## 1 Introduction
To explore the influence of changing ground surface moisture conditions on observed VI changes, Land Surface Temperature (LST) trends have been used as a proxy for changing soil saturation (comparatively cool) or dryness (comparatively warm) [39; 40; 41; 42; 43; 44; 45]. While radar-based remote sensing techniques are capable of estimating soil moisture [46], their applicability is often limited by inconsistent spatial and temporal coverage, particularly in large-scale or long-term studies [47]. The over-arching goal of this study is to identify any landcovers and associated ecotonal changes where canopy characteristics and VI patterns systematically converge or diverge in space or through time over a remote and dynamic northern wetland complex: the Peace-Athabasca Delta (PAD), found in north-eastern Alberta, Canada. To address the need for spatially extensive field observations of vegetation structure, bi-temporal lidar-derived canopy height, cover and change (2000 and 2016/2018) were compared to Landsat-derived NDVI and EVI trends across a range of wetland landcover classes. The availability of lidar measurements provides three-dimensional canopy structure and elevation of the landscape including canopy height [48; 49], wetland and riparian environments [48; 50; 51] and if temporal data exist, change in these structures over time [9; 50; 51; 52; 53; 54; 55; 56]. Understanding vegetation responses to hydroclimatic change in the PAD provides insight applicable to similar wetland ecosystems globally, many of which are undergoing rapid ecological transitions [57; 58; 59; 60]. More specifically, this study will address three objectives:  
1. To evaluate the hypothesis that Landsat-derived VIs are correlated with spatio-temporally coincident lidar-derived Canopy Height Models (CHMs) for at least some landcovers--specifically woody wetlands (e.g., shrub swamp, treed swamps) and upland forest areas--where VI values are expected to better reflect vertical vegetation structure, given that VIs are proxies for green leafy foliage cover and biomass tends to increase with mean canopy height [61]. This is evaluated through two sub-hypotheses: 1. Based on the assumption that EVI is more sensitive to variations in canopy structure and density, and typically yields higher values in areas of taller canopy [62], the first sub-hypothesis tests for a stronger positive correlation between CHM and EVI than for NDVI; 2. Given that foliage cover and vegetation height are not the same quantity, the second sub-hypothesis tests for significant differences in the relationships between CHM and VI (and their changes/trends) across distinct landcover classes [63]. 2. To examine how trends in NDVI and EVI correspond with changes in canopy height over time and characterize spatial correspondences between regions of contiguous ecosystem or landcover expansion (or shrinkage) and regions of VI trend increase (or decrease). It is not expected that NDVI or EVI increasing (greening) or decreasing (browning) trends will consistently or strongly correlate with increases or decreases in lidar-derived CHM magnitudes at the grid cell level. Specifically, it is expected that any spatial correspondence between aggregate regions of VI trend- and CHM-based change will be most apparent where ecosystem height growth and foliage infilling are most pronounced, i.e., those associated with woody (shrub or tree) ecotonal expansion. 3. To explore differences in the EVI and NDVI trend response to changing wetland conditions that are associated with long term changes in soil surface saturation inferred from trends in LST, particularly in non-woody wetland types.