GLASGOW NATURALIST Vol. 23 Part 5 pp 13-17 (2000) NATURAL REGENERATION OF LIMES (TILIA SPP.) IN SCOTLAND: Locally widespread and more numerous in 1999 R.K.S. Gray1 and N.R. Grist2 ^‘Langdale”, 6 Prince Albert Road, Glasgow G12 9JX 25A Hyndland Court, 6A Sydenham Road, Glasgow G12 9NR ABSTRACT an increased number of seedlings at three locations as opposed to two. This paper explores the degree of lime regeneration found in Glasgow and other parts of Scotland in 1999. Large-leaved lime (T. platyphyllos) regeneration Regeneration was more widespread than noted followed a similarly increased pattern in terms of previously, although summer temperatures in 1997, the number though not oflocation. yearproducing the fertile seeds, were not the hottest on record nor in the past decade. Detailed analysis of In the Milngavie area natural regeneration was regeneration in one specific locality reinforced the observed in only two areas, namely, Auchenhowie - general trends found elsewhere. We noted more under a curious hybrid that may be a backcross - and vigorous development of seedlings having three the Community Education Centre - under T. cotyledons compared to those with the normal two. platyphyllos. The paucity of natural lime regeneration The higher threshold temperature sensitivity of small- in the Milngavie area may have been due to excessive leaved lime (T. cordata) compared to that of large- moisture, causing ground conditions to be leaved lime (T.platyphyllos) andcommon (hybrid) lime unsatisfactory for germination. Germination occurred (T. x europaea) were reflected in the seedling counts. in spring, 1999 of large-leaved lime seeds previously collected from six locations in the Milngavie area, namely,Allanderwalkway, C.E. Centre, Drymen Road, INTRODUCTION Kilmardinny House and the wooden bridge on Clober Road (Hansen, personal communication). Our previous paper forecast that “much (lime) regeneration can be anticipated in 1999 on the basis of Flowering of T. platyphyllos was first noted in the the 1997 temperatures” (Gray etal,1999). Since it was Milngavie area on 9th July, about two weeks after written, this forecast was substantiated by lime flowering at the lower, more sheltered altitude of the regeneration mainly in the Glasgow area, and also to a West End ofGlasgow. lesser extent elsewhere. Outwith the Glasgow area 48 seedlings were found under a numberoflarge-leaved limes in the grounds of REGENERATION IN 1999 Dalzell House, Motherwell where also 10 seedlings were discovered under a few common limes. Some 63 Our earliest observation of lime seedlings (common seedlings were observed under a single T. platyphyllos lime, T. x europaea) was on 26th March, 1999 in the in the Royal Botanic Garden, Edinburgh in the springof garden of9VictoriaCircus in theWest End ofGlasgow. 1999. Reports were received of regeneration of T. x Three were noted. europaea in Darvel, Ayrshire and Cardross, Dunbartonshire. Hence it is evident that limes can The 1999 results show firstly, that common lime produce fertile seed over a wide part of the central regeneration was locally abundant, measurable in lowlands of Scotland from Glasgow to Edinburgh, hundreds, and greater than the local numbers found in Ayrshire, Dunbartonshire and north Lanarkshire. previous years. Secondly, common lime regeneration Previous reports extend this area as far north as Perth was more widespread in the West End ofGlasgow than (Gray etal., 1999). in previous years. We observed it in 25 sites compared with 14 in 1998: the same sites were examined in both years. The scale and relative increase in seedlings in 1999 is illustrated by counts of new seedlings at Hyndland Court, 6 Sydenham Road: NS 560675, which numbered 53 in 1997, 16 in 1998 and 275 in 1999 - a remarkable increase in this last year. Small-leaved lime (T. cordata) regeneration showed 13 ) Figure 1: Numbers ofnew seedling limes (T.x europaea emerging each week in Plot A, Hyndland Court, Glasgow - 1999 I I I I L april 2000 may 2000 june2000 Hyndland Court The crop of 235 seedlings under one lime contrasts with the single seedling in asimilarareaofmossy grass New seedlings in the whole garden numbered 275 in a few metres farther north in the garden adjacent to two 1999, most of them in one grass plot. Close other common limes in the same row. This difference observations ofthis 64 m2 plot ofmossy grass with one further supports our view that the different genetic ofthe row oflimes (T. xeuropaea) in its corner showed constitution of individual limes is important to their a total of235 emergent seedlings inApril-June, most of ability to produce fertile seeds. which surfaced in early May (Fig. 1). Three of these had three instead ofthe normal two cotyledons. Twoof these were potted, as were 5 of the normal seedlings, FACTORS AFFECTING REGENERATION one of which died. It was soon evident that the seedlings with three cotyledons grew more vigorously Temperature than the others (Table 1). All those in pots, including five from 1998 and one from 1997, survived in the roof It was on the basis ofthe temperature data above the garden whereas most ofthose in the groundbelow were 20 degree threshold forboth July andAugust, 1997 that destroyed by gardeners strimming, damaged by the forecast was made of substantial lime regeneration trampling or grazed apparently by invertebrates as in in 1999. If temperature were the sole determining previous seasons, or plucked for pressing before the factor controlling lime fertile seed formation and gardeners strimmed the plot in July. Invertebrates subsequent regeneration the number of seedlings damaged leaves in the roof garden also, including the anticipated in 1997 (on the basis of the 1995 darker green leaves of seedlings 99.1 & 99.2 which temperature data) would have been greater than in were reduced to lacework. 1999. Table 1: Comparison ofpotted seedlings in July & September, 1999 Seedling no. No. of Leaves Leaves Leafmax. Height Height No. lateral cotyledons (no.) (no.) size (mm.) (mm.) (mm.) branches 25 July 12 Sept 12 Sept 25 July 12 Sept 12 Sept 99.1* 3 7+ 5+ 42 40 45 2 99.2* 3 9+ 9 45 35 43 2 99.3 2 3 3 n.r. 25 33 0 99.4 2 2 0 eaten 0 15 33 0 99.6 2 n.r. 1 remnant n.r. 30 0 99.7 2 n.r. 3 tiny n.r. 25 0 n.r. = not recorded Leafnumbers reduced in late summer by predation by slugs etc. * = on Aug. 3rd these seedlings were potted on because oftheir more vigorous growth. 14 9 The opposite was the case. The 1996 temperatures germinate after 6 months and most of the remainder suggest less germination in 1998 than in either 1997 or after 18 months. Seed hanging on the tree is normally 1999 as was certainly the case for both T. x europaea subjected to air drying prior to fall. Hence it was and T. platyphyllos. The lack of precise correlation suggested in our previous paper that “If the 1998 between temperature and amount of regeneration regeneration developed from the fertilisation of the indicates theoperation offactors otherthantemperature 1997 hot summer then, on a moisture basis, the alone in controlling lime regeneration. Exact anticipated percentage germination in 1999 in this area correlation is not to be expected since the temperature might be considerably more than in 1998.” The records were not from within the northwest area of regeneration numbers for 1999 clearly substantiate this Glasgow itself. Alsoenvironmental conditionsbetween claim. The figures also suggest that the 1998 the time offertilisation and regeneration may differ. regeneration resulted from 10 - 15% of the 1997 fertilised seed, although it is possible that some of this The smaller amount of T. cordata regeneration 1998 regeneration arose after 18 months from 1996 observed reflects the higher temperature requirement when the July/ August monthly mean temperature for fertilisation compared to T. platyphyllos and T. x maxima almost reached the 20°C. threshold. europaea (Pigott, unpublished). On the basis of the 1998 temperature data, adjusted SURVIVORS to sea level, since neither the July nor August figures achieved the 20degree threshold, it was anticipated that Survivors refer to specimens one or more years old, little or no new germination would occur in spring, i.e. survivors from previous years. 2000. In the event, however, from March 1 th, 2000 the cotyledons ofnew seedlings have been appearing under It is apparent from the tables that survival of any T. x europaea and T. platyphyllos and our observations seedling beyond the one year stage is fairly uncommon continue. These seedlings may resulteitherfromfertile in this area. The apparent decline of T. platyphyllos fruit formation in 1998 or represent the remains of the numbers from 10 to 6 probably has more to do with the 1997 fruiting year. difficulties associated with observing these saplings within a tended privet hedge than any real change in Moisture their numbers. It has been shown experimentally (Pigott, 1991) that ifseed is airdried and then sown in the open, 10-15% Table 3: Sites ofNatural Regeneration 1999 Table 2: Summary ofLime Regeneration in 1997, 1998 & 1999 species survivors ’99 survivors ’98 New in "99 New in ’98 New in ’97 T. x europaea 7 (0 saplings) 24 (0 saplings) several hundreds >50<100 100’s T. platyphyllos 12 (inch 36 (inch 145 13 >40 6 saplings) 10 saplings) T. cordata 2 (inch 3 (inch 20 2 0 2 saplings) 2 saplings) Table 4: Monthly Mean Temperature Maxima (degrees C.) (Mugdock* 1999,Abbotsinch 1998 to 1996 and Renfrew 1995) 1999 1998 1997 1996 1995 June 15.6 16.7 17.9 18.0 19.5 July 18.9 17.9 20.3 19.2 20.8 August 18.1 18.5 21.6 20.2 22.8 September 16.6 17.0 16.6 17.7 16.7 *Mugdock (160 metres above sea level) temperatures amended using the lapse rate of1°C. per 160m 15 ) T. x europaea Kingsborough Gardens. On9/4/99- 13 seedlings. 2 saplings flushed in hedge. 9 Victoria Circus. On 26/3/99 - 3 seedlings. Marchmont Terrace. On 12/4/99 - 69 seedlings. Hughenden Lane. SE comer of playing fields. On Dalzell House grounds. On 25/4/99 -48 seedlings. 9/4/99 - seedling. Kingsborough Gardens. On4/5/99- 14 seedlings. 2 1 Princes Place /PrinceAlbert Road. On 9/4/99 - 1 x x '98 survivors, 6 older survivors. '98 survivor in hedge. Knightswood Triangle. On 5/5/99 - 1 seedling. Great Western Road. N side. Balgray. On 9/4/99 - Marchmont Terrace. On 27/8/99 - 27 surviving '99 20 seedlings. seedlings. 4 x ’98 survivors. ‘Stazione’ restaurant area. On 9/4/99- 24 seedlings. Hughenden rugby stand. On 9/4/99 - 16 seedlings. T. cordata 6 Prince Albert Road lawn. On 12/4/99 - 33 seedlings. Kingsborough Square, N side. On 9/4/99 - 2 N-D school garden. On 12/4/99 - 4 seedlings. seedlings. Glasgow Botanic Gardens. On 12/4/99 Under T. Kingsborough Square. On 4/5/99 - 12 seedlings. 'Petiolaris' - 6 seedlings. Under T x europaea - 1 Crown Terrace. On 4/5/99 - 2 seedlings. seedling. Victoria Circus, Northcote Surgery. On 1/8/99 -4 x 9 Victoria Circus. On 12/4/99- 15 seedlings. '99 survivors. W Balgray, gate. On 14/4/99 - 5 seedlings. 6 Prince Albert Road back garden. On 14/4/99 - 20 ACKNOWLEDGEMENTS seedlings. We are grateful to Professor C.D. Pigott for making 6 Prince Albert Road front garden. On 14/4/99 - 33 available to us some of his unpublished data, and to seedlings. Professor J.H. Dickson for his helpful criticisms of a Dalzell House grounds. On 25/4/99 - 10 seedlings. draft ofthis paper. Baron’s Haugh. On 25/4/99 - seedling. 1 6 Prince Albert Road front garden. On 26/4/99 - 83 We thank M.H. Hansen for details of his seedlings. observations and experimental work and Ian McCallum 6 Prince Albert Road back garden. On 26/4/99 - 38 and Alan McG. Stirling for reports of their seedlings. observations. We are grateful to Mike Matthews ofthe 3 Sydenham Road. On 30/4/99 - 5 seedlings. x Scottish Weather Centre for making temperature data 1 '98 survivor in hedge. available to us 6 Sydenham Road. Between 2/4/99 & 20/6/99-235 seedlings (cf. Fig.1 8 Sydenham Road. On 30/4/99 - 3 seedlings. REFERENCES PrinceAlbert Road, S side. On 4/5/99 - 1 seedling. N-D school garden. On 4/5/99 -4 seedlings. Gray, R.K.S., Grist, N.R. & Hansen, M.H. (1999). Crown Road North. On 4/5/99 - 30 seedlings. 4 x Natural Regeneration of Limes (Tilia spp.) in '98 survivors in hedge. Scotland. The Glasgow Naturalist 23, 19-25. Crown Terrace. On 4/5/99 - 2 seedlings. 'Rock' car park. On 4/5/99 -5 seedlings. Mitchell, A. (1996). Trees ofBritain. Harper Collins Publishers. London. Laurel Park School, Great George Street. On 13/5/99- seedling. Pigott, C.D. Unpublished draft. Biological Flora of 1 Lilybank Gardens. On 13/5/99 - 3 seedlings. Tilia platyphyllos Scopoli (1998, personal Queen’s Gardens. On 13/5/99 - 5 seedlings. communication). Princes Terrace. On 13/5/99 - 10 seedlings. Pigott, C.D. (1991). Biological Flora of the British Great Western Road, S side. On 20/6/99 - 6 Isles. T. cordata Miller. Journal ofEcology 79, seedlings. 174-1207. 1 9 Victoria Circus. On 25/7/99 - 4 surviving ’99 seedlings. BT Linfern Entrance. On 1/8/99 - 10 surviving '99 seedlings. 10 Victoria Circus. On 1/8/99 - 8 surviving '99 seedlings. Marchmont Terrace. On 27/8/99 - 1 surviving '99 seedling. T. platyphyllos 16