Mary Ann Fajvan

A Comparison of Multispectral and Multitemporal Information in High Spatial Resolution Imagery for Classification of Individual Tree Species in a Temperate Hardwood Forest

Multitemporal, small-format 35-mm aerial photographs were combined in a coregistered database to determine the relative value of spectral and phenological information for overstory tree crown classification of digital images of the Eastern Deciduous Forest. A one-hectare study site, located in a second-growth forest 15 km east of Morgantown, West Virginia, USA, was photographed from a light aircraft nine times from May to October 1997 using both true-color and false-color infrared film. Using this imagery, differences in the spectral properties and timing of phenologic events between tree species made it possible to discriminate four deciduous tree species, namely Liriodendron tulipifera, Acer rubrum, Quercus rubra, and Quercus alba, which made up nearly 99% of the trees at this study site. Optimally timed photography acquired during peak autumn colors provided the best single date of imagery, while photography from spring leaf-out was the second best. The best individual image band for tree species discrimination was the blue band. Classifications using all four spectral bands (blue, green, red, and infrared) and four dates (05/23/97, 06/23/97, 10/11/97, and 10/30/97) provided the best classification accuracies. Variable canopy illumination made digital classification of individual trees complex. A Likelihood Ratio test confirmed that the number of spectral bands included in the classification procedure (spectral resolution) and the number of dates (temporal resolution) significantly influenced the ability to identify tree species correctly. This study suggests that although multispectral data appear to be more valuable than multitemporal data, it may be possible to compensate for the limited spectral resolution of planned high-resolution sensors by combining multiple dates of low spectral resolution images.

Oak establishment and canopy accession strategies in five old-growth stands in the central hardwood forest region

Using a radial growth averaging technique, decadal-scale changes in growth rates of overstory oaks were used to identify canopy accession events at five old-growth sites. A review of tree-ring chronologies yielded three growth strategies: (1) one-half of the oaks originated in a large opening and achieved overstory status before canopy closure; (2) 38% originated in a smaller opening and required a second gap event to attain overstory status; and (3) 13% achieved overstory status after an extended period of very low growth in understory shade and one or two subsequent gap releases. For trees that required a major canopy release, understory residence times averaged 89, 54, 50 and 38 years for white oak, northern red oak, black oak, and chestnut oak, respectively. Average diameters (inside bark) at canopy accession were 13.3, 11.7, 10.0, and 6.2 cm for the four oak species, respectively. Although there is some historical precedence for these values, few contemporary second-growth forests contain understory oaks of this age, particularly red oak. These long understory residence times suggest that the level of understory shade, and by inference, the abundance of shade tolerant understory species, was considerably less before 1900.

Stand structure and development after gypsy moth defoliation in the Appalachian Plateau

Abstract The vegetation structures of Appalachian hardwood stands in southwestern Pennsylvania were examined before, and 4 years after, defoliation by the gypsy moth (Lymantria dispar L.) on a range of site aspects. Gypsy moth-induced mortality of oaks (Quercus spp.) was associated with growth increases in subcanopy species such as Acer spp., regardless of aspect. Density of non-oak tree seedlings and other woody vegetation 1 m in height showed declines that were correlated with increases in basal area of overstory trees, most notably Acer spp. Results suggest that the gypsy moth-related, disturbance in this region has altered the species composition and initiated a new cohort in these previously oak-dominated, single cohort stands.

The effects of thinning and gypsy moth defoliation on wood volume growth in oaks

Stem dissection and dendroecological methods were used to examine the effects of thinning and defoliation by gypsy moth (Lymantria dispar L.) on wood volume increment in oaks (Quercus rubra L., Q. alba L., Q. prinus L.). A model was developed to evaluate radial volume increment growth at three time periods: before defoliation, during defoliation and after defoliation, as a function of species, defoliation intensity and crown position. Volume increment during these same time periods was also compared at different stem locations. Trees were defoliated for two consecutive years and results indicated that volume loss was greater during the second year of defoliation with complete recovery taking 2–3xa0years after defoliation. Oaks in thinned stands had similar reductions in annual volume increment during defoliation as those in the unthinned stand. Annual volume increment demonstrated a decreasing trend from stump to base of the live crown and volume increment of the lowest log (from stump height to 1.37xa0m), was always higher than upper log sections, even during defoliation. Both earlywood and latewood increments were reduced during defoliation; however, latewood reductions were distributed along entire stems while earlywood reductions were greater on upper stem sections within the crown.

Comparison of hardwood stand structure after partial harvesting using intensive canopy maps and geostatistical techniques

Abstract Intensive canopy mapping and geostatistical techniques were used to evaluate spatial heterogeneity in stand structure after diameter-limit harvests and a shelterwood seed cut in an Appalachian hardwood stand. The size, density, and location of tree crowns and stems were mapped to provide baseline data for predetermined locations within treatment blocks. Spatial data were collected from the same areas. Variogram models were used to compare spatial dependence in canopy cover and regeneration among the harvests. Kriged estimates of canopy cover were obtained and compared to intensive canopy maps. Canopy cover was spatially dependent on a range of 11.5xa0m in the shelterwood seed cut, 7.5xa0m in the 30xa0cm, and 8.1xa0m in the 41xa0cm diameter-limit harvests. Spatial dependence of regeneration extended to a range of 9.7xa0m in the shelterwood seed cut and 7.3xa0m in the 41xa0cm diameter-limit harvest. There was little dependence in regeneration presence within the 30xa0cm diameter-limit harvest at the scale sampled. Shade-tolerant regeneration had longer ranges of spatial dependence in the shelterwood seed cut. Shade-intolerants were autocorrelated at greater distances within the 41xa0cm diameter-limit harvest. Tolerant regeneration was positively correlated with the presence of canopy to a distance of 5–10xa0m. Likewise, the presence of shade-intolerant regeneration was negatively correlated with canopy cover at the same distance. Kriged and intensive canopy maps appeared to match well; however, when sampled, only the kriged maps of the 30xa0cm diameter-limit harvest corresponded with the intensive canopy maps to a significant extent. Geostatistics provided an excellent means of depicting spatial dependence in these harvests. Future refinements of these techniques could allow larger areas to be sampled with less error, as well as with a large reduction in both cost and effort when compared to intensive canopy mapping.