Do Polylepis australis trees tolerate herbivory? Seasonal patterns of biomass production and its consumption by livestock

GIORGIS, M. A., CINGOLANI, A.M., TEICH, I., & RENISON, R.

PLANT ECOLOGY

SPRINGER

Año: 2010 vol. 207 p. 307 - 319

1385-0237

Browsing is one of the main factorsdetermining survival, growth rate, woodland structure,and distribution of the high mountain tree Polylepisaustralis. This species has a substantial regrowthcapacity, which may function as a mechanism totolerate herbivory, but it is unknown to what extent itmay compensate for the impact of herbivory. In 15low-density tree stands subject to exclusion, moderate,and heavy livestock pressure, we selected 12 P. australisindividuals\2 mtall, tagged four new shoots pertree and measured shoot length every month during ayear. At the stand and at the tree level, we analyzedmonthly dynamics of growth and browsing, and theannual output in terms of total browsing and total grossand net growth (not discounting and discountingconsumption, respectively). In addition, we assessedthe influence of stand, tree and microsite characteristicson growth and browsing patterns. Polylepisaustralis fully compensated for herbivory in terms ofshoot gross growth at moderate, but not at heavylivestock pressure. In terms of net growth, this speciesdid not fully compensate for herbivory at any stockingrate. We found a strong coupling between browsingand growth along the year, suggesting that regrowthattracts browsing, and browsing promotes regrowth. Atthe stand level, annual gross growth was not affectedby habitat characteristics, while at the tree level, annualgross growth decreased on more rocky microsites forbrowsed but not for unbrowsed trees. We concludedthat stocking densities should be limited to allow for areasonable annual net growth, as its nitrogen richleaves are a valuable food resource and P. australisforests provide important ecosystem services.