Cavity-nesting birds show threshold responses to stand structure in native oak forests of northwestern Tunisia Moez Touihri a,⇑ , Marc-André Villard b , Faouzia Charfi a a Université de Tunis El Manar, Faculté des Sciences de Tunis, UR11-ES11 Unité de Recherche de Bio-Ecologie Animale et Systématique Evolutive, 2092 Tunis, Tunisia b Département de Biologie, Université de Moncton, Moncton, NB E1A 3E9, Canada article info Article history: Received 2 January 2014 Received in revised form 17 March 2014 Accepted 21 March 2014 Keywords: Conservation targets Ecological thresholds Mediterranean forest Woodpeckers Dead wood Forest harvesting abstract The detection of thresholds in forest bird response to gradients in forest alteration is a powerful approach to quantify their ecological requirements and to develop evidence-based targets for conservation. For this purpose, we analyzed the response of 31 forest bird species to a gradient in forest alteration by human activities (e.g. fire; grazing; firewood collection) in the Kroumirie region of northwestern Tunisia. We sur- veyed forest birds using point counts at 48 stations located throughout Feija National Park. From a data set of 12 vegetation variables, we obtained a gradient in forest alteration using a principal component analysis. Then, we modeled the probability of detection of bird species along this gradient using logistic regression. We selected the five most sensitive species as target species as indicated by the area under the receiver-operating characteristic curve (AUC). Then, we quantified thresholds in their probability of detection as a function of four habitat structure variables: density of large-diameter trees (dbh > 30 cm), canopy closure, density of snags, and downed woody material. Nineteen of 31 species exhibited a significant response to forest alteration (PCA1), including 7 positive and 12 negative responses. Among these, the five best models (AUC > 0.8) corresponded to Levaillant’s Woodpecker (Picus vaillantii), Great Spotted Woodpecker (Dendrocopos major), Lesser Spotted Wood- pecker (Dendrocops minor), Short-toed Treecreeper (Certhia brachydactyla), and Atlas Flycatcher (Ficedula speculgera). On the basis of their threshold values, we recommend to protect stands with densities of large-diameter trees of at least 650 stems ha À1 , and 207 stems ha À1 of snags, to meet the structural requirements (90% probability of detection) of the most demanding species, respectively Levaillant’s Woodpecker and Atlas Flycatcher. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction Habitat degradation is considered as one of the main threats to biodiversity worldwide (Pimm and Raven, 2000). Millennia of anthropogenic activity in native Mediterranean forests have caused a decline in critical habitat components such as large-diam- eter trees and dead wood (Clavero et al., 2011), along with an alter- ation of ecosystem processes such as natural regeneration, mainly through overgrazing (Blondel and Aronson, 1999; Plieninger, 2007) and the use of agricultural land depends on the native forests (Plieninger et al., 2011). Hence, landscapes are composed of a mosaic of native woodland, maquis and grassland (Pereira and Da Fonseca, 2003). Several studies have documented the environ- mental degradation in the Mediterranean basin and the resulting landscape structure (Atauri and de Lucio, 2001; Pereira and Da Fonseca, 2003; Blondel, 2006; Geri et al., 2010; Pereira et al., 2014a). Others have documented relationships between avian assemblages and habitat structure using bird occurrence and abun- dance data (Camprodon and Brotons, 2006; Diaz, 2006; Kati and Sekercioglu, 2006; Gil-Tena et al., 2007; Pereira et al., 2014a). A few more studies have identified potential threats to native Medi- terranean oak forests and proposed management actions (Godinho and Rabaca, 2011; Robles et al., 2011; Pereira et al., 2014b). In the Mediterranean region, Santos and Tellería (1992) and Diaz (2006) have shown that pine plantations host fewer species and a lower abundance than the primary forests they are intended to replace. Barrientos (2010) found that a habitat generalist, the Great Spotted Woodpecker (Dendrocopos major), mainly used native oak trees to nest in a landscape dominated by pine planta- tions. However, the breeding habitat requirements of other forest bird species in managed landscapes remain poorly documented, http://dx.doi.org/10.1016/j.foreco.2014.03.050 0378-1127/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Address: 6 rue Beji Massoudi, Ariana 2080, Tunisia. Tel.: +216 98942148. E-mail address: mzti1981@gmail.com (M. Touihri). Forest Ecology and Management 325 (2014) 1–7 Contents lists available at ScienceDirect Forest Ecology and Management journal homepage: www.elsevier.com/locate/foreco