Raw height-increment series along the two altitudinal gradients.

<p>Raw height-increment series along the two altitudinal gradients.</p

The location of the Sygera Mountains on the Tibetan Plateau, and topographic map showing the location of the seven research plots and the meteorological station at Nyingchi, southeastern Tibet, China.

<p>SE1 and N1 represent southeast- and north-facing slopes, respectively; numbers (3800, 4000, 4200, 4390) denote the elevation in m a.s.l.</p

Mean annual height-growth rate of the trees from 1991–2009 along the two altitudinal gradients.

<p>Mean annual height-growth rate of the trees from 1991–2009 along the two altitudinal gradients.</p

Linear or nonlinear relationships among height, DBH and age of the trees along the two altitudinal gradients.

<p>Linear or nonlinear relationships among height, DBH and age of the trees along the two altitudinal gradients.</p

Number of trees per height class along the two altitudinal gradients; n, number of trees per plot.

<p>Number of trees per height class along the two altitudinal gradients; n, number of trees per plot.</p

Does Forest Continuity Enhance the Resilience of Trees to Environmental Change?

<div><p>There is ample evidence that continuously existing forests and afforestations on previously agricultural land differ with regard to ecosystem functions and services such as carbon sequestration, nutrient cycling and biodiversity. However, no studies have so far been conducted on possible long-term (>100 years) impacts on tree growth caused by differences in the ecological continuity of forest stands. In the present study we analysed the variation in tree-ring width of sessile oak (<i>Quercus petraea</i> (Matt.) Liebl.) trees (mean age 115–136 years) due to different land-use histories (continuously existing forests, afforestations both on arable land and on heathland). We also analysed the relation of growth patterns to soil nutrient stores and to climatic parameters (temperature, precipitation). Tree rings formed between 1896 and 2005 were widest in trees afforested on arable land. This can be attributed to higher nitrogen and phosphorous availability and indicates that former fertilisation may continue to affect the nutritional status of forest soils for more than one century after those activities have ceased. Moreover, these trees responded more strongly to environmental changes – as shown by a higher mean sensitivity of the tree-ring widths – than trees of continuously existing forests. However, the impact of climatic parameters on the variability in tree-ring width was generally small, but trees on former arable land showed the highest susceptibility to annually changing climatic conditions. We assume that incompletely developed humus horizons as well as differences in the edaphon are responsible for the more sensitive response of oak trees of recent forests (former arable land and former heathland) to variation in environmental conditions. We conclude that forests characterised by a long ecological continuity may be better adapted to global change than recent forest ecosystems.</p></div

Variation of radial growth of sessile oak (<i>Quercus petraea</i>) among historical land-use types between 1896 and 2005.

<p>Data represent site chronologies based on 10 trees per sample site; a) former arable land (10 sites), (b) former heathland (8 sites), and (c) continuously existing forests (7 sites).</p

Pearson’s correlations between mean tree-ring widths (of sample sites; n = 21) and soil parameters.

<p>Only significant correlations (* = <i>P</i><0.05, ** = <i>P</i><0.01) with r>|0.5| are considered; ns = not significant; period of tree-ring analyses: 1896–2005. For abbreviations of soil parameters see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0113507#pone-0113507-t002" target="_blank">Table 2</a>.</p><p>Pearson’s correlations between mean tree-ring widths (of sample sites; n = 21) and soil parameters.</p

Similarity in temporal variation of growth rates in response to past land-use.

<p>Non-metric multi-dimensional scaling ordination (stress: 0.10) of site chronologies (period 1896–2005) of sessile oak (<i>Quercus petraea</i>) growing in oak forests with different land-use histories: Former arable land (FAL), former heathland (FH) and continuously existing forests (CEF). Site scores represent mean tree-ring width series derived from 10 trees per site.</p