Time series analysis of the behavior of natural rubber prices in the international market

Este trabalho analisou o comportamento dos pre\ue7os da borracha natural no mercado internacional, no per\uedodo de janeiro de 1982 a dezembro de 2006, em fun\ue7\ue3o de sua oferta e demanda agregadas, evidenciando os principais pa\uedses produtores e consumidores. Especificamente a pesquisa analisou a evolu\ue7\ue3o dos pre\ue7os e do quantum comercializado da borracha natural no mercado internacional. Caracterizou, identificou, estimou e analisou modelos para a s\ue9rie de pre\ue7os reais mensais da borracha crua RSS 1 (US/t) e; testou a precis\ue3o dos modelos estimados na previs\ue3o dos pre\ue7os dessa commodity, no per\uedodo de jan./2006 a dez./2006. Os modelos estudados foram das classes ARIMA-ARCH. Os principais resultados encontrados foram: 0s pre\ue7os reais da borracha natural, no per\uedodo estudado, apresentam tend\ueancia decrescente; A identifica\ue7\ue3o e estima\ue7\ue3o dos modelos da fam\uedlia ARIMA mostraram a exist\ueancia de heteroscedasticidade na s\ue9rie estudada e a necessidade de identificar, estimar e analisar os modelos da fam\uedlia ARCH; O modelo que melhor ajustou os retornos da s\ue9rie de pre\ue7os da borracha crua RSS 1 foi o AR(1) para um GARCH(1,1); Os modelos da fam\uedlia ARIMA n\ue3o satisfizeram as condi\ue7\uf5es de previs\ue3o da s\ue9rie estudada; o modelo AR (1)-GARCH (1,1) se mostrou preciso para a realiza\ue7\ue3o de prognoses do pre\ue7o da borracha.This work analyzed the behavior of natural rubber prices in the international market from January 1982 to December 2006 in function of its aggregated demand and supply, pointing out the main producing and consuming countries. Specifically, the research studied the evolution of prices and of the marketed quantum of natural rubber in the international market. It was characterized, identified, estimated and analyzed models for the real monthly prices series of raw rubber RSS 1 (US/t), and the accuracy of the estimated models for forecasting prices of this commodity was tested from Jan/2006 to Dez/2006. The studied models were of ARIMA-ARCH class. The main results were: the real natural rubber prices presented decreasing tendency in the period being studied; the ARIMA family estimated model indicating the existence of heteroskedasticity in the series, making it necessary to identify, to estimate and to analyze the models of ARCH family; the model which best adjusted the returns of the price series of the raw rubber RSS1 was AR(1)-GARCH(1,1); the models of the ARIMA family didn't satisfy the prognosis conditions of the series being studied; the AIR (1)-GARCH (1,1) model was accurate for forecasting rubber prices

Allometric relationships in Leucaena leucocephala (Lam.) De Wit

Ecossistemas florestais s\ue3o respons\ue1veis pelo maior ac\ufamulo de carbono da biosfera terrestre. A quantifica\ue7\ue3o da biomassa para esp\ue9cies florestais vem contribuir com informa\ue7\uf5es diretas sobre seu potencial para o seq\ufcestro do carbono atmosf\ue9rico. O ensaio objetivou ajustar equa\ue7\uf5es que permitam estimar a biomassa a\ue9rea e subterr\ue2nea de Leucaena leucocephala (Lam.) De Wit por meio do m\ue9todo direto. Para estimar a potencialidade da Leucaena leucocephala na fixa\ue7\ue3o do carbono, foi utilizado o fator de convers\ue3o 0,5. Do total da biomassa e do carbono em indiv\uedduos de Leucaena leucocephala, 24% correspondem ao sistema radicular e 76% correspondem ao sistema a\ue9reo. De forma geral, a biomassa total apresentou a distribui\ue7\ue3o: fuste > galhos vivos > ra\uedzes > folhas. O modelo linear com transforma\ue7\ue3o logar\uedtmica utilizando CAP vari\ue1vel independente foi estatisticamente significativa para estimar biomassa seca total.The objective of this study was to calculate simple allometric equations in order to estimate above and below ground dry biomass from Leucaena leucocephala individuals. Results indicated that biomass components show the following pattern: stem > branches > roots > leaves. Independently from individual size, 24 % of total sampled dry biomass was located below-ground, and 76 % above-ground. Log transformed linear equations using CBH (circumference at breast height) as independent variable was statistically significant (P<0.05) to estimate leucaena total dry biomass