Understanding the constraints on sexual reproduction of a plant species are important for predicting stability of the species in its natural habitat. In the absence of such data, any conservation efforts are arbitrary and remain ineffective. We investigated the reproductive ecology and breeding system of a rare and threatened tree species of central and western Himalaya, Ulmus wallichiana. The phenology, floral biology and pollination mechanism were observed in two populations for three consecutive years. In addition, breeding system and pollen limitation were examined using hand-pollination experiments. Flowering in U. wallichiana begins in early March during which trees are leafless and small, pinkish-white flowers cover the entire tree. Pollination is accomplished exclusively by wind with short average distances for pollen dispersal (~50 m). Pollination manipulation experiments showed high fruit set on outcrossing indicating U. wallichiana is xenogamous. However, a small percent of fruit set in autogamous and geitonogamous treatments indicates partial self-incompatibility. Fruit set augmented when pollen was supplemented indicating that natural fruit set in U. wallichiana is limited due to unavailability of adequate pollen. Thus, it can be concluded that reproductive success of U. wallichiana is compromised due to scarcity of conspecifics and partial SI may partly ensure reproductive assurance in the low pollen exchange environment. The present study emphasizes on establishment of minimum population size with optimum distance between trees for effective conservation interventions.

中文翻译：

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喜马拉雅中西部珍稀濒危树种Ulmus wallichiana Planchon (Ulmaceae)的授粉生物学及育种系统分析

了解植物物种有性繁殖的限制对于预测物种在其自然栖息地的稳定性很重要。在缺乏此类数据的情况下，任何保护工作都是武断的并且仍然无效。我们调查了喜马拉雅中西部珍稀濒危树种Ulmus wallichiana的生殖生态和繁殖系统。连续三年在两个种群中观察了物候、花生物学和授粉机制。此外，使用手工授粉实验检查了育种系统和花粉限制。开花在U. wallichiana开始于三月初，在此期间树木无叶，粉白色的小花覆盖整棵树。授粉完全由风完成，花粉传播的平均距离很短（~50 m）。授粉操作实验显示异交时坐果率高，表明U. wallichiana是异种的。然而，在自交和异性交配处理中的一小部分坐果表明部分自交不亲和。当补充花粉时坐果增加，表明由于没有足够的花粉，U. wallichiana 的自然坐果是有限的。因此，可以得出结论，U. wallichiana 的繁殖成功由于同种的稀缺性而受到损害，部分 SI 可能部分确保低花粉交换环境中的生殖保证。本研究强调建立最小种群规模和最佳树木之间的距离，以进行有效的保护干预。