Nothofagus alessandrii forests in Chile 229
of N. alessandrii forests were confined to a mosaic of many small (,2 ha) and scattered fragments surrounded by ama- trix of exotic pine plantations (Grez et al., 1998;Santelices et al., 2012),making themprone to disturbances such as forest fires and invasive species. Anthropogenic fires and the invasion of exotic species
are significant threats to the survival of the Maulino forests. Since 2010 forest fire activity has increased in south-central Chile, particularly in the coastal range of the Maule region (Carvajal & Alaniz, 2019). Droughts and heatwaves are the main factors associated with increasing numbers of large wildfires and the burning of larger areas (Garreaud et al., 2017; González et al., 2018; Bowman et al., 2018). During the 2016–2017 fire season, an extreme and destructivemega- fire (named LasMáquinas) initiated by human action burnt an area of 160,000 ha, including 55%(172 ha) of the last remnants of N. alessandrii forests (Valencia et al., 2018). Pine plantations may favour the spread of large fires (McWethy et al., 2018;Bowman etal., 2018) and promote the invasion of N. alessandrii fragments by massive seedling recruitment of P. radiata, a pyrophytic species (i.e. adapted to fire). Key drivers of ecosystem change can interact with and
reinforce each other, and can shift entire landscapes into undesirable and potentially irreversible states (i.e. landscape traps) in which major functional and ecological attributes are compromised (Lindenmayer et al., 2011). For instance, post-fire salvage logging in tropical rainforests and the sub- sequent increase of fire-prone grassland species can lead to an altered fire regime that limits recovery (van Nieuwstadt et al., 2001; Cochrane & Laurance, 2008). Similarly, alter- ation of the stand structure in temperate forests by logging can increase the occurrence and severity of wildfires through modification of fuel types and loads (Odion et al., 2004; Lindenmayer et al., 2009, 2011). In north Patagonia, Araucaria araucana forests affected by extreme wildfire events and re-burns after short intervals, attributed to chan- ging climate trends and land-use practices, have favoured a transition to a fire-prone landscape, creating a potential landscape trap, especially when invaded by Pinus species (Cóbar-Carranza et al., 2014; González et al., 2020). Forest fires and invasion by exotic species are critical emer-
ging pressures, especially for the coastal range Maulino forests (San Martín & Sepúlveda, 2002;Bustamanteetal., 2003; Santelices et al., 2018; Carvajal & Alaniz, 2019;González et al., 2019;Leal, 2020). Here we examine the effects of the 2017 Las Máquinas mega-fire on the last remnants of forests harbouring N. alessandrii, a rare, endemic deciduous tree spe- cies of the coastal range of central Chile. Ourmain goals were to: (1) assess the severity of the fire in the N. alessandrii forest fragments affected by the mega-fire, (2) determine the land- cover composition and configuration of the main land uses surrounding the N. alessandrii forest fragments, (3) assess the invasion of P. radiata into N. alessandrii forests, and (4)evalu- ate the survival and post-fire responses of these threatened
forests 2 years after the fire. Finally, considering the critical state of these forests, we recommend restoration andmanage- ment strategies at the landscape and forest scales to avoid the loss of the last remnants of these threatened N. alessandrii for- est ecosystems.
Study area
The study area lies in the coastal range of the Maule region of central Chile. The predominant climate is Mediterranean, characterized by winter rainfall, with dry summers in September–April (Beck et al., 2018). Nothofagus alessandrii (familyNothofagaceae) grows inrelativelydeep soils (.50cm) of metamorphic and granitic origin, which are relatively poor, with low phosphorus content, and are highly suscep- tible to erosion (San Martín et al., 2013). We studied nine N. alessandrii populations burnt by the 2017 mega-fire. Six of these populations are in the southern burnt area and three in the northern burnt area (Fig. 1). Nothofagus alessandrii is an endemic, broad-leaved de-
ciduous tree species that occurs in small patches on south, south-west or south-east facing aspects at elevations of 160– 440m(Donoso&Lara, 1996). This species forms nearly pure or mixed second-growth post-fire forests originated mostly from vegetative reproduction (i.e. suckers arising from the base of a tree). In mixed stands it is associated with Noth- ofagus glauca and other hygrophyllous (Aextoxicon punc- tatum, Nothofagus obliqua, Gevuina avellana)and meso- phytic (Cryptocarya alba, Peumus boldus) species of the sclerophyllous forests (SanMartín et al., 1984; Donoso, 1996). The present distribution of N. alessandrii forests is restricted and fragmented along 100 km of the coastal range of central Chile within a landscape dominated by extensive industrial forest plantations of P. radiata, and shrublands (San Martín et al., 1984). These forests are thought to be remnants of a much larger population (Baldwin et al., 2018). The small forest patches include 15 populations of 1–67 ha, with a total forest cover of 314 ha (Donoso, 1996; San Martín & Donoso, 1996; San Martín & Sepúlveda, 2002; Santelices et al., 2012, 2018). Currently, N. alessandrii is one of the most threatened tree species in continental Chile and is recognized as a Natural Monument (Hechenleitner et al., 2005; MMA, 2021) and categorized as Endangered on the IUCN Red List (Barstow et al., 2017; Baldwin et al., 2018).
Methods Remote-sensing data and fire severity assessment
We used radar-based and optical information from the Sentinel-1 and Sentinel-2 satellites, respectively, to assess the fire severityof
thenineburntN.alessandrii populations (172 ha).
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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