Technical guidelines for genetic conservation and use Service tree Sorbus domestica Peter Rotach Department of Forest Sciences, Swiss Federal Institute of EUFORGEN Technology, Zürich, Switzerland These Technical Guidelines are intended to assist those who cherish the valuable 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 The service tree is a close relative of rowan (S. aucuparia L.), the wild service tree (S. tormi- nalis Crantz.) and whitebeam (S. aria (L.) Crantz). Young trees are easily mistaken for rowan, having very similar leaves and overall mor- phology. Once it is mature, it is very distinct, mainly due to the coarse and pear-like bark, green and “gluey” buds and the 2- 3 cm large apple or pear shaped fruits. In its natural niche of poor, dry sites, the service tree grows to a medium size of 15-20 m in height. On rich, fresh soils, however, it can outgrow oak and surpass 30 m in height and 60 cm in diameter within 130 years. S. domestica has a dense and tough wood of high value used for special purposes. It flowers regularly and produces large amounts of fruits which are dis- persed effectively by birds and mammals. In spite of this, natural Sorbuservice treeSorbus domesticaService treedomesticaSorbus domesticaService treeSorbus domesticaS regeneration from seed is scarce with standard type forests or in Distribution throughout Europe, and it is still other favourable situations such not understood why. Vegetative as forest fringes or extreme propagation by root suckers slopes. The natural range of the service however, is common, especially tree is restricted to southern and on warm and favourable sites. central Europe, centred in the Although S. domestica is win- Balkan peninsula, Italy and ter hardy, able to withstand -30°C southern France. The com- and is less susceptible to late plete, potential distribu- frost than sessile oak, it prefers tion is currently unknown, warm and mild climates with as inventories are still extended vegetation periods. In required in many areas. It central Europe it occurs on warm, is also unclear how much South facing slopes below 650 m of this is natural distribu- in altitude, whereas in the tion, since S. domestica Mediterranean it is found at high- has spread through culti- er elevations. It is tolerant to soil vation since Roman times. conditions, and occurs on a wide variety of sites. The service tree is a light demanding species and only tolerates shade in the first few years. Despite its rather good growth capacity, it is a very weak competitor. It does not withstand or tolerate lateral crown closure and consequently, the service tree never domi- nates and is usually pres- ent as a few individuals in a mix of less competi- tive species. Due to its high drought toler- ance, which compares to that of downy oak (Q. pubescens L.), it finds its niche on warm, dry to extremely dry, poor, shallow sites. As the result of human activity, it may also be found in coppice and former coppice aService treeSorbusSorbus domesticaService treeSorbus domesticadomesService treeSorbus domestic Importance and use Genetic knowledge and a mixed reproductive system may be key elements for main- taining genetic diversity in rare The service tree has been highly Very little is known about the species like S. domestica. While valued since Roman times. The genetics of the service tree. vegetative reproduction con- fruit has been used as produce, However, due to its scarce serves genetic diversity even in to cure intestinal problems, and numbers, low density and high the smallest populations, long- as an additive for conserving degree of fragmentation and distance pollen and seed disper- apple cider. The wood was used isolation, reduced genetic diver- sal guarantee recolonisation. for mechanical parts, yardsticks, sity and high differentiation inlays or instruments. Today, the would be expected according to fruits are still used to conserve population genetics theory. How- apple cider, to produce high ever, a study of quality liquors, and for Swiss and Ger- specialist products man popula- such as mar- tions has not malades. There is confirmed these now little wood pro- expectations, duction due to its and genetic low abundance. diversity was Nevertheless, S. found to be domestica has a similar to that of high economic potential if widespread species. planting material of excellent Even small, isolated genetic quality is used. In most demes of less than 20 countries in central Europe, the trees had remarkably high levels service tree is very rare and of diversity. Sub-populations threatened, and is considered a were found to be more genetical- valuable biological resource wor- ly differentiated than in wide- thy of conservation. spread species, but less than expected for fragmented and isolated populations. Pollen gene flow was found to be surprising- ly high. Supported by similar findings in other dispersed species, results suggest that the genetic system of naturally rare species seem to be well adapted to low densities. Long-distance gene flow, dynamic meta-popu- lation structures with local extinction and recolonisation, long-distance migration events through effective seed dispersal caticaService treeSorbus SorbusdomesticaService treeSorbus domestica Servicedom treeSorbus dome Threats to Guidelines for genetic need to be clearly defined, docu- genetic diversity conservation and use mented and integrated into local management plans. S. domestica is very rare and Conservation priorities and Where additional measures threatened in many European measures depend on the current are feasible, other core popula- countries. The species and its population size, population struc- tions should be added to create genetic diversity are threatened ture and existing or potential a network of conservation units. by: 1) an overall reduction in the threats. Thus, in situ conservation If possible, core populations number of individuals; and 2) dis- efforts must begin with invento- should be linked with neighbour- turbance of the natural meta- ries, assessing population size ing cores or should be enlarged population structure due to and structure, core populations, in order to guarantee their long human impact. Intensive forestry, fragmentation, threats and term survival. In addition, smaller overstocked and dense stands, threatening processes, as well as demes and even single trees, silvicultural practices, loss of conservation needs and priori- which serve as stepping stones suitable habitats, neglect, and ties. for gene exchange, should be insufficient knowledge and No rule can be given regard- integrated into the network. Until perception, all contribute to a ing the minimum number and further information on gene flow reduction in population size. size of populations to be con- is available, demes and in- Insufficient or missing recoloni- served since it depends on the dividuals may be considered sation events and opportunities specific situation of the species linked if they are closer than 3 lead to a change in population (demography, threat, habitat km. In most cases, conservation and age structures, a reduction availability etc) and the available and promotion of S. domestica in population size and a higher financial means. At the very requires plantations, since natu- degree of fragmentation and least, the most viable core popu- ral regeneration is sparse or isolation of fragments. Reduced lation should be designated as a inexistent. These should be re- levels of gene flow and migration conservation unit in which S. stricted to favourable sites where and higher levels of inbreeding domestica is favoured above all the service tree is able to with- will eventually result in a loss of other species in regeneration stand natural com- genetic diversity and higher and tending operations. Focus- petition with little inter- genetic differentiation among the ing efforts on these core vention. fragments. populations, which are the largest and most viable, should ensure maximum success with minimum costs. As a rule of thumb, at least 50 inter- breeding individuals should be selected for such a conservation unit. Management should guar- antee individual survival, favour vitality and fertility, and attempt to create a sustainable age structure for the future. All objec- tives and necessary measures SorbusService treeSorbus domesticaService treedomestiSorbus domesticaService treeSorbus do Distribution range of service tree It is highly recommended that perception of the species in the in situ conservation measures forest service are thus decisive are accompanied by ex situ col- for successful conservation and lections even if sufficiently large it is hoped that these guidelines core populations still exist. Seed serve as a starting point for this orchards can produce genetical- purpose. ly diverse planting material which is difficult or impossible to collect from wild populations. In addi- tion, ex situ collections may serve as genebanks or for breed- ing activities. High quality plant- ing material is important since regeneration