Initial growth of Parkia platycephala (Benth.) and Enterolobium timbouva (Mart.) under field conditions in a Cerrado area

ABSTRACT The objective of the present study was to analyze the growth of Parkia platycephala and Enterolobium timbouva (Mimosaceae), tree species native to Cerrado, in a strictus sensus Cerrado area in the municipality of Porto Nacional, Tocantins. Twenty plants of each species were evaluated at thirty-day intervals during twenty-five months (February/2008 through February/2010). The following variables were analyzed: number of leaves produced, plant height, and stem diameter. Foliar phenology was also studied (August/2008 through February/2010) by analyzing five randomly-selected individuals of each species. Three branches of each individual were marked and all their leaves were evaluated in terms of emergence and abscission periods. Foliar herbivory was determined based on interval-scale classes of twenty-five per cent each. The results revealed that leaf production and growth in height in Parkia platycephala and Enterolobium timbouva were predominant during the rainy season. In terms of stem diameter, Parkia platycephala presented a better development when compared to Enterolobium timbouva. The relative growth rate increased expressively along the rainy season in both species. An increase in leaf predation was also observed during the wet season in the two species studied. As both species were exposed to the same environmental conditions, the greater relative growth rate observed in P. platycephala can be attributed to its physiological and anatomical features, which among other factors, contributed to a lower leaf predation by herbivores.

摘要：本研究旨在分析托坎廷斯州波尔图纳孔达尔市严格型塞拉多（strictus sensus Cerrado）区域内，两种塞拉多（Cerrado）原生树种——阔荚合欢（Parkia platycephala）与铁木豆（Enterolobium timbouva，含羞草科Mimosaceae）的生长状况。本研究于2008年2月至2010年2月的25个月周期内，每隔30天对每个物种的20株植株开展评估，测定指标包括新生叶片数、植株高度及茎干直径。此外，本研究于2008年8月至2010年2月期间开展叶物候学研究：选取每个物种的5株随机个体，为每株标记3个枝条，对其所有叶片的萌发与脱落周期进行观测。叶部植食危害程度则以每25%为一个区间等级进行分级测定。研究结果表明，阔荚合欢与铁木豆的叶片生成及株高生长均集中于雨季；就茎干直径生长而言，阔荚合欢的生长表现优于铁木豆。两个物种的相对生长率均在雨季显著提升，同时两物种的叶部植食危害程度在湿季均有所上升。由于两个物种所处环境条件一致，阔荚合欢所展现出的更高相对生长率，可归因于其生理与解剖学特征——这类特征使得其受植食动物取食的叶片比例更低。