Individual study: Removal of browse-tolerant turf communities, induced by grazing of introduced Sika deer Cervus nippon, enhances mountain beech Nothofagus solandri cliffortioides seedling growth and establishment, Kaimanawa Ecological Region, North Island, New Zealand
Husheer S.W., Robertson A.W., Coomes D.A. & Frampton C.M. (2005) Herbivory and plant competition reduce mountain beech seedling growth and establishment in New Zealand. Plant Ecology, 183, 245-256
The tree Nothofagus solandri is endemic to New Zealand; var. cliffortioides (mountain beech) is an upland form that grows up to the treeline. In central North Island, intense browsing by introduced sika deer Cervus nippon appears to have induced shifts in ground cover composition towards browse-tolerant, turf-forming communities of herbs, bryophytes and ferns, whilst suppressing mountain beech regeneration through browsing of seedlings. These compact, deer-induced turf communities may also prevent beech regeneration. Two experiments were undertaken. The experiment summarised here used manipulations on transplanted mountain beech seedlings (turf-removal, nutrient addition, clipping to simulate deer browsing and shading) to assess the effects on beech seedling growth and establishment.
The other experiment tested whether deer inhibited mountain beech regeneration through browsing of seedlings, or indirectly by maintaining turf communities (for a summary see: www.conservationevidence.com/ViewEntry.asp?ID=1187).
Study area: The study was undertaken in the Kaimanawa Ecological Region, a series of hill and mountain ranges in central North Island (39ºS, 176ºE), New Zealand.
Twelve sites (average distance 1.8 km apart) were located in open mountain beech dominated forest near the treeline (1,300 - 1,430 m). Two 10 x 10 m plots were established at each site, one of the pair was fenced to exclude deer. Eight of the sites had dense turf communities (>50% turf cover) and these were selected for this experiment.
Experimental design: At each site in winter 2000, five beech seedlings (4.0-30.6 cm tall) were planted within 16, 20-cm radius (0.126 m²) sub-plots systematically located >1 m apart, on ground with <25% cover of woody plant species (5 -135 cm tall) within the deer exclosures.
Treatments: Nutrient addition, turf removal and simulated herbivory treatments were applied to transplanted seedlings for 2 years, both within and adjacent to a shade tunnel (a steel frame with shade cloth attached) designed to remove 80% of available light. All combinations of treatments occurred at each site.
Nutrient addition - 50 g of slow-release fertilizer (Osmocote12 month; 15% N, 3% P, 9.1% K, 1.2% Mg) was applied over randomly selected sub-plots, i.e. equivalent to 60 g of N mˉ².
Turf-removal - sub-plots selected for turf removal had all bryophytes, herbs and woody seedlings removed prior to planting, and at 6 month intervals thereafter.
Simulated deer browsing - on selected seedlings, stems and branches >1.5 mm diameter were clipped with scissors in winter 2001, clippings were removed. This reduced seedling height by on average, 30%.
Vascular plant, bryophyte and lichen cover was estimated for sub-plots without turf removal. Seedling heights were measured at planting, when clipping was applied in 2001, and immediately prior to being uprooted for weighing of roots and stems in winter 2002 to calculate stem-root indices for each treatment.
Following the removal of turf vegetation, transplanted seedlings had taller stems (on average c.195 mm) compared to seedlings with no turf removal (c.175 mm) by 2002. Clipped seedlings were significantly shorter than unclipped seedlings in 2002. There were no significant effects of shading or nutrient addition on stem heights, nor were there any significant interactions between shading, nutrient addition, turf removal or clipping on stem heights. There was no compositional response of turf communities over the 2 years following fencing.
Stem-root index: Seedlings in plots with nutrient addition had 3-times higher average stem–root index values than seedlings in plots with no nutrient addition (1.2 vs. 0.4) i.e. increased nutrient availability increased stem weight relative to root weight.
Clipping and turf removal had the opposite effect: clipped seedlings had nearly 5-times lower stem-root index values compared to unclipped seedlings and seedlings with turf removal had a nearly 3-times lower index than seedlings without turf removal. This effect may be partly due to incomplete harvesting of roots in the uncleared sub-plots.
Survival: Seedling survival was higher when turfs were removed (average c.3.7/5) compared to seedlings without turf removal (c.3.1/5). There was lower seedling survival in plots with nutrient addition (c.2.9/5) compared to without addition (c.3.9/5). There were no significant differences in survivorship between seedlings in plots with clipping or shading, but clipping reduced seedling survival.
These results indicate a negative effect of deer browsing on mountain beech regeneration. Indirect negative effects of deer on regeneration were caused by competition with the deer-induced turf communities.
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