Trees and Regeneration in Rubber Agroforests and Other Forest-derived Vegetation in Jambi (Sumatra, Indonesia)

The rubber agroforests (RAF) of Indonesia provide a dynamic interface between natural processes of forest regeneration and human's management targeting the harvesting of latex with minimum investment of time and financial resources. The composition and species richness of higher plants across an intensification gradient from forest to monocultures of tree crops have been investigated in six land use types (viz. secondary forest, RAF, rubber monoculture, oil palm plantation, cassava field and Imperata grassland) in Bungo, Jambi Province, Indonesia. We emphasize comparison of four different strata (understory, seedling, sapling and tree) of vegetation between forest and RAF, with specific interest in plant dependence on ectomycorrhiza fungi. Species richness and species accumulation curves for seedling and sapling stages were similar between forest and RAF, but in the tree stratum (trees > 10 cm dbh) selective thinning by farmers was evident in a reduction of species diversity and an increase in the proportion of trees with edible parts. Very few trees dependent on ectomycorrhiza fungi were encountered in the RAF. However, the relative distribution of early and late successional species as evident from the wood density distribution showed no difference between RAF and forest

Stapelia indet.

<div><p>In semiarid drylands water shortage and trampling by large herbivores are two factors limiting plant growth and distribution. Trampling can strongly affect plant performance, but little is known about responses of morphological and mechanical traits of woody plants to trampling and their possible interaction with water availability. Seedlings of four shrubs (<em>Caragana intermedia</em>, <em>Cynanchum komarovi</em>, <em>Hedysarum laeve</em> and <em>Hippophae rhamnoides</em>) common in the semiarid Mu Us Sandland were grown at 4% and 10% soil water content and exposed to either simulated trampling or not. Growth, morphological and mechanical traits were measured. Trampling decreased vertical height and increased basal diameter and stem resistance to bending and rupture (as indicated by the increased minimum bend and break force) in all species. Increasing water availability increased biomass, stem length, basal diameter, leaf thickness and rigidity of stems in all species except <em>C. komarovii</em>. However, there were no interactive effects of trampling and water content on any of these traits among species except for minimum bend force and the ratio between stem resistance to rupture and bending. Overall shrub species have a high degree of trampling resistance by morphological and mechanical modifications, and the effects of trampling do not depend on water availability. However, the increasing water availability can also affect trade-off between stem strength and flexibility caused by trampling, which differs among species. Water plays an important role not only in growth but also in trampling adaptation in drylands.</p> </div

Results of ANOVA for the effects of species (S), trampling (T), water (W) and their interactions on mechanical properties of four species.

<p><i>F</i> values and the significance levels (^***<i>P</i><0.001, ^**<i>P</i><0.01, ^*<i>P</i><0.05 and ^ns<i>P</i>≥0.05) are given. Data were Ln-transformed before analyses.</p

Effects of water availability and trampling on mechanical traits of the four species.

<p>The panel A, B, C, D, E, F, G and H are for Young’s modulus, second moment of area, flexural stiffness, break stress, yield stress, minimum lateral break force (<i>F</i>_break), bend force (<i>F</i>_bend) and <i>F_break/F_bend</i> respectively. Data are mean ± SE. Except for h, values of y axis are Ln-transformed as a result of low values of <i>C. komarovii</i>.</p

Tuber size variation and organ preformation constrain growth responses of a spring geophyte

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