| 其他摘要 | Walnut is of great economic value plant and becomes one of the most important economical woody species in some mountain areas in China. However, with the expanding of walnut planting scale, its influence to local woodland conservation and biodiversity is now appearing. Based on the interviews to local growers focused on economic profitability, damage, and pest species of walnut-planting in mountain regions of Yunnan province in Oct 2009 and Oct 2010, two natural villages (Dacun village and Shaniucun village) in Xizhang village, Manwan Township, Jingdong County in Wuliang Mountain region, central Yunnan were chosen to be our study sites. Squirrel damage to walnut was monitored in the two natural villages from Mar 2011 to Mar 2012 in sampling sites, distance sampling method was adopted to investigate the squirrels population density, andAd Libitum sampling method was applied to observe ecological behavior of the species. This study is intended to evaluate the walnut damage and understand the damage pattern by squirrels, especially to analyze the correlation among the pest control strategy, walnut production and biodiversity conservation by monitoring the squirrels’ population dynamics and studying their ecological behavior. According to the interviews to local people and observation in filed, we got the data on walnut plantation, production, as well as the damage degree and pattern of squirrel in the study area. The result showed that the 41 families owned 153 hm2 of walnut cultivation in 2011, of which almost half wlnut trees (73 hm2) are in fruiting. The total revenue was 1.08 million yuan and maximum family income was 98,000 yuan. The total economic loss due to squirrel damage was nearly 200,000 yuan and the average familly loss rate was 16.64%, 125 out of 300 walnut trees selected with five-point sampling method at five sampling walnut field were damaged by squirrels. The damage period was from Mid-June to mid-September, and the most serious damage occurred in July and August. The squirrels almost extirpated all walnuts tree by tree from natural forest. The distance to natural forest, the height and the cover rate of the grass in walnut plantation are the main factors affecting the damage degree in sampling sites. Red-bellied squirrel (Callosciurus erythraeus) and red-cheecked squirrel (Dremomys rufigenis) are dominant species causing damages. The red-bellied squirrel mainly eats walnuts in upper part of the crown and the red-cheecked squirrel often forages in lower part or even on the ground. The two species population dynamics in natural forest and walnuts forest was monitored for 13 consecutive months, which turned out that the population destiny of the red-bellied squirrel in the natural forest is 5.15 ind./hm2 and in walnuts field is 43.08 ind./hm2, while that of red-cheecked squirrel in the two type forest is 2.00/hm2 and 21.80 ind/hm2 respectively. Squirrel population in the natural forest and the adjacent walnut field showed a source - sink relationship: in the season of squirrel damage occurring, although squirrels in the walnut field were captured or killed consecutively, no change of the population density was found. During the field study, I also noted 2934 feeding records using Ad Libitum sampling method. In the natural forest, the two squirrel species both spent most of their time in moving and followed by feeding, but in the walnut field we found a opposite pattern with more time in feeding than in moving. The two squirrels mainly fed on fruits, and more walnuts from June to September, but fruits composing 77.52% and 94.18% in the diet of red-bellied squirrels and red-cheeked squirrels respectively. The two squirrels are sympatric in the study area and use the same habitat, but the red-bellied squirrels’ spatial niche breadth was 0.9362, much higher than that of the red-cheeked squirrels’ (0.2994), and the niche overlap was 0.4405. However, the food niche breadth was 0.3238 and 0.2252 respectively, and the niche overlap was 0.8241. This result indicates that the spatial niche overlap is much higher than the food niche overlap in the two species. In the study area, both the total walnut loss and the loss rate caused by squirrels reached a high level, and the squirrels have brought a serious economic loss to local farmers. The large number and the high population density of the squirrels in the surrounding natural forests became the pest source to the walnut plantation since the squirrels maintained a relative stable population in walnut lands. Based on the population dynamics, activity patterns pest species (squirrels), we suggested that the local farmers take the efficient artificial interferences in the time (peak time activity in a day and specific months in a year) and sites of frequent and/or serious damage occurred to reduce the loss in the situation of large plantation area and limited human resources. At the same time, we recommend that the local people should improve management for increasing the yield per unit area instead of continuing expanding planting area by destroying the natural forest. |
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