Nurse Trees Research Articles

Nurse rock microclimates significantly buffer exposure to freezing temperature and moderate summer temperature

Nurse tree canopies mitigate exposure to freezing temperatures that could result in injury or mortality to the saguaro cactus (Carnegiea gigantea). Abiotic objects have been hypothesized to provide similar beneficial microclimates. We used data loggers at 11 nurse rock sites to record daily daytime summer maximum and winter nighttime minimum temperatures at Saguaro National Park, Arizona, to examine the effectiveness of rocks to moderate seasonal temperature extremes in the microclimate. Temperatures at rock sites averaged 2 °C warmer than exposed open control sites in winter. We found that the efficiency of rocks to act as insulators significantly increased as temperature at control sites decreased, consistent with studies of tree canopies, and that the insulation effect lasted throughout the night. In summer, rocks reduced exposure to maximum temperatures but did not offer significantly more cooling at higher temperatures. Our results suggest that the protection from freezing temperature offered by rocks in winter is more ecologically beneficial to the saguaro than extreme temperature amelioration during summer in the cold-limited frontiers of the species’ range.

Nurse Trees as a Forest Restoration Tool for Mixed Plantations: Effects on Competing Vegetation and Performance in Target Tree Species

AbstractMulti‐species mixed plantations can be designed to meet social, economic, and environmental objectives during forest restoration. This paper reports results from an experiment in southern Sweden concerning the influence of three different fast growing nurse tree species on the cover of herbaceous vegetation and on the performance of several target tree species. After 10 years, the nurse trees had reduced the competing herbaceous vegetation but the effect was weak and it may take more than a decade to achieve effective vegetation control. The nurse tree species Betula pendula and Larix x eurolepis did improve stem form in some target tree species, but had a minor effect on survival and growth. The open conditions before crown closure of nurse trees strongly influence seedling performance and so delayed planting of target tree species may provide a means to avoid those conditions. Survival and growth differed greatly among the tree species. Besides the two nurse tree species mentioned above, high survival was found in Picea abies and Quercus robur and intermediate survival in Fagus sylvatica, Tilia cordata, and in the N‐fixing nurse tree Alnus glutinosa. Survival was low in the target tree species Fraxinus excelsior L. and Prunus avium. For restoration practitioners, our results illustrate the potential of using nurse trees for rapidly building a new forest structure and simultaneously increase productivity, which might be a cost‐effective strategy for forest restoration.

Impact of silvicultural methods on vascular epiphytes (ferns, bromeliads and orchids) in a temperate forest in Oaxaca, Mexico

The impact of silvicultural management on the populations of epiphytes in pine-oak forest was evaluated in an area of Oaxaca State in Mexico, where the Method for Silvicultural Development (MSD) is practiced. Sampling was carried out in 5 management categories and their border areas (−B): Reforestation with Pine only (RP, RP-B), Reforestation with Pine with Nurse Trees (RPNTr, RPNTr-B), Harvest and Regeneration in Stands (HRSt, HRSt-B), areas where a First Thinning has been carried out (1stThin, 1stThin-B) and Conservation areas (CONSV, with no border area). Four transects measuring 50×4m were set up in each management category of which 2 were in the managed area and 2 in the border area. A total of 32 tree species acting as phorophytes hosting epiphytes, and 31species of epiphytes were recorded (15 orchids, 5 bromeliads and 11 ferns). There was significantly greater abundance of epiphytes in the categories 1stThin-B (2353 ind.) and CONSV (2195 ind.) compared to RPNTr (67 ind.) and RP with only 18 individuals. There was a significant difference between management categories for the abundance of orchids and ferns but not for bromeliads. Rhynchostele aptera (Orchidaceae), Tillandsia violacea (Bromeliaceae) and Polypodium sp. (Polypodiaceae) were common throughout the study area, whereas Alamania punicea, Lepanthes schiedei, Rhynchostele cordata (Orchidaceae), Asplenium cuspidatum (Aspleniaceae), Elaphoglossum peltatum (Dryopteridaceae) and Ceradenia oidiophora (Polypodiaceae) were only found in a single category of silvicultural management or conservation area. The biodiversity indices used (Shannon–Weiner, Simpson and True Diversity), indicated that HRSt and CONSV were the most diverse, and RP and RPNTr the least diverse categories. The phorophytes with the greatest abundance of epiphytes were Quercus crassifolia, Ternstroemia lineata and Rapanea juergensenii. We conclude that the silvicultural management category Harvest and Regeneration in Stands (HRSt) favors the conservation of epiphytes, that trees of the genus Quercus are the best phorophytes, that Pinus ayacahuite is a phorophyte for a variety of species especially orchids whereas Pinus patula is a relatively poor phorophyte, and suggest that the borders of managed areas, and reforestation with a diversity of tree species make an important contribution to epiphyte conservation.

Nurse tree canopy shape, the subcanopy distribution of cacti, and facilitation in the Sonoran Desert

Facilitation between different plant species has been documented in terrestrial and marine ecosystems worldwide. The classic example of such positive relationships, the large keystone saguaro cactus (Carnegiea gigantea), always establishes under nurse plants that provide protection to young seedlings through subcanopy climate and environmental modification. Plants (e.g., nurse plants) are not necessarily symmetrical and variations in shape and zone of influence may impact the distribution of other species associated with them. The saguaro is distributed disproportionately to the south of its nurse tree Cercidium microphyllum (palo verde) where subcanopy temperatures are warmer on cold winter nights. I determine whether the tree's canopy shape contributes to the non-random pattern of its protégé cacti in its subcanopy. Data for tree canopy width for each of the four cardinal directions were collected. ANOVA and circular statistics (Rayleigh and V tests) found a significant canopy bias to the southwest. A second dataset shows that Carnegiea are found significantly more often to the south of Cercidium trunks than to the north. When the center of canopy is used rather than the trunk, the statistical bias no longer holds. The observed biases in distribution may be a function of the nurse's canopy shape and resultant microclimate effects. The findings of this study provide an explanation to several already documented observations: 1) winter temperatures are more ameliorated to the south of the trunk than to the north, 2) more of the shade-dependent cacti are found on the south side of their Cercidium nurse's trunk than to the north, and 3) saguaro cacti show a distributional preference to dense-canopied nurses. Variations in nurse canopies become crucial elements of the microenvironment and will alter patterns of establishment and survival of the protégé species that rely on them as even small changes can dramatically alter distributional patterns and expected survivorship. Nurse protection may lead to patterns quite different from the seed rain, and ultimately has a dominant role in the population dynamics of the species.

The Role of Nurse Trees in Mitigating Fire Effects on Tropical Dry Forest Restoration: A Case Study

The threat of fire is always a consideration when establishing a forest restoration program. Two wildfires occurred in 2006 and 2007 in an established dry forest restoration project in Puerto Rico. The original goal of the project was to determine differential growth responses of native trees under the nurse tree Leucaena leucocephala versus in open sites. Tree species growth, mortality and response to the fires were evaluated according to their leaf habit, successional status, and prefire tolerance to environmental conditions. Results showed that regardless of a species' leaf habit and successional status, trees attained greater height and lower mortality under nurse trees. In open sites, sprouting was the most common fire response and mature-forest and evergreen species had greater postfire survival than pioneers and deciduous species. Although nurse trees are typically used to help manage nutrient or light environments in reforestation projects, these trees also appear to provide a secondary benefit of limiting fire damage by reducing fuel load.

Acacia mangium, a Nurse Tree Candidate for Reforestation on Degraded Sandy Soils in the Malay Peninsula

Abstract We investigated the suitability of Acacia mangium Willd., a fast-growing tropical leguminous tree, as a nurse tree for reforestation with indigenous species on severely degraded sandy soils in southern Thailand. Planting A. mangium yielded a survival rate of 91% and satisfactory growth (7.7 m height, 56 mm dbh, 59 Mg dry weight ha−1 aboveground biomass) 45 months after planting, indicating the species' suitability for reforestation. Three dipterocarp species (Dipterocarpus alatus Roxb. ex G. Don, Hopea odorata Roxb., and Shorea roxburghii G. Don.) planted simultaneously with A. mangium showed better growth than when planted alone. Seedlings of all three dipterocarp species that survived transplanting showed better survival when planted with A. mangium. The findings suggest A. mangium is an effective nurse tree for dipterocarp seedlings. The carbon and nitrogen contents of surface soil did not increase in the A. mangium stands. Microclimate measurements showed moderated air temperature, relative humidity, and soil temperature in the mixed planting. The moderated microclimate under the A. mangium canopy is thought to be responsible for the improved growth of the dipterocarp seedlings. If dipterocarp seedlings are planted after A. mangium grows enough to provide shade, initial survival rates should improve. FOR. SCI. 51(5):498–510.

Inter-Planting Loblolly Pine with Nitrogen Fixing Nurse Trees on a Reclaimed Surface Mine in Virginia

Inter-Planting Loblolly Pine with Nitrogen Fixing Nurse Trees on a Reclaimed Surface Mine in Virginia

Saguaros and Nurse Trees: A New Hypothesis to Account for Population Fluctuations

Saguaros and Nurse Trees: A New Hypothesis to Account for Population Fluctuations