Long-term effect of carbohydrate reserves on growth and reproduction of Prosopis denudans (Fabaceae): implications for conservation of woody perennials

Abstract

Prosopis denudans, an extreme xerophyte shrub, is consumed by ungulates and threatened by firewood gathering, because itis one of the preferred species used by Mapuche indigenous people of Patagonia. In a scenario of uncontrolled use of vegetation,it is very difficult to develop a conservation plan that jointly protects natural resources and its users. We performed a fieldexperiment to assess the impact of defoliation on growth, reproduction and stores of a wild population of P. denudans. Weimposed four levels of defoliation (removal of 100, 66, 33 and 0% of leaves) and evaluated the short- and long-term (3 years)effects of this disturbance. Seasonal changes in shoot carbohydrates suggested that they support leaf-flush and blooming.Severely defoliated individuals also used root reserves to support growth and leaf-flush after clipping. Vegetative growth wasnot affected by defoliation history. Leaf mass area increased after the initial clipping, suggesting the development of structuraldefenses. The depletion of root reserves at the end of the first year affected inflorescence production the followingspring. We conclude that P. denudans shrubs could lose up to one-third of their green tissues without affecting growth orinflorescence production. The removal of a higher proportion of leaves will diminish stores, which in turn, will reduce or completelyprevent blooming and, therefore, fruit production the following seasons. Very few studies integrate conservation andplant physiology, and we are not aware, so far, of any work dealing with long-term plant carbon economy of a long-livedperennial shrub as an applied tool in conservation. These results might help the development of management strategies thatconsider both the use and the conservation of wild populations of P. denudans.