Inferring shifts in tree species distribution using asymmetric distribution curves: a case study in the Iberian mountains

Abstract

Questions The objectives of this study were to examine altitudinal shifts in tree species distributions over one decade to quantify the potential for tree migration. Location Spain. Methods We analysed presence–absence data using two successive surveys of the Spanish Forest Inventory in five Fagaceae tree species (two temperate: Fagus sylvatica and Quercus petraea, one sub‐Mediterranean: Q. faginea and two Mediterranean: Q. suber and Q. ilex) in two mountain ranges (the Pyrenees and the Iberian system). Half of the fitted altitudinal distributions were skewed and required use of an asymmetric model for unbiased estimates of optimum altitude and changes in the probability of presence along the altitudinal gradient. For each species and mountain range, shifts were considered to have occurred when the difference in optimum altitude was significant or when differences in probability of occurrence between the two surveys demonstrated the occurrence of colonization or extirpation events. Results Overall, depending on species and mountain range, shifts in optimum altitude ranged between −34 m and +181 m. The altitudinal distribution of the Mediterranean species at the core of their latitudinal distribution range presented no sign of change. For the temperate and sub‐Mediterranean Fagaceae species, the patterns demonstrated the existence of distribution changes over a 10‐yr period. The largest, although not statistically significant, upward shift in optimum altitude was observed for Q. petraea in the Iberian system. More interestingly, its distribution indicated colonization events at higher altitudes. For Q. faginea in the Pyrenees, the shift in optimum altitude was the second largest and statistically significant, and was associated with large extirpation events at the lower altitudes. No evidence of shifts was observed for F. sylvatica. Conclusion This work demonstrates that changes in altitudinal distribution could occur over a 10‐yr time period for tree species located at the southern limit of their distribution, such as some temperate and sub‐Mediterranean oaks, whereas no movement was detected for Mediterranean oaks in the core of their distribution area.

Prediction of Dominant Forest Tree Species Using QuickBird and Environmental Data

“…According to the RF results, elevation was introduced as the most important factor in the process of modelling. Our results corroborated previous studies [22,26,36,80,81] when we tried to examine the relationship between elevation and the spatial occurrence of species. However, our results contradicted the results of Wheatley et al [32].…”

Reply to Sklenář: Upward vegetation shifts on Chimborazo are robust

“…Some will be too conservative because of overlooked individuals or exclusion of individuals with nonverified identifications. Contrary to Sklenár's claim (1), the rates reported are within previous observations (6)(7)(8). Furthermore, Sklenár uses post-Humboldt collections to compare shifts, but most were collected by Meyer and Whymper on the northwestern and western slopes (3,9), and hence are incomparable to our study.…”

The high vulnerability of Quercus robur to drought at its southern margin paves the way for Quercus ilex

“…An increasing body of empirical studies has shown that tree species populations located at their colder limits moved poleward or upward due to global changes (e.g., Walther et al 2005;Penuelas et al 2007; Batllori and Gutierrez 2008;Beckage et al 2008;Devi et al 2008;Parolo and Rossi 2008;Zhu et al 2012;Delzon et al 2013). On the contrary, evidences of extirpation events at their warmer edges remain rare (Allen and Breshears 1998;Penuelas and Boada 2003;Beckage et al 2008;Zhu et al 2012;Urli et al 2014). The difference in detecting colonization and extirpation events of populations located at each edge are explained by the apparent higher stability of local populations at their warmer limit compared to those located at the colder edge.…”