Satellite-Based Monitoring of Primary Production in a Mediterranean Islet Post Black Rat Eradication

Miguel Ibañez-Álvarez,Niall G Burnside,Carlos Rouco,Jordi Bartolomé,Juan Antonio Calleja,Elena Baraza,Emmanuel Serrano,Pol Farràs Santasusana,Matthew Brolly

doi:10.3390/rs14010101

Abstract

Invasive rodents have a detrimental impact on terrestrial ecosystem functioning, this is often exacerbated on small islands. Rat eradication campaigns are often used to deal with this environmental perturbation given their classification as invasive species. Studies assessing the effects of rodent control at ecosystem scale are scarce and thus little is known about the subsequent functional response of vegetation subsequent to rat control. In this work, we use remote sensing to assess the effects of black rat (Rattus rattus) eradication on Mediterranean vegetation productivity in the Sa Dragonera Islet, Mallorca (Spain). Rats feed on seeds, sprouts, and leaves of woody vegetation and hence we expect primary production to increase nine years after the rodenticide campaign. The Break Detection approach for additive season and trend (BFAST method) was adopted to examine changes in vegetation density before and after the eradication campaign in Sa Dragonera Islet (Balearic Islands), using a temporal series of monthly NDVI data extracted from Landsat imagery. The same temporal trends were examined for a control zone where no rat eradication took place, in order to control for weather-driven changes. The results of this study revealed changes across the 21-year monthly NDVI time series. However, the dates, magnitude, and trend of these changes could not be explicitly attributed to the action of rats, when compared to the historical changes on the islet and the changes found to co-occur within the control zone. These finding could, perhaps, be explained by the high resilience of Mediterranean shrubs to browsing including that of rat invasion. However, the results from the study appear to show that rat damage on specific plant species, with little contribution to global NDVI values, would be overshadowed by the effects of broader environmental factors in this remote sensing approach. The results suggest that the current passive restoration scheme imposed following eradication is not sufficient for effective ecosystem restoration.

Highlights

Invasive alien species (IAS) are those that have reached new geographic areas by way of human introduction, and are populations which can survive, reproduce and spread over the natural environment leading to major impacts on the environment or society [1]
This study is the first of its kind to examine the effectiveness of remote sensing and BFAST timeseries analysis in island ecosystems post black rat eradication
To interpret the changes found, a 21year time series of NDVI data extracted from satellite images was analyzed and compared with hydrological data, which was found to be the likely driver of NDVI changes in water limited environments as is the case for our study area

Summary

Introduction

Invasive alien species (IAS) are those that have reached new geographic areas by way of human introduction, and are populations which can survive, reproduce and spread over the natural environment leading to major impacts on the environment or society [1]. IAS can cause serious disturbance to other indigenous species and the ecosystems they invade, Remote Sens. In particular, the black rat (Rattus rattus), brown rat (R. norvegicus) and Pacific rat (R. exulans) [7,8,9]. Records of black rat density are highly variable ranging from 36.4 rats ha−1 in New Zealand islands [15], to 50 rats ha− 1 in some Mediterranean islands [17]. In the Mediterranean basin the black rat is the most invasive species due to its broad tolerance to dry climates [18,19]

Methods

Findings

Discussion

Conclusion