Fire and Plant Diversification in Mediterranean-Climate Regions

Abstract

Despite decades of broad interest in global patterns of biodiversity, little attention has been given to understanding the remarkable levels of plant diversity present in the world’s five Mediterranean-type climate (MTC) regions, all of which are considered to be biodiversity hotspots. Comprising the Mediterranean Basin, California, central Chile, the Cape Region of South Africa, and southwestern Australia, these regions share the unusual climatic regime of mild wet winters and warm dry summers. Despite their small extent, covering only about 2.2% of world land area, these regions are home to approximately one-sixth of the world vascular plant flora. The onset of MTCs in the middle Miocene brought summer drought, a novel climatic condition, but also a regime of recurrent fire. Fire has been a significant agent of selection in assembling the modern floras of four of the five MTC regions, with central Chile an exception following the uplift of the Andes in the middle Miocene. Selection for persistence in a fire-prone environment as a key causal factor for species diversification in MTC regions has been under-appreciated or ignored. Mechanisms for fire-driven speciation are diverse and may include both directional (novel traits) and stabilizing selection (retained traits) for appropriate morphological and life-history traits. Both museum and nursery hypotheses have important relevance in explaining the extant species richness of the MTC floras, with fire as a strong stimulant for diversification in a manner distinct from other temperate floras. Spatial and temporal niche separation across topographic, climatic and edaphic gradients has occurred in all five regions. The Mediterranean Basin, California, and central Chile are seen as nurseries for strong but not spectacular rates of Neogene diversification, while the older landscapes of southwestern Australia and the Cape Region show significant components of both Paleogene and younger Neogene speciation in their diversity. Low rates of extinction suggesting a long association with fire more than high rates of speciation have been key to the extant levels of species richness.

Evolutionary history of fire‐stimulated resprouting, flowering, seed release and germination

“…We find it telling that researchers (and reviewers/editors) who consider climate and soils as controlling the evolution and distribution of plants fail to consider alternative explanations, such as the level of disturbance or plant–animal interactions; but those who study fire routinely take other factors into account as alternative explanations for the origin of the traits that they study in an evolutionary context (Lamont et al, ; He et al, ; Rundel et al, ; Tonnabel et al, ). This seems to reflect the general belief that climate and poor soils have a long history as selective agents among plants but fire is recent, so that fire can be ignored as it is not a primary constraint.…”

Fire as a key driver of Earth's biodiversity

“…Fire has been present since terrestrial plants invaded land 420 million years ago (Scott, ). It has long been recognised that fire is a natural ecological factor in many forest, woodland, shrubland, and grassland systems around the world (Rundel, ; Bond & Keeley, ; Bond, ; Pausas & Keeley, ), and that it has a major role in maintaining biodiversity and ecological processes in fire‐prone ecosystems (Bond & Parr, ; Rundel et al, , ; Pausas & Keeley, ). Fire plays many important ecological roles in ecosystems that cannot be duplicated by any other natural events.…”

“…The relatively stable post‐Miocene history and establishment of semi‐arid and highly seasonal (Mediterranean‐type) climates in southwestern Africa have also been assumed to be major contributors to diversity (Goldblatt & Manning, ). Although a role for the presence of wildfire as a stimulus for species diversification was proposed long ago (Mutch, ), it has only received attention more recently (He, Lamont & Manning, ; Rundel et al, , ) and has been shown to have a dominant, even pre‐emptive, role compared with other likely environmental constraints (Hu et al, ; Lamont, He & Yan, ). In attempts to understand the distribution and diversity of species, disturbance by fire as a key agent of selection has long been overlooked, and continues to be so (Pausas & Lamont, ; Magadzire et al, ; Pausas & Bond, ).…”

Response of Mediterranean Ornamental Plants to Drought Stress

“…Drought stress strongly limits the growth of plants in Mediterranean regions. In the world, there are five Mediterranean-climate regions (i.e., areas surrounding the Mediterranean Sea, parts of western North America, parts of western and southern Australia, southwestern South Africa, and parts of central Chile) located between 32 • -40 • N and S of the Equator [1]. The Mediterranean climate is defined by precipitation and temperature, and it is characterized by a high seasonality summarized as hot and dry summers and cool and wet winters [2].…”