AOBPreview originally published online on July 18, 2003
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Annals of Botany 92: 365-375, 2003
© 2003 Annals of Botany Company
Growth and Architecture of Small Honey Mesquites under Jackrabbit Browsing: Overcoming the Disadvantage of being Eaten
1 Laboratorio de Ecología del Comportamiento, Centro de Investigaciones Fisiológicas, Universidad Autónoma de Tlaxcala, carr. Tlaxcala-Puebla km 1·5 s/n Tlaxcala,Tlaxcala 90070 Tlaxcala, México and 2 Instituto de Ecología, AC Departamento de Ecología Vegetal, Apartado Postal 63 Xalapa 91000 Veracruz, México
* For correspondence. Fax (228) 8187809, e-mail lopez-p{at}ecologia.edu.mx
Received: 21 October 2002; Returned for revision: 1 April 2003; Accepted: 20 May 2003 Published electronically: 18 July 2003
Browsing is an important mortality factor in seedlings and small plants. However, the induced changes in the architecture of plant survivors may influence subsequent browsing, opening the possibility of compensating for the damage done. How jackrabbit (Lepus californicus) browsing affects the growth and architecture of small individuals of honey mesquite, Prosopis glandulosa var. torreyana, a tree/shrub that produces spines at every node, was explored. Naturally established mesquites of unknown age were selected in one site, and 2-year-old mesquites were transplanted in another site. In both cases, half of them were exposed to jackrabbits and the other half were excluded as controls. After 4 years, shoot production (height, length and number of derived shoots) and plant growth (height and cover) increased 1·4–2·5-fold in naturally established controls relative to exposed plants, depending on the measured variable. In the transplant experiment, the increases were 2·8–7·1-fold in controls relative to exposed plants 2 years after initiation of the experiment. The net loss of biomass in treatment vs. control plants in these experiments suggests a negative response to browsing which has been defined as under-compensation. Alternative architectures in honey mesquites were evident at the end of the exclusion experiments: controls had long branches and an extended crown cover, while exposed plants had short branches and a compact crown cover. Results indicated that mesquites were able to grow under browser pressure by packing many stems in a compact matrix armed with spines and producing one or more shoots tall and wide enough to escape from jackrabbits.
Key words: Exclusion treatments, honey mesquite, jackrabbit browsing, Lepus californicus, spines as mechanical defences, plant architecture and growth, Prosopis glandulosa var. torreyana, semi-arid communities, stem modular demography.
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