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RESUMENE n los sistemas silvopastoriles, las leguminosas arbustivas de alta calidad nutricional representan una alternativa para la escasez de pastos en periodos secos del año. En este estudio se evaluó el efecto de diferentes edades de rebrote (6, 9, 12 y 15 semanas) en tres épocas del año (lluvia, invierno y seca, 2007-2008) de cuatro accesiones de Cratylia argentea (18516, 18666, 18668 y 18676) en Veracruz, México, para el rendimiento de materia seca (RMS), fibra en detergente neutro (FDN), fibra en detergente ácido (FDA), lignina (Lig), proteína cruda (PC) y degradación in situ de MS (DISMS). El rendimiento de materia seca (RMS) (media ± error estándar) fue afectado por la época y la edad de rebrote, pero no se encontró efecto por la accesión o sus interacciones. El mayor RMS se logró en la temporada de secas (3632 ± 306 kg·ha -1 ), lo que representó 45 % del rendimiento del forraje total, seguido por la temporada de lluvias (33 %, 2615 ± 188 kg·ha -1 ) y la temporada de invierno (22 %, 1733 ± 61 kg·ha -1 ). Se encontraron efectos significativos en la edad de rebrote en las tres épocas para FDN, FDA, Lig y PC. La mayor DISMS ocurrió en las temporadas de lluvias y secas promediando 66 y 65 %, respectivamente, después de 72 h de incubación. La temporada de secas fue el mejor período para RMS y DISMS. Estos resultados sugieren que C. argentea es una fuente confiable de forraje para sistemas silvopastoriles. ABSTRACTI n silvopastoral systems, high nutritional quality shrub legumes represent an alternative to shortage of grasses in dry periods of the year. The effect of different regrowth ages (6, 9, 12 and 15 weeks) in three climatic seasons (rainy, winter and dry seasons, 2007-2008) of four Cratylia argentea accessions (18516, 18666, 18668 and 18676) were evaluated in Veracruz, Mexico, for dry matter yield (DMY), neutral detergent fiber (NDF), acid detergent fiber (ADF), lignin (Lig), crude protein (CP) and in situ DM degradation (ISDMD). Dry matter yield (mean ± standard error) was affected by season and regrowth age, but not by accession or interactions. The dry season showed the largest DMY (3632 ± 306 kg·ha -1 ), representing 45 % of total forage yield, followed by the rainy (33 %, 2615±188 kg·ha -1 ) and winter (22 %; 1733 ± 61 kg·ha -1 ) seasons. For NDF, ADF, Lig and CP, statistical effects were found for regrowth age in all three seasons. The largest ISDMD occurred in the rainy and dry seasons, reaching average values of 66 and 65 % at 72 h of incubation, respectively. The dry season was the best period for DMY and ISDMD, making Cratylia argentea a reliable feed resource for silvopastoral systems.

Stocking rate manipulation was examined as a means of improving plant diversity (as a measure of pasture sustainability and forage value) in a native grass pasture used for dairy production in the humid tropics of Veracruz, Mexico. Given that environmental impact reduces biotic diversity, plant phylogenetic and functional diversity should decline with increased stocking rate. Stocking rates of 2, 3, and 4 cows Á ha À1 and a rotational grazing plan of 3 d of occupation and 27 d of rest per pasture were applied continuously over 5 yr. Across 200 quadrats in each of two replicate paddocks per treatment, observed species richness, phylogenetic diversity (average taxonomic distinctness based on species presence/absence), and functional diversity (life-cycle duration and growth habit) were assessed. Most species were forb/herbs and forb/herb-subshrubs. Perennial species declined with increased stocking rate (F¼16.36, 0.05. P. 0.02) while annual-perennial species increased (F¼76.88, 0.01. P. 0.005); the proportion of annual species was least prominent and did not differ significantly. Observed species richness and phylogenetic diversity did not differ significantly with stocking rate. The correlation between functional diversity for life-cycle duration and phylogenetic diversity was significant and positive, suggesting that plant communities were predominantly assembled randomly from the surrounding species pool rather than through interspecies interactions acting to naturally filter immigrant species, thus leading to more opportunistic and undesired species. Although grazing pressure was not sufficient to alter indices or production measures, they did reveal shifts that may precede further pasture decline, indicating pasture sustainability was not being achieved. These rapid assessment methods permit monitoring for early warnings of reductions in pasture sustainability and forage quality for cattle.

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