Vine species diversity across environmental gradients in northwestern Mexico

The presence of vines has been described as a distinctive feature of tropical forests. However, vine species diversity exhibits trends across environmental gradients that are not well documented. Here we use a latitudinal and a rainfall gradient along the Pacific slope of Mexico to explore the influence of environmental factors on vine species diversity. A total of 630 vine species were detected on the Pacific slope of Mexico. Tropical deciduous forest (TDF) floras were composed of greater percentages of vines (5-16%) than desert floras (1-3%). Four families (Convolvulaceae, Fabaceae, Cucurbitaceae and Asclepiadaceae) composed 40-60% of the vines of the region. Changes in vine composition were gradual along the Pacific slope. The percentage of vines in floras declines with latitude. Annual rainfall and the minimum temperature of January were significantly associated with the latitudinal decline in the percentage of vines. A total of 43 species, mostly herbaceous vines, were detected along a rainfall gradient in northwestern Mexico. Along the rainfall gradient, the number of vine species increased from 3 to 28 as summer rainfall, plant cover and canopy stature increased. Vine species richness and diversity increased from the desert to the TDF, especially along streams. Leaf area (LA) ranged from 0.6 to 284 cm(2) and specific leaf area (SLA) from 80 to 904 cm(2)/g among the most common vine species. Community averages of LA and SLA decreased toward drier sites. These results are discussed within the context of our current knowledge about the role of the environment in limiting the distribution of vines.