Grazing exclosure increases fruit and seed production but reduces seed viability in Myrtus communis
Plants have compensating mechanisms to alleviate the loss of vegetative and reproductive tissues by herbivores. In this study, we evaluated how reproductive traits (size and production of fruit and seed, as well as germination and viability of seeds) of Myrtus communis (myrtle) were affected by goat grazing exclosure of forest understory in the Doñana Natural Park. One hundred and fifty myrtles were selected in three sites with similar environmental characteristics, although with a different length of grazing exclusion: (1) exclosure for 2 years (GE2); (2) exclosure for 3 years (GE3); and (3) long ago grazed plots (GE15): non-accessible to goat for at least 15 years. Fruit production, fruit and seed morphology and seed viability and germination were evaluated. Length of exclosure to goats increased fruit production, mass and volume of the fruits and seed, and endocarp mass. However, seed viability was higher in more recently grazed plots (70–90%) than in GE15 plots (51%). The final balance of viable/germinable seeds produced by an average sized myrtle in each treatment showed that the recently grazed myrtles (GE2) produced nearly five times less seeds (1200) than the myrtles grazed 15 years ago (5500). However, myrtles recovered the ability to produce viable seeds quickly, almost tripling, each year of non-grazing the number of viable/germinable seeds. The results of this study indicated that goat grazing could affect regeneration of myrtle because it reduced reproduction output and the number of viable propagules. Future studies should evaluate other related ecological aspects, such as fruit consumption by potential frugivores and seed dispersal (distance and place of seed deposition).
KeywordsDoñana Fruit Goats Viability Germination
We thank the management of the Doñana National Park and Dehesa de Gatos S.L. for their helpful support. This study was funded by the Consejería de Medio Ambiente (Junta de Andalucía) (OG-052/07). We also thank Dra. Rocío Fernández-Ales and Sandra Astorga for their useful comments on the earlier version of this manuscript. The authors wish to thank the Associate Editor and anonymous referees for their useful suggestions, which led the revision. Mr. I. Knutson revised the English version of the manuscript. J.M. Mancilla-Leytón acknowledge the receipt of a Postdoctoral Research Contract (V Plan Propio de Investigación de la Universidad de Sevilla, Ref. II.5.B/2015).
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