The influence of carbon—nutrient balance on herb and woody plant abundance in temperate forest understories

Abstract

Question: We present a general structural carbon—nutrient balance hypothesis parallel to Bryant et al.'s defensive chemistry hypothesis. Our hypothesis suggests that because herb species require a lower investment of carbon per unit length of stem than do woody plants, herbs should be at a competitive advantage where the leaf area of plants in the ground layer is limited by light (or fixed carbon, C) rather than soil resources (R) such as nutrients or water. We test the derivative predictions that in temperate deciduous forests (1) herb cover and species richness increase as soil resources increase, and (2) woody ground‐layer cover, density, and species richness increase as soil resources decrease. Location: To maximize generality, the eight temperate deciduous forest sites were dispersed along an 800 km band from the Coastal Plain of eastern North Carolina to the Central Basin of middle Tennessee, USA. Methods: Soil nutrients and moisture, herb cover and woody stem densities were observed in six plots at each site, randomly located in high, medium, and low herb cover areas. Multiple regression, correlation, and Redundancy Analysis ordination were used to test predictions. Results: Plants with herbaceous (low C:R) stems are generally abundant where soil moisture and basic cations (Ca, Mg) are high (low C:R environments), and woody (high C:R) plant cover, basal area, stem density, and species richness are all greatest on dry or nutrient‐poor soils (high C:R environments). Plots with intermediate soil resource availability and herb cover have the most species, and maximum herb species richness occurs at higher soil resource levels than maximum woody species richness. Conclusions: Our observations are consistent with our structural carbon—nutrient balance hypothesis.

Savanna land use and its effect on soil characteristics in southern Ethiopia

“…For instance, the negative correlation between pH and grass biomass was consistent with the suggestion made by Barnes et al (1991) that grass biomass is influenced by the increased level of soil pH. According to Graves et al (2006), herbaceous species were abundant under improved soil conditions suggesting that soil conservation is crucial for the restoration of herbaceous species richness and diversity. In contrast, increased grass biomass under high silt-clay particles could be an indicator of the positive relationship between organic carbon and silt-clay particles.…”

“…Generally, our results show that soil pH, EC, CEC, CaCO 3 and certain nutrients (i.e., K þ , Ca 2þ , Mg 2þ , N, OC and P) promote the invasion of bush encroachment. Essentially, results from a concurrent study indicate that some soil characteristics may trigger the spread of bush encroachment (Graves et al, 2006). According to Jackson et al (2002), processes such as an increase in soil carbon content can cause the invasion of bush encroachment under low rainfall conditions.…”

“…We suggest that bush encroachment is more triggered by the suppression of fire than heavy grazing and soil related effects induced by land use modification. According to Graves et al (2006), herbaceous species were abundant under improved soil conditions indicating that better soil condition is crucial for the restoration of herbaceous species diversity.…”

Drivers of secondary succession rates across temperate latitudes of the Eastern USA: climate, soils, and species pools

“…Secondary succession studies conducted across the EDF show a clear contrast of seral herbaceous communities across regions: in the Northeast, rapid colonization by clonal, fast-growing herbs such as Solidago altissima is typical except on very coarse soils, whereas southern old fields are more typically dominated by perennial bunchgrasses such as Andropogon virginicus (Wright and Fridley 2010), a species widely believed to be tolerant of drought and nutrient stress (Bazzaz 1968). At the same time, soils of lower C to nutrient ratios may stoichiometrically favor herbs in competition with woody seedlings of higher tissue C to nutrient Table 4 ratios (Larcher 2001;Sterner and Elser 2002;Graves et al 2006); furthermore, the greater evaporative demands and lower water retention capacity of coarser southern soils may limit the apical growth of species with herbaceous stems via turgor loss. Although our experiment was not designed to differentiate between direct effects of soil properties on seedling growth versus indirect effects of herbaceous competitors, we were able to compare the effects of a general axis of site fertility to that of climate, and soils were a stronger predictor of seedling performance.…”

Quantifying the influence of environmental texture on the rate of species turnover: evidence from two habitats

“…However, here again additional analyses utilizing slope and aspect (not shown) indicated that these variables also only contributed a small fraction of explained variance. Moisture and nutrient availability are also known to shape herbaceous understory community composition (Ludwig et al 2004;Galhidy et al 2006;Graves et al 2006), but we did not collect information on either of these variables. There are many other potential biological drivers of community structure in our study system which include, but are not limited to, Janzen-Connell effects, herbivory, competitive exclusion, dispersal limitation, variation in growth forms, extent of rooting zone, and patterns of vegetative reproduction.…”