Applied Vegetation Science 2: 189-200, 1999 ? IAVS; Opulus Press Uppsala. Printed in Sweden 189 Quercus rugosa seedlingdynamics in relationto its re-introduction in a disturbed Mexican landscape Bonfil, C.1,3* & Sober6n, J.2 IFacultad de Ciencias, Universidad Nacional Aut6noma de Mixico, Mixico; 2lnstituto de Ecologia, Universidad Nacional Aut6noma de Mixico, A.P. 70-275, Mixico D.F. 04510; *Corresponding author; 3Present address:Centre de RecercaEcolbgica i Aplicacions Forestals, Facultat de Cikncies, Universitat Aut6noma de Barcelona,08193 Bellaterra, Barcelona, Spain; E-mail consuelo.bonfil@uab. es Abstract. In order to define the 'regeneration niche' andthen promote the re-introduction of Quercus rugosa into a dis- turbed area we studiedseed predation, germination, seedling survivaland growth of this species at threedifferentsites: the forest interior, the forest borderand a disturbed site, along a disturbance gradient. Acorn removal on the ground was high at the sites, with higher removal rates from 25-seed clusters thanfrom 5- and 1-seed clusters.More seeds were removedat the forest borderthan at the other two sites, although in all cases some seeds remained in the soil for periodslong enough for them to germinate and produceseedlings. Seed germina- tion and seedling establishmentwere more successful and similar in the forest interior and the forest border, and much less successful at the disturbed site, due to acorndesiccation. Seedling survival was strongly affected by site, with the highest survivalat the forestborder and the lowest survivalat the disturbed site aftera year. The subsequent dry season, which was particularly harsh, caused a drop in survival both at the forest border and the disturbedsite. In the former, a closer analysis revealed that partially shaded microsites enhanced survival, while in the latteroverall survivalwas very low, with approximately 5 % of the seedlings surviving, compared to 50 %final survival at the othersites. Therewas a positive correlation between seed size and seedling survivalat the forest border. The three size variables measured (seedlingheight, basaldiameter andcrown area) did not increase noticeably during the 20-month study period at the forest interior, while growth still occurred at the forest border and the disturbed site. However, during the two dry seasonsthere were largedrops in mean seedlingheight and crown areaat the disturbed site, due to more frequent dieback, causing large variation in seedling size. These results show that extensive re-introduction of this species to the disturbed area will probably fail under present conditions, and that careful selection or duplication of micrositesthat mimic the partial shadeof the forestborder is a sound methodfor improving oak establishment at this site. Keywords: Central Mexico; Herbivory; Oak regeneration; Resprouting; Seed predation; Seedling growth;Seedling sur- vival. Introduction Oaks are dominanttrees in many forests but their regeneration has often proved difficult (e.g. Carvell & Tyron 1961; Griffin 1971; Crow 1988; Lathrop & Osborne 1990). Mexico has a great diversity of Quercus species, (between 130 and 200 (Zavala 1990; Nixon 1993), many of which occupy areas particularly well suited to humansettlement and agriculture (Rzedowski 1981). On the lower parts of the hills surrounding the Mexico City basin Quercus forestsare disappearing at a high rate and those that remain suffer the impacts of increasing human disturbance (Ezcurra1990; Arag6n 1993). Very little is known about the ecology of these forests.In particular, we need to know the requirements for establishment and growth of the different Quercus species (Grubb 1977) in order to achieve successful re- introduction as part of ecological restoration programs in the disturbed areasthatare now under protection. Most studies concernedwith Quercusregeneration have been carried out on high-quality mesic sites in the United States and Europe (Shaw 1968; Crow 1988; Lorimeret al. 1994; Gardiner & Hodges 1998) while less attention has been paid to the ecology of seasonally dry oak forests, except for some mediterranean-type areas (Griffin 1971; Muick 1991; Callaway 1992; Espelta et al. 1995; Li & Romane 1997; Retana et al. 1999), and a few semi-arid species of North-America (Nyandiga & McPherson 1992; Germaine & McPherson 1998). Sea- sonally dry oak forests are important in Mexico, both regarding extension and biodiversity and their ecologi- cal significance for society. This study used an experimental approach to assess the establishment, survivaland growth of seedlings of Quercus rugosa at three different sites along an environ- mental gradient created by two disturbance events: (1) a natural disturbance (i.e. a lavaflow whichcovered an area of 80 km2 ca. 2000 yearsago) and (2) a recent temporary human settlement. Knowledge of seedling dynamics in these three contrasting patches will help to define 'safe