Mapping deciduous rubber plantations through integration of PALSAR and multi-temporal Landsat imagery Jinwei Dong a , Xiangming Xiao a, ⁎, Bangqian Chen b , Nathan Torbick c , Cui Jin a , Geli Zhang d , Chandrashekhar Biradar a a Department of Microbiology and Plant Biology, and Center for Spatial Analysis, University of Oklahoma, Norman, OK 73019, USA b Rubber Research Institute, Chinese Academy of Tropical Agricultural Sciences, Danzhou, Hainan, 571737, China c Applied Geosolutions, Durham, NH, 03857, USA d Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, 100101, China abstract article info Article history: Received 20 November 2012 Received in revised form 1 March 2013 Accepted 18 March 2013 Available online xxxx Keywords: Rubber (Hevea brasiliensis) plantation Phenology Hainan Island Landsat PALSAR Field Photo Library Due to increasing global demand for natural rubber products, rubber (Hevea brasiliensis) plantation expan- sion has occurred in many regions where it was originally considered unsuitable. However, accurate maps of rubber plantations are not available, which substantially constrain our understanding of the environmental and socioeconomic impacts of rubber plantation expansion. In this study we developed a simple algorithm for accurate mapping of rubber plantations in northern tropical regions, by combining a forest map derived from microwave data and unique phenological characteristics of rubber trees observed from multi- temporal Landsat imagery. Phenology of rubber trees and natural evergreen forests in Hainan Island, China, was evaluated using eighteen Landsat TM/ETM+ images between 2007 and 2012. Temporal profiles of the Normalized Difference Vegetation Index (NDVI), Enhanced Vegetation Index (EVI), Land Surface Water Index (LSWI), and near-infrared (NIR) reflectance for rubber trees and natural forest were constructed. The results showed that rubber plantations are distinguishable from natural evergreen forests in two phenolog- ical phases: 1) during the defoliation (leaf-off) phase in late February–March, vegetation index (NDVI, EVI, LSWI) values were lower in rubber plantations than in natural evergreen forests; and 2) during the foliation (new leaf emergence) phase in late March–April, rubber plantations had similar NDVI and LSWI values but higher EVI and NIR reflectance values than in natural forests. Therefore, it is possible to delineate rubber plan- tations within forested landscapes using one to two optical images acquired in the defoliation and/or foliation period. The mapping technique was developed and applied in the Danzhou Region of Hainan. Phased Array type L-band Synthetic Aperture Radar (PALSAR) 50-m Orthorectified Mosaic images were used to generate a forest cover map and further integrated with the phenological information of rubber plantations extracted from Landsat TM images during the foliation phase. The resultant map of rubber plantations has high accu- racy (both producer's and user's accuracy is 96%). This simple and integrated algorithm has the potential to improve mapping of rubber plantations at the regional scale. This study also shows the value of time series Landsat images and emphasizes imagery selection at appropriate phenological phase for land cover classifi- cation, especially for delineating deciduous vegetation. © 2013 Elsevier Inc. All rights reserved. 1. Introduction Plantation development by the agroforestry industry, such as the expansion of Pará rubber tree (Hevea brasiliensis) plantations, has been a critical driver of land cover change around the world, particu- larly in the tropics. The Food and Agriculture Organization (FAO) of the United Nations Global Forest Resources Assessment (FRA) 2010 reported that globally rubber plantation extent has steadily increased by 25% during the past two decades (FAO, 2010). Approximately 97% of global natural rubber supply comes from Southeast Asia (Li & Fox, 2012). This land use is a primary driving factor for the conversion from swidden to monocultural cash plantations in montane areas of mainland Southeast Asia (Fox & Vogler, 2005). This land use change process has both economic and environmental outcomes. On the one hand, local farmers can improve financial stability as rubber plantations provide greater agricultural profit due to the increased demand for rubber products. Further, rubber plantations tend to have greater agricultural resiliency compared to traditional cash crops that are more stressed by adverse weather. On the other hand, the Remote Sensing of Environment 134 (2013) 392–402 ⁎ Corresponding author at: Department of Microbiology and Plant Biology, and Center for Spatial Analysis, University of Oklahoma, 101 David L. Boren Blvd. Norman, OK 73019, USA. Tel.: +1 405 325 8941. E-mail address: xiangming.xiao@ou.edu (X. Xiao). 0034-4257/$ – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.rse.2013.03.014 Contents lists available at SciVerse ScienceDirect Remote Sensing of Environment journal homepage: www.elsevier.com/locate/rse