Richard L. Boyce

Choosing the best similarity index when performing fuzzy set ordination on binary data

. Fuzzy set ordination (FSO) may be used with either abundance data or binary (presence/absence) data. FSO requires a similarity index that returns values between 0 and 1. Many indices will do so, but their suitability for FSO has not been tested. Nine binary indices were evaluated in this study. Simulated plant community data sets were generated with COMPAS; they contained five levels of β-diversity, two levels of qualitative noise, and two sampling arrangements (regular or random) along one gradient. Indices were evaluated with rank and linear correlations between the apparent ecological gradient positions generated by FSO and actual gradient positions; the abilities of the best-performing indices to minimize the curlover effect were also compared. All indices performed best at intermediate levels of β-diversity and with regular sampling. Five indices had consistently higher rank and linear correlations (Baroni-Urbani & Buser, Jaccard, Kulczynski, Ochiai and Sorensen), whereas four were consistently lower (Faith, Russell & Rao, Rogers & Tanimoto and Simple Matching). There were no significant differences in curlover among the five best indices. A step-across algorithm, a flexible shortest path adjustment, improved correlations and reduced curlover for the five best indices at higher β-diversity levels. We recommend that one of the five best-performing similarity indices be used with FSO on binary data; a flexible shortest path adjustment should also be employed at higher β-diversities when possible.

Partial cambial mortality in high-elevation Pinus aristata (Pinaceae).

Partial cambial mortality is a growth form that is characteristic of Pinus aristata trees. To better elucidate their cambial death pattern, tree size and aspect of cambial death data were gathered from three Pinus aristata forests in central Colorado, USA. Stripping frequency tended to be higher for larger diameter classes. Partial cambial mortality exhibits significant directionality within each stand. Furthermore, cambial death was measured to be most frequent on the wind-exposed side of stripped trees in two of the three study sites and appeared to be at the third. Data presented here support the hypothesis that wind plays a role in the occurrence of partial cambial mortality in Pinus aristata. The mechanisms by which wind causes cambial mortality remain unclear.

Fuzzy set ordination along an elevation gradient on a mountain in Vermont, USA

Fuzzy set ordination was used to examine relationships between tree species and site factors on Mt. Ascutney, Vermont, USA. Prism plots were estab- lished at four elevations (455, 610, 760 and 915 m) along contour lines that encircled the mountain. In addi- tion to elevation, which was the most important factor affecting tree species composition, slope, aspect and exposure to solar radiation all affected composition; however, these latter three factors were important only at 455 m. Topographic position was important at higher elevations as well. The responses of tree species to any of these factors were highly individualistic. Plots of the upper bounds of relative basal area of each species against the apparent elevation of sites where that species was found were useful in predicting how important an individual species could become over the course of forest succession. For example, northern hardwoods, which comprise the most common forest type of this region, are not very common on this mountain. This approach shows, however, that they are currently at levels well below their potential maximum; this is prob- ably due to past disturbance.

Winter and early spring microclimate of a subalpine spruce-fir forest canopy in central New Hampshire

Abstract Recent evidence suggests that the decline of red spruce in the northeastern United States is directly related to freezing injury during winter. As part of a study on the relationship between red spruce decline and winter conditions, within-canopy micrometeorological measurements were taken in a subalpine red spruce (Picea rubens Sarg.)-balsam fir (Abies balsamea (L.) Mill.) forest on Mt Moosilauke in central New Hampshire during the winter and early spring of 1990 and during the late fall, winter and early spring of 1991. At 880- and 1010-m elevation in 1990 and at 880-m elevation in 1990–1991, solar radiation and relative humidity were recorded at one height within the canopy, and air temperature and wind speed were recorded at two heights within the canopy. Hourly mean and maximum temperatures were slightly greater in the upper canopy than in the lower canopy. Both the maximum (26.1°C) and minimum (−27.6°C) temperatures of the study were recorded in the upper canopy at the 1010-m elevation study site. The maximum temperature drop that occurred within one hour and also spanned freezing was 9°C. Temperature minima below −35°C and much greaer rapid temperature drops are believed to be necessary to cause or induced red spruce freezing injury. It appears that conditions during the study period were not severe enough to cause freezing injury; this conclusion was supported by the relatively small amount of visible injury observed in the periods following the study. These data on winter microclimate in a spruce-fir forest should be of value to investigators studying freezing injury and to other forest scientists.

Chlorophyll fluorescence response of red spruce and balsam fir to a watershed calcium fertilization experiment in New Hampshire

Decreases in soil exchangeable calcium (Ca) due to acid deposition have been linked with declines of forest species in the northeastern United States, particularly red spruce (Picea rubens Sarg.). In 2005, chlorophyll fluorescence measurements were taken on red spruce and balsam fir (Abies balsamea (L.) Mill.) trees growing on two watersheds at the Hubbard Brook Experimental Forest (HBEF) in New Hampshire. One watershed had been fertilized with CaSiO3 in 1999 to replace the soil Ca losses of the past 50 years, and the other was a reference watershed. In March, there were no differ- ences in any chlorophyll fluorescence parameter between sites or species. In August, however, dark-adapted ratios of vari- able fluorescence to maximum fluorescence (Fv/Fm) were significantly greater (p = 0.05) in the Ca-treated watershed for both spruce and fir, and spruce values were significantly greater than fir. No differences were found in the light-adapted fluorescence parameters. These results suggest that both spruce and fir respond to increases in Ca availability, even though fir does not exhibit the decline symptoms seen in spruce. It is unclear what physiological effect is responsible for the ob- served differences in Fv/Fm. The Fv/Fm values appear to respond to differences in Ca availability in forest tree species; thus, the ratio has the potential to be used in these two watersheds at HBEF to determine if other forest species are also re-

Effects of a major ice storm on the foliage of four New England conifers

Abstract The mechanical damage to forests caused by winter ice storms is well known. The January 1998 ice storm in the northeastern United States and adjacent regions of Canada caused major forest damage to the area. Here we report on the physiological effects on four conifers that did not show visible signs of damage after the January 1998 ice storm. Cuticular conductances normally increase during winter. In this winter, they were high immediately after the storm, then fell 17-74% in the following 30-45 days in hemlock, red pine, and red spruce. We hypothesize that this was caused by the loss of damaged foliage, with high cuticular conductances, over that period. Alternatively, damaged cuticles may have been repaired, although this seems less likely. Relative water contents were higher than normal in some species in the weeks after the storm, due either to an artifact of measurement introduced by the ice that coated needles or to short-term changes in the water-holding capacity of foliage. Water relations of white pine were least affected by this ice storm, whereas hemlock’s were most affected. These ecophysiological results contrast with the structural effects of ice storms. Red pine is considered to be most sensitive to mechanical injury, while hemlock and red spruce are the least; white pine is intermediate. The order of sensitivity to physiological effects from a major ice storm appears to be hemlock and red spruce, followed by red pine, with white pine the least sensitive. Results from this study suggest that the physiological effects of ice storms can linger long after the ice melts from the canopy.

Factors Determining Alpine Species Distribution on Goliath Peak, Front Range, Colorado, U.S.A

Abstract The effect of environmental factors on the distribution of alpine plant community types has been extensively studied in Colorado. Much less attention has been paid to the effects of these factors within community types, however. Transects were placed in the alpine zone of Goliath Peak in the Front Range of the Colorado Rocky Mountains. Species presences were tallied in 1-m2 rectangular plots. Fuzzy set ordination (FSO) was used to determine which environmental factors were responsible for changes in species composition. Most sites fell into the fellfield or dry meadow community types. Water availability, as indicated by elevation, estimated winter snow depth and, less strongly, soil texture, was a strong factor associated with changes in plant community composition, both within and among community types. Temperature, as indicated by aspect, was also associated with these changes. The lack of Kobresia myosuroides at Goliath Peak appears to be caused by snow depths too deep or too shallow for this species. FSO proved to be more effective when environmental factors were ordinated separately rather than sequentially, as originally suggested. This was confirmed by a Bray-Curtis ordination. A species-site biplot showed how species and sites can be displayed together on the same fuzzy set ordination.

The Effect of Age, Canopy Position and Elevation on Foliar Wettability of Picea rubens and Abies balsamea: Implications for Pollutant-Induced Epicuticular Wax Degradation

The epicuticular wax layer is the outermost layer of the cuticular barrier between the atmosphere and the plant interior. A number of air pollutants can degrade this wax layer, increasing interactions between the plant and atmospheric deposition and thereby inducing stress. However, a number of natural factors also influence the development and degradation of epicuticular wax in evergreen tree species, and any changes induced by air pollution will be superimposed upon these natural variations. Using the contact angle method, the wettability of red spruce (Picea rubens Sarg.) and balsam fir (Abies balsamea (L.) Mill.) foliage in subalpine regions of the northeastern U.S. was determined. In both species, foliar wettability increased as the foliage aged. Wettability also increased with increasing elevation in both species. Foliage from the bottom of the canopy was more wettable than foliage from the top. Fir foliage was generally less wettable than spruce foliage, particularly the younger age classes. These results indicate that spruce, due to its greater wettability, may be more greatly affected by pollutant-induced epicuticular wax degradation. For the same reason, older conifer foliage, foliage near the bottom of the canopy and foliage at higher elevations may all be more likely to be affected by epicuticular wax degradation caused by air pollutants.