F. Herbert Bormann

Effects of Forest Cutting and Herbicide Treatment on Nutrient Budgets in the Hubbard Brook Watershed‐Ecosystem

All vegetation on Watershed 2 of the Hubbard Brook Experimental Forest was cut during November and December of 1965, and vegetation regrowth was inhibited for two years by periodic application of herbicides. Annual stream—flow was increased 33 cm or 39% the first year and 27 cm or 28% the second year above the values expected if the watershed were not deforested. Large increases in streamwater concentration were observed for all major ions, except NH4+, SO4 = and HCO3—, approximately five months after the deforestation. Nitrate concentrations were 41—fold higher than the undisturbed condition the first year and 56—fold higher the second. The nitrate concentration in stream water has exceeded, almost continuously, the health levels recommended for drinking water. Sulfate was the only major ion in stream water that decreased in concentration after deforestation. An inverse relationship between sulfate and nitrate concentrations in stream water was observed in both undisturbed and deforested situations. Average streamwater concentrations increased by 417% for Ca++, 408% for Mg++, 1558% for K+ and 177% for Na+ during the two years subsequent to deforestation. Budgetary net losses from Watershed 2 in kg/ha—yr were about 142 for NO3—N, 90 for Ca++, 36 for K+, 32 for SiO2—Si, 24 for Al+++, 18 for Mg++, 17 for Na+, 4 for Cl—, and 0 for SO4—S during 1967—68; whereas for an adjacent, undisturbed watershed (W6) net losses were 9.2 for Ca++, 1.6 for K+, 17 for SiO2—Si, 3.1 for A1+++, 2.6 for Mg++, 7.0 for Na+, 0.1 for C1—, and 3.3 for SO4—S. Input of nitrate—nitrogen in precipitation normally exceeds the output in drainage water in the undisturbed ecosystems, and ammonium—nitrogen likewise accumulates in both the undisturbed and deforested ecosystems. Total gross export of dissolved solids, exclusive of organic matter, was about 75 metric tons/km2 in 1966—67, and 97 metric tons/km2 in 1967—68, or about 6 to 8 times greater than would be expected for an undisturbed watershed. The greatly increased export of dissolved nutrients from the deforested ecosystem was due to an alteration of the nitrogen cycle within the ecosystem. The drainage streams tributary to Hubbard Brook are normally acid, and as a result of deforestation the hydrogen ion content increased by 5—fold (from pH 5.1 to 4.3). Streamwater temperatures after deforestation were higher than the undisturbed condition during both summer and winter. Also in contrast to the relatively constant temperature in the undisturbed streams, streamwater temperature after deforestation fluctuated 3—4°C during the day in summer. Electrical conductivity increased about 6—fold in the stream water after deforestation and was much more variable. Increased streamwater turbidity as a result of the deforestation was negligible, however the particulate matter output was increased about 4—fold. Whereas the particulate matter is normally 50% inorganic materials, after deforestation preliminary estimates indicate that the proportion of inorganic materials increased to 76% of the total particulates. Supersaturation of dissolved oxygen in stream water from the experimental watersheds is common in all seasons except summer when stream discharge is low. The percent saturation is dependent upon flow rate in the streams. Sulfate, hydrogen ion and nitrate are major constituents in the precipitation. It is suggested that the increase in average nitrate concentration in precipitation compared to data from 1955—56,as well as the consistent annual increase observed from 1964 to 1968, may be some measure of a general increase in air pollution.

NUTRIENT RELEASE FROM DECOMPOSING LEAF AND BRANCH LITTER IN THE HUBBARD BROOK FOREST, NEW HAMPSHIRE'

Rates of weight loss and nutrient release (N, P, S, K, Mn, Ca, Zn, Fe, Mn, Cu. Na) were measured in decomposing leaf and branch tissue from yellow birch, sugar maple, and beech, and in branch tissue from red spruce and balsam fir. Neither leaf nor branch decomposition differed significantly over an elevational range of 220 m. Decomposition rates for leaves varied with yellow birch > sugar maple > beech. The decomposition rate for hardwood branches was greater than that for conifer branches, but differences between hardwoods were not significant. Maximum decomposition rates occurred during the summer for both branch and leaf tissue. The rate of nutrient release from decomposing branch and leaf litter appears to be correlated with nutrient concentration in current litter fall, precipitation, and leaf wash. The concentration and absolute weight of N, S, and P in the leaf litter of all species increased with time. The amount of the increase as well as the initiation of nutrient release was influenced by C:element ratios in the leaf tissue. These studies also indicate that P levels can influence the mineralization or immobilization of other important nutrients. Carbon-to-element ratios in decomposing litter varied between species and elevation at different times of the year, but element:P ratios were much more uniform. In branch tissue the physical loss of N- and P-rich bark and buds offset any increase in concentration that would have occurred through decomposition. Potassium and magnesium were rapidly released from the litter by leaching. Similar minimum concentrations in leaf tissue indicate that critical C:element ratios also exist for these elements. Calcium release was similar to dry weight loss, indicating that it is a structural component primarily released by decomposition. Maximum nutrient release from current litter occurred in the autumn and summer. It was not correlated with the nutrient output from the ecosystem which occurred primarily

Acid Rain: A Serious Regional Environmental Problem

At present, acid rain or snow is falling on most of the northeastern United States. The annual acidity value averages about pH 4, but values between pH 2.1 and 5 have been recorded for individual storms. The acidity of precipitation in this region apparently increased about 20 years ago, and the increase may have been associated with the augmented use of natural gas and with the installation of particle-removal devices in tall smokestacks. Only some of the ecological and economic effects of this widespread introduction of strong acids into natural systems are known at present, but clearly they must be considered in proposals for new energy sources and in the development of air quality emission standards.

Linkages between Terrestrial and Aquatic Ecosystems

prehending the implications of this disposal downstream. The implications of this are more and more evident in the widespread cultural eutrophication of rivers and lakes. Attempts to understand these problems have been based upon information pieced together from separate (independent) aquatic and terrestrial studies. This ignores important linkages, is inadequate, and shows the need for a comprehensive understanding of the intricate and complicated interactions between land and water. The purpose of this paper, then, is to consider some of the ecological interactions and linkages that occur between

Nutrient Content of Litter Fall on the Hubbard Brook Experimental Forest, New Hampshire

Litter fall was collected throughout the year beneath a mature northern hard- wood forest in New Hampshire. The material, separated by species and plant part, was an- alyzed for dry weight and for 11 elements. Total aboveground litter fall averaged 5,702 kg/ha per year; leaves, branches, stems, and bark contributed 49.1%, 22.2%, 14.1%, and 1.7%, respectively. Other deciduous structures (i.e., bud scales, flowers, fruit), as well as insect frass and miscellaneous tissues, contributed 10.9%. The overstory contributed 98.0% of the total, and shrub and herbaceous layers contributed only 1.2% and 0.8%, respectively. The nutrient content of the litter totaled 140.4 kg/ha per year. The relative abundance for these 11 ele- ments was N > Ca > K > Mn > Mg > S > P > Zn > Fe > Na > Cu. Nitrogen, Ca, and K accounted for 80.6% of the total, and Zn, Fe, Na, and Cu contributed only 0.8%. The overstory, shrub, and herbaceous layers supplied 96.6%, 1.7%, and 1.6% of the nutrients, respectively. Litter fall occurred throughout the year, but there were seasonal peaks for many types of tissues. Autumn was most important, accounting for 49.7% of the litter and 56.0% of the nutrients. Summer and winter seasons supplied similar quantities of litter, 21.2% and 22.4%; however, 22.6% of the total nutrient fall occurred during summer compared with only 17.2% during the winter. Spring months supplied 6.7% and 4.1% of litter and nutrients,. respectively. Storms were very important in the timing of litter and nutrient fall. The extreme variability of litter fall is the result of differences between species, tissues, vertical structure of the vegetation, elevation, site, and time of year. In spite of this variation, nutrient-budget- studies reveal relatively small losses from the ecosystem. Large fluctuations in rates of nutrient flow, via litter fall, are readily absorbed within the ecosystem, thus preventing nutrient loss and maintaining efficient nutrient cycling.

Organic matter and nutrient dynamics of the forest and forest floor in the Hubbard Brook forest

SummaryThe forest floor is a major reservoir of organic matter and nutrients for the ecosystem and as such it influences or regulates most of the functional processes occurring throughout the ecosystem. This study reports on the nutrient and organic matter content of the forest floor of the Hubbard Brook Experimental Forest during different seasons and attempts to correlate results from studies of vegetation, litter, decomposition, stemflow, throughfall, and soil. An organic matter budget is presented for an undisturbed watershed.Average weight of the forest floor on an undisturbed watershed ranged from 25,500 to 85,500 kg/ha. The weighted watershed average was 46,800 kg/ha. Although the F and H horizons did not vary significantly with time, the L horizon increased significantly during the period June to August largely as a result of a severe hail storm. The order of abundance of elements in the forest floor was Nτ;Ca≷Fe>S>P>Mn>K>Mg>Na>Zn>Cu. The concentrations of Ca, K, and Mn decreased with depth in the forest floor while N, P, S, Na, Fe, Zn, and Cu concentrations increased. N:P ratios were similar in decomposing leaf tissue, the forest floor, litterfall, and net stemflow plus throughfall suggesting a similar pattern of cycling. S was proportional to N and P in decomposing leaf tissue, the forest floor, and litterfall. Net stemflow and throughfall were affected by a relatively large input of SO4=-S from the atmosphere. Residence times for elements in the forest floor were affected by inputs other than litterfall (precipitation, stemflow, and throughfall). Calculation of residence times using all inputs caused smaller values than if litterfall alone was used. While all residence times were reduced, the major differences occurred for K, S, and Na. N and P showed relatively long residence times as a result of retranslocation and immobilization by decomposers. The slow turnover rate because of the strong demand and retention by all biota must account for the efficiency of the intrasystem cycling process for N and P. K showed the shortest residence time. A rapid and efficient uptake of K by vegetation seems to account for the efficient cycling of this element. The patterns of nutrient cycling are several depending on the chemical properties of the forest floor, and nutritional requirements of the biota.

Rapid, plant-induced weathering in an aggrading experimental ecosystem

To evaluate whether rates of weathering of primary minerals are underestimated in watershed mass-balance studies that fail to include products of weathering accumulating in plants and in developing soil, changes in the calcium and magnesium content of vegetation and soil fractions were measured in large, monitored lysimeters (sandbox ecosystems) at Hubbard Brook Experimental Forest, New Hampshire. Weathering was evaluated over 4–8 yr in sandboxes planted with red pine (Pinus resinosa Ait.) and kept mostly free of vegetation (nonvegetated). Three mass-balance equations were used that cumulatively include (a) Ca and Mg in precipitation inputs and drainage outputs, (b) accumulation of Ca and Mg in vegetation, and (c) changes in products of weathering in soils. Soil products were evaluated with an extraction process designed to avoid removing ions from primary minerals. Relative to the input-output equation, the estimated rate of weathering increased 2.4 (Ca) and 1.8 (Mg) times when accumulation of Ca and Mg in pine biomass was accounted for, and 8 (Ca) and 23 (Mg) times when changes in soil products were also included. Weathering estimates that included accumulation in vegetation and soil products were 261 (Ca) and 92 (Mg) kg ha-1 yr-1 in the pine sandbox. These rates were 10 (Ca) and 18 (Mg) times higher than the rates in the nonvegetated sandbox, which were not significantly greater than zero. This study raises the possibility that weathering can play a significant role in the release of nutrients available to plants over short periods. Faster rates like this become extremely important where managers are trying to balance nutrients available to plants from precipitation and weathering release with outputs including harvest removals.

Role of Erythronium americanum Ker. in Energy Flow and Nutrient Dynamics of a Northern Hardwood Forest Ecosystem

The aboveground activity of the spring herb, Erythronium americanum, is restricted to the period between snowmelt and forest canopy development. Its phenology and production capacity closely adapt the species to this temporal niche in northern deciduous forests. While E. americanum has a minor effect on energy flow, it may reduce losses of potassium and nitrogen from the ecosystem during the period of maximum removal by incorporating these elements in accumulating biomass. Later, during the summer, these nutrients are made available when the above-ground, nonperennating tissues decay.

Rapid N^2 Fixation in Pines, Alder, and Locust: Evidence From the Sandbox Ecosystems Study

Not all nitrogen (N) inputs have been accounted for in forested ecosystems. We sought to account for N2 fixation and dry deposition using a lysimeter mass—balance approach. Large sand—filled, field lysimeters were used to construct 5—yr nitrogen budgets for two N2—fixing trees, two pines, and a nonvegetated control soil. This approach is a promising and straightforward technique for quantifying otherwise difficult—to—measure fluxes. Accurate assessment of changes in N storage combined with direct measurement of N inputs in precipitation and losses from leaching allowed as to estimate fluxes. Gains of N in pine systems were greatest in vegetation and litter, overshadowing combined losses from mineral soil and leaching by about threefold. Rapid acetylene reduction in pine rhizospheres and in cultures from washed roots suggests that unexplained gains are due to associative N2 fixation. These results provide strong evidence for N2 fixation in pine systems of °50 kg°ha—1°yr—1 N. The symbiotic N2—fixing trees black locust and black alder fixed 2 and 5 times more N2, respectively, than did pines. In all systems, input in precipitation and dry deposition were relatively unimportant to the N budget. Unexplained losses of N from the nonvegetated control suggest that denitrification is an important flux. Mineral soil organic matter declined sharply and significantly in pines (20%) and even more so in the nonvegetated control (40%). Symbiotic N2—fixing trees caused a small, nonsignificant increase in mineral soil organic matter and large, significant increases in litter layer organic matter and large, significant increases in litter layer organic matter. Bulk density (0—20 cm) declined by 5% under symbiotic N2—fixing trees and increased by 5% in one pine sandbox. Correction for soil expansion or collapse did not greatly alter estimates of unexplained N or N2 fixation. Pines with rhizospheres that fix N2 at the rates we observed might be used to restore degraded land and to create silvicultural systems that are N self sufficient. We first need to better understand the microbiology, tree genetics, and soil conditions that lead to rapid N2 fixation in pine ecosystems.

Comparison of nutrient-use efficiency and biomass production in five tropical tree taxa

Abstract Casuarina equisetifolia, Albizia procera, Eucalyptus robusta and two varieties of Leucaena leucocephala (K8 and P.R.) were grown for 5.5 years in an experimental plantation in the Lajas Valley of Puerto Rico (18°N, 67°W). Rates of biomass accumulation were high, resulting in correspondingly high rates of nutrient accumulation in harvestable biomass. A comparison among species and among tissue types within species indicated that nutrient-use efficiency for N, P, K, Ca and Mg varied widely among species (ranging up to 10-fold differences) and tissues (up to 15-fold). With the highest growth rate, Casuarina was most efficient in using nutrients (N, P, K and Mg) to build biomass. With a quarter of Casuarinas growth rate, Leucaena K8 was the least efficient (N, K, Ca and Mg). For most of the studied nutrients, stem wood and large branches were the most nutrient-efficient tissue, followed by small branches, bark and then leaves. Nutrients stored in the litter layer below these species varied up to three-fold among species. Using a variety of species and biomass harvest scenarios, this study demonstrated the potential for significant alterations in the high rates of nutrient removal associated with short-rotation, intensively managed plantations.