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Our knowledge of the ecology of tropical rain-forest trees is limited, with detailed information available for perhaps only a few hundred of the many thousand of species that occur. Yet a good understanding of the trees is essential to unravelling the workings of the forest itself. This book aims to summarise contemporary understanding of the ecology of tropical rain-forest trees. The emphasis is on comparative ecology, an approach that can help to identify possible adaptive trends and evolutionary constraints and which may also lead to a workable ecological classification for tree species, conceptually simplifying the rain-forest community and making it more amenable to analysis.

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SUMMARYThe fracture toughness of sun-leaves of 42 tropical tree species growing in Singapore was measured along a 'least tough' path using an instrumented cutting technique. Punch-and-die (penetrometer) tests were also conducted. Intercostal material was analyzed for crude fibre and crude protein (total nitrogen concentration x 6-25) and the ratio of the two, the index of sclerophylly, calculated for each species. Leaf anatomy was examined and specific leaf area was calculated. Thirty-seven of the species were from three definable plant communities, namely mangroves, trema belukar (secondary forest on undegraded sites) and adinandra belukar (secondary forest on highly degraded soils).There was a highly significant positive correlation between fracture toughness and index of sclerophylly for the 42 species (R^ = 0 43, P < OOOl) brought about largely by a high correlation between toughness and crude fibre content. Fracture toughness was not correlated with lamina tissue dorsi-ventral thickness but high toughness was clearly associated with the presence of sclerenchyma bundle sheaths and sheath extensions. Analysis of the fracture path for 26 leaves of ten mangrove species showed a high correlation between the area fraction occupied by veins and fracture toughness if one species, Avicennia rumphiana, was excluded. The regression equation for the other nine species gave estimates of the fracture toughness of vein tissue and lamina matrix of 6053 and 327 J m~r espectively. Punch-and-die test results only correlated well with the cutting tests when values were divided by lamina thickness.The ratio of protein to fibre in a leaf (the reciprocal of the index of sclerophylly) has been established as a good predictor of leaf palatability and digestibility to generalist chewing folivores. The high correlation between fracture toughness and the index of sclerophylly for a large sample suggests that leaf toughness could be the factor used as a proximate cue for determining food quality in herbivore foraging strategies.

In 1995, a multidisciplinary geophysical experiment targetted the intermediate spreading Valu Fa Ridge (full rate 60 mm yr−1 ), which is centred on 22°20′S, 176°40′W in the Lau Basin. As part of this experiment, wide‐angle and normal‐incidence seismic profiles were collected both along‐ and across‐axis to determine the crustal structure of the Central Valu Fa Ridge (CVFR) and its overlap with the Northern Valu Fa Ridge (NVFR). Controlled‐source electromagnetic profiles and underway gravity, magnetic and bathymetry data were also collected.  In this paper we describe the results of forward modelling of the along‐ and across‐axis wide‐angle and normal‐incidence seismic data. An axial low‐velocity block and its underlying slightly broader zone of depressed seismic velocities (low‐velocity zone) have been identified, and these features are interpreted as corresponding to a melt lens and underlying magma chamber. The low‐velocity block is 1–2 km wide and has a first‐order upper boundary, from which large‐amplitude reflections are observed; amplitude analysis of these indicates an interconnected melt fraction. The nature of the lower boundary is more poorly constrained, as no reflection event corresponding to the base of the low‐velocity block is observed. Modelling indicates that velocities similar to those observed at the base of layer 2 within the axial region (~5.5 km s−1) are achieved by 250 m below the upper boundary, possibly suggesting a gradational lower boundary with high velocity gradient. The low‐velocity zone (LVZ) is interpreted as an ~4 km wide magma chamber delineated by a seismic velocity anomaly of −0.2 km s−1, extending down through layer 3 to within 1.5–2 km of the Moho. The velocity anomaly and dimensions of the LVZ are generally smaller than those observed at the East Pacific Rise (EPR) and Mid‐Atlantic Ridge (MAR).  The observed along‐axis continuity of the low‐velocity block is remarkable, extending from the southern tip of the CVFR to the overlapping spreading centre (OSC) with the NVFR. A low‐velocity block is modelled beneath the inside flanks (i.e. the slopes that dip into the overlap basin) of both ridges at the OSC, although the existence of a single low‐velocity block beneath the overlap basin itself cannot be ruled out. The identification of a single LVZ centred on the overlap region, rather than two merged LVZs beneath each segment, implies that the material in each low‐velocity block originates from the same crustal magma source. A reflection event from the Moho is observed from directly beneath the axis on both across‐axis profiles, which indicates that a distinct crust–mantle boundary may be formed within the axial region. Many of the observations at the Valu Fa Ridge are consistent with those at the EPR and the Reykjanes Ridge (MAR), which implies that, regardless of spreading rate, crustal accretionary processes at mid‐ocean ridges with similar magmatic budgets are also broadly similar.

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