Does functional redundancy exist in terrestrial plant communities? Results from a removal experiment in central Argentina

GURVICH DE, DÍAZ S, URCELAY C, CHAPIN FS III, CUEVAS E, PÉREZ HARGUINDEGUY N, CABIDO M.

Oaxaca

Conferencia; DIVERSITAS Open Science Conference; 2005

DIVERSITAS

According to the hypotheses of functional redundancy and compensation, diversity provides an insurance against local species extinctions. We tested this hypothesis in a mountain shrubland ecosystem in central Argentina. We removed either the dominant species of dominant plant functional type (PFT) or the whole PFT. We predicted that when removing the dominant species, subordinate species of the same PFT should compensate for this loss. The removal of whole PFTs, should not lead to functional compensation, because different PFTs should have different effects on ecosystem processes. The experiment consisted in: a) 4 removal treatments where whole PFTs were removed (deciduous shrubs, graminoids, perennial, and annual forbs), 2) 4 treatments where the dominant species of each PFT were removed (Acacia caven, Stipa eriostachya, Hyptis mutabilis y Bidens pilosa, respectively), and 3) an intact control and a disturbed control. We measured the number and abundance of each species and : Leaf Area Index, soil available ammonium, nitrate and phosphate, decomposition of standard materials and litter mixtures, and soil temperature. After 3 years from the beginning of the experiment we found evidences of compensation in abundance. Only when Acacia and Stipa were removed, species of the corresponding PFTs increased their abundance, suggesting abundance compensation. However, there was no sign of abundance compensation in the case of perennial or annual forbs. Although the removal treatments affected the indicators of ecosystem processes (soil temperature increased when the deciduous shrubs or Acacia were removed, and soil nitrate decreased when the deciduous shrubs, Acacia or the perennial forbs were removed), we did not find evidence of functional compensation. Our 3-year results challenge the relevance of the redundancy and functional compensation hypotheses in ecosystems dominated by terrestrial vascular plants.