Experimental Investigation of Nutrient Limitation of Forest Growth on Wet Tropical Mountains

Abstract

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.

Fine root dynamics along a 2,000-m elevation transect in South Ecuadorian mountain rainforests

“…In the upper part of the Ecuador transect (1,890-3,060 m) relative root loss increased by about 50%, suggesting that temperature effects on root turnover are overlaid by other influential factors despite a decrease in mean annual temperature of 6.3 K. The growth of tropical montane forests has widely been found to be limited by the availability of nitrogen (Tanner et al 1998;Benner et al 2008). Several lines of evidence indicate that N availability decreases with elevation in South Ecuador, including topsoil C/N-ratios and foliar and root N concentrations (Röderstein 2006;Moser, unpublished).…”

Using experimental manipulation to assess the roles of leaf litter in the functioning of forest ecosystems

“…Furthermore, water stress, competition for nutrients, and the degree of retranslocation of scarce nutrients will determine foliar nutrient concentrations, and therefore litter nutrient concentrations, to some extent ; all of these factors are also site-specific and species-specific. Differences in leaf production and tree growth may mask increases or decreases in foliar nutrient concentrations, especially nitrogen (Tanner, Vitousek & Cuevas, 1998), a phenomenon that is known from fertilization experiments (Waring & Schlesinger, 1985 ;Tanner et al, 1998). Nitrogen fertilization has been shown to have little effect on foliar nutrient concentrations, even though the additional nitrogen caused increased plant growth (Healey, 1989 ;Tanner et al, 1998); decreased tree growth in litter removal treatments may therefore explain the modest changes -or lack of change -in foliar nitrogen concentrations.…”

“…Differences in leaf production and tree growth may mask increases or decreases in foliar nutrient concentrations, especially nitrogen (Tanner, Vitousek & Cuevas, 1998), a phenomenon that is known from fertilization experiments (Waring & Schlesinger, 1985 ;Tanner et al, 1998). Nitrogen fertilization has been shown to have little effect on foliar nutrient concentrations, even though the additional nitrogen caused increased plant growth (Healey, 1989 ;Tanner et al, 1998); decreased tree growth in litter removal treatments may therefore explain the modest changes -or lack of change -in foliar nitrogen concentrations. Evidence for this is provided by litter manipulation studies where an increase or decrease in soil nutrients or tree growth was not accompanied by a corresponding change in foliar nutrient concentrations (Wittich, 1951 ;Němec, 1929 ;Baar & Ter Braak, 1996 ;Lopez-Zamora et al, 2001).…”

Fingerprinting the impacts of global change on tropical forests

“…N mineralization rates increased following experimental soil warming of a mid-latitude hardwood forest (Melillo et al 2002). However, N may not be limiting to mature trees in most tropical forests, with the probable exceptions of montane forests and those on very young or white-sand soils (Vitousek & Farrington 1997;Tanner et al 1998;Sollins 1998;Martinelli et al 1999;Hall & Matson 1999). Thus, increasing N availability may not cause increased growth in most tropical forests.…”

“…Evidence in favour of this scenario is the general trend for leaf nutrient concentrations (N, P, Ca, Mg, K) and the cycling of nutrients in leaf litter to both decrease with altitude (and hence decreasing temperatures) when sampled on the same tropical mountain (Tanner et al 1998;Silver 1998). This may result from the greater immobilization of nutrients in the soil caused by slower soil organic-matter decomposition, which may be temperature controlled (Tanner et al 1998;Silver 1998). Thus, higher temperatures may generally increase soil nutrient availability, and hence growth, via increases in soil organic matter decomposition rates.…”