Evidence of non‐stationary relationships between climate and forest responses: Increased sensitivity to climate change in Iberian forests

Abstract

Climate and forest structure are considered major drivers of forest demography and productivity. However, recent evidence suggests that the relationships between climate and tree growth are generally non-stationary (i.e. non-time stable), and it remains uncertain whether the relationships between climate, forest structure, demography and productivity are stationary or are being altered by recent climatic and structural changes. Here we analysed three surveys from the Spanish Forest Inventory covering c. 30 years of information and we applied mixed and structural equation models to assess temporal trends in forest structure (stand density, basal area, tree size and tree size inequality), forest demography (ingrowth, growth and mortality) and above-ground forest productivity. We also quantified whether the interactive effects of climate and forest structure on forest demography and aboveground forest productivity were stationary over two consecutive time periods. Since the 1980s, density, basal area and tree size increased in Iberian forests, and tree size inequality decreased. In addition, we observed reductions in ingrowth and growth, and increases in mortality. Initial forest structure and water availability mainly modulated the temporal trends in forest structure and demography. The magnitude and direction of the interactive effects of climate and forest structure on forest demography changed over the two time periods analysed indicating non-stationary relationships between climate, forest structure and demography. Above-ground forest productivity increased due to a positive balance between ingrowth, growth and mortality. Despite increasing productivity over time, we observed an aggravation of the negative effects of climate change and increased competition on forest demography, reducing ingrowth and growth, and increasing mortality. Interestingly, our results suggest that the negative effects of climate change on forest demography could be ameliorated through forest management, which has profound implications for forest adaptation to climate change.

Forest resilience to global warming is strongly modulated by local‐scale topographic, microclimatic and biotic conditions

“…We provide evidence for a significant within population variation in resilience, emphasising in our case study the relevance of microclimatic variability in the dynamics of rear edge populations. Furthermore, our results also support the existence of non‐stationary effects of climate determining forest growth responses (Table 2; Astigarraga et al., 2020; Carnicer, Domingo‐Marimon, et al., 2019; Peltier & Ogle, 2020). Finally, as previously mentioned, our results also emphasise an important role of other interacting global change drivers such as imbalanced recruitment due to increased herbivore pressure in locally altered, defaunated trophic networks, that we discuss in detail below.…”

Occurrence but not intensity of mortality rises towards the climatic trailing edge of tree species ranges in European forests

“…Further studies should look at more recent data from NFIs and investigate whether drivers of mortality are changing over time, especially in the last decades, because temperatures, drought frequency and drought intensity are increasing (Astigarraga et al., 2020; Trenberth et al., 2014). Further investigation could also focus on whether drivers of mortality differ between deciduous and evergreen trees, as reported in other regions (Clark et al., 2011), or between shade‐tolerant and shade‐intolerant species (Luo & Chen, 2011).…”

Long-Term Tree Regeneration of Fragmented Agroforestry Systems Under Varying Climatic Conditions

“…In addition, alleviation of plantplant competition though forest clearing seemed to have little scope to attenuate the negative impacts of drought, as shown by weak or no interactive effects of climate and tree cover or isolation. Management options aimed at decreasing adult tree mortality under climate change scenarios (Ruiz-Benito et al, 2013;Astigarraga et al, 2020) would then have little or no effects on tree recruitment.…”

“…Increasing tree mortality associated to drought events (Jump et al, 2017) and to introduced pests (Roy et al, 2014) is threatening forests worldwide. Several recent papers conclude that forest thinning can be an efficient management option to deal with the negative effects of global change on tree growth and mortality (Ruiz-Benito et al, 2013;Astigarraga et al, 2020). Tree recruitment during benign inter-event periods may also compensate for increasing tree mortality (Jump et al, 2017).…”