Armesto, J.J.

Celis-Diez, J.L.

Holmgren, M.

English

NARCIS 

Tree-seedling establishment in fragmented Mediterranean forests of central Chile

Wageningen Yield 

153
Experimental analysis of dryland forest restoration techniques
Box 5.10  Tree-seedling establishment in fragmented Mediterranean 
forests of central Chile
M. Holmgren, J.L. Celis-Diez, J.J. Armesto
Mediterranean-type ecosystems are global biodiversity hotspots on all continents. Vegetation 
cover is extremely fragmented by the combination of natural and man-induced disturbances. 
Regeneration of these semi-arid ecosystems has proved difﬁcult but can be strongly facilitated 
by plant-nurse interactions. We studied whether the interaction of micro-climate and herbivores 
under remnant vegetation patches deﬁnes a patch-size threshold for tree seedling recruitment 
and whether that threshold is dependent on overall climate conditions and plant functional types.
We used a combination of correlational and experimental approaches to investigate this problem. 
Field observations and experiments were conducted in Andean and coastal Chilean shrublands, 
representing a gradient in rainfall (350 and 500 mm annual precipitation, respectively). We planted 
one-year old seedlings of relatively drought-tolerant (Quillaja saponaria) and drought intolerant 
(Cryptocarya alba) species under open and shaded conditions considering a gradient of shrub patch 
sizes (1, 5, 10–15, >30 m in diameter, n = 10 per patch size) and at increasing distances from the 
canopy edge (5 and 0.5 m outside of the border of the patch, 0.5, 2, 5, 15 m inside of the patch). Half 
of the seedlings were protected against mammal herbivores (mostly rabbits and horses).
We found no naturally established tree seedlings in the drier foothills of the Andes. In the moister 
coastal range, seedlings were frequently under the canopy of small and medium-sized shrub 
patches (5–15 m diameter). Seedlings in open areas were found only at the edge of large shrub 
patches (>30 m). Herbivore pressure by rabbits and hares is enormous in the Andean foothills where 
no seedlings survived in the experimental non-protected plots. At the moister coastal range site, 
herbivore pressure was lower and was further reduced under larger patches. Seedling mortality 
due to drought stress was reduced under the shrub canopy and signiﬁcantly decreased with shrub 
patch size, particularly in the drier Andean site. Large shrub patches are cooler and moister which 
ameliorates plant thermal and water stress particularly at the drier site. Seedling survival was strongly 
linked to physiological performance under different water and irradiance conditions.
Our results indicate that shrub fragmentation might be irreversible at the drier end of semi-arid 
ecosystems as shown in the Andean foothills of central Chile. Conservation of large remnant shrub 
patches in the landscape, wherever possible, is essential here to facilitate ecological restoration by 
combining herbivore exclusion and shrub shade. Under moister conditions (coastal sites and wet 
years), herbivore protection may be sufﬁcient to enhance tree regeneration. In such areas, seedling 
establishment will also increase along large patch edges and under existing small shrub patches. 
ENSO events in central Chile increase precipitation to levels comparable to those found in the coastal 
region, and could potentially increase the probability of seedling establishments in Andean foothills.
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Tree-seedling establishment in fragmented Mediterranean forests of central Chile

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