Building wood debris piles benefits avian seed dispersers in burned and logged Mediterranean pine forests

https://doi.org/10.1016/j.foreco.2010.04.003Get rights and content

Abstract

Salvage logging is a common practice carried out in burned forests worldwide, and intended to mitigate the economic losses caused by wildfires. Logging implies an additional disturbance occurring shortly after fire, although its ecological effects can be somewhat mitigated by leaving wood debris on site. The composition of the bird community and its capacity to provide ecosystem services such as seed dispersal of fleshy-fruited plants have been shown to be affected by postfire logging. We assessed the effects of the habitat structure resulting from different postfire management practices on the bird community, in three burned pine forests in Catalonia (western Mediterranean). For this purpose, we focused on the group of species that is responsible for seed dispersal, a process which takes place primarily during the winter in the Mediterranean basin. In addition, we assessed microhabitat selection by seed disperser birds in such environments in relation to management practices. Our results showed a significant, positive relationship between the density of wood debris piles and the abundance of seed disperser birds. Furthermore, such piles were the preferred microhabitat of these species. This reveals an important effect of forest management on seed disperser birds, which is likely to affect the dynamics of bird-dependent seed dispersal. Thus, building wood debris piles can be a useful practice for the conservation of both the species and their ecosystem services, while also being compatible with timber harvesting.

Introduction

Wildfires are one of the most important disturbances affecting ecological processes and economic interests in forest ecosystems worldwide (Blondel and Aronson, 1999, Hessburg and Agee, 2003, FAO, 2007). In many countries postfire salvage logging (i.e., the harvesting of burned timber for mainly commercial purposes) is the most extended forestry practice intended to compensate for the economic losses caused by wildfires (Hutto, 2006, Lindenmayer et al., 2004). Salvage logging is also justified by other objectives, such as reducing the fuel load, enhancing future tree survival, preventing the proliferation of xylophagous insects or making it easier and safer for people to pass through the burned area or for future forest management work to be carried out (Ne’eman et al., 1995, Martínez-Sánchez et al., 1999, Lindenmayer and Noss, 2006).

In the Mediterranean Basin, where there has been a long history of landscape management, fires often take place in lowland pine forests, most of which grow on abandoned agricultural land (Trabaud, 1981). In this type of forest, after a fire, salvage logging is the most frequently used management method, because pine wood is still commercially profitable for use as boards until two years after a fire, and even later if ground down (e.g., to produce biomass fuel). In general terms, salvage logging involves a drastic habitat change—from a burned forest structure to open grassland and shrubland—a short time after the fire. However, on a smaller scale the characteristics of these new open habitats also depend on the interests and decisions of landowners and managers, and therefore on the ownership structure of each burned forest. When forests are divided into small privately owned lots, as is often the case in Mediterranean areas, individual decisions lead to the coexistence of multiple management models in burned stands in close proximity. These strategies result in clearcuts (where wood debris may be completely removed, left on the ground or piled up), areas where isolated snags remain, and unlogged stands of partially burned pines. Furthermore, restoration measures such as log erosion barriers can be found in burned public forests, which are managed essentially for restoration purposes. The administrative authority concerned may also issue management recommendations, and grant subsidies to, or reach agreements with, local landowners, who may then delegate postfire management to public managers.

The habitat disturbance induced by postfire salvage logging affects animal communities, an issue that has sometimes been studied using birds as the focal group (Kotliar et al., 2002, Hutto and Gallo, 2006, Cahall and Hayes, 2009). It has been shown that salvage logging can have a greater impact than the fire itself on the forest bird community, including the substitution of forest specialists by open-land species (Izhaki, 1993, Llimona et al., 1993, Morisette et al., 2002, Castro et al., in press). Such changes are likely to affect frugivorous bird species, some of which are involved in important ecological processes such as seed dispersal of fleshy-fruited shrubs and climbers. In the Mediterranean, fleshy-fruited plants produce ripe fruit during the fall and winter (Mooney and Kummerow, 1981, Jordano, 1992), when various species of small and medium-sized birds disperse their seeds (Herrera, 1984, Herrera, 1998). In burned areas, early succession gives rise to a shrubland-like habitat (Trabaud and Lepart, 1980), which hosts a diverse winter bird assemblage, including some species that attain high densities thanks to postfire fruit and seed production (Pons and Prodon, 1996, Pons, 2001, Tellería et al., 2004). Izhaki and Adar (1997) showed that winter bird communities in eastern Mediterranean burned and logged forests were dominated by shrubland species, some of which were seed dispersers. However, the habitat and microhabitat use of these species under different scenarios of postfire management has not yet been studied in depth. Previous studies have reported that bird-dependent seed rain strongly relies on habitat structures that act as dispersal foci, such as isolated trees that act as perches (Guevara and Laborde, 1993, Pausas et al., 2006, Herrera and García, 2009). After logging, wood debris piles and barriers built in a burned pine forest can also act as dispersal foci (Rost et al., 2009). Thus, the variability of postfire treatments after logging, which leads to the presence of different microhabitats on a small scale, may have important implications for bird-dependent seed rain, depending on the differential use that seed dispersers make of the resulting microhabitats.

The aims of this study are: (1) to investigate the effects of postfire management on winter bird communities in burned Mediterranean pine forests, (2) to determine whether certain management practices have positive effects on species richness and abundance of seed dispersers in winter, and (3) to analyze microhabitat selection by seed dispersers in order to describe patterns in their use of the microhabitats. If postfire management practices had an effect on seed dispersers distribution and microhabitat use, this would also affect seed rain and the regeneration of fleshy-fruit producing shrub or climber species. We took advantage of the availability in three study areas of examples of different postfire logging practices (ranging from completely logged areas to unlogged ones, and including different methods of managing wood debris) to investigate which of these practices may be more favorable to the presence of bird species involved in seed dispersal.

Section snippets

Study area

The study was carried out in three burned areas located in Catalonia, in the northeast of the Iberian Peninsula: Torroella de Montgrí (henceforth TM, 3°7′ E, 42°3′ N), Ventalló (VE, 3°2′ E, 42°7′ N) and Cistella (CI, 2°50′ E, 42°17′ N) (Fig. 1). The maximum distance between any two areas was 30 km. All three areas have a meso-Mediterranean climate, limestone substrates, and altitudes ranging from 80 to 210 m above sea level. Before the fire, they featured a vegetation mosaic composed of Aleppo

Results

In the point counts we recorded a total of 744 birds belonging to 38 species (Table 1). The most abundant species were the Sardinian warbler, the Dartford warbler, the European robin, the Hedge accentor (Prunella modularis) and the Chaffinch (Fringilla coelebs). The seed disperser group is composed by nine species (Table 1), which accounted for 58% of the total abundance, the three most abundant accounting for 48% of the total abundance.

RDA results showed that habitat variables explained 16% of

Discussion

Habitat heterogeneity in burned Mediterranean pine forests allows the coexistence of bird species with different habitat requirements during winter, and thus we found a mixture of open-land, shrubland and forest birds in our study sites. Such habitat and bird community heterogeneity likely results from the management carried out in these areas, as well as from the regeneration of the low plant cover. We found that different management practices favored different bird species in winter. Indeed,

Acknowledgements

The authors would like to thank David Meya and Joan Real for kindly providing us with advice and information. This study was funded by the Spanish Ministry of Science and Innovation (CGL2005-0031/BOS and CGL2008-05506/BOS) and J.R. held a FPU grant of the Ministry of Education.

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