ECOPHYSIOLOGY OF TWO LIANA SPECIES Calamus ovoideus AND Coscinium fenestratum UNDER DIFFERENT CANOPY REMOVAL TREATMENTS

Calamus ovoideus Thw. and Coscinium fenestratum Colbr. are naturally growing economicallyimportant liana species, around the Sinharaja MAB reserve, Sri Lanka. Growth performance andphysiological attributes of these species were examined using plants established in 1991 underthree different canopy removal treatments ina Pinus caribaea plantation in the buffer zone ofSinharaja forest. They were 3 pine rows and 1 pi lie row removed, 3 pine rows under plantingand the Pinus underplanting control where the initial light intensities were 22, 10, 5 and 3mol/m21 day respectively.The results showed that height after 8 years and the annual height increments were significantlyhigher among the three canopy removal treatments compared to that in the closed canopy controlfor both species. In C. ovoideus greatest height was in the three-pine rows removal treatment andleast in the closed canopy under planting . .In contrast, Cifenestratum showed no significantheight difference among the three canopy removal treatments compared to the control. The meanroot collar diameter after 8 years and its increments in C. fenestratum were significantly higherin the canopy removal treatments compared to that of the control. In the physiological studies,both species showed significant differences in their net photosynthetic rate and stomatalconductance when grown under different light regimes. The higher photosynthetic rate of C.ovoideus was in the one pine removed treatment ar.d in C. fenestratum it was in the three pinerows removed treatment.After 8 years of establishment, for both study species the three and one pine rows removed andthree pine rows underplanting treatment were better than the Pinus underplanting (closedunderstorey) treatment. This study revealed that these liana species could be successfullyintroduced to the monocuIture Pinus caribaea plantations in the lowland wet zone of Sri Lanka.

Soil nutrients and beta diversity in the Bornean Dipterocarpaceae: evidence for niche partitioning by tropical rain forest trees

1   The relative importance of niche- and dispersal-mediated processes in structuring diverse tropical plant communities remains poorly understood. Here, we link mesoscale beta diversity to soil variation throughout a lowland Bornean watershed underlain by alluvium, sedimentary and granite parent materials ( c . 340 ha, 8–200 m a.s.l.). We test the hypothesis that species turnover across the habitat gradient reflects interspecific partitioning of soil resources. 2   Floristic inventories (≥ 1 cm d.b.h.) of the Dipterocarpaceae, the dominant Bornean canopy tree family, were combined with extensive soil analyses in 30 (0.16 ha) plots. Six samples per plot were analysed for total C, N, P, K, Ca and Mg, exchangeable K, Ca and Mg, extractable P, texture, and pH. 3   Extractable P, exchangeable K, and total C, N and P varied significantly among substrates and were highest on alluvium. Thirty-one dipterocarp species ( n  = 2634 individuals, five genera) were recorded. Dipterocarp density was similar across substrates, but richness and diversity were highest on nutrient-poor granite and lowest on nutrient-rich alluvium. 4   Eighteen of 22 species were positively or negatively associated with parent material. In 8 of 16 abundant species, tree distribution (≥ 10 cm d.b.h.) was more strongly non-random than juveniles (1–10 cm d.b.h.), suggesting higher juvenile mortality in unsuitable habitats. The dominant species Dipterocarpus sublamellatus (> 50% of stems) was indifferent to substrate, but nine of 11 ‘subdominant’ species (> 8 individuals ha −1 ) were substrate specialists. 5   Eighteen of 22 species were significantly associated with soil nutrients, especially P, Mg and Ca. Floristic variation was significantly correlated with edaphic and geographical distance for all stems ≥ 1 cm d.b.h. in Mantel analyses. However, juvenile variation (1–10 cm d.b.h.) was more strongly related to geographical distance than edaphic factors, while the converse held for established trees (≥ 10 cm d.b.h.), suggesting increased importance of niche processes with size class. 6   Pervasive dipterocarp associations with soil factors suggest that niche partitioning structures dipterocarp tree communities. Yet, much floristic variation unrelated to soil was correlated with geographical distance between plots, suggesting that dispersal and niche processes jointly determine mesoscale beta diversity in the Bornean Dipterocarpaceae. Journal of Ecology (2005) doi: 10.1111/j.1365-2745.2005.01077.xPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72822/1/j.1365-2745.2005.01077.x.pd

Old-growth mixed dipterocarp forests show variable losses and gains in aboveground biomass and standing carbon over forty years

Background: No studies have documented long-term trends in aboveground biomass (AGB) for mixed-dipterocarp forests (MDF), the dominant rain forest type in tropical wet equatorial Asia. In our study, we sought to document such trends over forty years across three sites representing lowland to lower montane elevations. Methods: To do this, we established fifty 100 ​m ​× ​25 ​m plots in 1978 across three sites sampled along an elevation gradient, identified as mature old-growth forest. We measured trees for diameter at breast height that we identified to species and tagged. We took wood samples to calculate species wood-specific gravity. We re-measured plots in 1998 and again in 2018. Results: We show standing AGB for all sites combined to be 517.52 ​Mg⋅ha−1 in 1978, but this declined by 17% over 40 years to 430.11 ​Mg⋅ha−1. No differences exist among sites in AGB primarily because of considerable within site variation; but interactions of time with site show declines across sites were not uniform, one remained about the same. Relatively few species represented a high proportion of the AGB with the top five species comprising between 34% and 65%, depending upon site and year sampled. One species, Mesua nagassarium, represented a disproportionately large amount of AGB and decline over time, particularly at the low elevation site. Conclusions: Our results are directly relevant to estimating AGB and standing carbon sequestered in MDF. Our study is the first to demonstrate varying but overall, declining trends in amounts of AGB among forests making predictions of biomass and standing carbon in MDF difficult over wide regions

Multispecies coexistence of trees in tropical forests: spatial signals of topographic niche differentiation increase with environmental heterogeneity

Neutral and niche theories give contrasting explanations for the maintenance of tropical tree species diversity. Both have some empirical support, but methods to disentangle their effects have not yet been developed. We applied a statistical measure of spatial structure to data from 14 large tropical forest plots to test a prediction of niche theory that is incompatible with neutral theory: that species in heterogeneous environments should separate out in space according to their niche preferences. We chose plots across a range of topographic heterogeneity, and tested whether pairwise spatial associations among species were more variable in more heterogeneous sites. We found strong support for this prediction, based on a strong positive relationship between variance in the spatial structure of species pairs and topographic heterogeneity across sites. We interpret this pattern as evidence of pervasive niche differentiation, which increases in importance with increasing environmental heterogeneity