Pseudoreplication is defined. as the use of inferential statistics to test for treatment effects with data from experiments where either treatments are not replicated (though samples may be) or replicates are not statistically independent. In ANOVA terminology, it is the testing for treatment effects with an error term inappropriate to the hypothesis being considered. Scrutiny of 176 experi- mental studies published between 1960 and the present revealed that pseudoreplication occurred in 27% of them, or 48% of all such studies that applied inferential statistics. The incidence of pseudo- replication is especially high in studies of marine benthos and small mammals. The critical features of controlled experimentation are reviewed. Nondemonic intrusion is defined as the impingement of chance events on an experiment in progress. As a safeguard against both it and preexisting gradients, interspersion of treatments is argued to be an obligatory feature of good design. Especially in small experiments, adequate interspersion can sometimes be assured only by dispensing with strict random- ization procedures. Comprehension of this conflict between interspersion and randomization is aided by distinguishing pre-layout (or conventional) and layout-specifit alpha (probability of type I error). Suggestions are offered to statisticians and editors of ecological j oumals as to how ecologists' under- standing of experimental design and statistics might be improved.

/pdf/pseudoreplication-and-the-design-of-ecological-field-44o8kzdaoi.pdf

Pseudoreplication and the Design of Ecological Field Experiments

Nitrogen is a key element controlling the species composition, diversity, dynamics, and functioning of many terrestrial, freshwater, and marine ecosystems. Many of the original plant species living in these ecosystems are adapted to, and function optimally in, soils and solutions with low levels of available nitrogen. The growth and dynamics of herbivore populations, and ultimately those of their predators, also are affected by N. Agriculture, combustion of fossil fuels, and other human activities have altered the global cycle of N substantially, generally increasing both the availability and the mobility of N over large regions of Earth. The mobility of N means that while most deliberate applications of N occur locally, their influence spreads regionally and even globally. Moreover, many of the mobile forms of N themselves have environmental consequences. Although most nitrogen inputs serve human needs such as agricultural production, their environmental conse- quences are serious and long term. Based on our review of available scientific evidence, we are certain that human alterations of the nitrogen cycle have: 1) approximately doubled the rate of nitrogen input into the terrestrial nitrogen cycle, with these rates still increasing; 2) increased concentrations of the potent greenhouse gas N 2O globally, and increased concentrations of other oxides of nitrogen that drive the formation of photochemical smog over large regions of Earth; 3) caused losses of soil nutrients, such as calcium and potassium, that are essential for the long-term maintenance of soil fertility; 4) contributed substantially to the acidification of soils, streams, and lakes in several regions; and 5) greatly increased the transfer of nitrogen through rivers to estuaries and coastal oceans. In addition, based on our review of available scientific evidence we are confident that human alterations of the nitrogen cycle have: 6) increased the quantity of organic carbon stored within terrestrial ecosystems; 7) accelerated losses of biological diversity, especially losses of plants adapted to efficient use of nitrogen, and losses of the animals and microorganisms that depend on them; and 8) caused changes in the composition and functioning of estuarine and nearshore ecosystems, and contributed to long-term declines in coastal marine fisheries.

/pdf/human-alteration-of-the-global-nitrogen-cycle-sources-and-1xgqgm60gm.pdf

Human alteration of the global nitrogen cycle: sources and consequences

. Abstract Research on fragmented ecosystems has focused mostly on the biogeograpbic consequences of the creation of habitat “islands” of different sizes and has provided little of practical value to managers. However, ecosystem fragmentation causes large changes in the physical environment as well as biogeograpbic changes. Fragmentation generally results in a landscape that consists of remnant areas of native vegetation surrounded by a matrix of agricultural or other developed land. As a result fluxes of radiation, momentum (La, wind), water, and nutrients across the landscape are altered significantly. These in turn can have important influences on biota within remnant areas, especially at or near the edge between the remnant and the surrounding matrix. The isolation of remnant areas by clearing also has important consequences for the biota. These consequences vary with the time since isolation distance from other remnants, and degree of connectivity with other remnants. The influences of physical and biogeographic changes are modified by the size, shape, and position in the landscape of individual remnant, with larger remnants being less adversely affected by the fragmentation process. The Dynamics of remnant areas are predominantly driven by factors arising in the surrounding landscape. Management of, and research on, fragmented ecosystems should be directed at understanding and controlling these external influences as much as at the biota of the remnants themselves. There is a strong need to develop an integrated approach to landscape management that places conservation reserves in the context of the overall landscape

Biological consequences of ecosystem fragmentation: a review

/pdf/biological-consequences-of-ecosystem-fragmentation-a-review-2z02qtnwxh.pdf

Biological Consequences of Ecosystem Fragmentation: A Review

Soil erosion is a major environmental threat to the sustainability and productive capacity of agriculture. During the last 40 years, nearly one-third of the world's arable land has been lost by erosion and continues to be lost at a rate of more than 10 million hectares per year. With the addition of a quarter of a million people each day, the world population's food demand is increasing at a time when per capita food productivity is beginning to decline.

https://science.sciencemag.org/content/sci/267/5201/1117.full.pdf

Environmental and Economic Costs of Soil Erosion and Conservation Benefits

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.

https://www.jstor.org/stable/pdfplus/1942440.pdf

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

Both harvest removal and leaching losses can deplete nutrient capital in forests, but their combined long-term effects have not been assessed previously. We estimated changes in total soil and biomass N, Ca, K, Mg, and P over 120 years from published data for a spruce-fir site in Maine, two northern hardwood sites in New Hampshire, central hardwood sites in Connecticut and Tennessee, and a loblolly pine site in Tennessee. For N, atmospheric inputs counterbalance the outputs, and there is little long-term change on most sites. For K, Mg, and P, the total pool may decrease by 2%–10% in 120 years depending on site and harvest intensity. For Ca, net leaching loss is 4–16 kg/ha/yr in mature forests, and whole-tree harvest removes 200–1100 kg/ha. Such leaching loss and harvest removal could reduce total soil and biomass Ca by 20%–60% in only 120 years. We estimated unmeasured Ca inputs from rock breakdown, root-zone deepening, and dry deposition; these should not be expected to make up the Ca deficit. Acid precipitation may be the cause of current high leaching of Ca. Although Ca deficiency does not generally occur now in acid forest soils, it seems likely if anthropogenic leaching and intensive harvest removal continue.

Long-term depletion of calcium and other nutrients in eastern US forests

We report the effects of deforestation on the export of particulate matter, erodi- bility of the ecosystem, and the relative importance of dissolved substances and particulate matter in exported materials. The mature forested ecosystem is little affected by erosion, with an average annual particulate matter export of only 2.5 MT (metric tons) km-2 yr-1. Defor- estation and repression of growth for 3 yr increased export to a maximum of 38 MT km-2 yr-1, but the increase in export was exponential with rather minor increases in the first 2 yr after cutting and a sharp increase in the 3rd yr. This resulted because the ecosystem continued to exercise considerable control over erodibility for 2 yr after cutting without annual renewal of biotic regulation by primary productivity. Increases in particulate matter export are pri- marily due to increases in erodibility rather than increased flow rates. In the mature ecosystem, the average ratio of annual net export of dissolved substance to particulate matter is 2.3. Deforestation shifts this ratio to > 8.0 during the first 2 yr after cutting. This shift results because the export trends, for dissolved substances and particu- late matter following deforestation, are not synchronous. The first response to deforestation is mobilization of nutrients from the available nutrient and organic matter compartments and leakage in stream water. After 2 yr, particulate matter output rises sharply as biotic control of erodibility weakens, while dissolved substance export declines, probably because of diminu- tion of readily available nutrients stored within the system. This nonsynchrony, coupled with the action of natural species adapted to take advantage of the abundance of nutrients and water that results immediately after disturbance, may be considered as part of a homeostatic mechanism that allows rapid recovery of a forest ecosystem while minimizing the effects of erosion.

The export of nutrients and recovery of stable conditions following deforestation

Six West Thornton, New Hampshire watersheds are characterized by a near climax, northern hardwoods ecosystem, humid continental climate, and acid metamorphic rock. Concentration of Ca/sup + +/, Mg/sup + +/, K/sup +/, and Na/sup +/ in weekly precipitation samples was variable. The annual weighted average values (mg/liter) were; 1973-74, Ca 0.26, mg. 0.06, K 0.21, Na 0.09; 1964-65, Ca 0.30, Mg 0.12, K 0.19, Na 0.22. Differences were not related to elevation. The contribution of cations from dry fallout was negligible. Cation content of stream water was relatively very low. The weighted average content for the entire area (mg/liter) was Ca 1.18, Mg 0.38, K 0.26, Na 0.87 during 1963-64; and Ca 0.80, Mg 0.38, K 0.22, Na 0.91 during 1964-65. In general, the cationic concentrations in drainage water were constant although discharge of water varied greatly. Statistically, the relationship between concentration and discharge was not significant for Ca/sup + +/ and Mg/sup + +/ in any of the watersheds, but was inversely significant for Na/sup +/, and was possibly direct for K/sup +/ in a few instances. The budget for dissolved cations was calculated from determinations of input (cation concentration times volume of precipitation) and output (cation concentration timesmore » volume of runoff.) During 1963-64 the average inputs in kg/ha were 3.0 Ca/sup + +/, 0.7 Mg/sup + +/, 2.5 K/sup +/, and 1.0 Na/sup +/, while the output averaged 8.0 Ca/sup + +/, 2.6 Mg/sup + +/, 1.8 K/sup +/, and 5.9 Na+. During 1964-65 the values were: input, 2.8 Ca/sup + +/, 1.1 Mg/sup + +/, 1.8 K/sup +/, and 2.1 Na/sup +/; and output, 3.9 Ca/sup + +/, 11.8 Mg/sup + +/, 1.1 K/sup +/, and 4.5 Na/sup +/. Assuming that the vegetation is near synamic equilibrium, the net losses of Ca/sup + +/, Mg/sup + +/, and Na/sup +/ represent conservative measurements of geochemical weathering in the system. The K/sup +/ budget is probably near balance.« less

The Calcium, Magnesium, Potassium, and Sodium Budgets for a Small Forested Ecosystem.

We report the effects of deforestation on the export of particulate matter, erodibility of the ecosystem, and the relative importance of dissolved substances and particulate matter in exported materials. The mature forested ecosystem is little affected by erosion, with an average annual particulate matter export of only 2.5 MT (metric tons) km—2 yr—1. Deforestation and repression of growth for 3 yr increased export to a maximum of 38 MT km—2 yr—1, but the increase in export was exponential with rather minor increases in the first 2 yr after cutting and a sharp increase in the 3rd yr. This resulted because the ecosystem continued to exercise considerable control over erodibility for 2 yr after cutting without annual renewal of biotic regulation by primary productivity. Increases in particulate matter export are primarily due to increases in erodibility rather than increased flow rates. In the mature ecosystem, the average ratio of annual net export of dissolved substance to particulate matter is 2.3. Deforestation shifts this ratio to >8.0 during the first 2 yr after cutting. This shift results because the export trends, for dissolved substances and particulate matter following deforestation, are not synchronous. The first response to deforestation is mobilization of nutrients from the available nutrient and organic matter compartments and leakage in stream water. After 2 yr, particulate matter output rises sharply as biotic control of erodibility weakens, while dissolved substance export declines, probably because of diminution of readily available nutrients stored within the system. This nonsynchrony, coupled with the action of natural species adapted to take advantage of the abundance of nutrients and water that results immediately after disturbance, may be considered as part of a homeostatic mechanism that allows rapid recovery of a forest ecosystem while minimizing the effects of erosion. Thus, following destruction of the vegetation, the ecosystem maintains a residual resistance to erosion and has a high potential for repair through successional productivity. Nutrient flux and erosion losses return to previous levels as the intrasystem aspects of the hydrologic—nutrient cycle interaction and erodibility are increasingly regulated by biotic factors. These results relative to stable conditions and their reestablishment following disturbance may have applicability to a wide range of terrestrial ecosystems.

Robert S. Pierce

Papers

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

Long-term depletion of calcium and other nutrients in eastern US forests

The export of nutrients and recovery of stable conditions following deforestation

The Calcium, Magnesium, Potassium, and Sodium Budgets for a Small Forested Ecosystem.

The Export of Nutrients and Recovery of Stable Conditions Following Deforestation at Hubbard Brook