Back to Forests of the Central Appalachians |
Back to Forests of the Central Appalachians | Feedback
pH of Freshly Fallen LeavesAugust, 2001
Fallen leaves of 33 deciduous and coniferous species were collected over a two month period from October to December 2000. A caveat here, however, is that leaves of most conifers were taken from recently dead material on trees. Most samples were from terrain underlain by Ordovician Beekmantown dolomitic limestone, but seven were from a north — facing colluvial slope underlain by Cambrian Elbrook limestone (Rader, 1967). Six forest types were represented, and although most samples were from calcareous substrates, some were from substrates developed on highly acidic chert within the calcareous terrain (see our section on Hydrastis canadensis L) . The period of collection was exceptionally dry, with only a few light rains. Thus, there is an increased probability that chemical leaching of the leaves was minimal.
All leaf samples were shredded with the fingers and slurries formed with the fragments and rainwater. The initial pH determinations of each sample were done after the slurry stood for 24 hours and these were followed by others, usually after an additional 24 hours. A Hydrion Ultrafine pH Test Paper Set (Fisher) was employed. These papers had the advantages of simplicity, small sample size and low cost. Color matches every 0.2 — 0.3 pH units may in principle be obtained over the range of interest here, and usually several overlapping papers could be employed. All determinations were at room temperature. The pH determinations were observed to be independent of the leaf / water ratio and the pH of the water used, as might be expected. Also, little or no difference was noted between several pH determinations of each sample done after either the 24 or 48 hour soaking periods or between the two period results. Reproducibility for each individual sample was usually within 0.2 units.
As indicated in the table captions, 40 samples were from trees on Beekmantown dolomitic limestone. Of these 17 were from calcareous colluvium, 10 were from ericaceous oak forest associated with chert, 8 were from an old field 1 was from chert talus, 2 were from a calcareous flood plain and 2 from trees that had been planted in shallow soil above limestone. To obtain wider coverage seven samples were also collected from the north — facing slightly acid / mesic colluvial slope on Elbrook Formation. In the following table the leaves of the species are arranged roughly from low to high pH.
No Species pH Date Forest Type 1 Cercis canadensis 4.3 10-30-00 1 2 Quercus coccinea 4.3 11-1-00 2 3 Quercus coccinea 4.5 11-19-00 2 4 Pinus virginiana 4.4 11-14-00 3 5 Pinus rigida 4.4 11-28-00 3 6 Prunus serotina 4.5 11-8-00 3 7 Acer saccharum 4.5 11-24-00 1 8 Acer saccharum 4.6 11-22-00 3 9 Quercus alba 4.6 11-3-00 2 10 Nyssa sylvatica 4.6 11-2-00 2 11 Quercus stellata 4.6 11-12-00 1 12 Juglans nigra 4.6 11-27-00 4 13 Juglans nigra 4.7 11-4-00 1 14 Carya cordiformis 4.6 12-10-00 (1) 15 Pinus pungens 4.6 11-29-00 3 16 Acer rubrum 4.7 10-26-00 2 17 Pinus strobus 4.8 12-17-00 2 18 Quercus velutina 5.0 10-24-00 2 19 Quercus velutina 5.5 10-18-00 1 20 Carya glabra 5.0 10-28-00 2 21 Carya ovalis 5.0 10-29-00 5 22 Quercus rubra 5.2 12-12-00 (1) 23 Carya tomentosa 5.2 10-27-00 1 24 Quercus muehlenbergii 5.3 10-23-00 1 25 Quercus prinus 5.3 10-25-00 2 26 Quercus prinus 5.3 12-12-00 (1) 27 Acer nigrum 5.4 10-24-00 p 28 Populus grandidentata 5.5 11-11-00 2 29 Cornus florida 5.5 10-31-00 2 30 Cornus florida 6.0 11-3-00 1 31 Juniperus virginiana 5.8 11-9-00 3 32 Fraxinus americana 5.8 11-15-00 1 33 Fraxinus americana 6.1 11-14-00 4 34 Fagus grandifolia 5.8 12-10-00 (1) 35 Fagus grandifolia 6.4 12-10-00 (1) 36 Fagus grandifolia 6.9 11-25-00 p 37 Liriodendron tulipifera 5.8 12-12-00 (1) 38 Liriodendron tulipifera 6.1 11-25-00 1 39 Crataegus crus-galli 6.5 11-16-00 3 40 Tilia heterophylla 6.7 11-21-00 1 41 Tilia heterophylla 6.7 12-12-00 (1) 42 Ulmus rubra 7.0 12-1-00 1 43 Ulmus rubra 7.6 11-20-00 1 44 Ulmus rubra 7.9 11-17-00 1 45 Celtis occidentalis 8.0 11-5-00 3 46 Celtis occidentalis 8.0 11-6-00 1 47 Celtis occidentalis 8.0 11-7-00 1
Observed pH values of freshly fallen leaves of 33 species from the Shenandoah Valley of Virginia. Forest Types represented are as follows: From Beekmantown dolomitic limestone terrain: 1= calcareous colluvial slope, 2= ericaceous oak forest, 3= old field, 4= calcareous flood plain, 5= chert talus, p= planted trees. From Elbrook limestone: (1)= slightly acidic colluvium. Click column headings to re-sort.
In general results meet expectations. There is a general increase in leaf pH from acid / xeric to mesic forest type and species, with some notable exceptions. Most striking of these exceptions is the low pH of Redbud (Cercis canadensis ) leaves, since this is a characteristically mesic species frequently found, as here, on limestone. Similarly, those of Sugar Maple (Acer saccharum) lie at somewhat unexpectedly low pH, while those of American Beech, ( Fagus grandifolia) fall in a higher than expected range. Although supported by few samples, there may be a correlation between character of substrate and leaf pH. Thus the values for Black Oak (Quercus velutina), Flowering Dogwood (Cornus florida ), American Beech and Tuliptree (Liriodendron tulipifera) are higher in samples from calcareous substrates than from more acidic ones. Of these the planted Beech (No 36), which occupies thin soil above limestone, is clearly unstable as distinguished from metastable (Mueller, 2000), as indicated by its slow growth, chlorotic leaves and general lack of vigor at this site, although it was a very vigorous seedling at its original site on acid / mesic colluvium. It was found necessary to acidify the soil around this tree to save it. Additionally, the other planted tree, the Black Maple ( Acer nigrum), had leaves with markedly higher pH than those of either Sugar Maple, a very closely related species. However, unlike the Beech, Black Maple is strongly calciphile ( Mueller, 2000) and thrives at this site.
As expected, the pH values of all oak leaves are quite acid, with Scarlet oak (Quercus coccinea), a species confined to acid substrates, showing the lowest values. Given the prominence of the oaks in many forests, it is readily apparent why heavy leaf mats are associated with acid soils However it is likely that acidification is further enhanced by the partial decay process which leads to the raw humus layer (mor) that usually underlies these leaf mats. In the experience of this reporter, the pH of this raw humus as well as that of the underlying mineral soil is frequently considerably lower than the range of most oak leaves shown in the table. While no systematic search of the literature was made of leaf pH (the writer would appreciate any pertinent leads to such data), a reference was found regarding that of Sugar Maple as well as related chemical data. Thus Fowells (1965) provides a pH range 4.0 to 4.9 for leaves of this species, in good agreement with values obtained in this study. These leaves were found to contain 1.81 % Ca, 0.24 Mg and 0.25 K, and Ca was observed to drop when soil pH fell below 4.5. Additionally, the leaves of Flowering Dogwood were found to be particularly high in calcium, with a range of 2.7 — 4.2 %, while magnesium had values of 0.3 — 0.5% (Coile,1940; Oosting, 1942) .Also, American Basswood (Tilia americana) leaves were found to have the highest percentage of Ca and Mg among those of 24 hardwoods and conifers analyzed (Fowells, 1965). Although the "species" here is White Basswood, it is very close to and even gradational to American Basswood in the area in which it is found. This finding of high base content also is in harmony with the relatively high pH of basswood leaves found here. While no determinations of the pH of American Beech leaves were found in the literature, the observed relatively rapid degradation of these leaves is compatible with values found here. Thus, these leaves not only degrade rapidly on the ground but, if still on the tree, bleach white, behaviors quite unlike those of the oaks.
Coile, Theodore S., 1940, Soil changes associated with loblolly pine succession on abandoned agricultural land of the Piedmont Plateau.Duke University Forestry Bulletin 5, 85 pp.
Fowells, H. A., 1965, Silvics of Forest Trees of the United States. Agricultural Handbook No 271. U.S. Dept. of Agriculture, Forest Service. Washington, D. C.
Mueller, R. F., 2000, Stability Relations in Forests. Forests of the Central Appalachians Project. Virginians For Wilderness Web Site.
Oosting, Henry J., 1942, An ecological analysis of plant communities of Piedmont, North Carolina. American Midland Naturalist 28, 1 — 126.
Rader, Eugene K., 1967, Geology of the Staunton, Churchville, Greenville and Stuarts Draft Quadrangles, Reportof Investigations 12. Virginia Division of Mineral Resources, Charlottesville, Virginia.