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Abstract. 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 em or 39% the first year and 27 em 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 NH 4 +, S0 4 = and HC0 3 -, 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% forK+ 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 N0 3 -N, 90 for Ca++, 36 forK+, 32 for Si0 2 -Si, 24 for AI+++, 18 for Mg++, 17 for Na+, 4 for C!-, and 0 for SOrS during 1967-68; whereas for an adjacent, undisturbed watershed (W6) net losses were 9.2 for Ca + +, 1.6 for K +, 17 for Si0 2 -Si, 3.1 for AI+++, 2.6 for Mg+ +, 7.0 for Na +, 0.1 for Cl-, and 3.3 for SO~-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, stream water temperature after deforestation fluctuated 3-4 o 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...

A small watershed in the White Mountains of New Hampshire bearing mesophytic, cool—temperate, broadleaf—deciduous forests was studied. Acer saccharum, Betula lutea, and Fagus grandifolia are dominant, but toward higher elevations Picea rubens and Abies balsamea also occur and indicate the transition toward subalpine climate. The stands are young (following cutting in 1909—17) but contain older trees; stand composition is thought reasonably representative of the climax. For application of the Brookhaven system of forest dimension analysis, 93 sample trees of major species were cut and roots excavated. Mean dimensions of sample trees, and the constants for the system of logarithmic regressions relating volume, surface, mass, and growth to diameter at breast height and other independent variables, show decrease in tree sizes and height/diameter ratios toward higher elevations. Stand characteristics, based on application of the regressions to forest samples, show trends of decrease for the elevation belts from low to high: stem basal area 26.3, 23.7, and 22.0 m2/ha, weighted mean tree height 16.9, 16.7, and 10.8 m, weighted mean age 124, 95, and 83 yr, stem wood volume 176, 155, and 103 m3/ha, aboveground biomass (dry matter) 162, 152, and 102 t/ha, estimated volume increment 379, 365, and 223 cm3/m2/yr, aboveground net primary productivity (1956—60) 1127, 1041, and 790 g/m2/yr, and leaf area ratio 6.2, 5.7, and 5.5 m2/m2. Biomass (and, presumably, production) of root systems is 18%—21% of that aboveground. Different estimations suggest that a mean climax biomass for the watershed may be around 350 t/ha, aboveground. Net ecosystem production (i.e., addition to the pool of woody biomass in the community) is estimated as 350 g/m2/yr aboveground and 85 belowground for 1956—60, 238 and 52 g/m2/yr for 1961—65. Analysis of stem wood volume increments reveals an abrupt and striking (18%) decrease in volume growth and productivity from 1956—60 to 1961—65. The net primary productivity of the former period, with a weighted mean for the watershed of 1110 g/m2/yr above and below the ground, is thought more nearly normal for the forest. Both drought and effects of increasing air pollution (notably increasing acidity of rainfall) may be responsible for the recent decrease in productivity.

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 form 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 during the spring. The net output of Ca, Mg, and K from the watershed was very small compared to quantities released from current litter. Factors which contribute to the complex nature of decomposition are: seasonal heterotroph activity, heterotroph nutrient demand, environmental conditions regulations heterotroph activity, species tissue palatability, species composition of litter, tissue composition of litter, nutrient content of litter, nutrient mobility, and nutrient input (i.e., leafwash, litter fall).

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.