Viburnum Alnifolium Research Articles

Can the nutrient dynamics of a northern hardwood forest explain variation in its trophic structure?

Abstract Background/Question/Methods: A time series of Lepidoptera larvae (caterpillar) abundance and biomass in the northern hardwood forests of central New Hampshire, USA, shows large interannual fluctuations in aggregated caterpillar biomass (52-fold variation in mg caterpillars/ 8000 leaves) that were spatially correlated across a regional landscape. Primary production of these mature forests has not varied over this period, and many hundreds of Lepidoptera species share comparatively few host plants. Therefore, interannual changes in nutritional quality of even one host plant species may be capable of generating correlated population dynamics for many species in the Lepidoptera community. We tested the hypothesis that variation in soil nutrient availability influences foliar chemistry and ultimately produces a bottom-up force capable influencing the aggregated biomass of the forest's dominant herbivores. Results/Conclusions: Over a period of four years, measures of nutritional quality for herbivores in three of the forest's four dominant understory tree species (Acer saccharum, Acer pensylvanicum, and Viburnum alnifolium) displayed considerable variation that was consistent across the landscape. Foliar nitrogen (N) content and two metrics of secondary metabolite concentration—total phenolics and condensed tannin—all varied by up to 20% among years. Resin bag extracts of NH4+, NO2- /NO3- and PO4+ showed soil mineral nutrient availability displayed six-fold variation that was consistent with the pattern in foliar N, and a whole tree in situ fertilization experimental manipulation produced rapid effects on foliar chemistry. Finally, variation in the forewing lengths of free-flying moths showed an interannual concordance among species within the group of early season feeders that was also consistent with patterns in foliar quality—suggesting collections of species experience correlated variations in larval growth performance.

Can the nutrient dynamics of a northern hardwood forest explain variation in its trophic structure?

Background/Question/Methods:A time series of Lepidoptera larvae (caterpillar) abundance and biomass in the northern hardwood forests of central New Hampshire, USA, shows large interannual fluctuations in aggregated caterpillar biomass (52-fold variation in mg caterpillars/ 8000 leaves) that were spatially correlated across a regional landscape. Primary production of these mature forests has not varied over this period, and many hundreds of Lepidoptera species share comparatively few host plants. Therefore, interannual changes in nutritional quality of even one host plant species may be capable of generating correlated population dynamics for many species in the Lepidoptera community. We tested the hypothesis that variation in soil nutrient availability influences foliar chemistry and ultimately produces a bottom-up force capable influencing the aggregated biomass of the forest's dominant herbivores.Results/Conclusions:Over a period of four years, measures of nutritional quality for herbivores in three of the forest's four dominant understory tree species (Acer saccharum, Acer pensylvanicum, and Viburnum alnifolium) displayed considerable variation that was consistent across the landscape. Foliar nitrogen (N) content and two metrics of secondary metabolite concentration—total phenolics and condensed tannin—all varied by up to 20% among years. Resin bag extracts of NH4+, NO2- /NO3- and PO4+ showed soil mineral nutrient availability displayed six-fold variation that was consistent with the pattern in foliar N, and a whole tree in situ fertilization experimental manipulation produced rapid effects on foliar chemistry. Finally, variation in the forewing lengths of free-flying moths showed an interannual concordance among species within the group of early season feeders that was also consistent with patterns in foliar quality—suggesting collections of species experience correlated variations in larval growth performance.

Understory vegetation in old-growth and second-growth Tsuga canadensis forests in western Massachusetts

We compared the understory communities (herbs, shrubs, and tree seedlings and saplings) of old-growth and second-growth eastern hemlock forests ( Tsuga canadensis) in western Massachusetts, USA. Second-growth hemlock forests originated following clear-cut logging in the late 1800s and were 108–136 years old at the time of sampling. Old-growth hemlock forests contained total ground cover of herbaceous and shrub species that was approximately 4 times greater than in second-growth forests (4.02 ± 0.41%/m 2 versus 1.06 ± 0.47%/m 2) and supported greater overall species richness and diversity. In addition, seedling and sapling densities were greater in old-growth stands compared to second-growth stands and the composition of these layers was positively correlated with overstory species composition (Mantel tests, r > 0.26, P < 0.05) highlighting the strong positive neighborhood effects in these systems. Ordination of study site understory species composition identified a strong gradient in community composition from second-growth to old-growth stands. Vector overlays of environmental and forest structural variables indicated that these gradients were related to differences in overstory tree density, nitrogen availability, and coarse woody debris characteristics among hemlock stands. These relationships suggest that differences in resource availability (e.g., light, moisture, and nutrients) and microhabitat heterogeneity between old-growth and second-growth stands were likely driving these compositional patterns. Interestingly, several common forest understory plants, including Aralia nudicaulis, Dryopteris intermedia, and Viburnum alnifolium, were significant indicator species for old-growth hemlock stands, highlighting the lasting legacy of past land use on the reestablishment and growth of these common species within second-growth areas. The return of old-growth understory conditions to these second-growth areas will largely be dependent on disturbance and self-thinning mediated changes in overstory structure, resource availability, and microhabitat heterogeneity.

Interference to Hardwood Regeneration in Northeastern North America: Controlling Effects of American Beech, Striped Maple, and Hobblebush

Abstract When American beech (Fagus grandifolia Ehrh.), striped maple (Acer pensylvanicum L.), and hobblebush (Viburnum alnifolium Marsh.) become dense in the understory they interfere with regeneration of other species. This review identifies threshold levels that causeproblems in regenerating desirable hardwoods in northeastern North America, and summarizes methods for controlling the interference in conjunction with a reproduction method cutting. It also forwards some ideas about management based on information in published sources.

Interference to Hardwood Regeneration in Northeastern North America: Ecological Characteristics of American Beech, Striped Maple, and Hobblebush

Abstract Several woody species may inhibit regeneration of desirable northern hardwoods. This includes a dense understory of American beech (Fagus grandifolia Ehrh.) that commonly occurs in stands infected with beech bark disease. Root injuries during logging and by natural causes alsopromote new suckers that, along with some stump sprouts, often maintain or increase the abundance of beech saplings. Additionally, browsing deer primarily bypass beech in favor of more palatable species. Where any of these factors has resulted in a dense understory of small beech, overstorycutting will promote its development, increase ground-level shading, and lead to a site conversion to beech. Similarly, striped maple (Acer pensylvanicum L.) often interferes with hardwood regeneration after overstory cutting. This species persists in heavy shade, grows rapidly afterrelease, and produces abundant seed. When dense, striped maple may interfere with the regeneration of other species. Hobblebush (Viburnum alnifolium Marsh.), a shrub, reproduces by rhizomes to form thickets when damaged during overstory cutting. Heavy shade by these thickets may preventregeneration of trees. This review summarizes characteristics of these three species with respect to their interference with desirable hardwoods in northeastern North America. It highlights the limited information about striped maple and hobblebush, and the abundance of sources that deal withAmerican beech.

Pigment dynamics and autumn leaf senescence in a New England deciduous forest, eastern USA

The leaves of woody plants at Harvard Forest in Central Massachusetts, USA, changed color during senescence; 70% (62/89) of the woody species examined anatomically contained anthocyanins during senescence. Anthocyanins were not present in summer green leaves, and appeared primarily in the vacuoles of palisade parenchyma cells. Yellow coloration was a result of the unmasking of xanthophyll pigments in senescing chloroplasts. In nine red‐senescing species, anthocyanins were not detectable in mature leaves, and were synthesized de novo in senescence, with less than 20 µg cm−2 of chlorophyll remaining. Xanthophyll concentrations declined in relation to chlorophyll to the same extent in both yellow‐ and red‐leaved taxa. Declines in the maximum photosystem II quantum yield of leaves collected prior to dawn were only slightly less in the red‐senescing species, indicating no long‐term protective activity. Red‐leaved species had significantly greater mass/area and lower chlorophyll a/b ratios during senescence. Nitrogen tissue concentrations in mature and senescent leaves negatively correlated to anthocyanin concentrations in senescent leaves, weak evidence for more efficient nitrogen resorption in anthocyanic species. Shading retarded both chlorophyll loss and anthocyanin production in Cornus alternifolia, Acer rubrum, Acer saccharum, Quercus rubra and Viburnum alnifolium. It promoted chlorophyll loss in yellow‐senescing Fagus grandifolia. A reduced red : far‐red ratio did not affect this process. Anthocyanins did not increase leaf temperatures in Q. rubra and Vaccinium corymbosum on cold and sunny days. The timing of leaf‐fall was remarkably constant from year to year, and the order of senescence of individual species was consistent.

Comparison of the Ground Vegetation in Spruce Plantations and Natural Forest in the Greater Fundy Ecosystem, New Brunswick

We studied changes in ground vegetation associated with the conversion of natural, mature, mixed-species forest into conifer plantations in southeastern New Brunswick. This was done to determine the degree to which plant-associated biodiversity was affected by this forestry practice. Species of lichens, bryophytes, and vascular plants were examined in a 21-year chronosequence of 12 Black Spruce (Picea mariana) plantations and compared to 8 stands of natural forest of the type replaced. The richness, diversity, and density of species were greatest during younger stages of the plantation sere, with as many as 170 species occurring in a 6-year-old stand. Species occurred in successional stages according to their abilities to: (a) survive disturbances associated with clear-cutting and plantation establishment; (b) regenerate vegetatively; (c) re-establish from a persistent seedbank; (d) invade disturbed habitat by dispersed seeds; and/or (e) tolerate environmental stress imposed by the overtopping canopy during stand development. Multivariate analyses suggested that successional factors had the strongest influence on differences in the ground vegetation among stands of various ages. Gaps in the canopy of reference forest and older plantations provided microsite conditions similar to those of early seral stages, allowing some ruderal species to persist in older stands. Nonindigenous species were almost entirely limited to younger plantations. Some species of natural forest were rare or absent from plantations and may be at risk from the extensive development of these agroforestry habitats in our study region; these included Acer pensylvanicum, Cephaloziella spp., Chiloscyphus spp., Fagus grandifolia, Lepidozia reptans, Nowellia curvifolia, Odontoschisma denudatum, and Viburnum alnifolium.

Stand-Level Effects on the Role of Decaying Logs as Vascular Plant Habitat in Adirondack Northern Hardwood Forests

GREGORY G. MCGEE (State University of New York-College of Environmental Science and Forestry, 1 Forestry Drive, Syracuse, NY 13210). Stand-level effects on the role of decaying logs as vascular plant habitat in Adirondack northern hardwood forests. J. Torrey Bot. Soc. 128:370-380. 2001.-The objectives of this study were to determine (1) if decaying logs provide critical habitat for any vascular plants in Adirondack northern hardwood forests; and (2) whether environmental factors that vary at the stand-scale influence the role of decaying logs as vascular plant habitat. Herbaceous ramet densities and woody seedling/sapling basal area were characterized on well-decayed logs and adjacent forest floor microsites in three northern hardwood stand types: old-growth, partially-cut, and 15to 29-year-old shelterwoods. No common herbaceous species were restricted to the log microsites, although Dryopteris intermedia had greater densities on logs. Betula alleghaniensis, Tsuga canadensis and Abies balsamea all attained greater basal areas (stems --15.0 cm diameter at the root collar) on decaying logs, while Acer pensylvanicum, Acer saccharum, Fagus grandifolia and Viburnum alnifolium had greater basal areas on forest floor microsites. Average (+ 1 SD) total basal area of woody stems was greatest in the shelterwoods (1775 + 615 mm2 m-2), compared to the partially-cut (714 + 266 mm2 m-2) and old-growth (503 + 657 mm2 m-2) stands. Betual alleghaniensis accounted for a substantial proportion of the basal area in the shelterwoods. In these shelterwood stands B. alleghaniensis basal areas were not statistically discernible between the forest floor and log microsites (P = 0.07). However, in partially-cut stands, B. alleghaniensis basal area was greater on the decaying log microsites (P = 0.05). In the old-growth stands, no B. alleghaniensis stems > 2 cm diameter were sampled. This study indicates that decaying logs provide early establishment sites for some tree species and the fern, D. intermedia, in northern hardwood forests. While B. alleghaniensis favored logs as establishment sites in the partially-cut stands, this species was capable of widespread establishment throughout the shelterwood stands. Even though B. alleghaniensis readily germinated on decaying logs, its recruitment into larger sapling size classes appeared to be consistently limited by factors varying at the stand level (e.g., light levels).

Leaf phenology, photosynthesis, and the persistence of saplings and shrubs in a mature northern hardwood forest

We quantified leaf phenologies of saplings and overstory trees of sugar maple (Acer saccharum Marsh.) and American beech (Fagus grandifolia Ehrh.), and the shrub hobblebush viburnum (Viburnum alnifolium Marsh.) in a 72-year-old northern hardwood forest. Seasonal changes in irradiance in the shrub layer, and in the leaf CO(2) exchange of viburnum, and sugar maple and beech saplings were also measured. Leaf expansion occurred earlier in the spring and green leaves were retained later in the autumn in saplings and shrubs than in overstory trees. During the spring light phase (before overstory closure), large CO(2) gains by all three shrub-layer species occurred as a result of a combination of relatively large leaf area, high photosynthetic capacity, and high irradiance. Throughout the summer shade phase, photosynthetic capacity at a given irradiance remained relatively constant, but CO(2) gain was typically limited by low irradiances. Even though irradiance in the shrub layer increased during the autumn light phase as the overstory opened, CO(2) gains were modest compared to springtime values because of declining leaf area and photosynthetic capacity in all three species. The CO(2) gains during the spring light phase, and to a lesser extent during the autumn light phase, may be important to the carbon balance and long-term persistence of saplings and shrubs in the usually light-limited shrub layer of a northern hardwood forest. Therefore, for some late-successional species, leaf phenology may be an important characteristic that permits their long-term persistence in the shrub layer of mature northern hardwood forests.

Colonization Dynamics of Herbs and Shrubs in a Disturbed Northern Hardwood Forest

Modes of recruitment of herbs and shrubs, and the extent to which availability of propagules affected distribution of the various species after disturbance were examined in a field experiment of canopy removal at the Hubbad Brook Experimental Forest, New Hampshire, U.S.A. The most common shrubs after canopy removal were Rubus idaeus and Viburnum alnifolium; the most common herbs were Aster acuminatus, Dennstaedtia punctilobula and Dryopteris spinolusa. All of the first-year recruitment or Rubus occurred through germination of buried seeds (...)

Nest-Site Selection and the Importance of Nest Concealment in the Black-Throated Blue Warbler

Nest-site selection of Black-throated Blue Warblers (Dendroica caerulescens) was studied for two summers in a northern hardwood forest in the White Mountains of New Hampshire. Nest placement in the shrub layer was examined to evaluate several alternative hypotheses concerning the selection of nest-site microhabitat. Nest-sites tended to be in dense patches of hobblebush (Viburnum alnifolium) with denser vegetation below 1.5 m and more open vegetation between 1.5-3 m than at random points. Shrub densities at nests and at random points within hobblebush patches were, in nearly all cases, statistically indistinguishable. Nests were placed in large patches of shrubs much more often than at random points and in larger patches of hobblebush more often than at random points within hobblebush patches. Black-throated Blue Warblers placed their nest in more concealed locations compared to empty nests placed at random locations. Concealment indices of successful and depredated nests, however, were not significantly different from one another. Several reasons why this species chose particular microhabitats within the shrub layer are discussed.

Ecological Relations and Social Interactions of Philadelphia and Red-Eyed Vireos

-The ecological and social interactions of the interspecifically aggressive Red-eyed (Vireo olivaceus) and Philadelphia (V. philadelphicus) vireos were studied during four breeding seasons in the Hubbard Brook Experimental Forest, New Hampshire. The two species here have extensively overlapping territories but occupy different vegetational strata during most of the breeding season. The aggressiveness of the Philadelphia Vireo towards the Red-eyed Vireo varies within a breeding season, being most frequent and intense during the periods of greatest vertical overlap. The aggressiveness of Red-eyed Vireos towards Philadelphia Vireos varies between years, being most frequent and intense in years of high Red-eyed Vireo population density. In one year no aggression was apparent between the two vireos. During some aggressive encounters, the smaller, subordinate Philadelphia Vireo used what appeared to be distraction displays when Red-eyed Vireos came close to their young. I hypothesize that resource competition may be the underlying cause of the aggression between these two ecologically similar species, largely because the most intense and frequent interspecific interactions occurred during periods of maximum overlap in foraging microhabitat. A comparison of these findings with those in another study illustrates the importance of forest height and vegetation structure in facilitating their coexistence. The ecological and evolutionary significance of interspecific aggression in birds has been the subject of controversy in recent years (Orians and Willson 1964, Cody 1969, 1974, Murray 1971, 1976). Support for the adaptiveness of interspecific aggression (cf. Cody 1974) has come from Rice's (1978a, b, c) study of the Red-eyed (Vireo olivaceus) and Philadelphia (V. philadelphicus) vireos where they occur together in the woodlands of northeastern Ontario. In this region the two species occupy exclusive non-overlapping territories, the smaller (12 g) Philadelphia Vireo successfully defending territories against its larger (17 g) congener. Rice (1978a) considered this horizontal separation to be a form of ecological segregation, because in nearly all other respects (habitat, use of vertical strata, foraging behavior) the two species were found to be essentially identical. In a study of the ecological relations of these same two species in a late successional forest in New England, I have observed that their territories overlap extensively and that interspecific aggression occurs at certain times during the nesting cycle. In this paper I examine the interaction of these two vireos at this site, compare the results to those of Rice (1978a, b, c) and consider reasons for the aggression between the two species. STUDY AREA AND METHODS This study was conducted in the 3,076-ha Hubbard Brook Experimental Forest, West Thornton, New Hampshire. In this late successional northern hardwoods forest the canopy layer (13-27 m) is dominated by sugar maple (Acer saccharum), American beech (Fagus grandifolia) and yellow birch (Betula alleghaniensis) with occasional white ash (Fraxinus americana). The sapling layer (2-12 m) is relatively sparse (Sherry 1979) and consists primarily of beech, sugar maple and some striped maple (A. pensylvanicum). The shrub layer (0-2 m) is a very dense and heterogeneous mixture of hobblebush (Viburnum alnifolium), striped maple, mountain maple (A. spicatum), sugar maple and beech. Most of my data were gathered on or near a 10-ha study plot at an elevation of 600 m. This plot is marked by a 50 m by 50 m grid, and has been the site of an intensive study of bird community dynamics and struc. ture since 1969 (Holmes and Sturges 1975, Holmes et al. 1979a). From late May through late July during 1975-1978 I visited this plot nearly every day for a total of over 200 days and 1,200 hours. Unless otherwise stated, all observations used in this paper were made on or within 100 m of the study plot. Other sections of the forest, especially those with Philadelphia Vireos, were also visited regularly each summer. To characterize the ecological and social relations of the two species, I measured their spacing, microhabitat use, habitat selection and reproductive success, each of which is treated separately below. Spacing. I mapped territories and estimated population densities of vireos on the study plot by methods similar to those of Holmes and Sturges (1975). Briefly, I made cumulative maps of all individuals heard, seen and/or captured in mist-nets and of their nest locations hen known. An average of 65% of the Red-eyed Vireos (REVs) on the 10-ha plot were color-banded by

Effects of Sludge Applications on Soil Water Solution and Vegetation in a Northern Hardwood Stand

AbstractDewatered and limed sludge from a primary treatment plant was applied at two rates, 25 and 125 wet metric tons/ha (5.8 and 28.0 dry metric tons/ha), on sandy loam soils in a northern hardwood forest in central New England. Changes in soil water solution were assessed from water samples collected with suction lysimeters at 20‐ and 45‐cm depths below the mineral surface. The light application of 25 metric/ha had little effect, but the heavy application of 125 metric tons/ha caused an increase in the concentration of most ions in soil water. At 20 cm, or just below the B21h horizon, Cl reached a mean maximum of 27.5 mg/liter after heavy application compared to control values of &lt;0.4 mg/liter. Sulfate rose above mean background levels of 5.0 mg/liter to a maximum concentration of 13.5 mg/liter. Mean Ca values rose to over 13.5 mg/liter compared to background concentrations of about 2 mg/liter. Magnesium, Na, K, H, and NO3 indicated maximum increases in concentration that averaged two‐ to threefold greater than control values of &lt;0.5 mg/liter. NH4 and TOTAL‐P were unchanged. At 45 cm or in the B23 horizon just above a fragipan, the increases in ionic concentrations following the heavy application were less than one‐half the increases that occurred at 20 cm. The concentrations of most ions returned to background levels within 1 year after sludge application. From the time sludge was applied in June 1975 until the end of the growing season in October 1976, leaching losses for calcium were estimated as 18 kg/ha for the control plots, compared to 39 kg/ha from plots receiving the heavy application. Comparable estimates for SO4 were 35 kg/ha for the control plots and 64 kg/ha for plots receiving the heavy sludge application.There were no significant differences in basal‐area growth among control and treated plots for the first two growing seasons after sludge application. In the herb and shrub layer only 3 of the 31 commonly occurring species showed statistically significant changes in frequency. All three changes were on plots receiving the heavy application. Sugar maple (Acer saccharum F.) seedlings declined from an average of 22/m2 before application to 17/m2 in the second summer after application. The shrub Viburnum alnifolium Marsh, increased from an average of 5/m2 before application to 11/m2 after and the herb Viola pallens Brainerd increased from 15/m2 before to 21/m2 after.

Digestibility and Related Nutritional Data for Seven Northern Deer Browse Species

Energy use and related data are presented for seven northern winter foods of white-tailed deer (Odocoileus virginianus). Hemlock (Tsuga canadensis), balsam fir (Abies balsamea), red maple (Acer rubrum), striped maple (A. pensylvanicum), mountain maple (A. spicatum), hobblebush (Viburnum alnifolium), and hazelnut (Corylus cornuta) were fed in mixed rations to captive deer. Species tested had gross energy digestibilities ranging from 30 (red maple) to 54 percent (hobblebush). The amount of digestible, metabolizable, and net energy in each of the three maple species evaluated was very sim- ilar. Metabolizable energy ranged from 24 percent (1.2 kcal/g) for striped maple to 46 percent (2.2 kcal/g) for hobblebush. The lowest net energy was observed for striped maple (5 percent or 0.2 kcal/g), the highest for hobblebush (37 percent or 1.8 kcal/g). Crude protein was digested poorly in hemlock, balsam, and red maple (-5, 11, and 1 percent digestible, respectively) as compared with an average value of 47 percent for the remaining 4 species. The digestibilities of fat, fiber, and nitrogen-free extract of the seven plant species are presented and discussed. An example of the calculation of browse require- ment during a northern winter period, based on these and related data, is presented. J. WILDL. MANAGE. 40(4):630-638

The Vegetation of the Ravines of the Southern Finger Lakes, New York, Region

The vegetation pattern of the forested ravines found in the southern Finger Lakes region of New York State was analyzed, using several approaches, including community-type and agglomerative classifications, direct gradient analysis (composite transects and weighted averages), and Bray and Curtis ordination. These tended to converge upon a single interpretation, although there were variations depending upon the method. The most important axis of vegetational variation was along the ravine-side gradient from bottom to top. The bottomlands were dominated by sugar maple and beech with basswood and elm, and sometimes bitternut hickory. Low-slope trees were primarily sugar maple, beech and basswood. Hemlock became more important going upslope, dominating almost completely on middle to upper-middle-slope stands. Oak-hemlock stands characterized the uppermost ravine slopes. Understory shrubs and herbs were most dense and diverse on lower to middle slopes. Lower-slope understory species included Taxus baccata, Viburnum alnifolium, Ribes cynosbati, Solidago flexicaulis, Caulophyllum thalictroides, Actaea alba and Viola spp. Maianthemum canadense, Medeola virginiana and Aralia nudicaulis were common under hemlock. On the upper slopes, in the more open oak stands, the understory was richer than in the hemlock stands. Upper-slope understory species included Viburnum acerifolium, Phryma leptostachya, Sanicula spp. and Osmorhiza claytoni, as well as some of the common lower-slope species. Certain structural features were associated with the ravine-side gradient as well. This pattern bears some similarity to those found in other New York ravines, and in the eastern deciduous forest in general. However, there are several differences, depending upon size of the ravine, aspect and geography. The relative merits of the methods used are briefly discussed. It is concluded that direct gradient analysis provides the most accurate pattern of ravine vegetation, but simple intuitive community classification can often be used for general purposes. INTRODUCTION Numerous steep ravines and vertical gorges provide one of the most striking and beautiful physiographic features of the southern Finger Lakes region of New York State. The ravines support well-developed forest vegetation which varies in composition with different ravine environments. Perhaps because of the general disturbance of natural communities throughout the whole region, there have been no quantitative ecological studies of the southern Finger Lakes vegetation. The more inaccessible ravines, however, are relatively undisturbed and, therefore, amenable to ecological analysis. This research was undertaken to examine the pattern of plant communities in these ravines. Of the many different approaches to vegetation study, no single one is entirely adequate for all kinds of vegetation. A clearer and more understandable picture of the vegetation is

The Hubbard Brook Ecosystem Study: Productivity, Nutrients, and Phytosociology of the Herbaceous Layer

The herb and shrub layers of the control northern hardwood forest ecosystem at Hubbard Brook contain 96 species of plants. This ecosystem, 13.2 ha in size, has a southeast—facing aspect, an average slope of 26%, and an altitudinal range of 545 to 791 m. Vascular cryptogams, woody saplings, shrubs, tree seedlings, and herbaceous phanerogams contributed 38%, 22%, 18%, 13%, and 8% respectively to the aboveground current growth in the herb—shrub layer. Ninety—three per cent of the current growth was localized in eight species in the 1966 summer growth aspect. Dryopteris spinulosa, Viburnum alnifolium, Acer saccharum, and Fagus grandifolia contributed 67% of the cover in the herb layer, and, respectively, made up 70% of the current growth of herbs, 83% of shrubs, 61% of tree seedlings, and 90% of saplings. For the ecosystem as a whole, the herbaceous layer contained 1.8 kg/ha K, 0.3 Mg, 0.3 Ca, 0.1 S, 0.09 Mn, 0.007 Fe, 0.008 Zn, 0.001 Na, and 0.001 Cu in the aboveground current growth. The herb—shrub layer responded in several ways to the elevational complex gradient. Species diversity increased by 50% and productivity tripled in the higher portions of the ecosystem coincident with a decrease in the productivity of the overstory. Increased productivity in the herb—shrub layer resulted from more luxuriant growth of species distributed throughout the ecosystem rather than from increased species diversity. Based on a phytosociological comparison of sites occurring at similar elevations but under different geological conditions, the Hubbard Brook ecosystem is placed near the oligotrophic end of a nutrient scale for northern hardwood forest ecosystems in the mountains of New England.