# Sensitivity of Optical Satellites to Estimate Windthrow Tree-Mortality in a Central Amazon Forest
## 2 Materials and Methods  
### Study Area and Sampling Design  
This research was conducted in a remote old-growth forest located near Manaus, Brazil (2\({}^{\circ}\)53\({}^{\circ}\)41\({}^{\prime\prime}\)S, 60\({}^{\circ}\)16\({}^{\prime}\)26\({}^{\prime\prime}\)W). This forest was impacted by a convective storm that occurred in November 2015, which propagated destructive wind gusts and rain and caused widespread tree mortality across an area of \(\sim\)70 hectares (Figure 1a-c). The windthrown area is covered by a forest transitioning from _terra-firme_ (at the higher portions of the relief) to _campinarana_, such as described in adjacent areas [54; 55; 56; 57]. _Terra-firme_ is the most common upland forest type in the Amazon basin [58; 59]. The lower portions of valleys (regionally known as _baixios_) can be temporally flooded by relatively small streams [60]. The _terra-firme_ forests have a continuous canopy, dense understory, and high diversity of tree species [1; 61; 62; 63]. _Campinaranas_ are the predominant forest type that cover sandy soil patches with low nutrient content and poor drainage during the rainy season [64]. Compared to _terra-firme_ forests, _campinaranas_ have lower species richness and a distinct floristic composition due to their oligotrophic conditions [65]. In comparison to _terra-firme_, these forests usually have a decreased tree density, basal area, and biomass; shorter canopy; and are dominated by few tree species [55]. The transition between  
Figure 1: Windthrown forest located near Manaus, Central Amazon, Brazil (**a,b**), and inventory and virtual plots used to quantify tree mortality (**c–e**). Subfigures (**c,e**) are an RGB-composition from WorldView 2 image from 27 July 2016.  
terra-firme_ and _campinaranas_ can aggregate species from both environments, and thus produce relatively high species diversity--for instance, having between 63 to 137 species in a single hectare [54]. Our study site is located in a remote area not affected by previous human or other large-scale natural disturbances during the last several decades. The average annual temperature and precipitation in the region of Manaus (40 km from our study site) is 26.9 \(\pm\) 0.17 \({}^{\circ}\)C and 2.231 \(\pm\) 118 mm, respectively (mean \(\pm\) 95% confidence interval for the period of 1970-2016, [2]). This region has an evident dry season from July to September, with monthly precipitation usually being less than 100 mm [13; 16]. Soils on the plateaus have generally high clay content that transition to sandy soils in the lower portions [66; 67]. In general, the soils have low fertility, low pH, high aluminum concentration, and low organic carbon content [60]. The local relief in our study region is undulating, including plateaus, slopes, and small valleys associated with perennial drainages [60; 67]. To quantify windthrow tree-mortality in the field, we carried out a detailed forest inventory following a protocol built up from previous studies [1; 2; 13; 14; 23]. Following previous research conducted across different regions of the Amazon [1; 2; 4; 23], we selected areas spanning the entire gradient of tree mortality within the affected forest, which were inspected in the field and through previous assessments that were performed by following well-established protocols [1; 2]. Since this is a remote area for which no accessing infrastructure was available (e.g., roads and trails), our sampling also considered logistics limitations and the safety of our field crew. The forest inventory was performed over two campaigns conducted in December 2016 (\(\sim\)1 year after the windthrow) and April 2017 (\(\sim\)1.5 years after the windthrow). We established three 20 m \(\times\) 125 m transects, subdivided into 10 subplots of 10 m \(\times\) 25 m (250 m\({}^{2}\)) (total of 30 subplots, hereafter referred to as field subplots).