El control ecológico de la floración

Global Ecology and Biogeography, (Global Ecol. Biogeogr.) (2004) 13 , 409–425

Blackwell Publishing, Ltd.

RESEARCH

PAPER

Environmental control of flowering

periodicity in Costa Rican and Mexican

tropical dry forests

Rolf Borchert†*, Stefanie A. Meyer‡, Richard S. Felger§ and

Luciana Porter-Bolland¶

† Division of Biological Sciences, University of

Kansas, Lawrence, KS 66045–7534, USA, ‡ Las

Delicias 11, Alamos, Sonora, Mexico, § Drylands

Institute, PMB 405, 2509 North Campbell

Avenue, Tucson, AZ 85719, USA, ¶ Instituto de

Ecología, A. C., Km. 2.5, Antigua Carretera a

Coatepec 351; C.P. 91070 Xalapa, Veracruz,

México. E-mail: borchert@ku.edu

ABSTRACT

Aim We analyse the proximate causes of the large variation in flowering periodicity

among four tropical dry forests (TDF) and ask whether climatic periodicity or biotic

interactions are the ultimate causes of flowering periodicity.

Location The four TDFs in Guanacaste (Costa Rica), Yucatan, Jalisco and Sonora

(Mexico) are characterized by a 5 –7 month long dry season and are located along a

gradient of increasing latitude (10–30 ° N).

Methods To dissect the differences in flowering periodicity observed at the com-

munity level, individual tree species were assigned to ‘flowering types’, i.e. groups of

species with characteristic flowering periods determined by similar combinations of

environmental flowering cues and vegetative phenology.

Results Large variation in the fraction of species and flowering types blooming

during the dry and wet season, respectively, indicates large differences in the severity

of seasonal drought among the four forests. In the dry upland forests of Jalisco,

flowering of leafless trees remains suppressed during severe seasonal drought and

is triggered by the first rains of the wet season. In the other forests, leaf shedding,

exceptional rainfall or increasing daylength cause flowering of many deciduous

species at various times during the dry season, well before the summer rains. The

fraction of deciduous species leafing out during the summer rains and flowering

when leafless during the dry season is largest in the Sonoran TDF.

Main conclusions In many wide-ranging species the phenotypic plasticity of

flowering periodicity is large. The distinct temporal separation of spring flowering

on leafless shoots and subsequent summer flushing represents a unique adaptation

of tree development to climates with a relatively short rainy season and a long dry

season. Seasonal variation in rainfall and soil water availability apparently con-

stitutes not only the proximate, but also the ultimate cause of flowering periodicity,

which is unlikely to have evolved in response to biotic adaptive pressures.

*Correspondence: Rolf Borchert, Division of

Biological Sciences, University of Kansas,

Lawrence, KS 66045-7534, USA.

E-mail: borchert@ku.edu

Keywords

Costa Rica, flower induction, flowering phenology, Mexico, photoperiodic control,

rainfall periodicity, tropical deciduous forest, tropical tree phenology.

Annual repetition of consecutive developmental stages, collec-

tively referred to as phenology, is a characteristic property of

trees as large perennial plants. Seasonal patterns of development

in forest trees, the dominant producers in terrestrial ecosystems,

have a major influence on animal populations and ecosystem

properties. In marked contrast to cold temperate trees, there is a

large diversity of phenological patterns among tree species of tropical dry forests (TDF) characterized by a 5–7 month long

dry season. Vegetative phenology varies with soil water avail-

ability during the dry season and ranges from evergreen species

at moist or riparian sites to deciduous species at dry upland

sites (Fig. 1a vs. 1d) (Borchert et al., 2002; Borchert, 1994a, 2003).

Most tree species flower and form new leaves during relatively

short periods (flushing), which vary among species of different

functional types (Fig. 1). Flushing may be induced by the first

heavy rains of the wet season (Fig. 1d), by leaf shedding during

© 2004 Blackwell Publishing Ltd www.blackwellpublishing.com/geb 409

INTRODUCTIONR. Borchert et al.

Figure 1 Vegetative and reproductive

phenology of tropical dry forest trees. (A–D)

Vegetative phenology in trees of different

functional types and flowering patterns

observed in different species during

specific phases of seasonal development.

(E) Annual variation in daylength and rainfall

in Guanacaste, Costa Rica; (F) Flowering types

with specific flowering periods caused

by different environmental signals.

(G) Flowering patterns observed in tropical

trees. Arrows indicate environmental causes of

vegetative phenology or flowering. Gradients

of grey tones represent increasing or

decreasing leaf area.

the dry season (Fig. 1a) or by increasing photoperiod after the

spring equinox (Fig. 1b,c) (Borchert & Rivera 2001; Rivera et al.

2002). With declining annual precipitation, the fraction of ever-

green species generally declines and forest physiognomy changes

from evergreen to semideciduous or deciduous (Woodward,

1987; Neilson, 1995).

Seasonal distribution of species-specific flowering periods

varies widely among five neotropical forests that are located

along a gradient of increasing latitude (Fig. 2). In the evergreen

wet forest at La Selva, Costa Rica, similar numbers of species

flower during most months, i.e. there is no distinct seasonal

variation in flowering periodicity at the community level (Fig. 2a).

With declining annual precipitation and increasing severity of

the dry season flowering periodicity becomes more distinct

(Fig. 2b,c). In the semideciduous forests of Guanacaste, Costa

Rica, and Yucatan, Mexico, about half of the tree species flower

during the wet and dry season, respectively (Fig. 2b,c) (Frankie

et al., 1974; Porter-Bolland, 2003). In contrast, very few species

bloom during the dry season in the deciduous forest of Jalisco

(Fig. 2d, Nov–May) (Bullock & Solis-Magallanes, 1990), but the

majority of species do so in the Sonoran TDF at the northern

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