Conservation values of understory vascular plants in even- and uneven-aged Nothofagus antarctica forests.
Usually, stands with aging trees are considered forests with higher conservation values, regardless their structural diversity and other functional attributes. Natural stands present a wide range of age structures, from even-aged stands growing at different development growth phases (e.g. CO=stands at initial or final optimum development growth phase, MD=stands at mature or decaying development growth phases) to uneven-aged stands with mixed development growth phases (e.g. UOG=stands combining mature or decaying development growth phases with initial or final optimum development growth phases, UMD=stands combining only mature and decaying development growth phases). The aim of this work was to compare richness and cover of understory vascular plants of even- and uneven-aged stands of Nothofagus antarctica (ñire) forests in Tierra del Fuego (Argentina), and relate these characteristics with abiotic, soil and forest structure variables. A total of 75 stands were sampled across the natural range distribution of the forests, where understory (point intercept method), forest structure (angle count sampling and eye-fish photos) and environmental (soil) variables were measured. 17 one-way ANOVAs were conducted using Tukey test at p < 0.05 to compare the means. Among forest structure and environmental variables, cover (F=4.3, p=0.007), radiation (F=4.4, p=0.006), phosphorous (F=3.9, p=0.012), tree density (F=10.3, p < 0.001), tree diameter (F=10.3, p < 0.001) and stand growth (F=4.9, p=0.004) showed significant differences, and in general with a positive or negative trend across the MD-UMD-UOG-CO gradient. Total (F=6.5, p < 0.001) and native species richness of the understory (F=7.2, p < 0.001) were significantly different among forest types, where UMD > UOG > MD > CO (17-28 total, and 13-24 native species, respectively). Neither exotic species richness (4-5 species) nor understory cover significantly changed among treatments (total, dicots, ferns and bryophytes). However, monocots cover significantly differed among treatments (F=3.9, p=0.012), where UMD > MD > UOG > CO. Finally, indicator species cover for environmental degradation did not present significant differences (F=2.1, p=0.106), but they were positive related to forests growing in mature stages. We concluded that uneven-aged stands presented significantly higher conservation values compared to even-aged stands, where mature/decay stands have better conservation values than optimum growth development phases. These findings can be used for better silviculture practices that combine silvopastoral use and conservation strategies.