PARENT SESSION
Oral Session #48: Vegetation Change and Response.
Presiding: D. Zobel
Tuesday, August 6. 1:00 PM to 4:45 PM. Mesquite Room, Radisson.

Study of seedling establishment in shrubland communities in southern Chihuahua, Mexico.

FLORES-FLORES, JOSE^*,1, YEATON, RICHARD², GARCIA-MOYA, EDMUNDO³, ¹ INSTITUTO POTOSINO DE INVESTIGACION CIENTIFICA Y TECNOLOGICA, SAN LUIS POTOSI, SAN LUIS POTOSI, MEXICO² UNIVERSIDAD AUTONOMA DE SAN LUIS POTOSI, SAN LUIS POTOSI, SAN LUIS POTOSI, MEXICO³ COLEGIO DE POSTGRADUADOS, TEXCOCO, EDO. MEXICO, MEXICO

ABSTRACT- Biotic and abiotic factors both play an important role during seedling establishment of enchroaching shrubs in grasslands. In the past, mostly the effects of abiotic site characteristics have been studied in the context with seedling establishment, while less attention has been paid to effects of biotic risks such as herbivory or ant shoot cutting. We compared the ability of three woody species, Prosopis laevigata, Acacia schaffneri, and Yucca decipiens, to establish in two grassland types differing in successional stage in the southern Chihuahuan Desert, central Mexico. In an abandoned field, we monitored seedling establishment on three microsites, open areas, near ant nests, and nutrient rich patches. In shrub-grass communities, we evaluated, how canopies of native woody species, Larrea tridentata, Prosopis laevigata, Acacia schaffneri and Yucca decipiens could potentially benefit seedling establishment. On each microsite, 25 one-year-old seedlings of each species were transplanted. Seedling damage, survival and growth were recorded biweekly. The effect of biotic risk was inferred from survival of damaged seedlings on each site after 6 months. Site quality for shrub establishment was inferred from height data. Seedlings of Prosopis developed best on nutrient rich patches, however they were severely damaged by ants, rodents and lagomorphs. Acacia established best in shaded conditions, but was also vulnerable to biotic damage. The seedlings of Yucca were least affected by ants and were most resisted to predation. Even though there was a clear difference between species in respect to survival to biotic risks after one year, a severe drought in the following year killed all seedlings. Our results suggest that long-term studies need to be conducted to characterize the effects of biotic and abiotic effects on seedling establishment.

KEY WORDS: SEEDLING ESTABLISHMENT, CHUHUAHUAN DESERT, MEXICO, ACACIA SCHAFFNERI, PROSOPIS LAEVIGATA