232 M. E. González et al.
FIG. 2 (a) Invasions of pine Pinus radiata into N. alessandrii forest fragments in the southern study area in the Maule region of central Chile, and (b) magnification illustrating the invasion of pine at the edges of N. alessandrii fragments.
The land-use and land-cover map indicated that 60%of the area surrounding N. alessandrii forests corresponded to P. radiata plantations and clear cuts of this tree species (Fig. 1). Shrublands were the primary native vegetation type surrounding N. alessandrii forests, with 16% cover, and only 8% of the area was classified as native forests (Fig. 1b), with a fragmented spatial pattern.
Pinus radiata invasion inside N. alessandrii forests before the mega-fire
We estimated that P. radiata had invaded and become a dominant species in the forest canopy in 16%(28 ha) of the total area of the nine N. alessandrii populations (172 ha) before the mega-fire occurred in 2017 (Fig. 2). These inva- sions were mainly along the edges of the fragments close to plantations and clear cuts (Fig. 2b). The range of P. radiata cover in the nine populations was 11–40%. Smaller fragments had a greater cover of pine compared to larger fragments.
Forest composition and structure, and post-fire responses of burnt N. alessandrii forests
The structure of N. alessandrii stands indicates that at the time these fragments were affected by the 2017 mega-fire, they were in an intermediate state of development, with a density of 1,200–3,240 trees/ha and a basal area of 17–74 m2/ha. The diameter distribution of these second-growth
patches shows a greater number of trees in the smallest size class (5–15 cm diameter at breast height) representing an evenly aged cohort established after a high-severity fire (Fig. 3a). In addition, N. alessandrii stands feature adult P. radiata (.50 cmdiameter at breast height) trees established in forest clearings in recent decades. The survival status measured 2 months after the 2017
mega-fire demonstrated high mortality of N. alessandrii trees independent of fire severity (Fig. 3a). Nevertheless, by April 2019 .80% of the N. alessandrii trees had re- sprouted, demonstrating their ability to survive high- severity fires (Fig. 3b, Plate 1b). Evidence for recurrent and severe fires having shaped these fragments comes from the protuberances formed at the bases of many trees as a result of continuous re-sprouting. Post-fire recruitment of N. ales- sandrii from seedswas lowby 2019 (,17%) and restricted to the fragments affected by low- and moderate-severity fires. All adult P. radiata affected by moderate severity fires were killed. During the 2 years after the fire, seedlings of P. radiata co-
lonized the burnt sites at high density from seeds stored in serotinous cones, particularly in fragments burnt with high severity (Plate 1c). By 2019 the number of seedlings of P. radiata was 1,600–15,000 per ha in the burnt sites (Fig. 3b).
Discussion
Since 1750, N. alessandrii forest stands have been degraded and destroyed as a result of fires set by people, and by
Oryx, 2023, 57(2), 228–238 © The Author(s), 2022. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605322000102
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