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Riegl, Bernhard ; Walentowitz, Anna J. ; Sevilla, Christian ; Chango, Rafael ; Jäger, Heinke:
Invasive blackberry outcompetes the endemic Galapagos tree daisy Scalesia pedunculata.
In: Ecological Applications.
(2023)
.
- e2846.
ISSN 1939-5582
DOI: https://doi.org/10.1002/eap.2846
Abstract
Island florae are under threat from habitat loss and competition with introduced speciesworldwide. In the Galapagos Islands, the endemic tree daisy Scalesia pedunculata(Asteraceae) is the dominant tree in the cloud forest of Santa Cruz Island but suffers from competition with the invasive blackberry Rubus niveus. At the site Los Gemelos, aS. pedunculatapopulation was monitored from 2014 to 2021 following mechanical and chemical removal of R. niveus from 17 plots and compared with 17 additional plots where R. niveus remained. The aim of this study was to evaluate the impacts of the R. niveus invasion on S. pedunculataby characterizing the effects of R. niveus removal. Parameters measured in S. pedunculatawere diameter at breast height (DBH, from which annual growth rates were determined), total height, survival of individual plants, and recruitment. In the presence of R. niveus, S. pedunculatatrees had smaller DBH stems and shorterasymptotic maximum heights, growth rates declined for thin trees, the mortality of larger trees was elevated, and S. pedunculata recruitment was absent. R. niveus removal resulted in DBH ratios of S. pedunculatamore frequently meeting our threshold for fast growth (1.2), trees growing significantly thicker and taller, annual mortality being lower (12.5 vs. 16.2% per year), and recruitment being successful. In the presence of R. niveus, lower survival, growth, and absent recruitment suggested that S. pedunculatacould reach quasi-extinction in ~20 years. Swift and decisive management action is needed to prevent the Scalesia forest on Santa Cruz Island from disappearing in less than two decades.