Spring water deficit and soil conditions matter more than seed origin and summer drought for the establishment of temperate conifers

Abstract

In anticipation of more severe summer droughts, forestry in temperate Europe is searching for drought-resistant ecotypes of native tree species that might maintain ecosystem services in the future. We investigated how spring precipitation and soil conditions interact with summer drought and affect the establishment of conifer seedlings from different climatic origin. Emergence, establishment and subsequent performance of seedlings originating from autochthonous, Central Alpine, continental Eastern European, and Mediterranean Pinus sylvestris and Picea abies populations were studied in the dry Alpine Rhine valley, Switzerland, at three sites with differing soil water holding capacities and in 3 years with contrasting weather conditions. In addition to this natural inter-annual variation, precipitation was manipulated within sites with throughfall reduction roofs. Seedling establishment and growth were principally affected by the spring weather in the year of emergence. In years with average to positive spring water balance, seedlings grown at the site with the highest water holding capacity had 2-5 times more aboveground biomass than seedlings grown at sites with less favourable soils. Effects of seed origin were marginal and only detectable at the drier sites: contrary to our expectations, seedlings from the Central Alpine Rhone valley, where the climatic spring water deficit is large, outperformed those from the Mediterranean. Consequently, plantation of non-native populations from dryer origin will mitigate the effects of increased summer drought at driest sites only, while the inter-annual variability of spring precipitation will continue to enable temperate conifers to regenerate on a wide range of forest soils independent of seed origin.

Memory of environmental conditions across generations affects the acclimation potential of scots pine

“…Similar to the results of seed germination success, the offspring growth (leaf area and biomass) and mortality during the initial period (until Week 14 after sowing) was primarily driven by watering. The importance of water supply for Scots pine seed germination and offspring growth or mortality during the initial period has also been reported by other studies (Bachofen, Wohlgemuth, & Moser, ; Castro, ; Moser et al, ). Thus, the environmental legacy to which the mother trees have been exposed to did not influence the early offspring development, which was mainly affected by direct environmental cues.…”

“…In nonwatered seed beds of the field experiment, 90–100% of germinated offspring were dead by the end of the 16th week since sowing of the seeds independent of the treatment of the mother trees. Comparable overriding effects of direct extreme environmental drivers have, however, also been observed for tree genotypes with different (local) adaptation (Moser et al, ).…”

“…Especially younger stages of a tree's life cycle are more sensitive to climate variations and extremes than the adult stage (Poorter, Bongers, Sterck, & Wöll, ), but the potential of seedlings to acclimate to the prevailing environmental conditions determines the future of a forest ecosystem. Seedling growth performance and plasticity is generally assumed to be determined by its genetic makeup and the initial resources provided by the seed and modified by the environmental conditions (light, water, and nutrients; Castro, ; Moles & Westoby, ; Moser, Walthert, Metslaid, Wasem, & Wohlgemuth, ). Energy storage in seeds is driven by the seed mass, which is genetically controlled by the seed bearing (i.e., mother) and by the pollinating tree (i.e., father) through the embryo (Berger & Chaudhury, ; Ingram, ).…”

No carbon “bet hedging” in pine seedlings under prolonged summer drought and elevated CO2

“…Accordingly, seedlings reduced g S relatively late during the growing season when carbon demands for growth may already have been declining (Swidrak, Gruber, & Oberhuber, ). Even though early season drought might be more decisive for pine trees and seedlings than summer drought (Lévesque et al., ; Moser, Walthert, Metslaid, Wasem, & Wohlgemuth, ), climate change scenarios have been projecting a decrease of summer rather than spring precipitation across Central Europe (CH2011, ). We hypothesise that after successful establishment in sporadic wet years (Moser, Walthert, et al., ), increased frequency of summer droughts is unlikely to result in widespread seedling die‐off in regions with annual precipitation well above 300 mm, as e.g.…”

Anticipating fire‐mediated impacts of climate change using a demographic framework

“…Drought can also limit postfire recruitment of shrubs establishing from seed, such as Artemisia tridentata (Nelson, Weisberg, & Kitchen, ). It is likely that the strongest bottleneck occurs during the very early stages of germination, in the first few weeks after emergence, when securing a reliable water source is critical (Moser, Walthert, Metslaid, Wasem, & Wohlgemuth, ). Despite the importance of the delivery of water from roots to above‐ground tissues, we know very little about hydraulic traits or drought tolerance strategies of young seedlings, and how these vary by species (Johnson et al., ).…”