Changes in large-scale vegetation structure triggered by processes such as deforestation, wildfires, and tree die-off alter surface structure, energy balance, and associated albedo-all critical for land surface models. Characterizing these properties usually requires long-term data, precluding characterization of rapid vegetation changes such as those increasingly occurring in the Anthropocene. Consequently, the characterization of rapid events is limited and only possible in a few specific areas. We use a campaign approach to characterize surface properties associated with vegetation structure. In our approach, a profiling LiDAR and hemispherical image analyses quantify vegetation structure and a portable mast instrumented with a net radiometer, wind-humidity-temperature stations in a vertical profile, and soil temperature-heat flux characterize surface properties. We illustrate the application of our approach in two forest types (boreal and semiarid) with disturbance-induced tree loss. Our prototype characterizes major structural changes associated with tree loss, changes in vertical wind profiles, surface roughness energy balance partitioning, a proxy for NDVI (Normalized Differential Vegetation Index), and albedo. Multi-day albedo estimates, which differed between control and disturbed areas, were similar to tower-based multiyear characterizations, highlighting the utility and potential of the campaign approach. Our prototype provides general characterization of surface and boundary-layer properties relevant for land surface models, strategically enabling preliminary characterization of rapid vegetation disturbance events.

Ecologists continue to debate the role of fire in forests of the southern Appalachian Mountains. How does climate influence fire in these humid, temperate forests? Did fire regimes change during the transition from Native American settlement to Euro-American settlement? Are fire regime changes resulting in broad vegetation changes in the forests of eastern North America? I used several approaches to address these questions. First, I used digitized fire perimeter maps from Great Smoky Mountains National Park and Shenandoah National Park for 1930-2009 to characterize spatial and temporal patterns of wildfire by aspect, elevation, and landform. Results demonstrate that fuel moisture is a primary control, with fire occurring most frequently during dry years, in dry regions, and at dry topographic positions. Climate also modifies topographic control, with weaker topographic patterns under drier conditions. Second, I used dendroecological methods to reconstruct historical fire frequency in yellow pine (Pinus, subgenus Diploxylon Koehne) stands at three field sites in the southern Appalachian Mountains. The fire history reconstructions extend from 1700 to 2009, with composite fire return intervals ranging from 2-4 years prior to the fire protection period. The two longest reconstructions record frequent fire during periods of Native American land use. Except for the recent fire protection period, temporal changes in land use did not have a significant impact on fire frequency and there was little discernible influence of climate on past fire occurrence. Third, I sampled vegetation composition in four different stand types along a topographic moisture gradient, including mesic cove, sub-mesic white pine (Pinus strobus L.) hardwood, sub-xeric oak (Quercus L.), and xeric pine forests in an unlogged watershed with a reconstructed fire history. Stand age structures demonstrate changes in establishment following fire exclusion in xeric pine stands, sub-xeric oak stands, and sub-mesic white pine-hardwood stands. Fire-tolerant yellow pines and oaks are being replaced by shade-tolerant, fire sensitive species such as red maple (Acer rubrum L.) and hemlock (Tsuga canadensis L. Carr.). Classification analysis and ordination of species composition in different age classes suggest a trend of successional convergence in the absence of fire with a shift from four to two forest communities.