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10/7/2010 A.Defined Edges known to be most productive (hunters, birdwatchers). Edges g & Edge g Effects Edge effect - apparent increase in wildlife where 2 habitats meet Many spp frequent edges more commonly than interior areas. 1. Attraction of simultaneous access to more than one environmental need – food, cover, water etc. Exact mechanism unknown 2 Hypotheses 2. A greater variety of vegetation including species common to each type of habitat plus some plants characteristic of edge only. B. Types 1. Inherent edges Natural edges, caused by changes in soil, topography eastern North America – deciduous, coniferous edge grasslands, woodland edge along rivers 1 10/7/2010 2. Induced edges May occur where floods or fires have reversed succession May occur where humans have created patchwork of tilled land interspersed with fencerows and wood lots Edge effects on deer Williamson and Hirth 1985. An evaluation of edge use by White-tailed Deer. Wildlife Soc. Bulletin 13:252-257. Browsing by WTD in clear cuts adjacent to h d hardwood d forests f t Clearcutting – stimulates abundant regeneration of woody sprouts of value as deer browse. Availability of browse was homogenous throughout clear cut stand but deer preferred feeding near edge. Exception – 2 spp. highly sought after browse Which edge hypothesis do these results support? Deer moved as far as 100m into opening for preferred browse (red maple, pincherry) Level of nutrition provided by browse offset additional predation risk?? Management Recommendation Large clearcuts in which the centers are more than 100 m from shelter would be less useful for deer Represents p case where 2 resources occur in proximity instead of reflecting larger diversity of species near edge. 2 10/7/2010 Grouse – greater hunting pressure on those along edges Paradox – Gates and Gysel (1978) found that nest densities higher on both sides of forest – field edge compared to interior But… Desired mix of aspen (stands 3 age classes) creates lots of edges. How can one minimize? Nest parasitism and predation higher on nests along edges!!! Why do birds select fragmented or edge sites??? Ecological Trap Hypothesis Ecological Trap Ecological Trap 1) Areas that have all the cues which trigger animals to perceive it as its habitat and settle but some critical resource is missing or in short supply so that th t survival i l or reproductive d ti success is i reduced. d d 2) Areas that have all the cues and resources of high quality habitat but some feature, event or organism is present that causes increased mortality t lit or d decreased d reproduction. d ti 3 10/7/2010 Edge effects on birds TIPS FOR EDGE MANAGEMENT • When harvesting timber, make several small, irregularly shaped cuts to increase the amount of edge • Retain strips of forest along streams for water protection and for wildlife travel lanes TIPS FOR EDGE MANAGEMENT TIPS FOR EDGE MANAGEMENT • Leave about 5% of recently harvested areas untreated to provide brushy edges • Allow native vegetation to take over fencerows, terraces, roadsides, and field borders • When possible, allow fingers of native vegetation to creep out into open areas • Plant trees and shrubs to speed p up p the development of cover along edges • Plant wildlife travel lanes (corridors) or hedgerows to connect large forested areas where edge is limited 4 10/7/2010 TIPS FOR EDGE MANAGEMENT • Create brush piles in pastures, clearcuts, and other open areas • Cut and leave large trees on field edges to provide cover 5