Microclimate in forests with varying leaf area index and soil moisture: potential implications for seedling establishment in a changing climate
Georg Von Arx, Elisabeth Graf Pannatier, Anne Thimonier & Martine Rebetez
| Résumé |
1. Forest microclimate is crucial for the growth and survival of
tree seedlings and understorey vegetation. This high ecological
relevance contrasts with the poor functional and quantitative
understanding of how the properties of forest ecosystems influence
forest microclimate. 2. In a long-term (1998-2011) trial, we
investigated how temporal patterns of microclimate below sparse and
dense forest canopy related to those of nearby open areas and how
this relationship was influenced by soil moisture and seasonality.
Air temperature (T), vapour pressure deficit (VPD), soil matrix
potential and leaf area index (LAI) were measured in a unique
set-up of below-canopy and open-area meteorological stations at
eleven distinct forest ecosystems, characteristic of subalpine and
temperate climate zones. Data from these plots were analysed for
the moderating capacity of the canopy, that is, the differences
between below-canopy and open-area microclimate, with respect to
(i) long-term means, (ii) dynamics within homogeneous moist- vs.
dry-soil periods and (iii) diurnal patterns. 3. The long-term mean
moderating capacity of the canopy was up to 3.3 degrees C for daily
T-max and 0.52kPa for daily VPDmax, of which soil moisture status
alone accounted for up to 1.2 degrees C (T-max) and 0.21kPa
(VPDmax). Below dense canopy (LAI>4), the moderating capacity was
generally higher when soils were dry and increased during dry-soil
periods, particularly in spring and somewhat less in summer. The
opposite pattern was found below sparse canopy (LAI<4). At the
diurnal level, moderating capacity below dense canopy was strongest
in mid-afternoon and during dry-soil conditions, whereas peak
moderation below sparse canopy occurred in mid-morning and during
moist-soil conditions. 4. Synthesis. Our results suggest a
threshold canopy density, which is probably linked to site-specific
water availability, below which the moderating capacity of forest
ecosystems switches from supportive to unsupportive for seedling
establishment. Under supportive moderating capacity, we understand
a stronger mitigation during physiologically most demanding
conditions for plant growth. Such a threshold canopy density sheds
new light on forest resilience to climate change. Climate change
may alter forest canopy density in a way that precludes successful
establishment of tree species and ultimately changes forest
ecosystem structure and functioning. |
| Mots-clés |
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| Citation | von Arx, G., Pannatier, E. G., Thimonier, A., & Rebetez, M. (2013). Microclimate in forests with varying leaf area index and soil moisture: potential implications for seedling establishment in a changing climate. Journal of Ecology, 101(5), 1201-1213. |
| Type | Article de périodique (Anglais) |
| Date de publication | 2013 |
| Nom du périodique | Journal of Ecology |
| Volume | 101 |
| Numéro | 5 |
| Pages | 1201-1213 |