Technical guidelines for genetic conservation and use Lime Tilia spp.

Jan Svejgaard Jensen EUFORGEN Forest and Landscape Research Institute, Hørsholm, Denmark

These Technical Guidelines are intended to assist those who cherish the valuable lime 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

Limes (Tilia spp.) are tall trees that can live for up to 500 years. Tilia flowers at the end of June until early July, and T. cordata flowers later than T. platyphyl- los. Mast years are infre- quent. Tilia sets flowers at the age of 30, and up to ten years earlier on solitary trees. In northern Europe, seed regeneration is sparse, which is assumed to be caused by low tem- peratures. Tilia species are out- crossing, and at least some of the individuals within a population are self- sterile. Seeds can be stored for a maximum of three - five years. The trees favour good, loamy sites, but can also be found on sandy, infertile soils, and are drought resistant. Dor- mant shoots of T. cordata can LimeTiliaTilia spp.Lime Tiliaspp. spp.LimeTilia spp.LimeTilia spp.TiliaLimeTilia spp.Lime sppTilia spp.LimeTilia spp

resist winter frost temperatures Distribution Threats to as low as -34°C. In most places genetic diversity throughout Europe, T. cordata grows in several types of mixed The ecological range of the most Climatic conditions and human species forest and many insects important lime species in impact have reduced the distri- and fungi are associated with Europe, T. cordata, is very broad. bution of Tilia in Europe in the Tilia. Within the common range T. cordata shares roughly the past 2000 years. The competitive of the two species, hybrids same distribution area as Acer ability of beech is also consid- between T. cordata and T. platy- platanoides. It is found in most ered as a threat. In many lowland phyllos have been observed. altitudes, and up to 1500 m in areas, Tilia may have disap- Hybridization and introgression the central Alps. In eastern peared when humans began take place rarely. Examples of Europe, it is found in pure farming these areas, limiting the hybridization include Tilia x stands, but normally exists in species to marginal sites, and in euchlora – a hybrid between T. mixed stands. northern Europe they are thought cordata and T. dasystyla, and Three additional species are to have disappeared on many Tilia x flaccida (between T. platy- also present in Europe: Tilia sites due to low seed fertility. phyllos and an American platyphyllos, T. tomentosa and T. However, other stands have evi- species, T. americana). Leaf, dasystyla. The distribution range dently been established by flower and fruit morphology are of T. platyphyllos is quite limited humans. used for identification of the and is commonly found on sites Inbreeding caused by the species. containing T. cordata, and is rare extensive fragmentation and T. cordata and T. platyphyllos in northern Europe. T. tomentosa destruction of biotopes is trees easily reproduce vegeta- and T. dasystyla occur in south- expected to have an impact on tively through cuttings and root eastern Europe and around the both T. cordata and T. platyphyl- layers, and cuttings can Black Sea. los. Hybridization, introgression even be propagated and widespread domestication from old trees. of foreign species and prov- Somatic embryogenesis enances may also impact the has been carried out existing genepool. both for T. platyphyl- los and T. cordata. p.pp.Lime TiliaTilia spp.LimeTilia spp. Limespp.Tilia spp.LimeTilia spp. LimeTiliaTilia spp.LimeTilia spp.spLimeTilia

Genetic knowledge Importance and use important for honeybees and honey production, especially in eastern Europe. Tilia spp. are Investigations of morphological Owing to their aesthetic and cul- also important for amenity use, characteristics of T. cordata have tural value as domesticated, shelterbelts and game plantings revealed little variation between urban and landscape trees, limes in the open landscape, in urban populations (Pigott 1991). General have become increasingly areas and recreational forestry. genetic properties have been important in Europe in recent described by Giertych (in decades. The importance of T. Bialobok 1991), but genetic cordata in Europe is well illustra- knowledge is sparse. Repro- ted by the common use of its ductive biology and name for geographic genetic variability localities. Tilia wood is have been used for carving, and reported by almost all parts of the Fromm (2001). tree can be used for As for Quercus fodder, ropes or fire- robur and Q. wood. Bast and honey, petraea, leaf, which were historically flower and the main products of Tilia, fruit morpholo- may have been an important gy can be used for iden- factor in the spread of the tification of the species. How- species and its status ever, no single morphological as a typical agro- trait alone can separate the forestry tree in the species due to large variation Middle Ages. Lime within the populations for each trees are insect individual trait (Mauer 1995). pollinated, and are pp.a spp.LimeTilia spp. LimeTiliaTilia spp.Lime Tilia spp.spp.LimeTilia spp.LimeTilia spp.TiliaLimeTilia spp.Lime T

Guidelines for genetic Marginal regions: In some costly and extensive precau- conservation and use regions, large gene tions are not taken. Alterna- reserves of Tilia are lack- tively, these resources A network of conservation ing, and these genetic could be used to pro- stands is needed to conserve the resources may be mote the establishment genetic variation of limes, which extensively frag- of new populations have evolved through adaptation mented. They may from local seed collec- to different ecological and envi- also be subject to tions. ronmental conditions. Conser- pollen contami- vation and breeding programmes nation from new in all countries where lime is found plantations origi- is required to ensure the conser- nating from non-local vation of the genepool. Specific seed sources. For strategies should include: these situations, in situ Sampling strategies: Inven- conservation may not be tories are needed to provide an effective. In some of the overview of the status of genetic marginal regions the regen- conservation in each individual eration of Tilia is lacking or country and at the European inadequate. Ex situ conser- scale. For practical purposes, vation of Tilia genetic provenance regions can be iden- resources is therefore rec- tified on the basis of ecogeo- ommended in marginal graphic variation and can be regions. Preferably, these ex modified to take into account situ conservation stands either expected gene flow or should be established on general knowledge about gen- the basis of reproductive etic variation within the species. material from within the local Central core regions: Large regions, in accordance with in genetic reserves within the cen- situ silvicultural management tral core regions of distribution principles. In situ conservation in are needed for effective gene marginal regions should include conservation purposes and a larger number of populations. should be given high priority, as Use and management of large genetic variation is expec- genetic resources: Breeding, ted to be present in the core dis- improvement and management tribution area. In general, Tilia of genetic resources of Tilia occurs in mixed species forest should be combined with gene and is associated with a number conservation to allow evolution- of different plant species. Exist- ary forces to continue. Com- ing protected areas will only bining conservation and use is partly serve as genetic conserva- especially necessary for species tion areas, as they are not selec- of low economic interest (“use it ted at random nor do they cover or lose it”). At some locations the the core regions of distribution. lime trees may be eradicated, if TiliaLimeTilia spp.Lime Tiliaspp. spp.LimeTilia spp.Lime Tilia Tiliaspp.LimeTilia spp. LimespTilia spp.Lim

Distribution range of Tilia cordata.

Distribution range of Tilia platyphyllos. pp.meTilia spp.Lime Tilia spp.LimeTilia spp. Limespp.Tilia spp.LimeTilia spp. LimeTiliaTilia spp.LimeTilia spp.

EUFORGEN

These Technical Guidelines were Selected bibliography produced by members of the EUFORGEN Noble Hardwoods Network. The objective of the Net- Bialobok, S. (ed.). 1991. Nasze Drzewa Lesne. Our Forest Trees. Popular Monograph. Vol 15. Limes - Tilia cordata Mill., Tilia platyphyllos Scop. [in work is to identify minimum genet- Polish]. Arkadia, Poland. ic conservation requirements in Fromm, M. 2001. Reproduction of an entomophileuos tree species in low den- the long term in Europe, in order sity – Small leaved linden (Tilia cordata Mill.) as an example - Dissertation to reduce the overall conserva- [in German]. Niedersachsische Staats- und Universitätsbibliothek Göttin- tion cost and to improve the qual- gen, Germany. Http://webdoc.sub.gwdg.de/diss/2001/fromm/fromm.pdf ity of standards in each country. Mauer, W. 1995. Isoenzymatiche und morphologische untersuchungen zur Linde [in German]. Pp 234-243 in Genetics and silviculture with special ref- erence to native oak species (W. Mauer, and U. Tabel). Mitteilungen aus der Forstlichen Versuchsanstalt Rheinland Pfalz 34. Pigott, C.D. and J.P. Huntley. 1981. Factors controlling the distribution of Tilia cordata at the northern limits of its geographical range. III Nature and caus- Citation: Svejgaard Jensen, J. es of seed sterility. New Phytologist 87:817-839. 2003. EUFORGEN Technical Guidelines for genetic conserva- tion and use for lime (Tilia spp.). International Plant Genetic Resources Institute, Rome, Italy. 6 pages.

Drawings: Tilia cordata, Giovanna Bernetti. © IPGRI, 2003.

ISBN: 92-9043-608-5

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