Integrating the Aerial Photos and DTM to Estimate the Area and Niche of Arundo formosana in Jiou-Jiou Peaks Natural Reserve of Taiwan

Jeng-I Tsai and Fong-Long Feng

Abstract Earthquakes and typhoons have affected land use and land cover (LU/LC) in Taiwan, but an endemic grass, Arundo formosana, remains widely distributed. However, we lack knowledge about the niche of A. formosana. The purpose of this study was to estimate the area of A. formosana distribution by using scientific evidence and to describe its niche. In 2000, the Jiou-Jiou Peaks Natural Reserve was reported to be used to protect the unusual topography and complex biodiversity in the region. Several vegetation types can no longer grow in this region because of natural disturbances. However, A. formosana is able to grow. Because of the abundant roots and foliage of A. formosana, erosion is reduced. A. formosana can hang downward and thrive in crevices and cliffs, so its niche area might be underestimated if researchers ignored this characteristic. Today, most remote sensing images are two dimensional (2D), and sometimes 2D spatial information is insufficient to explain all natural phenomena. Therefore, we integrated ortho-aerial photographs and the digital terrain model (DTM) to estimate and analyze the niche area of A. formosana. The results indicated that the niche area of the species increased from 26.34 % to 32.86 % after the slope factor was considered. The results also exhibited that surfaces facing northeast, east, south, and southeast from 22.5° to 202.5° were more suitable for the growth of A. formosana. The slopes of the surfaces with A. formosana growth ranged from 0.00° to 81.82°, with an average of 53.99° ± 13.45°; slopes of 74° to 78° were the most suitable for A. formosana growth. The steeper peaks

J.-I Tsai

Department of Forestry, Graduate Student, National Chung Hsing University, 250, Kuo Kuang Rd, Taichung 402, Taiwan, R. O.C e-mail: d9833003@mail. nchu. edu. tw

F.-L. Feng (*)

Professor, Department of Forestry, National Chung Hsing University,

250, Kuo Kuang Rd, Taichung 402, Taiwan, R. O.C. e-mail: flfeng@nchu. edu. tw

N. Nakagoshi and J. A. Mabuhay (eds.), Designing Low Carbon Societies in Landscapes, Ecological Research Monographs, DOI 10.1007/978-4-431-54819-5_18, © Springer Japan 2014

(steeper than 79°) were still covered with bare soil. This niche information could provide land managers with valuable information for water and soil conservation and eco-technology.

Keywords Arundo formosana • DTM • Ortho-aerial photographs • Jiou-Jiou Peaks Natural Reserve • Niche

18.1 Introduction

The 921 (Chi-Chi) earthquake occurred in the Chi-Chi and the Sun Moon Lake area on the morning of 21 September 1999. It was a serious disturbance, with a magnitude of 7.3 on the Richter scale, and caused severe casualties and damage in Taiwan. The Jiou-Jiou Peaks area was one of the most seriously affected areas. Lin et al. (2001) indicated that the loose, unstable ground and the stones that had accumulated on the surface of the slopes were responsible for the occurrence of expanding mudflows and landslides during rainy seasons. Moreover, the amount of water retained in the soil for plants was critical for the recovery of vegetation in this area (Lin et al. 2005). The landscape still changes at the inner sides and outer edges of terraces every year (Chang 2000). According to data of Nantou Forest District Office in 2004, the vegetational composition differed before and after earthquake. Distinct types of pioneer species cover the landslides area of the Jiou-Jiou peaks, and Arundo formosana grows best in steeper slopes (Nantou Forest District Office 2004).

Arundo formosana (Formosan giant reed, pendent reed, Tagai, and Gaogan; called A. formosana later) is a grass endemic to Taiwan and an evergreen perennial herb. A. formosana is also considered a rock plant that can hang downward and thrive in rock crevices and cliffs. Because its seeds are small, light, and can float in the wind, the species is widely distributed in low altitudes in Taiwan [below 1,800 m mean sea level (MSL)], Lanyu, and Lutao. The reed is a high-pulp material, and the roots and stems are often used in the manufacture of handicrafts and baskets. The soil conservation capacity of A. formosana is an important function in preservation of the ecosystem and topography. We lacked information about the niche (ecological site) of this species and have tried to understand it. A researcher might underestimate the niche area of a rock plant because the plant can grow on steep slopes. For this reason, ortho-aerial photographs (spatial resolution, 0.25 m x 0.25 m) and a digital terrain model (DTM; 5 m x 5 m) were integrated in this study to analyze the distribution and niche of A. formosana. Field survey data were also collected for accurate assessment of image classification and identification.