**3.1. Sampling process**

Band10 Band9 753.75 708.75 Band9 Band8 708.75 681.25

where *R*753.75, *R*708.75, and *R*681.25 are the MERIS reflectance at wavelength 753.75, 708.75, and

**Figure 1** illustrates the global (Level 3) MERIS terrestrial chlorophyll index (MTCI) estimated at 31 May 2011. Highest MTCI values are located in the tropical forest biomes around the world.

The red-edge position is a unique feature of green plants related to leaf chlorophyll content and to LAI. REP is defined as the inflection point (or sharp change) of the low red reflectance caused by chlorophyll absorption near 680 nm and high infrared reflectance governed by the internal structure of leaves near 750 nm [51]. REP has been used as an indicator of chlorophyll content in vegetation, as increasing chlorophyll content implies an enlargement of the chlorophyll absorption peak: this moves the red-edge to longer wavelengths while a decrease in chlorophyll shifts the red-edge toward shorter wavelengths [12]. However, the REP has been reported not to be an accurate indicator of chlorophyll content in vegetated areas showing high chlorophyll content values because of the asymptotic relationship between REP and chloro-

Several methods have been proposed to estimate REP from spectral data coming from field and satellite sensors. Dawson and Curran [54] developed a three-point Lagrangian interpolation technique, but this method has shown some problems when the reflectance spectrum exhibits more than one maximum in its first derivative [51]. Another method was developed by Guyot and Baret [55], which applies a linear model to the red-NIR slope. This method has been reported to be robust when it was applied to various datasets [11]. A third method identifies the red-edge inflection point as the maximum of a curve fitted to the first derivative of the reflectance spectrum. This method has been closely related to chlorophyll content per unit area at leaf and canopy level [56] and has shown sensitivity to detect vegetation stress by

Fieldwork was undertaken from April to Jul 2012 at three sites in the Amazon tropical rainforest of Ecuador (**Figure 1**). The first and second study sites are located in a lowland evergreen secondary forest in Sucumbios province, Tarapoa region (0°11' S, 76°20' W). Site 1 has a history of petroleum pollution during the last decades. Mean annual rainfall is 3800 mm and the average annual temperature is 23°C with relative humidity close to 90% [58]. The area is located at 232–238 m above mean sea level. The third study site is a highly diverse lowland evergreen primary forest located in the Orellana province, in the northern section of Yasuní National Park (0°41' S, 76°24' W). The area lies 216–248 m above mean sea level and receives

*RR RR* (1)


56 Tropical Forests - The Challenges of Maintaining Ecosystem Services while Managing the Landscape

681.25 nm, respectively.

phyll content [52, 53].

quantifying changes in chlorophyll content [57].

**3. Materials and methods**

**2.5. The red-edge position (REP)**

Well-developed branches were carefully selected and collected by using a telescopic pruner, tree-climbing techniques, and canopy towers at different levels of the vertical profile of the forest (**Figure 2**). The collected branches were sealed in large polyethylene bags to maintain their moisture content and stored in ice coolers. The foliar material was transported to a local site, and fully expanded mature leaves with no damage by herbivores or pathogens were selected for analysis. A total of 1134 samples were collected in the three fieldwork sites. The sampling process accounted for three levels of the vertical profile and included a wide range

**Figure 2.** Map of the study area—north-east Amazon region of Ecuador. Site 1 and Site 2 are located in Sucumbios province and Site 3 is located in Orellana province. Background is a Landsat image. Source of zoom-in map: Color shaded relief image, WorldSat International, Inc.

of vegetation heterogeneity related to species distribution, phenological stage, and leaf structure. (Detailed information about the sampled process can be found in Ref. [62].)

### **3.2. Chlorophyll meter readings**

Depending on the size and shape of the leaf, different cork borers of variable size between 2.5 and 8.5 cm diameter were used to clip a leaf disk from the central and widest portion of the leaf blade, avoiding the major veins (**Figure 3**).

**Figure 3.** Photographs of leaf sampling process. (a) Collecting leaves using the telescopic pruner (b) climbing trees (c) telescopic pruner 9 m long (d) climbing trees techniques and (e) canopy towers in the study area.

All leaf disks were clipped from the midpoint of the leaves since it has been documented that it is the best position from which to take chlorophyll readings [37]. Three readings were taken from each disk using a portable SPAD-502 chlorophyll meter at different positions of each leaf disk, and a mean index value was used in further analysis.
