Legacy of harvesting methods on coppice-rotation Eucalyptus at experimental and operational scales

Abstract

Coppice-rotation stands comprise 20 to 30% of the Eucalyptus forests in Brazil and understanding the factors influencing the production ecology of the coppice-rotation is fundamental to improving silvicultural prescriptions. We investigated the effect of harvesting method, stump height and stump cleaning on survival, uniformity, growth, above-ground biomass and light use efficiency in a short rotation of a highly productive E. grandis x E. urophylla clone at two scales in Brazil. At the field experiment scale, treatments were composed of harvesting techniques (Chainsaw and Feller Buncher), stump height (High and Low) and stump cleaning (No harvesting residues over the stump or with residues). The treatments strongly affected growth in height and volume, with less effect on diameter. The largest response came from harvesting method, with mechanized harvesting with a 33% lower mean annual increment (MAI, 33 m³ ha−1 y−1) than harvesting with the chainsaw (50 m³ ha−1 y−1). Stump height did not influence growth in chainsaw clear-cut, but low stumps after Feller Buncher harvesting reduced growth by 23% (30 m³ ha−1 y−1) compared with high stumps (36 m³ ha−1 y−1). Stumps cleaning increased survival only in the semi-mechanized harvest but did not result in a difference in yield. Leaf area index and light use efficiency at the end of rotation were impacted by the clear-cut method, with an average of 3.3 and 2.1 m² m−2, and 0.7 and 0.57 g MJ−1 for chainsaw and Feller Buncher clear cut, respectively. The percentage of stumps that remained intact, the uniformity among individuals, the light capture and the light use efficiency, presented a r² of 67%, 55%, 60% and 86% (p-value < 0.001), respectively. At the operational scale of 12 plantations, we measured MAI, uniformity and survival of the two harvesting methods, all with high stump height and no stump cleaning (current operational prescription). The reduction in coppice-rotation MAI from Feller Buncher harvesting was consistent with the experimental scale, but the difference in MAI (age 4 years) was not as large: 37 m³ ha−1 y−1 for the Feller Buncher harvest and 44 m³ ha−1 y−1 for chainsaw harvest. Harvesting with the Feller Buncher, lowered survival (88%, compared with to 96% with chainsaw harvest) and stand uniformity. Overall, the impacts of harvesting treatment were large enough to those silvicultural systems that include a coppice rotation need to carefully account for the costs and efficiencies of operations for harvesting the planted rotation with subsequent impacts on coppice survival and production.