diff --git a/simgear/scene/material/Effect.cxx b/simgear/scene/material/Effect.cxx
index 16458407..fa99ccb5 100644
--- a/simgear/scene/material/Effect.cxx
+++ b/simgear/scene/material/Effect.cxx
@@ -1392,10 +1392,11 @@ public:
     
     void valueChanged(SGPropertyNode* node)
     {
-        _tniq->refreshValidity();
+        if (_tniq.valid())
+            _tniq->refreshValidity();
     }
 protected:
-    osg::ref_ptr<Technique> _tniq;
+    osg::observer_ptr<Technique> _tniq;
 };
 
 template<typename T>
diff --git a/simgear/scene/material/Effect.hxx b/simgear/scene/material/Effect.hxx
index 6daa279f..ab795289 100644
--- a/simgear/scene/material/Effect.hxx
+++ b/simgear/scene/material/Effect.hxx
@@ -24,6 +24,7 @@
 #include <boost/functional/hash.hpp>
 
 #include <osg/Object>
+#include <osg/observer_ptr>
 #include <osgDB/ReaderWriter>
 
 #include <simgear/props/props.hxx>
@@ -158,7 +159,7 @@ protected:
             bool operator()(const Key& lhs, const Key& rhs) const;
         };
     };
-    typedef std::tr1::unordered_map<Key, osg::ref_ptr<Effect>,
+    typedef std::tr1::unordered_map<Key, osg::observer_ptr<Effect>,
                                     boost::hash<Key>, Key::EqualTo> Cache;
     Cache* getCache()
     {
diff --git a/simgear/scene/material/TextureBuilder.cxx b/simgear/scene/material/TextureBuilder.cxx
index 8e90064a..88355e36 100644
--- a/simgear/scene/material/TextureBuilder.cxx
+++ b/simgear/scene/material/TextureBuilder.cxx
@@ -279,7 +279,7 @@ public:
     Texture* build(Effect* effect, Pass* pass, const SGPropertyNode*,
                    const SGReaderWriterOptions* options);
 protected:
-    typedef map<TexTuple, ref_ptr<T> > TexMap;
+    typedef map<TexTuple, observer_ptr<T> > TexMap;
     TexMap texMap;
     const string _type;
 };
@@ -290,11 +290,20 @@ Texture* TexBuilder<T>::build(Effect* effect, Pass* pass, const SGPropertyNode*
 {
     TexTuple attrs = makeTexTuple(effect, props, options, _type);
     typename TexMap::iterator itr = texMap.find(attrs);
+
     if (itr != texMap.end())
-        return itr->second.get();
+    {
+        T* tex = itr->second.get();
+        if (tex)
+            return tex;
+    }
+
     T* tex = new T;
     setAttrs(attrs, tex, options);
-    texMap.insert(make_pair(attrs, tex));
+    if (itr == texMap.end())
+        texMap.insert(make_pair(attrs, tex));
+    else
+        itr->second = tex; // update existing, but empty observer
     return tex;
 }
 
diff --git a/simgear/scene/material/makeEffect.cxx b/simgear/scene/material/makeEffect.cxx
index 477328ff..4ca288b8 100644
--- a/simgear/scene/material/makeEffect.cxx
+++ b/simgear/scene/material/makeEffect.cxx
@@ -44,7 +44,7 @@ using namespace osg;
 using namespace effect;
 
 typedef vector<const SGPropertyNode*> RawPropVector;
-typedef map<const string, ref_ptr<Effect> > EffectMap;
+typedef map<const string, observer_ptr<Effect> > EffectMap;
 
 namespace
 {
@@ -122,7 +122,8 @@ Effect* makeEffect(const string& name,
     {
         OpenThreads::ScopedLock<OpenThreads::ReentrantMutex> lock(effectMutex);
         EffectMap::iterator itr = effectMap.find(name);
-        if (itr != effectMap.end())
+        if ((itr != effectMap.end())&&
+            itr->second.valid())
             return itr->second.get();
     }
     string effectFileName(name);
@@ -207,7 +208,8 @@ Effect* makeEffect(SGPropertyNode* prop,
                 itr = cache->find(key);
                 if (itr != cache->end()) {
                     effect = itr->second.get();
-                    effect->generator = parent->generator;  // Copy the generators
+                    if (effect.valid())
+                        effect->generator = parent->generator;  // Copy the generators
                 }
             }
             if (!effect.valid()) {
@@ -219,8 +221,13 @@ Effect* makeEffect(SGPropertyNode* prop,
                     lock(effectMutex);
                 pair<Effect::Cache::iterator, bool> irslt
                     = cache->insert(make_pair(key, effect));
-                if (!irslt.second)
-                    effect = irslt.first->second;
+                if (!irslt.second) {
+                    ref_ptr<Effect> old = irslt.first->second.get();
+                    if (old.valid())
+                        effect = old; // Another thread beat us in creating it! Discard our own...
+                    else
+                        irslt.first->second = effect; // update existing, but empty observer
+                }
                 effect->generator = parent->generator;  // Copy the generators
             }
         } else {
diff --git a/simgear/scene/sky/newcloud.cxx b/simgear/scene/sky/newcloud.cxx
index 04fb2207..02f04c19 100644
--- a/simgear/scene/sky/newcloud.cxx
+++ b/simgear/scene/sky/newcloud.cxx
@@ -64,7 +64,7 @@ using namespace std;
 
 namespace
 {
-typedef std::map<std::string, osg::ref_ptr<Effect> > EffectMap;
+typedef std::map<std::string, osg::observer_ptr<Effect> > EffectMap;
 EffectMap effectMap;
 }
 
@@ -102,7 +102,13 @@ SGNewCloud::SGNewCloud(const SGPath &texture_root, const SGPropertyNode *cld_def
 
     // Create a new Effect for the texture, if required.
     EffectMap::iterator iter = effectMap.find(texture);
-    if (iter == effectMap.end()) {
+
+    if (iter != effectMap.end()) {
+        effect = iter->second.get();
+    }
+
+    if (!effect.valid())
+    {
         SGPropertyNode_ptr pcloudEffect = new SGPropertyNode;
         makeChild(pcloudEffect, "inherits-from")->setValue("Effects/cloud");
         setValue(makeChild(makeChild(makeChild(pcloudEffect, "parameters"),
@@ -111,10 +117,14 @@ SGNewCloud::SGNewCloud(const SGPath &texture_root, const SGPropertyNode *cld_def
                  texture);
         ref_ptr<SGReaderWriterOptions> options;
         options = SGReaderWriterOptions::fromPath(texture_root.str());
-        if ((effect = makeEffect(pcloudEffect, true, options.get())))
-            effectMap.insert(EffectMap::value_type(texture, effect));
-    } else {
-        effect = iter->second.get();
+        effect = makeEffect(pcloudEffect, true, options.get());
+        if (effect.valid())
+        {
+            if (iter == effectMap.end())
+                effectMap.insert(EffectMap::value_type(texture, effect));
+            else
+                iter->second = effect; // update existing, but empty observer
+        }
     }
 }
 
diff --git a/simgear/scene/sky/newcloud.hxx b/simgear/scene/sky/newcloud.hxx
index f6e55733..1f207d41 100644
--- a/simgear/scene/sky/newcloud.hxx
+++ b/simgear/scene/sky/newcloud.hxx
@@ -84,7 +84,7 @@ private:
         
         // The density of the cloud is the shading applied
         // to cloud sprites on the opposite side of the cloud
-        // from the sun. For an invidual cloud instance a value
+        // from the sun. For an individual cloud instance a value
         // between min_density and max_density is chosen.
         float min_density;
         float max_density;
@@ -102,7 +102,6 @@ private:
         static float sprite_density;
 
         osg::Geometry* createOrthQuad(float w, float h, int varieties_x, int varieties_y);
-
 };
 
 
diff --git a/simgear/scene/tgdb/TreeBin.cxx b/simgear/scene/tgdb/TreeBin.cxx
index f8980c6d..a0203ebc 100644
--- a/simgear/scene/tgdb/TreeBin.cxx
+++ b/simgear/scene/tgdb/TreeBin.cxx
@@ -208,7 +208,7 @@ void addTreeToLeafGeode(Geode* geode, const SGVec3f& p)
     }
 }
 
-typedef std::map<std::string, osg::ref_ptr<Effect> > EffectMap;
+typedef std::map<std::string, osg::observer_ptr<Effect> > EffectMap;
 
 static EffectMap treeEffectMap;
 
@@ -299,9 +299,14 @@ osg::Group* createForest(SGTreeBinList& forestList, const osg::Matrix& transform
     for (i = forestList.begin(); i != forestList.end(); ++i) {
         TreeBin* forest = *i;
       
-        Effect* effect = 0;
+        ref_ptr<Effect> effect;
         EffectMap::iterator iter = treeEffectMap.find(forest->texture);
-        if (iter == treeEffectMap.end()) {
+
+        if (iter != treeEffectMap.end())
+            effect = iter->second.get();
+
+        if (!effect.valid())
+        {
             SGPropertyNode_ptr effectProp = new SGPropertyNode;
             makeChild(effectProp, "inherits-from")->setStringValue("Effects/tree");
             SGPropertyNode* params = makeChild(effectProp, "parameters");
@@ -309,11 +314,12 @@ osg::Group* createForest(SGTreeBinList& forestList, const osg::Matrix& transform
             params->getChild("texture", 0, true)->getChild("image", 0, true)
                 ->setStringValue(forest->texture);
             effect = makeEffect(effectProp, true, options);
-            treeEffectMap.insert(EffectMap::value_type(forest->texture, effect));
-        } else {
-            effect = iter->second.get();
+            if (iter == treeEffectMap.end())
+                treeEffectMap.insert(EffectMap::value_type(forest->texture, effect));
+            else
+                iter->second = effect; // update existing, but empty observer
         }
-        
+
         // Now, create a quadtree for the forest.
         ShaderGeometryQuadtree
             quadtree(GetTreeCoord(), AddTreesLeafObject(),
diff --git a/simgear/scene/tgdb/pt_lights.cxx b/simgear/scene/tgdb/pt_lights.cxx
index 59003fcb..e4ec0d59 100644
--- a/simgear/scene/tgdb/pt_lights.cxx
+++ b/simgear/scene/tgdb/pt_lights.cxx
@@ -159,7 +159,7 @@ gen_standard_light_sprite(void)
 namespace
 {
 typedef boost::tuple<float, osg::Vec3, float, float, bool> PointParams;
-typedef std::map<PointParams, ref_ptr<Effect> > EffectMap;
+typedef std::map<PointParams, observer_ptr<Effect> > EffectMap;
 
 EffectMap effectMap;
 
@@ -174,7 +174,8 @@ Effect* getLightEffect(float size, const Vec3& attenuation,
     PointParams pointParams(size, attenuation, minSize, maxSize, directional);
     ScopedLock<Mutex> lock(lightMutex);
     EffectMap::iterator eitr = effectMap.find(pointParams);
-    if (eitr != effectMap.end())
+    if ((eitr != effectMap.end())&&
+        eitr->second.valid())
         return eitr->second.get();
     // Basic stuff; no sprite or attenuation support
     Pass *basicPass = new Pass;
@@ -204,7 +205,7 @@ Effect* getLightEffect(float size, const Vec3& attenuation,
     spritePass->setTextureAttribute(0, attrFact->getStandardTexEnv());
     Pass *combinedPass = clone(spritePass, CopyOp::SHALLOW_COPY);
     combinedPass->setAttributeAndModes(point);
-    Effect* effect = new Effect;
+    ref_ptr<Effect> effect = new Effect;
     std::vector<std::string> parameterExtensions;
 
     if (SGSceneFeatures::instance()->getEnablePointSpriteLights())
@@ -232,8 +233,11 @@ Effect* getLightEffect(float size, const Vec3& attenuation,
     Technique* basicTniq = new Technique(true);
     basicTniq->passes.push_back(basicPass);
     effect->techniques.push_back(basicTniq);
-    effectMap.insert(std::make_pair(pointParams, effect));
-    return effect;
+    if (eitr == effectMap.end())
+        effectMap.insert(std::make_pair(pointParams, effect));
+    else
+        eitr->second = effect; // update existing, but empty observer
+    return effect.release();
 }