Mortality rates of 205 tree and shrub species were estimated during two intervals, 1982-1985 and 1985-1990, in two size classes, 1-10 and ?10 cm in diameter, in a 50-ha census plot in tropical moist forest on Barro Colorado Island in Panama. The severe dry season of 1983 was the focus of the study, since prior observations had dem- onstrated that it caused mortality in the forest. Here we document that forest-wide mortality was z3%/yr during the drought interval but only 2%/yr during the period afterwards, and that excess mortality during the first interval amounted to 2% of stems in the larger size class and 1% in the smaller. Overall, just under 70% of all species had higher mortality during the first census interval, but not all species were equally affected. Canopy trees had significantly higher mean mortality rates during 1982-1985 than during 1985-1990, but treelets and shrubs showed no or slight differences. This was counter to our prediction that species with short root systems would suffer more from a long drought. Shrubs did, however, have higher mortality rates than trees and treelets during both census intervals. We also evaluated mortality rates for subgroups of species that specialized on different microhabitats in the forest. As we predicted, colonist species (those associated with light gaps) had higher mortality rates than generalist species, 7-10%/yr compared to 2-4%/yr, but only in the smaller size class. Unexpectedly, colonizers had similar mortality rates as non-colonizers in the larger size class. Gap colonizers and generalist species were similarly affected by the drought-both had elevated mortality during 1982-1985. Species whose distributions were associated with moister soils (on the slopes around the island's plateau or in a swamp in the midst of the 50-ha plot) also had elevated mortality during the drought period, but no more so than generalist species. This was counter to our prediction that species from moist microhabitats would suffer more during an extended drought than generalists. Understory treelets that were slope specialists had higher mortality than generalists during both census intervals, but not large trees that were slope specialists. Our conclusions emphasize diversity as well as pattern. Every trend we illustrated had well-documented exceptions: large trees with lower mortality during the drought period, for example. Clearly, accurate predictions about how tropical forests will respond to climatic perturbations will require much detailed information from many species.

Mortality Rates of 205 Neotropical Tree and Shrub Species and the Impact of a Severe Drought

This article reviews literature and summarizes experiments to investigate the extent to which productivity of tropical montane rain forests is constrained by low nutrient supply. On any one mountain, with increase in altitude foliar N decreases, and P and K usually decrease, but Ca and Mg show no consistent trend. However for a wide range of sites N, P, K, Mg, and Ca show no trends. Litterfall contents of N and P and often K, Ca, and Mg are lower in montane forests than in lowland forests, mainly because of reduced litterfall mass, but N and P concentrations are also lower in forests above 1500 m. Tropical montane soils usually have more soil organic matter per unit ground area; N mineralization levels are lower at higher altitudes in Costa Rica, and extractable and total soil P are lower in sites with lower litterfall P concentrations. We speculate that many lowland forests are limited by P and many montane forests by N.

Fertilization studies on ash-derived montane soils in Hawai‘i showed a trend for a switch from N limitation on young soils to P, or N and P, limitation on soils over older substrates. Jamaican montane trees were limited by N and by P separately. Venezuelan montane trees were limited by N. The sites in Jamaica and Venezuela have soils of indeterminate age. Taken together these results show that nutrient limitation is widespread in montane soils (all sites have responded to at least one nutrient) and that the particular nutrient(s) that limit(s) production may differ for explicable reasons. First results from lowland forests on sandy soils in Kalimantan show N or simultaneous N and P limitation. Many more experiments, especially in lowland forests, are needed to test our speculation that P usually limits productivity in tropical lowland rain forests and that N limits productivity in tropical montane rain forests.

Experimental investigation of nutrient limitation of forest growth on wet tropical mountains

Heavy metal concentrations in soils and plant accumulation in a restored manganese mineland in Guangxi, South China.

Summary

1
We measured above-ground net primary productivity (ANPP) and ecosystem structure and processes in eight rain forest stands at four elevations (700, 1700, 2700 and 3100 m) and on two geological substrates (sedimentary vs. ultrabasic rock) on Mount Kinabalu, Borneo.

2
All ultrabasic sites had smaller pools of total soil phosphorus (P) and of labile inorganic P than did the sedimentary sites at the same altitudes. We predicted that the magnitude of altitudinal changes in ANPP would be less on ultrabasic than on sedimentary substrates, reflecting lower temperature dependency of ANPP under stronger P limitation.

3
Although ANPP declined with increasing altitude on both substrates, the slopes of the two regression lines were similar. The intercept was, however, marginally greater on sedimentary than on ultrabasic substrate.

4
Stand-level nutrient-use efficiencies (the ratio of litterfall mass to nutrient return) for N and P were only affected by altitude on ultrabasic substrate where they increased exponentially. Mean foliar N and P contents per unit leaf area of the canopy species increased with altitude on both substrates, but differed between substrates at the same altitude only for P (lower on ultrabasic).

5
Leaf area index (LAI) decreased upslope on both substrates. We assumed that half of primary production was allocated below-ground in order to evaluate stand level net assimilation rate (NAR). This was nearly constant on sedimentary substrate, but declined linearly with increasing altitude on ultrabasic substrate, where it may have to be added to LAI to explain ANPP patterns.

6
We suggest that on sedimentary substrate trees may be able to maintain NAR under colder environments by increasing foliar N and P per unit leaf area, but P deficiency prevents them from adjusting on ultrabasic substrate.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1046/j.0022-0477.2001.00634.x

Ecosystem structure and productivity of tropical rain forests along altitudinal gradients with contrasting soil phosphorus pools on Mount Kinabalu, Borneo

Evergreen broad-leaved tropical forests can have high rates of productivity and large accumulations of carbon in plant biomass and soils. They can therefore play an important role in the global carbon cycle, influencing atmospheric CO2 concentrations if climate warms. We applied meta-analyses to published data to evaluate the apparent effects of temperature on carbon fluxes and storages in mature, moist tropical evergreen forest ecosystems. Among forests, litter production, tree growth, and belowground carbon allocation all increased significantly with site mean annual temperature (MAT); total net primary productivity (NPP) increased by an estimated 0.2-0.7 Mg C x ha(-1) x yr(-1) x degrees C(-1). Temperature had no discernible effect on the turnover rate of aboveground forest biomass, which averaged 0.014 yr(-1) among sites. Consistent with these findings, forest biomass increased with site MAT at a rate of 5-13 Mg C x ha(-1) x degrees C(-1). Despite greater productivity in warmer forests, soil organic matter accumulations decreased with site MAT, with a slope of -8 Mg C x ha(-1) x degrees C(-1), indicating that decomposition rates of soil organic matter increased with MAT faster than did rates of NPP. Turnover rates of surface litter also increased with temperature among forests. We found no detectable effect of temperature on total carbon storage among moist-tropical evergreen forests, but rather a shift in ecosystem structure, from low-biomass forests with relatively large accumulations of detritus in cooler sites, to large-biomass forests with relatively smaller detrital stocks in warmer locations. These results imply that, in a warmer climate, conservation of forest biomass will be critical to the maintenance of carbon stocks in moist tropical forests.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1050&context=nrem_pubs

Temperature Influences Carbon Accumulation in Moist Tropical Forests

SUMMARY (1) The rates of several processes in the rain forests, at a range of altitudes, on an ultrabasic mountain, Gunung Silam, Malaysia, were investigated. In spite of the unusual soil chemistry, none of these processes occurred at an exceptionally low rate. (2) Herbivory (judged from the percentage area missing from large numbers of leaf samples of several species) in four plots was: 7 6% (330 m), 6 8% (610 m), 6 9% (790 m) and 7 1% (870 m). (3) Annual mortality of trees (?, 10 cm d.b.h.) was estimated over twelve or thirteen years in ten plots. This was (i): 0 025 (280 m), 0 012 (330 m), 0015 (410 m), 0 011 (480 m), 0 008 (540 m), 0 011 (610 m), 0 008 (700 m), 0 008 (790 m), 0 010 (790 m) and 0 016 (870 m). (4) Median diameter increment of tree boles was estimated over twelve or thirteen years in six plots. This was (mm year- ): 1 56 (280 m), 1 13 (330 m), 1 31 (480 m), 0 93 (610 m), 0 91 (790 m) and 0-77 (870 m). (5) Small litter fall was estimated from twenty 0 25 m2 litter traps in each of six plots over twelve months. It was (t ha-' year-'): 6 51 (280 m), 7 37 (330 m), 5 22 (480 m), 5 60 (610 m), 5 53 (790 m) and 4 80 (870 m). There was no correlation between small litter fall and median diameter increment. (6) Chemical analyses of the small litter fall showed a number of important features, including an excess of calcium concentrations over magnesium concentrations and relatively high concentrations of nickel. (7) Chemical analyses were made of the leaves of a large number of species in four plots. These suggested that the tree species rooted in ultrabasic soil have an ability to grow at low foliar nutrient concentrations and that they are able to concentrate calcium relative to magnesium. A comparison with the results of the litter-fall analyses suggested that there may be an excretion of nickel into the senescing leaves. (8) Shorea tenuiramulosa (Dipterocarpaceae) appeared to accumulate nickel and had up to 1 -0 mg'- nickel in its leaf dry matter. An unidentified Eugenia species (Myrtaceae) had 13-7 mg g' foliar manganese.

http://www.jstor.org/stable/pdfplus/2260752.pdf

F. M. Robertson

Papers

Ecological studies on Gunung Silam, a small ultrabasic mountain in Sabah, Malaysia. II: Some forest processes