Today many care about our forests. They have educated themselves to a great degree, and always want to learn more. We have just now the opportunity to easily understand some vital unseen forest workings we have never widely considered before -- forest nutrients.

More frequently scientists question whether there will continue to be an adequate supply of nutrients for maintaining optimum productivity of our forests and streams. These concerns are magnified when it is remembered that many forested sites in eastern U.S. had past uses, such as cropping, grazing, or timber harvest, that involved substantial nutrient removals from the original forest that itself had very limited geological fertility. Today increasing use of whole tree harvests at shorter intervals also increases concern about site impoverishment. Also, in more recent times, these forests have been subjected to atmospheric deposition which accelerates nutrient losses. Finally the rapidly regrowing forest is internally locking up nutrients in its tree biomass.

Calcium is a logical element for illustrating nutrient considerations. Harvests remove a substantial amount of calcium in forest products, and also trigger increased leaching of calcium from forest soils to streams and groundwater. A recent paper by Federer, et al, "Long-term Depletion of Calcium and Other Nutrients in Eastern U.S. Forests" (1989), has demonstrated the need to be concerned about timberstand depletion of calcium from forests in the eastern U.S. Stream impoverishment cannot be long behind site impoverishment. Calcium is a vital mega-nutrient for brook trout.

U.S. Fish & Wildlife Service trout physiologists in New York found that the Adirondack brook trout could absorb over half its body building calcium through its gills, rather than as dietary calcium. When it was held in water with little dissolved calcium it elevated its metabolic uptake rate as though it was held in 15 degrees F warmer water to try to pick up more calcium. This is very stressful and unthrifty. Calcium additionally directly neutralizes acidity and offsets aluminum toxicity, and in nutrient poor (low calcium) water acidity and aluminum are what kill fish.

Likens et al. (1977) show that the calcium cycle for northern hardwood forests can be divided into 13 interrelated pathways for transfer of calcium from one storage pool to another, and there are at least eight major pools. Generally 80% of all nutrients are in the soil pool. Calcium’s relationship to other nutrients is shown in Table 1 for six east U.S. sites. Generally nutrients are tightly cycled within the Forest, and only 2% are "lost" each year to streams. This is what nourishes trout.¹

Calcium removed during whole-tree harvest was 344 kg/ha for northern hardwoods, 494 kg/ha for spruce-fir, and 530 kg/ha for central hardwoods. A kilogram per hectare equals a little over 1/10 more than a pound per acre; 344 becomes 307 lbs/ac. They are about the same.

Harvesting has two major impacts on calcium capitals. First, the calcium incorporated in the harvested products is carried away from the site. Second, for the first few years after harvest, there are no live tree roots to take up moisture and twice as much flow works its way through the site carrying away nutrients. Without shade bio-chemical activity is increased as it warms. As a result, more calcium leaches from the cut-over site, increasing the amount of dissolved calcium in stream flow or more often just maintaining its concentration in an increased flow.²

Increased losses of calcium nearly disappeared by the end of the third year after harvest, but totals of increased losses to leaching for the three years were 30 kg/ha for northern hardwoods, 43 kg/ha for spruce-fir, and 28 kg/ha for central hardwoods. At Parsons, WV, the nutrient loss was 40 lbs/ac, and this equaled one-half the normal annual loss to the stream. In North Carolina their calcium loss at clear cut was more than their normal annual loss of calcium. This can be called the "Nutrient Shock at Clearcutting" and the average nutrient loss of calcium due to clearcutting (40 lbs/ac) may equal about 1/10 of the nutrients in a whole-tree harvest (500 lbs/ac).

One way of evaluating these losses is in terms of how they drain the capitals of the forest floor and mineral soil (see Table 1). For example, in Maine combined leaching ("Nutrient Shock") losses (43) and harvest removal (484) of calcium for the spruce-fir site is 537 kg/ha, and represents a depletion of about 5% of the capital in the forest floor and mineral soil (10,770 kg/ha). This rather small depletion of a fairly large calcium capital would not seem to present a problem for future productivity. On the other hand, the leaching losses and removals for the Connecticut central hardwood site (558 kg/ha) represent a depletion of over 16% of the capital in the forest floor and mineral soil (3,420 kg/ha). The greater depletion of an already small capital raises a concern regarding future timberstand productivity.

Atmospheric deposition raises concerns about calcium depletion beyond those associated with nutrients removed in the harvest and the loss ("Shock") during harvesting. Input-output budgets for today’s eastern U.S. forests show a net annual loss of calcium. "Acid Rain" is largely sulfuric Acid. As mobile sulfate anions in acid precipitation pass through the forest ecosystem, the hydrogen ions they were coupled with in precipitation are exchanged for other cations, such as calcium, potassium, and magnesium. The hydrogen ions stay behind to acidify the forest ecosystem while the cations are leached to streams and groundwater in the form of nutrients coupled with the sulfate ion. The net losses appear small on an annual basis (5 kg/ha) but assume greater importance when extrapolated over longer times, such as a 100-year timber rotation. A loss of 5 kg/ha/yr in the last 50 years becomes a loss of 250 kg/ha.

Acid Rain, however, has not been as intensively acid as it is today, (pH 4.2), and probably 70 years ago it was 5.2 or ten times less actively dissolving out nutrients. Additionally, a sulfate sink may have existed in these soils, so not all that fell left the soil carrying away nutrients. The 10-year national acid rain study estimates the sulfate sink shrunk over the last 40 years to only 3% retention today. We cannot say there was a deficit beyond 50 years ago. Prior to Acid Rain we would have expected more of an equilibrium, These added Acid Rain losses would surely have been an impoverishment of over 200 lbs/ac.³ The accounting follows.

A small amount of calcium, 2.5 kg/ha, is added to forest ecosystems in annual precipitation. Dry forest interception adds the same amount. Total input then is 5 kg/ha. Acid Rain dissolves out nutrients; consequently 8 to 17 kg/ha are lost each year as dissolved calcium in stream flow with an average of about 12 kg/ha. This is a deficit of at least 5 kg/ha per year from today’s eastern regrowing forests. This would seem to be an impoverishment of an otherwise undisturbed eastern forest in an era of "Acid Rain."

We do not know what the "natural" export of nutrients would be without Acid Rain, because Acid Rain has been everywhere for the last 50+ years; also "natural" processes were profoundly altered by the first logging, and our knowledge of the "natural" is greatly limited.4 However as Federer and others note, Acid Rain could not have been around much longer than 100 years or we would have little nutrients left in extensive forested areas today. Also with a pH near 5.2, 1/10 as active, watersheds would perhaps be exporting only 1/10 as much today; and this would be in near equilibrium with nutrient inputs from air and rock -- 100+ years ago.

The original forest may have accumulated many nutrients by trapping airborne wet and dry (dust) deposition over its 10,000+ years. In this great time interval the slow weathering rate we note today of new nutrients from underlying rock could have accumulated at least some fertility in its trees, deep forest floor, and soil. Large trees with deep roots and old rooting systems in deep soils may have mined nutrients and moisture efficiently. We do not know, all this was lost at the first logging.

Nearly all eastern forests are second growth. In many cases, the early harvests were intensive and were followed by fire burning deeper than ever before in the great logging slash created by man. The forest floor and top soil washed or blew away. The subsoil, always slow to re-vegetate, could have been lost particularly on slopes, if the rate of erosion was faster than re-vegetation. Clearing and burning for farms and grazing also caused nutrient loss. The nutrients removed in the first harvest, from the start of land clearing until reversion to forest in the early 1900's, included approximately 1,000 kg/ha of calcium, according to U.S. Forest Service researchers (Martin, and others) in New Hampshire.

Consideration of past land use is an absolute necessity for sites like the central hardwood forest in Connecticut. Present-day nutrient capitals are small, as evidenced by the total of just over 3,400 kg/ha of calcium in mineral soil and forest floor, partly because of removals during earlier land uses. Any additional removals and leaching losses could have serious consequences for site productivity. Studies indicate that additional inputs from rock breakdown, root-zone deepening, and dry deposition cannot begin to replace this lost calcium. The best estimate is only 1 mm of rock breakdown every 10,000 years, and nutrient regeneration from weathering is then near zero - perhaps 1 kg/ha/yr. See Federer, et al., 1989).

These net losses of calcium to "Acid Rain" leaching over a 100 year rotation easily total 200 kg/ha. The estimated losses from the original site from the start of land clearing until reversion to forest in the early 1900's were approximately 1,000 kg/ha of calcium. This is a loss of calcium from every hectare (acre) of the eastern forest of 1200 kilograms (pounds).

It is unlikely the West Virginia infertile sandstone mountains had originally more nutrients than the Connecticut site -- perhaps about 6000 kg/ha calcium to begin with here. The original logging disturbance may have been responsible for the loss of 1000 kg/ha. With the most Acid Rain in the nation, I would estimate at least another 200 kg/ha to have been leached out in the last 50+ years. These mountains then today have a remaining calcium capital of 4800.

The original calcium capital in the sandstone forest of WV above rotten rock may have been roughly 6000 kg/ha or lbs/ac. (Near Oak Ridge, TN. values of 5,400 and 6,310 today were obtained.) This 6000 is what produced this original forest. It is reduced to 4800 or 80% of this today. What can be expected then of today's 100 year old rapidly growing forest with 1/5 less calcium? At what rate will its soil and forest floor fertility, biomass and structure recover? To what degree is timber a "renewable resource" in infertile watersheds?

Any whole-tree clear cut will remove another 500 lbs/ac, but a more common stem-only clear cut would remove only 300. Let us use 300. Also there is a nutrient ("Shock") loss at clear cut harvests of 40. A second harvest would then reduce today’s nutrient capital of 4800 by 300 plus 40 to 4,460 lbs/ac, and reduce the original calcium supply of 6000 to 4460 or by 25%.

Can we expect a harvest (a loss of 300 kg/ha more) of a recovering forest? Should we tolerate an added clear cut nutrient loss ("shock") of 40 lb/ac? Also what of its trout stream nutrient supply in impoverishing, acidifying, growing forests. Besides the loss of nutrients from the watershed there has been for 100 years in the rapidly growing eastern forest an internal cycling of nutrients into tree growth that locks-up more and more nutrients. If a whole tree harvest today may remove 500 lbs/ac of calcium, then this is the present tree calcium "pool." Further, then for 100 years the average calcium up-take into tree regrowth has been 5 lbs/ac/yr. This diversion from stream nutrient supply is then roughly quantified also. In New England between 1952 and 1976 the volume of standing wood has increased by about 70%. In West Virginia from 1975 to 1989 it has increased over 1/3 or 2.6%/yr. The uptake of nutrients by trees is roughly equal to the nutrients leached away in stream flow, 5 lbs/ac/yr.

This diversion perhaps did not much take place in the original forest. It is significant that slower growing old stands may be taking up nutrients at a slower rate and returning more, but if evapotranspiration also slows, stream flows will increase and nutrient concentrations then being more dilute may not increase.

This 5 lbs/ac/yr diversion of calcium to tree growth is incidentally generally equal to the Acid Rain accelerated watershed leaching impoverishment rate. Both impoverish the site (soil), but not the stream. In streams these two processes off-set, maintaining a nutrient status quo in streams. Fortunately for trout and associated fish species in many infertile stream reaches Acid Rain, by leaching out nutrients, enriches streams today. Obviously trout populations in our forest streams then are "hooked on Acid Rain." (Acid Rain scientists first said this among themselves with great consensus in 1990.) How much longer watersheds can continue the present export rate of nutrients is unknown. "Fish-loss" is occurring, and impoverishment would then seem to have reduced nutrient supply and export even though Acid Rain accelerates nutrient export to streams today. We must stop Acid Rain and not further damage our forest watersheds.

The six sites studied in the east do average 8,000 kg/ha in calcium capitol today - Table 1. There is little reason to believe it ever was this rich here, but the WV (or PA) figure is the least certain because the studies have been done elsewhere. However, with such data as this at last available, professionals and citizens can better understand what they are charged to project and what a critical condition some portions of the eastern forest and their streams are in. Clearly we need a prompt and thorough clean-up of sulfur emissions that would reduce Acid Rain. Clearly also we need a wider and more thorough understanding of our forest resource. This rough, early quantitative data also clarifies why the maintenance of nutrient poor trout stream populations must be a legitimate, critical concern of multi-use forests. Trout are considered every bit as much a product of a public multi-use forest as is timber. Short term stream enrichment should not occur at the expense of forest nutrient capital. My very preliminary estimate indicates it may require 20 lbs/ac/yr export of calcium from the watershed to nourish a reproducing brook trout population year-round enabling them to withstand the springtime acidity and toxic aluminum exposures in strong flows with 2 mg/l concentrations of dissolved calcium. To supply a steady necessary affordable nutrient level to pure trout streams, hopefully with a timber harvest, is a challenge to the watershed management concepts of professionals and others.

Total nutrients today above Rotten Rock (particles <2mm) in kg/ha., in a Conn. (Oak, Beech, Maple forest), in Maine (Spruce and Hemlock),

in 2 New Hampshire sites (Beech, Maple), in a Tenn. Pine site, and a Tenn. Oak, Hickory, Tulip & Maple site - Federer, et al., "Environmental Management", 13(5),1989.

¹ There are 200 miles of fishless, otherwise native brook trout streams that are "too pure for trout" (too nutrient poor) in and just west of the Monongahela National Forest. These have about one part per million calcium.

² Elsewhere, and with six other authors, Hornbeck states - "Streamflow for the first year after whole-tree clearcutting was increased by 63% in Maine, 45% in N.H. and 22% in Conn."

³ Some scientists, including Jim Hornbeck himself, multiply this Acid Rain annual leaching loss of 5 kg/ha/yr by 100 years and get 500 kg/ha total calcium impoverishment. This loss occurred everywhere so would then be equal to a whole-tree clearcut of the entire eastern forest - as both leaching loss and a harvest loss equal 500 lb./ac. This Acid Rain effect would be a harvest forgone; and then the proposed second cut is not the second, but nutrient-wise, the third.

4 Writing elsewhere more recently (1992) with six other authors Jim Hornbeck (et al.) state: "Because acid precipitation in New England causes large annual losses of calcium, even in the absence of cutting, we are concerned about the general depletion of calcium from northern forests. With whole-tree clearcuts, the loss of calcium is 13-33% in 100 years for one harvest and 21-58% for three harvests at the four sites examined. Acid precipitation and whole-tree clearcut harvest removal contribute about equally to calcium depletion. It is likely that repeated harvests over short rotations will lead eventually to calcium deficiencies. Calcium depletion already may contribute to Red Spruce mortality at high elevations." _