Factors influencing recruitment of honey mesquite Prosopis glandulosa var. glandulosa in a savanna woodland, Texas.

摘要

Pod production by Prosopis tree populations increased with removal of understory woody vegetation both in upland and drainage habitats. Pod production appears to be inversely related to annual rainfall and was observed to attain highest levels in the driest years. There appeared to be a significant interaction between pod production and level of competition from subordinate shrubs. In years of high rainfall, pod production was low regardless of competition; in years of low rainfall pod production was significantly stimulated, but only for plants experiencing reduced competition. Prosopis trees with intact understory shrubs in upland habitats supplied with phosphorous fertilizer produced pods with comparable density and attributes to non fertilized populations with cleared understory and continued to produce pods even when the former had no obvious pod production.;Of the seed ingested by cattle, 53% were lost through mastication and digestion, 13% were excreted as non viable, 14% as germinable in moist dung with almost no chance of survival, and 20% as viable hard seed which have a potential of contributing to recruitment following dung decomposition.;Rodent were by far more important than birds and ants in utilizing of Prosopis pods and seeds. Moon light increased rodents efficacy in locating and harvesting pods and seed at all locations. Probabilities for a seed or a pod to escape predation increased with increasing distance from clusters perimeter. Rodents and birds significantly preferred Prosopis and Celtis seed to seed of other associated shrubs, whereas ants preferred seed of Zanthoxylum, Celtis and Condalia to seed of Prosopis.;More seedlings emerged in herbaceous zones away from parent trees than within clusters. Their number as well as their duration of survival increased with increasing distance from parents. The data indicated that this gradient of success at the seedling stage is not attributable to seed availability, seedling predation, soil properties or moisture along the cluster center-to-herbaceous zone gradient. It is more likely the result of light gradient and possibly the underground interference from parents and associated shrubs appear to be the prominent factors controlling this pattern. This implications of the above for Prosopis population biology and dynamics within the Southern Texas Plains are discussed.