Species diversity and regeneration of old-growth seasonally dry Shorea robusta forests following gap formation

Abstract

Diversity and regeneration of woody species were investigated in two ecological niches viz. gap and intact vegetation in old-growth seasonally dry Shorea robusta (Gaertn. f.) forests in Nepal. We also related varieties of diversity measures and regeneration attributes to gap characteristics. Stem density of tree and shrub components is higher in the gap than in the intact vegetation. Seedling densities of S. robusta and Terminalia alata (B. Heyne ex Roth.) are higher in the gap than in the intact vegetation, while contrary result is observed for T. bellirica (Gaertn. ex Roxb.) and Syzigium cumini (L. Skeels) in term of seedling density. The complement of Simpson index, Evenness index, and species-individual ratio in the seedling layer are lower in the gap than the intact vegetation. Gap size can explain species richness and species establishment rate. Gaps created by multiple tree falls in different years have higher seedling density of S. robusta than gaps created by single and/or multiple tree falls in the same year. In conclusion, gaps maintain species diversity by increasing seedling density, and favor regeneration of Sal forests. In addition to gap size, other gap attributes also affect species diversity and regeneration.

Keywords

Canopy gap / intermediate disturbance hypothesis / Nepal / Sal (Shorea robusta Gaertn. f.) forest

References

[1] Anonymous. Operational forest management plan for Nawal Paransi district (1995–2000). 1994, Kathmandu: Forest Research and Survey Centre

[2] Arriaga L.. Gap-building-phase regeneration in a tropical montane cloud forest of north-eastern Mexico. Journal of Tropical Ecology, 2000, 16: 535-562.

[3] Babaasa D., Eilu G., Kasangaki A., Bitariho R., McNeilage A.. Gap characteristics and regeneration in Bwindi Impenetrable National Park, Uganda. African Journal of Ecology, 2004, 42: 217-224.

[4] Barik S.K., Pandey H.N., Tripathi R.S., Rao P.. Microenvironmental variability and species-diversity in treefall gaps in a subtropical broadleaved forest. Vegetatio, 1992, 103: 31-40.

[5] Behera S.K., Misra M.K.. Aboveground tree biomass in a recovering tropical Sal (Shorea robusta Gaertn. f.) forest of Eastern Ghats, India. Biomass and Bioenergy, 2006, 30: 509-521.

[6] Bertrand B., Shachak M., Gutterman Y., Brand S.. Patchiness and disturbance: plant community responses to porcupine diggings in the central Negev. Ecography, 1995, 18: 410-422.

[7] Brokaw N.V.L.. Gap-phase regeneration in a Tropical forest. Ecology Letters, 1985, 66: 682-687.

[8] Brokaw N.V.L., Scheiner S.M.. Species composition in gaps and structure of a tropical forest. Ecology, 1989, 70: 538-541.

[9] Bullock J.M.. Fenner M.. Gaps and seedling colonization. Seeds: the ecology of regeneration in plant communities. 2000, Wallingford UK: CABI Publishing, 375 395

[10] Chambers J.C.. Relationships between seed fates and seedling establishment in an Alpine ecosystem. Ecology, 1995, 76: 2124-2133.

[11] Chandrashekara U., Ramakrishnan P.. Gap phase regeneration of tree species of differing successional status in a humid tropical forest of Kerala, India. Journal of Biosciences, 1993, 18: 279-290.

[12] Clarke P.J., Allaway W.G.. The regeneration niche of the grey mangrove (Avicennia marina): effects of salinity, light and sediment factors on establishment, growth and survival in the field. Oecologia, 1993, 93: 548-556.

[13] Connell J.H.. Diversity in tropical rain forests and coral reefs: High diversity of trees and corals is maintained only in a nonequilibrium state. Science, 1978, 199: 1302-1310.

[14] Dalling J.W., Hubbell S.P., Silvera S.. Seed dispersal, seedling establishment and gap partitioning among tropical pioneer trees. Journal of Ecology, 1998, 86: 674-689.

[15] Deb P., Sundriyal R.C.. Tree species gap phase performance in the buffer zone area of Namdapha national park, Eastern Himalaya, India. Tropical Ecology, 2007, 48: 209-225.

[16] Denslow J.S.. Disturbance and diversity in tropical rain forests: the density effect. Ecological Applications, 1995, 5: 962-968.

[17] Denslow J.S., Aaron M.E., Sanford R.E.. Treefall gap size effects on above- and below-ground processes in a tropical wet forest. The Journal of Ecology, 1998, 86: 597-609.

[18] Garwood N.C.. Leck M.A., Parker V.T., Simpson R.L.. Tropical soil seed banks: a review. Ecology of Soil Seed Banks. 1989, New York: Academic Press, Inc.

[19] Gautam K.H., Devoe N.N.. Ecological and anthropogenic niches of Sal (Shorea robusta Gaertn. f.) forest and prospects for multiple-product forest management - a review. Forestry, 2006, 79: 81-101.

[20] Gotelli N.J., Graves G.R.. Null models in ecology. 1996, Washington: Smithsonian Institution

[21] Huang W., Pohjonen V., Johansson S., Nashanda M., Katigula M.I.L., Luukkanen O.. Species diversity, forest structure and species composition in Tanzanian tropical forests. Forest Ecology and Management, 2003, 173: 11-24.

[22] Hubbell S.P., Foster R.B., O’Brien S.T., Harms K.E., Condit R., Wechsler B., Wright S.J., de Lao S.L.. Light-gap disturbances, recruitment limitation, and tree diversity in a Neotropical forest. Science, 1999, 283: 554-557.

[23] Jackson J.K.. Manual of afforestation in Nepal, 1994 2 Kathmandu, Nepal: Forest Research and Survey Center

[24] Lawton R.O., Putz F.E.. Natural disturbance and gap-phase regeneration in a wind-exposed tropical cloud forest. Ecology, 1988, 69: 764-777.

[25] Pakeman R.J., Attwood J.P., Engelen J.. Sources of plants colonizing experimentally disturbed patches in an acidic grassland, in eastern England. Journal of Ecology, 1998, 86: 1032-1041.

[26] Pande P.K.. Comparative vegetation analysis and Sal (Shorea robusta) regeneration in relation to their disturbance magnitude in some Sal forests. Tropical Ecology, 1999, 40: 51-61.

[27] Pandey S.K., Shukla R.P.. Regeneration strategy and plant diversity status in degraded Sal forests. Current Science, 2001, 81: 95-102.

[28] Pitman N.C.A., Terborgh J., Silman M.R., Nuez P.. Tree species distributions in an upper Amazonian forest. Ecology, 1999, 80: 2651-2661.

[29] Li Q.Z., Bogaert J., Nijs I.. Gap pattern and colonization opportunities in plant communities: effects of species richness, mortality, and spatial aggregation. Ecography, 2005, 28: 777-790.

[30] Rautiainen O., Suoheimo J.. Natural regeneration potential and early development of Shorea robusta Gaertn.f. forest after regeneration felling in the Bhabar-Terai zone in Nepal. Forest Ecology and Management, 1997, 92: 243-251.

[31] Richards L.A., Coley P.D.. Seasonal and habitat differences affect the impact of food and predation on herbivores: a comparison between gaps and understory of a tropical forest. Oikos, 2007, 116: 31-40.

[32] Runkle J.R.. Patterns of disturbance in some old-growth Mesic forests of eastern North America. Ecology, 1982, 63: 1533-1546.

[33] Runkle J.R.. Pickett S.T.A., White P.S.. Disturbance regimes in temperate forests. The ecology of natural disturbance and patch dynamics. 1985, New York: Academic Press, 17 34

[34] Schnitzer S.A., Carson W.P.. Treefall gaps and the maintenance of species diversity in a tropical forest. Ecology, 2001, 82: 913-919.

[35] Stevens M.H.H., Carson W.P.. The significance of assemblage-level thinning for species richness. Journal of Ecology, 1999, 87 490

[36] Tabachnick B.G., Fidell L.S.. Using multivariate statistics, 2001 4 Needham Heights, MA: Allyn & Bacon

[37] Tabarelli M., Mantovani W.. Gap-phase regeneration in a tropical montane forest: the effects of gap structure and bamboo species. Plant Ecology, 2000, 148: 149-155.

[38] Uhl C., Clark K., Dezzeo N., Maquirino P.. Vegetation dynamics in Amazonian treefall gaps. Ecology, 1988, 69: 751-763.

[39] Vetaas O.R.. The effect of canopy disturbance on species richness in a central Himalayan oak forest. Plant Ecology, 1997, 132: 29-38.

[40] Webb E.L., Sah R.N.. Structure and diversity of natural and managed Sal (Shorea robusta Gaertn.f.) forest in the Terai of Nepal. Forest Ecology and Management, 2003, 176: 337-353.

[41] Whitmore T.C.. Canopy gaps and the two major groups of forest trees. Ecology, 1989, 70: 536-538.

[42] Whitmore T.C.. Swaine M.D.. A review of some aspects of tropical rainforest seedling ecology with suggestions for further enquiry. Ecology of Tropical Forest Tree Seedlings. 1996, Paris/Canforth: UNESCO/Parthenon

[43] Yu D., Zhai L., Dai L., Wang Q.. Dynamics of dominant tree species in a forest ecotone on the northern slope of Changbai Mountain. Journal of Forestry Research, 2006, 17: 216-220.

[44] Zang R.G., Tao J.P., Li C.Y.. Within community patch dynamics in a tropical montane rain forest of Hainan Island, south China. International Journal of Ecology, 2005, 28: 39-48.

[45] Zang R.G., Wang B.S.. Study on canopy disturbance regime and mechanism of tree species diversity maintenance in the lower subtropical evergreen broad-leaved forest, south China. Plant Biosystems, 2002, 136: 241-250.