diff --git a/tools/broccoli/broccoli-merge-trees.spec.ts b/tools/broccoli/broccoli-merge-trees.spec.ts
new file mode 100644
index 0000000000..f420a77fff
--- /dev/null
+++ b/tools/broccoli/broccoli-merge-trees.spec.ts
@@ -0,0 +1,47 @@
+/// <reference path="../typings/node/node.d.ts" />
+/// <reference path="../typings/jasmine/jasmine.d.ts" />
+
+let mockfs = require('mock-fs');
+import fs = require('fs');
+import {TreeDiffer} from './tree-differ';
+import {MergeTrees} from './broccoli-merge-trees';
+
+describe('MergeTrees', () => {
+  afterEach(() => mockfs.restore());
+
+  function mergeTrees(inputPaths, cachePath, options) {
+    return new MergeTrees(inputPaths, cachePath, options);
+  }
+
+  function MakeTreeDiffers(rootDirs) {
+    let treeDiffers = rootDirs.map((rootDir) => new TreeDiffer('MergeTrees', rootDir));
+    treeDiffers.diffTrees = () => { return treeDiffers.map(tree => tree.diffTree()); };
+    return treeDiffers;
+  }
+
+  function read(path) { return fs.readFileSync(path, "utf-8"); }
+
+  it('should copy the file from the right-most inputTree', () => {
+    let testDir: any = {
+      'tree1': {'foo.js': mockfs.file({content: 'tree1/foo.js content', mtime: new Date(1000)})},
+      'tree2': {'foo.js': mockfs.file({content: 'tree2/foo.js content', mtime: new Date(1000)})},
+      'tree3': {'foo.js': mockfs.file({content: 'tree3/foo.js content', mtime: new Date(1000)})}
+    };
+    mockfs(testDir);
+    let treeDiffer = MakeTreeDiffers(['tree1', 'tree2', 'tree3']);
+    let treeMerger = mergeTrees(['tree1', 'tree2', 'tree3'], 'dest', {});
+    treeMerger.rebuild(treeDiffer.diffTrees());
+    expect(read('dest/foo.js')).toBe('tree3/foo.js content');
+
+    delete testDir.tree2['foo.js'];
+    delete testDir.tree3['foo.js'];
+    mockfs(testDir);
+    treeMerger.rebuild(treeDiffer.diffTrees());
+    expect(read('dest/foo.js')).toBe('tree1/foo.js content');
+
+    testDir.tree2['foo.js'] = mockfs.file({content: 'tree2/foo.js content', mtime: new Date(1000)});
+    mockfs(testDir);
+    treeMerger.rebuild(treeDiffer.diffTrees());
+    expect(read('dest/foo.js')).toBe('tree2/foo.js content');
+  });
+});
diff --git a/tools/broccoli/broccoli-merge-trees.ts b/tools/broccoli/broccoli-merge-trees.ts
new file mode 100644
index 0000000000..e5d9bb67ef
--- /dev/null
+++ b/tools/broccoli/broccoli-merge-trees.ts
@@ -0,0 +1,86 @@
+import fs = require('fs');
+import fse = require('fs-extra');
+import path = require('path');
+var symlinkOrCopySync = require('symlink-or-copy').sync;
+import {wrapDiffingPlugin, DiffingBroccoliPlugin, DiffResult} from './diffing-broccoli-plugin';
+
+function pathExists(filePath) {
+  try {
+    if (fs.statSync(filePath)) {
+      return true;
+    }
+  } catch (e) {
+    if (e.code !== "ENOENT") {
+      throw e;
+    }
+  }
+  return false;
+}
+
+function outputFileSync(sourcePath, destPath) {
+  let dirname = path.dirname(destPath);
+  fse.mkdirsSync(dirname, {fs: fs});
+  fse.removeSync(destPath);
+  symlinkOrCopySync(sourcePath, destPath);
+}
+
+export class MergeTrees implements DiffingBroccoliPlugin {
+  private mergedPaths: {[key: string]: number} = Object.create(null);
+
+  constructor(public inputPaths: string[], public cachePath: string, public options) {}
+
+  rebuild(treeDiffs: DiffResult[]) {
+    treeDiffs.forEach((treeDiff: DiffResult, index) => {
+      let inputPath = this.inputPaths[index];
+      let existsLater = (relativePath) => {
+        for (let i = treeDiffs.length - 1; i > index; --i) {
+          if (pathExists(path.join(this.inputPaths[i], relativePath))) {
+            return true;
+          }
+        }
+        return false;
+      };
+      let existsSooner = (relativePath) => {
+        for (let i = index - 1; i >= 0; --i) {
+          if (pathExists(path.join(this.inputPaths[i], relativePath))) {
+            return i;
+          }
+        }
+        return -1;
+      };
+      treeDiff.changedPaths.forEach((changedPath) => {
+        let inputTreeIndex = this.mergedPaths[changedPath];
+        if (inputTreeIndex !== index && !existsLater(changedPath)) {
+          inputTreeIndex = this.mergedPaths[changedPath] = index;
+          let sourcePath = path.join(inputPath, changedPath);
+          let destPath = path.join(this.cachePath, changedPath);
+          outputFileSync(sourcePath, destPath);
+        }
+      });
+
+      treeDiff.removedPaths.forEach((removedPath) => {
+        let inputTreeIndex = this.mergedPaths[removedPath];
+
+        // if inputTreeIndex !== index, this same file was handled during
+        // changedPaths handling
+        if (inputTreeIndex !== index) return;
+
+        let destPath = path.join(this.cachePath, removedPath);
+        fse.removeSync(destPath);
+        let newInputTreeIndex = existsSooner(removedPath);
+
+        // Update cached value (to either newInputTreeIndex value or undefined)
+        this.mergedPaths[removedPath] = newInputTreeIndex;
+
+        if (newInputTreeIndex >= 0) {
+          // Copy the file from the newInputTreeIndex inputPath if necessary.
+          let newInputPath = this.inputPaths[newInputTreeIndex];
+          let sourcePath = path.join(newInputPath, removedPath);
+          outputFileSync(sourcePath, destPath);
+        }
+      });
+    });
+  }
+}
+
+export default wrapDiffingPlugin(MergeTrees);
diff --git a/tools/broccoli/trees/browser_tree.ts b/tools/broccoli/trees/browser_tree.ts
index 3df98400cf..e3abe11d23 100644
--- a/tools/broccoli/trees/browser_tree.ts
+++ b/tools/broccoli/trees/browser_tree.ts
@@ -3,7 +3,7 @@
 var Funnel = require('broccoli-funnel');
 var flatten = require('broccoli-flatten');
 var htmlReplace = require('../html-replace');
-var mergeTrees = require('broccoli-merge-trees');
+import mergeTrees from '../broccoli-merge-trees';
 var path = require('path');
 var replace = require('broccoli-replace');
 var stew = require('broccoli-stew');
diff --git a/tools/broccoli/trees/dart_tree.ts b/tools/broccoli/trees/dart_tree.ts
index b6848e8afc..b2c9b263e6 100644
--- a/tools/broccoli/trees/dart_tree.ts
+++ b/tools/broccoli/trees/dart_tree.ts
@@ -6,7 +6,7 @@ import {MultiCopy} from './../multi_copy';
 import destCopy from '../broccoli-dest-copy';
 var Funnel = require('broccoli-funnel');
 var glob = require('glob');
-var mergeTrees = require('broccoli-merge-trees');
+import mergeTrees from '../broccoli-merge-trees';
 var path = require('path');
 var renderLodashTemplate = require('broccoli-lodash');
 var replace = require('broccoli-replace');
diff --git a/tools/broccoli/trees/node_tree.ts b/tools/broccoli/trees/node_tree.ts
index 575197cf9f..d2f7a660ea 100644
--- a/tools/broccoli/trees/node_tree.ts
+++ b/tools/broccoli/trees/node_tree.ts
@@ -4,7 +4,7 @@ import destCopy from '../broccoli-dest-copy';
 import compileWithTypescript from '../broccoli-typescript';
 import transpileWithTraceur from '../traceur/index';
 var Funnel = require('broccoli-funnel');
-var mergeTrees = require('broccoli-merge-trees');
+import mergeTrees from '../broccoli-merge-trees';
 var path = require('path');
 var renderLodashTemplate = require('broccoli-lodash');
 var replace = require('broccoli-replace');