way to colonize disturbed areas and to survive the competition from oth- er species. sservice Sorbus treeSorbus torminalisWild service tree torminaliSorbus torminalisWild service treeSorbus Genetic knowledge six effective pollen revealed rather donors contribute to high levels of the pollen cloud of a within-population Investigations of the population given mother tree. diversity, for both genetics of wild service tree have But at the same nuclear and begun only recently. To date, the time, a proportion of cytoplasmic available results are based on the pollen donors are markers. surveys with neutral genetic far away from the The level of markers. These surveys high- mother tree. differentia- lighted some important genetic These mating pat- tion between processes that shape the level terns are consistent with populations observed and organization of genetic pollination ecology in wild with cytoplasmic mark- diversity in the wild service tree. service tree: social bees ers was surprisingly low Hybridization with other intensively exploit local compared with other European species of the Sorbus genus resources, but some bees scattered broadleaves. For wild occurs predominantly as wild and especially bumblebees service tree, neither pollen- nor service tree (father) to white- are also able to fly long distances seed-mediated geneflow effect beam (mother). It is rarely fol- to find new nectar resources. was predominant (genes are lowed by cytoplasmic introgres- Similar trends have been propagated on average at equal sion. As a consequence, inter- observed for ongoing patterns of distance by seed and pollen). specific geneflow should not sig- seed dispersal. Most seeds are Patterns of genetic diversity nificantly affect the diversity dispersed in the close neigh- on a large scale thus indicate dynamics within wild service bourhood; 174 m on average that, even though pollen and tree. between an established seedling seed are predominantly dis- Wild service tree is a pre- and its mother tree. But at least persed a short distance in wild dominantly outcrossing tree. The 17% of the seedlings collected in service tree as in most plant rate of self-fertilization is esti- the middle of a 470-ha forest species, rare events of long-dis- mated at <1% in open-pollinated stand originated from outside of tance pollen and seed dispersal progenies, and is very variable that stand. deeply affect the long-term across mother trees. This very These patterns of pollen and dynamics of genetic diversity in low rate of self-fertilization sup- seed dispersal result in strong this species. This may be a gen- ports the hypothesis of a partial levels of spatial genetic structure eral trend in species combining self-incompatibility system as in at a local scale. Wild service good dispersal abilities and col- Sorbus aucuparia. trees were observed to be dis- onizing dynamics. Patterns of pollen exchanges tributed in aggregates of 150- Chloroplast DNA studies on a in wild service tree show two 300 m in radius, corresponding European scale revealed a weak main trends: preferential mating to individuals more genetically phylogeographic structure. Dif- between neighbouring trees due related than expected by ferences in haplotype frequen- to local pollen dispersal, com- chance. These aggregates are cies observed between the west- bined with long-distance disper- likely to correspond to success- ern and eastern parts of Europe sal (up to 2.5-km dispersal ful colonization of favourable could indicate the presence of events have been documented). sites by sibling trees. different refuges in Europe dur- This results in a low pollination In contrast, genetic surveys ing the last glaciations. On a effective size: on average, only at regional and larger scales regional scale, no phylogeo- istorminalis WildSorbus service treeSorbus torminalisWild service tormina treeSorbus torminalisWild servi graphic structure was found. Threats to Guidelines for genetic Intensive seed movement since genetic diversity conservation and use postglacial recolonization could have blurred a pre-existing phy- Wild service tree is a scattered In situ measures logeographic structure. tree and its genetic diversity can Dynamic conservation maintains Genetic structure shows little be considered at risk in certain the diversity of evolving popula- evidence of the impact of human conditions. tions thanks to the combined management on wild service tree Wild service tree is sensitive effects of environmental pres- dynamics. Within management to competition. Therefore there sure and sexual reproduction. In units, a mixing of progenies of may be a risk in dense regular situ conservation is applied local mature trees and distant high forests which contain a high through a network of conserva- mature trees from neighbouring proportion of long-lived species. tion units (natural stands). management units has been The high level of interspecific For species with extinction- found. Thus, regeneration within competition could impede the recolonization dynamics, it is not management units must account regeneration process and lead to possible to define units of conser- for the presence of seed trees all local extinction. Thus the species vation. Indeed, the extinction- over the forest. may be in great danger if no new colonization events and high lev- sites are available for coloniza- els of seed flow could not be tion and establishment. maintained in conservation units. As for all forest trees, habitat Here, the issue is not to limit the fragmentation could induce a large geneflow but rather to con- strong decrease of genetic diver- serve it. It is also necessary to sity through reduction of popula- maintain the entire ecosystem tion size and ruptures of gene- dynamic because wild service flow. Habitat fragmentation tree dynamics are closely related could result either to forest succession. Therefore, from forest destruc- wild service tree conservation tion or by manage- should not be practised at the ment not oriented local level (several hectares) but in favour of wild at the landscape level or even at service tree. This the regional scale. For now, it is species is par- not possible to indicate a critical ticularly threat- population size below which the ened by habitat populations would be threatened.