Differences between tree species seedling and adult altitudinal distribution in mountain forests during the recent warm period (1986–2006)

Abstract

Spatial fingerprints of climate change on tree species distribution are usually detected at latitudinal or altitudinal extremes (arctic or alpine tree line), where temperatures play a key role in tree species distribution. However, early detection of recent climate change effects on tree species distribution across the overall temperature gradient remains poorly explored. Within French mountain forests, we investigated altitudinal distribution differences between seedling (550 cm tall and 1 yr old) and adult (8 m tall) life stages for 17 European tree taxa, encompassing the entire forest elevation range from lowlands to the subalpine vegetation belt (50Á2250 m a.s.l.) and spanning the latitudinal gradient from northern temperate to southern Mediterranean forests. We simultaneously identified seedlings and adults within the same vegetation plots. These twin observations gave us the equivalent of exactly paired plots in space with seedlings reflecting a response to the studied warm period (1986Á2006) and adults reflecting a response to a former and cooler period. For 13 out of 17 species, records of the mean altitude of presence at the seedling life stage are higher than that at the adult life stage. The low altitudinal distribution limit of occurrences at the seedling life stage is, on average, 29 m higher than that at the adult life stage which is significant. The high altitudinal distribution limit also shows a similar trend but which is not significant. Complementary analyses using modelling techniques and focusing on the optimum elevation (i.e. the central position inside distribution ranges) have confirmed differences between life stages altitudinal distribution. Seedlings optima are mostly higher than adults optimum, reaching, on average, a 69 m gap. This overall trend showing higher altitudinal distribution at the seedling life stage in comparison to the adult one suggests a main driver of change highly related to elevation, such as climate warming that occurs during the studied period. Other drivers of change that could play an important role across elevation or act at more specific scales are also discussed as potential contributors to explain our results.

Vegetation databases provide a close-up on altitudinal tree species distribution in the Bavarian Alps

“…Woodall et al (2009) found significant northward advances of saplings over trees in boreal species of North America. The fact that Lenoir et al (2009) found only insignificant advances of seedlings at upper limits in French mountains is attributable to the exclusion of plots in the treeline ecotone. The finding of these authors that seedlings have significantly higher low elevation limits than trees is not visible in the Bavarian Alps, giving no sign of range contraction induced by recent warming.…”

“…Apparently, before the climate change debate, the study of tree species distributions was considered unrewarding. The present study demonstrates the value of high resolution observation databases in obtaining more explicit and exact information (Ewald 2001, Guisan et al 2007, Lenoir et al 2009, Dengler et al 2011 along the altitudinal gradient can be studied; (3) tree and regeneration occurrences can be discerned from layer information; and (4) plot locations can be intersected with spatially interpolated climate variables or re-visited for field measurements. Depending on the underlying sampling strategy, the sources differ in their potential to find upper limits of trees.…”

Robust detection of plant species distribution shifts under biased sampling regimes

“…The changes we wish to detect might be the edges of distributions (Murphy et al 2010) or the means of distributions (Kelly and Goulden 2008, Lenoir et al 2009, Shoo et al 2006, but regardless, test statistics should be used that are robust to Type 1 errors in the face of sampling bias. This study has taken the approach of simulating data that is analogous to the type of Fig.…”

“…While it is not original to use museum specimens and historical surveys to search for evidence of shifts in species distribution in modern time (Kelly and Goulden 2008, Lenoir et al 2008, Lenoir et al 2009, Moritz et al 2008, Willis et al 2008) these studies have two distinct advantages that essentially moot the sample selection bias issues outlined above: they are based on intensive surveys that characterize both absence and presence; and the modern surveys are designed to resample the exact locales of the historic effort. To the extent that sampling intensity varies in time, presence/absence surveys can be stratified and resampled to ensure equal sampling intensity over time (Lenoir et al 2008, Shoo et al 2006).…”

Інтегральна Оцінка Стану Популяцій Рідкісних Видів Рослин

“…Стійкість популяцій рідкісних видів рослин і тренди їх розвитку визначаються не тільки чисельністю особин (N), але й низкою інших важливих популяційних параметрів (Elderd et al, 2003;Lenoir et al, 2009;Hampe, 2011). До таких належать популяційна щільність (PD), індекс відновлюваності (IR), індекс генеративності (IG), віталітет популяції (Q), індекс віковості популяції (Δ), індекс ефективності популяції (ω).…”