We tested the Walker and Syers (1976) conceptual model of soil development and its ecological implications by analyzing changes in soil P, vegetation, and other ecosystem properties on a soil chronosequence with six sites ranging in age from 300 yr to 4.1 x 106 yr. Climate, dominant vegetation, slope, and parent material of all of the sites were similar. As fractions of total P, the various pools of soil phosphorus behaved very much as predicted by Walker and Syers. HCI—extractable P (presumably primary mineral phosphates) comprised 82% of total P at the 300—yr—old site, and then decreased to 1% at the 20,000—yr—old site. Organic phosphorus increased from the youngest site to a maximum at the 150 000 yr site, and then declined to the 4.1 x 106 yr site. Occluded (residual) P increased steadily with soil age. In contrast to the Walker and Syers model, we found the highest total P at the 150 000—yr—old site, rather than at the onset of soil development, and we found that the non—occluded, inorganic P fraction persisted through to the oldest chronosequence site. Total soil N and C increased substantially from early to middle soil development in parallel with organic P, and then declined through to the oldest site. Readily available soil P, NH4+, and NO3— were measured using anion and cation exchange resin bags. P availability increased and decreased unimodally across the chronosequence. NH4+ and NO3— pools increased through early soil development, but did not systematically decline late in soil development. In situ decomposition rates of Metrosideros polymorpha litter were highest at two intermediate—aged sites with soil fertility (20 000 yr and 150 000 yr), and lowest at the less—fertile beginning (300 yr) and endpoint (4.1 x 106 yr) of the chronosequence. M. polymorpha leaves collected from these same four sites, and decomposed in a common site, suggested that leaves from intermediate—aged sites were inherently more decomposable than those from the youngest and oldest sites. Both litter tissue quality and the soil environment appeared to influence rates of decomposition directly. The highest mean soil N2O emissions (809 mg°m—2°d—1) were measured at the 20 000—yr—old site, which also had the highest soil nitrogen fertility status. Plant communities at all six chronosequence sites were dominated primarily by M. Polymorpha, and to a lesser extent by several other genera of trees and shrubs. There were, however, differences in overall vegetation community composition among the sites. Using a detrended correspondence analysis (DECORANA), we found that a high proportion of species variance among the sites (eigenvalue = 0.71) can be explained by site age and thus soil developmental stage. Overall, long—term soil development across the chronosequence largely coincides with the conceptual model of Walker and Syers (1976). How P is distributed among different organic and inorganic fractions at a given stage of soil development provides a useful context of evaluating contemporary cycling of P and other nutrients, and for deter...

The exotic nitrogen-fixing tree Myrica faya invades young volcanic sites where the growth of native plants is limited by a lack of nitrogen. Myrica quadruples the amount of nitrogen entering certain sites and increases the overall biological availability of nitrogen, thereby altering the nature of ecosystem development after volcanic eruptions.

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Metrosideros polymorpha, a dominant tree species in Hawaiian ecosystems, occupies a wide range of habitats. Complementary field and common-garden studies of M. polymorpha populations were conducted across an altitudinal gradient at two different substrate ages to ascertain if the large phenotypic variation of this species is determined by genetic differences or by phenotypic modifications resulting from environmental conditions. Several characteristics, including ecophysiological behavior and anatomical features, were largely induced by the environment. However, other characteristics, particularly leaf morphology, appeared to be mainly determined by genetic background. Common garden plants exhibited higher average rates of net assimilation (5.8 μmol CO m s) and higher average stomatal conductance (0.18 mol HO m s) than their field counterparts (3.0 μmol CO m s, and 0.13 mol HO m s respectively). Foliar δC of most common-garden plants was similar among sites of origin with an average value of -26.9‰. In contrast, mean values of foliar δC in field plants increased substantially from -29.5‰ at low elevation to -24.8‰ at high elevation. Leaf mass per unit area increased significantly as a function of elevation in both field and common garden plants; however, the range of values was much narrower in common garden plants (211-308 g m for common garden versus 107-407 g m for field plants). Nitrogen content measured on a leaf area basis in common garden plants ranged from 1.4 g m to 2.4 g m and from 0.8 g m to 2.5 g m in field plants. Photosynthetic nitrogen use efficiency (PNUE) decreased 50% with increasing elevation in field plants and only 20% in plants from young substrates in the common garden. This was a result of higher rates of net CO assimilation in the common garden plants. Leaf tissue and cell layer thickness, and degree of leaf pubescence increased significantly with elevation in field plants, whereas in common garden plants, variation with elevation of origin was much narrower, or was entirely absent. Morphological characteristics such as leaf size, petiole length, and internode length decreased with increasing elevation in the field and were retained when grown in the common garden, suggesting a potential genetic basis for these traits. The combination of environmentally induced variability in physiological and anatomical characteristics and genetically determined variation in morphological traits allows Hawaiian M. polymorpha to attain and dominate an extremely wide ecological distribution not observed in other tree species.

Wednesdays will be devoted to lectures and discussion of the theories behind sampling and vegetation analysis methods ... Aims and Methods of Vegetation Ecology ... A BIBLIOGRAPHY OF LITERATURE ON FLORA, ECOLOGY, ENVIRONMENT ... http://perl.psc.isr.umich.edu/papers/Dangol_A%20Bibliography%20of%20Literature_Flora.pdf Aims and methods of vegetation ecology. Wiley-Interscience, ... Multivariate methods in plant ecology. I. Association analysis in plant communities. J.