Light Transmissivity of Tree Shelters Interacts with Site Environment and Species Ecophysiology to Determine Outplanting Performance in Mediterranean Climates

Plastic tree shelters are commonly used in plantations under Mediterranean climates to protect against herbivory and enhance outplanting performance. However, effects on outplanting performance cannot be generalized due to the complexity of plant responses to microenvironmental conditions within the tube wall. The interactions between the light transmissivity of the tubes and species-specific responses to light and site environment on two-year outplanting performance were studied in two species with contrasting shade tolerance planted inside tree shelters with four different light transmissivities and a non-tree shelter control at two Mediterranean sites with contrasting rainfall and temperature. In general, increasing light transmissivity enhanced biomass accumulation, suggesting that the use of clear tubes might be advisable. However, the shade-tolerant Q. ilex did not benefit from the greater light transmissivity in the most arid site, indicating that the positive effect of clear tubes depends on water stress experienced by seedlings, which ultimately is determined by drought resistance strategies and site conditions. The growth of both species and survival of P. halepensis were higher within clear tubes in the continental site than in unsheltered plants, which suggests that factors other than light, such as warmer daytime temperatures or the prevention of dust deposition, can explain this beneficial site-dependent effect of tree shelters. In conclusion, our results confirm the hypothesis that the effect of tree shelter and its light transmission on outplanting performance is site and species-specific, but further research is needed to identify the effect of other effects not related to light transmission.

Pasture-tree systems - Modelling potential implications for animal performance and greenhouse gas emissions

The potential animal performance and greenhouse gas (GHG) abatement benefits from pastures and wide-spaced poplars on a typical lower-North Island sheep and beef farm operation were explored using farm-scale models. The analysis included reductions in understory pasture production, increased ewe reproductive performance (i.e., lambing and weaning percentage) with additional tree shelter and increased dry matter intake from poplar foliage. The pasture-tree systems demonstrated reductions in sheep stocking rates and total meat production, but increases in ewe efficiency and emissions intensity, reflecting a shift in feed energy use from maintenance to production. Inclusion of ewe fecundity and supplementary feed benefits largely overcame reductions in stocking rate and meat production due to pasture shading. An integrated assessment of the multiple benefits of pasture-tree systems should be incorporated in future farming scenario testing, strengthening our knowledge on the impacts of these systems compared with pastureonly systems. Keywords: pasture-tree systems, animal performance, greenhouse gas emissions.

Reforestation of a Salvage-Logged High-Elevation Clearcut: Engelmann Spruce Seedling Response to Tree Shelters after 11 Growing Seasons

High-elevation clearcut sites in the southern Rocky Mountains are difficult to reforest successfully and many sites remain poorly stocked decades after harvest. This article presents results after 11 growing seasons of a project designed to examine use of tree shelters to provide initial shade for planted Engelmann spruce (Picea englemannii Parry ex Engelm.) seedlings. Seedlings were planted in 1996 on a 48-ha site at an elevation of approximately 3,273 m in southwestern Colorado, with different shelter colors providing various shading levels. A control, consisting of shading using debris within the site, was also included. Results after 2 years were presented previously. To examine seedling response to tree shelter removal after seedling establishment, half of shelters were removed in 2000 and seedlings were reassessed in 2007. Control seedlings had lower survival (35%) than any other treatment (ranging from 59 to 78%). Shelter removal in the lightest two shelter color treatments did not reduce survival, suggesting that seedlings can grow in full sun after 4 years of shading. The best overall seedling development (i.e., survival, absolute height, and root collar diameter) occurred in the lightest shelter color with shelters removed. Tree shelters offer a viable means to restore high-elevation spruce-fir sites where past reforestation has proven difficult.