James B. McGraw

Detection and analysis of individual leaf-off tree crowns in small footprint, high sampling density lidar data from the eastern deciduous forest in North America

Leaf-off individual trees in a deciduous forest in the eastern USA are detected and analysed in small footprint, high sampling density lidar data. The data were acquired February 1, 2001, using a SAAB TopEye laser profiling system, with a sampling density of approximately 12 returns per square meter. The sparse and complex configuration of the branches of the leaf-off forest provides sufficient returns to allow the detection of the trees as individual objects and to analyse their vertical structures. Initially, for the detection of the individual trees only, the lidar data are first inserted in a 2D digital image, with the height as the pixel value or brightness level. The empty pixels are interpolated, and height outliers are removed. Gaussian smoothing at different scales is performed to create a three-dimensional scale-space structure. Blob signatures based on second-order image derivatives are calculated, and then normalised so they can be compared at different scale-levels. The grey-level blobs with the strongest normalised signatures are selected within the scale-space structure. The support regions of the blobs are marked one-at-a-time in the segmentation result image with higher priority for stronger blobs. The segmentation results of six individual hectare plots are assessed by a computerised, objective method that makes use of a ground reference data set of the individual tree crowns. For analysis of individual trees, a subset of the original laser returns is selected within each tree crown region of the canopy reference map. Indices based on moments of the first four orders, maximum value and number of canopy and ground returns, are estimated. The indices are derived separately for height and laser reflectance of branches for the two echoes. Significant differences (p<0.05) are detected for numerous indices for three major native species groups: oaks (Quercus spp.), red maple (Acer rubrum) and yellow poplar (Liriodendron tuliperifera). Tree species classification results of different indices suggest a moderate to high degree of accuracy using single or multiple variables. Furthermore, the maximum tree height is compared to ground reference tree height for 48 sample trees and a 1.1-m standard error (R 2 =68%

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.

Natural Selection and Ecotypic Differentiation in Impatiens Pallida

One possible response of plant populations to heterogeneous environments is genetic adaptation resulting in the formation of distinct ecotypes. Genetic adaptation to stressful environments may affect both the limits to species boundaries and the potential for response to a changing environment. Reciprocal transplant experiments have frequently been used to describe ecotypic differentiation and to infer the role of natural selection when there is evidence for home site advantage. The demonstration of a home site advantage, however, does not reveal which plant characters are responsible for conferring increased fitness on populations planted in their native site. Here, we combine the classic reciprocal transplant experiment with multivariate regression analysis of selection to ask a series of questions relevant to understanding adaptive genetic differentiation in natural plant pop- ulations. Impatiens pallida plants from a mesic floodplain and a dry hillside site were reciprocally transplanted. We initially presumed the hillside to be a stressful site for Impatiens given its sparser population of consistently smaller individuals. This study describes the two environments from the perspective of the plant to ask whether it is stressful. In addition, we investigate genetic differentiation between populations and ask whether the two pop- ulations are distinctly adapted to their home sites. To identify traits that may be important for conferring home site advantage, we quantify present-day natural selection in these sites and ask whether the observed selective forces can explain genetic differences. Finally, because phenotypic correlations may play an important role in a populations response to its environment, we investigate relationships among traits to determine the extent to which they are genetically and/or environmentally controlled. The large reduction in total seed production when plants from both populations were grown on the hillside supported our initial bias that this site was stressful to Impatiens. In addition, the higher relative fitness of each population planted in its native site demonstrated that these populations represent distinct ecotypes. Genetic differences between populations were observed for several life history and morphological characters. In particular, plants from the hillside population were smaller and produced cleistogamous flowers earlier than floodplain plants. Selection analysis revealed that, while there is strong selection favoring early flowering on the hillside, there is no advantage to early flowering for plants grown on the floodplain. An increased developmental rate, which allows plants to produce seeds before they succumb to drought stress, appears to be the most important mechanism re- sponsible for the greater relative fitness of the hillside population in its native site. While greater total plant leaf area is favored by selection on the floodplain, there is no evidence for selection on this trait on the hillside. Phenotypic covariances among traits differed between sites and populations, resulting in differences in the action of indirect selection. There is evidence that indirect selection on correlated traits is responsible for some of the observed genetic differences.

COMPETITIVE ABILITY AND ADAPTATION TO FERTILE AND INFERTILE SOILS IN TWO ERIOPHORUM SPECIES

We investigated the role of competition in adaptation to varying nitrogen (N) levels for two Alaskan species of Eriophorum found naturally in low- vs. high-nutrient soils. In a growth-chamber experiment, seedlings were grown at a range of proportions (0, 0.5, 1.0) of the two species and at a range of densities (n = 1, 2, and 4 plants per pot) under low- and high-N treatments. In a field experiment, plants were reciprocally transplanted between low- and high-nutrient sites into both unvegetated (noncompetitive) and vegetated (competitive) plots. The two species responded similarly to density and nitrogen in pure cultures, but in mixtures the species from the high-nutrient site (E. scheuchzeri) showed a greater growth response to N than did the species from the low-nutrient site (E. vaginatum). Analyzed as a replacement series, the experiment showed a reversal in relative competitive ability (as measured by the relative crowding coefficient) of the two species between low- and high-N treatments at high density. Tissue N concentrations were higher and more responsive to N addition for E. scheuchzeri. Nitrogen use efficiency was higher for E. vaginatum in all treatments, while N uptake efficiency was higher for E. scheuchzeri in all treatments. In the field, survival, growth, and flowering responses to reciprocal transplanting sug- gested local adaptation of the two species to their respective home sites. In noncompetitive plots, the growth response mirrored that seen in the growth chamber. However, after 2 yr there was a clear reversal between sites in relative aboveground masses of the two species. The local species acquired more nitrogen than the alien species at both sites. We conclude that Eriophorum vaginatum and E. scheuchzeri possess traits typical of species adapted to infertile and fertile soils, respectively. The contrasting ecological re- sponses of the two species are due, at least in part, to differences in their nutritional physiology, including differences in nutrient use efficiency, nutrient uptake efficiency, and root: shoot ratio. In the field, these differences result in differential growth, reproduction, and survival, while in the growth chamber, the differences result in differential ability to accumulate biomass and reversal in competitive ability as a function of nutrient availability. This and other studies suggest that adaptations to low, as well as high, resource levels may confer improved competitive ability.

Ecological Genetic Variation in Seed Banks I. Establishment of a Time Transect

In cold enrivonments, such as Arctic tundra, buried seeds can potentially persist in the soil for centuries or millennia. The possibility of obtaining time-stratified seed populations from Alaskan tundra was investigated in two ways. First, a deep layer of organic soil was sampled from a vertical profile through accumulating peat in Eriophorum-tussock tundra. Secondly, an organic soil buried by the slow, downslope erosional deposition of mineral soil (solifluction) was sampled; the progression of samples taken upslope under the deposit represented progresively older buried soils (...)

ENVIRONMENT-DEPENDENCE OF QUANTITATIVE GENETIC PARAMETERS IN IMPATIENS PALLIDA

Population response to selection depends on the presence of additive genetic variance for traits under selection. When a population enters an alien environment, environment‐induced changes in the expression of genetic variance may occur. These could have large effects on the response to selection. To investigate the environment‐dependence of genetic variance, we conducted a reciprocal transplant experiment between two ecotypically differentiated populations of Impatiens pallida using the progeny of a standard mating design. The floodplain site was characterized by high water availability, moderate temperatures, and continuous dense stands of Impatiens. The hillside site was drier, with larger temperature extremes and supported only scattered patches of Impatiens with significantly lower seed production and earlier mortality. Estimates of heritability were low for each of the 13 traits measured in each population and site (range from 0–28%). Additive genetic variance for life‐history traits tended to be larger than for morphological traits, but genetic variance in fitness was estimated to be not significantly different from zero in all cases. Significant heritability was detected in both populations for one trait (date of first cleistogamous flower) known to be closely related to fitness on the hillside. In general, heritability was reduced for populations when grown in the hillside site relative to the floodplain site, suggesting that stress acts to reduce the expression of genetic variance and the potential to respond to selection there. Consistent reductions in heritability associated with more stressful environments suggest that populations invading such sites may undergo little adaptive differentiation and be more prone to local extinction.

Evidence for decline in stature of American ginseng plants from herbarium specimens

American ginseng (Panax quinquefolius L.) has been harvested from the wild to supply the Asian herbal market for more than 200 years. As a CITES Appendix II listed species, ginseng trade has been monitored since 1975 and evidence for no detrimental effects of harvest is required annually by the US government. One kind of evidence gathered to gauge harvest effects has been mean root size and age, however the short-term nature of the data set limits possible inferences. In this study, 915 herbarium specimens from 17 herbaria were aged and measured to extend the time-transect to 186 years. Nine of 11 size-related traits showed statistically significant declines, most of this change occurring since ca. 1900. Multivariate analyses confirmed the overall decline in plant size. Age of herbarium specimens did not significantly decline during the same interval. Plants collected from northern populations did not decline in size, while plants from midwestern, Appalachian and southern states showed sharp declines in stature. Assuming herbarium specimens are representative of a consistent portion of natural populations, either direct or indirect effects of environmental change or human harvest could explain the rapid change in ginseng stature. Understanding the implications of such plant stature changes will require examining the effects of size on harvest probability and reproduction in the context of population viability analyses.

Demographic Growth Analysis

We present demographic growth analysis, a hybrid approach that retains the formal mathematical structure of growth analysis, while incorporating the advantages of modular demography.

Size and characteristics of a natural seed bank in Antarctica

The seed banks of Colobanthus quitensis and Deschampsia antarctica, the only two vascular plants native to Antarctica, were assayed by collecting soils from two sites near Palmer Station, Antarctic...

Recovery of Populations of Goldenseal (Hydrastis canadensis L.) and American Ginseng (Panax quinquefolius L.) Following Harvest

Abstract Goldenseal (Hydrastis canadensis L.) and American ginseng(Panax quinquefolius L.) have been harvested commercially for the past few centuries. Harvested populations can recover if vegetative propagules remain in the soil. Experiment I tested the efficacy of vegetative reproduction in goldenseal and ginseng. Partial and intact rhizomes and roots were planted in garden experiments in West Virginia and monitored for 1 y (goldenseal), and for 4 y (ginseng). During the experiment more than 40% of the propagule types of goldenseal (n = 5) and ginseng (n = 7) sprouted. Sprouting varied from year to year in ginseng, and dormancy and/or death occurred in both species. Of the ginseng propagules that sprouted, 77% were dormant for at least 1 y and half of those were not present in the final year of the experiment. Sprouting and reproductive status were dependent on propagule type for both species. In Experiment II we monitored recovery of wild populations of goldenseal and ginseng following natural and simulated harvests. After a harvest event leaving only 4 visible plants at the site, a goldenseal population recovered to 932 stems in the first growing season. In the subsequent 3 y, the population declined numerically, but the size of individuals increased significantly. In a harvested ginseng population, less than half the original number of ginseng plants were present 1 y after harvest. By the second year, stem number exceeded the preharvest count, but the demographic structure of the population had changed dramatically: 78% of the population was reproductive before harvest, while 0%, 4%, 7%, 18% and 26%, respectively, were reproductive in the 5 y following harvest. Both rhizomes and roots of goldenseal and ginseng are capable of regenerating plants, conferring a degree of short term resiliency following harvest.