A Hierarchical Bayesian model of wildfire in a Mediterranean biodiversity hotspot: Implications of weather variability and global circulation

Abstract

In this study we combined an extensive database of observed wildfires with high-resolution meteorological data to build a novel spatially and temporally varying survival model to analyze fire regimes in the Mediterranean ecosystem in the Cape Floristic Region of South Africa (CFR) during the period 1980-2000. The model revealed an important influence of seasonally anomalous weather on fire probability, with increased probability of fire in seasons that are warmer and drier than average. In addition to these local-scale influences, the Antarctic Ocean Oscillation (AAO) was identified as an important large scale influence or teleconnection to global circulation patterns. Fire probability increased in seasons during positive AAO phases, when the subtropical jet moves northward and low level moisture transport decreases. These results confirm that fire occurrence in the CFR is strongly affected by climatic variability at both local and global scales, and thus likely to respond sensitively to future climate change.Comparison of the modeled fire probability between two periods (1951-1975 and 1976-2000) revealed a four year decrease in an average fire return time. If, as currently forecasted, climate change in the region continues to produce higher temperatures, more frequent heat waves, and/or lower rainfall, our model thus indicates that fire frequency is likely to increase substantially. The regional implications of shorter fire return times include shifting community structure and composition, favoring species that tolerate more frequent fires.Keywords: Fire regime, Cape Floristic Region, Mediterranean, fynbos, climate change, hierarchical Bayesian 3 IntroductionOver half of the world's terrestrial ecosystems are dependent on fire to maintain ecological structure and function (Shlisky et al. 2007). Fire regimes in these regions have a profound ecological role (Bond 1995) that can be strongly influenced by weather and climate (McKenzie et al. 2004). Thus in addition to the direct physiological impacts of changes in temperature, precipitation, and CO 2 concentration due to climate change, changes in the fire regime will have potentially major effects on these fire-driven ecosystems (Bond et al. 2003). Since the 1980s there has been speculation about the impact of climate change on wildfire regimes (Balling et al. 1992;Clark 1988;Layser 1980), and some studies have produced evidence of changes in fire regimes associated with recent climate change (Gillett et al. 2004;Westerling et al. 2006).However, most of this work has been limited to North America, Europe, and Australia, and much uncertainty remains regarding the sensitivity of wildfire to weather trends and variability in many other fire-prone regions of the world. In this study we present a novel model for fire return times that allows integration of decades of regional-scale weather data at high spatial and temporal resolution, while retaining the temporal dependence structure of a fire survival model.We apply this model to some of the richest fire oc...

Intensifying postfire weather and biological invasion drive species loss in a Mediterranean-type biodiversity hotspot

“…Fire is a ubiquitous driver of disturbance across the globe and is essential for the healthy functioning and maintenance of many ecosystems (10,11), but changes in fire regime or postfire weather may drive major shifts in the composition, structure, and function of ecosystems (12). Changes in climate and weather can alter fire regimes (7,8), whereas increasingly extreme or prolonged periods of heat or drought in the years immediately after fire may affect ecosystem resilience and diversity by inhibiting seed germination or increasing mortality of seedlings or sprouting individuals (13)(14)(15). Where these impacts alter the functional composition of communities, this change can drive major changes in ecosystem structure and function (16)(17)(18).…”

“…Many resprout from storage organs or retain seeds in fireproof (serotinous) cones that open after fire, whereas others use dispersal vectors such as ants or rodents to facilitate underground storage of seed, later triggered to germinate by heat or smoke (20). Postfire weather conditions and the frequency, season, and intensity of fires are important determinants of vegetation structure and composition (21,22), and there is increasing concern that these properties of the disturbance regime are changing, resulting in altered ecosystems and biodiversity loss (7,21,23).…”

“…Cape Floristic Region | Fynbos | South Africa | biodiversity | climate change A mid mounting evidence of climate change impacts on living systems (1)(2)(3), there is increasing concern about changing disturbance-climate interactions and their potential impacts on biodiversity and ecosystem function (4)(5)(6)(7)(8)(9). Fire is a ubiquitous driver of disturbance across the globe and is essential for the healthy functioning and maintenance of many ecosystems (10,11), but changes in fire regime or postfire weather may drive major shifts in the composition, structure, and function of ecosystems (12).…”

Fire-mediated disruptive selection can explain the reseeder–resprouter dichotomy in Mediterranean-type vegetation

“…In that case, populations of resprouters would be sensitive to the occurrence of occasional intense fires, with only one intense fire in 100 years resulting in negative population growth of resprouters in our simulations. The frequency of intense fires could well increase with likely climate change scenarios forecast for the fynbos (Wilson et al 2010).…”

“…The dry summer season when fires naturally happen are followed by predictably wet winters, particularly in the west where diversity is greatest (Cowling 1992). Human modification (mainly acceleration) of the fire cycle is thought to have occurred in the past few hundred years, and this may accelerate further under climate change scenarios (Wilson et al 2010). There is thus an important need to understand how biodiversity components may be affected by fire frequency in order to assess species vulnerability and implement conservation action.…”