fine roots, and a low turnover in stems, branches and thick roots. In those cases, the allocation of growth and the final biomass allocation may diverge quite strongly over the years. There have been attempts to give these three different levels of allocation different names (a.o. partitioning, distribution, fractionation), but so far they have been applied inconsistently. The fractions of biomass present in leaves and roots are also relevant variables in Plant growth analysis. Calculation and units A common way to characterize the biomass allocation of a vegetative plant is to separate the plant in the organs of interest (e.g. leaves, stems, roots) and determine the biomass of these organs – generally on a dry mass basis - independently. The Leaf Mass Fraction (LMF) is then calculated as leaf dry mass / total plant dry mass, the Stem Mass Fraction (SMF) as stem dry mass / total plant dry mass, and Root Mass Fraction (RMF) as root dry mass / total plant dry mass. Generally, units are g g−1 (g organ / g total plant biomass). For generative plants, there is the additional compartment related to reproduction (flowers and flower stalks, seeds or fruits). The relative amount of biomass present in this compartment is often indicated as 'Reproductive Effort'. A related variable which is often used in agronomy is the 'Harvest index'. Because roots are seldom harvested, the harvest index is the amount of marketable product (often the seeds), relative to the total above-ground biomass. Alternative terminology that has been used are Leaf, Stem and Root Mass Ratios, or shoot:root or root:shoot ratios. The latter two convey less information, as they do not discriminate between leaves and stems. Normal ranges Young herbaceous plants generally have LMF values in the range of 0.3 - 0.7 g g−1 (0.5 on average), SMF values ranging from 0.04 - 0.4 (0.2 on average), and RMF values between 0.1 and 0.5 (0.3 on average). Young tree seedlings have values in the same range. For older and bigger plants, the LMF decreases and SMF increases. For large trees (> 1000 kg) LMF is below 0.05, SMF around 0.8 and RMF around 0.2 g g−1. At that stage most of the stem biomass consists of highly lignified material, which still may serve the important function of contributing to the support function of stems, but is physiologically not active anymore. Environmental effects The effect of the environment generally